USER Manual

AR25
2

Table of Contents accumet®

RESEARCH

Connectors

Attaching pH and ISE electrodes

Touch Screen Operation

Choosing a Channel

Button Functions

System Setup

pH Setup

mV Setup

Ion Setup

Standardization

Measurement

Absolute mV Measurement

Relative mV Measurement

4

5

6

8

10

12

14

16

18

44

80

88

102

104

108

110

111

111

Introduction

Unpacking the Meter

Specifications

Getting Started

Using the Meter 

Setup Operations

pH Operations

mV Operations
3

accumet Table of Contents

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Direct Reading with Standards

Direct Reading with Blank Offset

Incremental Methods

Known Addition Measurement

Known Subtraction Measurement

Analate Addition Measurement

Analate Subtraction Measurement

Determining Isopotential Points Experimentally 

Data Management

Factory Default Settings

pH Theory

ISE Theory

112

114

117

120

122

126

128

130

132

133

134

135

137

138

139

141

146

150

Ion Operations

Cleaning

Trouble Shooting

Warranty

Compliance

Appendix

Replacement Parts
4

Introduction accumet®

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Thank you for selecting a Fisher Scientific accumet pH meter. This 

manual describes the operation of the accumet AR25 meter. The 

state-of-the-art meter that you have purchased is easy to operate and 

will guide you through the various functions by displaying easy to 

understand prompts. This operating manual should answer any 

questions that might arise in operating your meter; however, do not 

hesitate to call our Fisher Lab Equipment Technical Support Hotline at 

1-800/943-2006 or 412/490-6260, if you need any assistance.

This meter is designed to provide all the information necessary to guide

you through the process of measuring pH, mV, or ion concentration with

a series of prompts on the screen.

The accumet Research AR25 provides microprocessor precision in a 

compact benchtop design that is easy to use. One touch screen controls

all procedures, letting you:

• Measure pH, absolute mV, relative mV, ion concentration 

• Select one of three sets of standard buffer groups.

• Implement automatic buffer recognition.

• Standardize with up to five standard or custom buffers.

• Customize your display screen and operating parameters.

• Assign operator and sample identification numbers.

• Specify ion selective electrode type.

• Store 250 data points in the meter’s memory or transfer data

to a computer or printer.

• Access extensive online help with just a touch of a button.

It all adds up to rapid, completely automatic, intuitive operation.
5

accumet Unpacking the Meter

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The following is a listing of what you should have received with your new

accumet AR25 pH/mV/Ion/meter.

Meter with kit includes

meter 

power supply

electrode arm support bracket

electrode arm

electrode (13-620-285)

ATC probe (13-620-19)

manual and literature

Meter only includes

meter

power supply

electrode arm support bracket

manual and literature

If any of these items are missing, please contact the Fisher Products 

Group Electrochemistry Operation by dialing 412/490-6267.

Ion Selective Electrodes are available and can be ordered by 

calling Fisher Customer Service at 800/766-7000.
6

Specifications accumet®

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640x480 digit LCD

4 1/2” x 6”

3/4” 

1/4” 

extensive

extensive

yes

context specific touchscreen

250 data pts

yes

store on stable, time, manual

output on stable, time, manual

1 to 9,999 sec

yes

-2.000 to 20.000

0.1/0.01/0.001

± 0.002

yes

yes

5

yes

yes

± 1800.0

0.1

± 0.1

1x10-6 to 9.99x1010

0.1/0.01/0.001

± 0.17n%

5

KA, KS, AA, AS

screen size

measurement display height

temp/etc. display height

menu options

help screens

configurable display

keypad controls

internal diagnostics

programmable data storage

programmable data output

print interval

programmable alarm

range

resolution

relative accuracy

automatic buffer recognition

manual buffer recognition

calibration points

auto lock

FET

range

resolution

accuracy

range

resolution

relative accuracy

calibration points

incremental methods

Display

Memory

pH Mode

mV Mode

Ion Mode
7

accumet Specifications

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-5.0 to +105.0 °C

0.1 °C

± 0.2 °C

2BNC, 2Pin, 2ATC

RS232, DIN (for FET)

115 V/60 Hz, 230 V/50 Hz 

12VDC, 500mA

± 10%

>1012 ohms

5.5” x 7.5” x 3.25”

1.86 lb.

5-45 °C

5-80 % noncondensing

2000m

II

2

range

resolution

accuracy

inputs/outputs

electrical requirements

output from PSU

line voltage tolerance

input impedance

meter size

meter weight

operating temperature

operation humidity

maximum operating altitude

installation category

Pollution category degree

Temperature Mode

General

Operating Conditions
8

Getting Started accumet®

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CONNECTORS

POWER RS-232 FET ATC 1 Ref 1 Input 1

AccuFET pH electrode

Automatic Temperature Compensation (ATC)

BNC input connector

Reference pin jack

1 Review the layout and arrangement of the rear connector panel.

ACT 2 Ref 2 Input 2

Power

Computer/Printer
9

accumet Getting Started

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CONNECTORS

To connect RS-232, see

Data Management on

page 138.

2 Connect the electrode arm to the base.

Connect the power cable to the 

rear connector panel power 

jack and to a power source.

3

electrode arm support

POWER
10

Getting Started accumet®

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pH and ION SPECIFIC ELECTRODES

If both a conventional 

electrode and an AccuFET

electrode are connected to

the meter, do not put them

in a solution together

because you will get 

inaccurate measurements.

Do not discard the BNC 

shorting cap.

This meter allows you to use two types of pH electrodes: the 

conventional glass pH electrode and the AccuFET field effect 

transistor (FET) pH electrode. If both types of pH electrodes are

connected, the meter will read the AccuFET electrode. This meter

also allows you to use ion specific electrodes.

Carefully remove the protective cover from 

the end of the electrode. Before first using 

your glass pH electrode, or whenever the 

electrode is dry, soak it 2-4 hours in an 

electrode storage solution, pH 4 Buffer, or 

KCl solution. Before using your ion specific 

electrode, consult the manufacturer’s 

instructions for electrode preparation.

Remove the shorting cap on BNC connector. 

Connect the combination pH electrode by 

plugging it into the BNC input connector 

(twisting to lock in place).

If a combination electrode isn’t used, connect 

the indicating pH electrode into the BNC 

input connector. Plug the reference electrode

into the reference pin jack. Also, install the ATC

probe into the ATC jack.

Note: Be sure to connect all probes to the 

appropriate channel connectors (for 

example: Input 1, Ref 1, and ATC 1).

Option: Connect the optional AccuFET 

electrode by plugging it into the FET jack 

on the back meter panel. Allow the AccuFET 

to warm up five minutes before use.

Connect ion specific electrodes in the same 

manner as pH electrodes.

2

1
11

accumet Getting Started

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pH and ION SPECIFIC ELECTRODES

Proper electrode care is 

fundamental to obtaining

reliable pH measurements.

Improper care of the 

electrode may cause the

meter reading to drift,

respond slowly, or 

produce erroneous 

readings. For this reason,

the electrode should

always be conditioned

and used in accordance

with manufacturer’s 

instructions.

Rinse and blot-dry (don't wipe) electrodes 

between each measurement. Rinse electrodes 

with distilled or deionized water, or a portion of 

the next solution to be measured.

Between measurements, store conventional pH 

electrodes in electrode storage solution, pH 4 

buffer, or KCl solution. Always leave the filling

hole of liquid filled combination electrodes 

open. Refill when the level of solution gets 

below the manufacturer’s recommended level.

Store ion specific electrodes according to 

electrode manufacturer’s recommendations.

3

4
12

Using the Meter accumet®

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TOUCH SCREEN OPERATION

Touch anywhere to resume

11:11am

Fisher Scientific

Standby screen
13

accumet Using the Meter

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TOUCH SCREEN OPERATION

The new accumet Research benchtop pH meters operate with a 

state-of-the-art touch screen. The touch screen makes this the easiest

meter on the market to operate and care for. When the meter is first

plugged in, the STANDBY screen will appear. Touch anywhere on this

screen to access the functions of the meter. 

The buttons on the right side of the screen control all of the functions of

the meter. A light touch on the screen is all that you need to access the

various functions. Once you touch a button you will get an audible tone;

the screen will not change until you lift your finger. This

design prevents rapid uncontrolled scrolling through the various function

screens. Function buttons and options change from screen to screen.

Easy to understand prompts guide you through the operation of the

meter in the selected mode. If you are ever in doubt about what to do,

just touch help on the bottom right corner of the screen for detailed

information about that screen. 

The touch screen is made of a durable polyester material that is 

chemically resistant. Maintenance is simple with this meter. To clean 

the screen you just need to wipe it with a damp cloth and dry it 

with a clean dry towel. For additional information, see cleaning 

and troubleshooting sections of the manual (page133).
14

Using the Meter accumet®

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CHOOSING A CHANNEL

Measure

stdby

help

9.295

pH

print

STND Last std: Sep 17 @ 10:10 am

0.010

uS/cm

BUFFERS Last std: Sep 17 @ 10:17 am

ATC

slope 

mV

26.2°C

000.0%

0000.0

ID#

auto buffer

auto read

00000

ON

ON

September 17, 1997 11:11 am

1

2

channel 1

channel 2

ATC

Ref 

Co

26.2°C

25°C

0.00%/°C

ID#

Cell K

00000

1.00/cm

Channel screen Main screen

Dual screen

Select your desired measurement channel

stdby

help

Fisher Scientific

accumet AR25

dual

1

2

September 17, 1997 11:11 am

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11am

Fisher Scientific

accumet AR25
15

accumet Using the Meter

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CHOOSING A CHANNEL

If you are in any measure

mode, touch mode until

you access the main

screen.

The accumet Research AR25 is a Multi-channel pH meter. With this

meter you can switch from channel 1 to channel 2. You can also view

both channels at the same time by accessing the dual channel mode. 

If you set the meter to view both channels, you cannot change the 

parameters without choosing the screen that you want to modify. The

setup parameters for each screen are setup independently of one 

another.

Choosing a Channel

Touch anywhere on the Standby screen.

OR

Touch channel on the main screen.

THEN

Touch 1, 2 or dual to access the channel that you want to view.

To access System Setup from the Standby screen

Touch anywhere on the Standby screen.

Touch 1 or 2 on the channel screen to access either channel.

Touch setup. 

Touch system on the Setup screen.

1

2

1

2

3

4
16

accumet®

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BUTTON FUNCTIONS

The touch screen of your accumet Research pH meter has “buttons” along the

right side of the screen that are common to many of the screens. The following

indicates the function of these common buttons.

channel

stdby

mode

enter

exit

save

help

close

more

back

Using the Meter

This button allows you to access the channel screen to choose what

channel you want to view. This button appears only on multichannel

meters such as the accumet AR25 and AR50. This button also allows

you to move from the main mode screen to the channel screen to access

the standby mode.

The mode button allows you to switch between the various operations

of the meter. These operations, depending upon which meter you have,

include four measuring modes (pH, mV, ion, conductivity) as well as a

setup mode.

The enter button allows you to accept any changes that you have made

on setup screens or accept values that you have input with keypads.

When touched, enter will save the changes and return you to the previous

screen.

The save button allows you to save multiple changes you have made on

one screen as a group. It functions like the enter button does for individual

changes.

The help button allows you to access helpful information on any screen.

When you touch the help button, information about the current screen

appears. This information will include step-by-step instructions for operating

the meter from the current screen and possible applications information for

that screen.

The close key appears on the bottom of all help screens and allows you

to exit the help screen and return to the previous screen. 

The more button appears on the help screens and allows you to

advance to the next help screen for additional information.

The back button appears on the help screens and allows you to 

move back to a previous help screen.

The exit button allows you to leave the screen you are currently viewing

and return to the previous screen without making any changes.

This is the standby button and it allows you to access the standby

mode. When in standby, the meter will not take measurements. It is in a

state of rest. When you touch stdby the meter will return to the standby

screen which says “Fisher Scientific” and displays the time. 
17

accumet Using the Meter

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BUTTON FUNCTIONS

meas

std

setup

print

edit

clear

BS

delete

prev

next

This button accesses the standardization screen from the various

measure modes and initiates standardization of the meter once the

standardization screen is accessed.

This button is the measure button and directs the meter to measure your

sample when in the Auto Read function of the pH or Ion modes.

This button will access the setup screens for the measuring mode that

you are currently using. It can also be used to access the system setup

screen that allows you to set parameters that are not related to measurements such as the time and the date. 

The print button will send information to the output device that you

have connected to your accumet meter. The output device can be a

printer, data logger or a computer. In addition to this, touching the print

button will also send data to the data storage center of the meter if a

sample ID# has been assigned to your sample.

The arrow keys on the screen move the cursor up and down in order

to highlight parameters that you would like to review or edit.

The edit button appears on the setup screens. After you have highlighted

a parameter that you would like to change, the edit button allows you to

access the available options for that parameter.

The BS button is a backspace button. It appears on keypad screens and

it allows you to back up and delete a character entered in error.

The delete button appears on the “View Stored Data” screens. This

button allows you to erase the data from the memory of the meter.

The prev button appears on the Data Screens when the data stored in

the meter’s memory has been accessed. It allows you to scroll through

data points sorted and stored prior to the current data point displayed.

The next button appears on the Data Screens when the data 

stored in the meter’s memory has been accessed. It allows you 

to scroll through data points sorted and stored after the current data

point displayed.

The clear button allows you to remove a setup parameter or standard

buffer value from the meter’s memory that may have been entered at a

previous time or by a previous user that is no longer of value to you.

Touching the clear button erases the value so you may enter a new one.

It can also erase a parameter that you may have entered erroneously. 
18

Setup Operations accumet®

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SYSTEM SETUP

System Setup 

edit

exit

help

SYSTEM SETUP OPTIONS

 - Select Language

 - Set Date 

 - Set Time

 - Set Beeper Status

 - Select Procedural Level

 - Set Print Configuration

- Set Operator

 - Set Display Contrast

 - Display Meter Information

 - Reset to Factory Defaults
19

accumet®

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TABLE OF CONTENTS Setup Operations

Access SYSTEM SETUP

Select LANGUAGE

Set DATE

Set TIME

Set BEEPER STATUS

Select PROCEDURAL LEVEL

Set PRINT CONFIGURATION

Set OPERATOR

Set DISPLAY CONTRAST

Display METER INFORMATION

Reset to FACTORY DEFAULTS

20

22

24

26

28

30

32

34

35

36

37

38

40

42

43

Set BAUD RATE

Set NUMBER OF BITS

Set STOP BITS

Set PARITY
20

System Setup accumet®

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Access SYSTEM SETUP

System Setup 

edit

exit

help

SYSTEM SETUP OPTIONS

 - Select Language

 - Set Date 

 - Set Time

 - Set Beeper Status

 - Select Procedural Level

 - Set Print Configuration

- Set Operator

 - Set Display Contrast

 - Display Meter Information

 - Reset to Factory Defaults

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11 am

Fisher Scientific

accumet®AR25

Select your desired measurement channel

stdby

help

Fisher Scientific

accumet®AR25

dual

1

2

September 17, 1997 11:11 am

Setup

Ion

system

exit

Select from the setup options to the right

mV

pH
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accumet System Setup

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Access SYSTEM SETUP

The system setup function allows you to customize the meter display

options to meet your personal preference. Once set, these will rarely

need to be changed.

To access System Setup

Touch anywhere on the Standby screen.

Touch 1 or 2 on the Channel screen to access either channel.

Touch setup on the Main screen.

Touch system on the Setup screen.

The System setup options are now displayed on the screen.

To access a System Setup option

Use the arrow keys to scroll through the setup options and 

highlight the option to be reviewed.

Touch edit to view the current status of the selected option.

1

2

3

1

2

The following is a detailed description of the System setup option screens.

4
22

System Setup accumet®

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Select LANGUAGE

Remember, HELP is always

just a touch of the button

away.

Select Language

enter

exit

help

Use arrow keys to highlight desired

language and then touch enter to accept

Current LANGUAGE

English

French

English 
23

accumet System Setup

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Select LANGUAGE

This option allows you to choose the language in which all prompts 

and directions will appear on the touch screen. 

To Select Language

Access the Select Language screen from the System Setup screen. 

The current language is displayed on the screen. 

Use the arrow keys to highlight the desired language.

Touch enter to accept the language and return to the 

System Setup screen.

OR

Touch exit to return to the System Setup screen, 

without making any changes.

