Analytica Chimica Acta, 64 (1973)431--438
0~) Elsevier Scientific Publishing C o m p a n y , A m s t e r d a m - P r i n t e d in The N e t h e r l a n d s
ION-SELECTIVE CARBON-PASTE
AND SILVER(I) IONS
ELECTRODES
431
FOR HALIDES
~. MESARIC'* a n d E. A. M. F. D A H M E N
Department of Chemical Technology, Twente University of Technology, Enschede (The Netherlands)
(Received 4th July 1972)
E l e c t r o d e s b a s e d on s o l i d - s t a t e crystals d e v e l o p e d by F r a n t a n d Ross 1 h a v e
received c o n s i d e r a b l e a t t e n t i o n 2-5.
T h e sensing e l e m e n t o f m o s t o f t h e ion-selective e l e c t r o d e s in use t o d a y is a n
ion-selective h o m o g e n e o u s m e m b r a n e ( O r i o n R e s e a r c h - t y p e electrodes) o r an ionselective h e t e r o g e n e o u s m e m b r a 0 e ( P u n g o r - t y p e electrodes). T h e h e t e r o g e n e o u s
m e m b r a n e c o n t a i n s a n electroactive species a n d inert b i n d e r material. As binder,
paraffin 6, c o l l o d i o n 7, polyvinyl c h l o r i d e s, p o l y e t h y l e n e 9 and: silicone r u b b e r I o. 11
h a v e b e e n used.
Recently, a n e w type o f e l e c t r o d e , the u n i v e r s a l ion-selective solid-state
e l e c t r o d e has b e e n d e v e l o p e d by Ru~i~ka a n d L a m m xz-t4. W h i l s t t h e ion-selective
e l e c t r o d e s p r o d u c e d p r e v i o u s l y c o n t a i n e d t h e e l e c t r o a c t i v e species in the b u l k o f the
e l e c t r o d e m e m b r a n e , t h e universal ion-selective s o l i d - s t a t e e l e c t r o d e h a s o n l y a
superficial layer o f t h e active species r u b b e d into a c o m p r e s s e d p a s t e o f g r a p h i t e a n d
a h y d r o p h o b i z i n g m a t e r i a l s u c h as teflon. I m p r e g n a t e d g r a p h i t e r o d a n d c a r b o n
p a s t e s h a v e l o n g b e e n used in v o l t a m m e t r y xS-tT, as s u b s t i t u t e s for n o b l e m e t a l
electrodes.
I n this p a p e r t h e b e h a v i o u r o f ion-selective e l e c t r o d e s c o n t a i n i n g a c t i v a t e d carb o n p a s t e in a plastic b o d y is described. T h e e l e c t r o a c t i v e p a s t e s are m a d e f r o m spectralg r a d e g r a p h i t e p o w d e r , nujol o r p a r a f f i n w a x a n d m e t a l s a l t s ~o f low solubility.
E l e c t r o d e s c o n s i s t i n g o f silver c h l o r i d e , silver c h l o r i d e - s i l v e r s u l p h i d e , silver b r o m i d e silver s u l p h i d e o r silver i o d i d e - s i l v e r s u l p h i d e w i t h c a r b o n - n u j o l o r c a r b o n - p a r a f f i n
w a x h a v e been investigated. T h e ion-selective c a r b o n - p a s t e e l e c t r o d e s a r e suitable
for d e t e r m i n a t i o n o f halide ions as well as silver i o n in a q u e o u s s o l u t i o n s by direct
potentiometric measurement and potentiometric titration.
EXPERIMENTAL
Reagents
A n a l y t i c a l r e a g e n t - g r a d e c h e m i c a l s a n d twice-distilled w a t e r were u s e d in all
experiments.
.
.
.
.
:
Silver n i t r a t e (0.1 M ; Titrasol, E. M e r c k A G ) a n d s o d i u m ' c h l o r i d e (0.2 M ;
Titrasol, E, M e r c k A G ) were used. S t a n d a r d s o l u t i o n s (0.1 M ) o f s o d i u m b r o m i d e a n d
p o t a s s i u m i o d i d e w e r e p r e p a r e d by d i s s o l v i n g the a p p r o p r i a t e a m o u n t s o f t h e salts
, * Present a d d r e s s : Institute "Rudjer Bo~kovi6", Zagreb, Yugoslavia.
