8/13/2019 F AC 21 08 Potentiometry
1/64
Dong-Sun Lee / cat - lab / SWU 2012 -Fall version
Chapter 21
Potentiometry
Copyright
8/13/2019 F AC 21 08 Potentiometry
2/64
Electroanalytical techniques
1) Ionics---- Conductance
2) lectro!ics
a) Static (I = 0) --- Potentiometry
b) Dynamic (I 0)
Controlled current --- Coulometric titration
Controlled potential
Stirred solution Controlled potential
Hydrodynamic oltammetry
!mperometry --- !mperometic titration
"uiescent solution Potential scan --- Cyclic oltammetry# Polarography
Small amplitude pulse techni$ue
Di%%erential pulse oltammetry
S$uare &ae oltammetry
Potential step --- Chronoamperometry# Chronocoulometry
Pulse oltammetry# Chronoabsorptometry
8/13/2019 F AC 21 08 Potentiometry
3/64
Classification of electrochemical methods
1" P#$%$I#&$'(
'easure electrical potential deeloped by an electrode in an electrolyte solution at ero current
%lo& *se +,+S. ,"*!.I/+ relating potential to concentration o% some ion in solution
2" #L$*&&$'(
Determine concentration o% ion in dilute solutions %rom current %lo& as a %unction o% oltage &hen
P/!I1!.I/+ o% ion occurs around the electrode
P/!I1!.I/+ = depletion o% concentration caused by electrolysis
I% using a dropping mercury electrode# method is termed P/!/2!PH3
+" ,#UL#&$'(
,lectrolysis o% a solution and use o% 4araday5s la&6relating $uantity o% electrical charge to amount
o% chemical change
76essentially states that it ta8es 9:; < 0>Coulombs o% electrical charge to cause electrolysis o%
mole o% a unialent electrolyte species?
" ,#%DU,$I&$'(
'easure conductance o% a solution# usingINERT ELECTRODES, ALTERNATING CURRENT, AND
AN ELECTRICAL NULL CIRCUIT- thereby ensure no net current %lo& and no electrolysis .he
concentration o% ions in the solution is estimated %rom the conductance
+/.,@
&et.o!s 1 an! #
%# L,$'#L(SISo% solution Sample recoerable# unaltered by analysis
&et.o!s 2 an!+ must cause L,$'#L(SIS #F $ S*&PL" http@AA&&&scienceutseduauAsubBectsA9:ASectionAsectionhtml
8/13/2019 F AC 21 08 Potentiometry
4/64
Potentiometry
!n electroanalytical techni$ue based on
the measurement o% the electromotie
%orce o% an electrochemical cell
comprised o% a measuring and a re%erence
electrode
.he simplest e
8/13/2019 F AC 21 08 Potentiometry
5/64
eneral Princiles
e%erence electrode E salt bridge E analyte solution E indicator electrode
,re% ,B ,ind
,cell = ,indF ,re% G ,B
e%erence cell @
a half cell having a known electrode otential
Indicator electrode@
ha! aotential that varie!in a known wa"
with variation! in the concentration of an anal"te
! cell %or potentiometric determinations
8/13/2019 F AC 21 08 Potentiometry
6/64
) Saturate! calomel electro!e(S","")
Hg(l) E HgCl(satd)# Cl (satd) E E
electrode reaction in calomel hal-cell
HgCl(s) G e = Hg(l) G ClF
Eo= G 0:JK
E=EoF (00;9:A) log7ClF?= 0>> K
.emperature dependent
! calomel electrode saturated &ith Cl is called a saturated
calomel electrode# abbreiated S",""
!dantage @ using saturated Cl is that 7Cl-? does not changei% some li$uid eaporates
'eerence electro!e
# $aintain! afi%ed otential#
a half cell having a known electrode otential
8/13/2019 F AC 21 08 Potentiometry
7/64
HgCl= HgG
G ClF
sp = J L0FJ
Saturated Cl = >: ' Cl
.he crystal structure o% calomel(HgCl)#
&hich has limited solubility in &ater
(sp = J L0FJ)
8/13/2019 F AC 21 08 Potentiometry
8/64
4ig - Diagram o% a typical commercial
saturated calomel electrode
4ig - ! saturated calomel electrode
made %rom materials readily aailable in
any laboratory
8/13/2019 F AC 21 08 Potentiometry
9/64
) Silver-silver c.lori!e electro!e
!g(s) E !gCl (satd)# Cl (%') E E
!gCl(s) G e = !g(s) G ClF
Eo= G0>>K
E=EoF (00;9:A) log 7ClF?
