Chlorine Dioxide and Chlorite in 

Drinking Water by Amperometry using

Disposable Sensors

 

November 2013

PALINTEST LTD

1455 Jamike Avenue (Suite 100)

Erlanger

Kentucky 41018

(859) 341 7423

 
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Acknowledgements

This method was prepared by Stephen W Birch of Palintest Ltd.

The method was developed by S. W. Birch & S.R. Johnston of Palintest Ltd.

Disclaimer

The mention of trade names or commercial products does not constitute

an endorsement or recommendation for use.
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iii

Introduction

The electrochemical sensor method was developed by Palintest Ltd to provide a simple and 

rapid analysis of drinking water for chlorine dioxide and chlorite removing almost all sources 

of technique dependence.

This method is applicable to the determination of chlorine dioxide and chlorite. Water 

samples are analyzed by amperometry using pre-calibrated disposable sensors. Chlorite 

determination requires the addition of reagents to the sample.

Copies of the method can be obtained from, or questions concerning this method or its 

application should be addressed to:

Palintest Ltd

1455 Jamike Avenue (Suite 100)

Erlanger

Kentucky 41018

(859) 341 7423
________________________________________________________________

1

Method 

A Method for the Determination of Chlorine dioxide and Chlorite in Drinking 

Water by Amperometry using disposable sensors 

1.0 Scope and Application

This method is for the determination of chlorine dioxide and chlorite in drinking water.

1.1 The method detection limit (MDL), minimum level (ML) and application range 

for each analyte is shown below. The MDL was calculated from analysis of 

seven aliquots of analyte free water fortified to 0.1mg analyte/L.

 

Analyte MDL (mg/L) ML (mg/L) Application Range 

(mg/L)

Chlorine dioxide 0.02 0.05 0.02-50

Chlorite 0.02 0.05 0.02-50

1.2 The laboratory is not allowed to omit any quality control analyses. Each 

operator that uses this method must demonstrate the ability to generate 

acceptable results using the procedure in Section 9.2.

 

1.3 Chlorine dioxide is a volatile, reactive gas. Care was taken during method 

development to minimize steps that could result in the loss of chlorine dioxide 

during analysis. Analyst technique can affect the method precision and 

accuracy.

2.0 Summary of Method

2.1 This is an extension of the ChloroSense method (see Reference 16.1). It 

utilises a disposable sensors, the ChlordioX Plus sensor. Chlorine dioxide

present in the sample can be reduced directly at the surface of the 

ChlordioX Plus sensor. The current that flows is directly proportional to the 

amount of chlorine dioxide in the sample. To determine chlorite, any chlorine 

dioxide in the sample must be removed. This is done by degassing the 

sample using a degassing unit and portable air pump. Chlorite is determined 

by first adding potassium iodide (KI) to the sample at a pH where the chlorite 

does not react but any free or total chlorine in the sample does react to 

liberate iodine. The amount of iodine released is reduced at the surface of 

the ChlordioX Plus sensor. The current that flows is directly proportional to 

the amount of free and total chlorine in the sample (Reading A). The sample 

is then acidified by the addition of dilute hydrochloric acid. The iodide then 

reacts with chlorite and free and combined chlorine to release iodine. The 

amount of iodine released is reduced at the surface of the ChlordioX Plus 

sensor. The current that flows is directly proportional to the amount of 

chlorite and free & combined chlorine in the sample (Reading B). The 

amount of chlorite can then be calculated by subtracting Reading A from 

Reading B. The current is converted to mg analyte/L by reference to 

calibration parameters stored in the instrument software. The appropriate 

calibration parameters are transferred from a calibration chip that is provided 

with each batch of sensors. Quality is assured through calibration and 

verification with externally referenced standard solutions.
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2.2 Chlorine dioxide: The test container is filled with a sample of water, 

approximately 50mL. 6 drops of glycine solution are added and gently stirred. 

A disposable ChlordioX Plus sensor is inserted in to the instrument and the 

lid is closed to begin the test. After completion of the test, the value for

chlorine dioxide is read from the instrument display. 

2.3 Sample Degassing: The degasser unit is filled with a second sample of water 

(50mL). Air is passed through the water sample using a portable air pump to 

remove the chlorine dioxide from the sample. The degassing time is 

determined by the amount of chlorine dioxide found to be in the sample in 

section 2.2 and is timed by the instrument. 

2.4 Chlorite: The test container is filled with the degassed sample. Potassium 

iodide solution is added from a dropper bottle (6 drops) to the degassed 

sample. A disposable ChlordioX Plus sensor is inserted in to the instrument 

and the lid is closed to begin the test. The sensor is then discarded and an 

acidification solution (2.9M HCl) is added to the sample. The instrument lid is 

closed and a timer is started. After a 2 minute reaction period, a new 

disposable ChlordioX Plus sensor is inserted in to the instrument and the lid 

is closed to begin the test. After completion of the test, the value for chlorite 

is read from the instrument display. 

