pH ȒŊ/̶ǥ4̒8ƿ

By Erich L.Springerʘ˘ Ǟű·ɜmPOpamYrU©
2013 Ũ 7 ǐ 7 ǂ

by T&C TechnicalɌ  Ǭ
1.

5!A2.......................................................................................................................... 5
1.1 ǕǍ2+- ............................................................................................................. 72.

PH 4c[ ................................................................................................................ 83.

PH ȒŊ ......................................................................................................................... 12
3.1 sco4ű ........................................................................................................ 123.2 PH ȒŊacm

...................................................................................................... 16

3.2.1 ȒŊ̶ǥ ........................................................................................................... 16
3.2.1.1 Vc̶ǥ ................................................................................................. 18
3.2.1.2 Vcʤ ..................................................................................................... 19
3.2.2 ĂȪ̶ǥ ........................................................................................................... 21
3.2.3 ˇď̶ǥ ........................................................................................................... 22
3.2.4 KCl ʥ÷»(\)LĂȪȽ̶ː˱/'ˇď̶ǥ ............................................ 23

3.2.5 ̛ď»()4̶ː˱Lơ+ĂȪ̶ǥȉ»FĤ»: .......................... 24
3.2.5.1 g|4̥ɇ ...................................................................................... 25
3.2.6 ̶¹ş4ȒŊpH h ............................................................................. 26
3.3 PH ȒŊɸ4ȰƂ ...................................................................................................... 27
3.3.1 ˇď̶ǥ4½H̶¹ş ...................................................................................... 28
3.3.2 ̶ǥacm

4fȦ ...................................................................................... 29

3.3.3 ̹őɠ̶¹ ........................................................................................................ 31
3.3.4 pH ̶ǥacm4c}H5ƎŮ ....................................................... 32

2

by T&C Technical3.3.5 ɭȑʍ­şȦ .................................................................................................... 34
3.4 ̯ʤ .......................................................................................................................... 36
3.4.1 ƟƸ̶¹ ........................................................................................................... 40
3.4.2 ÷ņąƅ2EH̯ʤ4Ǻǚ............................................................................... 42
3.4.4.1 Sv{ĂȪ̶ǥacm(EVEREF).................................................... 42

3.4.4.2 Sv{-B ©ǱȉʃĂȪacm

...................................................... 43

3.5 OU/̙2EGˡş ......................................................................................... 44
3.5.1 OUˡş .................................................................................................... 44
3.5.2 ̙ˡş ............................................................................................................... 45
3.6 ȑŮ4Ź̻/ȑŮ˅Ñ ............................................................................................. 46
3.7 ĺǧ1̶ǥ4ŷ ........................................................................................................ 48
3.8 ó÷ .......................................................................................................................... 51
3.8.1 ȒŊ̶ǥ4ó÷................................................................................................. 51
3.8.2 ĂȪ̶ǥ4ó÷................................................................................................. 52
3.9 ǝǮ .......................................................................................................................... 54
3.9.1 pH Ǩȗʎˀȉ/©Ǭʎˀȉ ............................................................................. 54
3.9.2 ǝǮ4Ɩ̾ ........................................................................................................ 57
3.9.2.1 OqZh4ǝǮ............................................................................ 58
3.9.2.2 QY}ek_L¾Ƚ

' pH h.4ǝǮ .......................... 61

3.9.3 ÞǝǮ ............................................................................................................... 62
3.9.4 ƅɯǉ̦ ........................................................................................................... 62
3.9.5 ǝǮǉ4ě̈́/%4ÿĠ ..................................................................................... 643

by T&C Technical

3.10 ǓŻIHɷŮ ...................................................................................................... 65
4. ̶ǥ4ćGƘ ............................................................................................................. 66
4.1 ÅŅ .......................................................................................................................... 66
4.1.1 ȒŊ̶ǥ4ÅŅ................................................................................................. 67
4.1.2 ĂȪ̶ǥ4ÅŅ................................................................................................. 68
4.1.3 ˇď̶ǥ4ÅŅ................................................................................................. 68
4.2 ̶ǥacm

4Ȃȅ ................................................................................................. 69

4.3 ĂȪȽ̶ːȉ4˅ÔH5­ƭ ........................................................................... 71
5. PH ̶ǥ4 PH h:4Ʃʈ .................................................................................. 72
5.1 ȒŊ̶ǥ4Ʃʈ[| ......................................................................................... 72
5.2 ĂȪ̶ǥƩʈ̮[| ......................................................................................... 72
5.3 ˇď̶ǥƩʈ[| ............................................................................................. 73
5.4 [|4ȗÍ/̖ʖ ............................................................................................. 73
5.5 }ZH5[|͜ ...................................................................................... 75

4

Page 3

1.

5!A2

͈?ȯC͇;ȯL͇pH Measurement
utilising
pH Measurement
Glass Electrodes
utilising
Theory and Practice
Glass by
Electrodes
Erich K. Springer

Page 3

by T&C Technical'ǉ Theory̙*7/ʯ4̏L®5Ǝ!H/.>"and Practice¿6by Erichɓ͎Ƕ5ʯƎ!>"
K. Springer̘ bc5̙*7Ǝ!
ȉ»4B+IF4ȰƂ

1
1

INTRODUCTION%4̙*7H5ʯLȶ"25
ÉLȽ>"
pH Éɛ"ƍĕ5
¿6}
Since
the creation of man, he could pH
differentiate
betweensour and bitter wheneating liquid or

INTRODUCTION
solid foods. We say that vinegar and lemon juice taste sour and that soap water tastes bitter.
4 pH É5HŊ4ť21HE2-H/10L̅!¯ǂĺ4®2ɑFIĈThischaracteristic
and thebetween
marked degreeof bittersour orbittereatingis indicatedby the pH
Since thecreationof man,ofhethese
couldliquids
differentiate
sour andwhen
liquid orvalue.
the pHvalue
is todayto athatgreat
portionof tastes
our population
solid foods.
WeThesaysignificancethat vinegarof and
lemon
juice
taste known
sour andsoap
water
bitter. alone
×IFI->"͇;ȯ5'M4ǶLĒ?
% swimming-pool-͈?ȯ5üɺ25ʭ/͊G4
through
the
fact
that
it
is
accepted
that
the
pH
value
of
water
has
to
bepH
kept within
This characteristic of these liquids and the marked degree of sour or bitter is indicated by thecertainlimits. The
foodeatiscontains
a lot toofa waterand ourofdrinks
are nothingelse thanvalue. The
significanceof thepHwevalue
today known
great portion
our populationalone²'Ƕ."%-%4Ƕ5̙*7*'Gʯ*'G>"%IFL˒ƭI6
andit flavoured
water,
andpH
thisvalue
waterofcan
be either souror bitter;
inkeptotherwithinwords, it willthrough coloured
the fact thatis acceptedthat theswimming-poolwater
has toorbe
have aThecertainvalue.
certain limits.
foodpHweeat contains a lot of water and our drinks are nothing else than
%I5H pH ÉLơ*-H/21G>"
coloured and flavoured water, and this water can be either sour or bitter; or in other words, it will
In general we can say that water is the mosthave a certain pH value.
important substance on earth. Withoutwater thereĨȷ.Ƕ5ɄĻä1˰Ȗ."ǶȨ .
will belife onplanet.
Peoplelivingin areas ofIn general
wenocansayourthat
water
is themost
5ėHȯ51on+/-ȻH/5.>severedrought
haveexperienced
the importanceofimportant
substanceearth.
Without water
there
water
for
their
existence.
Continuous
droughts
dowill be no life on our planet. People living in areas of$Mȳȧ1¤ȫĨţ2ȻH®
5Ȼʈ
not onlyaffectthe farmers,
are a disasterforsevere drought
haveexperienced
thethey
importanceofthetheir
entireeconomyContinuousof a nation.
It is thereforeofwater forexistence.
droughts
do-for liquid
utmostimportancetreat
this precious
not onlyH.%4ĻäL˷L´-»͌
affect thefarmers,that
theywearea disaster
with
care,
use
it
responsibly
andtry
to savethe entire economy of a nation. It is thereforeof every>"drop ofƯ̊1HŦ6+5˼Ǥ:4Ź̻2/0
it. that we treat this precious liquid
utmost importancewith care, use it responsibly and try to save every>F#ĥ/Ļ4ʁȎ2>.ɕķɉ
drop of it.
Water is everywhere! Three quarters of thesurfaceof the earth
is covered with water in the1Ź̻L>"%ID2ǏB̛ˈ1
formof oceans,Threerivers,lakes ofandtheswamps.
Water iseverywhere!
quarters
whiskey,beer,withwine,
cool-drinks,
fruit
/5
ǶLĻä2
surface Brandy,of the ɝ')54ˮ̛1ȯ˱earth
is covered
waterin thecoffeeand teaconsistwater containing
form ofjuices,
oceans,rivers,lakes
andof swamps.
certainadditiveswhichchangethepropertyand% -ˬ¶Lơ*Brandy, Ƙ/ǸAFI>"
whiskey, beer, wine, cool-drinks,
fruit
the tastetheconsist
water. ofBlood,
vital liquid of ourjuices, coffee
andofteawaterthecontainingbodywater, thein fact
our entire-Ƚis 1mainlyȚ 1 ȚLɲɹ"H/LǸAFI
certain additives
whichchangepropertyand bodyof approximately
65%liquidwater.
the tasteconsistsof the water.
Blood, the vitalof our->"
body is Water
mainlyis water,
fact ourentire bodyused ininindustry
as coolingwater, wash
consists water,of approximately
65%
water.
boiler water, steam, condensate and solvent. Dirty water is usually disposed of as effluent.
Ƕ502.BG>"Ĩȷ4˂̺4
2/3
Notablychemicalindustry
especially
Water is used inthe
industry
as coolingwater,
wash makes use of this universal solvent, because mostsubstances
are somewhat
solublewater. Dirty water is usually disposed of as effluent.
water, boiler
water, steam,condensate
andinsolvent.
5ȆǶ2ˉKI

̭25ǽŜ

ȓ

ȔĨG

ǂǕ̗

|n

RQcW

y

ǙǷ͈Ƽ

]x

ʱ5

Ƕ2ȯòKH/.Ȱƈ/ĕNotably the chemical industry especially makes use of this universal solvent, because mostsubstances are somewhat soluble in water.


Q

ß'͈Ƽ

5

by T&C TechnicalĸK*'ȯ.

G>$M%I5¡2Ƕ..->"Ƕ5ȼǤ4%ŋ̰ɝ')4»4 65%5Ƕ..->".5 ßýǶ ȂȅǶ QǶ ʶǵ ȢʐH5Ţ̚2¾KI>"-ǺI'Ƕ5%4>>ůǡI-

÷ņŝǤ.5Ȱ2ʡ1Șł/÷Lʽȉ5ɝ')4»4ȃðLʉơ"H'A4ȉ»."

>"

%

-ǶLèȽ

ĺ4ȯ˱5Ƕ2FȘ>"

>"%IF4Ƕ5¾ȽIH-ǏBĸ÷4Ļȯ5ǶɼȢŮ."

QTȢŮɅ1G
>" %

>>"

%IF5̙H5OUƈ

ĺǧ1ĸŞ˕2Ǎ'Ø-4Șȉ5Ƕɼ̙*7ʯ/̏Lơ*--IF4ǶȘȉ2HǶɼQTȢŮLȒG %4ȢŮLȶ"4 pH É//21G>"®4ʩB pH ȒŊĝ/˒/B.> ǶȘȉ4̙ƈH5OUƈLǻŊ"H/ ̶¹şLȒŊ"Hƿű4 pH ȒŊĝ(Ōˏɉ.Ǯɘ Þȶƈ4HʂǙLƬÀ.
>"pH ȒŊ5%IDȻȯņH˂̺áȸ

ˆɻ

øņ

ʔȯǖƼ

͇ęƙʿ
÷ņ

͈ƼǶ4áȸ

ɓǾ÷ņ

˼Ǥ

̞ȯņ

̝Śáȸ2ʖ

>'Đǧ2ȺĴÅ˩4'AŝİůǶ

ǺǶáȸ.5ǥA-̛ˈ1ƍĕLơ)>"ȼǤ2Hǂ
ě̈́ɇȻ

4 pH ȒŊ5EG̛ˈŮLĵ-G }ec4êƀ2-5ƾːǻǸAFI->" >'ɔɦƕ2-BEG͍ɷŮ4 pH ȒŊ/Þȶƈ5̛ˈ1ˈɼ/-ˈǸI->"ǕǍ4Ɍɉ5 pH ȒŊ2ʖHĭǕɉ1ɑ˨L.H(ɴü2 ȸː
H/."



pH ȒŊ4ȸːLÄ̊"HƖô/1I6ũ."

6C"ŷ.ƬÀ"by T&C Technical1.1

ǕǍ2+-

̶¹şȒŊ/ pH ̶ǥ4ǫʡLȸːǮɘ1 pH ȒŊL"H25 ÷ņ4ĭǕɉ1ɑ˨Lơ+ƄˈG>"uoɜ5˕4˒ʴF EGǮɘ1 pH ȒŊLʾ'A4VQp/>'-ǕǍL½G>'%4ȸːLȊAH42Ƅˈ1÷ņă8ȯȸ4ÿȸ2+-4ɴü1ːˢLǕǍ4²ŚƻǍ/-Ȍ²->"

IF4ˢǅ5ǶɼQTȢŮ4Ŋʗ:/ʂ8+

E21*->"ǕǍ5 pH 4c[4ŊʗFŁA sco4ű %Ǖ2+-̀;->"-ĂȪ̶ǥ/Vc̶ǥ4ĭ

pH 2̧̈"HȰǯ1ȽˠȽFI->"

ˢǅLȸː"H/.ĺǧ1 pH ̶ǥ %%4Ƚˠ4-uo4 pH ̶ǥ4¾Ƚƿǿ/%4ȒŊ4Ɠñ:/ŕ/.H/ʙ->"ǝǮ2ȽHʎˀȉEGʬȒŊɷŮL̎Ɠ"H/5.1uoƬÀ"H pH Ƚʎˀȉ2+-5 pH ȒŊĝ4ǝǮ4̽´̩.ˢǅ
4

25 pH ȒŊ2ȽHĎɣ̶ǥ2ő

ʾ*-ʬ½Ǥ ʾ*-51½Ǥ2+->/AFI->"ǕǍĬɬ2Ŷ'G

˕4ƿ

>" %

2ȊƎ˧ȿ

>"

Dr.Hannes Bühler, Andreas Brügger, Dirk Tillich,and thank to my loving wife7

by T&C Technical2.

pH 4c[ǶȘȉ4B+ǶɼQTȢŮLãŃ̜.˂ȶ"Hǉ
10-14mol/L /c[.ȶ

2 THE pH SCALEɝ')5 1(100)F 10-7 LʁPage 5>"4c[5ȶŋ25¾2/F4ƹÉL˫4őƹLȽŋƹ4˂˕:/If we express the hydrogen ion concentration of an aqueous solution in relation to its molecularvalue we derive a scale of 1 (100) via 10-7 to 10-14 mole/litre.
ĸƭüɺ2 0 F 14 /c[L+G>'

IL pH 4c[/-This scale is impractical but if written as a function of its negative logarithm a real and simple
scale >"of 0 – 14
has been created:
the pH scale.
´2ãŃ̜/pH 4c[4̧ÃL˂.ɛ
>"H+ concentration(mole/litre)Ƕɼ4ȢŮ
͑mol/L͒OH- concentration(mole/litre)xpWaĭ4ȢŮ͑mol/L͒

pH

1
0.1
0.01
0.001
0.00010.00001
0.000001

0.00000000000001
0.0000000000001
0.000000000001
0.00000000001
0.0000000001
0.000000001
0.00000001

0
1
2
3
4
5
6

0.0000001

0.0000001

70.00000001
0.000000001
0.0000000001
0.00000000001
0.000000000001
0.0000000000001
0.00000000000001

0.000001
0.00001
0.0001
0.001
0.01
0.1
1

8
9
10
11
12
13
14

hydrogenii
4Ƀˠ.
4Ƚˠ5This
1909term
pH is pHthe5mˠ4
abbreviationpondus
of pondushydrogeniiandǶɼ4̛Lƍĕmeans the weight>"
of hydrogen.
was introduced in 1909 by the Danish biochemist S. P. L. Sørensen (1868 – 1939).
ŨnY4Ȼ÷ņʚ S.P.L. SØrensen (18681939 Ũ)2EGŕ×I>'

The pH scale covers the active concentration of the H+ ions and OH¯ ions and therefore the pH
value is defined as the negative + common logarithmof the active hydrogen ion
pH 4c[5ȃƈ÷ -H H QT/ OH-QT4ȢŮɳĢ/ ->" %4'A
concentration in an aqueous solution.
pH É5ǶȘȉ4.ȃƈ÷-HǶɼQTȢŮ4˫4ŤȽőƹ4É/ŊʗI->1

pH = log hydrogen ion concentration ( mole/litre)"

If the H+ ion concentration changes by a factor of ten, the pH value changes by one unit. Thisillustrates how important it is to be able to measure the pH value to a tenth of a unit or even ahundredth of a unit in special applications.
The pH definition refers to the active hydrogen ion concentration and not just to the hydrogen ion
concentration. It is important to understand this difference. Only in dilute solutions are all anions
and all cations so far apart that they are able to produce the maximum of the chemical energy,
8i.e. the H+ ion concentration and the H+ ion activity are identical. For instance 0,01 molehydrochloric acid is still classified as a dilute solution which dissociates completely and therefore
concentration equals activity.

by T&C Technical1
pH = LogǶɼQTȢŮ(mol/L)
H+QTȢŮ 10 4Èƹ2EGĸ÷"I6 %4 pH É5 1 #+ĸ÷"H/21G>"
Iɛ"̅G

ȒŊĝ5ȒŊő˪2EG 0.1 4ü¹H5 0.01 4ü¹.ȒŊ.HƄ

ˈH4."
pH 4Ŋʗ5ȃƈ÷-HǶɼQT4ȢŮLĂȪ"H/21*-H/F Ŷȩ%I´Ĺ4ȱƏ4ǶɼQT4ȢŮ5Ē>I>$M
1H÷ņSsXL½Gâ"/J/5

4̏5/-B̛ˈ."Ƕ2Ș'ȱƏ2-ǏĻ/

Ø-OrT̬͑

H+QT4ȢŮ/ȃƈ H+QT

QT͒/";-UjT̮͑QT͒/1*'ȱƏ."4ȢŮ4̏.Hİď4¿L´2ƣ-?>"¿6 0.01 4Ĳ̙Ƕ2Ș'ȱƏ/-ã͆I'İď

ɼ/ĲɼQT2ã̴̧ÃƓGɩ)>"ȢŮ/ȃƈŮ5ɭ

Ƕ.5Ĳ̙5ŉØ2Ƕ

0.01 mol HCl: ȢŮ ͚ ȃƈŮ
.Ĳ̙4ȢŮLǄ$>"ďȠ"

1*->""H/UjT(H+)/OrT(OH-)5Ǭɫ2ª2ŀI5ɡö.HccŖ1*--H'A.

ȃƈQT5Ǭɫ2D*G/1G>GȢŮLI6H<0

QTȢŮ/-4ąƅL

11G>"+

ȃƈQT5ŋ̰4QTȢŮ/0M0MɅ1*-H

4."
1 mol HCl: ȢŮ ͛ ȃƈŮ
4E2ǶȘȉ4 pH ȒŊLʾ. ȃƈǶɼQT4ȢŮ4?LȒŊ
¨ŋI5ǶɼQT4ØȢŮLȶ

-H/

-1//Lȸː"H/Ļä."9

by T&C TechnicalɺǶLȽƍ%4ȑŮLǄ$-?>"

̴ĵ->"5Ȑ*-Lƍ˨"H/ǶɼQT/xpWaĭQT4ã

pH 5ȃƈǶɼQTȢŮ4?Lȶ"//F

>>"



ɺǶ5

1. ¿6HȑŮ.ȒŊ

ƈ14."

pH 4É5ŋ̰+>G¢̴Ŋƹ/ȑŮ4̦4̧Ã' pH 4ÉLB/2Ʌ1HȑŮ. pH 4ÉLǸA

H/5.1//."pH 4c[4ƍĕ5 pH0  1mol/L 4Ĳ̙ȢŮ. pH14  1mol/L 4Ƕ̙÷qoR
ȢŮLǳ˺"H/.ȸːC"1G>"

ƿ4ǶȘȉLĐ!̜.ȋď

'İď

HCl + NaOH

pH0 + pH14ǶȘȉ4̙ƈ/OUƈ4Ȱƈ5
G%4ƈ˱Ȩ1G>"´4űƓGɩ)>"→

HOH + NaCl→

H2O + NaCl→

pH7

ǶɼQT/xpWaĭʂď"H/.Ƕ/1

ąƅ4ʂǙ NaCl .

%I5

ƈ4'A pH 4É25¼

4Ź̻B>$M
IF4/F´4E2>/AH/.>"͓ HǶȘȉ
%4ǶȘȉ54ȃƈǶɼQT/ȃƈxpWaĭQT4ȢŮĐ!İď
ƈ/1H͑pH É= 7͓͒ ǶȘȉxpWaĭ4ȃƈQTȢŮEG͍ȃƈǶɼQTȢŮLB+/

%I5̙ƈ/1H͑pH É͙7͓͒ ǶȘȉȃƈǶɼQTȢŮEG͍xpWaĭ4ȃƈQTȢŮLB+/

%I5OUƈ/1H͑pH É͙8͒

10

by T&C TechnicalPage 7

pH 4c[The pH Scale-1

mol/L HCl
-1 mole
1010
HCl

pH 0

1

2

3

-1

10 mol/L NaOH
10-1
mole NaOH

HOH
HOH

4 5

6

7

8 9 10 11 12 13 14

1mol/L HCl

1mol/L NaOH

1 mole/l HCl

1 mole/l NaOH ̙ƈ:
increasing
acidity

pH 0

1

2

3 4

5

ƈ
neutral

6

7

8OUƈ:
increasing alkalinity

9 10 11 12 13 14

Gastric

Milk Well
Sour
Ȯ£
Milk
Coffee ʽȉWaterǙǷOrOǶ(30%wt)
HouseholdYoghurt£̙«Ƕ Soap
Ammonia
Suds
Beer
Zo
Blood ɓ͎ǶMilk
Lemon
of
Juice
]x
Ƕ̙÷ZsaRȘȉ
Magnesia

ʠȉ
Juices3 THE pH MEASUREMENT
3.1 The NERNST Equation
To determine the active hydrogen ion concentration, a pH measurement is necessary.
Three methods are generally used for the direct determination of the pH value in aqueous
solutions:
111) The visual method, a colour comparison with pH sensitive indicator paper(litmus) to a standard colour scale.

by T&C Technical

3.

pH ȒŊ

3.1 sco4ű
pH ȒŊ5ȃƈǶɼQTȢŮLȒH/ǶȘȉ

4 pH ÉLɍƩȒŊ"H25 3 +4ƿǿG>"

1͒ˌˍɉ1ƿǿ

pH 2ƎŮLɇʭƈ4ɻ oc˚͌ɻLȽHƿǿ.ĭȗ/1HU
c[/ǳ˺-ȒŊ>"2 ãÖ˓

ãÖ͍Ů˓LȽpH 2ƎŮ4Hʭ4ȉ»4Ȁ̢LȒŊ"H3̶͒ǵɉȒŊ

̶ǵ÷ņȒŊ.

̝Ś͆/ĲȘȉ4̦2H÷ņąƅ4E2

.Ȼ!'˲̶ðLȒŊ
ǶȘȉ

%

>"

4 pH 4ÉL̶ǵɉȒŊ2EGǻŊ"Hƿǿ5 QQ.4ȒŊ4E1}

ecêƀ2-¾/.HĚ4ƿǿ." 4'AǕǍ.5%I2̪Ŋ- pH

4É4ȒŊ2+-̀;->"pH 4ȒŊƿǿ5sco4ű2ĭ,-ʾKI>"Ǧ̇Lơ+Vvr̶¹/sco4ű5

ǻ>*'̶ǥ

ȒŊ"HǶȘȉ4QTȢŮ4÷ņąƅ4̦2Ha}

1ŷű4̧Ã2+-̀;'B4/1G>"̶ǥǦ̇5ȒŊ̶ǥ

I5ȒŊIHQT4ȃö2ő̶ǥ.ǦƓI>"

4̹Ť2üɺ1ŷűLơ+̶ǥǦ̇4Ʊ½+-5´4¿2E

G̾ūɩ--ˢǅƎŮHB4

%

-ĂȪ

->"

©+4Ƕɼ̶ǥ(%I&I4̶ǥ5ʺɚI'}jq.âǘ->")©+4Ʌ1*'ǶɼQTȢŮLơ+ǶȘȉ2ȇȝI->"4̶¹LȒŊ.HE2"H'A ©+4ǶȘȉ5ĲǪ(̶ː˱4Ǫ).ƩʈI->" %icLơ+̶Ħ˓2ʓI->"-©+4̶ǥ5͍Qz

ǶȘȉ5Ù2ɺɵ1ǶɼVc2EG͉Ę
12'ȱ

If two hydrogen electrodes (each a thin plate of polished platinum) are immersed in two solutions,having different hydrogen ion concentrations, each electrode will generate a potential which
depends on the active hydrogen concentration of the solution in which the electrode is immersed.
To be able to measure this potential, the two solutions are connected by a salt bridge (electrolyte
bridge) and the two electrodes are connected to a high impedance voltmeter. Both solutions are
by T&C Technicalsaturated with pure hydrogen gas.
Since

passing during such anegligible, the chemicalcomposition of the sample solution is not altered.
4ğ˶LȄIH̶Ȅ5Ȩˌ.H<0
The bridge acts as a phase boundary between
solution C1 and solution C2 and closes theŖȯ/>" ǶȘȉ4÷ņɉǦ̇
electric circuit.

͍QzicLơ+̶Ħ˓
High
impedance mV meter

0
-1500

+1500

mV

the

current

ƏLÅ*->"measurement is

A potential difference will be generated between
1B4/ >" ĲǪ5 C1,C2
the two platinum electrodes by the different activehydrogen-ion concentrations in the solutions. The
4̦4ɎĴɁ/ -9H>>" %relationship is expressed by the NERNST
equation:5ĸ÷Electrolyte BridgeĲǪ-̶ǵğ˶L̤!HźîLơ*->"
̶¹ş5

RxT
C
E
x
log
ǶɼQTȢŮ2EG©+4}jq̶
nxF
C2

Pt

Pt
C2

C1

©+4ǶȘȉ4Ʌ1*'ȃƈ
1ǥ4̦2ɇȻ

>"%4̧Ã5swhere:

co4ű2EG˂ȶI>"

E = potential difference (mV)R = gas constant (8,31439 J x mol-1 x K-1)
R  T constant (96495,7
C1 C x mol-1)
F = Faraday
E=



Log

n  F

C2

E = ̶¹ş mV
R = VcŊƹ(8.31439J×mol-1×K-1)
F = {NnŊƹ(96495.7C×mol-1)
T = ʆőȑŮ (K)n = ȒŊIHQT4̶ʲ(.5 nH = 1)C1 = C1 ǶȘȉ4ȃƈǶɼQTȢŮC2 = C2 ǶȘȉ4ȃƈǶɼQTȢŮ

13

by T&C Technical

R  T
E=

C1


Log

n  F

C2

C1 / C2 4̦4ȢŮǳ 10:1 /

E=

10


n  F

Log

/

-ɑFI

- UN /²FI->"¹4ĸ÷L 10 Èü¹.ȶ

%4a

UN 5ȃƈ2EH̶

->"

R/F5

1

R  T
E=

-?