1

2

3
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System Setup accumet®

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Set DATE

Set Date

D/M/Y

exit

help

Touch clear to delete current date 

enter

Use numeric touchpad to input the new

date and then touch enter to accept

1 2 3

4 5 6

7 8 9

0

Current MM/DD/YY 11/11/97

clear

BS /
25

accumet System Setup

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Set DATE

If you do not use the /,

the meter will not accept

the date.

This screen can be used to set the present date which will be displayed

on the measure screens. This date will also be printed on demand and

stored in the data storage center of the meter when data is saved. There

are two format options for the date: month/day/year (M/D/Y) or the

European format of day/month/year (D/M/Y).

To Set Date

Access the Set Date screen from the System Setup screen. The 

current date and numeric keypad are displayed on the screen.

Touch clear to delete the current entry.

Touch D/M/Y or M/D/Y to set the date format. 

Use the numeric touch pad to enter the desired date, separating the

day, the month and the year by touching the / key on the keypad. 

Touch enter to accept the date in the current format.

OR

Touch exit to return to the System Setup screen, 

without making any changes.

1

2

3

4

5
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System Setup accumet®

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Set TIME

Set Time

enter

exit

help Use numeric touchpad to input the new 

time and then touch enter to accept

24hr

pm

Touch clear to delete current time setting

1 2 3

4 5 6

7 8 9

BS 0 :

Current 12HR 10:40 am

clear
27

accumet System Setup

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Set TIME

If you do not use the :, the

meter will not accept the

time.

This screen can be used to set the present time which will be displayed

on the measure screens. This time will also be printed on demand and

stored in the data storage center of the meter when data is saved. 

There are two format options for the time. The clock can be set as 

either a 12 hour clock or a 24 hour clock.

To Set Time

Access the Set Time screen from the System Setup screen. The 

current time and numeric keypad are displayed on the screen.

Touch clear to delete the current entry.

Touch the 24hr or 12hr button to format the clock as either a 12 

hour or a 24 hour clock.

Touch am or pm to set the appropriate time. 

Use the numeric touch pad to enter the desired time, separating 

the hour and the minutes by touching the : key on the keypad. 

Touch enter to accept the time in the current format.

OR

Touch exit to return to the System Setup screen, 

without making any changes.

1

2

3

4

5

6

Current 12HR 5:15 pm

Current 24HR 17:15 
28

System Setup accumet®

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Set BEEPER STATUS

Remember, HELP is always

just a touch of the button

away.

Set Beeper Status

ON

exit

help

Use arrow keys to highlight beeper

option and then touch ON/OFF to 

change

save

Current BEEPER STATUS

After STABLE Reading ON

After KEY Touch OFF

On LIMIT Exceeded ON

Touch save to accept changes
29

accumet System Setup

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Set BEEPER STATUS

This screen allows you to turn on or turn off the beeper. You may choose

to have an audible signal when the meter recognizes that the current

measurement is stable, each time a function button is touched and/or

when the set limits of a measurement mode have been exceeded. 

After STABLE Reading 

When active, the meter delivers an audible tone each time the meter recognizes

the current measurement as stable. If deactivated, you will not hear an audible

tone at a stable measurement. You will still see the STABLE indicator even if there

is no audible tone.

After KEY Activation

When active, the meter delivers an audible tone each time you touch a function

button or a key on an alphanumeric keypad. If deactivated, you will not hear a

tone after a key touch. The changes will only be visible on the screen.

On LIMIT Exceeded

When active, the meter delivers an audible tone each time the set limits in a

measurement mode have been exceeded. If deactivated, you will not hear an

alarm tone when the limits in the measurement modes have been exceeded. 

You will see the LIMIT indicator on the measurement screen. For additional 

information on the Alarm Limits of the meter, see the setup sections of this 

manual for each of the measurement modes.

To Set Beeper Status

Access the Set Beeper Status screen from the System Setup 

screen. The current beeper status is displayed on the screen.

Use the arrow keys to highlight the beeper status option that 

you would like to modify. 

Touch ON or OFF until the desired status is visible in the 

current beeper status box.

Touch save to accept the changes and return to the System 

Setup screen.

OR

Touch exit to return to the System Setup screen, 

without making any changes.

1

2

3

4
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System Setup accumet®

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Select PROCEDURAL LEVEL

Select Procedural Level

enter

LEVEL 1 - Basic Level

LEVEL 2 - Advanced Level 

1

2

Current LEVEL 1

25.0 °C

100%

September 17, 1997 11:11 am

Procedural Level 1 

Temperature

Electrode Performance

ATC

slope

mV

25.0 °C

100%

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

Procedural Level 2 
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accumet System Setup

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Select PROCEDURAL LEVEL

This Selection screen allows you to choose the amount of information 

that you want to have displayed on the screen. There are two levels 

to choose from. Both of the levels provide identical results. The amount 

of information appearing on the measure screens and the number of

setup parameters you can manipulate will vary from Basic to Advanced

procedural levels.

LEVEL 1 - Basic Level 

This level option offers a full set of prompts to guide you through the basic 

operation of the meter. The information provided on the screen is minimal to

reduce clutter. It includes the measurement and the last standardization time 

and buffer values. The data box at the bottom of the measure screen includes the

current date, time, sample temperature and the electrode performance. 

In addition to the limited information appearing on the measure screen, 

there are also fewer options available to you in the setup screens of the 

various measurement modes.

LEVEL 2 - Advanced Level 

This option allows you access to all of the features available on the meter. 

A full set of prompts is available on virtually every screen to lead you through 

the operation of the meter. You are also given access to all setup parameters for

the various measurement modes. Any parameter not appearing on the Basic

Level Setup screens will maintain the value previously set in the Advanced Level

Setup screens. They will not automatically default to factory default settings. This

is ideal if you want to “lock” in a parameter in the Advanced Level and switch to

the Basic Level so others cannot accidentally modify the parameter.

To Select Procedural Level

Access the Select Procedural Level screen from the System Setup 

screen. The current procedural level is displayed on the screen.

Use the numbered buttons on the right of the screen to select the 

desired procedural level.

Touch enter to accept the procedural level and return to the System

Setup screen.

OR

Touch exit to return to the System Setup screen, 

without making any changes.

1

2

3
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System Setup accumet®

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Set PRINT CONFIGURATION

Set Print Configuration

edit

exit

help

Use arrow keys to highlight desired

print setting and then touch edit to 

change

save

Current PRINT CONFIGURATION

19200

8

1

NONE

- Baud Rate

- # of Bits

- # of Stop

- # Parity

Touch save to save the print settings
33

accumet System Setup

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Set PRINT CONFIGURATION

You can adjust the print configuration of the meter from this screen. 

The configuration of the following screens must match the configuration

of the printer or computer to which the data will be sent.

To Set Print Configuration

Access the Print Configuration screen from the System Setup screen.

The current Print Configuration is displayed on the screen.

Use the arrow keys to highlight the configuration option to 

be modified.

Touch edit to access the parameters for the highlighted option. 

OR

Touch exit to return to the System Setup screen, 

without making any changes.

1

2

3
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System Setup accumet®

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Set BAUD RATE

This configuration option will control the speed at which the data will be

transmitted to the printer. This parameter needs to match the baud rate

designated by the printer or computer.

To Set Baud Rate

Access the Set Baud Rate screen from the Set Print Configuration

screen. The current baud rate is displayed on the screen.

Use the arrow keys to highlight the baud rate option that matches 

the baud rate of your printer or computer.

Touch enter to accept the baud rate and return to the Set Print

Configuration screen.

OR

Touch exit to return to the Set Print Configuration screen, 

without making any changes. 

1

2

3

Set Baud Rate

Current BAUD RATE

enter

9600

110

300

600

1200

2400

4800

9600

19200

38400
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accumet System Setup

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Set NUMBER OF BITS

To Set Number of Bits

Access the Set Number of Bits screen from the Set Print Configuration

screen. The current number of bits is displayed on the screen.

Touch 7 or 8 to select the number of bits.

Touch enter to accept the bit value and return to the Set Print

Configuration screen.

OR

Touch exit to return to the Set Print Configuration screen, 

without making any changes. 

1

2

3

Set Number of Bits

Current NUMBER OF BITS

enter

7

8
36

System Setup accumet®

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Set STOP BITS

To Set Stop Bits

Access the Set Stop Bits screen from the Set Print Configuration 

screen. The current number of bits is displayed on the screen.

Touch 1 or 2 to set the desired number of stop bits.

Touch enter to accept the stop bit value and return to the Set 

Print Configuration screen.

OR

Touch exit to return to the Set Print Configuration screen, 

without making any changes.

1

2

3

Set Stop Bits

Current STOP BITS

enter

1

2
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Set PARITY

To Set Parity

Access the Set Parity screen from the Set Print Configuration 

screen. The current Parity is displayed on the screen.

Touch ODD or EVEN or NONE to set the desired parity.

Touch enter to accept the parity setting and return to the Set 

Print Configuration screen.

OR

Touch exit to return to the Set Print Configuration screen, 

without making any changes. 

1

2

3

Set Parity

Current PARITY

enter

NONE

EVEN

ODD
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Set OPERATOR

Set Operator

enter

exit

help

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clear

Current Operator
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Set OPERATOR

This option allows you to identify the user of the meter. This information

can be saved in the meter’s memory. It can also be printed out with

measurement data on demand. The operator identification can be up

to 9 characters in length.

To Set Operator

Access the Set Operator screen from the System Setup screen. 

The current operator identification is displayed on the screen.

Touch clear to remove the current operator identification.

Use the alphanumeric keys on the touch screen to enter the 

desired operator identification. The BS button will allow you to 

backspace to remove a character that was incorrectly entered. 

The operator identification code can be a maximum of 

9 characters in length.

Touch enter to accept the new operator identification. 

OR

To deactivate the operator identification:

1. Touch clear to erase the current user identification.

2. Touch enter to return to the System Setup screen.

OR

Touch exit to return to the System Setup screen, 

without making any changes.

1

2

3

4
System Setup

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Set DISPLAY CONTRAST

Set Display Contrast 

save

exit

help

Touch lighter or darker to adjust 

contrast and then touch save to accept

17

lighter

darker

The value displayed ranges from 

0 (darkest) to 25 (lightest)
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Set DISPLAY CONTRAST

This option allows you to change the contrast on the screen to improve

the readability of the information presented on the screen. The numbering

system that appears on the screen is from 0 to 25. The darkest setting is

0 and the lightest setting is 25. 

To Set Display Contrast

Access the Set Display Contrast screen from the System Setup screen. 

The current display contrast value is displayed on the screen.

Use the lighter or darker button to adjust the contrast of the screen 

to the desired level. 

Touch save to accept the contrast setting and return to the System 

Setup screen.

OR

Touch exit to return to the System Setup screen, 

without making any changes.

Note: The display contrast of the screen is affected by the internal temperature 

of the meter. The meter will warm up after being plugged in. During this period

(approximately 20 minutes), the display contrast of the screen will get lighter. You

may need to adjust the contrast during this period to meet your specifications.

1

2

3
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DISPLAY METER INFORMATION

This screen displays the model number, serial number and current 

software revision of your meter.

Unit Serial Number:

Software Revision:

exit

Fisher Scientific

accumet®AR25

AR71202101

1.00
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Reset To FACTORY DEFAULTS

This screen allows you to reset all functions and setup parameters of the

meter to the settings originally programmed at the factory. 

To Reset to Factory Defaults

Access the Reset to Factory Defaults screen from the System 

Setup screen.

Touch YES to reset all parameters to the original factory 

default settings.

OR

Touch NO to return to the System Setup screen, 

without making any changes. 

1

2

You are about to reset all parameters of the 

meter to factory default settings.

Are you sure you want to do this?

Reset to Factory Defaults

YES NO
pH Setup 

edit

exit

help

pH SETUP OPTIONS

 - Set Sample ID# 

 - Select Buffer Group

 - Select Buffer Recognition

 - Select Auto Read Mode

 - Set pH Stability Criteria

 - Set Default Temperature

 - Set Isopotential Point

 - Set Alarm Limits

 - Set Print Criteria

 - Set Print Interval 

 - Set Data Storage Criteria

 - Set Display Resolution

 - Set Display Configuration

 - View Stored Data

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pH SETUP
Access pH SETUP 

Set SAMPLE ID#

Select BUFFER GROUP

Set pH CUSTOM BUFFER GROUP

Select BUFFER RECOGNITION

Select AUTO READ MODE

Set pH STABILITY CRITERIA

Set DEFAULT TEMPERATURE

Set ISOPOTENTIAL POINT

Set ALARM LIMITS

Set PRINT CRITERIA

Set PRINT INTERVAL

Set DATA STORAGE CRITERIA

Set DISPLAY RESOLUTION

Set DISPLAY CONFIGURATION

View STORED DATA

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The operating parameters of the pH mode can be set and controlled from the

pH Setup screen. The following sections will guide you through the various

options available for the pH setup mode. 

46

48

50

54

56

57

58

60

62

64

66

68

70

72

74

76

TABLE OF CONTENTS pH Setup
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There are two ways to access the pH Setup screen. 

From the Setup screen

Touch setup on the main screen. Touch 

pH to access the pH Setup screen.

Use the arrow keys to highlight the setup 

option that you would like to review.

Touch edit to access the screen for the selected 

option.

1

2

3

pH Setup Access pH SETUP

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11 am

Fisher Scientific

accumet AR25

Setup

Ion

system

exit

Select from the setup options to the right

mV

pH

pH Setup 

edit

exit

help

pH SETUP OPTIONS

 - Set Sample ID# 

 - Select Buffer Group

 - Select Buffer Recognition

 - Select Auto Read Mode

 - Set pH Stability Criteria

 - Set Default Temperature

 - Set Isopotential Point

 - Set Alarm Limits

 - Set Print Criteria

 - Set Print Interval 

 - Set Data Storage Criteria

 - Set Display Resolution

 - Set Display Configuration

 - View Stored Data
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From the pH Measure screen

Touch pH on the main screen to access 

the pH mode. Touch setup on the pH 

Measure screen. The pH Setup screen is 

now displayed. 

Use the arrow keys to highlight the setup

option that you would like to review.

Touch edit to access the screen for the 

selected option.

1

2

3

Access pH SETUP pH Setup

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11 am

Fisher Scientific

accumet AR25

Measure

07.00

pH

std

meas

setup

mode

help

Touch meas to measure sample print

channel 1

Touch std to standardize

or

ATC

slope

mV

25.0 °C

NA

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

BUFFERS Last std: Sep 17 @ 10:17 am

7

pH Setup 

edit

exit

help

pH SETUP OPTIONS

 - Set Sample ID# 

 - Select Buffer Group

 - Select Buffer Recognition

 - Select Auto Read Mode

 - Set pH Stability Criteria

 - Set Default Temperature

 - Set Isopotential Point

 - Set Alarm Limits

 - Set Print Criteria

 - Set Print Interval 

 - Set Data Storage Criteria

 - Set Display Resolution

 - Set Display Configuration

 - View Stored Data
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Set SAMPLE ID#

Set pH Sample ID#

enter

exit

help

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Manual ID#

seq
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Set SAMPLE ID#

When this option is active, each time you touch print on the Measure

screen the pH value along with the date/time/channel and the sample

ID# will be sent to data storage. (See Data Storage Criteria page 99 

for additional information on saved parameters.) You can manually enter

an alphanumeric identification number of up to 10 characters for any

sample or you can have the meter sequentially number your samples

beginning at the number of your choice. You may also choose to 

deactivate the sample ID#. 

To Set Sample ID#

Manual ID# Assignment

Access the Set Sample ID# screen from the 

pH (mV, Ion) Setup screen.

Touch man for manual ID# entry. The current ID# is displayed on 

the screen.

Touch clear to delete the current ID#.

Use the alphanumeric keypad on the screen to enter the desired 

Sample ID#. The BS key will allow you to backspace to remove a 

character that was incorrectly entered. 

Touch enter to accept the current ID# and return to the pH 

(mV, Ion) Setup screen.

1

2

3

4

5
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Set SAMPLE ID#

Set pH Sample ID#

enter

exit

help Use numeric touchpad to input the new

starting ID and then touch enter to accept

clear

man

Touch clear to delete current ID

1 2 3

4 5 6

7 8 9

0 .

Sequential ID# 

BS
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Sequential ID# Assignment

Access the Set Sample ID# screen from the 

pH (mV, Ion) Setup screen.

Touch seq for sequential ID# assignment. The current ID# is 

displayed on the screen.

Touch clear to delete the current ID#.