• 432
~. MESARI(~, E. A. M. F. D A H M E N
in water, a n d s t a n d a r d i z i n g by t i t r a t i o n w i t h 0.1 M silver nitrate. A I M s o d i u m
s u l p h i d e w a s (freshly) p r e p a r e d f r o m s o d i u m s u l p h i d e m o n o h y d r a t e .
S p e c t r a l - g r a d e g r a p h i t e p o w d e r ( L e C a r b o n e L o r r a i n e , 45 r u e des Acacias,
Paris), n u j o l (paraffÉn l i q u i d for s p e c t r o s c o p y , E. M e r c k A G ) a n d paraffin w a x
( c o n g e a l i n g p o i n t a b o u t 55 °, B D H ) w e r e also used.
Preparation o f the electroactive precipitates
Silver c h l o r i d e a n d silver h a l i d e - s i l v e r s u l p h i d e ( 1 : 1) w e r e p r e c i p i t a t e d f r o m 0.1
M silver n i t r a t e s o l u t i o n w i t h 0.1 M s o d i u m c h l o r i d e o r 0.05 M s o d i u m h a l i d e + 0.05 M
sodium sulphide solution. The precipitates were washed with water by decantation,
filtered off a n d d r i e d o v e r n i g h t at 105 ° . S o m e p r e c i p i t a t e s w e r e m e l t e d a n d g r o u n d .
All silver s o l u t i o n s a n d p r e c i p i t a t e s w e r e shielded f r o m d i r e c t light.
Preparation o f the ion-selective carbon pastes
First, p u r e c a r b o n p a s t e s were m a d e by h a n d - m i x i n g m e a s u r e d q u a n t i t i e s
o f g r a p h i t e p o w d e r a n d n u j o l or paraffin wax. T h e best q u a l i t y p a s t e s were o b t a i n e d by m i x i n g c a r b o n a n d n u j o l in the ratio 5:1 (w/v) o r c a r b o n a n d paraffin
w a x in the r a t i o 3:1 (w/w).
T h e ion-selective p a s t e s w e r e p r e p a r e d by m i x i n g m e a s u r e d q u a n t i t i e s of elect r o a c t i v e p r e c i p i t a t e a n d p u r e c a r b o n paste. P a s t e s w i t h 13/o to 30~o e l e c t r o a c t i v e
m a t e r i a l w e r e p r e p a r e d a n d studied.
Instrumentation
P o t e n t i o m e t r i c m e a s u r e m e n t s w e r e m a d e w i t h a L a b o r p H m e t e r T y p e 23
( K n i c k , Berlin) a n d a flatbed r e c o r d e r B D 8 ( K i p p a n d Z o n e n , Delft).
R a d i o m e t e r t i t r a t i o n e q u i p m e n t w a s u s e d for p o t e n t i o m e t r i c t i t r a t i o n s ( R a d i o m e t e r p H m e t e r T y p e P H M 2 8 , T i t r a t o r T y p e T T T 1 I, A u t o b u r e t t e T y p e A U B 1 2 , a n d
R e c o r d e r T y p e SBR2). A n I n g o l d d o u b l e - j u n c t i o n c a l o m e l e l e c t r o d e T y p e 373-90.
M 5 - N S , filled w i t h 1 M p o t a s s i u m n i t r a t e w a s u s e d as reference electrode. All
p o t e n t i a l s w e r e r e c a l c u l a t e d t o S.C.E.
T h e p o t e n t i o m e t r i c m e a s u r e m e n t s w e r e c a r r i e d o u t in t h e c o n v e n t i o n a l m a n n e r
a n d all m e a s u r e m e n t s w e r e p e r f o r m e d in a t h e r m o s t a t e d cell ( c o n s t a n t t e m p e r a t u r e
w a t e r b a t h ) at 25 ° ___0.2 °. T h e s o l u t i o n s w e r e m i x e d b y a m a g n e t i c stirrer ( T e f l o n bar).
Jlf~
Construction and preparation o f the ion-selective carbon-paste electrodes
Electrode construction--Type 1. A m o d i f i e d A d a m s p o o l c o n f i g u r a t i o n elect r o d e (as u s e d in a n o d i c s t r i p p i n g v o l t a m m e t r y ) p r o v e d to be e q u a l l y useful in
p o t e n t i o m e t r y . T h e details o f t h e e l e c t r o d e a r e s h o w n in Fig. 1.