>"
E 5sco4̶¹/

R  T

ű2³×



2.303585

Ŋƹ."̶ʲ n 5QT4ɣ͆/2ɑFI->" %-ȑŮ T 5℃.ȒŊIH'A ILʆőȑŮ2ƭ>"n  F
T = 273.15 + 20 = 293.15 K
IF4ÉL³×"H/sco̶¹5
UN = 58.16mV
/1G>"

14

The values of R and F are constant. The charge number n is known for each kind of ion and thetemperature T can be calculated from the measured value in °C.
The values of R and F are constant. The charge number n is known for each kind of ion and theIf we assume the temperature of the solutions to be 20 °C, then:temperature T can be calculated from the measured value in °C.
T of= 273,15+ 20 =to293,15
If we assume the temperature
the solutions
be 20 Kelvin°C, then:by T&C TechnicalThis will give us a NERNST potential
T =of273,15 + 20 = 293,15 Kelvin
Page 7

pH 4c[/sco̶¹4This will give us a NERNST potential
UNof= 58,16 mV

The pH ScaleUN =58,16 mV
HOH
HOH

-1

mol/L HCl
1010-1 moleHCl-1

-1 mol/L NaOH
1010
mole NaOH

The pH Scale and the Related NERNST Potential-1-1

10 moleHCl
HOH
10 mole NaOH
ThepH Scaleand theRelated NERNST
Potential
pH 0 1 2 3 4 5
10-1 mole HCl

67

8 9 10 11 12 13 14
HOH
10-1 mole NaOH

1mol/L HCl

6

7

1 mole/l
8 9 10 11 12
13 14NaOH

1pH
mole/l
HCl2
0 1

3

4 5

increasing 0 1 ̙ƈ:
pH
2acidity
3 4 5neutral6ƈ7
1 mole/lHCl

1mol/L NaOH

alkalinity
OUƈ:
8increasing
9 10 11
12 13NaOH
14
1 mole/l

1 mole/l HCl

1 mole/l NaOH
0
0 1 2 3 4 5 6 mV
7 8 9 10 11 12 13 407,12
14+pH
407,120mVmVmV
407,12+ 407,12Gastric
mV
Milk Well
Sour
JuicespH
MilkpH CoffeepH Water
Household+58,16
2x
YoghurtSoap-58,16
mV
mVAmmonia
mV at 20 oC +58,16mV=
pH
pH
Suds
116,32
mVpH
Beer
Blood
+58,16-58,16
Milk
Lemon
2x
o
mV
mV at 20
C +58,16mV=
of mV
Juice
116,32 mV
MagnesiamV

As the ion activity is temperature dependent, so is the NERNST potential (refer to the
QT4ȃƈ5ȑŮÁŅƈGsco̶¹BĐǧ2ȑŮ4Ź̻LĈ>"´
NERNSTequation). The following table illustrates
the temperature dependency:
As the ion activity is temperature dependent, so is the NERNST potential (refer to the4˂5̶¹/ȑŮ4̧ÃL˂
NERNSTequation). The
table
UN ->"UN the temperature
UN dependency:
T following
T illustrates
T
o
o
o
C
C
C
mV
mV
mV
UN
UN
U
T
T
T
0o 54.20
35o 61.14
70o 68.08 N
5 C 55.19mV
40 C 62.13mV
75 C 69.08mV

54.20 45 3563.12
61.14 80 7070.07
68.08
10 056.18
55.19 50 4064.12
62.13 85 7571.06
69.08
15 557.17
56.18 55 4565.11
63.12 90 8072.05
70.07
20 1058.16
15
57.17
50
64.12
85
71.06
25 59.16
60 66.10
95 73.04
58.16 65 5567.09
65.11 100 9074.04
72.05
30 2060.15
25 59.16
60 66.10
95 73.04
Temperature Dependency of the NERNST Potential
30 60.15
65 67.09
100 74.04
Temperature Dependency of the NERNST Potentialsco̶¹4ȑŮÁŅƈ

3 THE pH MEASUREMENT
3.1 The NERNST Equation
To determine the active hydrogen ion concentration, a pH measurement is necessary.
Three methods are generally used for the direct determination of the pH value in aqueous
solutions:
151) The visual method, a colour comparison with pH sensitive indicator paper(litmus) to a standard colour scale.

by T&C TechnicalPage 11

3.2 The pH Measuring System
3.2 pH ȒŊacm
ȒŊacm
5´4Ǧ
AĭǕɉ1
basic pHpH
measuringsystemconsists of
0
-1500

mV

+1500

High impedance
voltmeter͍QzicL
ơ+̶Ħ˓Electrode̶ǥacmassembly(1)
Measuring
electrodeȒŊ̶ǥ(1) the measuring electrode,a pH sensitive electrode,̇Lơ)>"(3)(2)

the referenceelectrode͑1͒(2)ȒŊ̶ǥ͗pH2ƶƎ1̶ǥ.
andReferenceelectrodeĂȪ̶ǥ(3) a high impedance voltmeter.
"͑2͒ ĂȪ̶ǥ
͑3͒ ͍QzicLơ+̶Ħ˓

3.2.1 The
ȒŊ̶ǥ
3.2.1
Measuring ElectrodeThe
purpose of the measuring
electrodeis to determine the >"pH valueof an aqueous solution.
ȒŊ̶ǥ4Ɍɉ5ǶȘȉ
4 pHÉLȒŊ"H'A2¾Ƚ
}jq/Ƕɼ̶ǥ5
The platinum/hydrogen electrode was originally used to measure the hydrogen ion
1897 Ũ´ǘ inǶȘȉ
4ǶɼQTȢŮLȒŊ"H'A2ȽFI->% -¯standard
concentration
aqueoussolutions (since 1897) and today still serves as a'reference
for the electrometric pH determination. The hydrogen electrode consists of a platinised
ǂ2-5>(̶ǵɉpH ȒŊ4'A4ĂȪǨȗ/-ȽFI->"platinum
plate or rod (coatedwith platinum black), subjected
to a flow of Ƕɼ̶ǥ5Ƕ
gaseous hydrogen. A
silver wire coated with silver chloride serves as a reference electrode.
ɼVc4ȄILĈH}jqkWLǀ'}jqȬ͑͏Ɉ̝˂̺áȸ͒.½FI-

The basic theory, when employing a hydrogen electrode, is as follows: If a metal rod (electrode)is>"
immersed
into an aqueous solution containing its own
salt (silver electrode in silver nitrate), theĂȪ̶ǥ5Ĳ÷̟.kWI'̟ʍL¾Ƚ
->"
atoms on the surface of that metal rod will ionise. The water molecules will attract the positively
chargedmetal ionsfrom thesurface of the rod, which leaves the metal rod negatively charged.
Ƕɼ̶ǥL¾Ƚ'İď4ĭǕɉ1ȸ˦5´4E21G>"
This charge exchange develops a potential difference at the phase boundary metal/solution. The
potential depends
on the ion concentration->"(ɖ̙̟4ǶȘȉ2̶̟ǥȇȝ
in the solution and is known as the galvanic̶ǥ5%4̶ǥȽ4̶ːȉ2ȇȝ
potential.
Ƕ4ãŃ5̶ǥ4˂̺FǮ4̶
Today the -H)hydrogen̶ǥ˂̺4ÿŃ5QT÷I>"
electrode still serves as a reference
standard especially as its measuring
results are extremely accurate. However for practical reasons the hydrogen electrode has lost its
ʂǙ̶ǥ5˫4̶ʲLơ)>"importanceʲLŲ+>"
because of its difficultand complicated handling. 4̶ʲ4­ƭ5̝Ś/ǶȘ

Only the antimony electrode has survived out of various metal electrodes. Antimony is chemicallyȉ4ɎĴɁ2̶¹şLɇȻ >" %4̶¹5ǶȘȉ4ơ+QTȢŮ2ÁŅ
resistant to hydrofluoric acid and can therefore be used for the pH measurement in solutions
containing hydrofluoric acid. However, the accuracy and reproducibility of the measuring result
ILVvr̶¹/˒>"incorporates large tolerances.
16

by T&C Technical¯ǂǶɼ̶ǥ5̹Ť2ɷŮ4͍ȒŊʂǙLſH'A4ĂȪǨȗ/

$M

1F

ġ̵.ˇ̳1Ʊ½Ƅˈ//F¯ǂ.5ʫɉ2ȽFI->ĚOj̶ǥ̝Ś̶ǥ/

ȒŊ2ő-ȽFI->"ȽH/.H'A."-ȽFI->"I5{k̙Șȉ4 pH'(%4ȒŊÉ4ɷŮ/Þȶƈ4˗ŎɳĢ5Ļ

1B4/1*->"17

3.2.1.1 The Glass Electrode
It was not until the development of the glass electrode that pH measurement became a simple
and reliable tool for all kinds of applications. In recent years the glass electrode has outgrown allother types of indicator electrodes for pH measurements. The pH determination of an aqueous
by T&C Technicalsolution is today as common as temperature and pressure measurements,
thanks to thereliability and accuracy of the glass electrode in combination with extreme stable electronic
amplification.
However, the successful application of the glass electrode requires some
3.2.1.1 Vc̶ǥknowledge about its functionality and its maintenance, which this booklet will provide.
Vc̶ǥ4Ǧ̇
The Constructionof a Glass ElectrodepH[|
cablepH̶ǥ̼́̕head
Electrode̶ǥVcɱ
Electrodeglass shaft̑ʹScreenInternal conductorÜ̕ŕ̅Ƚ̶ǥelectrode(Ag/AgCl)Ü̕ʎˀȉ+KCl(pH7)
Innerbuffer + KCl (pH 7)

pH sensitive
pH ƎŮLơ+Vcʤ
glass
membraneȶħ4E1ĺǧ1O}[a.
LȒŊ
A glass electrode consists of a shaft pH
madefrom glass

which should be highly resistant to hot alkaline"H25
solutions Vc̶ǥ4˞Ȼ>.Ż+ƄˈG>and its electrical resistance must be several

times greater than that of the membrane glass. The pH' ȶ³2-Vc̶ǥ5%I´Ĺ4ȒŊ̶sensitive
part of the glass electrode is the normallycylindrically shaped electrode tip, the glass membrane.
ǥƿű2ǳ˺
ɨâis -ŪȽFI->"Ƕ
The membranemade from special hydrogenion
sensitive glass and is fused to the electrode shaft. TheȘȉpH ȒŊ5¯ǂ.5ȑŮ
Ħð/8Ǩȗ
glass4electrodeis partly filled witha buffer solution,
normally having a pH value of 7.
ɉ1ȒŊ̽Ɍ/1*->"I5Vc̶ǥ4

A defined amount of potassium chloride (KCl) is added
to this internal buffer.

B+ɷŮ/ňŊƈ

%I2K$-ňŊ'O}

A silver wire, coated with silver chloride (Ag/ AgCl) isinserted2ÁG>"into the glass
right downacm
 electrode1F4Ɠñ
'/into theinternal buffer and serves as a conducting electrode.
Via the core of the coaxial pH cable, the Ag/AgCl wireƆKIHVc̶ǥ4O}[a2is connected to one terminal of a pH meter.
%4ǫʡ/ÅŇ2+->(F4ɑ˨LƄˈ/>" ǕǍ.5%4Ȧ2+-̀;->"3.2.1.2 The Glass MembraneVc̶ǥ5Vc..'ɱ.âǘ->"%4Vc5͍ʛOUƈLơ)All types of glasses possess the property of producing a potential difference relative to thehydrogenion concentration in aqueous solutions. However only special types,
such as theVcʤ4ơ+̶ǵɉƞƛ2ǳ;ƹÈ4ƞƛLơ*-1-51G>$M
pH 2ƎŮL
conventional Mc-Innes glass (Corning 015) produce galvanic potentials which satisfy the
NERNSTequation over a wide rangeof the pH scale.
ơ+̕ã5Vcʤ/Ė6I̅ŤÝɮĩLVcɱ4Õɪ2²̕ę." Vcʤ
Every manufacturer of pH electrodes is constantly researching for better pH sensitive glasses.
5Ȱç1ǶɼQT2ƎŮLơ+Vcɼǖ.âǘ-G Ǖ»4Vcɱ2ʼɐIThroughconstant development HAMILTON has achieved results which have not previously been
available without unsatisfactory compromises.
>"Vc̶ǥ5̕ãɉ2 pH7 4ʎˀȉ.ȕ'IŊAFI'ȢŮ4 KCl òF

When the membrane glass of a measuring electrode comes into contact with an aqueous
solution,
it forms
a thin gel layer of approximately 10-4 mm thickness
betweenthe glassI->"Ĳ÷̟kWI'̟ʍ5Vc̶ǥ2ƥ×IÜ̕ʎˀȉ2ş
˽>Isurface and the solution. The thickness of the gel layer depends on the quality and compositionof >"the membrane
glass, the temperature and the pH value 4ʍ5of the measured
solution. As theI5̶ǥLĹ̕:/ŕ̅$H'A2ȽFI>"pH ȽĐ˸[|internal side of the glass membrane is in contact with the inner buffer (an aqueous solution of pH7) a4ʮʍ/Ʃʈ
gel layer is also
on the inside of the glass membrane.
pH formed˂ɛĝ4ȒŊ̶ǥɪŃ:/ƩʈI>"18

by T&C Technical3.2.1.2 Vcʤ
FDHVc5ǶȘȉ4
*->"



2HǶɼQTȢŮ2ǳ¿

1F Ǌă

-̶¹şLɇȻ"HȰƈLơ

-H Mc-Innes Vc(Corning 015)4E1Ȱǯ1°

ǧ4Vc( sco4ű.ȶIHŪɳĢ1 pH c[4Vv©̶¹LɇȻ
>"%I&I4 pH ̶ǥˆ̇·ɜ5EG pH 2ƎŮ4HVcLŤ2ˤǛ->" 4ˤ

Ǜ4

Ȳʦ4Vcˆ̇uo5ǁŅ4Vc2ő"Hȕƙʿ2EGƓǙL->'ȒŊ̶ǥ4VcʤǶȘȉ2Ʃˑ"H/4Ĺ/Ü2ȻƓI>"ƈʡ4Ŀû2ő

%4˂̺25þ 0.1µm 4\śVcʤ\ś4þ5Vcʤ4ʀƓ/ę˱ȑŮȒŊ"HǶȘȉ

4 pH 4É2ž*-ŷƓI>"
Vcʤ4ÜÌ.5Ü̕ʎˀȉ/Ʃˑ
>"

->"

%BĐ!E2\śŷƓI

Vcʤ4Ĺ/Ü4\śÜ.5 H+QT/ǶȘȉ4 H+QT4̈ʈ

ʾKI>"

4QT­ƭ5ƿ4ǶȘȉÜ̕ʎˀȉ/Ĺ4ȒŊǶȘȉ

'­ƭ

2EGêƀ

I>" %I&I4ǶȘȉ4ǶɼQTȢŮĐ1İď ȒŊǶȘȉÜ4 H+QT/\śÜ4 H+QT4̦.ŧˁȱƏ2̎
4ÜÌĹÌ4̶¹5Đ!/1G'ż QT­ƭËǭ%4̶¹4ş5 0mV 21G>"

Ü̕ʎˀȉ/Ĺ4ǶȘȉ4̦2ǶɼQTȢŮ4̏ɇȻ

->"

'/5

%4̶¹şV%4ş5Ü̕ʎˀȉ/ȒŊ-HǶȘȉ4 pH 2Hş/ǳ

ʤ4̶¹LȒŊ.HE2"H'A

ʤʦ˷5ŕ».1-51G>$

cʤ4Ü/Ĺ.ɇȻ
¿>" +>GVc

M %4'AVcʤÜ4OUQT͑</M04Vc5 Li+QTLȽ Ċȯ
5qoR

QTLȽ->"͒ɡö2EGŕ̶ƈLſHE2
19

->"

by T&C Technical\ś4þ/ʀƓ5Vc̶ǥ4ƅɯǉ̦/c}4ȰƈLǻŊ,>"%IƵ\ś5̶ǥ4ƈʡ2Ź̻"HǥA-̛ˈ1ˈɼ.H/˒>"+A continuous exchange of H ions in the gel layers and H+ ions of the solutions takes
both sides of the membrane. This ion exchange is controlled by the H+ ion concentrati\śȨ .5 pH ȒŊ5Gſ>$M \śLŉØ2ŷƓ"H25 1 ǂF 2 ǂ4ǉ̦solutions.
Ƅˈ." %IƵȒŊ̶ǥ5
24 ǉ̦´Ƕ2ȇȝ
</on both sides ofIf the hydrogenion concentrationǶĘ÷IHƄˈG>"of each solution is identicalmembrane, the ion exchange stops after an equilibrium has been reached between the

M04ˆ̇·ɜ5ɍ2¾HE̶ǥLǶĘ÷
->"the solutions and the H+ ions in 'ż2âʲ
the gel layers.
Therefore, both sides of the membrane gthe same potential and the potential difference is 0 mV.
Vcʤ

If a difference of a hydrogen ion conexists between the inner buffer and
Ag/AgCl
electrode̟/Ĳ÷̶̟ǥ
solution, a potential difference develops
Glass membrane
Inner
gel
layer
the inner and outer sides of the membrVcʤ
þ
appr. 0.5mm1mm
0,5 to 1mm thickʤÜÌ\ś
approx.
10 mm 0.1m þwhich is proportional to the differen
thick
between the inner buffer and the outer s
be able to measure the membrane pot
Limembrane itself has to be conductiv
pH 7
+ Li
+
H+= const.
+
achieved by the mobility of the alkaline
+
Li
+
++ Li
membrane glass (Li+ ions in most glasseLi
Na+ ions in older membrane glasses).
H+
H+
The Glass Membrane

+

+

+

+

+

< pH 7ʤĹÌ\śOuter gel0.1mlayer þapprox. 10 mm thick> pH 7ȒŊǶȘȉMeasuredmediumThe thickness and composition of thedeterminetheresponsetimecharacteristic slope of the glass
Therefore the gel layer is of critical im
to the electrode performance.

Without the gel layer there can be no pH measurement. Unfortunately it takes approxim
to two days until a gel layer is fully developed. Therefore a measuring electrode ne
hydrated (immersed into normal clean tap water) for at least 24 hours prior to
manufacturers deliver their electrodes already hydrated (the membrane is kept wet w
solution in a plastic cap) which renders the electrode ready for immediate use.

3.2.2 The Reference ElectrodeThe reference electrode represents a defined electrical connection between themedium and the pH meter. The accuracy of the pH measurement is often determin
reference electrode and therefore the choice of the reference electrode is of simportance. An ideal reference electrode should produce a predictable potential, wh
respond only in accordance with the NERNST equation. A good and stable reference
should also have a low temperature coefficient and possess no temperature hysteresis.

A reference electrode consists of an internal electrode (similar to the measuring electro
is immersed into a defined electrolyte. This electrolyte must be in contact with themedium. Over the years various reference systems have been employed, but only two
the mercury-mercurous
20 chloride (calomel) and the silver-silver chloride
electrodes were found reliable with respect to an accurate and stable potential.

HAMILTON applies exclusively the silver-silver chloride reference system. (refer als
EVEREF reference system” on page 25).

Page 14

by T&C TechnicalAt low and stable temperatures (max. 80 °C) the calomel electrode has a high potential stabilityandĂȪ̶ǥa high accuracy down to a hundredth of a millivolt.
3.2.2
But today the silver/silver chloride electrode has gainedĂȪ̶ǥ5ȒŊ"HǶȘȉ/ pH ˂ɛĝ4̦L̶ǵɉ
practical acceptance and is by far the most frequently
employed reference system. It is easy to manufacture, its2ʓŅħ." >' pH 4ɷŮ5ĂȪ̶ǥ4ȒŊɷpotential rapidly attains equilibrium between –30 °C and 135 °C,
and is very reproducible. The Ag-AgCl reference electrodeŮ2EGǻŊIH/ĺG ĂȪ̶ǥ4̒Ɲ
remains stable and accurate especially with wide temperaturefluctuations and at high temperatures up to 135 °C.

The Constructionof aĂȪ̶ǥ4Ǧ̇
Reference
ElectrodepH
pHcable[|̶ǥ̼́̕head
Electrode5̹Ť2̛ˈ/1G>" ȸƌɉ1ĂȪ̶ǥ5ȸ˦2

The internal electrode of an Ag-AgCl reference electrode consists
ofž*'̶¹Lơ+/."a silver chloride coated silver
wire which is immersed into%4̶¹5scopotassium chloride of 3 mole concentration situated in a large
chamber
formed bypH
thec[2ž//."glass body of the reference electrode.
4ű.ǸAFI'

Electrode̶ǥVcɱ
glass
shaft
̶ːȉÔĳ̥̤ʷ
Refillopening

A diaphragm (normally a small porous ceramic rod) is fitted at the>'ȑŮÃƹº
bottomof this chamberȑŮ2EHxcmacLơ'to permit the potassium chloride to diffuse
or leak into the measured medium. To complete the electric circuit
1B4ȸƌ."thesilver-silver chloride wire is connected via a coaxial cable tothe pH meter.

InternalÜ̕ĂȪacmreferencesystem33mol/Lmole KCl
KClĂȪ̶ǥ5ŊAFI'̶ːȉ2Ü̶̕ǥȇI

The Constructionof aCombination Electrode%4̶ːȉ5ȒŊ"HǶȘȉ/4ƩˑLɘŋ2"H

̯ʤ

DiaphragmǦ̇Lơ*->" ̢̦ ĺǧ1ĂȪacm
̥ɇƨȽI-->"

'*'©+4acm

3.2.3 The Combination (Single Rod) ElectrodepH cableU̶ǥ͑Ƕ̟/Ĳ÷
Electrode head

Ƕ̟.+FI->"͒̟/Ĳ÷̟.½FI'̶ǥ2̲ɹI->"
Since 1947 electrode manufacturers have combined theȸȾ5ňŊElectrodeglass shaft
measuring electrode and the reference electrode into one unit,'̶¹4ɷŮ/̢ǓňŊƈ2EG>"
hence the name combination electrode. Today, theRefill opening
combination electrode is almost exclusively employed in
3 mole KCluo5̟/Ĳ÷̶̟ǥ4?2̲
̥ɇˆ̇Lʾ*-G>"laboratories and industrial plants. Only
when the life expectancy%4ĂȪacm 5
is significantly different for the measuring and the reference
Referencesystem
EVEREFĂȪacm(Sv{)/Ė6I->"electrode,is the useof a pH measuring system consisting of
two separate electrodes recommended.

̟/Ĳ÷̶̟ǥ4ƨȽȸȾ5

Internal conductor
In a combination electrode the concentric space surrounding theelectrode (Ag/AgCl)measuring electrode is filled with the reference electrolyte and1) U̶ǥ5ºňŊ 'ȑŮ/͍ȑŮ(80℃).5 1/100mV 4̶¹ɷŮLơ*
contains the internal reference system. A diaphragm near thebottom of the electrolyte chamber serves as the junction->" ̟/Ĳ÷̶̟ǥ5%4ˆ̇ǳ˺ɉŎǆ.͍Ƕȗ.ę˱LƫC" Inner Buffer + KCl
between the KCl solution and the measured medium. As the(pH 7)
reference electrolyte is a conductive medium, it acts as a screen2) -30℃F 135℃>.4ĸ÷2ő ̶¹4ŧˁȱƏ21H>.̹Ť2̆ >'ÞpH sensitive
glass membrane
to the measuring electrode.
Diaphragm

ȶƈ͍
21

by T&C Technicalcalomel electrode has a high potential stability3) ̟/Ĳ÷̟ĂȪ̶ǥ5Ūť.4ȑŮĸö.ňŊƈ/ɷŮLʉơ. ǏĻ 135℃>.
volt.

lver/silver chloride electrode has gained
őƅ"H
nce and is by far the most frequently
ce system. It is easy to manufacture, its
ains equilibrium between –30 °C and 135 °C,
ducible. The Ag-AgCl reference electrode̯ʤ5ʫɉ25ĺńƈekY4ǢLVcɱ4Ŭ̕2ʼɐ ->" %Fd accurate especially with wide temperaturehigh temperatures up to 135 °C.
̶ǥÜ̕4 KCl LȒŊ"HǶȘȉ:/ƟƸH5țIHE2"H'A."

de of an Ag-AgCl reference electrode consists
coated silver wire
which is immersedinto̶ǵğ˶/"H'A
̟/Ĳ÷̶̟ǥ4ʍ5Đ˸[|4ʮʍ2Ʃʈ
of 3 mole concentration situated in a large
the glass body of Ȫ̶ǥ×ðɪŃ:/̖ʍI>"
the reference electrode.

Ǐż2

pH h4Ă

ally a small porous ceramic rod) is fitted at theber to permit the potassium chloride to diffuse
sured medium. To complete the electric circuit
3.2.3 ˇď̶ǥoride wire is connected
via a coaxial cable to1947 Ũ

ȒŊ̶ǥ/ĂȪ̶ǥ5 1 +2ʀ?ďKI

The Constructionof aˇď̶ǥ4Ǧ̇
Combination
Electrode

pHcable
[|
pH

˞Ȼ

>

-Hˇď̶ǥǦ̇' ˇď̶ǥacm

5ɔɦƕF}

o4}ec>.ťŪőƅ"HE21*-
>" %

ode

ȶħǏBǊă

-ĂȪ̶ǥ/ȒŊ̶ǥã̴'ŷ5Ü̕

Electrode
head
̶ǥ̼́̕

ombined theinto one unit,
Today, theemployed ine expectancy
he reference
consisting ofElectrode̶ǥVcɱ
glassshaft

̶ːȉ4Ȉʜ4vcɅ1Hİď24?¾Ƚ
IH/ƪĽI->"

Refill opening̶ːȉ˅ÔȽ̥̤ʷ
3 mole KCl
3mol/L KClˇď̶ǥ5ȒŊ̶ǥ4ĐƃÝ4ɧ̦2ĂȪȽ̶ː

ReferenceĂȪacmsystemȉLÔĳÜ̶̕ǥLƥ×

->" ̯ʤ5̶ːȉjv4Õɪ̕2ćG²FI KCl ȉ/ȒŊrrounding thelectrolyte andagm near thethe junction
dium. As thes as a screen

Internal
conductorÜ̕ŕ̶ƈ̶ǥelectrode(Ag/AgCl)(Ag/AgCl)Ü̕Ŧȏȉ+KCl(pH7)
Inner
Buffer + KCl(pH 7)"HǶȘȉ4ƩʈLʾ>" ĂȪȽ̶ː˱5ŕ̶ƈ
4ł».

pH
pHsensitive
ƎŮLơ+Vcʤglass membrane
Diaphragm̯ʤ

22%I5ȒŊ̶ǥ:4̑ʹ4ÏL>"

by T&C Technical3.2.4 KCl ʥ÷»(\)LĂȪȽ̶ː˱/ĂȪȽ̶ːȉLơ+ĂȪ̶ǥ5'ˇď̶ǥ̶ːȉùã2ȕ'I'ȱƏLÅ+'A2̲

ɉ1Å
Page 15ŇƄˈ."%4ʂǙÅŇLºȐ$H̶ǥǦ̇Lơ+ȯ/-\°ǧĂȪ̶ǥ̥

3.2.4 Combination Electrode filled with KCl-Gel as a Reference ElectrolyteɇI->"(\̶ǥ)\ĂȪ̶ǥLơ+ˇď̶ǥ

Reference electrodes incorporating a liquid reference\̶ǥ5ÅŇLºȐ"H'A
electrolyte
are maintenance intensiveĂȪȽ̶ːas their electrolyte levelhas to be controlled and regularly topped up. The search for aȉjv25
3mol/L assemblyKCl ̶ː˱L\2maintenance-freeelectrode
led to the developmentof the gel reference electrode.

pH [|

'ȯLÔĳ

-G>"

̯ʤ5̅Ťĺń

The gel electrode is a low-maintenance electrode. The
reference electrolyte chamber is filled with 3 mol/l KCl}cjkYc|.ŵƈekYL¾Ƚ ->" >'̶ǥV÷I'̶ǥVcɱ
electrolyte in gel form. The diaphragm is normally madefrom ceramic. The glass shaft is often reinforced with an outercɱ5ĹÌ2}cjkYˆ4ɱŵ÷Ƚ4\  ȱ 2 ' 3mol/Lplastic sleeve or the electrode shaft is made completely out of
KCl .͉Ę '̶ː˱plastic (Epoxy).
c|LćG²HÜ̕ĂȪacmÜ̕ŕ̶ƈ̶ǥ(Ag/AgCl)Ü̕ʎˀȉ+KCl(pH7)

Diaphragm̯ʤpH Ǝ Ů L ơ +Vcʤ

H5̶ǥɱØ»The gel electrode is mostly used in combination with portable
pH LSWaɸ4ǩʢ.ˆ̇
meters or laboratory pH meters
for simple measuring>"
applications, e.g. public swimming pools. This electrode does
not need
to be topped-up with reference electrolyte– which\̶ǥ5%4</M0h|4pH
reduces maintenance time. However it has to be taken into
accountthatH5ɔɦƕđ4
the gel electrode has
reduced accuracy andȒŊĝ
pHah2
a shorter life span than its counterpart with a liquid referenceelectrolyte.
ʀ?ďKI>" %4ȸȾ/ -5\̶The response time of a gel electrode is somewhat slower thanǥ4Œė̶ːȉ°ǧ2ǳ˺ ɒ ɷŮ4
an electrode filled with a liquid electrolyte.
ºǃ//2EG>">'ƅɯ

3.2.5 Reference Electrodewith POLISOLVE Electrolyte (Polymer)-D*G -H//BG>"

ǉ̦4̺.B̶ːȉ°ǧ2ǳ˺

In the early 1980s electrode manufacturers created the polymer electrode. The polymer
electrode is either a standard combination glass electrode or a separate reference electrode. In
both cases the reference electrolyte chamber is completely filled with a semi-solid
polymerised plastic material into which the KCl is embedded. No diaphragm junction isrequired. Therefore the KCl saturated polymer has direct contact with the measured
solution. The contact is established through an aperture, which could either be one or moreholes near the bottom of the reference electrolyte chamber or a fissure separating the bottom
electrolyte chamber from the measuring electrode.
- What does not exist can not clog up! –23

maintenance-freeelectrode assembly led to the developm
maintenance-free electrode assembly
led to the development
of
the
gel
referenceelectrode.
of the gel reference electrode.