Use the alphanumeric keypad on the screen to enter the number that 

you would like your sequential ID# assignment to begin with. Every 

time you touch print on the Measure screen, the ID# will increase by 1.

The BS key will allow you to backspace to remove a character that 

was incorrectly entered.

Touch enter to accept the first sequential ID# and return to the 

pH (mV, Ion) Setup screen. 

OR

To Deactivate the Sample ID# Assignment

Access the Set Sample ID# screen from the pH 

(mV, Ion) Setup screen.

Touch man for manual ID# entry. 

The current ID# is displayed on the screen.

Touch clear to delete the current ID#.

Touch enter. The ID# assignment is now deactivated. No number 

will be assigned to your samples. The meter will return to the 

pH (mV, Ion) Setup screen.

OR

Touch exit to return to the pH (mV, Ion) Setup screen

without making any changes.

1

2

3

4

5

1

2

3

4

Set SAMPLE ID# pH Setup
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Select BUFFER GROUP

Remember, HELP is 

always just a touch of the

button away.

Select pH Buffer Group

NIST

exit

help

Use keys to display desired buffer group 

and then touch enter to accept

Current BUFFER GROUP

2 4 7 10 12

enter

EURO

custom

USA
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Select BUFFER GROUP

This setup option allows you to select from 3 different buffer groups,

each containing 5 buffers, for auto buffer recognition. Or you can 

create a custom group of buffers for auto buffer recognition by 

touching custom. 

The 3 existing buffer groups are:

USA buffers: 2, 4, 7, 10, and 12

European buffers: 1, 3, 6, 8, and 10

NIST buffers: 1.68, 4.01, 6.86, 9.18, and 12.45

To Select Buffer Group

Access the Select pH Buffer Group screen from the pH Setup screen.

The current buffer group is displayed on the screen.

Touch USA or NIST or EURO or custom on the right of the 

screen to select a buffer group.

Touch enter to accept the buffer group to be used for auto

recognition.

OR

Touch exit to return to pH Setup Screen, 

without making any changes.

1

2

3
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Set pH CUSTOM BUFFER GROUP

Set pH Custom Buffer Group

exit

help

Use keys to display desired buffer group 

and then touch enter to accept

Current BUFFER GROUP

enter

edit

CUSTOM

Set pH Custom Buffer Group

exit

help

Use keys to display desired buffer group 

and then touch enter to accept

Current BUFFER GROUP

enter

edit

CUSTOM

1.78 3.65

Set pH Custom Buffer Group

edit

exit

help

Use keys to display desired buffer group 

and then touch enter to accept

Current BUFFER GROUP

clear

CUSTOM
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Set pH CUSTOM BUFFER GROUP

To Set pH Custom Buffer Group

This option allows you to create a custom buffer group of up to 5 buffers to 

be used for auto buffer recognition. To obtain optimal results, it is 

important to maintain at least 2 pH units between selected 

buffers in the custom group.

Touch custom on the Set pH Buffer Group screen. The current 

buffer box will show the current custom buffer group.

Touch edit to alter the present group or create a new custom buffer

group. The newly displayed Set pH Custom Buffer Group screen has 

5 beakers in the current buffer group box.

Use the arrow keys to highlight the beaker icon with the pH value 

you want to change. If there are no buffers in the group then proceed

to the next step.

Touch edit to add a buffer or make changes to the current buffer 

group OR touch clear to delete the highlighted buffer value. 

Use the numeric keypad that is now displayed to enter the pH buffer

value that you want in your custom buffer set. 

Touch enter to accept the value. If you have entered an erroneous

value, use the BS key on the keypad to erase the last digit entered and

correct the mistake. If you decide not to change the buffer value on the

highlighted beaker icon, touch exit on the numeric keypad to return to

the Set pH Custom Buffer Group screen.

Repeat steps 3 through 6 to add up to 5 buffers to your custom buffer

group.

Touch exit to return to the Set pH Custom Buffer Group screen to 

view the current Custom Buffer Group.

Touch enter to accept the group and return to the pH Setup screen, 

OR touch edit to modify the group and repeat steps 3 through 6.

OR

Touch exit to return to the Set pH Buffer Group screen, 

without making any changes to the custom buffer group.

1

2

3

4

5

6

7

8

9

If you use the custom

buffer group for auto

buffer recognition, when

you access the Set pH

Buffer Group from the pH

Setup screen, the 

current buffer group that

appears on the screen is

the custom buffer group.

In order to access the

edit option for the custom

buffer group, you need to

touch any of the other

buffer group buttons and

then touch custom to

access the edit screen.
This option allows you to select Automatic buffer recognition or 

manual buffer recognition when standardizing. With the Automatic 

buffer recognition activated, the meter will automatically recognize 

the buffers from the chosen buffer group and accept them when the meter

recognizes the reading as stable. When in the Manual buffer recognition

mode, you must enter the buffer value during the standardization 

procedure. The meter will accept the manually entered buffer when 

it recognizes that the measurement is stable. During the standardization

procedure, you may accept the buffer value before the meter recognizes

it as stable by touching std.

To Select Buffer Recognition

Access the Select Buffer Recognition screen from the pH Setup screen.

The current method of recognition is displayed on the screen.

Touch MAN or AUTO to choose the method of buffer selection.

Touch enter to accept the method of buffer recognition and 

return to the pH Setup screen.

OR

Touch exit to return to the pH Setup screen, without making 

any changes.

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Select BUFFER RECOGNITION

Regardless of which Buffer

Recognition Mode you

select, STABLE will appear

on the Measure screen

when the meter recognizes

the value as stable.

1

2

3

Select pH Buffer Recognition

enter

Current RECOGNITION

MAN

AUTO
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Select AUTO READ MODE

You can use this meter when the Auto Read function is active or when it

is inactive. When the Auto Read function is active, the meter will lock

onto a reading when the meter recognizes it as stable. The meter will 

not deviate from this reading until meas is touched. If the Auto Read

function is inactive, then the meter will continuously monitor the pH of 

the sample and the Measure screen display will indicate any fluctuation

in the sample pH. 

To Select Auto Read Mode

Access the Select Auto Read Mode screen from the pH (Ion) 

Setup screen. The current Read Mode is displayed on the screen.

Touch AUTO or MAN to choose the desired read mode.

Touch enter to accept the read mode and return to the pH (Ion) 

Setup screen.

OR

Touch exit to return to the pH (Ion) Setup Screen, 

without making any changes.

1

2

3

Select pH Auto Read Mode

enter

Current MODE

MAN

AUTO
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Set pH STABILITY CRITERIA

Set pH Stability Criteria

enter

exit

help

Use arrow keys to highlight stability

criteria and then touch enter to accept

Current CRITERIA Medium

Fast

Medium

Slow
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Stability criteria are more

stringent at the slower 

setting. Therefore, if the 

highest precision is

required, then a slow 

setting would be desired.

The default setting 

is the medium speed 

and this should be 

adequate for the majority

of applications.

This setup screen allows you to determine how quickly the meter will

respond to electrode drift. There are 3 speed settings: fast, medium 

and slow. 

To Set pH Stability Criteria

Access the Set pH Stability Criteria screen from the pH (Ion) Setup

screen. The current stability criteria are displayed on the screen.

Use the arrow keys to highlight the desired stability criteria.

Touch enter to accept the stability criteria and return to the pH 

(Ion) Setup screen. 

OR

Touch exit to return to the pH (Ion) Setup screen, 

without making any changes.

1

2

3

Set pH STABILITY CRITERIA pH Setup
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Set DEFAULT TEMPERATURE

Set pH Default Temperature

enter

exit

help Use numeric touchpad to input the new

temperature and then touch enter to accept

clear

F

K

Touch clear to delete current default temp

1 2 3

4 5 6

7 8 9

0 .

25.0 Current DEFAULT °C

BS
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Set DEFAULT TEMPERATURE

The use of an ATC probe

provides a measured 

temperature value to the

meter and will override

any value entered in the

default temperature

screen. This measured

value will be used by 

the meter to make pH

(Ion) calculations.

It is a well known fact that pH is a temperature dependent measurement.

The factory default setting is 25°C. If you are taking the pH of a solution

that is not 25°C and you are not using an Automatic Temperature

Compensation (ATC) Probe, then you should enter the temperature value

of that solution in order to get the correct pH value. The current default

temperature setting will be displayed when the Set Default Temperature

screen is displayed.

To Set Default Temperature

Access the Set Default Temperature screen from the pH (Ion) 

Setup screen. The current default temperature is 

displayed on the screen.

Touch clear to erase the current temperature value.

Select the temperature units by touching the appropriate unit key 

C (Celsius), F (Fahrenheit), or K (Kelvin). 

Use the numeric keypad to enter the desired default temperature.

Touch enter to accept the temperature setting and return 

to the pH (Ion) Setup screen.

OR 

Touch exit to return to the pH (Ion) Setup screen, 

without making any changes.

1

2

3

4

5
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Set ISOPOTENTIAL POINT

Set pH Isopotential Point

enter

exit

help Use numeric touchpad to input the new

Iso Point and then touch enter to accept

clear

Touch clear to delete current Iso Point

1 2 3

4 5 6

7 8 9

0 .

Current ISO POINT 0.0 mV

BS
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Set ISOPOTENTIAL POINT

The Isopotential Point is the millivolt reading for an electrode at which

temperature has no effect on the measurement. pH electrodes are 

constructed so that the isopotential point is theoretically zero millivolts.

This is very close to a pH of 7. Most pH electrodes do not achieve 

this value precisely. However, they are close enough so that it is not 

usually necessary to use an isopotential point other than zero. The 

true isopotential point of any given electrode must be determined 

experimentally. (See Appendix: Determining Isopotential Points

Experimentally, page 137)

To Set Isopotential Point

Access the Set Isopotential Point screen from the pH (Ion) Setup 

screen. The current isopotential point is displayed on the screen.

Touch clear to remove the current mV value.

Use the numeric keypad to enter the desired mV setting for the 

new isopotential point.

Touch enter to accept this value and return to the pH (Ion) 

Setup screen.

OR

Touch exit to return to the pH (Ion) Setup screen, 

without making any changes.

1

2

3

4
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Set ALARM LIMITS

Set pH Limits

edit

Current LIMITS

pH Alarm OFF

pH Minimum 0.00

pH Maximum 14.00

Set mV Limits

Current LIMITS

- mV Alarm OFF

- mV Minimum -1800.0

- mV Maximum 1800.0

Set Ion Limits

Current LIMITS

- Ion Alarm OFF

- Ion Minimum 0.00

- Ion Maximum 1.00E6
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Set ALARM LIMITS

This option allows you to set alarm limits for the pH measuring mode. If

the pH value of the measurement is outside of the boundaries set by the

minimum and maximum limits, an audible alarm and/or a visual warning

will appear to let you know that your sample measurement was outside of

the set limits.

To Set Alarm Limits

Access the Set Alarm Limits screen from the pH (mV, Ion) 

Setup screen. The current alarm limits are displayed on the screen.

Use the arrow keys to highlight the pH (mV, Ion) 

Alarm option you want to modify.

Touch ON or OFF to set the status of the alarm for the pH 

(mV, Ion) mode.

Use the arrow keys to highlight the desired pH (mV, Ion) 

alarm limit.

Touch edit to change the value.

Use the keypad to enter the new limit value. 

Touch enter on the keypad to accept this limit and return to the Set 

pH (mV, Ion) Limits screen. If you do not want to change the limit value, 

you can touch exit on the keypad and return to the Set pH (mV, Ion) 

Limits screen.

Repeat steps 4 through 7 to set the other pH (mV, Ion) Alarm limit.

OR

Touch exit to return to the pH (mV, Ion) Setup screen, 

without making any changes.

1

2

3

4

5

6

7

8
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Set PRINT CRITERIA

Set pH Print Criteria

Current PRINT CRITERIA

- Date/Time/Channel ON

- Sample ID# ON

- pH measurement ON

- Temperature - ATC ON

- Last Standardization OFF

- Current Buffers OFF

- Slope ON

- mV measurement ON

- Meter model #/serial # ON

- Operator ON

Set mV Print Criteria

Current PRINT CRITERIA

- Date/Time/Channel ON

- Sample ID# ON

- mV measurement ON

- Temperature - ATC ON

- Meter model #/serial # ON

- Operator ON

Set Ion Print Criteria

Current PRINT CRITERIA

- Date/Time/Channel ON

- Sample ID# ON

- Ion measurement ON

- Temperature - ATC ON

- Last Standardization OFF

- Current Standards OFF

- Slope ON

- mV measurement ON

- Meter model #/serial # ON

- Operator ON

- electrode/method ON
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Set PRINT CRITERIA

The Date/Time/Channel

option and the

Measurement option 

are always active 

and cannot be deactivated. These criteria will

always be printed.

Because they can not be

changed, they will not be

highlighted when using

the arrow keys.

This screen allows you to select which criteria are printed with the 

measurement when you print the data or send it to a computer. 

The status of the current print criteria is displayed on the screen. 

The criteria option is active if “ON” appears to the right of the 

option. It is inactive if “OFF” appears to the right of the option. 

Any active criteria will be printed on demand.

To Set Print Criteria

Access the Set Print Criteria screen from the pH (mV, Ion) 

Setup screen. The current print criteria are displayed on the screen.

Use the arrow keys to highlight the print criteria option you want 

to modify.

Touch ON or OFF change the status of the criteria.

Repeat steps 2 and 3 with the remaining criteria.

Touch save to save the entire group of print criteria and return 

to the pH (mV, Ion) Setup screen.

OR

Touch exit to return to the pH (mV, Ion) Setup screen, 

without making any changes.

1

2

3

4

5
You have three options for setting the print interval: manual printing, 

stable reading printing, and timed interval printing. 

For manual printing of data

In this mode, data is printed only when you touch print

on the pH (mV, Ion) Measure screen.

Access the Set Print Interval screen from the pH (mV, Ion) 

Setup screen. The current print interval is displayed on the screen.

Touch MAN to set the meter for manual printing.

Touch enter to accept the print interval mode and return to the pH 

(mV, Ion) Setup screen.

Printing is now done manually by touching print on the 

Measure screen.

OR

Touch exit to return to the pH (mV, Ion) Setup screen, 

without making any changes.

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Set PRINT INTERVAL

1

2

3

Set pH Print Interval

enter

exit

man

1 2 3

4 5 6

7 8 9

BS 0

Current INTERVAL

stable

timed

.

manual
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Set PRINT INTERVAL

For stable reading printing

In this mode, data is printed every time the meter recognizes 

the current pH (mV, Ion) measurement as stable.

Access the Set Print Interval screen from the pH (mV, Ion) 

Setup screen. The current print interval is displayed on the screen.

Touch stable to set the meter for stable reading printing.

Touch enter to accept the print interval mode and return 

to the pH (mV, Ion) Setup screen.

Printing is now done when the meter recognizes the present reading 

as stable.

OR

Touch exit to return to the pH (mV, Ion) Setup screen, 

without making any changes.

For timed interval printing

In this mode, data is printed at the timed interval that you select.

Access the Set Print Interval screen from the pH (mV, Ion) 

Setup screen. The current print interval is displayed on the screen.

Touch timed to access the timed interval mode and delete the 

current print interval time.

Use the keypad to enter the desired time for the print interval.

Touch enter to accept the new time interval for printing and 

return to the pH (mV, Ion) Setup screen.

Printing is now done at the set timed interval.

OR 

Touch exit to return to the pH (mV, Ion) Setup screen, 

without making any changes.

1

2

3

1

2

3

4
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Set DATA STORAGE CRITERIA

Set pH Data Storage Criteria

Current DATA STORAGE CRITERIA

- Date/Time/Channel ON

- Sample ID# ON

- pH measurement ON

- Temperature - ATC ON

- Last Standardization OFF

- Current Buffers OFF

- Slope ON

- mV measurement ON

- Meter model #/serial # ON

- Operator ON

Set mV Data Storage Criteria

Current DATA STORAGE CRITERIA

- Date/Time/Channel ON

- Sample ID# ON

- mV measurement ON

- Temperature - ATC ON

- Meter model #/serial # ON

- Operator ON

Set Ion Data Storage Criteria

Current DATA STORAGE CRITERIA

- Date/Time/Channel ON

- Sample ID# ON

- Ion measurement ON

- Temperature - ATC ON

- Last Standardization OFF

- Current Standards OFF

- Slope ON

- mV measurement ON

- Meter model #/serial # ON

- Operator ON

- electrode/method ON
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Set DATA STORAGE CRITERIA

The Date/Time/Channel 

criteria and the

Measurement criteria are

always active and cannot

be deactivated. These 

criteria will always be

stored with the measurement value. Because they

can not be changed,

they will not be highlighted when using the 

arrow keys.