 The manufacturer’s instructions should be followed regarding the use and 

care of the instrument.

 

3.0 Definitions

The definitions and purposes below are specific to this method, but have been 

conformed to common usage as much as possible.

 

3.1 Calibration Check (CC): A calibration standard containing the method analyte 

that is analyzed periodically to verify the accuracy of the existing calibration. 

 

3.2 Initial demonstration of capability (IDC): Four aliquots of the diluted Quality 

Control Standard (QCS) are analyzed to establish the ability to generate 

acceptable precision and accuracy. An IDC is performed the first time this 

method is used by each operator. 

3.3 Laboratory reagent blank (LRB): An aliquot of reagent water or other blank 

matrix that is treated as a sample including exposure to all glassware, 

equipment, solvents, and reagents that are used with the samples. The LRB 

is used to determine if method analytes or other interferences are present in 

the laboratory environment, the reagents or the apparatus.

3.4 Linear calibration range (LCR): The concentration range over which the 

instrument response is linear.

3.5 Laboratory Fortified Matrix Spike (LFMS) and Laboratory Fortified Matrix Spike 

Duplicate (LFMSD): Aliquots of an environmental sample to which known 

quantities of the analytes are added in the laboratory. The LFMS and LFMSD 

are prepared and/or analyzed exactly like a field sample. Their purpose is to 

quantify any additional bias and imprecision caused by the sample matrix. The 

background concentration of the analyte in the sample matrix must be 

determined in a separate aliquot and the measured values in the LFMS and 

LFMSD are corrected for background concentrations.
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3.6 Material Safety Data Sheet (MSDS): Written information provided for the 

chemical reagents concerning a chemical’s toxicity health hazards, physical 

properties, fire, and reactivity data including storage, spill and handling 

precautions.

3.7 Minimum Reporting Level (MRL): The lowest level at which the entire 

analytical system gives a reproducible signal that meets the method quality 

objectives. It is never lower than the concentration of the lowest calibration 

check (CC) standard.

3.8 Quality Control Sample (QCS): A solution of method analyte of known 

concentration. The QCS is obtained from a source external to the laboratory or 

is prepared from standards obtained from a different source than the calibration 

standards. The purpose is to check laboratory performance using test 

materials that have been prepared independently from the normal calibration 

process.

3.9 Reagent water: Water demonstrated to be free from the method analyte and 

interfering substances.

4.0 Interferences

4.1 Other disinfectant residuals such as bromine, iodine, ozone and peroxide 

may react with or KI or directly with the electrode surface and cause a 

positive interference.

4.2 The chlorite test gives a small positive intercept (equivalent to 0.16mg/l 

chlorite) in the presence of Fe3+ (5 mg/L). Fe3+ strongly catalyses the 

decomposition of chlorite. In the presence of Fe2+ chlorite is reduced to 

chloride.

4.3 No interferences have been encountered with the chemical species found 

naturally in drinking water or added as treatment chemicals. The method is 

without interference in the presence of 0.5 mg/L aluminium, 5 mg/L zinc, 10 

mg/l sodium tripoly-phosphate, 800 mg/L chloride, 4 mg/L fluoride, 4 mg/L 

phosphate, 500 mg/L sulfate, 300 mg/L CaCO3 alkalinity, 350 mg/L calcium 

hardness, 300 mg/L magnesium hardness or 1000mg/L total dissolved 

solids. 

5.0 Safety

5.1 Use good laboratory practice throughout the test procedure. Follow the test 

instructions carefully.

5.2 When working with chlorine dioxide standards it is necessary to use a fume 

hood.

5.3 This method does not address all safety issues associated with its use. The 

laboratory is responsible for maintaining a safe working environment and a 

current awareness file of OSHA regulations regarding the safe handling of the 

chemicals specified in this method. A reference file of material safety data 

sheets (MSDS) should be available to all personnel involved in these 
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analyses. Additional information on laboratory safety can be found in 

References 16.2 to 16.4. 

NOTE: Do not allow a water sample to remain in the instrument following analysis.

6.0 Equipment and Supplies

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Note: Brand names, suppliers and part numbers are for illustrative purposes only. No 

endorsement is implied. 

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6.1 Sampling equipment:

6.1.1 Sample collection bottles - amber glass bottles with PTFE-lined screw 

caps or opaque, high-density polyethylene (HDPE) bottles. 

6.1.2 Palintest ChlordioX Plus potentiostat dedicated to the analysis of 

chlorine dioxide and chlorite in drinking water. If measuring chlorine dioxide 

only, then the Palintest ChlordioXense potentiostat can also be used.