The gel electrode.
electrode is
The gel electrode is a low-maintenance
Thea low-maintenance electrode.
referenceelectrolytechamber is filled with 3 mol/l
reference electrolyte chamber is filled with 3 mol/l KClelectrolyte
in gel form.
diaphragm is normally melectrolyte in gel form. The diaphragm
is normallymadeby TThe&C Technicalfromceramic.with
Theanglassfrom ceramic. The glass shaft is often
reinforced
outershaft is often reinforced with an oor the out
electrodeshaft is made completely oplastic sleeve or the electrode shaft plastic
is madesleevecompletelyof
3.2.5 ̛ď»()4̶ː˱Lơ+ĂȪ̶ǥȉ»FĤ»:plastic(Epoxy).
plastic (Epoxy).

gel'electrodeis ɷŮ2-5žǘ
mostly used in combination with port
The gel electrode is mostly used in The
combinationwith\°ǧ4̶ː˱.5ÅŇLɴɃ2"H/5âǘ>Œėportable

pH formetersor measuringlaboratory pH meters for simple measu
pH meters or laboratory pH meterssimpleapplications,e.g. publicswimming
This electrode dapplications, e.g. public swimming pools.
This electrodedoes
4̶ːȉLȽ'ĂȪ̶ǥL˳HƈʡLȴſ"H/5.>$M%4'A
1980 pools.
Ũ
not need
to be topped-up
not need to be topped-up with referenceelectrolyte– which with reference electrolyte – w
reducesmaintenancetime. However it has to be taken
reduces maintenance time. However it has to betakenĂȪ̶ǥ4̶ː˱2̛ď»()LȽ'ȯ̥ɇI
žǘ4
pHintoȒŊ°ǧ/Đ!
thataccuracy
the gel electrodehas a reduced accuracy
account that the gel electrode has accounta reduced
anda shorter
span
than its counterpart with a liquid referea shorter life span than its counterpart
with a life
liquidreferenceˇďĩ ã̴ĩ4Ąƿ.ƨȽI->"electrolyte.
electrolyte.

hragm̶ː˱LƨȽĂȪ̶ǥ4Ǧ̇5ĻĸKG>The
response slower
time of thana gel'electrode is somewhat slower
The response'/2EGtime of a gel electrodeis somewhat
Diaphragm

an electrode filled with a liquid electrolyte.
an electrode filled with a liquid electrolyte.
1 KCl ʀ?˽>I'ǖƼ̶ːȉ2³KGÔĳI'

2 ̯ʤ2EHȉʃůǭIŖ1ɥH5ˇƹ4ɥ5ckoŷȱ2
Reference
Electrodewith POLISOLVEBElectrolyte(Polymer)
Reference Electrodewith3.2.5
POLISOLVE
Electrolyte(Polymer)In the1980s theelectrode
manufacturers
createdthe polymer electrode. The poly
early 1980s electrode 1G>
manufacturers
polymer
electrode. The
polymer' earlycreatedelectrodeiseitherastandard
combination
glass
electrodeode is either a standard combination glass electrode or a separate reference electrode. Inor a separate reference electrod
both cases
the isreferenceelectrolytechamberis completely filled with a semi-scases the reference3
electrolytechambercompletely
filled witha semi-solid2͒4ʂǙĂȪȽ̶ː˱2őȒŊ"HǶȘȉɍƩˑIH/ŷ21G>
plastic
material into
the KClis embedded.
No diaphragm junctio
merised plastic material intopolymerised
which the KCl
is embedded.
No which
diaphragm
junctionisrequired.
Therefore
KClcontact
saturated
has direct contact with the measu
ed. Therefore the KCl 'saturated
polymer
has thedirectwithpolymer
the measured
solution.
The
contact
isestablishedthroughanaperture,
on. The contact is established through an aperture, which could either be one or more which could either be one or mholeselectrolyte
near the chamberbottom oforthe
electrolyte
near the bottom of the referencea reference
fissure separating
thechamberbottom or a fissure separating the boelectrolytechamber from the measuring electrode.
olyte chamber from the measuring
electrode.
̶ːȉhQ}4ĂȪ̶ǥ4ȉʃǦ̇hQ}4ĂȪ̶ǥ4ȉʃǦ̇

Holeinĺń˱ekY4Ǣ
electrolyte chamberHoleinɥelectrolyte chamber

What- What does not exist can not clog-up!
– does not exist can not clog up! –̶ː˱4ƨȽ2EG´4ƳĜ̎ƓI>'

1 ̯ʤ4Ɍ˛>G11*'
2 ̶ː˱4ǶȘȉ:4ƟƸúĤ»4'A̹Ť2ŗ1
ĸKF1

24

ʂǙŒė̶ːȉhQ}/by T&C Technical3 ̶ǥ5 pH2 ´5ȒŊġ̵
4 ȑŮ5 90℃>.

őƅ.1

5 ȒŊ"Hȉ»2ǑǫȘìɭĒ>IHİď5ȒŊ.1

3.2.5.1 g|4̥ɇĂȪ̶ǥ4̶ǵɉƈʡȯȸɉƈʡ5̶ː˱2EGǅF2ƳĜI

ǰI'

ě̈́LƳĜ"H'A2uo5̶ː˱ g|(POLISOLVE)L̥ɇ
4Ȱ˗Lćſ>'%g|5´4ȰƂG>"1 ȒŊ5 pH0 Fʾ>"
2 ǑǫȘìLĒM(ǶȘȉ2ő
3 ǺI

ʢʟ

Ǿã

ºQTH5hwY˱LĒM(ǶȘȉ2őØ-ȒŊċʡ."̶ǥ.5ɇȻ

őƅ.>"

ƒȡȯ˱2EHɌ˛>G4ě̈́5</M0

̯ʤLơ'1

>$M

4 ǏĻ 130℃>.őƅ.HE21G>
5 Ü̶̕ǥǦ̇Lĸǌ'

Ħð5 600kPa >.ʛFI>"Ĳ÷̟4ȘâL̨ǭ.HE2

6 ȒŊ"HǶȘȉ2ɍƩĂȪȽ̶ː˱Ʃˑ"H/.

>'ĂȪ̶ǥ4̶ǵɉȰƈĻ

ť2ƳĜI ºŕ̶ȵ4ǶȘȉ͑2µS/cm͒.BǮɘ1 pH ȒŊċʡ/1G>'
4ʂǙ ĂȪ̶ː˱2g|LȽ' pH ̶ǥ5 ɔɦƕF}ec>.Ū¾Ƚ
I >'Ǐå2¾ȽLǣ˔"H pH ̶ǥ/˒>" >'vQTmYtb4ˆ̇ȶİ
4 SIP 2őƅ"H pH ̶ǥBg|LȽ-ˆ̇IHE21G>

25'

As the KCl saturated polymer is free of AgCl, there is no possibility of silver sulphidecontamination when measuring the pH value of solutions containing sulphides.
The high pressure rating of 600 kPa, its extended temperature rating of up to 130°C and its maintenance-free operation should make the POLISOLVE reference system always a first choice.
Electrodes, utilizing the POLISOLVE polymer electrolyte, are even suitable for steam sterilisation
by T&C Technicalin biotechnology applications.
3.2.6 ̶¹ş4ȒŊpH
h
3.2.6 The Measurementof the Potential
Difference

The pH measuring
electrode and the pH reference
pH ȒŊ̶ǥ/ĂȪ̶ǥLʀ?ďK$electrode form a so-called pH measuring chain
within the measured
medium. This chain canbeȒŊ"HǶȘȉ.ʓHɸL
pH ȒŊ
compared to a battery of which the voltage
produced depends
on the measured
ɸ/Ė8>"
ȒŊ medium.
-Hȯ5 Ƕ

0
-1500

mV

+1500

͍QzicL
High impedance
ơ+̶Ħ˓B5 pH
voltmeter
˂ɛO}Electrode̶ǥacmassembly

Reference
The difference in potential between the measuringĂȪ̶ǥelectrode
MeasuringȒŊ̶ǥȘȉ2ȇI-H
2+4̶ǥ4̦
electrode and the reference electrode is a function
electrodeof the pH value of the measured medium. In.ɇȻ"H̶Ħ.
%4̶Ħ5ǶȘȉ
theory the voltagechanges by
58,16 mV per
The
pH
pH unit at 20 °C according to the NERNST
measuring
pH
ȒŊɸ
chain
equation. The4ȃƈǶɼQTȢŮ2E*-ǻŊ
voltage produced by the pH
measuring chain is large enough not to presentȒŊ"HǶȘȉ
any problem IH/5´ë̀;>for a measurement. 'But theMeasuredmediummeasuring chain is a voltage source from which nopH .˂ȶ"HE2 >" ̶Ħ4current can be Ǐɿɉ2ȒŊ̶ǥ/ĂȪ̶ǥ4̦2ɇȻ"H̶¹şL
drawn, not even the low current
which a moving coil of a DC voltmeter draws. The potential difference of the measuring chain has
20℃.
58.16mVG>"
pH theȒŊɸ.ɇȻ"H
to be measuredĸ÷5sco4ű2EG
without drawing any current
from1pHthe'G
voltagesource,otherwisevoltagewould be reduced and the pH measurement would be drastically falsified. The reason is the high̶Ħ5ȒŊ2̱ōɇȻ
1ɢŮ4ùã1̶ðLơ*-I6ȒŊ5'C"1G>
electrical resistanceof theglass electrode which
is mainly determined by the resistance of theglass membrane.

Ȩ ̶¹LȒH pH h:Ʃʈ'ǉ̹Ť2͍/2GʂǙ%4ƞƛEG͍×ðƞƛLơ+hL¾Ƚ

1/Ǯɘ25ȒŊ.>$M̅ŤVcʤ4B+ƞƛ5 25℃. 10MΩ F 1000MΩ 4̦2" ŋ̰5%4ɸ2ȄIH̶Ȅ5Ɓ̜.

The resistance values of a glass membrane vary between 10 M: and 1 000 M: at 25 °C andincrease 10 times at a temperature decrease of 25 °C. The lowest possible operating%4×ðƞƛ2E*-5ȒŊ -H̶¹G Ǯ  pH ÉL˂ɛ"H/.1
temperature of a pH electrode is often determined by the resistance increase of the glass
membrane at low temperatures, the internal resistance of the measuring instrument, the required
1G>" 4h4×ðƞƛ4ě̈́ɇȻ"HÿĠ5 ¡2Vcʤ4ơ+ƞƛ
accuracy of the pH measurement and the freezing point of the electrolyte.

G 25℃Lĭȗ2ȑŮº"H/ƞƛ5 10 ÈɢŮǄǥ4ȒŊ̪4ȑŮ5/G>"

6->" 4'A pH ̶

6Vcʤ4ƞƛÉǄ4ě̈́2EGê̪I-

pH h4Ü̕ƞƛ5VcʤƞƛEG͍>̶ǥ4̶ːȉàʂ"H

Ȧ>.¾Ƚ.HɷŮLơ+/Ƅˈ." Ȱç1 pH ̶ǥ.5ºȑŮ.ȒŊ.H
B4G>"
HE2

I5Ȱǯ1Vc->"%-EGʺVcʤ2"H/.ƞƛÉL>'ɷŮL±0.1pH ´ÜH5%IEGŖ"H2526

ȒŊ̶

by T&C Technicalǥ4Ü̕ƞƛ5h4Ü̕ƞƛ4 1/100 L˳1E2

̪5 5000MΩ >./Vcʤƞƛ4

ʤ4ƞƛ>G2͍"H/ȒŊ̶¹5Ɓų/1GtQd4

Ź̻LĈ-ǮŤ2ȒŊ.11G>"
Ȼ"H˲̶ð5>"

4E2

͍ƞƛLơ+ȒŊɸ2EGɇ

EG͍×ðƞƛLơ+ǫĝ.4?ȒŊ.

%4'A4×ðƞƛ5ŗ

1/B 1012Ω ɢŮƄˈ."

3.3 pH ȒŊɸ4ȰƂ
pH ȒŊ4Ȱƈ5ȽHȒŊ̶ǥă8ĂȪ̶ǥ4Ȱƈ2EGǻŊI>"-H̶ǥ4ĺ5ˇď̶ǥ."

4'AȒŊɸ4Ȱƈ4̏2²-ˢǅ"Hİď5ˇď̶ǥLȽ-H/LëƬ2̀;-ˢǅ¯ǂ¾ȽI%4>"27.Ƅˈ2ƅ!-Ç4̶ǥ4Ȱƈ2²

3.3 The Characteristics of a pH Measuring Chain
The characteristics of a pH measuring chain are the result of the individual properties of themeasuring and the reference electrode. Most of the electrode assemblies in use today are
combination electrodes. For this reason we will refer to the combination electrode when
examining the different properties of a measuring chain. However everythingthat is said about
by T&C Technicalthe properties of a combination electrode may be applied to the individual measuring andreference electrode as well.
3.3.1 ˇď̶ǥ4½H̶¹ş

3.3.1 The Different Potentials of a Combination Electrode
Etotal Ø̶¹

E totalPotential developing on
EE11 :Vcʤ4ĹÌ4\ś.
the outer gel layer.

ɇȻ"H̶¹

Asymmetry potential of
EE22 :Vcʤ.ɇȻ"H̹őɠ

0
-1500

mV

̶¹
+1500

the glass membrane.

Potential developing on
EE33 :Vcʤ.ÜÌ4\ś.
the inner gel layer.
ɇȻ"H̶¹

Potential developing on
EE44 :Ü̕4ŕ̶ƈ̶ǥ.ɇȻ"the internal conductor
electrode.
H̶¹

Potential developing on
EE55 :ĂȪ̶ǥ.ɇȻ"H̶¹
the reference electrode.

E5

E6 ̯ʤ.ɇȻ"HƟƸ̶¹

potential of
E6 : Diffusion
the diaphragm.

E4
E3

E6

E2

T he5 pHto ta
l p ot e nt i a lEtȒŊɸ.ɇȻ"otal
EØ̶¹total : measured
by a pHH";-4̶¹ E1 F E6 4ʋĘelectrode assembly is/1G>"

the sum of potentials
E1 to E6.

E1
ˇď̶ǥȒŊ4'AǶȘȉ2ȇI'ǉś2̶¹ɇȻ

Vcʤ/ǶȘȉ4̦2ɎĴɁLŷƓ"H\>" 4̶¹5ȒŊ"HǶȘȉ4 pH 4É2ÁŅ

254É pH ȒŊÉ/1*->"Ç>'ģ2ɛ"̅Gĺ4ɎĴɁ.%I&I̶¹LɇȻ
¹L˴

'ʂǙL mV .ȒŊ

ģ25ȒŊ̶ǥLąǈ->"%4'AǏɿɉ

4̶¹LÇç2ȒH/5.#->"h.5Ø-4̶-H/21G>"

ĂȪ̶ǥ4ƿ. 6 +4ɎĴɁ/%I&I4̶¹G

E1  pH 4Éȸƌɉ25 E2 F E6 4̶¹Ť2Ŋ.I6 pH 2EGĸ÷"HE1 LȒŊ"H/âǘ>"28

by T&C Technical

E2 5Vcʤ4̹őɠ̶¹." ȒŊă8ĂȪ̶ǥĐ!Ü̕ŕ̶acm

Lơ*-G+Ü̕ʎˀȉ/Đ! pH Lơ+ʎˀȉ2̶ǥȇI'ǉ %4̶¹5 0mV /1G>"

ɇȻ

ŋ̰25
-

ƾ

>>"

ȱƏ4ʬ̶ǥacm.*-B̹őɠ̶¹ɇȻ"HÿĠ5̹őɠ̶¹ƹo¡2Ʌ1*'þ4\ś/Vc

ʤ4þ2EG>"E3 5Vcʤ4ÜÌ2ŷƓIH\ś.ɇȻ"H̶¹."
Ů2EG>"

4ʎˀȉ5ĸ÷L

>$M4.

Ü̕ʎˀȉ4ǶɼQTȢ

E3 5Ť2Ŋ4ÉLơ)>"E4 / E5 5ȒŊ̶ǥ ĂȪ̶ǥ4̝Ś/ʎˀȉ4ɎĴɁ.ɇȻ

>" ƿ4ŕ̶acm

5

Đ!. ʎˀȉ/̶ː˱BĐ!ȃƈĲɼQTLơ)>" ʂǙ E4 / E5 5ª2Ɨ)Ȉ
ď̧Ã."

4'AØ»4̶¹ȒŊ25Ź̻L>$M

E6 5̯ʤ4ƟƸ̶¹."

4̶¹5©+4̶ː˱4̦2HɎĴɁ.ɇȻ

ː˱Ʌ1*'ȢŮ/ʀƓLơ*-Hİď2ɇȻ

>"

©+4̶

I5Ʌ1*'ǥƈ/Ʌ1*'QTɡöŮLơ+ƟƸQT2EGǻŊI>"
Ǐå2ˢǅ
-<

'̅G E1 LǸAH25

4." ŋ̰5 E2 F E6 5ˡşLơ*->" I5ʂǙ/şLɇȻ"H//21G>"ʈ

E2 F E6 5Ŋ.H/ȸƌɉ1Ǘµ.*-ȒŊ

4'A¾Ƚë25Ƅ#fȦǝǮLʾ>'̈-Hİď5ŊǓɉ2fȦǝǮLʾƄˈG>"

3.3.2 ̶ǥacm̶ǥacm-fȦ4ˡ4fȦ2HfȦ/5 ̶ǥɇȻ
29-H̶¹ 0mV .H/." ȸ˦

by T&C Technicalɉ25ȒŊ̶ǥÜ4ʎˀȉ2EG pH ȒŊɸ4fȦ5ȒŊI>" %I5̅Ť4ȒŊȺ
Ĵ.5 pH7 /˂ɛI>"
0mV /1G>"
/
>"



B

ȒŊ

ŋ̰25

-HǶȘȉ4 pH 4É 7 .I6

Etotal  E1 F E6 .ɇȻ

%4É5-H̶¹4ʋĘ.H

%I&I4ɎĴɁ4̶¹5ȑŮ4ĸ÷CȒŊȘȉ4ʀƓ2EGɅ1*'É/1*-
%4'AŉØ2fLɛ" pH ̶ǥacm

L½H/5ċʡ."fȦ4˗ŎɳĢ5pQlŝǤˋǟ.5-30mV F+30mV 4ɳĢ/1*->" ĺ4pH ̶ǥacm

4ˆ̇·ɜ5ŋ̰5fȦLŗ-(ɹ pH6.8)ƬÀ

->"

I

5̶ǥǉ̦4ʁ̌//B2Ǭɫ2fȦ*-HÎđH'A."
pH ̶ǥacm4Þȶƈ(ɘ4ˈɼ)5șĺ2˂˕IH/5G>$M

ʁ͌ɛ"/J.5Þȶƈ4ɘ5±0.02pH(1.16mV)L˳H/5>#G>$M
Ǯɘ1 pH ̶ǥacm>"pH ̶ǥacm

4fȦ4Êş5`2EGȒŊë2ɘ˝IHƄˈG
Lh2ćG²fȦǝǮLʾ>"pH h/ockh2²Ś"HfȦ˅ǮȽ4ma.ˡş4ˤƺLʾ>"}ek_Lơ+h4İď5fȦǝǮLʦö.ŋǀ

˅Ǯ

QY

>"

fȦ4ɘ˝/ˤƺ5ȒŊ}ec2-5ǻ>*'ĔǓ.ʾ>"

fȦ#I-HˈĠ5´4ě̈́2EG>"a) ȒŊ-HǶȘȉ̯ʤL̅-ĂȪ̶ǥÜ2×*-b) Ü̕ʎˀȉ4ĸ÷ ͍ȑ2FI'ǉ
xpWaĭLÜ̕ʎˀȉ:ƴâc) ̶ǥacm>*-HȒŊ̶ǥ4VcʤOU4%I pH ȒŊÉLǄ$H4Ʃʈ}Ză8[|Ʃʈ̕4̝ŚƩȦ4Ʃˑƞƛʣ͇

ɭ2EGǄ

30

by T&C Technical3.3.3 ̹őɠ̶¹
ȸ˦ɉ2ȒŊ̶ǥ4Vcʤ4ɇȻ"H̶¹ş5Ü̕ʎˀȉ/ȒŊ"HǶȘȉ4 pH Đ!İď(̅Ť pH7)0mV .1-51G>$M

şVcʤ2ɇȻ->"̹őɠ̶¹ɇȻ4ÿĠ/˒>"I'ǂFŁ>G>"%ŋ̰5ƹo4̹őɠ̶¹

ÜÌă8ĹÌ4\ś4ŷƓǉ̦2Hş5̕ãɉ2
ÜÌ4\ś4ŷƓ5ˆ̇ŝɢ.̶ǥÜ2ʎˀȉL×-%4żØĸ÷ȨȱƏ:/̎ȒŊ"HǶȘȉ2EH÷ņąƅ2Ť2FI'ȱƏ2G
>>"

>"

ĹÌ4\ś5

ǉ25%4śƮʜ->'̹őɠ̶¹5Vcʤ4ˆ̇·ɜ2EHˆę4ŉØƈ2EHİďBG>"

VcʤLŵ̙H5OUȘȉ2F"/ĸ÷ǶɼQT:4Vcʤ4ƅɯ5Ǭɫ2ĸ÷

Vcʤ4˂̺ŪɳĢ.

->"̶ǥ4fȦǝǮǉ25̹őɠ̶¹±47mV(±pH0.8)L˳-1/Lɘ˝
ÉL˳-Hİď5 pH ̶ǥacm

L­ƭL

31

>"

%4

by T&C Technical3.3.4 pH ̶ǥacmpH ̶ǥacm4c}H5ƎŮ4c}5 1pH ǲ2ɇȻ"H̶¹4ǳȵ.ȶI>"
pH
c}

=
U

ȸ˦ɉ25 pH ̶ǥacm-58.16mV LɇȻ

5 58.16mV L 0 F pH7 .ɇȻ

1-51G>$M ŋ̰5ƾ

˦É4 99.8%ɢŮ21G>"

 ǶĘ÷I'̶ǥacmǉ̦//B2c}5Gǃ*->" 4'Ac}LǝǮ

pH7 F pH14 .5

Ǐå5D*G.Bȸ
Ǭɫ2

ÎL˅Ǯ"H'A pH hH5ockh4mahLˤƺ"HƄˈG>"fȦ4ˤƺL

ʾ4/Đǧ˅Ǯ5ŊǓɉ2ʾƄˈG>"pH ̶ǥacm4c}5sco4ű2EHE2ȑŮ2ÁŅ

Șȉ4ȑŮǄ"H/c}5ĢÃLǬ4ģ2ɛ>" ȒŊ"HǶȑŮH/c}5G>"

>"

32

%4

slope potentiometer of the pH meter/transmitter. As with the zero point adjustment, the slope
adjustment has to be performed at regular intervals.
The slope of a pH electrode assembly is temperature dependent in accordance with the
NERNST equation. The slope increases with the rise in temperature of the measured solution, as
by T&lines
C Technicalcan be seen from the diagram below. In theory, all temperature dependent slope
intersect
the theoretical zero point (pH 7).
pH ȒŊacm

450
400
350
300

4c}H5ƎŮ

The Slope or Sensitivity of a pH Electrode Assembly+

Slope =

pH

200
150
100
50

U
1

2

3

pH
4 5

6

mV
50
100
150
200
300
350
400
450

7

8

9

10 11 12 13 14

pH
ȸ˦ɉ1É

Theoretical ValuesoSlope at 0 C = 54,20 mVo

Slope at 20 C = 58,16 mV
0 oC
o
20 C
50 oC

o

Slope at 50 C = 64,12 mVsco4ű2ċʡ1̪GąƅL˾,H'A pH ̶ǥacm

5Ƅ#ŊAFI'ĭȗ

Lȕ'"ƄˈG>"a)Vcʤ4ÜÌ/ĹÌ4\ś5Ƅ#Đ!̶¹4c}Lơ'1-51G>$Mb)Ü̕ʎˀȉ5Ƅ#Ŋ4 pH É.1-51G>$Mc)̹őɠ̶¹5ċʡ1̪GŖd)̶ǥ̕5Ƅ#őɠ.1-51F1 ȒŊ̶ǥ/ĂȪ̶ǥ5%I&I4Vv©
̶¹LƗ)Ȉ

e)Ŋ.1-51F1

ď'AĐ!ŕ̶ƈacm̯ʤ4ƟƸ̶¹5ċʡ1̪GŖ
33

L¾K1-51F1Ŋ.1-51F1

d) The electrode assembly must be symmetrical, i.e. measuring andreference electrode must have identical conducting systems inorder to neutralise their galvanic potentials.
e) The diffusion potential of the diaphragm should be as small and as
constant as possible.
by T&C TechnicalSlopeand Asymmetry Potential
pH ̶ǥacm 4c}/̹őɠ̶¹of apH Electrode Assembly

450
400
350
300

+
200
150
100
50

U
pH

Slope =

pHas

U
1

2

3

pH
4 5

6

8

7

9

10 11 12 13 14

mV

pH

50
100
150
200

Asymmetry Potential̹őɠ̶¹4ȸ˦ɉÉ

Theoretical Values

Slope at 0 oC = 54,20 mV

300
350
400
450

Slope at 20 oC = 58,16 mV
o

0 C
20 oC
50 oC

Slope at 50 oC = 64,12 mV

3.3.5 ɭȑʍ­şȦ>(ŋ̰4ȒŊ/ȸ˦4̦25ʨG>"

ȸ˦ɉ2504ȑŮ2-Bc

}5ȸ˦fȦ(0mV pH7)LƄ#̅G>" ̹őɠ̶¹H/͑%I5+BŅħ"H˘."͒ 4fȦ5ČH5Ş40)F2#IH/21G>"
ȱƏLɛǬ4ģ2%4>"Ø-4 pH ̶ǥacm
ɘ25Ŋʗ.>$M
HȦ#I-

4̶¹5ȑŮ2EGĸ÷>" %I&I4̶¹4ȑŮÁŅƈ5Ǯ

ȸ˦ɉ1fȦFʂǙ/-ȑŮc}4ʍ­ş">'̹őɠ̶¹B%F#I-H/ãG>"

Uis(Uis=ɭȑʍ̶¹)/Ė6Iɭȑʍ4­şȦ/34-ɑFI->"4­şȦ

Page 223.3.5 The Isotherm Intersection Point
by T&C TechnicalAgain we have a disagreement between theory and practice. In theory all temperature dependent
slope lines intersect the theoretical zero point (0 mV/pH 7). When an asymmetry potential ispresent– andthat is always the case– this intersection shifts either to the right or to theǮɘ1
pH 4ȒŊLʾ'A25%4ɭȑʍ4­şȦã*-HƄˈG>" left of
the zero point, as can be seen from the diagram below.
4'A 2 ɣ͆4ȢŮ4ʎˀȉƄˈ/1G>"% -ɭȑʍ4­şȦ4¹ʖ5ˇƹ4ȑ
All potentials
of a pH electrode assembly vary with temperature.
The temperature dependency ofeach individual potential cannot be accurately defined, but it will shift the resultant intersection
Ů2ˤƺ'ʎˀȉLȽpH ̶ǥacmpH zeroȒŊLʾ>"pH ̶ǥ
pointof all temperatureslope lines
away from.%I&I4
the theoreticalpoint and awayfrom theasymmetry potential. This intersection point is then known as the isotherm intersection pointFɇȻ"HmV âð5ȒŊI' pH 4ÉLZ{Ƚɻ2˕× ->" %(Uisacm= isotherm
potential).