This screen allows you to select what criteria are stored in the meter’s

memory with the measurement when you save the data. Data is stored

only if a Sample ID# has been assigned. The status of the current data

storage criteria is displayed on the screen. The criteria option is active 

if “ON” appears to the right of the option. It is inactive if “OFF”

appears to the right of the option. All storage criteria will be stored in

the meter’s memory with the measurement. However, only active items

will appear on the View Stored Data screens. Changing the status of 

the storage criteria to active from inactive will allow the criteria to be 

displayed with the previously stored data.

To Set Data Storage Criteria

Access the Set Data Storage Criteria screen from the 

pH (mV, Ion) Setup screen. The current Data 

Storage Criteria are displayed on the screen.

Use the arrow keys to highlight the data storage criteria you 

want to modify.

Touch ON or OFF to change the status of the criteria.

Repeat steps 2 and 3 with the remaining criteria.

Touch save to save the entire group of data storage criteria 

and return to the pH (mV, Ion) Setup screen.

OR

Touch exit to return to the pH (mV, Ion) Setup screen, 

without making any changes.

1

2

3

4

5
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Set DISPLAY RESOLUTION

Set pH Display Resolution

enter

exit

help

Select desired display resolution and then 

touch enter to accept

X.X

X.XX

Current RESOLUTION

X.XXX

X.XX
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Set DISPLAY RESOLUTION

This mode allows you to set the display resolution that you desire on the

screen. You have the choice of one, two or three decimal places. 

To Set Display Resolution

Access the Set Display Resolution screen from the pH Setup screen. 

The current Display Resolution is displayed on the screen.

Touch X.X, X.XX or X.XXX to select the desired resolution of the 

display. This will be the format in which your measurement will be 

displayed.

Touch enter to accept the resolution and return to the pH Setup 

screen.

OR

Touch exit to return to the pH Setup screen, 

without making any changes.

1

2

3

07.0

pH channel 1

Example of X.X resolution

07.00

pH channel 1

Example of X.XX resolution

07.000

pH channel 1

Example of X.XXX resolution

Remember, HELP is

always just a touch of the

button away.
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Set DISPLAY CONFIGURATION

Set pH Display Configuration

Current DISPLAY CONFIGURATION

- Last Standardization ON

- Date ON

- Time ON

- measurement channel ON

- sample ID# ON

- auto buffer status ON

- auto read status ON

- temperature ON

- slope ON

- mV Display ON

Set mV Display Configuration

Current DISPLAY CONFIGURATION

- Date ON

- Time ON

- measurement channel ON

- sample ID# ON

- temperature ON

Set Ion Display Configuration

Current DISPLAY CONFIGURATION

- Last Standardization ON

- Date ON

- Time ON

- measurement channel ON

- sample ID# ON

- auto read status ON

- temperature ON

- slope ON

- mV Display ON

- electrode/method ON
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Set DISPLAY CONFIGURATION

This function will allow you to choose what information you would like 

to be displayed on the pH Measure screen, particularly the information

contained in the data box at the bottom of that screen. 

To Set Display Configuration

Access the Set Display Configuration screen from the pH (mV, Ion)

Setup screen. The current Display Configuration is displayed on 

the screen.

Use the arrow keys to highlight the Display Configuration criteria 

you want to modify.

Touch ON or OFF to change the status of the criteria.

Repeat steps 2 and 3 with the remaining criteria.

Touch save to save the entire group of Display Configuration criteria

and return to the pH (mV, Ion) Setup screen.

OR

Touch exit to return to the pH (mV, Ion) Setup screen, without 

making any changes. 

1

2

3

4

5

ATC

slope

mV

25.0 °C

100%

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

pH Display Configuration
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View STORED DATA

View Stored Data

enter

exit

help

Use arrow keys to highlight desired sort

option and then touch enter to accept

Data POINTS 17

Sample ID

Date

Operator
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View STORED DATA

This pH meter has memory capacity of up to 250 data points. The View

Stored Data screen allows you to sort and look at specific data points.

The stored data can be sorted by sample identification number, date or

operator identification number. 

To View Stored Data

Access the View Stored Data screen from the pH (mV, Ion) 

Setup screen. The number of data points in the memory and the 

sorting options are now displayed on the screen.

Use the arrow keys to highlight the desired data sort option.

Touch enter to access the sort option screen.

To sort by Sample ID#

Access the Sample ID sort option from the View Stored Data screen.

Use the keypad to enter the sample ID# of the data point(s) that you

want to view.

Touch clear to delete a Sample ID# entered in error and reenter 

the ID#.

Touch enter. All data will be sorted by the meter and the first data

point displayed on the screen will be the most recent data point saved

under the selected Sample ID#.

Touch next or prev to scroll through additional data points saved 

in the memory of the meter.

Touch print to send the data to a printer or computer, OR touch 

delete to erase the data point from the meter’s memory, OR touch 

exit to return to the pH (mV, Ion) Setup screen.

If a sample ID# is entered and no data points are stored with that sample ID#,

you will see a message indicating the sample ID# was not found. Touch OK to

return to the sample ID# keypad and enter a new sample ID#.

1

2

3

1

2

3

4

5

6
To sort by Date

Access the Date sort option from the View Stored Data screen.

Touch clear to delete the current date.

Use the numeric keypad to enter the date on which the data points

you want to view were saved. Be sure to use / to separate the month,

the day and the year.

Touch enter. All data will be sorted by the meter and the first data

point displayed on the screen will be the most recent data point saved 

under the selected Date.

Touch next or prev to scroll through additional data points saved 

in the memory of the meter.

Touch print to send the data to a printer, OR touch delete to erase 

the data point from the meter’s memory, OR touch exit to return to 

the pH (mV, Ion) Setup screen.

If a date is entered and no data points are stored with that date, you will see a

message indicating the date was not found. Touch OK to return to the operator

ID keypad and enter a new date.

To sort by Operator

Access the Operator sort option from the View Stored Data screen.

Use the keypad to enter the Operator ID of the data point(s) that you

want to view.

Touch clear to delete an Operator ID entered in error and reenter 

an ID#.

Touch enter. All data will be sorted by the meter and the first data

point displayed on the screen will be the most recent data point saved 

under the selected Operator ID.

Touch next or prev to scroll through additional data points saved 

in the memory of the meter.

Touch print to send the data to a printer, OR touch delete to erase 

the data point from the meter’s memory, OR touch exit to return to 

the pH (mV, Ion) Setup screen.

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1

2

3

4

5

6

View STORED DATA

1

2

3

4

5

6
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View STORED DATA

If an operator ID is entered and no data points are stored with that operator ID,

you will see a message indicating the operator ID was not found. Touch OK to

return to the operator ID keypad and enter a new operator ID.

NOTE:

Even if you do not know the appropriate information to access a specific 

data point, you can access the stored data through any of the sort options.

Highlight the sort option of interest and touch enter to access the sort screen.

Touch enter again and the meter will place you at a data point. 

* The sample ID# sort option will place you at the first data point in

numeric order by sample ID#.

* The Operator sort option will place you at the data point of the first

operator ID in alphabetic order. 

* The Date sort option will place you at the most recent point on the last

date that data was stored. 

Once you access the data storage center, you can touch prev and next to

scroll through the additional data points stored in memory.

View Stored Data

Current STORED DATA

September 17, 1997

11:11 am

Channel: 1

sample ID#: 110

Ion value: 1.0

Ion method: Known Addition

Ion electrode: AMMONIA

Temperature: 25.0°C

Last Std: Sep.17 @11:11am

Current Stds: 10.0 100

Slope: 102.2%

mV value: 0.6

model#/serial#: AR25/alpha 0001

Operator: Tom D.
mV Setup (channel 1) 

edit

exit

help

mV SETUP OPTIONS

 - Set Sample ID# 

 - Set Alarm Limit

 - Set Print Criteria

 - Set Print Interval

 - Set Data Storage Criteria

 - Set Display Resolution

 - Set Display Configuration

 - View Stored Data 

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mV SETUP
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TABLE OF CONTENTS

The operating parameters of the mV mode can be set and controlled from the

mV Setup screen. The following sections will guide you through the various

options available for the mV setup mode.

Access mV SETUP 

Set SAMPLE ID#

Set ALARM LIMIT

Set PRINT CRITERIA

Set PRINT INTERVAL

Set DATA STORAGE CRITERIA

Set DISPLAY RESOLUTION

Set DISPLAY CONFIGURATION

View STORED DATA

82

84

84

84

85

85

86

85

85
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Access mV SETUP

There are two ways to access the mV Setup screen. 

From the Setup screen

Touch setup on the main screen. Touch 

mV to access the mV Setup screen.

Use the arrow keys to highlight the setup

option that you would like to review.

Touch edit to access the screen for the 

selected option.

1

2

3

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11 am

Fisher Scientific

accumet AR25

Setup

Ion

system

exit

Select from the setup options to the right

mV

pH

mV Setup (channel 1) 

edit

exit

help

mV SETUP OPTIONS

 - Set Sample ID# 

 - Set Alarm Limit

 - Set Print Criteria

 - Set Print Interval

 - Set Data Storage Criteria

 - Set Display Resolution

 - Set Display Configuration

 - View Stored Data 
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Access mV SETUP

From the mV Measure screen

Touch mV on the main screen to access 

the millivolt mode. Touch setup on the

mV Measure screen. The mV Setup screen

is now displayed.

Use the arrow keys to highlight the

setup option that you would like to

review.

Touch edit to access the screen for the 

selected option.

1

2

3

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11 am

Fisher Scientific

accumet AR25

Measure

00.0

abs mV

REL

meas

setup

mode

help

Touch meas to measure sample

print

channel 1

Touch REL for Relative mV reading

or

ATC 25.0 °C

September 17, 1997 11:11 am

ID# 00000

mV Setup (channel 1) 

edit

exit

help

mV SETUP OPTIONS

 - Set Sample ID# 

 - Set Alarm Limit

 - Set Print Criteria

 - Set Print Interval

 - Set Data Storage Criteria

 - Set Display Resolution

 - Set Display Configuration

 - View Stored Data 
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To Set Sample ID#

When this option is active, each time you touch print on the Measure screen the

mV value along with the date/time/channel and the sample ID# will be sent to

data storage. You can manually enter an alphanumeric identification number of

up to 10 characters for any sample, or you can have the meter sequentially 

number your samples beginning at the number of your choice. You may also 

choose to deactivate the sample ID#.

The mV Sample ID# is set the same way as previously described in pH Setup.

See page 48 for instructions.

To Set Alarm Limit

This option allows you to set alarm limits for the mV measuring mode. If the mV

value of the measurement is outside of the boundaries set by the upper and

lower limits, an audible alarm and/or a visual warning will appear to let you

know that your sample measurement was outside of the set limits. 

The mV Alarm Limits are set the same way as previously described in pH Setup.

See page 64 for instructions.

To Set Print Criteria

This screen allows you to select which criteria are printed with the measurement

when you print the data or send it to a computer. The status of the current print

criteria is displayed on the screen. The criteria option is active if “ON” appears

to the right of the option. It is inactive if “OFF” appears to the right of the

option. Any active criteria will be printed on demand.

The mV Print Criteria are set the same way as previously described in pH Setup.

See page 66 for instructions.

Remember, HELP is

always just a touch of

the button away.
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To Set Print Interval

You have three options for setting the print interval: manual printing, stable 

reading printing, and timed interval printing. 

The mV Print Interval is set the same way as previously described in pH Setup.

See page 68 for instructions. 

To Set Data Storage Criteria

This screen allows you to select what criteria are stored in the meter’s memory

with the measurement when you save the data. The status of the current data

storage criteria is displayed on the screen. The criteria option is active if “ON”

appears to the right of the option. It is inactive if “OFF” appears to the right of

the option. All storage criteria will be stored in the meter’s memory with the measurement. However, only active items will appear on the View Stored Data

screens. Changing the status of the storage criteria to active from inactive will

allow the criteria to be displayed with the previously stored data.

The mV Data Storage Criteria are set the same way as previously described in

pH Setup. See page 70 for instructions.

To Set Display Configuration

This function will allow you to choose what information you would like to be 

displayed on the mV Measure screen, particularly the information contained 

in the data box at the bottom of that screen. 

The mV Display Configuration is set the same way as previously described in pH

Setup. See page 74 for instructions

To View Stored Data

This meter has memory capacity for up to 250 data points. The View Stored

Data screen allows you to sort and look at specific data points. The stored data

can be sorted by sample identification number, date or operator identification

number. 

The mV Stored Data is viewed the same way as previously described in pH

Setup. See page 76 for instructions.
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Set DISPLAY RESOLUTION

Set mV Display Resolution

enter

exit

help

Select desired display resolution and then 

touch enter to accept

X

X.X

Current RESOLUTION X.X
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Set DISPLAY RESOLUTION mV Setup

To Set Display Resolution

This mode allows you to set the display resolution that you desire 

on the screen. You have the choice of zero or one decimal place. 

Access the Set Display Resolution screen from the mV Setup screen. 

The current Display Resolution is displayed on the screen.

Touch X or X.X to select the resolution of the display that you desire.

This will be the format in which your measurement will be displayed.

Touch enter to accept the resolution and return to the mV setup screen.

OR

Touch exit to return to the mV Setup Screen, 

without making any changes.

1

2

3

0-177

mV channel 1

Example of X resolution

-177.0

mV channel 1

Example of X.X resolution
Ion Setup (channel 1) 

edit

exit

help

ION SETUP OPTIONS

 - Set Sample ID# 

 - Select Ion Method

 - Select Measurement Units

 - Select Auto Read Mode 

 - Set Ion Stability Criteria

 - Set Default Temperature

- Select Electrode Type 

 - Set Isopotential Point

 - Set Alarm Limits

 - Set Print Criteria

 - Set Print Interval

 - Set Data Storage Criteria

 - Set Significant Digits

 - Set Display Configuration

 - View Stored Data 

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Ion Setup
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TABLE OF CONTENTS

The operating parameters of the ion mode can be set and controlled from the

Ion Setup screen. The following sections will guide you through the various

options available for the ion setup mode. 

Access ION SETUP

Set SAMPLE ID#

Select ION METHOD

Select MEASUREMENT UNITS

Select AUTO READ MODE

Set ION STABILITY CRITERIA

Set DEFAULT TEMPERATURE

Select ELECTRODE TYPE

Set ISOPOTENTIAL POINT

Set ALARM LIMITS

Set PRINT CRITERIA

Set PRINT INTERVAL 

Set DATA STORAGE CRITERIA

Set SIGNIFICANT DIGITS

Set DISPLAY CONFIGURATION

View STORED DATA

90

92

92

94

95

95

95

96

98

98

98

99

99

100

101

101
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Access ION SETUP

There are two ways to access the Ion Setup screen. 

From the Setup screen

Touch setup on the main screen. Then touch 

Ion to access the Ion Setup screen.

Use the arrow keys to highlight the setup

option that you would like to review.

Touch edit to access the selected option 

screen.

1

2

3

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11 am

Fisher Scientific

accumet AR25

Setup

Ion

system

exit

Select from the setup options to the right

mV

pH

Ion Setup (channel 1) 

edit

exit

help

ISE SETUP OPTIONS

 - Set Sample ID# 

 - Select Ion Method

 - Select Measurement Units

 - Select Auto Read Mode 

 - Set Ion Stability Criteria

 - Set Default Temperature

- Select Electrode Type 

 - Set Isopotential Point

 - Set Alarm Limits

 - Set Print Criteria

 - Set Print Interval

 - Set Data Storage Criteria

 - Set Significant Digits

 - Set Display Configuration

 - View Stored Data 
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Access ION SETUP

From the Ion Measure screen

Touch Ion on the main screen to access 

the Ion mode. Touch setup on the Ion 

Measure screen. The Ion Setup screen is 

now displayed.

Use the arrow keys to highlight the 

setup option that you would like to review.

Touch edit to access the selected option 

screen.