 

6.1.3 Laboratory glassware and plastic ware required: includes sample 

containers, volumetric flasks, pipettes, sample storage vials, conical beakers 

(250 mL).

6.1.4 Sample degassing unit and portable air pump, Palintest number PT 553 

and PT 554 or equivalent.

7.0 Reagents and Standards

7.1 DISPOSABLE SENSORS – Palintest ChlordioX Plus sensors (catalogue 

number CDX310 or CDX350) are for the determination of chlorine dioxide and 

chlorite in drinking water. Disposable sensors have a shelf life of 24 months.

7.2 GLYCINE REAGENT – Palintest number PT 549

7.3 POTASSIUM IODIDE SOLUTION – Palintest number PT 546

7.4 ACIDIFICATION SOLUTION – Palintest number PT 547

7.5 REAGENT WATER – Purified water (typically either deionized or distilled) is 

acceptable. Reagent water can be purchased from a scientific supply 

company, if it is not available on site. If a chlorine dioxide/chlorine demand is 

present, suggested procedures for preparing chlorine demand-free water are 

included in ASTM D 1253-03 (Reference 16.5) and Standard Method 4500-Cl 

C (Reference 16.6). 

7.6 CALIBRATION STANDARD SOLUTIONS 

7.6.1 CHLORINE DIOXIDE STOCK SOLUTION (CDSS) – Chlorine dioxide 

solutions are unstable and must be prepared just prior to use. Chlorine 

dioxide solution can be prepared following the method described in Standard 

Methods (Reference 16.7). Chlorine dioxide solution should be stored in a 

glass-stoppered dark-colored bottle in a refrigerator. Chlorine dioxide 
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solution should be standardized by titration with sodium thiosulphate in the 

presence of potassium iodide, acid and starch indicator (Reference 16.7). 

Alternately, a rapid standard generation kit for chlorine dioxide is available 

from Palintest, number PT544, which produces approximately 95 mg/L. The 

actual Chlorine Dioxide concentration can be determined by measuring the 

absorbance at 360nm in a spectrophotometer using a cell with a 1cm light 

path. The concentration is given by Abs360nm*54 (assuming a molar extinction 

coefficient of 1250). Transfer to an amber bottle with PTFE lined cap or 

HDPE container. This solution should be stored at ≤6o

C. 

7.6.1.1 CHLORINE DIOXIDE PRIMARY DILUTION STANDARD (CDPDS)

(9.5mg/L) - This solution is used to prepare Calibration Standards and 

Continuing Calibration Check standards. It assumes that the CDSS is 

95mg/L. Partially fill a 100mL volumetric flask with reagent water. Add 10

mL of the chlorine dioxide stock standard solution (section 7.6.1) using a 

pipette and fill to the mark using reagent water. Invert the flask several times 

to ensure it is properly mixed and then transfer to an amber bottle with PTFE 

lined cap or HDPE container. This solution should be prepared when required 

and stored at ≤6o

C. The actual concentration will depend on the 

spectrophotometer measurement in 7.6.1.

7.6.1.2 CALIBRATION STANDARDS – 5 calibration standards are 

recommended that span the anticipated reporting range. All Calibration 

Standards are to be prepared using Class A volumetric or variable-volume 

pipettes and volumetric flasks. An example of the dilutions that were used to 

prepare the standards used in the development of this method is included in 

the table below. Transfer an aliquot of the appropriate Chlorine Dioxide

standard to a flask and dilute to the mark with reagent water. Mix the contents 

of the flask by inverting 3 to 4 times and transfer to an amber glass bottle or 

opaque plastic container. These solutions should be used immediately

 

Chlorine Dioxide 

Volume (mL)

Standard used

(CDPDS or 

CDSS)

Final volume 

(mL)

Calibration Std. 

Conc. (mg/L)

2 CDPDS 100 0.19

10 CDPDS 100 0.95

5 CDSS 100 4.75

10 CDSS 100 9.5

50 CDSS 100 47.5

7.6.2 CHLORITE STOCK STANDARD SOLUTION (SSS) (1000mg/L) – 

Certified chlorite standards are commercially available (e.g. Absolute 

Standards, cat.# 54109 or equivalent). Commercial standards should be 

stored at ≤6o

C in an amber bottle with a PTFE-lined cap or an HDPE 

container. 

7.6.2.1 CHLORITE PRIMARY DILUTION STANDARD (PDS) (10mg/L) - This 

solution is used to prepare Calibration Standards and Continuing Calibration 

Check standards. Partially fill a 500mL volumetric flask with reagent water. 