T h e e l e c t r o d e s w e r e p r e p a r e d as follows. A well for t h e p a s t e a n d a fine b o r e h o l e for t h e p l a t i n u m wire electric c o n n e c t i o n were drilled in a teflon rod. T h e teflon
p l u g with p l a t i n u m wire w a s c o n n e c t e d to a b a n a n a p l u g by rrieans o f plastic
tubing. A glass t u b e was i n s e r t e d to p r e v e n t twisting w h e n soft o r l o n g plastic t u b e
w a s used. T h e active c a r b o n p a s t e w a s t a m p e d into t h e well. A s m o o t h p a s t e surface
w a s o b t a i n e d by s m o o t h i n g w i t h a plastic s p a t u l a or b y p o l i s h i n g o n a s m o o t h p a p e r ,
plastic or stainless steel surface.
Electrode construction--Type 2. F i g u r e 2 s h o w s the e l e c t r o d e c o n s t r u c t i o n ,
c o n s i s t i n g o f plastic material, filled w i t h p a s t e a n d p r o v i d e d with a screw p l u n g e r
HALIDE-SELECTIVE ELECTRODES
433
5.
.J~f
f~
3O
270ram
5~
4~
3
2~
50-150mm
1
m
[_ i
~a
=:
Fig, 1. Electrode construction--Type 1. (1) P a s t e ; (2) teflon plug; (3) platinum wire; (4) plastic
tube; (5) glass tube; (6) plug. All dimensions in m m .
Fig. 2. Electrode construction--Type 2. (1) P a s t e ; (2) platinum wire; (3) rubber ring; (4) plexiglass
body; (5) screw; (6) banana plug; (7) lead. All dimensions in mm.
by m e a n s o f w h i c h a fresh paste surface could be restored at the lower end o f the
electrode. T h e screw c o u l d be raised and disconnected by rotating c o u n t e r c l o c k w i s e ,
so that the electrode c o u l d be filled w i t h paste ( a b o u t 0.5-5 g) from the t o p w h e n
the screw w a s d i s c o n n e c t e d or from the b o t t o m when the screw w a s in its higher
position. By turning the screw c l o c k w i s e the paste could be pressed o u t o f the l o w e r
end o f the electrode. A s m o o t h surface at the lower end w a s obtained by w i p i n g
it with a piece o f K l e e n e x or filter paper a n d by polishing on a s m o o t h paper, plastic
or stainless steel.surface.
.....
The paste electrode could b e refilled in a few m i n u t e s .
RESULTS
Silver c h l o r i d e and silver c h l o r i d e . s i l v e r •sulphide c a r b o n - p a s t e : e l e c t r o d e s
'
, E x p e r i m e n t s w e r e carried out w i t h 1~/o and 20% silver chloride, and 1~/o, 10%,
20% and 30~/o silver chloride:silve, r sulphide in c a r b o n - n u j o l a n d c a r b o n - p a r a f f i n w a x
pastes
•
,
,
.
?
,
;
434
TABLE
~. M E S A R I ¢ ~ , E. A . M . F . D A F I M E N
I
RESPONSE
OF SILVER
HALIDE
(10% AgX-Ag2S--carbon-nujol
Cx- °
ax-b
ELECTRODES
HALIDE
IONS
E ( m V ) vs. S.C.E. C
AgCI
1"I0 -t
1"10 -2
1"10 -a
1"10 -4
l'lO -5
1.10 -0
1"10-7
1"10-7
TO
paste electrodes)
7.7"10 -2
9.0"10 -3
9.8"10 -4
9.8"10 -5
9.8"10 -6
9.8.10 -7
9.8 " 1 0 - s .
9.8"10-9
AoBr
Ayl
Calc.
Found
Calc.
Found
Calc.
Found
49
104
161
220
279
47
101
163
223
263
--102
--47
10
69
128
187
--101
--48
11
69
119
165
--325
--270
--213
-- 1 5 4
--95
--36
23
82
--315,
--260,
.-201,
--140,
--80,
-- 19,
69,
" C x - =concentration of C I - ,
Br-
or I-.
b ax-=activity
of C I - ,
Br-
or I-.
¢ mV
--318
--262
-- 1 9 7
-- 141
--76
--16
42
69
found=average
value of three measurements.