E(saturated Cl) = G 099K (;oC)
8/13/2019 F AC 21 08 Potentiometry
10/64
) stan!ar! .y!rogen electro!e 3S)
.he most %undamental re%erence electrode in electrochemistry MNy
de%initionM its e$uilibrium potential is considered ero at any temperature#
because this electrode &as chosen as an arbitrary ero point %or electrodepotentials ! ero point is needed since the potential o% a single electrode
cannot be measured# only the di%%erence o% t&o electrode potentials is
measurable !ll electrode potentials are e
8/13/2019 F AC 21 08 Potentiometry
11/64
oltage ,onversions 4et5een Dierent 'eerence Scales
I% an electrode has a potential o% 0>:K &ith respect to a calomel electrode# &hat is the
potential &ith respect to a siler-siler chloride electrode Qhat &ould be the potential &ith
respect to the standard hydrogen electrode
8/13/2019 F AC 21 08 Potentiometry
12/64
Li6ui!-7unction otential
! potential di%%erence bet&een t&o solutions o% di%%erent compositions separated
by a membrane type separator .he simplest e
8/13/2019 F AC 21 08 Potentiometry
13/64
8unction otential@
a small potential that e
8/13/2019 F AC 21 08 Potentiometry
14/64
Fig" 21-9" Sc.ematicreresentation o a li6ui!
7unction s.o5ing t.e source
o t.e 7unction otential: 7"
$.e lengt. o t.e arro5s
correson!s to t.e relative
mobilities o t.e ions"
Fig 21-Diagram o% a silerAsiler chloride electrodesho&ing the parts o% the electrode that produce the
re%erence electrode potential ,re%and the Buction
potential ,B
8/13/2019 F AC 21 08 Potentiometry
15/64
8/13/2019 F AC 21 08 Potentiometry
16/64
Li6ui! 7unction otential
Cells &ithout li$uid Bunction
PtAH&g'# HClA!gClA!g
are to hae this type o% cell
Cells &ith li$uid Bunction
2lass %rit
Salt bridge
Deelop a potential by di%%erential migration rates o% the cation and anion
Tunction potential
HCl(0)AHCl(00) ,B= >0 mK (HG%aster than ClF)
Cl(0)ACl(00) ,B= F0 mK (G slo&er than ClF)
*sually e
8/13/2019 F AC 21 08 Potentiometry
17/64
In!icator electro!es
(etallic indicator electrode re!ond! to anal"te activit")
lectro!e o t.e irst tye
Direct e$uilibrium &ith analyte
!g %or !gG# !u %or !uG# etc
Potential described by +ernst e$uation
!s 7'? # ,
+ote potential linearly related to logo% the concentration U
emember - indicator N3 D,4I+I.I/+ cathode
measurement theoretically under ero-current (steady state)
lectro!e o t.e secon! tye
Indirect e$uilibrium &ith analyte
'A'VAVF
SilerASiler chloride %or chloride
also +ernstian response
as 7VF? # ,
Inert &etallic electro!e or 'e!o; systems
Proides a sur%ace %or the electrochemistry to occur
Pt# !u# Pd# C
VnG(a*) G ne = V(!)
,ind = ,oF (0;9:An) log (A7VnG?)