Add 5mL of the chlorite stock standard solution using a pipette and fill to the 

mark using reagent water. Invert the flask several times to ensure it is 

properly mixed and then transfer to an amber bottle with PTFE lined cap or 

HDPE container. This solution should be stored at ≤6o

C. If stored correctly 

this solution should be stable for 3months.
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7.6.2.2 CALIBRATION STANDARDS – It is recommended that 5 calibration 

standards are used to establish an initial calibration curve. The concentration 

of the standards must span the intended reporting range. All Calibration 

Standards are to be prepared using Class A volumetric or variable-volume 

pipettes and volumetric flasks. An example of the dilutions that were used to 

prepare the standards used in the development of this method is included in 

the table below. Transfer an aliquot of the appropriate Chlorite solution to a

flask and dilute to the mark with reagent water. Mix the contents of the flask 

by inverting 8 to 10 times and transfer to an amber glass bottle or opaque 

plastic container. These solutions should be stored at ≤ 6 °C. If stored 

properly, these solutions should be stable for 3 months.

Chlorite Volume 

(mL)

Standard used

(PDS or SSS)

Final volume 

(mL)

Calibration Std. 

Conc. (mg/L)

10 PDS 500 0.2

50 PDS 500 1.0

2.5 SSS 500 5

5 SSS 500 10

25 SSS 500 50

7.7 ROUTINE CALIBRATION CHECK STANDARD -- Calibration standards 

prepared above may also be used as calibration check standards. 

Calibration check standards must be freshly prepared as needed.

7.8 CONTINUING CALIBRATION CHECK (CCC) STANDARDS – calibration 

standards produced above can also be used as CCC standards.

8.0 Sample Collection, Preservation and Storage

 8.1 Collect samples in chlorine dioxide/chlorine demand free amber glass 

containers or opaque, high-density polyethylene (HDPE) bottles, filling the

container so there is no headspace. Avoid exposure to sunlight or agitation 

during sampling. Analyze immediately after sample collection as chlorine 

dioxide in aqueous solution is not stable. 

9.0 Quality Control

9.1 Quality Control (QC) requirements include the Initial Demonstration of 

Capability and on-going QC requirements that must be met when preparing 

and analyzing field samples. This section describes each QC parameter, its 

required frequency, and the performance criteria that must be met in order to 

meet EPA quality objectives. These QC requirements are considered the 

minimum acceptable QC criteria. Laboratories are encouraged to institute 

additional QC practices to meet their specific needs.

 9.2 INITIAL DEMONSTRATION OF CAPABILITY (IDC) – The IDC must be 

successfully performed prior to analyzing any field samples. Prior to 

conducting the IDC, the analyst must meet the calibration requirements 

outlined in Section 10. Requirements for the initial demonstration of 

laboratory capability are described in the following sections. 
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9.2.1 DEMONSTRATION OF LOW SYSTEM BACKGROUND – Analyze a 

LRB after processing through all sample collection steps outlined in Section 

8.1. The method blank concentration must be ≤ 1⁄3 the concentration of the 

lowest standard used to prepare/verify the calibration curve.

9.2.2 INITIAL DEMONSTRATION OF ACCURACY – Prepare and analyze a 

method blank (reagent water) and five independent reference samples at the 

same concentration. The concentration of the samples should be in the mid 

range of the calibration curve or near the expected concentration of the water 

samples. Complete for each of the analytes, chlorine dioxide and chlorite. 

Calculate the average concentration for the five analyses for each analyte. 

The average concentration for the five replicates must be within ± 15% of the 

expected value for each analyte.

9.2.3 INITIAL DEMONSTRATION OF PRECISION – Using the same set of 

replicate data generated for Section 9.2.2 calculate the standard deviation 

and relative standard deviation (RSD) of the replicate values. The RSD is 

calculated using the equation

 where 

 S is the standard deviation for the replicate values,

 and is the average value for the replicates. 

The RSD of the results of the replicate analyses for each analyte must be 

≤15%.

 9.3 ONGOING QC REQUIREMENTS – This section describes the ongoing QC 

criteria that must be followed when processing and analyzing field samples.

9.3.1 DEMONSTRATION OF LOW SYSTEM BACKGROUND – Analyze a 

LRB with each analytical batch. The LRB should be processed through all 

sample collection steps outlined in Section 8.1. The method blank 

concentration must be ≤ 1⁄3 the concentration of the lowest standard used to 

prepare/verify the calibration curve.

9.3.2 CONTINUING CALIBRATION CHECK – Analyze a CCC standard for 

each analyte with each analytical batch. Prepare an aqueous calibration 

check standard at a concentration near the expected concentration of the 

water samples (as in Section 7). Over time, vary the calibration check 

standard concentration. The measured concentration of the calibration check 

standard must be within ± 15% of the expected value. If this criterion is not 

met, then the analyst must identify and resolve the problem.