TABLE
lI
RESPONSE
OF
SILVER
HALIDE
(10% AgX-Ag2S--carbon-nujol
CA8"
I'10 -l
1"10 -2
1"10 -3
1"10 -4
1-10-5
1"10 -6
1"10 -7
1"10 -e
a^s*
7.4"10
9.0"10
9.8"10
9.8"10
9.8.10
9.8"10
9.8"10
9.8"10
ELECTRODES
TO
SILVER
IONS
paste electrodes)
E ( m V ) vs. S.C.E.
-2
-3
-4
-5
-6
-7
-s
-9
Calc.
ABC!
Found
ABBr
Found
Ayl
Found
491
437
379
320
261
202
143
84
472
418
360
299
255
482
427
374
309
254
193
169
487
432
379
314
254
195
139
120
T h e potentials measured a n d the theoretical potentials for halides a n d silver(I)
with electrodes c o n t a i n i n g 10% silver c h l o r i d e - s i l v e r sulphide are presented in
Tables I a n d II. A typical electrode r e s p o n s e to c h a n g e in chloride i o n c o n c e n t r a t i o n
(bro~en line) a n d activity (solid line) is s h o w n in Fig. 3.
T h e reproducibility of the p o t e n t i a l s for different s o l u t i o n s o f the same chloride
or silver i o n c o n c e n t r a t i o n w a s w i t h i n -4- 1 inV. T h e numerical values for the s a m e
solution, o b t a i n e d with pastes c o n t a i n i n g different percentages of active material, did
not deviate by mo~'e than 10 m V f r o m each other. Electrodes with s u c h l o w c o n c e n trations as 13/o silver halide were satistactory w h e n freshly prepared, t h o u g h slower
in response than electrodes containix/g m o r e active material; but such electrodes
HALIDE-SELECTIVE
ELECTRODES
435
are m o r e liable in the l o n g r u n to interference f r o m f o r m a t i o n o f precipitates on the
surface.
T h e silver c h l o r i d e as well ~s the silver c h l o r i d e - s i l v e r s u l p h i d e c a r b o n paste e l e c t r o d e s s h o w e d N e r n s t i a n r e s p o n s e to c h l o r i d e a n d silver ion activity as
low as 5 - 1 0 - s M . H o w e v e r , the potential values at chloride o r silver ion c o n c e n t r a t i o n s b e l o w 5 . 1 0 -5 M varied f r o m e l e c t r o d e to electrode, as well as f r o m
m e a s u r e m e n t to m e a s u r e m e n t .
1'
E l e c t r o d e p o t e n t i a l s w e r e a t t a i n e d rapidly. In general, in solutions a b o v e
• 10 -3 M the p o t e n t i a l b e c a m e stable (to
+ 1 m V ) after 0.2-1 rain a n d below
this c o n c e n t r a t i o n after 5 - 1 0 rain.
T h e influnce o f p H o n the potential o f the electrode in 1.10 -3 M s o d i u m
chloride w a s s t u d i e d . It w a s s h o w n t h a t nitric acid up to 1.5 M a n d s o d i u m h y d r o x i d e
up to 0.1 3 / / d o n o t interfere.
Silver bromide-silver sulphide and silver iodide-silver sulphide ion-selective carbon-paste
electrodes
T h e b e h a v i o u r o f 1~/o, 10% a n d 20% silver b r o m i d e - s i l v e r s u l p h i d e a n d 1%, 10~/o
a n d 20% silver i o d i d e ' s i l v e r s u l p h i d e c a r b o n - n u j o l pastes was investigated. It was
found useful to m e l t the a c t i v e precipitates in o r d e r to o b t a i n stable potentials.
T h e e l e c t r o d e r e s p o n s e s t o c h a n g e in b r o m i d e , iodide a n d silver ion activity
are p r e s e n t e d in T a b l e s I a n d II. T h e silver b r o m i d e - s i l v e r sulphide electrodes s h o w e d
N e r n s t i a n r e s p o n s e to b r o m i d e a n d silver ion c o n c e n t r a t i o n d o w n to a b o u t 1" 10- s M.
The silver i o d i d e - s i l v e r s u l p h i d e e l e c t r o d e s s h o w e d N e r n s t i a n r e s p o n s e to iodide a n d
silver ion c o n c e n t r a t i o n s d o w n to as low as 5" 10-7 M. T h e potentials b e l o w these
values varied a n d will be d i s c u s s e d below. G e n e r a l l y , the b e h a v i o u r o f t h e b r o m i d e
o r iodide e l e c t r o d e s was s i m i l a r to the c a r b o n - p a s t e electrodes a c t i v a t e d with silver
chloride.