In order to perform an accurate pH measurement, the position of the isotherm intersection point4ʂǙɭȑʍ4­şȦǸAFI>" ̶Ħ/ɭȑʍ̶¹ Uis 4ǥƈ5 Uis ˅ǮȽma
has to be established. Two buffer solutions are required. The position of the isotherm intersection
point can then be determined by measuring the potential difference of the pH electrode assemblyhLơ*-H pH h ockh.ˤƺ"H/âǘ>" >against various temperatures (heated buffer solutions). The mV outputs of the electrodeassembly are then plotted against their pH value on graph paper and thereby the position of the'ȶ³4QY}ek_~c4 pH h.5 Uis ̶¹L˅Ǯ"H'A4ǫʡ
isotherm intersection point is established. The voltage and polarity of the established isotherm
potential Uis can only be compensated for if the pH meter/transmitter used is equipped with an Uis
5".2ÜʸI->"
potentiometer. Nowadays, only the microprocessor based pH meters/transmitters have thecapacity to compensate for the Uis potential.
uoFâʲIHƾę4 pH ̶ǥacm

25℃.ǝǮ

.5

'İď

60℃2ĸ

New electrodes from HAMILTON show a maximum compensation error of 0,1 pH when
÷ '/4#I4ǏĻ˅Ǯ̜50.1pH /1*->"calibrated
at 25 °C and thereafter measuring
in a solution having 60 °C.
pH ̶ǥacm

450
400
350
300

+

200

mV
50
100
150
200
300
350
400
450

Isotherm
Intersectionɭȑʍ­şȦ
Point

U

150
100
50

4c}/ɭȑʍ̶¹

Slope and Isotherm Potentialof apH electrode Assembly

pH
1

2 3
Uis

4

5

6

7

8

9

Slope =

UpH

10 11 12 13 14pHȸ˦É

Theoretical Values
Slope at 0 oC = 54,20 mVo

Slope at 20 C = 58,16 mVoSlope at 50 C = 64,12 mV

35

o

0 C
o
20 C
o
50 C

by T&C Technical

3.4 ̯ʤ
ĂȪ̶ǥ2/*-̯ʤ5̹Ť2̛ˈ1̕ã."ȇȝ%I5̟/Ĳ÷̟.½FI'ŕ̶acm-H̶ː˱/ȒŊ"HǶȘȉLʓǫʡLƬÀ

3.4 The Diaphragm>"ʤ5ĂȪ̶ǥ4Vcɱ4Ŭ4Ķ2ĺńƈekY}ZLʼɐ

</M04İď

Page 23̯

->"(ĺńƈeThe diaphragm is a very important and critical part of the reference electrode. It provides anelectrolyticinterface between the silver/silver chloride conducting system and the measured
kY̯ʤ)
solution. In most cases the diaphragm consists of a porous ceramic plug fused into the glass wallat theǦ̇/ŷȱ2Hǧlower end of a referenceelectrode (porous ceramic diaphragm).
1̏Lơ+̯ʤG>"
%I&I4hQ}5Ǒè1Ȧ/
Various diaphragm types (differing in construction and shape) are available, each type has its
ê̪IH/JG>" ̅ŤȒŊǗµ2ž%4ŷȱ5ǻŊI>"
advantages
and limitations. It is normally the measurement application which determines the useof a specific diaphragm.
a) Porous Ceramic Diaphragma) ĺńƈekY̯ʤ

The porous ceramic diaphragm is probably the most frequently used today. It possess a high chemical resistanceĺńƈekY̯ʤ5ǏBE¾KIH̯ʤ." ͍and it is easy to manufacture.
Thisjunction provides a reproducible electrolyte flow butʛʻęƈ/Ȼȼƈ4ʬȰƂ."
because of its large surface it is very vulnerable tocontamination.
4ȉʃ5̶ː˱4ȄILÞȻ.>" %4Ū˂̺ɤ2EGǺǚ2ő -5̹Ť2ų/JG>"b) Platinum
Fibre Diaphragmb) PlatinumɈ̝ʒʉ̯ʤ
fibre diaphragms consist of very fine platinum

wires which are spun loosely together and fused into theɈ̝ʒʉ̯ʤ5 ̹Ť2Ɓɾ1Ɉ̝ʍLʎC2ɽV
glass.
This type of junction resist contamination to a certain extent
c4 2ʼɐ 'B4."
but their electrolyte flow is less reproducible than ceramic
diaphragms.
4hQ}4ȉʃ5HɢŮ4Ǻǚ2ő-ʛƈGc) SINGLE(Trademark of HAMILTON) Diaphragm>" PORE
̶ː˱4ȄI5ĺńƈekY̯ʤ2ǳ˺
The
SINGLE PORE diaphragm is strictly speaking not aÞȻº/ě̈́G>"
diaphragm at all. It is a very small glass capillary whichallows a larger leakage rate than a ceramic or platinum
diaphragm. A constant and very reproducible electrolyte
flow is assured. Clogging or contamination is barely
possible. It gives the most accurate and repeatable results.
In combination with a polymeric electrolyte the SINGLE
PORE principle is adapted for industrial electrodes. Due tothe lack of36contamination and maintenance it has a lot ofadvantages.
The German Federal Physical Technical Institute (PTB) decided during a traceability test in 1997

Platinum fibre diaphragms consist of very fine platinum
wires which are spun loosely together and fused into theglass.
This type of junction resist contamination to a certain extent
but their electrolyte flow is less reproducible
than ceramic
by T&C Technicaldiaphragms.
c) aZO(üń)̯ʤ

c) SINGLE PORE (Trademark of HAMILTON) DiaphragmaZO5uo4opY." I5

The SINGLE PORE diaphragm is strictly speaking not adiaphragm at all. It is a very small glass capillary whichǮɘ25̯ʤ.51 Ŗ1Vc4Ǵɾɱ.±4©+
allows a larger leakage rate than a ceramic or platinum
diaphragm. A constant and very reproducible electrolyte
4̯ʤ2ǳ;EGĺ4̶ː˱4Șâʾ>" Ŋ4flow is assured. Clogging or contamination is barely
possible. It gives the most accurate and repeatable results.
%-͍̶ː˱4ȄI4ÞȻÅ˙I>" Ɍ˛>G

In combination with a polymeric electrolyte the SINGLE
PORE principle is adapted
for industrial electrodes. Due to4ɇȻ5</M0Ȩ>'Ǻǚ̹Ť2ŗ14ȰƂ
the lack of contamination and maintenance it has a lot ofadvantages.
."%4'AǏBǮɘ.Þȶƈ4HȒŊʂǙLB'F>"
The German Federal Physical TechnicalInstitute (PTB) decided during a traceability test in 1997
that the SINGLE PORE pH electrode is the most accurate laboratory electrode. (“Traceability of̶ː˱/aZO4ʀ?ďK$2%pH measurement” by Petra Spitzer; ISBN3-89429-877-4 or ISSN 0947-7063)
4ÿȸ5ŝǤ̶ǥ2̐ď
/>" Ǻǚ42/ ʂǙ-ÅŇŗ1/2- ǏBÒI'ƈʡLơ)>"

pQl̈̔ȯȸŝņɔɦƕ(PTB)5aZO pH ̶ǥǏBɷŮ4͍ɔɦȽ̶ǥ.H/L 1997 Ũ2ʾ*'o_ymP˚͌.̀;->"(“Tracebility of pH measurement” by Petra Spitzer; ISBN3-89429-877-4 B

37

5 ISSN 0947-7063)

Page 24
Page 24d) Annular Ceramic Diaphragmby T&C Technicald) Annular Ceramic Diaphragmd) ȺȱekY̯ʤ
The
annular ceramic diaphragm is formed by a porous
ceramic
layer ceramic
between two
glass tubes.
The directionof theThe
annulardiaphragm
is formed
by a porousȺȱekY̯ʤ5ĺńƈekYśL©+4V
measuredmediumis
notcriticalduetotheannularshapeceramic layer between two glass tubes. The direction of theof this junction.
Theelectrolyte
flow tois thenotannular
reproducible.
measuredmediumis notcritical due
shapec̦4̦2×I'B4."
ȒŊ"HǶȘȉ4ƿđƈ5Hence
is mainlyTheappliedin gel-typeofthis itjunction.
electrolyte
flowelectrodes.
is not reproducible.
Hence it is mainly applied in gel-type electrodes.
Ⱥȱ2ȉʃ
M

'(

-Hŷȱ2EG%I<0ě̈́5G>$

̶ː˱4ȄI5ÞȻ>$M%4'A¡2e) Ground Sleeve DiaphragmElectrolyte
Electrolytee) Ground
Sleeve Diaphragm\̶ː˱Lơ+̶ǥ2¾ȽI>"
Ground sleeve diaphragms are ideally suited for
applications
in suspensions
as these
Groundsleevediaphragmsandareemulsions,
ideally suitedfore) Zpc|ű̯ʤ
diaphragms
canbecleanedeasilyby
onlypullinguptheapplications in suspensions and emulsions, as theseglass sleeve.
successful
diaphragms
can Anotherbe cleaned
easily byapplication
only pullingofup thistheZpc|ű̯ʤ5ƒȡȯ˱H5£ȉ4O}
diaphragm
is theAnother
pH measurement
in lowionic solutionsor
glass
sleeve.
successful
applicationof thisin non-aqueous
The electrolyte
flowrate
diaphragm
is themedia.
pH measurement
in lowionic depends
solutions onor[a2ǏB̐'˖˓."
IF4̯ʤ5V
theroughnessofthegroundglass
surfaceofthesleevein non-aqueous media. The electrolyte flowrate depends on
and roughness
the tightness
thegroundsleeveglass
fit. However
the
of of
the
surfacethis
of diaphragmthe sleevec4c|LŲ*Ŵ*-Ɯ(.ɴü2Ȃȅ.
is notthe this
pH diaphragm
electrodeandthesuitabletightnessfor
of applications
the sleeve fit.where
However
assembly
is subjected
to vibrationwhereas thisthemightloosentheisnotsuitablefor applications
pHelectrode>"±4Ɠñ'¿.5ºQTǶȘȉ
H5̹
diaphragmissleeve.
assembly
subjected to vibration as this might loosen thediaphragm
sleeve.
Ƕɸ4Șȉ.4ȒŊG>"
̶ː˱4Ȅ̜5Z

The selection of the right diaphragm for a measuring application is of utmost importance but not
pVc4˂̺ɶ/c|4ćG²Ĥ2EGĸalwayseasy. Very
the experimental“trial anderror” method
will leadto a successfulTheselectionof theoften
right only
diaphragm
for a measuring
application
is of utmost
importancebut notapplicationof Verya certain
type. For detailed
one haswill
to consult
technical
alwayseasy.
oftendiaphragm
only the experimental“trial informationand error” method
lead to thea successful
KG>"
 1F4̯ʤ5 pH ̶ǥacm 
datasheetsoftheelectrode
manufacturers.
application of a certain diaphragm type. For detailed information one has to consult the technicaldata
sheets ofprovides
the electrodemanufacturers.
A diaphragma deliberateleak Ƥö2FIHE1ȺĴ.5̯ʤc|ʎ@ċof the electrolyte solution into the measured medium
whilstpreventing
unrestricted
mixingofthe
bothsolutionssolution
within into
the thereferenceelectrode.
A diaphragm provides a deliberate leak ofelectrolyte
measuredmediumPenetrationof the unrestrictedmeasured solution
intothereferenceelectrolyte,
andthuspoisoningof thewhilstpreventing
mixingofbothsolutions
withinthereferenceelectrode.
ʡƈG>"
reference conducting
system solution
occurs frequently
during pHelectrolyte,
measurements,
especiallywhen
Penetrationof the measured
into the reference
and thus
poisoningof themeasured conducting
solution is pressurised.
referencesystem occurs frequently during pH measurements, especially when themeasuredis pressurised.
There are solution
pH electrodeson the market where the electrolyte storage vessel can be pressurisedȒŊȽ̄2EHǮ
̯ʤ4̒Ɲ5ȒŊ2-ǏB̛ˈ1/."Ť2ɴü/
in orderto pH
counteract
theonpenetrationof where
the measured
solutionstorage
throughvessel
the diaphragm.
As a rule
There
areelectrodes
the market
the electrolyte
canbe pressurised
of
thumb
a
pressure
of
100
kPa
above
the
pressureofthemeasuredsolutionwill
normally
in order to counteract the penetration of the measured solution through the diaphragm. As
a ruleK25>$M̹Ť2ĺ4İď
ʁ͌/
˚?/ļƷ
4ƿǿ4?
ȰŊ
suffice.
result aofsmallof electrolyte
solution
penetrate
into theofthumbAsa apressure
100 amountkPa above
the pressureof thewill
measuredsolution
willmeasured
normally
solution As
which
is generally
no significanceto theprocess.
However thisthesuffice.
a result
a small ofamountof electrolyte
solution
will penetrate
into decreases
the measured
4̯ʤǦ̇4Ɠñ¿:/ŕ/21G>"
˜ɾƋį2²-5̶ǥˆ̇·ɜ4ƙʿnresistanceof theisreference
to between 0,1
k: and2 k:, improvesofsolutionwhich
generallyelectrodeof no significanceto theprocess.
However thethisreproducibility
decreases thethemeasurement
andprevents
thediaphragm
fromcloggingup.
resistance of the reference electrode to between 0,1 k: and 2 k:, improves the reproducibility ofhaoLˤ;HƄˈG>"themeasurement
and prevents
theisdiaphragmup.
Beforethe electrodeassembly
immersedfrom
intoclogging
the measured
medium the stopper whichcloses the electroderefill opening
must beremoved. Periodic
the electrolyte
level should
Beforeassembly
is immersed
into the inspection
measuredofmedium
the stopper
which
be
part
of
the
electrodemaintenanceprogramme.
closes the refill opening must be removed. Periodic inspection of the electrolyte level shouldbe part of the electrode maintenance programme.
38

by T&C Technical̯ʤ5˓ɀɉ2ĂȪ̶ǥÜ4̶ːȉL̶ːȉ/ȒŊ

ȒŊ"HǶȘȉ:țIHE2"Hƿ.

-HǶȘȉ4ȋďL̨ǭ

ǶȘȉ4Â× %-ĂȪŕ̶acm

->"

:4Ǻǚ5

GKȒŊ"HǶȘȉòĦI-Hİď2ɇȻ

6



Ü̕

ĂȪȽ̶ːȉ:4ȒŊ"H

6 pH ȒŊ4̦2ɇȻ

>" /

>"

̯ʤL̅!-ȒŊ"HǶȘȉ4Â×L̨'A òĦI'̶ːȉŎĝLB+̶ǥ4 pH ̶ǥacmŠİ25Ȅ̅

100kPa ²ò
×->"*72˒6

ȒŊ"HǶȘȉ4ĦðEG'Ħð.̅Ťùã." ʂǙ ̹Ť2ŗ1̶ːȉȒŊ"HǶȘȉ:/Â-/21G>"

%I5Ø̛ˈ1ŝɢ.514."

ƞƛL 0.1 F 2kΩ 4̦.Ȑŗ$ȒŊ4ÞȶƈLƳĜ

"/F̨4."

LȒŊ"HǶȘȉ2ȇ"ë2̶ǥacm!-HcokwLƄ#Ĺ
4ÅŇ}Z--(

4 1 +."

39

òĦ5ĂȪ̶ǥ4>'̯ʤɌ˛>GL˲˅Ôȉ4̥ĉ̕L̶̤ːȉ4~4ŊǓɉ1ɘ˝5̶ǥ

by T&C Technical3.4.1 ƟƸ̶¹Page 25

3.4.1 The1Diffusion
Potential
̯ʤ2HB+4ŀōˈɼ5ƟƸ̶¹."(E6) 4̶¹5Ť2©+4Ʌ1HȢŮ4Another disturbing factor of the diaphragm is its diffusion potential (E6). This potential always>" >'ƟƸ̶¹5ɣ 4QT4ɡö̆Ů4̏2Ź̻"Hdevelops at the phase boundary between two electrolytes of different concentration orcomposition. The diffusion potential can be contributed to the different migration velocities of
/G %4Ź̻5ǥƈ/QTɣ4_Qd2BEG>"
ions, which again depends on the polarity and size of the ion type.
̶ːȉ4ɎĴɁ.ɇȻ

The illustration below explains the
diffusion
potential between
two HCl solutions of different´2ɛ"ģ5©+4Ʌ1*'ȢŮLơ+HCl
Șȉ4ƟƸ̶¹Lˢǅ->"
concentration:
H+QT5ɹ 5 ÈǃƟƸ
The
H+ ions Cl-2ǳ˺
diffuse nearlyfive times faster to the rightthan the Cl¯ ions. This creates a potential across the>" I5©+4Șȉ4ĴɁL>'̶
boundaryof the two solutions. In order to keep the
diffusion potential at the diaphragm of a reference¹2EGɇȻ
>"asĂȪ̶ǥ4̯ʤ2ɇelectrodeas smallpossible, the different ions in thereference electrolyte should have identical ionic mobility.
Ȼ"HƟƸ̶¹Lċʡ1̪GŖÅ+With
a 3 mole KCl solution this ideal condition is nearlyreached.

̶¹

Diffusion Potential

Potential

ƟƸ̶¹

Cl

H+
H+

Cl
Cl

H+
Cl

H Cl

H+
H+

+

H

+

+

Cl
Cl
Cl

H+
Cl

Cl

H+

H
Cl
H+

H+

Cl

25 ĂȪ̶ǥ4̶ːȉÜ4Ʌ1HQTH+In general it can be said:Cl͆LâǘH̪GĐ4QTɡöŮLơ
1. The higher the KCl concentration of the reference

Distance
˵̴electrolyte, the lower the diffusion potential.
+ƄˈG>" %4'A 3mol/L 4 KCl

2. The larger the flowrate of the reference electrolyte
through the diaphragm, the smaller the diffusionȘȉLȽ-QT4ɡö̆ŮLǧ2Å-HE2 ->"potential.
ʫɉ2ƟƸ̶¹2+-5´4E1ȰƂG>"
The more the pH value of the measured solution differs from pH 7, the larger the diffusion

potential.

1. ĂȪ̶ǥ4̶ːȉ4 KCl LEG͍ȢŮ2"H/ƟƸ̶¹5EGº1H

Diffusion Potentials
which develop betweenEGºƟƸ̶¹21H
various solutions
2. ̯ʤL̅HĂȪ̶ǥ̶ːȉ4Ȅ̆LEĞ"H/and a saturated KCl electrolyte
3. ȒŊ"HǶȘȉ pH7 EGĻɅ1H
pH
ÉLơ+İď
1,0moleHCl= EGĻ1ƟƸ̶¹/1H
14,1 mV
0,1
mole HCl
0,01
mole HCl
0,1mole KCl
Buffer pH 1,68
Buffer pH 4,01
Buffer pH 4,65
Buffer pH 7,00
Buffer pH 10,01
0,01
mole NaOH
0,1mole NaOH
1,0mole NaOH

=
=
=
=
=
=
=
=
=
=
=

4,6 mV3,0 mV
1,8 mV3,3 mV2,6 mV3,1 mV
1,9 mV
1,8 mV2,3 mV-0,4 mV-8,6 mV

40

From the above it can be seen that different measured solutions will create different diffusion
potentials at the diaphragm of a reference electrode.

Distanceelectrolyte, the lower the diffusion potential.
2. The larger the flowrate of the reference electrolyte
through the diaphragm, the smaller the diffusion
potential.
by T&C Technical

The more the pH value of the measured solution differs from pH 7, the larger the diffusion
potential.
Diffusion Potentials
which develop between various solutions
and a saturated KCl electrolyte
1,0mole HCl
0,1mole HCl
0,01
mole HCl
0,1mole KCl
Buffer pH 1,68
Buffer pH 4,01
Buffer pH 4,65
Buffer pH 7,00
Buffer pH 10,01
0,01
mole NaOH
0,1mole NaOH
1,0mole NaOH

=
=
=
=
=
=
=
=
=
=
=
=

14,1 mV
4,6 mV3,0 mV
1,8 mV3,3 mV2,6 mV3,1 mV
1,9 mV
1,8 mV2,3 mV-0,4 mV-8,6 mVFrom
the above pH7
it canbe seen pH
thatÉLơ+ǶȘȉLȒŊ"H/different measured solutions
will create different diffusion
4ˎFFɅ1H
Ʌ1*'ƟƸ̶¹L̯ʤ
potentials at the diaphragm of a reference electrode.
2ɇȻ"H/ãG>"41

by T&C Technical3.4.2 ÷ņąƅ2EH̯ʤ4ǺǚĂȪ̶ǥȽ̶ː˱/ȒŊ"HǶȘȉ4̦2H̯ʤ.4÷ņąƅ5
̓H;ˣ̈́."ŊLȻ!>"

Page 26ąƅ5̯ʤ4Ǻǚ2ʓG]co*-BʂǙ̯ʤ4ƞƛLǄ$Ǯɘ1Ȓ

ĂȪ̶ǥ5÷ņąƅLȻ!C"Ĳ÷̟Lơ*-G/GKɗ÷ȯ2

ő ąƅ>" 4'Aɗ÷ȯ4Įɤȯ2EG̯ʤǺǚI1E
3.4.2
Diaphragm
Contamination through Chemical Reaction pH LȒŊ"H

Chemical
reaction at the diaphragm between the reference electrolyte and the measured solution
ǶȘȉ2ɗ÷ȯĒ>I-1̹Ť2ȁƍ"HƄˈG>"
must be avoided at all costs. This reaction will lead to diaphragm contamination, increase ofresistanceacross the diaphragm and falsified
measuring results. TheǺǚ4ʂǙ
reference electrolyteɗ÷̟ǺǚɇȻ"H/̯ʤ5͏ĸʭɴü2ˊãH/âǘ>"
contains silver chloride which is prone to chemical reactions, especially with sulphides. For thisreasongreat 4ƅɯǉ̦ǅF2ɅŤ/ãHFHE21G>"
care must be taken when measuring pH in solutions containingI5̯
sulphides, as the̶ǥacmdiaphragm may be contaminated with silver sulphide deposits.
ʤƞƛ4ïɉǄ2EHB4.
Ǻǚ'̶ǥacm.5ǝǮBċʡ21G>"
Silversulphide contamination caneasilybe identified bya blackened diaphragm. As a result, theresponse time of an electrode assembly increases substantially, the diaphragm resistanceincreases radically and it may be impossible to calibrate such a contaminated electrodeassembly.
3.4.4.1 Sv{ĂȪ̶ǥacm(EVEREF)

3.4.2.1 The EVEREF Reference SystemĂȪ̶ǥȽŕ̶̟ʍ
Reference
conductor
Silver wire

Reference electrolyteĲ÷̟LØĒ>with constant1 Ŋ4Ĳɼ
chlorideconcentration,
ȢŮLơ+ĂȪȽbutfree of AgClĲ÷̟˭ʸ̕
Silverchloride
reservoir͍ Ő Ů pipe2ʊLÔ
Diffusion
filledcotton wool
ĳ with'ƟƸɱ̶ːȉDiaphragm̯ʤ̕5̯ʤ2ʖHɗ÷̟Ǻǚ2őƅ"HIn order to counteract silver sulphidecontaminationat
the
HAMILTON'Auo5 diaphragmSv{have invented the EVEREF reference
system.
This system consistsof a silver(EVEREF)ĂȪ̶ǥacmLɇǅchloride reservoir from which the silverreferenceleads to 5
the ̟.â
electrode plug.
> ' wire4acm
The reservoir is separated from thereferenceelectrolyte by a diffusion barrierǘ'ĂȪȽ4̶ǥʍ4Õɪ2ǜ/1
consisting of densely packed cotton wool inaHE2Ĳ÷̟Șȉ4Vc.âǘ
glass tube. The barrier prevents the loss of
silver chloride into the reference electrolyte
inducedby temperature variations.
'˭ʸ̕˖ʖI->"˭ʸĂȪȽ̶ːȉ:4̶ǥ̶ːȉ4ƟƸLʾ'A͍ŐŮ2ĦʐI'ʊÕɪ2˛A

FI->"
͍ŐŮ4ʊ5ȑŮşH/2Ų˲IH̶ːȉ2EHĲ÷̟Șȉ
The
EVEREF reference
system enhances the stability of the reference potential and extends thelife of the combination electrode considerably.
4ȈʜL̨>"3.4.2.2 The EVEREF-B Double Liquid Junction
Sv{ĂȪ̶ǥacm5ĂȪ̶¹4ňŊƈLŵ÷

ˇď̶ǥ4ŒėLĻť2Ű̢

If a chemical reaction at the diaphragm is unavoidable, the application of a reference electrodehaving an inter-mediate electrolyte provides a solution.
42

The EVEREF-B double liquid junction system from HAMILTON with its intermediate
electrolyte reservoir provides such a solution. The reference electrolyte is completely separated
from the EVEREF reference system by an internal diaphragm situated in a second reservoir filledwith an intermediate electrolyte. The life of the pH electrode is greatly prolonged as the reference

by T&C TechnicalPage 27>"

3.5 Alkaline and Acid Error
3.5.1 Alkaline Error

3.4.4.2 Sv{-B ©ǱȉʃĂȪacm

pH Electrode̶̦ːȉ̕Lơ+pH ̶ǥacm“ChemotrodeBridge”uo
[op|kb
with Intermediate
Electrolyte
Electrode
Head
̶ǥ̼́̕
(Variopin or SMEK)

VP B
SMEK

5

˅Ôȉ×ĉʷ
Refillopening̶̦ːȉ̕Intermediate
electrolyte
ReferenceĂȪ̶ǥacmsystemSv{-B
EVERREF-B
̦̯ʤInternal
diaphragm
3 moleKCl
3mol/LKCl

At a value above pH 10 the gel layer structure at themembrane of a measuring electrode issubject to certain̯ʤ.4÷ņąƅ̓FI1İď̶̦changes which lead to a measuring inaccuracy, the alkaline
error. This alkaline error is causedby the presence of a highːȉ̕Lơ+ĂȪ̶ǥacm
%4ːǻƿǿ
concentration of alkaline ions, especially sodium ions (Na+).
These
ions replace, partly or completely, the hydrogen ions/-G>"
in the outer gel layer of the glass membrane, and by doingso, contributeSv{-B(EVEREF-B)©Ǳȉto the potential at the outer phase boundary.
uo
As a result a lower pH value will be measured than the actualʃĂȪacm̶̦ːȉ̕Lơ)pH value of the5measured
solution.