 9.4 Laboratories/water systems are encouraged to institute additional QC 

practices to meet their specific needs. The remainder of this section 

describes various optional QC procedures that may be incorporated into a 

QC program for grab sample verification. 

 9.4.1 SAMPLE DUPLICATE – Analysis of duplicate samples (two samples 

collected at the same time) provides an estimate of the precision of the 

sample analyses. Calculate the relative percent difference (RPD) between 

the Sample (FD1) and the Sample Duplicate (FD2) as shown below. The 

RPD for samples with concentrations greater than the lowest calibration 

RSD

S

X

= × 100%

X
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standard should not exceed 15%. The RPD at concentrations at or near the 

lowest calibration standard should not exceed 50%.

 

If the RPD for the Sample and the Sample Duplicate falls outside the 

designated range, then perform duplicate analyses of a calibration check 

standard to verify that the grab sample method is in control. 

 9.4.2 INDEPENDENT REFERENCE SAMPLE – Analysis of a sample from an 

external source (different from the calibration standards) provides an 

independent check of the calibration of the method. It is recommended 

semiannually or any time a new calibration curve is validated. In cases where 

there may not be many external vendors, it is acceptable to evaluate a 

different lot of material from that used to prepare the CAL standards.

 9.4.3 PROFICIENCY TESTING (PT) or PERFORMANCE EVALUATION (PE) 

SAMPLE – Successful participation in a PT or PE Study is a good QC tool for 

demonstrating proficiency with the grab sample method. A certified solution 

of chlorite whose concentration is unknown to the analyst can be purchased 

by the laboratory/water system. An aliquot of the certified solution is added to 

a known volume of reagent water and analyzed as a grab sample. The 

analytical results are reported to the PT/PE Study Provider where they are 

compared to data from all analyses of the sample. Acceptance criteria are 

established by the provider for each study. Because of the nature of chlorine 

dioxide it is not possible to obtain a certified solution. 

10.0 Calibration and Standardization

10.1 Verify the initial calibration curve for each analyte. This must be done for each 

instrument according to the procedure described below. This must also be 

performed when a new calibration code or lot of disposable sensors is put 

into service. These steps can be performed by laboratory personnel or field 

samplers. A record of the calibration results must be maintained for each 

instrument.

10.1.1 Prepare a set of at least three aqueous calibration standards. The 

lowest concentration calibration standard must be at or below 0.2 mg/L. The 

standards must span the concentration range that is expected to be observed 

in the grab samples. 

10.1.2 Analyze the calibration standards and method blank according to the 

grab sample procedure. (Note: If the highest concentration standard is above 

the maximum concentration specified for the instrument, dilute and analyze it 

according to manufacturer’s instructions. Use the data from this analysis to 

check the accuracy of the dilution process, not the calibration curve.)

10.1.3 To verify the factory set calibration curve, compare the measured 

concentration of each standard to the expected value. Each calibration point 

must be within ± 15% of its expected value. If the internal curve does not 

meet these criteria, the internal curve must be updated by following the 

manufacturers’ instructions for generating or inputting a curve. Otherwise, 

send the instrument to the manufacturer for repair/updating.
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11.0 PROCEDURE

11.1 Press and hold the power button until the title screen is displayed.

11.2 When the instrument passes all internal functional checks on start up, the 

screen displays the current batch code. To accept the batch code, press the 

right arrow key. To change the batch code, see section 11.3. 

11.3 Ensure the calibration code shown on screen matches with the number on the 

foil of the batch of sensors in use. If it does not, press the left arrow key, the 

screen prompts to insert a calibration sensor (section 11.3.1). 

11.3.1 To enter the calibration code, slide the front catch to the right and open 

the instrument case fully. Press the blue lever to open the jaw and 

insert the ChlordioX Plus calibration sensor, connecting tracks 

uppermost, fully into the slot revealed. Release the blue lever. Close 

the instrument lid. The display indicates Reading Calibration. The 

calibration number will be displayed briefly and the display will then 

return to the start screen. Check that the new code number displayed 

on screen matches the number on the sensor packaging. Open the 

case and remove the calibration chip. Press the right arrow key to 

accept the batch code. A test can now be performed.

11.4 To begin an analysis slide the front catch to the right, and open the 

instrument case fully.

11.5 Remove the sample container. Rinse and then fill one half, to the stepped 

line, with the water sample.

11.6 Replace the filled sample container in the instrument with the filled half 

towards the front. 

11.7 Add 6 drops of glycine reagent (provided in the test kit) to the sample and stir 

gently for 5 seconds with the rod provided. 

11.8 Holding the sensor through the foil pack tear open the foil along the tear line

to expose the connecting tracks.