!gCl(s) G e = !g(s) G ClF(a*)
,ind = ,oF 0;9: log 7ClF?
! plot o% ,$uation - %or an
electrode o% the %irst 8ind
! plot o% ,$uation ->
%or an electrode o% thesecond 8ind %or ClF
8/13/2019 F AC 21 08 Potentiometry
18/64
In!icator electro!es
Indicator electrodes %or potentiometric measurements are o% t&o basic types#
namely#$etallicand $e$+rane
1) &etallic in!icator electro!es ?
8/13/2019 F AC 21 08 Potentiometry
20/64
Secon!-or!er electro!es or anions
! metal electrode can sometimes be indirectly responsie to the concentration o%
an anion that %orms areciitateor co$le% ion&ith cations o% the metal
,F Eo= 0K
E= 0 F (00;9:A) log (73>F? A7Hg3F?)
8/13/2019 F AC 21 08 Potentiometry
21/64
!g(s) E !gCl7satd?# Cl7%'? E E 4eG#4eG) E Pt
4eGGe = 4eG Eo= G00K
Ecell=EindicatorFEre%erence
= X00F (00;9:A) log 74eG?A74eG?Y F X0F (00;9:A) log 7ClF?Y
Inert electro!es
Chemically inert conductors such asgold, latin$# or car+onthat do
not participate# directly# in the redo< process are called inert electrodes .he
potential deeloped at an inert electrode depends on the nature and
concent-ration o% the arious redo< reagents in the solution
8/13/2019 F AC 21 08 Potentiometry
22/64
2) &embrane in!icator electro!es
.he potential deeloped at this type o% electrode results %rom an une$ual chargebuildup at opposing sur%ace o% a special membrane .he charge at each sur%ace is
goerned by the position o% an e$uilibrium inoling analyte ions# &hich# in
turn# depends on the concentration o% those ions in the solution
.he electrodes are categoried according to the type o% membrane they employ @
glass#
polymer#crystalline#
gas sensor .he %irst practical glasselectrode (Haber and
lemensie&c#.) /h"!)
Che$# 909# :;# J;
8/13/2019 F AC 21 08 Potentiometry
23/64
&embrane in!icator electro!es
lass membrane electro!es
.he internal element consists o% siler-siler chloride electrode immersed in a
pH bu%%er saturated &ith siler chloride .he thin# ion-selectie glass
membrane is %used to the bottom o% a sturdy# nonresponsie glass tube so that
the entire membrane can be submerged during measurements Qhen placed in a
solution containing hydrogen ions# this electrode can be represented by the hal%-
cell @
!g(s) E !gCl7satd?# ClF(inside)# HG(inside) E glass membrane E HG(outside)
E=EoF (00;9:A) log7ClF? G (00;9:A) log(7HG(outside)?A7HG
(inside)?)
E= Q G (00;9:A) log7HG(outside)?