1

2

3

Select from the options to the right

pH

mV

Ion

setup

channel

September 17, 1997 11:11 am

Fisher Scientific

accumet AR25

Ion Setup (channel 1) 

edit

exit

help

ISE SETUP OPTIONS

 - Set Sample ID# 

 - Select Ion Method

 - Select Measurement Units

 - Select Auto Read Mode 

 - Set Ion Stability Criteria

 - Set Default Temperature

- Select Electrode Type 

 - Set Isopotential Point

 - Set Alarm Limits

 - Set Print Criteria

 - Set Print Interval

 - Set Data Storage Criteria

 - Set Significant Digits

 - Set Display Configuration

 - View Stored Data 

Measure - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

print

channel 1

Touch std to access standardize mode

ID#

NH3

auto read

00000

ON

0.0

STANDARDS Last std: Jan 28 @ 10:17 am

meas
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Select ION METHOD

Remember, HELP is

always just a touch of

the button away.

To Set Sample ID#

When this option is active, each time you touch print on the Measure

screen the ion concentration value along with the date/time/channel

and the sample ID# will be sent to data storage. You can manually enter

an alphanumeric identification number of up to 10 characters for any

sample or you can have the meter sequentially number your samples

beginning at the number of your choice. You may also choose to 

deactivate the sample ID#. 

The Ion Sample ID# is set the same way as previously described in pH

Setup. See page 48 for instructions.

To Select Ion Method

Use the arrow keys to highlight the method you want to use.

Touch enter to accept the method and return to the Ion Setup screen.

OR

Touch exit to return to the Ion Setup screen, 

without making any changes.

1

2

Select Ion Method

enter

Current METHOD Blank

Direct Reading with Standards

Direct Read with Blank offset

Known Addition

Known Subtraction

Analate Addition

Analate Subtraction
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Select ION METHOD

Direct Reading with Standards

The direct reading method is the most common method of ion measurement.

When using this method, you will use standards of known values to standardize

the meter in the ion mode. An ionic strength adjuster (ISA) is added to both the

standards and the sample. Then 2 to 5 standards are used to standardize the

meter. The standards should bracket the expected value of the sample. The Ion

specific electrode is immersed in a stirring sample and the ion concentration is

read directly from the meter.

Direct Reading with Blank offset

The blank method is a method commonly used for determination of ion 

concentration in a sample with a very low level of ions present. Because of 

background interference at low concentration levels, a blank is used and the

value of the ion concentration in the blank is subtracted from the value of the

measured sample.

Known Addition

The known addition method is an incremental method used for samples with a

complex matrix. A standard with a known concentration of the ion species of

interest is added to the sample. The difference in mV potential is then used to 

calculate the concentration of the ion of interest. 

Known Subtraction

The known subtraction method is also an incremental method. The ion of interest

in the sample is not identical to the ion in the standard solution. The standard of

known ion concentration that is added to the sample quantitatively reacts in the

sample with the ion of interest. This reaction removes a fixed amount of the ion

of interest from the sample solution. The ion concentration is then calculated

based upon the difference in the mV potential. 

Analate Addition

The analate addition method is a modification of the known addition method. 

In the Analate Addition method, the initial mV measurement is recorded in a 

standard solution. The ion in the standard solution is the ion of interest and is

detected by the ion selective electrode in use. A sample containing the ion of

interest is then added to the standard solution. The difference in the mV potential

is then used in the calculation of the concentration of the ion of interest. This

method is useful if the sample temperature is significantly different than that of 

the standard. When the small volume of hot sample is added to the larger 

volume, the temperature impact becomes negligible.

Analate Subtraction

The Analate Subtraction method is particularly useful in the event that there is no

ion specific electrode available to directly measure the concentration of the ion 

of interest. This particular method employs the addition of a sample of the ion 

of interest to a standard containing a different ion of known concentration. 

The ion of interest will quantitatively react with the ion in the standard, creating 

a complex and removing the ion from the standard solution. The ion specific 

electrode is specific for the ion in the standard and not for the ion of interest. 

The difference in mV potential is used to calculate the concentration of the ion 

of interest based upon this quantitative reaction.
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Select MEASUREMENT UNITS

This screen allows you to select the units in which the meter will report

the concentration of the ion of interest. The current units are displayed

on the screen.

To Select Measurement Units

Access the Select Measurement Units screen from the Ion Setup screen.

The current units are displayed on the screen.

Use the arrow keys to highlight the desired units.

Touch enter to accept these units and return to the Ion Setup screen.

OR 

Touch exit to return to the Ion Setup screen, 

without making any changes.

1

2

3

Select Ion Measurement Units

enter

Current UNITS mg/ml

ppm

mg/ml

mg/L

mole/L

Percent
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Regardless of the status

of the Auto Read Mode, 

STABLE will be displayed 

as the meter recognizes

the measurement as 

stable.

Stability criteria are more

stringent at the slower

setting. Therefore, if the

highest precision is

required, then a slow 

setting would be desired. The medium or slow

setting is recommended

for Ion work.

Best results are obtained

when the standards and

the samples are at the

same temperature.

To Select Auto Read Mode

You can use this meter when the Auto Read function is active or when it

is inactive. When the Auto Read function is active, the meter will lock

onto a reading when the meter recognizes it as stable. The meter will 

not deviate from this reading until meas is touched. If the Auto Read

function is inactive, then the meter will continuously monitor the 

concentration of the ion of interest. The display on the measure screen

will indicate any fluctuation in the ion concentration. 

The Ion Auto Read Mode is set the same way as previously described 

in pH Setup. See page 57 for instructions.

To Set Ion Stability Criteria

This setup screen allows you to determine how quickly the meter will

respond to electrode drift. There are 3 speed settings. 

The Ion Stability Criteria is set the same way as previously described in

pH Setup. See page 68 for instructions.

To Set Default Temperature

Ion concentration is a temperature dependent measurement. The default

temperature option allows you to select the temperature that will be 

used by the meter to calculate the correct ion concentration. The factory

default setting is 25°C. You should enter the temperature value of that

solution as the default temperature in order to get the correct concentration value. The current default temperature setting will be displayed when

the Set Default Temperature screen is displayed.

The Ion Default Temperature is set the same way as previously described

in pH Setup. See page 60 for instructions.
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Select ELECTRODE TYPE

Remember, HELP is

always just a touch of

the button away.

Select Ion Electrode Type

exit

help Use arrow keys to highlight desired 

electrode type and then touch enter to accept

enter

Current CHLORIDE

AMMONIA

BROMIDE

CALCIUM

CARBON DIOXIDE

CHLORIDE

CYANIDE

FLUORIDE

NITRATE

POTASSIUM

SODIUM

MONOVALENT CATION

MONOVALENT ANION

DIVALENT CATION

DIVALENT ANION
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Select ELECTRODE TYPE

This screen allows you to select the type of electrode that is specific for

your ion of interest. Your choice of electrode informs the meter which

default slope to use in the calculations made for electrode efficiency and

sample concentration. Once you have selected an electrode, you will not

be required to enter the default slope numerically. 

Note: The default slope value specific for the electrode that you choose

is a theoretical slope value that is used in the calculations to determine

the efficiency of your electrode. This slope value is not the slope value

that is displayed in the data box of the measurement screen. You will 

still need to standardize the meter using ion standards to determine the

actual efficiency of your electrode. 

To Select Electrode Type

Access the Select Electrode Type screen from the Ion Setup screen. 

The current electrode type is displayed on the screen.

Use the arrow keys to highlight the electrode type specific for the Ion 

of interest.

Touch enter to accept the electrode type and return to the Ion Setup

screen.

OR

Touch exit to return to the Ion Setup screen, 

without making any changes.

1

2

3
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To Set Isopotential Point

The Isopotential Point is the millivolt reading for an electrode at which

temperature has no effect on the measurement. Ion selective electrodes,

unlike pH electrodes, are not designed to achieve any particular 

isopotential point. If samples and standards are at different temperatures

when performing ISE experiments, it will be necessary to experimentally

determine the isopotential point of your Ion Specific Electrode. (see

Appendix: Determining Isopotential Point Experimentally page 137.)

The Ion Isopotential Point is set the same way as previously described 

in pH Setup. See page 62 for instructions.

To Set Alarm Limits

This option allows you to set alarm limits for the Ion measuring mode. 

If the ion concentration measurement is outside of the boundaries set by

the upper and lower limits, an audible alarm and/or a visual warning

will appear to let you know that your sample measurement was outside

of the set limits. 

The Ion Alarm Limits are set the same way as previously described in 

pH Setup. See page 64 for instructions.

To Set Print Criteria

This screen allows you to select what criteria are printed with the 

measurement when you print the data or send it to a computer. The 

status of the current print criteria is displayed on the screen. The criteria

option is active if “ON” appears to the right of the option. It is inactive 

if “OFF” appears to the right of the option. Any active criteria will be

printed on demand.

The Ion Print Criteria are set the same way as previously described in

pH Setup. See page 66 for instructions.
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To Set Print Interval

You have three options for setting the print interval: manual printing, 

stable reading printing, and timed interval printing.

The Ion Print Interval is set the same way as previously described in 

pH Setup. See page 68 for instructions. 

To Set Data Storage Criteria

This screen allows you to select what criteria are stored in the meter’s

memory with the measurement when you save the data. The status of the

current data storage criteria is displayed on the screen. The criteria

option is active if “ON” appears to the right of the option. It is inactive 

if “OFF” appears to the right of the option. Any active criteria will be

stored with the measurement. All storage criteria will be stored in the

meter’s memory with the measurement. However, only active items will

appear on the View Stored Data screens. Changing the status of the 

storage criteria to active from inactive will allow the criteria to be 

displayed with the previously stored data.

The Ion Data Storage Criteria are set the same way as previously

described in pH Setup. See page 70 for instructions.
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Set SIGNIFICANT DIGITS

Set Ion Significant Digits

enter

exit

help

Select desired significant digits and then 

touch enter to accept

1

2

Current SIG DIGITS

3

1

Example of 1 significant digit

ppm channel 1

9E4

Example of 2 significant digits

ppm channel 1

9.3E4

Example of 3 significant digits

ppm channel 1

9.34E4
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Set SIGNIFICANT DIGITS

This option allows you to select the number of significant figures that will

be used when reporting your ion measurement. You have the choice of

one, two or three significant digits. 

To Set significant digits

Access the Set Significant Digits screen from the Ion Setup screen. 

The current Significant digits are displayed on the screen.

Touch 1, 2, or 3 to select the desired significant digits.

Touch enter to accept the number of significant digits and return to 

the Ion Setup screen.

OR

Touch exit to return to the Ion Setup screen, 

without making any changes.

To Set Display Configuration

This function will allow you to choose what information you would like to

be displayed on the Ion Measure screen, particularly the information

contained in the data box at the bottom of that screen. 

The Ion Display Configuration is set the same way as previously

described in pH Setup. See page 74 for instructions.

To View Stored Data

This meter has memory capacity for up to 250 data points. The View

Stored Data screen allows you to sort and look at specific data points.

The stored data can be sorted by sample identification number, date 

or operator identification number. 

The Ion Stored Data is viewed the same way as previously described 

in pH Setup. See page 76 for instructions.

1

2

3
102

pH Operation accumet®

RESEARCH

Measure

07.00

pH

std

meas

setup

mode

help

Touch meas to measure sample print

channel 1

Touch std to standardize

or

ATC

slope

mV

25.0 °C

100%

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

BUFFERS Last std: Sep 17 @ 10:17 am

4 7 10
103

accumet pH Operation

®

RESEARCH

In this mode, you will be able to measure the pH of a wide variety of

samples. Before measuring pH, you will need to standardize the meter

using buffers with known pH values. It is good practice to standardize

the meter frequently using a minimum of two buffers. Using two buffers

allows the meter to calculate and display an actual slope for the 

electrode, and therefore produce more accurate measurements. If there

is no standardization in the memory of the meter or if only one buffer

has been used to standardize the meter, the slope value will appear as

“NA”.

You can standardize your meter using automatic or manual buffer 

recognition. With the Automatic buffer recognition activated, the meter

will automatically recognize the buffers from the chosen buffer group

and accept them when the meter recognizes the reading as stable.

When in the Manual buffer recognition mode, you must enter the buffer

value during the standardization procedure. The meter will accept the

manually entered buffer when it recognizes that the measurement is 

stable. During the standardization procedure, you may accept the 

buffer value before the meter recognizes it as stable by touching std.

See page 56 to select desired buffer recognition.

At the Basic Procedural level the only setup options that you can access

are the Buffer Groups, the Print Interval and the Display Resolution. If

you need to change any other parameter such as Buffer Recognition or

Auto Read mode you will need to set the Procedural Level to Advanced

in the System Setup screen. Any values previously saved in the pH Setup

screen at the Advanced Procedural Level will become the default values

for the Basic Procedural Level. 

Remember to setup your pH measuring mode parameters. Refer to pages

44-79 for pH setup instructions. 

Connect the electrodes you will be using to the meter. See page 10 

for details.
104

pH Operation accumet®

RESEARCH

Standardizing

Remember, HELP is

always just a touch of

the button away.

Standardize

07.00

pH

std

meas

setup

mode

help

Insert electrode into buffer and stir

clear

channel 1

Touch std to standardize new buffer

ATC

slope

mV

25.0 °C

100%

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

BUFFERS Last std: Sep 17 @ 10:17 am

Current BUFFER GROUP USA

4 7 10

Touch clear to delete previous buffers

Measure

07.00

pH

std

meas

setup

mode

help

Touch meas to measure sample print

channel 1

Touch std to standardize

or

ATC

slope

mV

25.0 °C

100%

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

BUFFERS Last std: Sep 17 @ 10:17 am

4 7

STABLE
105

accumet pH Operation

®

RESEARCH

Standardizing

For optimal results, the

meter should be standardized at a minimum of

every 8 hours. For more

accurate measurements,

the meter should be standardized more frequently.

To Standardize the meter with Auto Buffer Recognition

Touch STD on the pH measure screen to access the standardize screen.

Touch clear to delete a previous standardization. All pH 

standardization values will be cleared. The meter will remain 

on the Standardization screen at this point. 

OR 

If the screen says “Not Standardized” proceed to step 3.

Immerse your rinsed electrode(s) in a buffer solution from the selected

buffer group that you chose during the setup process (see pages 54)

and stir gently.

Touch std again to standardize the meter using this buffer. The word

MEASURING will flash until the signal is stable. The meter will accept

the value once it recognizes that the reading is stable. At that time,

STABLE will appear on the screen. A beaker icon and the entered pH

value will also appear on the screen at this time. The meter will then

return to the measure screen. 

Touch std on the pH measure screen to access the standardization

screen and repeat steps 3 through 5 to standardize with up to 5

buffers.

Updating a standardization with Auto Buffer Recognition:

You can update a standardization at anytime. To update a standardization,

place your electrode in any of the buffers originally used to standardize the

meter and touch std on the touch screen twice. The value for that buffer will be

updated and stored in the meter’s memory. The time of standardization will also

be updated on the pH measurement screen.

The efficiency of the electrode is reported as the slope. When doing a multi-point

standardization, the slopes of the individual segments are calculated by the

meter. The slope that appears on the screen is the slope that is the least perfect,

or the farthest from 100%. 

1

2

3

4

5
106

pH Operation accumet®

RESEARCH

Standardizing

Standardize

07.00

pH

std

meas

setup

mode

help

Insert electrode into buffer and stir

clear

channel 1

Touch std to standardize new buffer

ATC

slope

mV

25.0 °C

100%

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

BUFFERS Last std: Sep 17 @ 10:17 am

Current BUFFER GROUP USA

4 7 10

Touch clear to delete previous buffers

Standardize

7.00

pH

std

meas

setup

mode

help

Insert electrode into buffer and stir

clear

channel 1

Touch std to standardize new buffer

ATC

slope

mV

25.0 °C

NA

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

BUFFERS Not standardized

Current BUFFER GROUP USA

Touch clear to delete previous buffers

1 2 3

4 5 6

7 8 9

exit

Enter pH

BS enter

- 0 .
107

accumet pH Operation

®

RESEARCH

Standardizing

To standardize the meter with manual buffer recognition

Touch std on the pH measure screen to access the standardize screen.

Touch clear to delete a previous standardization. All pH 

standardization values will be cleared. The meter will remain 

on the Standardization screen at this point. 

OR

If the screen says “Not Standardized” proceed to step 3.

Immerse your rinsed electrode(s) in a buffer solution and stir gently.

Touch std again to standardize the meter using this buffer. 

Using the displayed keypad, input the value of the buffer that you are

using to standardize the meter and then touch enter. The meter will

accept the value once it recognizes that the reading is stable. At that

time, STABLE will appear on the screen. A beaker icon and the 

entered pH value will also appear on the screen at this time. The 

meter will return to the pH measure screen. 