11.9 Press the blue lever to open the jaw of the sensor connector. Insert the 

exposed end of the sensor, connecting tracks uppermost, into the slot, and 

release the lever. The jaws will close to hold the sensor in place. Slide the foil 

pouch off to expose the sensor.

11.10 Gently close the instrument lid to immerse the sensor in the sample. The test 

starts automatically. The display indicates progress of the test. Do not disturb 

the instrument during the test.

11.11 In less than one minute the chlorine dioxide result will be displayed. All 

results are automatically stored in the instrument log.

11.12 To carry out a chlorite test press the right arrow key. The instrument 

prompts the user to discard the sample and sensor. Close the instrument lid. 

The display will show the sample degassing time required based on the 

chlorine dioxide result. 
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10

To measure chlorite, the chlorine dioxide must be removed from the sample. 

This is achieved using a degassing unit and portable air pump (Palintest no. 

PT 553 & PT 554) 

11.13 Place a second, identical sample in to the degasser cup. Attach the portable 

air pump and switch on. Press the right arrow key on the instrument to start 

the timer. At the end of the degassing period the instrument will display the 

sensor calibration code and prompt the user to insert the sample to carry out 

a chlorine test. The performance of the chlorine test is not covered by 

the scope of this method. For analysis of free chlorine see 16.1. 

11.14 To skip the chlorine test and proceed to the chlorite test press the right

arrow key.

11.15 Transfer the sample in the degasser cup to the sample container and place in 

the instrument, with the filled half towards the front.

11.16 The instrument prompts the user to add chlorite reagent 1 and insert a 

chlorite sensor.

 

A chlorite sensor is the same as a chlorine dioxide sensor. Sensors from 

the same batch should be used for chlorine dioxide and chlorite 

measurements

11.21 Chlorite reagent 1 is added using dropper bottles. Add 6 drops of reagent to 

the water sample in the sample container. Gently stir using the supplied 

plastic paddle to mix the reagents. 

11.22 Holding the sensor through the foil pack tear open the foil along the tear line 

to expose the connecting tracks.

11.23 Press the blue lever to open the jaw of the sensor connector. Insert the 

exposed end of the sensor connecting tracks, into the slot, and release the 

lever. The jaws will close to hold the sensor in place. Slide the foil pouch off 

to expose the sensor

11.24 Gently close the instrument lid to immerse the sensor in the sample. The test 

starts automatically. The display indicates progress of the test. Do not disturb 

the instrument during the test.

11.25 After one minute the instrument prompts the user to discard the sensor, add 

chlorite reagent 2 and close the lid. 

11.26 Chlorite reagent 2 is added using dropper bottles. Add 6 drops of reagent to 

the water sample in the sample container. Gently stir using the supplied 

plastic paddle to mix the reagents. Close the instrument lid.

11.27 Closing the lid starts a 2 minute countdown timer. When the 2 minutes are 

complete the instrument will prompt the user to insert a chlorite sensor and 

will display the calibration code.

 

11.28 Holding the sensor through the foil pack tear open the foil along the tear line 

to expose the connecting tracks.

11.29 Press the blue lever to open the jaw of the sensor connector. Insert the 

exposed end of the sensor connecting tracks, into the slot, and release the 
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11

lever. The jaws will close to hold the sensor in place. Slide the foil pouch off 

to expose the sensor.

11.30 Gently close the instrument lid to immerse the sensor in the sample. The test 

starts automatically. The display indicates progress of the test. Do not disturb 

the instrument during the test.

11.31 In less than one minute the chlorite result will be displayed. All results are 

automatically stored to the instrument log.

Do not leave water in the instrument on completion of the test.

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Note: The instrument is programmed to recognize a number of user errors, such as unable 

to read: sensor not responding or lid opened during test. The instrument will abort 

the test and display an error message. Never leave water in the sample container 

in the instrument following analyses.

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12.0 Data Analysis and Calculations

12.1 Reporting

12.1.1 Report results in milligrams per liter (mg /L).

12.1.2 Report results to two significant figures.

13.0 Method Performance 

13.1 Performance data – standards

 Three certified laboratories tested the performance of ChlordioX Plus using 

laboratory prepared standard solutions for chlorine dioxide and chlorite. The 

accuracy and precision was found to be better than the acceptance criteria 

shown in 17.1 (see Table 17.7 & 17.8) 

 

13.2 Performance data – drinking water samples

 Three certified laboratories tested the performance of ChlordioX Plus using 

real water samples. The accuracy and precision was found to be better than 

the acceptance criteria shown in 17.1 (see Table 17.7 & 17.8)

 

13.3 Performance data – Method Comparison

 ChlordioX Plus was shown to give equivalent performance to the approved 

method (SM 4500-ClO2 E, amperometric titration), see 17.2,17.3 & 17.9

14.0 Pollution Prevention

 14.1 Used sensors and calibration chips can be returned to Palintest for recycling. 

Get in touch with your nearest Palintest office for details.
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14.2 The quantity of chemical purchased should be based on expected usage 

during its shelf-life and disposal cost of unused material.