ĂȪȽ

In earlier days the alkaline error of glass electrodes alreadydeveloped between pH 9 and pH 10. Today, where the glass
membranes contain lithium instead of sodium, the alkaline
ʤ2EGŉØ2Sv{ĂȪ̶ǥacm error is only noticeable from between pH 12 and pH 13.
̶ːȉ5©ǱɌ2˖ʖI'̶ːȉ˭ʸ̕4̯Fã̴I>"
I2EGĂȪȽ̶ːȉ25
The alkaline error
increases with increasing pH value,with higher alkaline concentration and with rising̟Ø×F1ȱƏLÅ)pH ̶ǥ4Œė5
temperature.

InternalÜ̕ŕ̶ƈ̶ǥ
conductor
̟-Ĳ÷̟
electrode (Ag/AgCl)Ļť2đÜ̕ʎˀȉ͔KCl
Internal
bufferplus KCl

pH ȒŊLʾ>" >'¡/1HĂȪȽ̶ːȉIn order to counteract the alkaline error, electrode>"manufacturers use special membrane glasses with low
alkaline errors for electrodes which are used to measure highSv{-B 5ɗ÷ȯLĒ@ǶȘȉÜ.ʬľ1
pH values.

50

External̯ʤdiaphragm

4?˅Ô

>"

1

2

3

4

5

6

7

8

9

10 11 12 13 14

0
50
100
150

mV

200
250
300
350
400

43

Alkaline
Error

3.5 Alkaline and Acid Error
3.5.1 Alkaline Error
At a value above pH 10 the gel layer structure at themembrane of a measuring electrode is subject
certainby T&CtoTechnicalchanges which lead to a measuring inaccuracy, the alkaline
error. This alkaline error is caused by the presence of a highElectrode Head
3.5 OU/̙2EHˡşconcentration of alkaline ions, especially sodium ions (Na+).
(Variopin or SMEK)
These ions replace, partly or completely, the hydrogen ions3.5.1 OUˡş
in the outer gel layer of the glass membrane, and by doingso, contribute to the potential at the outer phase boundary.

pH Electrode“Chemotrode Bridge”
with Intermediate Electrolyte

pH10 ´4ǶȘȉ2- ȒŊ̶ǥ4\ś4Ǧ̇5ȒŊɷŮLƊ÷$Hƿđ:ĸ÷

As a result a lower pH value will be measured than the actual
pH value of the measured solution.

Refill opening

LȻ!>"I5OUˡş/Ė6I

͍ȢŮ4OUQT2E*-Ų˲In earlier days the alkaline error of glass electrodes alreadydeveloped between pH>"
9 andIF4QT5
pH 10. Today, where
the glassI>" Ȱ2qoR QT.5ͅʵ2ɇȻ̕ãɉ2H
Reference
membranes contain lithium instead of sodium, the alkalinesystemEVERREF-B
error is only noticeable from between
pH 12 andpH 13.
5ŉØ2Vc̶ǥ˂̺4\ś4ǶɼQTLʖƭ
- >>"
4'AȒŊ̶Internal
Intermediate
electrolyte

diaphragm

The alkaline error increases with increasing pH value,ǥ4ĹÌ\ś4ɎĴɁ4̶¹2Ź̻%4ĸ÷5ŋ̰EGº
pH ÉȒŊIH
3 mole KClwith higher>"alkaline
concentration andwith risingȱƏ21G>"
Internal

temperature.

ǃǂƹ.

pH9 F 10 4̦.OUˡşVcʤ2ɇȻ

>"In order to counteract the alkaline error, electrodemanufacturers use
special membrane
glasses pH12
with FlowȶħVcʤ5qoR 2ĸKGjR
L¾E21G
ʂǙ¯ǂ.5alkaline errors for electrodes which are used to measure high13 4̦.ˡşɇȻ >"pH values.
conductor
electrode (Ag/AgCl)

Internal buffer
plus KClOUˡş5 pH Ǆ"H2+I

50
1

External
diaphragm

2

3

4

5

6

7

8

9

10 11 12 13 140ĵ >'EG͍OUȢŮ/%

50

4ȑŮǄ.EGĻ1G>"

100
150

OUˡş2őƅ"H'A ͍OUǶȘȉ2¾Ƚ.HE̶ǥˆ̇·ɜ5ºOUˡş21HȰ

mV

200
250
300
350

ç1VcʤLơ+ȒŊ̶ǥLˆ̇

Alkaline
Error

OUˡş
400

->"

44

by T&C TechnicalPage 28

3.5.2 Acid̙ˡşError
3.5.2

At low
values (< pH 2) the potential differenceº
pH pHÉLơ+ǶȘȉ.5ȒŊ̶ǥ/ĂȪ̶

400

between measuring and reference electrode will notconform exactly to the NERNST equation. Throughǥ4̦4̶¹5sco4ű/5Ʌ1*'É
experiments it has been proven that the gel layer ofthe membrane
will absorb
acid æǅ
molecules
at very low
Lơ*>>"
ŋ͌L̅'/pH values.

Acid
Error
̙ˡş

350
300

+

250

mV 200150

5pH Éº̀ī.̙
ThisVcʤ4\ś5absorption decreases
the activity of the H+ ions100

and results in a lower potential at the outer4ãŃLēĆ"H/˙ǅI->"
membrane phase boundary. The pH measurementshows a higher pH value than the actual pH value of
4ēĆ5
H+QT4ȃöLȐŗ$the measured
solution. This effect isʂǙºknown as theacid error.

50
1

2

3

4

5

6

7

8

9

10 11 12 13 14050

̶¹VcʤĹÌ4ɎĴɁ2ɇȻ

>"

%4ʂǙ

pH ȒŊÉ5ŋ̰EG͍ pH É

As with the alkaline error, manufacturers supply measuring electrodes with membrane glasses
having specially low acid errors.
Lɛ>"

4Ź̻̙ˡş/-ɑFI->"HAMILTON membrane glasses show no acid error above pH 1.
OUˡş/Đ!E2

ˆ̇·ɜ5͍̙ƈȘȉ.ˡşŖ̶ǥLȽƍ->"

3.6 Temperature Influence and Temperature Compensation>'uo4Vcʤ5̙ˡş5 pH1 >.ɇȻ>$M

The pH measurement is temperature dependent. Three temperature factors have to beconsidered in order to perform a nearly perfect pH measurement:
1. the temperature dependency of the NERNST equation
2. the position of the isotherm intersection point
3. the pH/temperature dependency of the measured solution

450
400
350
300

+

Measuring Error
without
Temperature Compensation
31.72 mV

Calibration at 25 oCoMeasurement at 65 C

200
150
100
50

mV
50
100
150
200
300
350
400
450

The temperature dependency of the
Nernst equation and with it thetemperature dependency of the theoreticalslope of a pH electrode assembly has
already been discussed in paragraph 3.1.

The slope of a pH electrode assembly is temperaturedependent in accordance with the NERNST equation.

0,47 pH

1

2

3

4

5

6

7

8

9

10 11 12 13 14

pH

Theoretical Values
Slope at 25 oC = 59,16 mV

o

25 C
65 C
o

o

Slope at 65 C = 67,09 mV

45

The temperature dependency of the
NERNST equation is easily calculated, andas a rule, only this temperature influence isconsidered by instrument manufacturers
when they incorporate conventional manualor automatic temperature compensation in
their pH measuring products. The adjacentgraph illustrates the theoretical error whichis compensated for by conventionaltemperature compensation.

100
50
1

2

3

4

5

6

7

8

9

10 11 12 13 14

050

and results in a lower potential at the outermembrane phase boundary. The pH measurementshows a higher pH value than the actual pH value ofthe measured solution. This effect is known as theacid error.
by T&C TechnicalAs with the alkaline error, manufacturers supply measuring electrodes with membrane glasses
having specially low acid errors.
3.6 ȑŮ4Ź̻/ȑŮ˅Ñ

HAMILTON membrane glasses show no acid error above pH 1.
pH ȒŊ5ȑŮÁŅƈG>"<=ŉȹ1 pH ȒŊLʾ'A25+4ȑŮ2+-

3.6 Temperature Influence and Temperature Compensation
4ˈɼLʙHƄˈG>"The pH measurement is temperature dependent. Three temperature factors have to beconsideredinȑŮÁŅƈ4Hsco4ű
order to perform a nearly perfect pH measurement:
1
1. the temperature dependency of the NERNST equation2 ɭȑʍ­şȦ4¹ʖ

2. the position of the isotherm intersection point3 ȒŊ"HǶȘȉ4
pH/ȑŮÁŅƈ dependency of the measured solution
3. the pH/temperatureThe
slope of a pH electrode assembly is temperaturesco4ű2EHȑŮÁŅƈLB+pH ̶ǥacm
dependent in accordance with the NERNST equation.

450
400
350
300

+

Measuring Error
withoutȑŮ˅ÑȨ/4ȒŊˡşTemperature Compensation
31.72 mV

25.ǝǮ
Calibration'/4c}
at 25 oCo
Measurement
at 65 C65.ȒŊ
'/4c}

200
150
100
50

0,47 pH

1

2

3

4

5

mV

7

8

9

10 11 12 13 14

pH

50
100
150
200
300
350
400
450

6

Theoretical Values
ȸ˦É
Slope at 25 oC = 59,16 mV
254c}͚59.16mV
654c}͚67.09mVoSlope at 65 C = 67,09 mV

o

25 C
65 oC

Thesco4ű4ȑŮÁŅƈ/temperature dependencypHof the
Nernst equation and with it thetemperatureof the theoretical̶ǥacmdependency
4ȸ˦c}2+slope of a pH electrode assembly has
alreadybeen
in paragraph-5
3.1discussed.̀;'̅G."s 3.1.
The temperature dependency of theco4ű2HȑŮÁŅƈNERNSTequation is easily calculated, andas a rule, only this temperature influence is5ɴü2˓ɰ"H/âǘ>"consideredby instrument manufacturers
when they incorporate conventional manual-ǻ>G/- 4ȑŮ4Źor %automatic
temperaturecompensation in
their pH measuring products. The adjacent̻4?
ƖöH5ʦöȑŮ˅
graphillustrates
the theoretical error whichis compensated for by conventionalÑLʀ?˽M(
pH h2Ƚ
temperaturecompensation.
FI->" Z{5ʫɉ1ȑŮ˅Ñ2EGɇȻ"Hȸ˦ɉˡşLɛ->".ɭȑʍ­şȦ4¹ʖ2+-Đǧ2ȑŮ4Ź̻LʙƑ"HƄˈG>"
Ⱦ5ɭȑʍ­şȦ4Ņħ/%4ȒŊ2+-5 3.3.5 .ˢǅ-(ȶħ̶ǥˆ̇·ɜ5%4ȸ

->"4.%)FLĂȪ

ɭȑ­şȦ4¹ʖâǘH̪G pH7 2˾1HE

pH ȒŊ̶ǥLˆ̇->" I2EG̅Ť4ȑŮ˅Ñ.5̫ā.1ˡşLȐF%

/

-ȶħ

->"

ʡ5ɏI

%

Ǉ pH hơ*-' Uis mah4ǫǏƾ4QY}ek_.ȒŊ"H pH ȒŊĝ.5 Uis L˅Ǯ"HʡðL
46

by T&C Technicalơ*->"
3 +Ɍ4ˈɼ

pH/ȑŮÁŅƈ4HǶȘȉ5

4ãŃ4ː̴5͍ȑŮ2ÁŅ
Ů4ĸ÷LB'Fş/->"ʂǙ pH ÉBĸ÷ǶȘȉ4ȑŮÃƹ/BĖ6I->"%ȒŊ"HǶȘȉ4ȑŮ4ĸ÷5ǶɼQTȢ->"

4 pH 4ĸ÷5ȶŋ.GȒŊˡ-ˢǅ"H/5.>$M

Ø-4̙/OUǶȘȉ4 pH/ȑŮÁŅƈ5ɑFI->$M %4'AȒŊ"HǶȘȉ4ȑŮ/ pH É4̧ÃLëB*-ǻAH/ǏB̛ˈ/1G>"%4 pH ȒŊ5ƍĕȨ1G>"

47%ILʾK1İď

by T&C Technical

3.7 ĺǧ1̶ǥ4ŷ
Ø-4 pH ȒŊ2őPage 30˪

Đ!ŷȱ4̶ǥLȽH/5ġ̵." ɔɦƕ.5°ǧ2ďK$'̶ǥŷȱƄˈ/I

6

6ȒŊő

ʂǙĺǧ1ŷȱG>"Page
30̶ǥˆ̇·ɜ5ȒŊ°ǧ4</M0LUv.HE2"H'AĺŸ1̶ǥǦ̇LƬ

3.7 Various Electrode ShapesÀ->"

VariousElectrode
Shapes
It is 3.7
not possible
to useone electrodeshape for every application. More often in the laboratory
different electrode shapes are required as there are numerous pH measurement applications.
It is not possible to use one electrode shape for every application. More often in the laboratory
Electrode manufacturers try to cover most of these applications by offering varying electrodedifferent electrode shapes are required as there are numerous pH measurement applications.
constructions.
ŷȱ a) manufacturers try to cover most of these applications by offering varying electrode
ElectrodeForma)constructions.
Form a)This is the most common electrode shape and a wide field of applications can be covered withǏBʫɉ1̶ǥ4ŷȱ. ŪȒŊ°ǧ ɔɦƕF}ecêƀ>.őƅ >" Ȓthis type of electrode, both in the laboratory and in process control. Measuring, reference andThis is the most common electrode shape and a wide field of applications can be covered withcombination electrodes are manufactured using this construction.
Ŋ̶ǥă8ĂȪ̶ǥ
thistype of electrode, %both-ˇď̶ǥ54Ǧ̇LĭǕ2ˆ̇I>"
in the laboratory and in process control. Measuring, reference andcombination electrodes are manufactured using this construction.
Form b)

Form
ŷȱ b)
b)

A standard combination electrode construction with a ground sleeve diaphragm. This electrode ismainly used in the laboratory where dirty or strongly contaminated solutions have to be4̶ǥ5ǺIH5̹Ť2
A Zpc|̯ʤǦ̇Lơ+Ǩȗɉ1ˇď̶ǥ."standard combination electrode construction with a groundsleeve diaphragm. This electrode ismeasured. Its application includes non-aqueous media as well. The diaphragm can easily bemainly used in the laboratory where dirty or strongly contaminated solutions have to becleaned by pushing the sleeve upwards. There is a limited use for this construction in processǺǚ4Ƞ Its
ǶȘȉLȒF1-51F1/2¡2ɔɦƕ.¾ȽI>"
measured.
application includes non-aqueous media
as well. The diaphragm >'̹
can easily becontrol (be aware of vibration).
cleaned by pushing the sleeve upwards. There is a limited use for this construction in processǶȘȉɸ4ȒŊȉ2B¾ȽI>"
̯ʤ5c|L2ơ)H/.ɴü2Ȃȅ
control(be aware of vibration).
Form c).>"4Ǧ̇4̶ǥ5}ec.4¾Ƚ5ê̪I>"

Ƥö2ő

-4ȁƍƄ

Form c)ˈ."This construction example includes two electrode features: a ground sleeve diaphragm and apipe connector. In order to minimise maintenance time and to pressurise the reference electrolyte
This construction
two electrodegroundsleevediaphragm
and aan external
electrolyteexample
reservoirincludes
is connectedto the features:electrode avia
the pipe
connector.
This
pipe
connector.
In
order
to
minimisemaintenance
time
and
to
pressurise
thereferenceelectrolyte
electrode construction can be used in the laboratory and in process control, especially for highexternal
electrolyte
reservoir is connected to the electrode via the pipe connector. This
purityanwater
controlin power stations.
electrode construction can be used in the laboratory
and in process control, especially for high48
purity water control in power stations.

A standard combination electrode construction with a ground sleeve diaphragm. This electrode ismainly used in the laboratory where dirty or strongly contaminated solutions have to bemeasured. Its application includes non-aqueous media as well. The diaphragm can easily becleaned by pushing the sleeve upwards. There is a limited use for this construction
process
by T&C in
Technical
control (be aware of vibration).
ŷȱ c)Form c)This construction example includes two electrode features: a ground sleeve diaphragm and a4Ǧ̇¿5Zpc|̯ʤ/wQ}]sYh4©+4ǫʡLơ+̶ǥ."Å
pipe connector.
In order to minimise maintenance time and to pressurise the reference electrolyte
an external electrolyte reservoir is connected to the electrode via the pipe connector. This
electrodeŇ4ǉ̦LǏɒ2"H'A/
construction can be used in wQ}]sYhL̅!-Ĺ̕4̶ːȉ˭ʸhY/Ʃʈ
the laboratory and in process control, especially for highpurity water control in power stations.
ĂȪ̶ǥÜ2ĦðL>""

4̶ǥǦ̇5ɔɦƕ/}ecêƀ.ȽFI->Ȱ2ɇ̶ƕ4ɺǶ2-ȽFI>"

Page 31ŷȱ d)Form d)Page 31

Form d)This electrodeconstruction is vQTmYtbȼǤ4}ec.¾ȽI->"
mainly used in the chemical industry and in biotechnological4̶ǥ5¡2÷ņȼǤ̶ǥ
processes. The electrode features a large electrolyte vessel which is sometimes combined withan intermediate
electrolyte vessel.ǉ25
The electrolyte
can be pressurised andalso sterilised with5Ļ1̶ːȉŎĝLơ)̶̦ːȉ˭ʸ̕Lơ)>"̶ːȉ5òĦI
SIP hot
steam. A special electrode holder is required for this electrode. No laboratory application.
Thiselectrode construction>"
is mainly
used in the chemical Ȱç1̶ǥiƄˈ
industry and in biotechnological4ʶǵ2EHșʳ2őƅ4̶ǥLćG²Hİď
processes. The electrode features a large electrolyte vessel which is sometimes combined with
Form e)an."intermediate
electrolyte vessel. The electrolyte can be pressurised and also sterilised with hotɔɦƕȽ̄.5ȽFI>$M
steam. A special electrode holder is required for this electrode. No laboratory application.

Form
ŷȱ e)
e)
The above electrode construction is used in the laboratory where small samples have to bemeasured.

Form f)
The
above electrode construction is used in the laboratory where small samples have to beɔɦƕɭ.ŗ̜4_}LȒŊ"H42¾ȽI>"
measured.

Form f)
The feature of this construction is the flat membrane which enables the operator to measure thepH of surfaces, e.g. skin, leather, paper etc. HAMILTON supplies this electrode with an
unbreakable plastic shaft, as it will often be carried
49 around and used with a portable pH meter.
The feature of this construction is the flat membrane which enables the operator to measure theForm g)pH of surfaces, e.g. skin, leather, paper etc. HAMILTON supplies this electrode with anprocesses. The electrode features a large electrolyte vessel which is sometimes combined withan intermediate electrolyte vessel. The electrolyte can be pressurised and also sterilised with hot
steam.
Form e)A special electrode holder is required for this electrode. No laboratory application.

The above electrode construction is used in the laboratory where small samples have to bemeasured.
Form e)by T&C TechnicalThe above
electrode construction is used in the laboratory where small samples have to be
Form
ŷȱ f)
f)
measured.
The above electrode construction is used in the laboratory where small samples have to bemeasured.
Form f)The
feature of thisconstruction
the flat membrane which enables the operatoruoto measure the4Ǧ̇5ʞ
Ɋɭ4˂̺4
pHisLȒŊ"H'AŧF1VcʤLơ*->"pH of surfaces, e.g. skin, leather, paper etc. HAMILTON supplies this electrode with an
Form f)unbreakable
plastic shaft, as it will often be carriedaroundand used withpH
a portable
pH meter.
5îI2}cjkYɱǦ̇.ƬÀ
->"̅Ťh|4
ȒŊĝ/ʀ?
The feature of this construction is the flat membrane which enables the operator to measure theďK$-¾ȽI>"
pH ofg)surfaces, e.g. skin, leather, paper etc. HAMILTON supplies this electrode with anFormunbreakable plastic shaft, as it will often be carried around and used with a portable pH meter.
The feature of this construction is the flat membrane which enables the operator to measure thepH of surfaces, e.g. skin, leather, paper etc. HAMILTON supplies this electrode with anŷȱ g)unbreakable
plastic shaft, as it will often be carried around and used with a portable pH meter.
Formg)This construction is used exclusively for combination electrodes featuring a gel or polymer
reference
Form g) electrolyte. The shaft is made completely from plastic. This design makes the shaft
unbreakable as it is often used with a portable pH meter.
\H5LȽ'ĂȪ̶ǥLơ+ˇď̶ǥ."Ǖ»4ɱ5}cjkY.

This construction is used exclusively for combination electrodes featuring a gel or polymer
reference
The shaft is made completely from plastic. This design makes the shaft
FormH) electrolyte.
½FI->"
îI2Ǧ̇Lơ+/Fh|hQ}4 pH ȒŊĝ/ʀ?ďK
unbreakable as it is often used with a portable pH meter.
This construction is used exclusively for combination electrodes featuring a gel or polymer$-¾ȽI>"
referenceelectrolyte. The shaft is made completely from plastic. This design makes the shaft
unbreakable
as it is often used with a portable pH meter.
Form H)The above construction, pointed electrode, are normally applied in the food laboratory and in the
dairy
They facilitate the pH measurement in meat and cheese.
Formindustry.
H)
ŷȱ h)

The above construction, pointed electrode, are normally applied in the food laboratory and in thedairy industry. They facilitate the pH measurement in meat and cheese.
The
above construction, pointed electrode,are normallyapplied in the food͇ę̧Ã4ɔ
laboratory and in theȦƩˑ̶ǥǦ̇Lơ*->"I5̅Ťvhjd104ˆ̇Ǥdairy industry. They facilitate the pH measurement in meat and cheese.
ɦƕ.¾ȽI>"ʝ͆jd4 pH ȒŊLŎǆ2ʾ>"50

by T&C Technical

3.8 ó÷
3.8.1 ȒŊ̶ǥ4ó÷
¾Ƚ

-1İď.B";-4VcȒŊ̶ǥ5ó÷->"

ó÷4̌ɢ5̈ʈ.ˆ̇ż"2Ł>G>"ó÷4ÿĠ/-FIH¡ˈ1B45

1 ʤVc4÷ņǦ̇
2 VcʤÜ̕\ś4̦ƽ4ȨƓ̢
3 ȒŊ

Ȃȅ

2˲HVcʤ4ĹÌ4\ś2ő"H÷ņɉ%-ǫǠɉˀư

2EHó÷ǅF2ò̆Ůɉ2̊@İď
4 60℃L˳H͍ȑŮ4ǶȘȉ4ȒŊ
5 ͍̙ƈ/͍OUƈǶȘȉ4ȒŊ
6 ǔ¾Ƚǉ4̐ä1̶ǥacm

4ćGƘ ¿͒Ȃȅ/ÅŅ4ļƷÛĩɉ1ó÷ȱƏ.4ȒŊ̶ǥ4Ɇȱa) ƅɯǉ̦̢1Hb) ʤ4ƞƛĵĻ"Hc) c}*-H

Ȱ2OUǶȘȉd) ̹őɠ̶¹4#I4ɇȻ
VcȒŊ̶ǥ4ŒėLǻAH/5ċʡ."
Ȼ

-Hİď


/GK˕2Hě̈́ˇď̶ǥ4ƈʡLƊ÷$->"̅Ť4ȑŮȺĴ. pH4 F pH8 4Ťȑ4ǶȘȉL̈ʈ.ȒŊ
%4ȟħŒė5 18 ǐ/ʙFI>"-ɇ

90℃L˳HȱƏ.ȒŊ
51'İď5 2 ǐ.Œė21G>"'İď

by T&C Technical

͍OU Ȱ2 pH13 L˳HOUƈǶȘȉ2FI 90℃´4Ƕȑʇʈ

-Hİď

2 F 3 ̦̉.Œė21G>"

ʤ4ƞƛ4Ǆ c}4º fȦ4#I̹͑őɠ̶¹4#I͒ %IF5ȶ³4 pH
hLȽ-ǝǮ"H/.˅Ǯ.HɳĢÜ.˅ÑI>"ƅɯǉ̦4Ɗ÷5Œė4˂ɛ/1G>"ďƾBƅɯǉ̦èȽ2̐1/æƽI'İ̶ǥ2­ƭ"H´ĹƈʡLÓ2Ɣ"ƖǱ5G>$M

3.8.2 ĂȪ̶ǥ4ó÷
ĂȪ̶ǥ5ÿȸɉ2ó÷"H/5G>$M
ǿL̦̏->/.ɒ1*-̶ǥacm

4ŕ̶ƈacm-H4."4ƅɯǉ̦5ʎƐ21*->"Ø»ɕķI-

ĂȪ̶¹5

ǥŮ2Ā

(2ňŊ/ȺĴ2ʖ-5̶ǥ>/G>"

ĂȪ̶ǥ4ǏB̛ˈ1̕ã.H̯ʤ5
Ŋ"HǶȘȉ̯ʤL̅%IF4Œė5èȽȺĴ/ÅŅƿ>>"ĂȪ̶ǥ5̶ːȉL̶ǥɱÜ2ùãȕ'1GŤ2ȍȅ1ȱƏLÅ'1-51G>$M-Ü̶̕ǥȉ2×H/5˗I#Ȓ̯ʤ2HØ-4÷ņ

ąƅ5̓1-51G>$M͑3.4 ̽LĂȪ͒\̶ː˱LèȽ"HĂȪ̶ǥ5̶ːȉ4˅ÔL"HƄˈ11G

ÅŇ4˯ȽLºȐ>' %IF5̯ʤF4ƟƸ4'AHɢŮ4ƞƛĦð(ǏĻ 200kPa)Lơ)>"

4ƞƛĦð5ƿ4ƿđ(̶ǥ4Ĺ/ÜÌ).ɇȻ

cm

2Ž

2̎

̶ǥǺǚI-

̦4ʁ̌//B2ȒŊ

>>"

ȒŊ

ò-\̶ː˱4 KCl 4ȢŮ5ǉ-HǶȘȉ2EGŢ̚I->"ȑŮĸ÷B>'\̶ː˱4ŒėLɒ-HǶȘȉĂȪa͍ȑŮH5̆

>" \̶ː˱Lơ+ˇď̶ǥ5 60℃´452

by T&C TechnicalȑŮLơ+ǶȘȉ.¾Ƚ"H/5̓1-51G>$M. 25℃4ȺĴ.¾Ƚ\̶ː˱L pH2 F 12'İď4ĿŶ1Œė5ɹ 6 ǐ/ˊFI->"uo4g|(POLISOLVE)̶ː˱LȽ'ĂȪ̶ǥ5 pH0 2ʧH͍̙ƈLɛ"ǶȘȉ.¾KI>"
̪5 130℃21G

4ĂȪ̶ǥ5ŉØ2ÅŇLˈ/ʫɉ1Qo4 90℃LĻğG>"

->"


ȑŮ

̶ǥŤǉ

1304ȑŮ2FIʈ'İď %4Œė5ƇȠ2ɒ1G>" %4ȦLȸːƄˈG>"-̅Ť4ȒŊȱƏ.g|4ơ+Œė5ǏĻ 12 ǐ21G>"

53

by T&C Technical

3.9 ǝǮ
̶ǥ5ǝǮɷŮ´4ɷŮLB+/5.>$M Ɏőɉ2Ǯɘ1 pH ȒŊLʾ'A2
5

ǝǮLʾ/2Ȱç1ȁƍƄˈ."