Touch std on the pH measure screen to access the standardization

screen and repeat steps 3 through 5 to standardize with up to 5

buffers.

Updating a standardization with Manual Buffer Recognition:

You can update a standardization at any time. To update a standardization with

manual buffer recognition, place your electrode in any of the buffers originally

used to standardize the meter and touch the std key on the touch screen twice.

Then using the keypad displayed on the screen enter the value of the buffer and

touch enter. The value for that buffer will be updated and stored in the meter’s

memory. The time of standardization will also be updated on the pH measure

screen.

1

2

3

4

5

6
108

pH Operation accumet®

RESEARCH

pH MEASUREMENTS

Remember, HELP is

always just a touch of

the button away.

Measure

07.00

pH

std

meas

setup

mode

help

Touch meas to measure sample print

channel 1

Touch std to standardize

or

ATC

slope

mV

25.0 °C

100%

0000.0

September 17, 1997 11:11 am

ID#

auto buffer

auto read

00000

ON

ON

BUFFERS Last std: Sep 17 @ 10:17 am

4 7 10
109

accumet pH Operation

®

RESEARCH

pH MEASUREMENTS

The measure screen provides a readout of the current sample measurement. You can use this meter when the Auto Read function is active or

when it is inactive. When the Auto Read function is active, the meter will

lock onto a reading when the meter recognizes it as stable. The meter

will not deviate from this reading until meas is touched. If the Auto

Read mode is inactive, then the meter will continuously monitor the pH of

the sample and the measure display screen will indicate any fluctuation

in the sample pH. Regardless of the status of the Auto Read mode, 

STABLE will flash as the meter recognizes the measurement as stable.

Once the meter is standardized, you are ready to take pH measurements

of your sample. 

To measure pH of a sample with Auto Read ON

Immerse the rinsed electrode(s) in the stirring sample.

Touch meas to begin measuring your sample. The meter will accept the

reading and display STABLE when the measurement meets the selected

stability criteria.

OR

To measure pH of a sample with Auto Read OFF

Immerse the rinsed electrode(s) in the stirring sample.

Record the reading once the measurement has become stable. STABLE

will appear once the meter recognizes that the measurement is stable.

NOTES: You can access other functions of the meter with the remaining buttons

on the measure screen. 

• Touching print will send the data to the meter’s memory if the sample ID# 

is activated and to a printer or computer if it is attached to the meter. The 

saved data can be accessed through the View Stored Data screen in the pH 

Setup mode. 

• Touching setup will access the pH Setup screen. For detailed information

regarding pH Setup see pages 44-79. 

• Touching meas will initiate a new measurement of a sample.

• At anytime, you can touch mode to access another mode of operation 

including: mV, rel mV, Ion or the setup mode or place the meter 

in the standby mode.

1

2

1

2
110

mV Operation accumet®

RESEARCH

This mode is used to measure oxidation/reduction potential (ORP/redox),

perform titration and to verify the function of the meter. The mV measure

function allows you to continuously monitor the mV potential of the 

electrodes in use. This can be done in either absolute or relative mV. 

In the millivolt mode, the current millivolt output from the electrodes being

used is monitored and displayed on the screen. The meter will continually

monitor the millivolt reading in this mode and will not lock onto a single

reading. However, once the reading has become stable, a stable 

message will be displayed. Remember to setup your mV measuring 

mode parameters. Refer to pages 80-87 for mV setup instructions.

Measure

00.0

abs mV

REL

setup

mode

help

print

channel 1

Touch REL for Relative mV reading

ATC 25.0 °C

September 17, 1997 11:11 am

ID# 00000
111

accumet mV Operation

®

RESEARCH

mV MEASUREMENT

Rinse the electrode with

water and blot dry. Do

not wipe the electrode.

Wiping the electrode can

cause a static charge on

the glass bulb that will

result in inaccurate 

readings.

In the mV mode, you will be able to make measurements in either

absolute or relative millivolts, access the mV Setup screens and print 

your results to a printer or a computer.

Connect the electrodes you will be using to the meter. See page 10 for details.

Absolute mV measurements

Access the mV Measure screen from the main screen.

Touch ABS to access the Absolute mV screen.

Immerse your rinsed electrode(s) in the sample and stir gently. 

Record the measurement when STABLE is displayed.

Touch print to store a measurement with an assigned ID# in the

data storage center of the meter or print the data to a printer or 

computer.

Relative mV measurements

In this mode, the first mV reading is set to zero and all subsequent readings are

relative to this initial mV measurement. 

Access the mV Measure screen from the main screen.

Touch REL to access the Relative mV screen.

Immerse your rinsed electrode(s) in the stirring sample. 

Record the measurement when STABLE is displayed.

Touch print to store a measurement with an assigned ID# in the data

storage center of the meter or print the data on a printer or computer.

1

2

3

4

5

1

2

3

4

5
112

Ion Operation accumet®

RESEARCH

Measure - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

102.2%

0.0

September 17, 1997 11:11 am

or

print

channel 1

Touch meas to measure sample

ID#

NH3

auto read

00000

OFF

17

STNDS Last std: Sep 17 @ 10:17 am

10.0 100

Touch std to access standardize mode

or measure blank

meas
113

accumet Ion Operation

®

RESEARCH

Remember to setup your

Ion measuring mode

parameters. Refer to

pages 88-101 for Ion

setup instructions.

The accumet AR50 meter offes you unparalleled versatility with respect to

ion analysis. You can choose one of 6 methods of analysis, the specific

electrode you will be working with and also the units that you would like

the meter to use when reporting the ion concentration. The Ion Measure

screen displays the direct readout of sample concentration in the desired

units, as well as the time and date of the last calibration. The standards

used in the calibration and the slope of the electrode are also displayed

on the screen. It is important to note that the concentration reported by

the meter is actually the concentration of free uncomplexed ions in 

your solution. 

At the Basic Procedural level the only setup options that you can access

are the Electrode Type, the Print Interval and the number of Significant

Digits. If you need to change any other parameter such as Ion method or

measurement units you will need to set the Procedural Level to Advanced

in the System Setup screen. Any values previously saved in the Ion Setup

screen at the Advanced Procedural Level will become the default values

for the Basic Procedural Level. 

Connect the electrodes you will be using to the meter. See page 10 

for details.

Remember, HELP is

always just a touch of 

the button away.
114

Ion Operation accumet®

RESEARCH

DIRECT READING METHODS

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

100.2%

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

Touch clear to delete previous standards

ID#

NH3

auto read

00000

OFF

- - -

STNDS Last std: Sep 17 @ 10:17 am

10.0 100

Touch std to standardize new standard

meas

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

1 2 3

4 5 6

7 8 9

exit

Concentration

BS enter

- 0 .
115

accumet Ion Operation

®

RESEARCH

DIRECT READING METHODS

There are two direct reading methods: Direct Reading with standards

and Direct Reading with Blank offset. These types of measurements allow

you to directly read the concentration of your sample after standardizing

the meter with ion standards of known values or blank values. 

Direct Reading with Standards

This is the most common method of ion measurement. You can directly read the

concentration of the sample after standardizing the meter with ion standards. 

An ionic strength adjuster (ISA) is added to both the standards and the sample.

Two to five standards are used to standardize the meter. The standards should

bracket the expected value of the sample. 

To Standardize the Meter

You must use a minimum of two standards to standardize the meter.

Touch std on the Ion Measure screen to access the standardization

screen.

Touch clear to remove a previous standardization.

Add ionic strength adjuster to your standard.

Immerse the ion selective electrode and the appropriate reference 

electrode (or combination ISE) into the standard containing the 

lowest concentration of the ion of interest. Stir. 

Touch std again to initiate the standardization process.

Use the numeric keypad to enter the value of the standard.

Touch enter on the keypad to accept this value. If you have entered 

a value in error, touch BS to clear the value and key in a new value. 

OR

Touch exit to return to the Ion Measure screen without entering a 

standard value.

Repeat steps 3-7 with up to 5 standards. A minimum of two standards 

is required to standardize the meter in this mode.

1

2

3

4

5

6

7

8

Generally, it is important

that an ionic strength

adjuster (ISA) is added 

to both samples and 

standards to obtain 

accurate results.

If the meter has not been

standardized with at

least 2 standards, a

series of dashes will

appear in place of a

measurement value.
116

Ion Operation accumet®

RESEARCH

DIRECT READING METHODS

Measuring ion concentration in the Direct Reading 

with Standards Mode

With Auto Read on

Add Ionic strength adjuster to the sample.

Immerse the ion selective electrode in the stirring sample.

Touch meas to begin measuring your sample. The meter will accept 

the reading and display STABLE when the measurement meets the 

selected stability criteria. The measure screen will fix onto this 

measurement and will not deviate until meas is touched.

Repeat steps 1-3 with additional samples.

With Auto Read off

Add Ionic strength adjuster to the sample.

Immerse the ion selective electrode into the stirring sample. The meter

will continually monitor the ion concentration value. When the meter

recognizes the reading as stable, STABLE is displayed on the measure

screen. With the Auto Read function deactivated, the display on the

measure screen will indicate any deviation in the concentration. 

Repeat steps 1-2 with additional samples.

1

2

3

4

1

2

3
117

accumet Ion Operation

®

RESEARCH

DIRECT READING METHODS

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 BLK

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

You have selected Direct Reading with 

Blank offset operation.

Is this reading a STANDARD or BLANK?

ISE Standardize

STND BLANK

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 BLK

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

or measure blank

meas

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 BLK

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

or measure blank

meas

blank

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 BLK

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

1 2 3

4 5 6

7 8 9

exit

Concentration

BS enter

- 0 .
118

Ion Operation accumet®

RESEARCH

Direct Reading with Blank Offset

This method presents you with the ability to measure samples with low

level concentrations of the ion of interest. It eliminates background

interference by subtracting the value of a blank concentration from 

the value for the sample. See ISE Theory page 146.

To Standardize the Meter

You will need to standardize the meter with one blank and a minimum of two

standards.

Touch STD on the Ion Measure screen to access the standardize screen.

Touch clear to delete the previous standards.

Add ionic strength adjuster to the standards and the blank.

Immerse the ion selective electrode in the standard containing the 

lowest concentration of the ion of interest.

Stir the standard and/or blank.

Touch STD again to initiate the standardization process. At this point,

the meter will display the question “Is this a standard or a blank?”

Touch STND if the sample that the electrode is immersed in is an Ion

standard solution. 

OR

Touch BLANK if the sample that the electrode is immersed in is the

blank solution.

1

2

3

4

5

6

7

DIRECT READING METHODS

Remember, HELP is

always just a touch of 

the button away.
If you touched STND

Use the keypad to enter the value of the standard.

Touch enter to accept the value. The meter will accept the standard

value when it recognizes the reading as stable. 

Repeat steps 4-7 with additional standards or steps 4-7 and 11 with 

a blank sample. 

If you touched BLANK

The meter will return to the Ion Measure screen and a beaker icon

labeled blank will be displayed.

Repeat steps 4-9 if the meter has not been standardized with at least 2

standards of known ion concentration.

119

accumet Ion Operation

®

RESEARCH

DIRECT READING METHODS

11

8

9

10

Measuring Ion Concentration in the Direct Reading with

Blank Mode

With Auto Read on

Add ionic strength adjuster to the samples.

Immerse the ion selective electrode in the stirring sample 

Touch meas. When the meter recognizes the reading as stable, 

STABLE will appear on the screen. The value that appears on the

screen is the value of the sample minus the value of the blank reading.

The measure screen will fix on this measurement and will not deviate

until meas is touched again.

Repeat steps 1-3 with additional samples. The meter will update the

reading each time meas is touched.

With Auto Read off

Add ionic strength adjuster to the sample.

Immerse the ion selective electrode in the stirring sample. The meter 

will continually monitor the ion concentration value. When the meter 

recognizes the reading as stable, STABLE is displayed on the measure 

screen. With the Auto Read function deactivated, the display on the 

measure screen will indicate any deviation in the concentration reading.

1

2

3

4

1

2
120

Ion Operation accumet®

RESEARCH

INCREMENTAL METHODS

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

100.2%

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

Touch clear to delete previous standards

ID#

NH3 IM

auto read

00000

OFF

- - -

STNDS Last std: Sep 17 @ 10:17 am

10.0 100

Touch std to standardize new standard

meas

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 IM

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

Standardize - Ion

ppm

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 IM

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

1 2 3

4 5 6

7 8 9

exit

Concentration

BS enter

- 0 .
121

accumet Ion Operation

®

RESEARCH

INCREMENTAL METHODS

The incremental methods which include known addition, known 

subtraction, analate addition and analate subtraction and are 

particularly useful with samples containing complex ionic backgrounds

which cannot be matched in standards. They are also useful with 

occasional samples whose temperatures vary. More information on 

these methods is available in the ISE Theory Section (see page 146).

Standardizing the meter for all incremental methods

Prior to conducting an analysis using any of the incremental methods, it

is necessary to standardize the meter with at least two standards. This

will establish a slope value for the electrode in use. The slope value is

required in the incremental method calculations which yield the ion 

concentration of the sample. See ISE Theory page 146.

Touch std on the Ion Measure screen to access the standardize screen.

Touch clear to remove the previous standardization from the memory of

the meter.

Add ionic strength adjuster to the standards.

Immerse the ion selective electrode in the stirring standard. Always

begin standardization with the least concentrated ion standard.

Touch std again to initiate standardization. 

Use the keypad to enter value of the standard.

Touch enter on the keypad to accept this value. If you have entered 

a value in error, touch BS to clear the value and key in a new value. 

Repeat steps 3-7 with additional standards.

1

2

3

4

5

6

7

8

Remember, HELP is

always just a touch of 

the button away.
122

Ion Operation accumet®

RESEARCH

KNOWN ADDITION METHOD

Measure - Ion

mV

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

102.2%

0.0

September 17, 1997 11:11 am

print

channel 1

ID#

NH3 KA

auto read

00000

OFF

0.0

STNDS Last std: Sep 17 @ 10:17 am

10.0 100

Touch std to access standardize mode

KA

1.00

Measure - Ion

mV

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

102.2%

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

print

channel 1

ID#

NH3 KA

auto read

00000

OFF

0.0

STNDS Not Standardized

Touch std to standardize new standard

KA

Measure - Ion

mV

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 KA

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

1 2 3

4 5 6

7 8 9

exit

Sample Volume

BS enter

- 0 .

Measure - Ion

mV

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 KA

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

1 2 3

4 5 6

7 8 9

exit

Standard Volume

BS enter

- 0 .
123

accumet Ion Operation

®

RESEARCH

KNOWN ADDITION METHOD

Measure - Ion

mV

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 KA

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

1 2 3

4 5 6

7 8 9

exit

ISA Volume

BS enter

- 0 .

Measure - Ion

mV

STABLE

std

setup

mode

help

ATC

slope

mV

25.0 °C

NA

0.0

September 17, 1997 11:11 am

Insert electrode into standard and stir

clear

channel 1

ID#

NH3 KA

auto read

00000

OFF

- - -

STNDS Not standardized

Touch std to standardize new standard

meas

1 2 3

4 5 6

7 8 9

exit

Concentration

BS enter

- 0 .

12.2ppm

Known Addition Result

OK print

Calculated Slope:

Reading 1:

Reading 2:

Sample Volume:

Standard Volume:

ISA Volume:

Standard Concentration:

58 mV

222.7 mV

200.6 mV

50

10

50

100 ppm
124

Ion Operation accumet®

RESEARCH

KNOWN ADDITION METHOD

Measuring Ion Concentration in Samples Using the

Incremental Methods

When performing known addition, you will add an aliquot of standard

solution containing the ionic species of interest to a known volume of

your sample. The mV readings of the sample are taken before and after

the addition of the standard. The concentration of the sample can then

be calculated based upon the difference in the mV readings. The use of

the incremental methods requires that certain parameters be identified. In

addition to the millivolt outputs of the electrode(s) in both the sample and

the sample plus the standard, it is necessary to enter into the meter the

volume of the sample, the volume of the standard, the volume of the

Ionic Strength Adjuster (ISA) if used, the concentration of the standard

and as previously stated the slope of the electrode in use. Your accumet

research meter will prompt you through the method, permitting you to

enter the appropriate parameters at the appropriate time. When the

meter has all of the data needed for the calculation, it will display the

ion concentration of the sample as well as the parameters entered for the

calculation. 