14.3 Standards should be prepared in volumes consistent with laboratory use to 

minimize the volume of expired standards to be disposed.

15.0 Waste Management

15.1 It is the laboratory’s responsibility to comply with all federal, state, and local 

regulations governing waste management, particularly the hazardous waste 

identification rules and land disposal restrictions, and to protect the air, water, 

and land by minimizing and controlling all releases from fume hoods and bench 

operations. Compliance with all sewage discharge permits and regulations is 

also required.

15.2 Excess reagents, samples and method process wastes should be 

characterized and disposed of in an acceptable manner. The MSDS sheet 

gives details of product composition and may be consulted for guidance on 

waste disposal.

15.3 For further information on waste management, consult “The Water 

Management Manual for Laboratory Personnel”, and “Less is Better: 

Laboratory Chemical Management for Waste Reduction”, both available from 

the American Chemical Society’s Department of Government Relations and 

Science Policy, 1155 16th Street N.W., Washington DC, 20036.

16.0 References

 

16.1 ChloroSense: “Measurement of Free & Total chlorine in Drinking water by 

Palintest ChloroSense”, Sept. 2009. Available at http://www.nemi.gov or 

from Palintest Ltd.

16.2 “Carcinogens-Working With Carcinogens”, Department of Health, Education, 

and Welfare, Public Health Service, Center for Disease Control, National 

Institute for Occupational Safety and Health, Publication No. 77-206, August 

1977.

16.3 “OSHA Safety and Health Standards, General Industry”, (29 CFR 1910). 

Occupational Safety and Health Administration, OSHA 2206 (Revised, January 

1976).

 

16.4 “Safety in Academic Chemistry Laboratories”, American Chemical Society, 

Committee on Chemical Safety, 3rd Edition, 1979

16.5 Standard Test Method For Residual Chlorine in Water, ASTM D1253-08

16.6 Standard Method 4500-Cl C, Standard Methods for the Examination of water 

and Wastewater

16.7 Standard Method 4500-ClO2 B, Standard Methods for the Examination of 

water and Wastewater
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17.0 Tables and Graphs

17.1 Acceptance Criteria for Performance Tests

 Acceptance Criterion Section Limit (%)

 Initial accuracy and precision 

Accuracy (X) 9.2.2 ±15

 Precision (s) 9.2.3 ≤15

 Continuing calibration Check

Accuracy (X) 9.3.2 ±15

 

 Calibration verification

Accuracy (X) 10.1 ±15

Matrix spike/matrix spike duplicate

 

Relative percent difference 9.4.1 ≤15

 
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14

17.2 Direct comparison between ChlordioX Plus and Amperometric titration (SM 

4500-ClO2 E) for determination of chlorine dioxide

17.3 Direct comparison between ChlordioX Plus and Amperometric titration 

(SM 4500-ClO2 E) for the determination of chlorite

y = 1.0245x

R2 = 0.9997

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10

Chlorine Dioxide determined by ChlordioX Plus (mg/l)

Chlorine Dioxide determined by AutoCat 9000 (mg/l)

Correlation between ChlordioX Plus and the AutoCat 9000 

Amperometric Titrator (equivalent to SM 4500-ClO2 E)

y = 0.9843x - 0.0008

R2 = 0.9992

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 0.5 1 1.5 2 2.5 3

Chlorite concentration determined by ChlordioX Plus (mg/l)

Chlorite Concentration determined by Amperometric titration (mg/l)

Correlation between AutoCat 9000 Amperometric Titration vs 

ChlordioX Plus for the determination of Chlorite

AutoCat 9000 - equiv. to Standard Methods 4500-ClO2E
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15

17.4 Graph 1 Example calibration graph 

17.5 Graph 2 Example calibration graph
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16

17.6 Graph 3 Example calibration graph
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18

17.7 Summary of Performance data from three Certified Laboratories (I) – Laboratory Standards

Mean values returned for Chlorine Dioxide and Chlorite in Part 1a to c of the Data Generation Plan

Acceptable limits : accuracy-%deviation = +/- 15%

precision-%RSD = +/- 15%

Utility Mean sd %RSD %deviation Mean sd %RSD %deviation Mean sd %RSD %deviation

Beaver Creek 0.45 0.018 4.0% 10% 0.54 0.027 5.0% 8% 0.47 0.02 4.3% 6%

Hamilton 0.45 0.018 4.0% 10% 0.42 0.015 3.6% 16% 1.04 0.03 2.9% 108% ClO2 converted to 

chlorite

Water One* 0.52 0.07 13.5% 4% 0.44 0.03 6.8% 12% 0.66 0.14 21.2% 32% treated river water