8/13/2019 F AC 21 08 Potentiometry
24/64
&eter
pH meter is a olt meter that measures the electrical potential di%%erence
bet&een a pH electrode and a re%erence electrode and displays the result in
terms o% pH alue o% the sample solution in &hich they are immersed
Intro!uction
.he pH meter measures the pH o% a solution using an ion-selectie electrode
(IS,) that responds to the HGconcentration o% the solution .he pH electrode
produces a oltage that is proportional to the concentration o% the HG
concentration# and ma8ing measurements &ith a pH meter is there%ore a %orm
o% potentiometry .he pH electrode is attached to control electronics &hich
conert the oltage to a pH reading and displays it on a meter
Instrumentation
! pH meter consists o% a HG-selectie membrane# an internal re%erence
electrode# an e
8/13/2019 F AC 21 08 Potentiometry
25/64
.ypical electrode system %or measuring pH (a) 2lass electrode (indicator) and saturated calomel electrode
(re%erence) immersed in a solution o% un8no&n pH (b) Combination probe consisting o% both an indicator glass
electrode and a silerAsiler chloride re%erence ! second silerAsiler chloride electrode seres as the internal
re%erence %or the glass electrode .he t&o electrodes are arranged concentrically &ith the internal re%erence in the
center and the e
8/13/2019 F AC 21 08 Potentiometry
26/64
pH Meters
8/13/2019 F AC 21 08 Potentiometry
27/64
meter #A gla!! co$+ination electrode
E 0 12 + (3)34567)log (Ain8 Aot)
1@A!"$$etr" otential
+ @electro$otive efficienc" ( close to 00)
A @Activit" of h"drogen ion
8/13/2019 F AC 21 08 Potentiometry
28/64
Composition o% glass membranes
0Z Si/
0Z Ca/# Na/# i
/# +a
/#
andAor !l/
Ion e
8/13/2019 F AC 21 08 Potentiometry
29/64
Potential o t.e glass electro!e
.he potential di%%erence across the glass pH electrode
depends on the actiity o% HGon each side o% the
glass membrane
,m= KF K = (.A4)lnaF (.A4)lna
= ,asymG 00;9: log(aA a)
i%A= constant#
,m= G 00;9: loga
= F 00;9: pH
Standardiationat pH=00 # , = 0 K
pH >00# ,= ;9: mKApH unit
Potential pro%ile across a glass membrane %rom the analyte solution to
the internal re%erence solution .he re%erence electrode potentials are
not sho&n
8/13/2019 F AC 21 08 Potentiometry
30/64
Isopotential
point,(mK)
pH
00oC > mKApH unit
0oC ;> mKApH unit
>
;00
0
8/13/2019 F AC 21 08 Potentiometry
31/64
,alibrating a glass electro!e
!l&ays 8eep the electrodes in distilled &ater# saturated Cl solution(') or bu%%er &hen not in
use
Po&er /+ S&itch to [S.!+DN3\ @ allo& to &arm %or 0 min
inse the electrode thoroughly &ith distilled &ater and then &ith pH 00 bu%%er solution
Nlot &ith clean tissue
> Determine the temperature o% the bu%%er solution &ith a thermometer
!dBust [.,'P,!.*,\ 8nob on the unit to the temperature
; Place the electrode inpH 00(isopotential point) bu%%er solution
otate the selector s&itch to [pH\ Qait %or a stable display
Ny using [C!IN!.I/+\ 8nob# set the meter to the pH alue o% the bu%%er at its measured
temperature S&itch to [S.!+DN3\
: inse the electrode thoroughly &ith distilled &ater and then &ith pH >00 bu%%er solution
Nlot &ith clean tissue
Place the electrode inpH >00 bu%%er solution otate the selector s&itch to [pH\
Qait %or a stable display *sing [S/P,\ 8nob# set the meter to the pH alue o% the bu%%er at its
measured temperatureS&itch to [S.!+DN3\
8/13/2019 F AC 21 08 Potentiometry
32/64
,alibration o t.e &eters 5it. an! 2 4uers