The standard concentration should be high enough to nearly double 

the sample ion concentration after its addition. However, the standard

volume should not significantly impact the sample volume. A 1:100 ratio

of standard to sample ratio is optimal. For a monovalent electrode, the

standard addition should result in a 15-30 mV change. For a divalent

electrode, a 7-10 mV change is adequate. If the millivolt change is too

high, the addition of the standard may affect the ionic strength and

therefore the activity coefficients. This could result in inaccurate 

measurements. If the millivolt change is too small, readability errors

are enhanced. See ISE Theory page 146.
125

accumet Ion Operation

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KNOWN ADDITION METHOD

To take a measurement

Immerse the ion selective electrode in a known volume of the sample solution.

Stir the sample.

Touch KA to take the first mV reading of sample. 

Wait for the reading to stabilize (STABLE will appear).

OR

Touch KA to accept the current reading.

Add a known volume of standard solution to the sample.

Touch KA to take the second mV reading of sample. 

Wait for the reading to stabilize (STABLE will appear).

OR

Touch KA to accept the current reading.

Use the keypad to enter the sample volume.

Touch enter to accept the value.

Use the keypad to enter the standard volume.

Touch enter to accept the value.

Use the keypad to enter the volume of ionic strength adjuster used. 

If no ISA was used, enter a value of zero.

Touch enter to accept the value.

Use the keypad to enter the concentration of the standard solution added to

the sample.

Touch enter to accept the value. Your Known Addition result is now displayed.

Touch print to send the data to memory if a sample ID# has been assigned 

or to print the data on the screen.

OR

Touch OK to return to the Measure screen for a new measurement.

1

2

3

4

5

6

7

8

9

10

11

12

13

14
126

Ion Operation accumet®

RESEARCH

KNOWN SUBTRACTION METHOD

The procedure for known subtraction is very similar to that for known

addition method. An aliquot of standard is added to a known volume 

of the sample. The difference is that the standard does not contain the

same ionic species that you are trying to measure in the sample. Instead,

it contains an ion that will complex or precipitate the ion of interest,

removing it from the sample. Like known addition, the mV readings are

taken before and after the standard is added to the sample and the 

difference in mV values can be used to calculate the concentration of

free ions of interest in the sample. This method will also require you to

enter values of certain parameters in order to obtain an ion concentration. See ISE Theory page 146.

To take a measurement

Immerse the ion selective electrode in a known volume 

of the sample solution.

Stir the sample.

Touch KS to take the first reading. 

Wait for the reading to stabilize (STABLE will appear).

OR

Touch KS to accept the current reading.

Add a known volume of standard solution to the sample.

Touch KS to take the second reading. 

Wait for the reading to stabilize (STABLE will appear).

OR

Touch KS to accept the current reading.

Use the keypad to enter the sample volume.

Touch enter to accept the value.

Use the keypad to enter the standard volume.

Touch enter to accept the value

1

2

3

4

5

6

7

8

9

Remember, HELP is

always just a touch of

the button away.
127

accumet Ion Operation

®

RESEARCH

KNOWN SUBTRACTION METHOD

Use the keypad to enter the volume of ionic strength adjuster used. 

If no ISA was used, enter a value of zero.

Touch enter to accept the value.

Use the keypad to enter the concentration of the standard solution

added to the sample.

Touch enter to accept the value. 

Your Known Subtraction result is now displayed.

Touch print to send the data to memory or to print the information 

on the screen.

OR

Touch OK to return to the Measure screen for a new measurement.

10

11

12

13

14
128

Ion Operation accumet®

RESEARCH

The analate addition method is useful when your sample is at an 

elevated temperature and you want to negate the effect that temperature

will have on the concentration calculation. This method is also useful 

if you have only a small amount of sample available. The analate 

addition method differs only slightly from the known addition method.

The difference being the solution that you are taking your initial mV 

reading in is actually the standard and not the sample of interest. The 

difference in mV readings of the standard before and after the sample is

added is used to calculate the concentration of the ion of interest. With

the analate addition method, both the sample and the standard solution

contain the ionic species of interest. See ISE Theory page 146.

To take a measurement

Immerse the ion selective electrode in a known volume 

of the standard solution.

Stir the standard.

Touch AA to take the first reading.

Wait for the reading to stabilize (STABLE will appear).

OR

Touch AA to accept the current reading.

Add a known volume of sample solution to the standard solution

Touch AA to take the second reading. 

Wait for the reading to stabilize (STABLE will appear).

OR

Touch AA to accept the current reading.

Use the keypad to enter the sample volume.

Touch enter to accept the value.

Use the keypad to enter the standard volume.

Touch enter to accept the value.

1

2

3

4

5

6

7

8

9

Remember, HELP is

always just a touch of

the button away.

ANALATE ADDITION
129

accumet Ion Operation

®

RESEARCH

ANALATE ADDITION

Use the keypad to enter the volume of ionic strength adjuster used. 

If no ISA was used, enter a value of zero.

Touch enter to accept the value.

Use the keypad to enter the concentration of the standard solution.

Touch enter to accept the value. 

Your Analate Addition result is now displayed.

Touch print to send the data to memory or send the information 

to a printer.

OR

Touch OK to return to the Measure screen for a new measurement.

11

12

13

14

10
130

Ion Operation accumet®

RESEARCH

The analate subtraction method is useful when no ion specific electrode is

available to measure the ion of interest directly. Like known subtraction

the sample and the standard contain different ionic species. However, 

the ion being measured is in the standard and not in the sample. The

reduction of free ions in the standard solution is proportional to the

concentration of the ion of interest in the sample. See ISE Theory 

page 146.

To take a measurement

Immerse the ion selective electrode in a known volume 

of the standard solution.

Stir the standard.

Touch AS to take the first reading.

Wait for the reading to stabilize (STABLE will appear).

OR

Touch AS to accept the current reading.

Add a known volume of sample solution to the standard. 

Touch AS to take the second reading.

Wait for the reading to stabilize (STABLE will appear).

OR

Touch AS to accept the current reading.

Use the keypad to enter the sample volume.

Touch enter to accept the value.

Use the keypad to enter the standard volume.

Touch enter to accept the value.

1

2

3

4

5

6

7

8

9

Remember, HELP is

always just a touch of

the button away.

ANALATE SUBTRACTION
131

accumet Ion Operation

®

RESEARCH

ANALATE SUBTRACTION

10 Use the keypad to enter the volume of ionic strength adjuster used. 

If no ISA was used, enter a value of zero.

Touch enter to accept the value.

Use the keypad to enter the concentration of the standard solution.

Touch enter to accept the value. 

Your Analate Subtraction result is now displayed.

Touch print to send the data to memory or send the information 

to a printer or computer.

OR

Touch OK to return to the Measure screen for a new measurement.

11

12

13

14
132

Cleaning accumet®

RESEARCH

The touch screen should be kept as clean as possible to preserve optical

properties. Attempt to keep the screen free of dirt, dust fingerprints, etc.

Long term contact with abrasive materials will scratch the surface, and

impair image quality. To clean, use a damp nonabrasive cloth towel and

any commercially available window cleaner. The cleaning solution

should be applied to the towel rather than the surface of the touch

screen.

The case is made out of durable ABS plastic. It can be cleaned 

with a damp cloth and a mild detergent. Do not use chemical 

solvents on the case.
133

accumet Trouble Shooting

®

RESEARCH

Your AR meter contains many error messages to provide aid should 

trouble occur with a measurement or meter operation (touchpad and

input errors). The messages are accompanied by a brief description of

the error, and in some cases advice on how to correct it. An example of

an error message is:

Bad Electrode Slope-The electrode you have standardized has a slope

which is out of the normally acceptable range of 90% to 102%. 

You should try to restandardize, or replace your electrode if the problem

persists. Note that you can continue to make measurements with this

electrode; however, the readings may be inaccurate.

Other error messages delivered by the meter are:

Data log full

Data log empty

Unrecognized date

Unrecognized time

Invalid pH limit

Invalid Ion limit

Invalid limit

Limit exceeded

Channel 1 limit exceeded

Channel 2 limit exceeded

Invalid Temperature

Invalid Isopotential

Invalid Print Interval

Invalid pH value

Sample ID not found

Operator not found

Also, whenever possible, touch help for complete information about the

meter operation in which you are currently engaged.
134

Warranty accumet®

RESEARCH

pH Meter and Electrode Warranty Statement

The Fisher Scientific Company (“Fisher”) warrants to the direct purchaser

that the accumet meters and Accumet, AccuTupH, AccuFET, AccupHast,

and Microprobe electrodes will be free from defects in material or 

workmanship for a specified warranty period. During that period, Fisher

will repair or replace the product or provide credit, at its sole option,

upon prompt notification and compliance with its instructions. For 

accumet meters, that specified period is 24 months from delivery date.

For electrodes, that specified period is 12 months - except for models 

13-620-532, 13-620-533, 13-620-534, 13-620-535, 13-620-536, 

13-620-537, 13-620-538 and 13-620-539 - which are warranted for 

six months. 

Unless otherwise agreed, the warranty is limited to the country in which

the product is sold.

No Fisher employee, agent or representative has the authority to bind

Fisher to any oral representation or warranty concerning any product

sold. Any oral representation or warranty made prior to purchase of any

product and not set forth in writing and signed by a duly authorized officer of Fisher shall not be enforceable by the purchaser.

FISHER EXPRESSLY DISCLAIMS ALL OTHER WARRANTIES, EXPRESS OR

IMPLIED, INCLUDING THE IMPLIED WARRANTY OF MERCHANTABILITY

AND FITNESS FOR A PARTICULAR PURPOSE.

Fisher’s sole responsibility and the purchaser’s exclusive remedy for any

claim arising out of the purchase of any product listed above is repair,

replacement or credit as described above, where applicable. In no event:

1) shall the cost of the exclusive remedy exceed the purchase price: 

2) shall Fisher be liable for any special, indirect, incidental, consequential, or exemplary damages, howsoever arising, even if Fisher has been

advised of the possibility of such damages.

Each article that Fisher furnishes will conform to the written specifications

given in this manual, or those of a further improved model. Changes are

made often to the information in the manual and will be incorporated

into future editions.
Notice of Compliance

WARNING: This meter generates, uses, and can radiate radio frequency

energy. If not installed and used properly, that is in strict accordance with

the manufacturer’s instructions, it may cause interference to radio communications. It has been tested and found to comply with the limits for a Class A

computing device pursuant to Subpart J of Part 15 of FCC Rules, which are

designed to provide reasonable protection against such interference when

operated in a commercial environment. Operation of this equipment in a

residential area may cause interference, in which case the user, at his own

expense, will be required to take whatever measures may be required to

correct the interference.

This product is to be used only as described in the manual. This product is

for indoor use only, and must be used in a well ventilated area.

WARNING: To meet or exceed FCC regulations and 

comply with CE requirements, the Fisher-supplied

power supply must be used. Use of a power supply that is not

approved by Fisher Scientific may cause safety hazards

and/or cause unit to exceed EMC limits and/or damage unit.

When using this meter with a computer or printer, a shielded

RS232 cable must be used to meet or exceed FCC regulations,

and comply with CE Mark requirements.

135

accumet Compliance

®

RESEARCH
136

Appendix accumet®

RESEARCH

TABLE OF CONTENTS

Determining Isopotential Points Experimentally

Data Management

Factory Default Settings

pH Theory

ISE Theory

137

138

139

141

146
137

accumet Appendix

®

RESEARCH

Determining ISOPOTENTIAL POINTS EXPERIMENTALLY

The isopotential point of an electrode system is the point at which 

electrode potential is unaffected by a change in temperature. 

The coordinates of this point would be reported as (pXiso, Eiso). 

For an ideal system, this point would be coincident with the system’s 

Zero Potential Point (pXiso, E0). 

In practical systems, however, this coincidence rarely occurs, and for some

systems, there is no true Isopotential Point but a general Isopotential area.

If a system exhibits an apparent Isopotential Point, or at least an

Isopotential area with relatively small spread, Isopotential coordinates may

be established and possibly used to some advantage. 

Isopotential correction may be used only in conjunction with a One- or

Two- Point Standardization; it is required only when both accuracy over a

significant temperature range as well as operation with an asymmetric

electrode system are contemplated. However, Isopotential correction is

never necessary if all measurements will be performed on samples which

are at similar temperatures. Most conventional pH electrode systems are

designed and manufactured to be highly symmetrical cells. Consequently,

for most pH work, unless ultimate accuracy over broad temperature ranges

is required, Isopotential may be ignored. Specifically, this is accomplished by setting the Isopotential at its reset value of zero millivolts. 

The following is an example for determining an Isopotential Point:

Data points are first established for three different standards at three 

different temperatures. The data points are then plotted and will produce

three isotherms which should resemble the plot in either figure 1 or 

figure 2. In figure 1, the Isopotential Point is well defined as the millivolt 

difference between the coincidence point of the three Isotherms 

(pXiso, Eiso) and the Zero Potential Point (E0). The Isopotential Point is 

not so well defined in figure 2, but a value may be interpolated with 

some accepted error.

Figure 1 Figure 2
138

Appendix accumet®

RESEARCH

Data MANAGEMENT

Your accumet pH meter is equipped with an RS-232 output port for 

sending measurement readings to a printer or computer. To use the meter

with a printer or computer, the printer or computer must have an RS-232

port, also. It should be capable of receiving data within the following

guidelines.

Baud rates 110 to 38,400 BPS

Data bits 7 or 8

Parity even, odd, or none

Stop Bits 1 or 2

The meter and the output device must be configured to match with

respect to these parameters.

A shielded RS-232 cable must be used. The RS-232 connector is on the

back of the meter. (see diagram page 8) The connector is a Female

DB9 style connector. If the output device has a 25-pin connector, an

adapter is required. If the meter and the printer or computer are to 

work together, the pin configurations must match. The meter’s 9-pin 

configuration is as follows.

Pin Description

1 Buffers analog copy of pH input 1

2 Send data from meter

3 Receive data to meter

5 Signal Common

9 Signal Common

To initiate printing, touch print if in the manual print mod, or set the

print interval for stable readings or at a prescribed timed interval. Refer

to the setup sections, Set Print Interval and Set Print Criteria.

To download data stored in memory to a printer or computer, access the

View Stored Data option in the setup screens. Access the desired data

point by sorting the data by one of the three options. Touch print on the

screen displaying the data 
139

accumet Appendix

®

RESEARCH

The following is the list of factory default settings for the accumet 

AR50 meter. You can reset your meter to the factory default settings 

by accessing the Reset to Factory Defaults screen from the 

System Setup screen. 

Mode Screen Default Setting

System Setup Time 12 hour time mode

Date month/day/year

Print Configuration Baud rate 19200

Parity none

Data bits 8

Stop bits 1

Procedural Level Advanced

Operator ID none

Beeper Status ON

Display Contrast 15

pH Setup Display Configuration All parameters ON

Print Configuration All parameters ON

Data Configuration All parameters ON

Buffer Group USA

Sample ID# none

Isopotential Point 0 mV

Print Interval manual

Display Resolution X.XX

Auto Buffer Recognition ON

Auto Read Mode OFF

Temperature Units Celsius

Default temperature 25.0°C

Stability Criteria Medium

Default slope 59.16 mV

Alarm limits OFF

Alarm limit low 0.000

Alarm limit high 14.000

mV Setup Display Configuration All parameters ON

Print Configuration All parameters ON

Data Configuration All parameters ON

Sample ID# none

Print Interval manual

Display Resolution X.X

mV readings Absolute mV

Alarm limits OFF

Alarm limit low -1800.0

Alarm limit high 1800.0

Factory DEFAULT SETTINGS
140

Appendix accumet®

RESEARCH

Factory DEFAULT SETTINGS

Mode Screen Default Setting

Ion Display Configuration All parameters ON

Print Configuration All parameters ON

Data Configuration All parameters ON

Sample ID# none

Isopotential Point 0 mV

Print Interval manual

Display Resolution 2 Significant digits

Auto Read Mode OFF

Temperature Units Celsius

Default temperature 25.0°C

Stability Criteria medium

Default slope 59.16 mV

ISE method Direct with Standards

Units ppm

Electrode Ammonia

Alarm limits OFF

Alarm limit low 0.00

Alarm limit high 1.00 E6
141

accumet Appendix

®

RESEARCH

pH THEORY

Since its introduction by the Danish chemist Sorensen in 1909, pH 

measurement has become one of the most commonly used and important

measurements in both laboratory and industrial settings. pH measurement

and control is vital to a wide array of endeavors including municipal and

industrial wastewater treatment, and textile, pharmaceutical, food, and

petroleum production. Even our very existence itself is dependent upon

pH. Most organisms can exist only within a narrow pH range. In humans,

for example, the pH of blood must be maintained within the pH range of

7.3 to 7.4 .