3.9.1 pH Ǩȗʎˀȉ/©Ǭʎˀȉ
pH 4Ǯɘ1ǝǮLʾë2 Ǐå2̐ä1vk{Nȉ4×Ɩċʡ.Hɘ˝>"

pH ʎˀȉ5ų̙/ŵĲĭLơ+IF4̙4Ĳ͆4ȋďȉ H5ųĲĭ/ŵ̙
LB+IF4Ĳĭ4Ĳ͆4ȋďȉ."÷$#ňŊʎˀȉ5Ɓ̜4̙H5ĲĭòK*-Bĸ-H/ȰƂ."OUĥɩǨȗƙʿɔɦƕ(NIST)5 pH LǮɘ2ǝǮ"H2'G 9 +4ʎˀȉLȽH
/LƪĽ->" IF4ʎˀȉ5 pH c[4ĂȪȦ/-ȽFI>" ȒŊ2EGǶɼQT4?4ƤHʪL˙ǅ"H/5ċʡ."
NIST 4ˤďƿǿ.½FI'Ø-4ʎˀȉ5Ǩȗʎˀȉ/Ė6I>"
ǶɼQT4ƤHʪ5ȑŮÁŅƈHE2 Ø-4ʎˀȉ4 pH ÉBĐǧ." NISTǨȗʎˀȉ4ȑŮÁŅƈ5˂.ɛIH̅G." Ǩȗʎˀȉ5ɷŮ 0℃F 60℃4̦
.±0.005pH

60℃F 95℃4̦.5±0.008pH ´Ü/1*->"ƕ.Ṛ́ɉ2¾ȽI>"

ŝǤȽ̄.5mYrUvk{N͚©ǬʎˀȉLȽ>"©ǬǨȗȉ5ǨȗʎˀȉEGňŊ
.±0.02pH Lơ)˕˻I>"-Gˆ̇BEGɴü."ˆ̇·ɜ2EG%4ɷŮ5Ʌ1G>"%IF4ɷŮ5Ǐʬ4ȯȑŮÁŅƈ5̅ŤÅŅŎĝ2ǹȽ4©ǬǨȗȉ5ÅŅǓ̦ŊAFI->"̥œȱƏ. 1 ŨɢŮ."

NIST ʎˀȉ5ɔɦ

</M04ʎˀȉ5ǔŮ̥œ"H/ƹǐ4Œė/1G>"

ˀȉ5Ļǵ4 CO2 4Ź̻.ɒ1G>"
54/GKOUʎ

by T&C Technicaluo̥ɇ

'nWʎˀȉ5Ʌ1G>"%4͍ɷŮ5ˆ̇F 5 Ũ̦Å˙Ǭʎˀȉ5žǘ4ŒėFĻť2Ű̢I->"I>"

IF4Ȱ˗÷I'©

>'OUʎˀȉ4 pH9.21 / pH10.01 ʎˀȉ5̥œż.B̢ŒėLơ)>"%I&I4Ŏĝ2ÅŅI-Huo4ʎˀȉ5
ȒŊÉ/ǑõǓ̪ǅ˕I->"%4ę˱˙ǅIŋ̰4 pH˙ǅǍ5 NIST ă8 PTB 4ǬǨȗ2ocćFI->"

pH Values ofNISTStandard
SolutionsǨȗʎˀȉ4Buffer
pH É
ac cording to NIST
NBS
NBS
A
]p
Code
Temp. Potassium
tetraC
oxalate
0
5
10
15
20
25
30
35
38
40
45
50
55
60
70
80
90
95

1,668
1,670
1,672
1,675
1,679
1,683
1,688
1,691
1,694
1,700
1,707
1,715
1,723
1,743
1,766
1,792
1,806

B

H

Potassiumhydrogentartrate
3,557
3,552
3,549
3,548
3,547
3,547
3,549
3,554
3,560
3,580
3,609
3,650
3,674

C

Potassium Potassium
dihydrogen hydrogen
phthalatecitrate
3,863
3,840
3,820
3,802
3,788
3,776
3,766
3,759
3,755
3,753
3,750
3,749
3,750
3,753
3,763
3,780
3,802
3,815

4,010
4,004
4,000
3,999
4,001
4,006
4,012
4,021
4,027
4,031
4,043
4,057
4,071
4,087
4,126
4,164
4,205
4,227

D

E

F

Phosphate

Phosphate

Borax

6,984
6,951
6,923
6,900
6,881
6,865
6,853
6,844
6,840
6,838
6,834
6,833
6,834
6,836
6,845
6,859
6,877
6,886

7,534
7,500
7,472
7,448
7,429
7,413
7,400
7,389
7,384
7,380
7,373
7,367
-

9,464
9,395
9,332
9,276
9,225
9,180
9,139
9,102
9,081
9,068
9,038
9,011
8,985
8,962
8,921
8,885
8,850
8,833

B ̗ɓ̙ǶɼUR

H UR

C ̙ǶɼUR

D ̙Ĳ

E ̙Ĳ

F ĞR̙qoR

4ùǶĘȯ

©ǶɼYS̙Ĳ

I ȥ̙qoRG Ƕ̙÷UaR

55

G/̛ȥ̙qoR

10,317
10,245
10,179
10,11810,062
10,012
9,966
9,925
9,903
9,889
9,856
9,828
-

13,423
13,207
13,003
12,81012,627
12,454
12,28912,133
12,043
11,984
11,841
11,705
11,574
11,449-Page 35

A ĞaR̙UR

I

Sodium carbonate/ Calcium
sodium hydrogen hydroxidecarbonate

by T&C TechnicalPage 36uoɜˆOUʎˀȉ/ʫɉ1OUʎˀȉ4ňŊƈǳ˺

Stability Comparison of HAMILTON Alkaline Buffer to Conventional Alkaline Bufferƿ4ʎˀȉ5Ļǵ2FI'ȱƏ."

Both buffer solutions have been exposed to blowing air
9,3

9,2Page 36

pH

Stability Comparison
of HAMILTON Alkaline Buffer to Conventional Alkaline Buffer
9,1Both buffer solutions have been exposed to blowing air
9,3

9,0

HAMILTON
Buffer 9,2uo4DURACAL
pH9.2 ʎˀȉ9,2

Conventional
ʫɉ1ʎˀȉBuffer

pH

8,9
-12

¾Ƚ

9,1 0

9,0

'ʎˀȉ5Ť2ůǡ"HE2

12

24

36

Hours

48

60

72

HAMILTONDURACAL Buffer 9,2-Ɣ1.(Ó4Ŏĝ25ǻ
Conventional Buffer

4

Used buffer solutions should always
be discarded and never be returned to their original storage
8,9'Auo.5ÅŅŎĝ2¾ȽȎ?4ʎˀȉƔF1Ǧ̇Lơ+ŎĝL̥ɇ>
60 storage
12
24
36
48
72
bottle.
For this reason HAMILTON -12
have0 developed
a uniquebottle which includesa
Hourscalibration compartment with a non-return valve at the bottom, preventing the used buffer' to4WwkYo(CALPAK)5´4ȰƂG>"
solutionbe returned into the storage bottle. This CALPACK bottle is practical: no additional
Used buffer
shouldbe discarded andonly
neverthebe returnedto theiroriginal
calibration container
is solutions
required,
andalways
it is economical:
requiredamountofstorage
buffer solution
bottle. For this reason HAMILTON have developed a unique storage bottle which includes a1 ʎˀȉLãH'A4ŎĝƄˈ1
is used.
calibration compartment with a non-return valve at the bottom, preventing the used buffer
solution to be returned into the storage bottle. This CALPACK bottle is practical: no additional
The Practicality of the HAMILTON CALPACK Calibration Bottle
calibration
container is required,¾K1
and it is economical: only the required amount of buffer solution2 Ƅˈ1̜4ʎˀȉ
is used.
The Practicality of the HAMILTON CALPACK Calibration Bottle

ʷL̥H

̶ǥLş

oL

˽?ǝǮ"H=*-ɟ̜"Hůǡ"H56

by T&C Technicaluoʎˀȉ pH É/ɷŮ
ʎˀȉ

pH É

ɷŮ

ŝİâʲǉF4
ǑõǓ̦(ǐ)

uo

1.09

±0.02pH

60

nWʎˀȉ

1.68±0.02pH

60(NIST/PTB)

2.00±0.02pH60

3.06±0.02pH60

4.01±0.01pH60

5.00±0.02pH60

6.00±0.02pH60

7.00±0.01pH60

8.00±0.02pH60

9.21±0.02pH60

10.01±0.02pH

60

uo

11.00

±0.05pH

24

uo

12.00

±0.05pH

24

ǝǮL/H/%4ɷŮ5vk{NȉL˳H/5G>$M

3.9.2 ǝǮ4Ɩ̾sco4̶¹(ȸ˦É)/ØĐ!ƅɯL"H pH ̶ǥacm´ë2Bˢǅ

'̅G

5G>$M%4ȸȾ5̶ǥ4ơ+ĺǧ1̶¹4ŅħG

ȑŮ4ĸ÷2EG%4É

ĸ÷"HF."ȒŊ̶ǥĂȪ̶ǥã̴"H'A>'Ǯɘ.Þȶƈ4H pH ȒŊLʾ'A

5ȽH̶ǥacm

'B4

H5ʌ21*-Hˇď̶ǥLõǙɉ2¾Ƚ
pH h͖ockh

4Ȱƈ2ďK$HƄˈG>"Íʙ̶͗ǥʦ˷5ǝǮ4ʂǙˤƺIH/51 ȽH pH ̶ǥacm57

4ŉØƈLby T&C Technical˅Ñ"H'A2 mV ȒŊĝ.HhCockhLˤƺȉLȽH/. pH ̶ǥacm

>"

ǁɑ4ʎˀ

4Ȱƈ pH h2ąǈI>"

OqZű/nbhű4 pH h4̦25ǝǮ4Ɩ̾2̏G>" %4Ɩ̾2+-5%I&I4h4ćƘˢǅǍLĂȪ
Ƚ'ǝǮ2+-ɴü2ˢǅ>"

.5%I&I4hL>"

3.9.2.1 OqZh4ǝǮ
1)

2 +4Ʌ1*' pH ÉLơ+ʎˀȉLȽƍ"HƄˈG>"

1 +4ʎˀȉ5 pH ̶

Page 38ǥ4fȦ2ǏB˾ÉLơ+
pH7 L̒Ɲ
3.9.2.1
Calibration of Analogue pH Meters>"B 1 +4ʎˀȉ5¾Ƚ"H pH

1) Two buffer solutions of different pH values have to be selected. The pH value of one buffer4ɳĢ.ǏB̴I'ÉL̒Ɲ+fȦFâǘH̪G̴I-H/ǒ>I
solutionshould be as close as possible
to the zero point of the electrode assembly, which is,under normal circumstances, pH 7.

>"second
ŗ1/B
2pH 4̏Ƅˈ."ȒŊb̙ă8OU4̀ī4İď
The
buffer solution
should have a pH value
which lies as near as possible at the endof the anticipated measuring range and the value should differ as much as possible from thezero
solution, at least 2 pH units. 2 +Ɍ̙4̀ī1F 3 +Ɍ5OU4̀ī
5 3buffer+Ɍ4ʎˀȉƄˈ21G>"
If the measuring range covers the acidity and the alkalinity range then a third buffer solution is/1G>"%value-Ù2fȦF
2pHsolution
4̏Lơ)>"
required.
The pHof the second buffer
should lie in the acid region and the third
buffer solution should lie in the alkaline region of the desired measuring range. Both values
should differ as much as possible.

pHpH
4c[
Scale
0

1

2

3

4

5

6

ȒŊ̀ī
1 I
measuring
range

7

8

9

10

11 12

13 14

measuringIIȒŊ̀īrange
2

Slope
Î4ǝǮ

Calibration

Zero
CalibrationfȦ4ǝǮǣ˙
Verifying

HAMILTON
Buffer Solutionsuoʎˀȉ2) The pH value of any buffer solution is temperature dependent. Therefore the temperature of
the applied buffer solution has to be measured in order to establish the correct pH value of thebuffer solution.
58
The temperature adjustment potentiometer (manual temperature compensation) must be set
to the buffer temperature. With automatic temperature compensation the temperature sensor,
connected to the pH measuring instrument, must be immersed into the buffer solution.

SlopeSlope
Calibration
Calibration

2)

Zero
Zero
Calibration
Calibration

Verifying
Verifying

by T&C Technical

HAMILTON
BufferSolutions
HAMILTON
BufferSolutionspH ʎˀȉ5ȑŮÁŅƈG>" Ǯ  pH ÉLȽȒŊ"H'Aʎˀȉ4ȑŮ

The
valueof anybuffersolutionis temperaturedependent.
Therefore
temperature
2) 2)
The
pHpH
value
of anybuffersolutionis temperaturedependent.
Therefore
thethetemperature
of of
LȒŊ
>"
ȑŮ4ˤƺȽmah(ƖöȑŮ˅Ñ)5ʎˀȉ4ȑŮ2ď
theappliedbuffersolutionhastobemeasured
in
order
to
establishthecorrectpH
valueof
the applied buffer solution has to be measured in order to establish the correct pH value of thethe
buffersolution.
buffersolution.
K$ˤƺ>"ȑŮe_²-GʦöȑŮ˅Ñ¾Ƚ.Hİď5

ȑŮ

The
temperatureadjustment
potentiometer(manualtemperaturecompensation)
must
The
temperatureadjustment
potentiometer(manualtemperaturecompensation)
must
be be
setsetto thebuffertemperature.
Withautomatic
temperature compensation the temperature sensor,
to thebuffertemperature.
Withautomatice_Lʎˀȉ2ȇ
'ȱƏ2>"temperature compensation the temperature sensor,
connected
to themeasuring
instrument,
must
immersedbuffersolution.
connected
to thepHpH
measuring
instrument,
must
be be
immersed
intointo
thethebuffersolution.
ManualTemperature
Compensation
ManualTemperature
CompensationƖöȑŮ˅Ñ

Temperature
Dependency
Temperature
Dependencyuo©ǬǨȗʎˀȉof of4ȑŮÁŅƈ
Technical
bufferSolutionsTechnical
bufferSolutions

7,00
pH pH
7,00
Uis

Uis

zero

pH
7,00

oC

zero
o

C

o

C

slope

slope

pH
4,01

pH
7,00

pH
4,01

pH
pH 10,01
10,01

     
3)

̶ǥacm

LɺǶ.Ȃȅ

5
10
15
18
20
22
25
30
35
40
45
50

oC

HAMILTON
BufferSolutions
HAMILTON
BufferSolutionsuoʎˀȉ10,19
54,014,01 7,097,09 10,19
10,15
104,004,00 7,067,06 10,15
10,11
154,004,00 7,047,04 10,11
10,08
184,004,00 7,037,03 10,08
10,06
204,004,00 7,027,02 10,06
10,04
224,004,00 7,017,01 10,04
10,01
254,014,01 7,007,00 10,01
304,014,01 6,996,99 9,979,97
354,024,02 6,986,98 9,929,92
404,034,03 6,976,97 9,869,86
454,044,04 6,976,97 9,839,83
504,054,05 6,976,97 9,799,79'4) pH7(0mV)fȦǝǮLʾ>" ̶ǥacm

5ŗ1/B 1 ã̦5%4>>ȇȝ'ȱƏLÅ)>"

ʎˀȉ4É2˾/J.
Page 39ȒŊÉňŊ

'F%4ÉLfȦˤƺȽmah.ˤƺ>"f3) After rinsing the electrode assembly with de-ionised water, it is immersed into the first buffer
solution for the zero point compensation (normally pH 7 = 0 mV). The electrode assembly hasȦˤƺmah5@pH H5 pHas /˂ɛ -HİďG>"to stay in the buffer solution for a short time, at least for one minute, till the indication of the pH
meter settles near the pH value of the buffer solution (pH 7) and becomes stable. Thereafter
OqZ pH h4fȦǝǮ5̹Ť2̛ˈ." c}ǝǮLŋǀ"Hë2Ƅ
the indicated value has to be adjusted with the zero potentiometer to the exact value of thebuffer solution. The zero potentiometer is sometimes marked @pH or pHas.
#ʾ*-(For analogue pH meters it is important that the zero point calibration is always
performed
the slope calibration.
4) beforefȦǝǮɿ¦'ż ̶ǥacm 5ɺǶ.Ȃȅ 'ż ¤'mPka14) After the zero point calibration, the electrode0.²-HǶãLēK$>"assembly has
to be rinsed again with deionised water and dried with tissue paper.
When drying̶ǥ4ȣILćHǉ5ʆő2"*the electrode, care must be
taken not to rub the membrane, i.e. only dab˹the electrode-ǶãLćF1.(with tissue paper. Under nocircumstances must an electrode be rubbed.
̶ǥ4˂̺L''E2˂̺4Ƕ
This might introduce
static electricity into theglass shaft of the electrode and could makean accurate pH measurement impossible forhours.

No rubbing!
ƲF1͐͐

ƲF1͐͐

59 second buffer solution (acid or base –5) The electrode assembly is then immersed into theaccording to the measuring range). After the indication of the pH meter has stabilised, theindicated value has to be adjusted with the slope potentiometer to the exact pH value of thesecond buffer solution. The slope potentiometer is sometimes marked 'mV/'pH.

Page 39

by T&C Technical3) After rinsing the electrode assembly with de-ionised water, it is immersed into the first buffer
solution for the zero point compensation (normally pH 7 = 0 mV). The electrode assembly has
to stay in theãL/G>"
buffer solution >'̶ǥ4˂̺L"HE1/5ʆő2
for a short time, at least for one minute, till the1.(
indication of theI
pH
meter settles near the pH value of the buffer solution (pH 7) and becomes stable. Thereafter
the indicated5̸̶ǵL̶ǥ4Vcɱ2ɇȻ$value has to be adjusted with the zeropotentiometer to the exact value of theƹǉ̦Ǯɘ1ȒŊʡ21G>"
buffer solution. The zero potentiometer is sometimes marked @pH or pHas.

5) ̶ǥacm5©ɄɌ4ʎˀȉ2ȇ>"(ȒŊb2E*-̙B
For analogue
pH meters
it is important thatthe zero point calibration5OU
is always
performed before the slope calibration.
L̒Ɲ)pH h4ÉňŊ'żc}ˤƺȽmah.ʎ

4) After the zero point calibration, the electrodeassembly has to be rinsed again with deˀȉ4É/ʨ"HE2ˤƺ >" mah4˂˕5 ΔmV/ΔpH /ionised water and dried with tissue paper.
When drying the electrode, care must be˂˕IH/BG>"
taken not to rub the membrane, i.e. only dab
the electrode with tissue paper. Under no͓ c}Lˤƺ 'żfȦ2ÞŮȇȝȒŊÉLɘ˝ >"circumstances must an electrode be rubbed.
No rubbing!
This might introduce static electricity into the͓ ǝǮ½Ǥ5Ƅ#̈ʈ -ŋǀ -( ̦L-ʾ/ǝǮ4Æ̓ƈļglass shaft of the electrode and could makean accurate pH measurement impossible forKI>"
hours.
6) ȒŊb̙ă8OU4ƿL¾Ƚ"HİďɄɌ4ʎˀȉLɘ˝4'A¾
5) The electrodeassembly is then immersed into the second buffer
solution (acid or base –according to the measuring range). After the indication of the pH meter has stabilised, theȽ has>"to befȦ4ǝǮLɿ©ɄɌ4ǝǮȦLɿ'ż
ɄɌ4ʎˀȉ.ȒŊ
indicated value
adjusted with the slope
potentiometer to the exact
pH value of thesecond buffer solution. The slope potentiometer is sometimes marked 'mV/'pH.
bǮ

ɘ˝

>"

4/̶ǥ̙ˡş

OUˡşɇȻIt is advisable to re-check the zero point after the slope calibration has been performed.

1

It is of utmost
importance/2ȁƍ
>" that the above calibration sequence must be adhered to,otherwise no valid calibration will be obtained.
7) ȑŮ2EHˡş6) If the measuring
range covers/GKƟƸ̶¹/ɭȑʍ­şȦ2EGɇȻ"HˡşLâǘH̪G
both the acidity and the alkalinity range the third buffer solution
serves as a verifying solution. After the zero point (with the first buffer) and the slope
ɾŖ2"H'A
calibration (withthe second ŋ̰2̶ǥ¾ȽIHǗµ4ȑŮ.ǝǮL/H/ǒ>I>"buffer) has been accomplished, the calibration over the entire
measuring range has to be verified with the third buffer solution (be aware of acid and alkaline
errors). 8) ǝǮǮŤ2ŉ¦ 'F ¾ȽȎ4ʎˀȉ5ůǡ >" ÞèȽ H5Ŏĝ2Ɣ

7) In order to keep the temperature error as low as possible, especially"/5ʆő2ʾK1.(errors due to the diffusion potential and the isotherm intersection point,
it is recommended that the calibration be executed at the temperature
at which the actual pH measurement will be performed.
8) After the successful calibration the used buffer solution should bediscarded. Never re-use buffer solution and never return it to its
original storage container.

6)

7)Technic
al Buffer Solution

pH 4,0 1

60

by T&C Technical3.9.2.2 QY}ek_L¾Ƚ
QY}ek_L¾Ƚ
Q˓ĝ/' pH h.4ǝǮ

-H pH h5ɔɦƕ%-ĺèȽI->"-ȼǤ}o4Th|hQ}B¯5QY}ek_.

pH ÉLȜɰ˂ɛ"HE21*->"IF4èȽƿǿ5̹Ť2üɺ.""H®5rVQp2žǝǮLŋʾ>"

1EVQp"HǫʡLơ*-H'A

IF4ǫĝ5ˡ*'ćGƘLɇȻȒŊS5̹Ť2ŗ11*->"%4ǝǮƖ̾5OqZh/5%I<0ĻĸKG>$M."

pH7 4fȦǝǮ5Ƅ̿.511G>'©Ȧ4ʎˀȉ5Ƅˈ

©+4ʎˀȉ5̒ƝfȦ

5ǝǮL""AHʦöɉ2ɰâI>"

2ž˓ɰI

c}

-H

b4cw4ŁA/ɿKG4Ȧ2˾/JLȽ>".";-}Z

̅ŤƱ½

ɭȑ­şȦ

ʫɉ25´4Ɩ̾.ǝǮ5ŋǀI>"1 ©+4 pH É4Ʌ1HʎˀȉLȽƍ
ŁȦ2˾/JL̒ƝL̒Ɲ>"

ɄɌ4ʎˀȉ4 pH É5ȒŊcw4̥>" ©ɄɌ4ʎˀȉ5ȒŊb4cwȦ2˾/J>"ǝǮp˲ö'ż ǝǮr5ǝǮ4Ɩ̾L½Ǥǲ2ɑF$>" İď2E*-5ʎˀȉ4ÉLƖö.×ð"HƄˈG>" ȶħ5ʎˀȉ4ÉLʦö.æŊ
-ǝǮȦLćſ
2 ʎˀȉ4ȑŮ5>"
pH ̶ǥacm

2²Ś"HȑŮ˅ÑȽȑŮe_LȽH

5ü»4VcȑŮ˓LȽȒŊI1-51G>$M ȑŮ4É5Ɩö.×ð"H H5h2ȑŮe_ćG²FI-Hİď5ʦöɉ2ȒŊI>"
pH ̶ǥ4ćGƘ5 3.9.2.1 ̽.̀;'4/Đǧ4ćGƘ/1G>"61

by T&C Technical3.9.3 ÞǝǮ
pH 4ǝǮ5ĔǓɉ2ŋʾ
%4ȸȾ/

1-51G>$M%4ĔǓ5Ŋʗ"H/.>$M-´4ˈɼG>"a) ȒŊ"H pH 4Éb) ȒŊ"HǶȘȉ4ȱƏc) ȒŊ"HǶȘȉ4ȑŮd) ̶ǥacm

4¾ȽǓ̦e) ˈǸIHɷŮǝǮĔǓ5ǉ̦ǂ̉H5ǐü¹G>"%-Çç4¾ȽȱƏ2ƅ!ɘɩ"HƄˈG>"°ǧ4ãF1}ecǶLȒŊ"Hǉ͂ʑ2ŋǀǅɘ1ĸ÷ǝǮ2E*-ɘ˝I1İď5¸6>"

Ǐå5âǘH̪GǝǮLǝǮ4ĔǓLŽ

->"

2Page 41ǝǮ4ĔǓ5ŋ͌ɉ2ɘɩI>"
The Frequency of re-calibration
has to be established experimentally
Ma y
2002

C alibra
pH ! teCalibra
pH ! teCalibra
pH ! teCalibra
pH ! te CalibrapH ! teCalibra
pH ! teCalibra
pH ! te

3.9.4 ƅɯǉ̦

3.9.4 Response TimepH ̶ǥacmLʎˀȉ2ȇȝ
pH É11˂ɛI1/ǮŤ of
If a pH electrodeassembly
is immersed 'ʎˀȉ4
into a buffer solution,
it does not show the pH valuethat buffer solution instantaneously. A response time of approximately 30 seconds is normal inpH ̶ǥacm4ƅɯǉ̦5<=30 ɞ.
0.01pH(0.6mV)´Ü2é̎4'A
order to1reachthe buffer value
with a toleranceof 0,01
pH units (0,6 mV). For>"
this reason
it isvery important to wait long enough during the calibration cycle for the indication of the pH meterto become stable. Only then can the indicated value
62 be adjusted to the buffer value. A prematureinterruption of the electrode adaptation to the buffer value is often a major source for incorrect pH
measurements.

The response time of an electrode assembly is especially slow if the electrode temperature andby T&C Technicalhʎˀȉ4 pH ÉLňŊ
" %

-ňŊ

-˂ɛ"H'A2 ƅɯǉ̦5ùã2/HƄˈG>'/J. pH ÉLǝǮʎˀȉ2×I'ǉ>" ˡ*' pH ȒŊʾKIHÿĠ4ĺ5

̶ǥ4ƅɯùãňŊ-1ȱƏ.ǝǮ

-H/ÿĠ.

H/EˊĈFI>"̶ǥ4ȑŮ/ʎˀȉ4ȑŮ4̏ 10℃´HİďʙFI>"
4ȑŮLHE2
E2>"'ʎˀȉ4ȑŮ2̶ǥé̎"H>.