Select the pH 'ode and set the temperature control 8nob to ;]C !dBust the cal 8nob
to read 00Z
inse the electrode &ith deionied &ater and blot dry using a piece o% tissue (Shur&ipesor im&ipes are aailable in the labs)
Place the electrode in the solution o%pH bu%%er# allo& the display to stabilie and# then#
set the display to read by adBusting cal emoe the electrode %rom the bu%%er
> inse the electrode &ith deionied &ater and blot dry using a piece o% tissue (Shur&ipes
or im&ipes are aailable in the labs)
; Place the electrode in the solution o%pH bu%%er# allo& the display to stabilie and# then#
set the display to read by adBusting cal emoe the electrode %rom the bu%%er
: inse the electrode &ith deionied &ater and blot dry using a piece o% tissue (Shur&ipes
or im&ipes# as be%ore)
%#$- Nu%%er solution are made aailable to you in indiidually labeled o bottles .he
bu%%ers are to be used in these containers# onlyU Do not pour them into other containers at
any time !%ter use# cap the bottles so that the bu%%ers can be re-used
8/13/2019 F AC 21 08 Potentiometry
33/64
&easuring
'a8e sure that the meter is set to the pH 'ode and adBust the temperature to ;]C
Place the electrode in the sample to be tested
.he pH o% the solution appears in the display
+/.,@ !llo& the display to stabilie be%ore ta8ing your readingU
> inse the pH electrode and place it bac8 in the storage solution
8/13/2019 F AC 21 08 Potentiometry
34/64
rrors t.at aect measurements 5it. glass electro!e
.he al8aline(sodium) error @ lo& readings at pH alues greater than 9
.he acid error @ some&hat high &hen the pH is less than about 0;
Dehydration may cause erratic electrode per%ormance
> Kariation in Bunction potential @ ^ 00 pH unit; ,rror in the pH o% the standard bu%%er @ 00 pH unit
,leaning glass electro!e@ Qashing &ith :' HCl
0 &A&Z a$ueous ammonium bi%luoride (+H>H4)
8/13/2019 F AC 21 08 Potentiometry
35/64
!cid and al8aline errors %or selected glass electrodes at ;
(4rom 2 Nates#Deter$ination of 9,nd ed# p :; +e& 3or8@ Qiley# 9)
8/13/2019 F AC 21 08 Potentiometry
36/64
Ion-Selective lectro!es 3IS)
Intro!uction
!n Ion-Selectie ,lectrode (IS,) produces a potential that is proportional to the
concentration o% an analyte 'a8ing measurements &ith an IS, is there%ore a %ormo% potentiometry .he most common IS, is the pH electrode# &hich contains a thin
glass membrane that responds to the HGconcentration in a solution
$.eory
.he potential di%%erence across an ion-sensitie membrane is@
, = F (0.An4)log(a)
&here is a constant to account %or all other potentials# is the gas constant# . is
temperature# n is the number o% electrons trans%erred# 4 is 4araday5s constant# and a
is the actiity o% the analyte ion ! plot o% measured potential ersus log(a) &illthere%ore gie a straight line
IS,s are susceptible to seeral inter%erences Samples and standards are there%ore
diluted @ &ith total ionic strength adBuster and bu%%er (.IS!N) .he .IS!N
consists o% ' +aCl to adBust the ionic strength# acetic acidAacetate bu%%er to
control pH# and a metal comple
8/13/2019 F AC 21 08 Potentiometry
37/64
IS 3ion selective electro!e)
!ny electrode that pre%erentially responds to one ion species
2lass membrane electrode @ HG
i$uid membrane electrodes
Solid state and precipitate electrodes
> 2as sensing electrodes
; ,nyme electrodes
Selectiity coe%%icient
kV#3
= (response to 3) A (response to V)
2eneral behaior o% IS,
, = constant (00;9:AnV) log 7AV G(kV#3A3nV n3)?