In general, pH is a measure of the degree of acidity or alkalinity of a 

substance. It is related to the effective acid concentration ("activity") of a

solution by this defining equation:

pH = -log aH3O+

with aH3O+ representing the activity or effective concentration of the

hydronium ion in solution.

Analysts traditionally work with concentration units rather than activity.

Therefore neglecting activity, pH can be defined by the 

following equation:

pH = -log [H3O+]

with [H3O+] representing the concentration in Moles/liter of the 

hydronium ion in solution.

The pH range includes values from 0 to 14. Values from 0 to 7 represent

the acidic half of the scale. Values from 7 to 14 represent the alkaline 

or basic half of the scale. The pH value 7 is considered neutral, as it is 

neither acidic or alkaline. 

The pH scale is based on the dissociation constant of water. Water, even

in its purest state, dissociates as follows producing a positively charged

hydronium ion (H3O+) and a negatively charged hydroxyl ion (OH-

):

2H2O = H3O+ + OH–
At 25°C in pure water, the concentration of hydronium ions is extremely

small, 1 x 10-7 Moles/liter, and balanced by an equal concentration of

hydroxyl ions. The equilibrium constant, Kw of water is the product of the

hydronium ion and hydroxyl ion concentrations:

Kw = [H3O+] [OH–] = [1x10-7] [1x10-7] = 1x10-14

Since the hydronium ion concentration is 1 x 10-7 Moles/liter, 

the pH of pure water is 7 , the neutral pH, as stated above:

pH = -log [1 x 10-7] = 7

In aqueous solutions at 25°C, the product [H3O+] [OH–] or 

the Kw of water must remain constant. Therefore, an increase 

in concentration of either term, [H3O+] or [OH–], will result in 

a decrease in the other. For example, if a strong base, sodium hydroxide 

(NaOH) is added to water to the extent that its final concentration is 0.01

Moles/liter, the concentration of the OH– ion is 0.01 Moles/liter, and the

concentration of the H3O+ must decrease according to the Kw equation as

follows:

[H3O+] = Kw/ [OH–] = 1 x 10-14/ 1 x 10-2 = 1 x 10-12

The pH of this solution is:

pH = -log [1 x 10-12] = 12

This high pH indicates that the 0.01 M NaOH solution is strongly alkaline;

the concentration of hydronium ions is extremely small.

142

Appendix accumet®

RESEARCH

pH THEORY

0123456 7 8 9 10 11 12 13 14

pH

Neutral

more acidic more basic

Strong Acid

Lemon Juice

Tomato Juice

Coffee

Pure Water

Baking Soda

Ammonia

Strong Base
143

accumet Appendix

®

RESEARCH

pH THEORY

pH Measurement

The pH value of a sample can be determined in several ways. These

include the use of organic dyes which change color in certain pH ranges.

The dyes can be added directly to the solution or impregnated onto paper

which may be dipped into the solution. At best, these "colorimetric" 

methods yield approximate pH values, often with an accuracy of plus 

or minus 0.5 pH units.

The preferred and most accurate way to measure a pH value is the 

potentiometric measurement, using a pH electrode, a reference electrode,

and a pH meter. This method is based on the fact that certain electrodes,

immersed in solution, produce a millivolt potential (i.e. voltage ) that is

related to the hydronium ion concentration or pH of a solution in a 

precise way.

The relationship between the electrode's voltage and the solution pH is

defined by the Nernst equation:

2.3RT

Emeas = E* – ( )(pH) nF

In this equation, Emeas is the voltage output of the electrodes, E* is the total

of all other voltages in the system including the reference voltage, R is the

Gas Law constant, T is the temperature in °Kelvin, n is the charge on the

hydronium ion (+1), and F is the Faraday constant.

pH Meter

The pH meter is a sensitive voltmeter capable of accurately measuring

small voltage differences between the pH electrode and the reference 

electrode. This voltage difference is amplified, and shown as a pH 

reading. Almost all modern meters are microprocessor controlled, and 

programmed to use electrode voltages, efficiency, and temperature to 

calculate an accurate pH for the sample. Since the voltage output from 

different electrodes will vary, it is essential to calibrate a pH meter. The

ability to calibrate or to standardize a pH meter permits the meter to match

the pH reading on the meter with the known pH value of a buffer solution.

For best accuracy, it is recommended that at least two buffer solutions be

used to calibrate a pH meter. Buffer solutions are available as ready-to-use

solutions, concentrated solutions, capsules, or prepackaged salts. The 

following table lists three of the most widely used NIST buffers along 

with their pH values at different temperatures.
144

Appendix accumet®

RESEARCH

pH THEORY

Temperature 4.01 6.86 9.18

0 4.003 6.984 9.464

10 3.998 6.923 9.332

20 4.002 6.881 9.225

25 4.008 6.865 9.180

30 4.015 6.853 9.139

40 4.035 6.838 9.068

50 4.060 6.833 9.011

pH Electrodes

The electrode system consists of two half cells: a pH indicating electrode,

which is primarily responsive to the acidity (the hydronium ion concentration) of a solution, and a reference electrode, which provides a constant

voltage and completes the electrical circuit. 

Traditional pH indicating electrodes use a tip made of pH sensitive glass.

Inside this electrode is a buffer solution with a fixed pH and ionic strength.

A silver wire coated with silver chloride is immersed inside this internal

solution, and establishes electrical contact between the solution and the

meter. The voltage associated with this wire and the voltage associated

with the pH of the internal solution and the inside wall of the pH sensitive

glass tip remain constant. Therefore, changes in voltage from this 

electrode result from the voltage developed between the solution and 

the outside of the glass tip.

If the pH sensitive glass tip or membrane is to function properly, it must 

be hydrated. A dry or dehydrated electrode membrane will not respond 

properly to changes in acidity. pH electrodes are also effected by changes

in temperature, and the presence of other ions. Temperature effects can be

countered by temperature compensation functions on the pH meter. While

temperature compensation will not allow you to predict what the pH of the

sample is at another temperature, it will permit you to accurately assess 

the pH at whatever temperature you are presently working. pH sensitive

membranes are also sensitive, though to a lesser extent, to other ions than

the hydronium ion. For example, most pH glasses are somewhat sensitive

to sodium ion as well. For some pH glasses, this means an error as high

as 0.5 pH units in highly alkaline, high-sodium solutions. The special FS-5

glass used in Fisher's pH electrodes exhibits much less sodium error 

in these solutions, <.05 pH units. 
145

accumet Appendix

®

RESEARCH

pH THEORY

Reference electrodes typically consist of three elements: an internal 

reference electrode, a filling solution, and a reference junction through

which the filling solution can "flow", and provide electrical contact with 

the sample and the internal reference electrode. The most convenient 

internal reference electrodes are made from a metal (such as silver or 

mercury) and its sparingly soluble salt (silver chloride or mercurous 

chloride). The filling solution is most often a concentrated solution of 

potassium chloride. Most problems with reference electrodes are 

associated with the interruption or blockage of flow of the potassium 

chloride fill solution through the reference junction.

The classic electrode pair, separate pH indicating and reference half 

cells, offer you unmatched versatility to match the needs of your sample.

This approach makes for the highest accuracy, as well as low replacement

costs, since usually only one of the pair is broken or malfunctioning.

However, the pH indicating half-cell and the reference half-cell can be

merged into one electrode - a combination electrode. Combination 

electrodes are quite popular for they offer distinct advantages in 

convenience and compactness. Some combination electrodes also 

incorporate an ATC probe into their body also, providing temperature

readout and compensation with meters equipped with these features.

Newer combination electrodes are available in which the glass pH 

membrane sensor has been replaced with a field effect transistor or FET.

All of Fisher Scientific's AB and AR meters are capable of using this type

of electrode by direct connection (except AB30).
146

Appendix accumet®

RESEARCH

ISE THEORY

Ion selective electrodes (ISE) respond to ionic activity or concentration in a 

liquid because of the characteristics of the electrode’s sensing membrane.

Ideally, the ISE develops an electrical potential which is proportional to the

activity or concentration of the ion for which the membrane is selective. For

example, the fluoride electrode can be used to directly sense fluoride ion

in drinking water. Analyses utilizing ion selective electrodes offer the

advantages of speed, ease-of-operation, low cost, and versatility over 

other analytical techniques. The ISE can measure the ion concentration of 

samples at very high levels ( > 1000ppm ) to very low levels ( < 1ppm ).

When an ISE, the indicator electrode, and a reference electrode are

placed in a solution, and connected to a pH/mV/ion meter, they form 

a potentiometric cell. At equilibrium, the meter measures the potential 

difference between the ISE and the reference electrode. This millivolt 

potential is proportional to the activity of the ion of interest, and the 

relationship is defined by the Nernst equation:

RT

E = E* ±2.3 (log a) where nF

E is the measured potential

E* is the sum of the standard potential and all other constant 

potentials of the system

R is the gas constant

T is the temperature in °K

F is Faraday’s constant

n is the valence of the ion being measured

Activity, a, is not the same as concentration. It is a thermodynamic 

function whose value is influenced by the ionic environment in which 

the ion exists. Activity and concentration are the same in very dilute, 

ideal solutions. In non-ideal solutions, activity and concentration are 

related by an “activity coefficient“. 

ISEs sense the activity of free, uncomplexed ions rather than concentration.

However, by calibrating the meter with standards with a similar ionic background as the sample, the difference between activity and concentration

becomes negligible. Most often this is achieved by adding an ionic

strength adjustor to both samples and standards. The Nernst equation

becomes:

RT

E = E* ±2.3 (log c) where nF

c is the concentration of the ion of interest.
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This form of the Nernst equation states that the electrode potential varies

directly with the log of the concentration in straight line manner, and

results are then expressed in the preferred concentration units. The slope 

of the line is equal to the value of :

Slope = S = 2.3RT/nF

The table below gives theoretical slope values at 25°C.

Slope Slope 

Species (mV/decade) Species (mV/decade)

Monovalent cation +59.16 Divalent cation +29.58

Monovalent anion -59.16 Divalent anion -29.58

The Nernst equation thus reduces to:

E = E* + S [log c]

Ion-selective Analysis Methods

Direct Analysis

In this method, a sample concentration is determined by measuring the

electrode potential and comparing to those obtained in standard solutions.

Normally, an ionic strength adjustor and/or pH adjustor must be added

to both the samples and the standards. This helps in that the closer the

standard solution matrix is to the sample matrix, the more valid is the

analysis. A number of standard solutions are used to standardize a

pH/mV/ion meter, or to construct a calibration curve (by plotting the 

electrode’s output in mV versus the log of the concentration). The sample

concentration is then read from the meter or the calibration curve.

The advantages of the direct method of analysis are:

1. Many samples (particularly those with relatively simple ionic 

backgrounds) can be quickly measured after a single calibration 

procedure.

2. The technique is valid over a wide range of concentrations.

3. Sample volume values are not required, and may also vary 

over a wide range.
Incremental Methods

These procedures can reduce errors caused by temperature variations,

complex matrices, and complexation. They are also useful for applications

where only occasional samples are analyzed. Incremental methods

include: Known Addition, Known Subtraction, Analyte Addition, and

Analyte Subtraction.

Known Addition and Known Subtraction

With the Known Addition and Known Subtraction methods, the initial 

millivolt output of the electrode in the sample solution is measured. Then 

an aliquot of standard solution is added, and a final millivolt potential is

measured. The concentration of the sample can then be computed from the

observed change in the millivolt readings before and after the addition.

The techniques differ in that with Known Addition the standard added is

the same ionic species as that being measured. With Known Subtraction,

the measured ion is not the same as the one being added via the 

standard. For example, a chloride ISE can be immersed in sample for 

a chloride measurement. If a silver standard is added to the sample, 

AgCl precipitates, effectively removing or subtracting chloride ion 

from the sample.

Equations for known addition and known subtraction calculations are as

follow:

Known Addition 

Cstd Vstd Cs =

(Vs + Vstd)10∆E/S – Vs

Known Subtraction

Cstd Vstd Cs = where

Vs – (Vs + Vstd)10∆E/S

Cs is the concentration of the sample; Cstd is the concentration of the 

standard; Vs is the sample volume; Vstd is the standard volume; ∆E is the

difference in millivolt readings from the electrode; and S is the slope of 

the electrode determined in a previous standardization.

Whereas the direct method is suitable for samples with fairly uncomplicated ionic matrices, the addition methods are advantageous with samples

that have complex matrices, samples in which no ISA is added, samples 

in which excess complexing species are present, and samples whose 

concentration is in the non-linear region on the electrode response curve. 

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Analyte Addition and Analyte Subtraction

In the Analyte methods, the initial millivolt reading is taken with the 

electrode immersed in the standard; then an aliquot of sample is added,

and the final millivolt reading is taken. Sample concentration is calculated

from the change in the millivolt readings.

Analyte Addition

C Vs + Vstd Vstd

s = Cstd [( )10∆E/S – ( )] Vs Vs

Analyte Subtraction

C Vstd Vs + Vstd

s = Cstd [( ) – ( )10∆E/S] Vs Vs

As with known addition, with analyte addition the sample and the 

standard solution contain the same ion being measured. With analyte 

subtraction, the ion being measured is in the standard solution, and not in

the sample solution. For example, a fluoride standard and a fluoride ISE

might be used to measure to aluminum concentration of a sample. When

the sample containing aluminum is added to the standard it reduces the

measured fluoride content of the standard. The amount of reduction is 

proportional to the aluminum in the sample.

The analyte methods offer the same advantages as do the addition 

methods in that they effectively deal with complex samples. A distinct

advantage of the analyte subtraction method is that it can be used in 

cases where an ISE does not exist for a given species, such as aluminum

in the example cited.
150

Replacement Parts accumet®

RESEARCH

Replacement Parts

Description Fisher Catalog Number

Accumet pH combination electrode, single junction, 

Ag/AgCl reference, glass body, BNC connector . . . . . . . . . . . . . . . . 13-620-285

ATC Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-620-19

AccuFlex electrode support arm. . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-637-671

Electrode support bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-637-671A

Power Supplies: 115V, US plug . . . . . . . . . . . . . . . . . . . . . . . . . . 13-636-100

230V, UK plug . . . . . . . . . . . . . . . . . . . . . . . . . . 13-636-101

230V, Europe plug. . . . . . . . . . . . . . . . . . . . . . . . 13-636-102

Operator’s Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-636-AR50M

BNC Shorting cap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-620-99

Accessories

pH Electrodes Fisher Catalog Number

Accumet pH combination electrode, single junction, 

calomel reference, glass body, BNC connector. . . . . . . . . . . . . . . . . . 13-620-286

Accumet 3-in-1 pH/ATC combination electrode, single junction,

Ag/AgCl reference, glass body, BNC connector . . . . . . . . . . . . . . . . 13-620-530

Accumet 3-in-1 pH/ATC combination electrode, single junction,

calomel reference, glass body, BNC connector. . . . . . . . . . . . . . . . . . 13-620-531

AccupHast pH combination electrode, double junction,

glass body, BNC connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-620-296

AccupHast pH combination electrode, double junction, 

epoxy body, BNC connector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-620-298

AccuFET solid state pH/ATC combination electrode, 

Ag/AgCl gel reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-620-755

pH Buffers and Solutions

pH Color Ingredients Size Fisher Catalog Number

4.00 Red Potassium Biphthalate 500 mL SB101-500

7.00 Yellow Potassium Phosphate Monobasic 500 mL SB107-500

& Sodium Hyroxide

10.00 Blue Potassium Carbonate, Potassium 500 mL SB115-500

Borate & Potassium Hydroxide

Fisher Buffer-Pac (500mL ea. of color coded 3x500 mL SB105

pH 4, 7, and 10 buffers)

4.00 Red Individual Tear open pH Packets 20/box SB4

7.00 Yellow Individual Tear open pH Packets 20/box SB7

10.00 Blue Individual Tear open pH Packets 20/box SB10

Gray Electrode Rinse Individual Tear 

open pH Packets 20/box SB15

Electrode Storage Solution 1L SE40-1

To place an order, call 1-800/766-7000

For technical support, call 1-800/943-2006

For a complete selection 

of electrodes and accessories, please refer to the

Fisher 1998/99 Catalog,

or contact your Fisher

Scientific sales 

representative.