ʎˀȉ

ǝǮ5Ż+

>"

̶ǥacm

2¾ȽI-HÅŅȽȘȉÿĠ/ʙFIHİďG>"

1̶ǥLʶɂǶ2ÅŅǅF2ƅɯD*G
/

òȑ

4İď

1.('B421G>"4ȱƏ.ÅŅ

>"/

¾Ƚ

-

̶ǥacm

5

3mol/L 4 KCl ǶȘȉVc̶ǥ4ÅŅȽ-ɄÒI->"QY}ek_.½FI' pH h5ňŊ'/4ǝǮÉL§ȒǃǝǮLɿH}ZLơ*->"͑ǝǮȦʦöćſǫʡ͒ ǣ˙ȒŊLʾ/4ʦöǝǮȦćſǫʡ5ƾ

'É/ǳ˺̶ǥLȽ'İď2-ǉ̦L-ňŊ

0.01pH L˳1ɳĢ2Ć>H/Lɛ

63

->"

'ȱƏ.ȒŊ

by T&C Technical3.9.5 ǝǮǉ4ě̈́/%4ÿĠpH ȒŊacm

3 +4ʬɑFI'ě̈́2ɍ̺"H/G>"LǝǮ"H/

1 fȦǝǮŉ¦2

2 c}ǝǮƓñ

1

3 ̢ƅɯǉ̦(3 ã´)ÿĠ2+-ǏBEɘ˝IHB45´4̅G."a) ¾Ƚ'ʎˀȉǺǚ

ʎˀȉL¾Ƚ

-HH5Ǔ̪äI.H-'b) ĂȪ̶ǥ4̶ː˱ǺǚI-Hc) Œė2̎d) ¾Ƚ-H̶ǥacm-H̶ǥacm

2ʖI'

̙.Ȃȅ

̶ǥLȍƧ

'̰

H5̯ʤı*-H

L¾Ƚ

-H

ùãǶĘ÷I-1(̢Ǔ̦¤ȫ'ȱƏ'/2ɇȻ)e) ȒŊ̶ǥ4ʤ2¥˄ɇȻf)

H5̦̏*'-H

˂̺Lšɭ.Ʋ*''A2̶ǥacm

2̸̶ǵɇȻ

-Hg) ̶ǥ/ʎˀȉ4ȑŮş 10℃´Hh) pH ̶ǥ4fȦ/ pH h4fȦ4̏ I5̹Ť2>I1[c." ̅Ť pH7 LfȦ/0mV Lĭȗ/Ȧ pH7 /5ĻɅ1Hİď2ɇȻ
i)

̶ǥacm

->" ¿Ĺɉ2̶ǥ4f>"/ pH h4Ʃʈ2ě̈́Ȼ!-H[|Ü4ƽʍH5aoH5Ʃʈ}Z4ě̈́͑Ȕǵ2EHó÷͒64

by T&C Technical

3.10 ǓŻIHɷŮ
pH ȒŊ4ɷŮ5ĺ4ˈɼ2ŞČI %4ˈɼ5êƀ.HİďBI6%.1İďBG>" êƀ.1ˈɼ2+-5 %I pH ȒŊ2HŹ̻Ů4Ůď5ǥ
ɪ.5G>$M

êƀ.Hˈɼ2+-5ɋˌLʾ%-ċʡ1̪G%4Ź̻LŖ"HƄˈG>"pH ȒŊacmAǮ

4ǝǮ5ǏB̛ˈ1ˈɼ4 1 +." ͍ȒŊɷŮLɘ1B42"H'ǝǮƖ̾LŇG>"ùãňŊ"Hǉ̦L/HE2

ƾ

%

>"

-Ǯɘ1ʎˀȉLȽ

ǝǮ4'A4ȒŊÉǝǮ4ĔǓ4ǉ̦5ċʡ1̪GɒȒŊ4ɷŮ5ǝǮ2B)'ʎˀȉ4ɷŮ´2E1H/5ǻ

>"-G>$MpH
4'AâǘH̪Gʎˀȉ4ȒŊ5ȸƌɉ1ȱƏ.ʾE2>"

ȑŮ5 pH ȒŊ4ʂǙ2Ź̻"H/LƳA-ʕG˿>" ͍ɷŮLʉơ"H'A

25

ȒŊ

/ǒ>



˕

-HǶȘȉ4ȑŮ/ǝǮ2¾Ƚ"Hʎˀȉ4ȑŮ5âǘH̪G˾,H>' pH ȒŊIHǶȘȉ4ȑŮ5Ǯɘ2ȒŊI1-51G>$M

ċʡ1F6ȒŊ"HǶȘȉ4ȑŮLŊ2Å+E2"H/.ȑŮ˅ÑLõǙɉ2¾ȽâǘHE2

͍ pH ȒŊɷŮLʉơ>"ĂȪ̶ǥ5}ec4ǶȘȉ4ĦðEG 100kPa òĦI-HƄˈG>" I5ĂȪ̶ǥ4̶ː˱4ȄILʉơ
L̨ǭ

>"

ȒŊ

-HǶȘȉĂȪ̶ǥÜ4̶ː˱2Â×"H4

̯ʤ5Ť2ȍȅ1ȱƏLÅ'1-51G>$M

4°ǧ2ďK$̐ä2̒Ɲ"H/.

̯ʤ4°ǧ5ȒŊő˪ȒŊ4ě̈́4ːȈă8ȒŊɷŮ4Ļť1ƳĜʾ

>"

65

by T&C TechnicalĂȪ̶ǥÜ4ŕ̶ƈ̶ǥacm/ȒŊ̶ǥÜ4ŕ̶ƈ̶ǥacmȒŊ̶ǥÜ̶ː˱

ĂȪ̶ǥÜ4̶ː˱5Đ.1-51G>$M

ȒŊ̶ǥ4Vcʤ5Ť2ȍȅ1ȱƏLÅ'1-51G>$M
ŊɷŮLƇȠ2º$ǓŻ"HɷŮ5Vcʤ4Įɤȯ5Ȓ

ǥɪ1İď25ȒŊʡ21G>"

ŋ˱ɉ2̎Ɠ.HʂǙLğH/5G>$M

ùã2ǶĘ÷I'̶ǥ 1012Ω 4×ðQzicLơ+ɷŮ4͍ňŊh2ƩʈI'İď

' pH 

%4ȶŋɉ1ɷŮ5±0.03pH F±0.05pH 4̦21G>"

ɔɦƕ4ȺĴ.5±0.02pH ̎Ɠ.>"4. ̶ǥ4ćGƘpH ȒŊacmcm

5Ǖ˱ɉ2ÅŇ4͂Ů͍ȯ."

4ǝǮ/Ȃȅ2đFI->"5 pH ȒŊacm

</M04ÅŇ4ȃö5 pH ̶ǥaÅŇǓ̦2H̶ǥacm

4Ǯ

ćGƘ

Ø»2ʖHȸƌɉ1ǫʡLʉơ"H'A4ǏB̛ˈ1ˈɼ/>"̐ä1ćGƘ5̶ǥ4ŒėLǅɈ2ʐAH5Æ̓ƈ4ºȒŊ/1G>"
4ǮćGƘ5ȒŊʂǙ4ƳĜ4?1F#̶ǥȨ͋1]co4ĵĻL̨>"

4.1 ÅŅ
pH ̶ǥacm4ÅŅLʙ'İď Çç4̶ǥ.ǦƓI' pH ̶ǥacmĂȪ̶ǥç

21*'B4)/ˇď̶ǥG>"
66

(ȒŊ̶ǥ

>'ÅŅǓ̦BʙƑ"HƄˈG

by T&C Technical>"͑ƹ̦̉

ƹǐH5ȒŊ/ɒǓ̦4ÅŅ4ʕG˿

10͒

4.1.1 ȒŊ̶ǥ4ÅŅ
ȒŊ̶ǥ5̢Ǔ̦ÅŅċʡ."
̅4Ƕ̍Ƕ2ȇ"

1F ¾Ƚ"Hë2̶ǥ5Ƅ# 48 ǉ̦´Ǌ

H5K#2̙ƈ4ǶȘȉ2ȇ

Vcʤ2\śŷƓIH4LŻ)>"
̅Ť̶ǥ5"2¾Ƚ.HȱƏLÅ*->"ǶĘ÷'ȱƏ.âʲ-Gcʤ2ćG²->"ƈ4ȘȉLȽ>"</M04ˆ̇·ɜ5%4ȒŊ̶ǥL}cjkYH5^

ˆ4Wk}2ȉ»L×IV

4Wk}5Ť2ȉ».ȕ'I

Ƕ̍ǶB

5ų̙

4áȸ2EGVcʤ5ǶĘ÷IĹÌ4\ś5ùã2ŷƓ

I>"ȒŊ̶ǥȒŊLĔǓɉ2ŋǀ"H'AɒǓ̦4ĔǓ.ÅŅIHİďǥLǶ̍ǶH5ų̙ƈ4ǶȘȉ2ȇ"E2>"%4Ǔ̦5̶

H5ʶɇL̨Ǧ̇Lơ*'VcʤÅ˩ȽWk}2Ƕ̍ǶH5ų̙ƈ4ǶȘȉL×IțI1E2ć
G²-ÅŅ

>"âʲǉ2²-*'Wk}5Ʀ-#2Åɱ67--(Page 44

If a measuring electrode has to be stored for short periods between measurements it should be
immersed in a container filled with tap water or be fitted with a watertight plastic cap filled with tap
water. Therefore one should not throw the supplied plastic caps away. They should
kept forby T&C be
Technical
re-use.
4.1.2
ĂȪ̶ǥ4ÅŅ
4.1.2 The
Storageof Reference Electrodes

Referenceelectrodes should̯ʤLÅ˩"H'A2ĂȪ
always be stored wet,ĂȪ̶ǥ4ÅŅ25
i.e. the diaphragm has to be covered with the samereferenceelectrolyte with which the referenceȽ̶ːȉ/Đ!̶ːȉLȽ3I'ȱƏ2>"electrode has been filled. Wet storage must also be
applied Ȱ2̢ǓÅŅ4İď5¤1E2ȁƍL
when the electrode is stored for a long time. It is not advisable to store reference electrodes dry as
(̅Ť5 will
3mol/L
4 KCl
LȽ>"
the referenceelectrolyte
slowlypenetrate
throughthe diaphragm and crystallise and subsequently cover¤'ȱƏ2>"/̯ʤL̅!-Ü̕4̶ːȉ
the completebottomof the electrode. The
crystallisation itself does not cause a problem but the̶ǥ4Ĺ2ǚ?â
referenceelectrode might dry ̯ʤʂǋ÷out completely'̶ː˱
whichwill result in a substantial increase in the diaphragm.Ǭɫ2ˉKI->"ʂǋ%4B45ě̈́
resistance.
Even when the referenceelectrode isrefilled with its respective electrolyte, the highLȻ!>$M
diaphragm
resistance will¤'ȱƏ5̯ʤƞƛL1G
not disappear immediately
and will result in large measuring errors or even makeǄ$>"
4ȱƏ5˅ÔȉĹò -Bɍ
a measurement
totally impossible.

˅ÔȉȽ̥̤ʷ5̤!>"
Closedrefill apertureKCl
3 mol/lor̶ːȉ(KClRubber
3mol/L)plastic cap
Lȕ' '
̯ʤL
filled withˉWk
} L ć electrolyte ( 3 mol/l KCl)
reference
G²>"

Therefore for short or long periods of time it is essential to store reference electrodes in their
G>$M ͍̯ʤƞƛ5Ļ1ȒŊˡşH5ȒŊØâǘ1ȱƏ2 >"respective reference electrolyte, with the refill aperture closed by a suitable stopper.
Storage%4'AɒǓH5̢Ǔ4ÅŅ2̧KF#
in tap water or in distilled water should be Ƅ#ĂȪ̶ǥ2¾ȽI-H̶ːȉ.̯
avoided. Any penetration of these liquids
through the diaphragm will increase the diaphragm potential considerably and will significantly
falsify thesubsequent pH measurement. >'˅ÔȽ̥̤ʷ5̐ä1ĤŊÚ.̥1E2
ʤL3I'ȱƏ2Å*-(-(
4.1.3 The
Storage of Combination Electrodes

A combinationelectrodeconsists of a measuring
electrode and 1.(a reference electrodecombinedǶ̍ǶB5ɺǶ5ÅŅȘȉ/-ĂȪ̶ǥ25¾ȽǶ5̯ʤL̅
into one single-rod electrode. The storage conditions must therefore be suitable for ameasuringand for a referenceelectrode.
As every referenceelectrolyte
is an aqueouš ĂȪ̶ǥÜ:/Â×>"%4ʂǙ̯ʤ4̶¹ǄǮɘ1pH ȒŊʾ11
solution it has been found that the optimum storage liquid is the respective reference electrolyteof that combinationelectrode. The refill aperture has to be closed during storage time.
G>"
All that has been stated about the storage of a reference electrode applies equally to the storageof a combination electrode.
Gel-filled combination electrodes are an exception to the rule. These electrodes have no refill
4.1.3 ˇď̶ǥ4ÅŅ
aperture and the drying-out of their diaphragm has to be avoided at all costs. Therefore gel-filled
combination electrodes must be stored wet in a 3 mol/l KCl solution.
ˇď̶ǥ4İď5ȒŊ̶ǥă8ĂȪ̶ǥ4ƿLÅŅ.HȘȉLȽ>"̅Ť5ĂȪ

This statement applies to polymer electrodes as well.
̶ǥ2¾ȽIH̶ːȉLȽÅŅ
ď5>"˅ÔȉȽ̥̤ʷ5Ƅ#̤!'ȱƏ2ĂȪ̶ǥ2˅ÔʾH°ǧ4ˇď̶ǥ4İ
-(
68

by T&C TechnicalĂȪȽ̶ːȉ2\̶ː˱L¾Ƚ-Hİď

ĂȪȉ4˅ÔǫʡLơ'Ȩ'A

1E2ȁƍ"HƄˈG>" Ƅ# 3mol/L 4 KCl .ĂȪ̶ǥ̯ȱƏ5ʆő2ɇȻʤȒŊ̶ǥ4VcʤLÅ˩

¤ȫɇȻ



I5̶ː˱L¾Ƚ

-HĂȪ̶ǥ2-BĐ!Ƙ."

4.2 ̶ǥacm-1ɘ˝LʾE2

-(

4Ȃȅ

ŝǤȽ pH ̶ǥacmʂǙ¤ȫ5}ec2EGVcʤH5̯ʤ4ǺǚɇȻ´4ě̈́ˇď

-ɇȻ

>" %4

>"

a) fȦ4#Ib) c}4ÎHc) ̢ƅɯǉ̦
5ȸƌɉ1 pH ȒŊLʾHE2"H'A Ť2̶ǥ4ȍƧƄˈÿȸɉ2̶ǥacm
."%4'AŊǓɉ1̶ǥ4ȍƧ5̅Ť4ÅŇ4ǂɢ/5ç2˖HƄˈG>"

Ȃȅ4͂Ů5ȒŊ-HǶȘȉ2EG>" 4'AÇ

Ň4ĔǓLɘɩ"HƄˈG>"

4 pH ̶ǥ2ď*'ŊǓɉ1Å

%I5ƹǉ̦ǲH5ƹ̦̉ǲ/Ʌ1*->"´2Ǻǚ4ɣ͆2EGȽHȂȅ4ƿǿL>" %4ż Ȃȅż4 pH ̶ǥ4ćGƘƿǿLˢǅ

>"1͕Ȃȅƿǿ
͓ ʺA'

ƈȂìLȽ-Vcʤ4ĮɤȯLćG̫

H5̯ʤ4²ɐȯLćG̫>"
͓ UaR4²ɐ5 0.1mol/L 4 HCl 2ƹã̶̦ǥLȇ͓ ǾãH5ʢʟ4»ɤ2őćG̫>"-̛ǎ͑ȥ̙ǶɼqoR
69

͒4ǶȘȉ

B



by T&C Technical5̛ǎ4ǶȘȉ2YS̙LȘ
ƿǿ.ǺIćI1İď

̦ȇȝ

>"

͓ ɗ÷ȯLĒM(ǶȘȉLȒŊ->"̯ʤ) ̶ǥ2²ɐ

4' 0.1mol/L 4 HCl ǶȘȉ2ƹǉ͓ ȨǫɊʤ5ʫ2Ȅ̅"HVcYqL¾Ƚ÷̟2ąƅćG̫>"'̶ǥ5Vcʤ/̯ʤǺǚIC"Îđ4İď5 1%4}aLȘ-E26Fȇ

SjO].ɒǉ̦Ȥ.?>"͓ hwY˱LĒ@ǶȘȉLȒŊ
G>"

'ǶȘȉ2

-Hİď

>"

ĂȪ̶ǥÜ4̶ːȉ4</M05Ĳ

4ąƅ5ɗ÷̟4ǺǚL̯ʤ2Ȼ!>"(͏ʭ21*''ɗ÷̟4ĮɤLćG̫25jTŘɼ/Ĳ̙Șȉ2̶ǥLȇŉØ2ʭƜH>.ƴʖ͓ ̹Ť2ćI2Įɤȯ2ő

>"-5̙̌÷ǶɼH5Ǭ¬Ĳɼ̙qoRLȽ>"͓ ±4̙H5OU2Șː"HĮɤȯ2ő

-5 0.1mol/L HCl H5

0.1mol/L NaOH .ƹã̦Ȥ/.̫ā.>"2͕Ȃȅż4áȸ̶ǥ4ȂȅLɿ¦>'F

Ƅ#̶ǥLÅŅȘȉ(3mol/L KCl)2 12 ǉ̦´ǶĘ÷2EHVcʤ4\ś4ŷƓ4'A .I6 1 ǂȇ--(͙ǝǮ͛ȂȅȘȉ5̯ʤ2ȇ̃
4ǶĘ÷Lʾ*'ż
Ȃȅ5

Ȥ



ȇȝ

ƟƸ̶¹Lĸ÷$HB

I>$M 4'A̶ǥƄ#ǝǮLʾ*-(4©+4ȱƏ.ʾ*-(70ǫǠɉ2̶ǥLȂȅ"H/

by T&C Technical5ʾK1.(͘š


̶ǥLķ

ɇȻ

>"

qQ{H5̡è1̍Úɭ.˂̺LƲ*'G>'š.̶ǥ˂̺4ǶǵLƠć*'G

̶ǥ4ƅɯ̢ǉ̦ɇȻǹȽɉ1̙Ȃȅȉ

1.(1.(̸̶ǵ11HƉIG>"OUȂȅȉ4ȢŮ2+-5´4ÉLƪĽ

>'IF4ȢŮ4Ȃȅȉ5uoEGwk[b2

-Àʄ

->"
->"

Ȃȅȉeko͗PN 238290
Ȃȅȉ A Ƕ̙÷qoR

500mL

ǶȘȉ(<3%)

Ȃȅȉ B Ĳ̙ǶȘȉ͑4%͒

500mL

3mol/L KCl

500mL

ÅŅȉ

4.3 ĂȪȽ̶ːȉ4˅ÔH5­ƭĂȪ̶ǥ

H5ˇď̶ǥ.ĂȪȽ̶ːȉLȽ-HİďLŤ2ɘ˝"HƄˈG>"-H̕ãLɘ˝'F

2Ǽ@>.ùã2˅Ô̶ːȉ4ȉ̺G̶ǥacm˅ÔȉÔĳ̥̤ʷL̥>"ĂȪȽ̶ːȉ4Ôĳ~̶ːȉF̷â̶ːȉL̶ǥacm

̶ːȉ4

4½Ǥ5abH5zkoLȽH/ɴü2ʾ>"ĂȪȽ̶ːȉ2ȒŊ-HǶȘȉȋ×

ã4ʶɇ2EGǄ-Hİď-HİďH5ĂȪȽ̶ːȉ4ȢŮǶÜ̕4̶ːȉ5ŉØ2­ƭ"HƄˈG>"uo5%I&I4̶ǥ4ɣ͆2ƅ!ɴü1ćGƘƿǿ/ÅŇ2+-4ˢǅǍL̶ǥ/Ù2ƬÀ->")FLƄ#ĂȪ("H/ċʡ."71

I2EGǉ̦/˯ȽLɲɹ

by T&C Technical

5. pH ̶ǥ4 pH h:4Ʃʈ
5.1 ȒŊ̶ǥ4Ʃʈ[|pH ȒŊ̶ǥ5Ǖ˱ɉ2͍Ü̕ƞƛLơ*->"͑ǏĻ 5×109Ω 4B4G>"͒ %4'A pH hH5ockh:4Ʃʈ5FDH̶əŀōLȻ!C"ȱƏ."

4'A4Ȱç1͍ˈǸ pH ȒŊȽ[|4ę˱2ǸAFI>"ȒŊ̶ǥ5Đ˸[|LȽÆčL̂G>"%4tQd̑ʹǦ̇2EGtQdLºƚȒŊĝ:/4[|5͍ʆʏƞƛLơ)zic(1012Ω)EG͍ȯLȽ>"%4É5Ť2ȒŊĝ4ơ+×ðQ̅ŤĐ˸[|4ʆʏƞƛ5 1m 'G

1014Ω F 1017Ω G>"%I´Ĺ4°ǧ/-[|4̶ǵŎ̜G>"

I5ȒŊ

-HÆč4ǉŊƹLĵĻ$H'Aċʡ1̪GºB4L¾>" ʁ͌ɉ2 pH Ʃʈ[|4̶ǵŎ̜5
150pF/m EGºB4L¾Ƚ
pH ̶ǥacm>"

200pF/m 4[|Ŏ̜4B4L 50m Ƚ>"/FHƅɯÆč 50 ɞ̋I-h2ř>" ȶħ pH ŔȽ4Đ˸[|5%4̶ǵŎ̜ 64pF/m F 102pF/m 4B4¾ȽI->"pH ̶ǥƩʈ[|4ŊǟȑŮ2+-pH ȒŊ 70℃´4°ǧ.5Ǩȗɉ1 pH Ʃʈ[|ơ+ŊǟȑŮ5-30℃F+80℃/1*->"130℃>.őƅ"Hİď5Ȱç1[|LȽ>"

5.2 ĂȪ̶ǥƩʈ̮[|ĂȪ̶ǥç2ćG²FIHȒŊǫĝ4İď
72

̶ə̱ō2őƅ

'[|LȽH̪by T&C TechnicalG[|5%I<0Ļ1ě̈́21G>$M
ŊǟȑŮ5ȒŊ̶ǥ/Đǧ2̒Ɲ̅ŤǨȗ4Đ˸[|L¾Ƚ

>"'°ǧ/Đ!/LʙƑ

[|

>"

5.3 ˇď̶ǥƩʈ[|ˇď̶ǥ2-BȒŊ̶ǥ/ĂȪ̶ǥã̴>"LǕ.>/AH'A͍ʆʏ©̛apĐ˸[|͑oQOkYc[|͒LȽHE22>"Đ˸[|4Ü̕ap5ˇď̶ǥ4ĂȪ̶ǥÌ2Ʃʈ"HE>"5.4 [|4ȗÍ/̖ʖ
pH ƩÐ[|4Ü̕ŕ̶»4ʆʏ»5

̠ʍ4ka͑ap͒.̑ʹI-H

(.1͏ʭ4ŕ̶ƈ˃ˉ²->"ɇȻ"H̶ĦLƚê"HÏG>"

4˃ˉ5Đ˸[|Lö'/2

4͏ʭ4˃ˉ5[|4ɿɪL̶ǥ4}

ZH5h:Ʃʈ"H'A2òŝ"H̰ȁƍ-í"ƄˈG>"

͏ʭ4˃ˉíI-1/Ü̕ŕ̶»/Đap4̦2aoɇȻĐ˸[|4˃ˉLí"ǉ
Lí'ż
aL¾Ƚ

O]
>"

ŝÚ/½Ǥʚ4Ɩ5¤ȫȍȞ1ȱƏ2Shtɭ.í'İƕLƠ>"ʆʏ 107Ω >.º

'İď

>"
˃ˉ

4ǉšH5|¾Ƚ"HšH5|aBŶȩȍȅ1ȯL¾Ƚ

'-.[|4ɿɪ2ˑI

>"

4

-(

Ǿ4+

aoɇȻ

>"%1H/ pH ȒŊ5ċʡ21G>"

pH Ʃʈ[|L̖ʍ"Hǉ5ʆő2öðʍ/ŧʾ2̖ʖ
73

1.( öðʍ/ŧ5.3 Combination
Electrode
Connection
Cable
voltages whichmight be created
when moving
the coaxial cable. It is of importance that this black
layer must be carefully removed when preparing the cable ends for connection to the electrode
What has been said about the cable requirements for a separate measuring electrode must alsoplug and/or to the measuring instrument. If the black layer is not removed, it will cause abe observed for the connection of a combination electrode. It is advisable to use a double
short circuit between the internal conductor and the copper screen. When stripping thescreened coaxial cable (triax cable). To save costs it is normal practice to connect the innercoaxial cable, tools and hands of the technician should always be dry and clean. After stripping,screen of the coaxial cable to the reference electrode part of the combination electrode.
the cable ends should be cleaned with alcohol or ether, which can bewith a cloth or aby doneT&C Technicalbrush, both of which should be absolutely clean. Touching the stripped cable ends with wet or
5.4 Cable
Preparation
and
Cable
fat-stained
fingers will
reducethe Routing
insulation resistance down to, or below, 107 ohms, which will
ʾ2˾Ʃ
-˖ʖ
'İď
resultin a shortcircuitof the̶əİ4Ź̻.˟ŕɇȻhigh resistance measuring>"
chain4̖ʖ504E1ȸ
– a pH measurement becomes
The insulation of the internal conductor of a pH connection cable is not only screened withimpossible.
copper wire ȾIǻmesh but alsowith an additional black
semiconductor layer. This layer suppresses-ʾ*-51G>$M
ˇď̶ǥ2¾Ƚ"HoQOkYc[|4ĹÌ
voltages whichmight
be createdmoving thecoaxialis takenof importancethat thisWhenrouting
the pHwhen
connection
cablecarecable.
must Itbe
not to route
theblack
pH connection
layer must be
carefully
removedwhen cables.
preparingParallel
the cable
ends
connection
cable
parallelto powersituated
power
cables tointhe
theelectrodevicinity of the pH
4ap5Ť2ȬÌ4?OcLćG>"
Ø-4
pHfor
Ʃʈ[|5Ǐɒ.ʾE2
plug and/orconnection
to the measuring
theelectro-magnetic
black layer is notremoved,(induction),
it will causea must becables instrument.
would leadIf tointerference
which
short circuit
betweeninternal
conductor
screen. When
stripping
the always be
avoidedallthecost.
The outerscreen ofandthe thetriaxcopper
cable(combinationelectrode)should>" at
50m
L˳H̖ʍ5ʾK1.(pH [|5Ĩ
2ĪAH/5âǘ
coaxial cable,
tools onandonehands
the Intechnician
alwaysbe dry andAfterstripping,earthedsideofonly.
principle,should
every pHconnection
cableclean.
shouldbe asshort as possible,
the cable ends
shouldbe cleaned
with alcoholor ether,which
can be done witha cloth-(or abutshouldunder
no circumstancebe longer
than
50 metres.
>$MĪ˖Ƅˈ1İď5̝ŚH5ǩʢˆ4]bkoɱ2̅
-Ī˖brush, both of which should be absolutely clean. Touching the stripped cable ends with wet or
pH connection cables cannot be buried straight into the ground. 7If this has to be done thesefat-stained fingers
will reduce the insulation resistance down to, or below, 10 ohms, which willcablesmust be installed in a metal or plastic conduit.
result in a short circuit of the high resistance measuring chain – a pH measurement becomes
impossible.
Triax cable
Coaxial cableĐ˸[|

PVC
PVCexternal
ʆʏ˃ˉ

PVC

PVC external

insulation
insulation
When routing the pH connection cable caremust be taken not to route the pH
connection
insulationapscreenParallel situated power cables inscreen
cable parallel to power cables.
the 1vicinity of the pHPEinsulation
connection cables
would
lead to electro-magnetic interference(induction), which must beSjʆʏ»PE insulation
avoided at all cost. The outer screen of the triax cable (combination electrode) should always beearthed on one side only. In principle, every pH connection cable should be as short as possible,
screen 2
black
internal
but should under no circumstancebe semiconductor
longer than 50 metres.
ŕ̶ʍ͏ŕ̶Ɋʤ
layer

conductor

internal

black semiconductor

conductor
pH connection cables cannot be buried straight into the ground.
If this has tolayer
be done thesecables must be installed in a metal or plastic conduit.
oQOkYc[|Coaxial cable

PVC external
insulation

Triax cable

PVCPVCʆʏ˃ap 1

screenscreen 1

Sjʆʏ»PE insulationinternal
conductor

insulation

PVC
PVCexternalʆʏ˃ˉ
insulation

PE insulation

black semiconductor
layer

screen22apinternalŕ̶ʍ
conductor

74

black semiconductor͏ŕ̶Ɋʤ
layer

by T&C Technical5.5 }ZH5[|̶͜ǥˆ̇·ɜ5ˆ̇

-H pH ̶ǥ2ő2 +4[|Ʃʈ°ǧLƬÀ

->"

1

+5 1m ɢŮ4[|ɍƩ̶ǥ4̼́̕2ćG²FI-HB4/}ZLơ+B
4."%I&I4Ʃʈƿű25̢ƕ/ɒƕG>"
Page 48

5.5 Plug or Cable?
pH ̶ǥ2[|ǁ2ćG²FI-HhQ}4İď
pH in̶ǥ4Ʃʈ.ɘ˝IH
Various electrode manufacturers supply their pH electrodes
two configurations: either withan integrally installed cable (normally 1 metre in length), or with an electrode plug/5connection. Both configurations have theiradvantages
and disadvantages.
Ʃʈ̕ãǶ2ŵ/Ȧ."̅ŤǶǵH5Ȕǵ4Ʃʈ̕2ő"H

Page 48

If the cable is installed to the electrode by the manufacturer, the customer can be assured that

5.5 Plug or Cable?
Ź̻2EGȒŊǮɘ2ʾ1/ĺF."̶ǥL­ƭ"H̰
the cable connection is water tight and measuring ƿfaultspH
attributed
normally to the[|electrode/cable
Variouselectrode
manufacturers
supply their
pH electrodes
two configurations:either handwith however, whenconnection(shortcircuit, moisture
ingress)
can beinruledout. On the otheranthe
integrally
installedcable(normally
1
metre
in
length),orwithanelectrodeplug
pH electrode assembly has to be replaced (remember: a pH electrode is a consumable item
Bʌ2­ƭ/1G>"
connection. Both configurations have their advantages and disadvantages.

with a certain life expectancy), the cable also has to be re-purchased.