I t t ti
8/13/2019 F AC 21 08 Potentiometry
38/64
Instrumentation
IS,s consist o% the ion-selectie membrane# an internal re%erence electrode# an
e
8/13/2019 F AC 21 08 Potentiometry
39/64
Li6ui! IS
Ca IS,
Calcium didecylphosphate dissoled in dioctylphenylphosphonate
7(CH(CH)JCH/)P/?Ca 7(CH(CH)JCH/)P/?FG CaG
Diagram o% a li$uid-membrane electrode %or CaG
8/13/2019 F AC 21 08 Potentiometry
40/64
8/13/2019 F AC 21 08 Potentiometry
41/64
Comparison o% a li$uid-membrane calcium ion electrode &ith a glass pH electrode
8/13/2019 F AC 21 08 Potentiometry
42/64
8/13/2019 F AC 21 08 Potentiometry
43/64
Photograph o% a potassium li$uid-ione
8/13/2019 F AC 21 08 Potentiometry
44/64
! homemade li$uid-membrane electrode
8/13/2019 F AC 21 08 Potentiometry
45/64
Soli! state crystalline membrane electro!e
'igration o% 4Fthrough a4doped &ith ,u4
8/13/2019 F AC 21 08 Potentiometry
46/64
8/13/2019 F AC 21 08 Potentiometry
47/64
;amle< Fluori!e 3F-) electro!e
Internal re% electrode
!gA!gCl
4illing soln
!$ueous +aCl G +a4
'embrane
a4crystal disc
!pplications
,lectroplating industry# &ater treatment (%luoridation)# toothpaste
*lications o ion selective electro!es
8/13/2019 F AC 21 08 Potentiometry
48/64
Ion-selectie electrodes are used in a &ide ariety o% applications %or determining the concentrations
o% arious ions in a$ueous solutions .he %ollo&ing is a list o% some o% the main areas in &hich IS,s
hae been used
Pollution 'onitoring@ C+# 4# S# Cl# +/etc# in e%%luents# and natural &aters
!griculture@ +/# Cl# +H
># # Ca# I# C+ in soils# plant material# %ertilisers and %eedstu%%s
4ood Processing@ +/# +/
in meat preseraties
Salt content o% meat# %ish# dairy products# %ruit Buices# bre&ing solutions
4 in drin8ing &ater and other drin8s
Ca in dairy products and beer
in %ruit Buices and &ine ma8ing
Corrosie e%%ect o% +/in canned %oods
Detergent 'anu%acture@ Ca# Na# 4 %or studying e%%ects on &ater $uality
Paper 'anu%acture@ S and Cl in pulping and recoery-cycle li$uors
,
8/13/2019 F AC 21 08 Potentiometry
49/64
Semi-con!uctor
Imper%ections or impurities in &hat are normally insulators may gie rise to a
temperature-dependent conductiity( metallic conductiity decreases &ith rise in
temperature) arising because the highest occupied energy leel is ery close to an
unoccupied leel
Classi%ication speci%ic resistance
semiconductor 0F>^ 0_m
conductor ^0FJ
insulator 0^00
8/13/2019 F AC 21 08 Potentiometry
50/64
,lemental or intrinsic semiconductor @ ten nine (9999999999Z purity)
II III IK K KIN C
!l Si P S
1n 2a 2e !s
Cd In Sn Sb Se
.e
Compounds or e
8/13/2019 F AC 21 08 Potentiometry
51/64
p-tye an! n-tye semicon!uctor
Si
Si
Si
Si
Si
Si
SiSi
Si
Complete coalent
bond
SiSi
SiSi
Si
Si
Si
SiSiSi
!l
Displaced by
trialent(acceptor)
impurity atom
Si
Si
Si
SiSi
Si P
hole
Conduction
electron
Displaced by
pentaalent(donor)
impurity atom
carrier
Pure silicon crystal
structure-type n-type
Dio!e < electron tube eacuated glass or metal enelope containing t&o electrodes a cathode
8/13/2019 F AC 21 08 Potentiometry
52/64
Dio!e < electron tube# eacuated glass or metal enelope containing t&o electrodes# a cathodeand an anode It is used as a recti%ier and as a detector in electronic circuits such as radio and
teleision receiers Qhen a positie oltage is applied to the anode (or plate)# electrons emitted %rom