*Water One used treated river water

Utility Mean sd %RSD %deviation Mean sd %RSD %deviation Mean sd %RSD %deviation

Beaver Creek 0.52 0.047 9.0% 4% 0.46 0.02 4.3% 8% 0.49 0.02 4.1% 2%

Hamilton 0.53 0.028 5.3% 6% 0.5 0.025 5.0% 0% 0.08 0.011 13.8% 84% ClO2 demand

Water One 0.51 0.02 3.9% 2% 0.54 0.08 14.8% 8% 0.46 0.02 4.3% 8%

DI water DI+Int Tap water

Chlorine dioxide 0.5mg/L

DI water DI+Int Tap water

Chlorite 0.5mg/L

Int - Hi Ionic Strength potential interferent

To 1000 mL reagent water add 1.40 g of NaHCO3, 1.48 g of Na2SO4 and 1.54 g of NaCl ( Fluka 71627, Fluka 

71959, Fischer S-271 respectively.) The concentration will be 1000 mg/L. Dilute to give 500 mg/L ionic 

interferent in the 100 mL sample to be analyzed, i.e. Add 50 mL to the 100 mL reagent water sample container. 

Add 50 mL reagent water. Then spike with chlorine dioxide/chlorite standard. Analyze.

Each Utility evaluated three fortified matrices (DI water, high ionic strength water and tap water). 

Seven replicates were evaluated st two fortification levels (0.5and 2.5mg/L chlorine dioxide and 

chlorite)
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17.8 Summary of Performance data from three Certified Laboratories (II) – Real water samples

Mean values returned for Chlorine Dioxide and Chlorite in Part 1a to c of the Data Generation Plan

Acceptable limits : accuracy-%deviation = +/- 15%

precision-%RSD = +/- 15%

Utility Mean sd %RSD %deviation Mean sd %RSD %deviation Mean sd %RSD %deviation

Beaver Creek 2.5 0.12 4.8% 0% 2.28 0.07 3.1% 9% 2.39 0.06 2.5% 4%

Hamilton 2.36 0.09 3.8% 6% 2.09 0.13 6.2% 16% 2.7 0.082 3.0% 8% Tap water ClO2 converted 

to chlorite

Water One 2.26 0.29 12.8% 10% 2.29 0.2 8.7% 8% 2.47 0.14 5.7% 1%

Utility Mean sd %RSD %deviation Mean sd %RSD %deviation Mean sd %RSD %deviation

Beaver Creek 2.5 0.05 2.0% 0% 2.47 0.07 2.8% 1% 2.51 0.055 2.2% 0%

Hamilton 2.52 0.065 2.6% 1% 2.5 0.09 3.6% 0% 2.19 0.036 1.6% 12% Tap water ClO2 demand

Water One 2.47 0.07 2.8% 1% 2.55 0.15 5.9% 2% 2.43 0.06 2.5% 3%

Chlorite 2.5mg/L

Chlorine dioxide 2.5mg/L

DI water DI+Int Tap water

DI water DI+Int Tap water

Hamilton Tap Water Results were obtained using Well water. The well water is 

known to have a chlorine dioxide demand. A blank test showed a chlorite 

residual of 0.14mg/L. ~0.3 to 0.4mg/L chlorine dioxide has been consumed, 

therefore the expected results for chlorite was ~1.0mg/L and ~2.9 to 3.0 mg/L
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17.9 Summary of Performance data from three Certified Laboratories (III) – Method Comparison

Utility mean sd %deviation from 

nominal mean sd %deviation from nominal

% difference Chlordiox vs 

SM 4500

Beaver Creek 2.5 0.11 0% 2.52 0.145 1% 1%

Hamilton 0.5 0.04 0% 0.44 0.018 12% 14%

Water One 1.93 0.62 23% 2.18 0.1 13% 11%

Utility mean sd %deviation from 

nominal mean sd %deviation from nominal

% difference Chlordiox vs 

SM 4500

Beaver Creek 2.34 0.08 6% 2.46 0.03 2% 5%

Hamilton 0.46 0.03 8% 0.53 0.03 6% 13%

Water One 2.61 0.3 4% 2.51 0.04 0% 4%

SM 45000

Chlordiox Plus

Chlorine dioxide 2.5mg/L

Chlorite 2.5mg/L

SM 45000

Chlordiox Plus

Hamilton carried out the method comparison with 0.5mg/L spike for chlorine dioxide and 

chlorite

Each Utility prepared fortified tap water samples. Seven replicates were evaluated using ChlordioX Plus and SM 

4500-ClO2 E to determine method equivalency