If the cable is installed to the electrode by the manufacturer, the customer can be assured thatAnelectrodeconnection
eases faults
the attributed
electroderemovalor replacement during the
the
cable
connectionplug
is watertight and measuring
normally
to the electrode/cablemaintenanceperiodmoistureand is ingress)
more economicalin therunhand(savingof cableconnection(short circuit,can be ruled out.
On long
the other
however,when cost). However,thepH electrodeassemblyhas
toalways
be replaced(remember:aelectrodepH electrodesocket
is a consumable
item
care
must
be
taken
to
connect
thefirmlyto thecable plug,}Z°ǧ4 pH ̶ǥ4İď pH 4̶ǥ4ćGĹ H5­ƭ5ɴü." %-[with a certain life expectancy), the cable also has to be re-purchased.

otherwise moisture, the biggest enemy to the electrode/cable connection, might penetrateAntheelectrodeplug connection
electrodereplacement
during pH
the measurement issocket/plug
coupling.eases
Once themoisture
hasremoval
enteredorthis
joint, a reliable|4­ƭBƄˈG>$M
̶ǥ4g[koL}Z2Ʃʈ"H/5ȁƍƄ
maintenanceperiod and is more
economicalin the long run (saving of cable cost). However,no longer possible.
care must be taken to always connect the electrode socket firmly to the cable plug,
moisture, the biggest enemy to the electrode/cable connection, might penetrate
ˈ." otherwiseȔǵ̶ǥ/[|4Ʃʈ̕2×H/Ļ1ě̈́21G>"
Ȕǵ4Ʃʈthe socket/plug coupling. Once moisture has entered this joint, a reliable pH measurement isElectrode socket – cable plug
no longer possible. Electrode headcable
̕2Â×"H/ňŊwith
'integrated
pH ȒŊ5ċʡ21G>"
andElectrode headdifferent
instrument[|²̶ǥ plugs

connection

Electrode socket – cable plugg[ko²̶ǥconnection

with integrated cableanddifferent instrument plugs

75

by T&C Technical´. pH ̶ǥ4ÿȸ

>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(ƻǍ5ʰˠȭ4?/1G>"

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>'Fǵ˹2ǏŏG

4³ȸŭ>.ěďK$(ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"Ư'(I6ũ."EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."uo pH ̶ǥ̥ɇchk{ĐTheory is necessary, Experience is essential.
By Hamilton, pH Electrode system R&D team76

%4̰5Ƣ

by T&C Technical_}2EHɔɦƕȽ pH ̶ǥɸʅģ

77

pH 測定と電極の選び方

付属参考文書150322_E-J
by T&C Technical

6．参考資料
水素イオン濃度´.
pH ̶ǥ4ÿȸ>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"
pH という用語を定義する前に、その化学的物理的構造について述べておく必要があります。その中心的なǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(
存在は二つの水素原子（H2）と、1 つの酸素原子で構成される水についてです。

ƻǍ5ʰˠȭ4?/1G>"

6.1

原子の構造

pH
ȒŊ2+-4Ɏ˥ pH ̶ǥ4̒Ŋ2+-˱ěɭG> 'Fǵ˹2ǏŏG
古代ギリシャの哲学において、原子という言葉の意味は、物質のこれ以上小さくできない大きさとされていました。この基本的な微粒子、現代においてこの概念に当たる用語として用いられるもの、はこれ以上

4³ȸŭ>.ěďK$(

分解しないものとして考えられていました。事実、ギリシャ語の原子は「これ以上分けられないもの」とǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"いう意味を持ちます。

%4̰5Ƣ

Ư'(I6ũ."
その寸法と原子というものについての知識は、数世紀にわかりゆっくりと思索され続けましたが、その内容は、まだ単にそれを推測するだけにとどまっていました。

EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."
それに変化が現れるのは、16 世紀から 17 世紀における実験的科学の発展により、原子理論の進歩が急速に進むようになりました。その中で化学者は、すべての液体、気体そして固体は、究極の構成元素あるいは元素に分析されると認識しだしました。
uo
pH ̶ǥ̥ɇchk{Đ
例えば塩は二つの異なった違いのある元素で構成されていることを見つけました。ナトリウムそして塩素

Theory is necessary, Experience is essential.

は、現代では化学合成として知られるように、相互に深い絆で結ばれています。

By Hamilton, pH Electrode system R&D team
原子は、1 つの元素の建築ブロック
あらゆる元素のすべての原子は化学的に同じ振る舞いをします。このように、化学視点から、原子とは考慮される最も小さな実体ということになります。元素の化学的特徴は大きな違いがあります。それらの原子は、多数の化学合成物を構成するための多数の異なる方法により結合しています。それは今日において、112 の元素として知られています。
1911 年、イギリスの物理学者アーネスト・ラザフォード（1837-1937）は原子構造の理論を組織的にまとめ上げました。それは原子を、電子の雲によって囲まれる高密度原子核として最初に視覚化したものでした。
ラザフォードは、「原子の質量はその原子核に集中している。原子核には電気の正電荷がある。一方電子には、おのおの負電荷がある。」としました。電子により生じる変化の量は、原子核にある正電荷と同じ電気の量になります。このため通常の原子の電気的状態は中性になります。ラザフォードは原子核を構成する
その微粒子を陽子と呼びました。このラザフォードの原子の捉え方は、1913 年、ニール・ボーア（1885-1962）

76

1

pH 測定と電極の選び方

付属参考文書150322_E-J
by T&C Technicalにより見直されることになります。（次章 ボーアの原子）´. pH ̶ǥ4ÿȸ

>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

1932 年、イギリスのジェームズ・チャドウイック（1891-1974）は、現在中性子として知られている原子ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(の原子核にある陽子以外の他の微粒子が存在することを発見しました。それは陽子と同じ質量を持っていƻǍ5ʰˠȭ4?/1G>"
るのですが、電荷を持っていません。この発見により、原子核は陽子と中性子で構成されていることを知ることになりました。
「すべての原子において、陽子の数は電子の数と同じである。ゆえに、それは原子の
原子番号となる。」（元素の周期律表における原子の位置）pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>'Fǵ˹2ǏŏG

4³ȸŭ>.ěďK$(
6.2 ボーアの原子原子の構造を説明する前に、デンマークの物理学者、ニールズ・ヘンドリック・デビッド・ボーアにより
ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"%4̰5Ƣ
1913 年に「ボーア原子の理論The Bohr Theory of the Atom」として知られる仮説が提唱されたことをƯ'(I6ũ."

知っておく必要があります。彼は、原子核からかなりの距離まで、電子は定められた殻、量子準位に配置されていると仮定していました。これら電子の位置は「電子配置」と呼ばれます。
EGǮɘ1pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."

ボーアの原子uo pH ̶ǥ̥ɇchk{Đ
電子の数は原子の原子番号と等しい：水素は 1 つの殻に一つの電子、酸素は 8 つ、そしてウランは 92 を

Theory is necessary, Experience is essential.

持ちます。電子の殻は第 1 の殻から第 7 の殻まで規則正しく並んでいます。それぞれの核は収納できる電子の数に上限があります。殻は内側の殻から外側の殻まで、K殻、L 殻から Q 殻と名付けられています。
By
Hamilton, pH Electrode system R&D team
K 殻は二つの電子まで持てます。L 殻は最大 8 つの電子まで満たすことができます。M 核は 18 の電子、そしてそれを一般化すれば、n 殻は 2n の電子で満たすことが2

できることになります。唯一外側のお殻における電子の数は、原子の化学的な振る舞いにより決定されます。
原初の殻は、殻毎に隙間なく電子で埋め尽くす必要はありません。元素の周期律表にある最初から 18 番目の元素までは、電子は規則正しく増加していき、それぞれの殻は新しい殻が始まる前まで制限いっぱいの電子で満たされています。

762

pH 測定と電極の選び方

付属参考文書150322_E-J
by T&C Technical

19 番目の元素からは、最も外殻の電子はそれより内側の殻の電子が完全に満たされている状態で始まりま´. pH ̶ǥ4ÿȸ

>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

す。規則性はまだ維持されています。しかし電子は満たされている内側の殻との間を行ったり来たりしだǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(
します。この原子量を増加させるためのその化学的性質の定性的な繰り返しは、元素の周期律表の並び方と一致する結果になります。



ƻǍ5ʰˠȭ4?/1G>"

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>'Fǵ˹2ǏŏG

4³ȸŭ>.ěďK$(ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"%4̰5Ƣ

Ư'(I6ũ."EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."uo pH ̶ǥ̥ɇchk{ĐTheory is necessary, Experience is essential.
6.3

元素の周期律表

By Hamilton, pH Electrode system R&D team
1869 年、ロシアの化学者ディミトリ・イワノビッチ・メンデレーエフ（1834-1907）は当時知り得たすべての元素の質量を表にまとめました。そうすることで、彼はある元素の性質はそれ自身周期的に繰り返すことを発見しました。それによりメンデレーエフは似たような化学的挙動を持つ元素をまとめ、それぞれ順番に行の下にまとめていきました。この元素の配置表は周期律表と呼ばれています。

年数を重ねることでより多くの元素が発見され、周期律表は数度にわたり配置し直されていきました。その表、今日私たちが知っているものは次のページに示されている通りです。元素は昇順の原子番号（原子核にある陽子の数の順番）で水平に 7 行にわたり配置されています。それぞれの行は原子の 7 つの電子殻
1 つを表します。1 番目の行の一番目にある水素は最も軽い元素になります。目下の一番重い元素、表の最後の元素はウンウンビウム（放射性超ウラン元素）で、原子質量 277、112 番目になります。なお表には
全部で 118 の元素が載っています。列のグループは、元素を化学的な動きにより 18 に分けています。これは最も外側の殻の電子の数に従っています。

763

pH 測定と電極の選び方´. pH ̶ǥ4ÿȸ

>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5

付属参考文書150322_E-J
by T&C Technical²Ś"HƻǍLĂȪ(ƻǍ5ʰˠȭ4?/1G>"

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>'Fǵ˹2ǏŏG

4³ȸŭ>.ěďK$(ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"%4̰5Ƣ

Ư'(I6ũ."EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."uo pH ̶ǥ̥ɇchk{ĐTheory is necessary, Experience is essential.
By Hamilton, pH Electrode system R&D team764

pH 測定と電極の選び方´. pH ̶ǥ4ÿȸ
6.4

付属参考文書150322_E-J
by T&C Technical>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

分子

ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(

分子とは、ある物質が同じ化学的性質を持つ化合物の最も小さい単位です。



ƻǍ5ʰˠȭ4?/1G>"

水の分子は 1 つの酸素原子と二つの水素原子を電気的な力、いわゆる化学結合により構成されています。
フランスの化学者アントワーヌ＝ローラン・ド・ラヴォアジエ（1743-1794）

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>により、古代の哲学者が考えていた「水は基本的な元素」、がそうではないこ'Fǵ˹2ǏŏG

4³ȸŭ>.ěďK$(とを証明しました。それは酸素と水素の化合物であり、現代の表現では H2Oという式で表されます。

ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"%4̰5Ƣ

分子はともに 2 つの電子を分かち合うことで保たれています（共有結合）。この結合を最大化するために、Ư'(I6ũ."

原子は相互に特定の位置を取ります。例えばそれぞれの分子はそれ自身定められた形を持ち、単純に見ると、水分子内の水素原子は酸素原子に対し104.5 の角度でくっついています。そのため水は水素の電子がEGǮɘ1pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."大きな酸素原子の原子核に向かってわずかに囚われている状態、双極子モーメントを持っています。それに対し、二酸化炭素 CO2 は酸素原子が直線に配置され、それゆえ双極子モーメントを持ちません。

uo pH ̶ǥ̥ɇchk{ĐTheory is necessary, Experienceis essential.
またある元素は他の元素と化合することはありません。
これらは希ガスのグループとなります。これらの原子は 2 つの電子（He）あるいは外By Hamilton, pH Electrode system R&D team

殻に 8 つの電子（Ne、Ar、 Kr、Xe、Rn）を持ちます。8 個以下の電子を外殻に持つ元素は、他の活性元素と結合することになります。

原子が作れる化合の数は原子価と呼ばれます。酸素は原子価が 2 となりますが、それは 6 つの電子をその外殻に持ち、そこを 8 つにするために 2 つの電子を必要としていることを意味します。水素は 1 つの電子をその唯一の外殻に持っています。そのため原子価は 1 となります。電子殻を充足させるため他の電子を獲得するか、もしくは 1 つ電子が足りない原子に 1 つ電子を与えることができます。このため 2 つの電子を必要とする酸素原子の場合、2 つの水素原子は酸素原子の足りない電子の需要を満たし、一緒になることで水分子を作ることになります。

765

pH 測定と電極の選び方´. pH ̶ǥ4ÿȸ

付属参考文書150322_E-J
by T&C Technical>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

ナトリウム元素と塩素元素がくっついて塩（NaCl：食卓塩）を作る場

ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5合、この結合はイオン結合となります。中世のナトリウム原子、それ²Ś"HƻǍLĂȪ(ƻǍ5ʰˠȭ4?/1G>" 7 つの電子を外殻に持つ塩は 1 つの電子を外殻に持ちますが、それを素原子と共有します。再びですが、この結合の場合、外殻は 8 つの電子で満たされます。

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>

この 1 つの電子の変化の過程は両方の原子の電気的平衡状態を放り出'Fǵ˹2ǏŏG

すことになります。ナトリウム原子は正の電荷を持つようになり（14³ȸŭ>.ěďK$(
つの電子を失う）Na となり、そして塩素は 1 つの電子を受け取り負の+ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"
電荷を持つようになります（Cl ）。新しいナトリウムイオンの殻の構造%4̰5Ƣ

は、ネオン原子のものに似ており、塩素イオンの新しい殻構造はアルƯ'(I6ũ."
ゴン原子のものに似ています。両方のイオンは互いにそれらのクーロEGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."
ン引力により保たれます。

6.5 イオン pH ̶ǥ̥ɇchk{Đuo
1 つのイオンは中性の原子が1 つあるいは複数の電子を獲得するあるいは失うときに作られる
1 つの粒子Theoryis necessary, Experienceis essential.
です。1 つの電子を失った 1 つの原子は、カチオンと呼ばれる正の電荷を持つイオンになります。電子を 1

By Hamilton, pH Electrode system R&D team

つ得た 1 つの原子は、アニオンと呼ばれる負の電荷を持つイオンになります。イオンという単語はギリシ
ャ語から派生し、「旅人」を意味します。電場（電界）の影響の元、イオンはそれとは逆の極性を持つものへと移動（旅）します。そしてその結果、気体や液体に導電率を発生させます。
もし NaCl のイオン結合が高温あるいは水に溶けることで壊されると、塩素原子は獲得した電子を保ち、そして負の電荷を持つイオンとして存在します。ナトリウムイオンは逆に正の電荷（電子を失う）を持つイオンとして存在します。

6.6

解離

水は 3 つの化合物のグループ、塩、酸、そして塩基にとって優れた 1 つの溶剤です。水にこれらの化合物を入れると、これらの化合物はイオンへと解離します。NaCl を水に入れると、水分子の極の作用は負と正の電荷を持つイオンの間で静電引力が減少し、それらのイオンを引き離すようになります。このためイオンの再結合を妨げるように働き、それらのイオンは水の分子に囲まれた状態になります（水和される）。
HCl（塩酸）も同じように水の中で解離し、H と Cl イオンになります。NaOH（水酸化ナトリウム）も同
+

-

76

6

pH 測定と電極の選び方

付属参考文書150322_E-J
by T&C Technical

じように解離し Na と、OH イオンになります。
+´. pH ̶ǥ4ÿȸ

->'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

水の中の塩の解離、酸と塩基の解離は水に対し優れた導電性を生じます。このように発生した溶液を電解ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5液と呼びます。

²Ś"HƻǍLĂȪ(ƻǍ5ʰˠȭ4?/1G>"

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>'Fǵ˹2ǏŏG

4³ȸŭ>.ěďK$(ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"%4̰5Ƣ

Ư'(I6ũ."EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."

もし二つの電極が電解液に差し込まれ電解液と電位の違いがこれらの電極に発生すると、負の電荷を持つ

uo pH ̶ǥ̥ɇchk{Đ

イオンは正の電荷を持つ電極（アノード）により捕らわれ、そしてアノードに達することでそれらの電荷

Theoryis necessary,
Experienceis essential.
を失います（電子を失う）。これによりアニオンと名付けられています。
同じように負の電荷を持つ電極（カソード）はその電荷は電子を受け取ることで失います（カチオン）。

By Hamilton, pH Electrode system R&D team

6.7

酸̶塩基̶塩化学において、私たちは三つの電解液、酸、塩基そして塩に分類してきました。
酸：

水の中に溶かすと水素イオン濃度 H+（プロトン）を発生し、それは純水の持つ量よりも高くなります。従って酸はプロトンドナー（陽子供与体）です（プロトン＝正の電荷を持つ水素イ767pH 測定と電極の選び方
オン）。

´. pH ̶ǥ4ÿȸ

付属参考文書150322_E-J
by T&C Technical>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

酸はその味は酸っぱくそしてリトマス試験紙を赤くします。リトマス試験紙は溶液が酸なのかǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(

塩基なのかを判別するために用いられる最も古い、そして最も使われるものです。それは地衣ƻǍ5ʰˠȭ4?/1G>"類、ある真菌の作り出した植物性有機物、そしてそれと共生しているある藻から分離された桃色の色素です。
最も知られている酸：pH ȒŊ2+-4Ɏ˥
塩酸pH ̶ǥ4̒Ŋ2+-˱ěɭG>
消化液を構成している成分

HCl4³ȸŭ>.ěďK$(
硝酸

HNO3

'Fǵ˹2ǏŏG

色素と爆薬で使用されます。

ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"
酢酸
CH COOH酢%4̰5Ƣ

3

Ư'(I6ũ."
蟻酸
HCOOH

染色と製革で使用されます。

H2SO4
電池
EGǮɘ1硫酸pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."リン酸

歯科用セメント、化学肥料

H3PO4uo pH ̶ǥ̥ɇchk{Đ塩基：

水の中に溶かすとヒドロキシルイオン濃度 OH-（プロトンアクセプター）を発生し、プロトン

Theory is necessary, Experience is essential.

を受け止めます。塩基は苦味を持ちリトマス試験紙を青に変色させます。塩基はぬるぬるした

感じになります。最も一般的な塩基は以下の通りです。
By Hamilton,
pH Electrode system R&D team

塩：

水酸化ナトリウム

NaOH

排水、オーブンクリーナ

水酸化カルシウム

Ca(OH)2

建築用モルタルに使われています。消石灰

水酸化アルミニウム

Al(OH)3

アルミニウム化合物を作る原料

水酸化カリウム

KOH

軟石鹸

水酸化マグネシウム

Mg(OH)2

マグネシア乳（緩下剤）

アンモニア

NH3

家庭用クリーナー

酸と塩基の水溶液が混ざった時、中性化する反応が発生します。この反応は瞬く間に進行し、一般的には水と塩を作ります。例えば硫酸と水酸化ナトリウムは水そして硫酸ナトリウムにな
ります。
例：

76

8

pH 測定と電極の選び方
硝酸ナトリウム

NaNO=

Na + NO3

硫化アルミニウム

Al2(SO4)3=2Al´. pH ̶ǥ4ÿȸ

+

付属参考文書150322_E-J
by T&C Technical-3>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"
3++ 3SO42-

ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5リン酸カルシウム

Ca3(PO4)2 =ƻǍ5ʰˠȭ4?/1G>"

6.8

モル（mol）

3Ca

2++ 2PO4²Ś"HƻǍLĂȪ(3-pH
ȒŊ2+-4Ɏ˥ pH中に存在する原子の数と等しい要素粒子を含む系の物質量の̶ǥ4̒Ŋ2+-˱ěɭG> 'Fǵ˹2ǏŏG
モルは、0.012Kg（12g）の炭素
SI 単位で12す。構成する要素粒子は原子、分子、イオン、電子、あるいは他の微粒子と特定されなくてはならない。

4³ȸŭ>.ěďK$(

本単位は国際的に用いられるために 1971 年に定められた。（Oxford Dictionary）

ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"%4̰5Ƣ

Ư'(I6ũ."
炭素 12（他の物質を測定する際の対象としての原子）の 12g に含まれる元素の粒子の数は 6.0221367 x 10

23

EGǮɘ1
pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."です。この数字はアボガドロ数として知られ、イタリアの物理学者アメデオ・アボガドロ（1776-1856）の功績を称え名付けられています。1811 年、アボガドロは、温度、圧力の等しい体積のガスは、同数の分子含むと仮定しました。1 モルはある物質の原子量が等しいもので、グラム重量で表されます。

uo pH ̶ǥ̥ɇchk{Đ

1mol の H2

Theory is necessary, Experience is essential.

1mol の H2O

＝

2g

＝

18g

By Hamilton, pH Electrode system R&D
team
1mol
の Cl2 ＝ 71g
1mol の Rn＝

222g

1mol の HCl

＝

36.5g

1mol の NaOH

6.9

＝

40g

水の中の水素イオン濃度

水は電解質を溶解、分離するだけでなく、それ自身、わずかな量の水分子は正の電荷を持つ水素イオン H+と、負の電荷を持つ水酸化イオン OH-に分離しています。
+

H2O = H + OH-

H+＝酸の反応を持つ正の電荷を持つ水素イオン

OH-＝アルカリ反応を持つ負の電荷を持つ水酸化イオン

769pH 測定と電極の選び方

付属参考文書150322_E-J
by T&C Technical

もし水素イオンの量が水酸化イオンの量と同じ場合、水は中性と呼ばれます。清浄な中性の水は 10 の水
7´. pH ̶ǥ4ÿȸ

>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

分子の 1 つだけが解離した状態です。

ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(

現実には水素イオンは 1 つのプロトンであり、1 つの電子を持つ水素イオンが水素イオン同士結合していƻǍ5ʰˠȭ4?/1G>"ます。そのため一般化された酸と塩基の理論においては、最も単純な酸と塩基の中性反応としてみることになります。
+

2H + 2e =H2

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>'Fǵ˹2ǏŏG

しかし実際は水素イオン、あるいはプロトンは水の中で自由に存在せず、水分子を伴っています。水のイ

4³ȸŭ>.ěďK$(
オン化はそのため正確には以下のように書かれる必要があります。
ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"+

2HOH = H3O + OHƯ'(I6ũ."%4̰5Ƣ

-水の中にある H3O はヒドロニウムイオンと呼ばれ、そのイオンは酸の性質を持ちます。この解離状態を単+EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."
純化にするため、この等式は通常 H を用いて書かれていることになります。
+++
uo
pH ̶ǥ̥ɇchk{Đ
1 つの酸を中性の水に入れることで、H
イオン濃度は酸の解離により作られる H イオンによりその濃度は上昇します。その水はその性質を変化させ、あたかも酢あるいはレモンジュースのように酸っぱくなりま

Theory is necessary, Experience is essential.

す。そしてそれは腐食性となり金属を分解します。

By Hamilton, pH Electrode system R&D team
1 つの塩基を中性の水に入れると、OH イオン濃度は塩基の解離により作られる OH イオンによりその濃度--は上昇します。それに対応する量の H イオンがありますが、それは減ることになります。水はその性質が+変わり、苦味があり濡れた石鹸のようにぬるぬるした感触を持ちます。
両方の場合において、私たちはそれを水と呼ぶことはできなくなり、それを「水溶液」として扱うことに
なります。

76

10

pH 測定と電極の選び方´. pH ̶ǥ4ÿȸ

付属参考文書150322_E-J
by T&C Technical>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

すべての酸と塩基の水溶液は、加えられた酸、塩基の化学的反応により、それらに対応した水素イオン H

ǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5-+²Ś"HƻǍLĂȪ(と水酸化イオン OH の濃度に変化を与えます。水溶液内の水素イオン濃度は 1 つの水素イオンに対応する


ƻǍ5ʰˠȭ4?/1G>"
解離していない水分子量により表現されます。
例もし 1 つの水素イオン H が 100 の水分子のなかに存在した場合、それは 1:100 あるいは 1/10+

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>

あるいは 10 と書かれます。

2'Fǵ˹2ǏŏG-2

4³ȸŭ>.ěďK$(

もし 1 つの水素イオンが 10,000,000 の水分子のなかに存在した場合、それは 1:10,000,000 あ

るいは 1/10 あるいは 10 と書かれます。
ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"
7-7%4̰5Ƣ

さらにもし 1 つの水素イオンが 1000,000,000 の水分子のなかに存在した場合、それはƯ'(I6ũ."
1:1000,000,000 あるいは 1/10 あるいは 10 と書かれます。
9-9EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."
水の中では H イオンと OH イオンに解離したイオン物質が 22℃、10 (mol/L)では一定の状態で存在しま
+

-

-14

す。そのため、純水中のH イオンと OH イオンの濃度が等しい時、H イオン濃度は 10 に必ずなり、OHuo
pH ̶ǥ̥ɇchk{Đ
+

-

+

-7

-

イオン濃度は同じように 10 になります。この状況は自動的に pH の定義へと導かれ、その結果 pH は以下-7

Theory is necessary, Experience is essential.
のように表現されます。

By Hamilton, pH Electrodesystem R&D team
水溶液中における活性水素イオン濃度のマイナスの常用対数

あるいは数学的表現では

1
pH = log

水素イオン濃度（mol/L）

76

11

pH 測定と電極の選び方´. pH ̶ǥ4ÿȸ

付属参考文書150322_E-J
by T&C Technical>'%4¾Ƚƿǿ2²-4ˢǅLɿKG>"

最後にǶɼQTȢŮ2+-ȸːLȊAH'A4˚Ƽ2+-5²Ś"HƻǍLĂȪ(

pH 測定において大切な点は以上です。



ƻǍ5ʰˠȭ4?/1G>"「理論は必要です ‒ 経験は欠かせません」
Erich L.Springer

pH ȒŊ2+-4Ɏ˥

pH ̶ǥ4̒Ŋ2+-˱ěɭG>'Fǵ˹2ǏŏG

4³ȸŭ>.ěďK$(ǕǍ4ÜŎ5ʘ˘4'A̕̐ä1˘Ē>I-HċʡƈG>"%4̰5Ƣ

Ư'(I6ũ."EGǮɘ1 pH ȒŊLʾ.ǕǍź2ɩ+/I6ũ."uo pH ̶ǥ̥ɇchk{ĐTheory is necessary, Experience is essential.
By Hamilton, pH Electrode system R&D team76

12