the heated cathode %lo& to the plate and return to the cathode through an e
8/13/2019 F AC 21 08 Potentiometry
53/64
Dr Tohn Nardeen# Dr Qalter Nrattain# and Dr Qilliam Shoc8ley discoered
the transistor e%%ect and deeloped the %irst deice in December# 9># &hile
the three &ere members o% the technical sta%% at Nell aboratories in 'urrayHill# +T .hey &ere a&arded the +obel Prie in physics in 9;:
http@AA&&&lucentcomAmindsAtransistorA Copyright 2002 Lucent Technologies. All rights reserved. *
http://c/8/13/2019 F AC 21 08 Potentiometry
54/64
$ransistor
!n actie component o% an electronic circuit &hich may be used as an ampli%ier#
detector# or s&itch
! transistor consists o% a small bloc8 o% semiconducting material to &hich at leastthree electrical contacts are made
.ransistors are o% t&o general types# bipolar and %ield e%%ect
:n:type n::ntype
emitter emitter base collector collectorbase
C C
, ,
Carrier@ hole Carrier@ conduction electron
N N
8/13/2019 F AC 21 08 Potentiometry
55/64
.ransistor
,miter Collector Nase Nase Carrier
( ) !" #$ %&'( )* +, -. /01 +, -.2
*nipolar .ransistor Nipolar .ransistor2 34'5 # 67 # 89 # :" ; ?@A B
'/S('etal /
8/13/2019 F AC 21 08 Potentiometry
56/64
ate
) p2 .ransistor Ge )* F 2 G5 # 9 g K
} F$ p 2
) +, > '/S .ransistor KA G = .2 Nipolar .ransistor
Nase }lG .
mitter
+P+# P+P O F .ransistor 2 K +,
,ollector
.ransistor 3
4ase &aterial3 )Z 2 F$ P $
-3 (carbon nanotube) p 2 (silicon microchip) A Y
,f MN2 1[ 00 J : { o1 3] (+ano etter) }
V IN' V- . T V] (. T Qatson esearch Center) -
> p< (Ph !ouris) (K Deryc8e)# ( 'artel)# &U (T
!ppeneller) 2 $ V {E -3 (Single &all carbon nanotube R SQC+.s)
@} RS X\'
8/13/2019 F AC 21 08 Potentiometry
57/64
Fiel! eect transistor
2ate
Drain
Source
channel
'/S4,.
nchannel
! metal o
8/13/2019 F AC 21 08 Potentiometry
58/64
/peration o% a iel! eect transister
(a) +early random distribution o% holes and electrons in the base in
the absence o% gate potential
(b) Positie gate potential attracts electrons that %orm a conductie
channel beneath the gate Current can %lo& through this channel
bet&een source and drain
8/13/2019 F AC 21 08 Potentiometry
59/64
/peration o% chemical-sensing %ield e%%ect transistor .he transistor is coated &ith an
insulating Si/ layer and a second layer o% Si+> (silicon nitride)# &hich is imperious
to ions and improes electrical stability .he circuit at the lo&er le%t adBusts the potential
di%%erence bet&een the re%erence electrode and the source in response to changes in the
analyte solution# such that a constant drain-source current is maintained
8/13/2019 F AC 21 08 Potentiometry
60/64
C/gas sensing electrode
8/13/2019 F AC 21 08 Potentiometry
61/64
esponse o% a li$uid-membrane electrode to ariations
in the concentration and actiity o% calcium ion
8/13/2019 F AC 21 08 Potentiometry
62/64
.itration o% >mmol o% chloride ion &ith 0000' siler nitrate
(a) .itration cure (b) 4irst-deriatie cure (c) Second-deriatie cure
!pparatus %or a potentiometric titration
8/13/2019 F AC 21 08 Potentiometry
63/64
Kolume o% 0= + +a/H (m)
0 5 10 15 20 25
pH
2
4
6
8
10
12
14
Experimental titration curve of 0.1 N HOAc with 0.1 N NaOH ( f = 0.9720.
C!.-abASQ*# Dong-Sun ee
Kolume o% 0= + +a/H (m)
0 5 10 15 20 25
mK
-400
-300
-200
-100
0
100
200
300
8/13/2019 F AC 21 08 Potentiometry
64/64
Q
E!
Thanks
Dong-Sun ee A C!. A SQ*
Top Related