T h e s e ion-selective c a r b o n - p a s t e electrodes can, like o t h e r silver h a l i d e - b a s e d
electrodes, serve as sensitive e n d - p o i n t d e t e c t o r s in p o t e n t i o m e t r i c p r e c i p i t a t i o n
titration o f silver o r halides. T h e e q u i v a l e n c e - p o i n t p o t e n t i a l s are p r e s e n t e d in
Table III. E x c e l l e n t results w e r e o b t a i n e d in p o t e n t i o m e t r i c titrations o f m i x t u r e s
o f iodide, b r o m i d e a n d c h l o r i d e . T h e titration c u r v e o f a m i x t u r e o f 5 . 1 0 - 4 M
s o d i u m c h l o r i d e , s o d i u m b r o m i d e a n d p o t a s s i u m iodide is s h o w n in Fig. 4.
TABLE I
I
SOLUBILITY
I
,
PRODUCTS
.
AND EQUIVALENCE-POINT
POTENTIALS
AgCI
AgBr
Agl
K
pK
1.72.10 - 1 °
9.75
3.3" I 0 - 1 3
12.31
8.5" 10 -17
16.06
Equivalence-point
potetztlal,
Calc, raV vs. S . C , E ,
F o u n d m V vs. S.C.E.
270
273
194
199
83
96
Solubility productt s
OF SILVER HALIDES
436
~. M E S A R I C , E. A. M. F. D A H M E N
O-
mV
,7
rnV
-100-
100.
O100200•
2003OO4OO-
300l o "5
l o .3
1~
" c l " ccr
ml
1x
~:o
10"2M AgNO3
2'o
Fig. 3. C a l i b r a t i o n curve of chloride electrode, acl- (solid line), Ccl- ( b r o k e n li'ne).
Fig. 4. Titration curve of 5.0.10 -4 M NaCI, 5.1.-10 -4 M NaBr a n d 5.05- 10 -4 M K I (10 ml) with
1.0.10- 2 M AgNO~. As indicator electrode served the 10% AgI-AgzS--carbon-nujol electrode.
DISCUSSION AND CONCLUSION
T h e potential of the silver halide c a r b o n paste is g o v e r n e d by the silver
ion activity, b u t this in t u r n d e p e n d s o n the halide ion activity via the solubility
p r o d u c t o f the silver halide.
T h e limit o f d e t e c t i o n o f the e l e c t r o d e s is a f u n c t i o n o f the solubility 4' x6 o f the
immobilized precipitate.
At very low levels of the free halide or silver(I) ions (Fig. 3, d o t t e d lines),
the activated c a r b o n - p a s t e electrodes suffered f r o m subsensitivity a n d supersensitivity
(see ref. 12). H o w e v e r , the s a m e d a t a w e r e o b t a i n e d w h e n the electrode w a s r e s u r f a c e d
b e t w e e n runs.
In n o r m a l usage, n u m e r o u s d e t e r m i n a t i o n s o f c h l o r i d e , b r o m i d e , iodide as well
as silver c o u l d be m a d e at the v a r i o u s c o n c e n t r a t i o n levels, over a p e r i o d o f
several m o n t h s w i t h o u t the necessity o f r e n e w i n g the e l e c t r o d e surface.
• T h e a c t i v a t e d c a r b o n electrodes a r e suitable for d e t e r m i n a t i o n s o f halide o r
silver ( c o n c e n t r a t i o n , o r activity) by a p p l y i n g direct p o t e n t i o m e t r i c m e a s u r e m e n t s in
a n y o f the usual ways, or by a p o t e n t i o m e t r i c p r e c i p i t a t i o n titration.
P o t e n t i o m e t r i c titrations offer a n increase in a c c u r a c y a n d precision. H o w e v e r ,
mixtures of halides c a n n o t be t i t r a t e d as a c c u r a t e l y as a single halide 19. T h e silver
halides have a g r e a t t e n d e n c y to coprecipitate. A positive e r r o r in the e n d - p o i n t s
for iodide a n d b r o m i d e was f o u n d w i t h a mixture w h i c h w a s 5 . 1 0 - 4 M in e a c h
o f chloride, b r o m i d e a n d iodide (Fig. 4).
I n the paste surface, a sufficiently small cavity for the test s o l u t i o n was easily
formed, so t h a t the p o t e n t i o m e t r i c d e t e r m i n a t i o n s c o u l d be c a r r i e d o u t in submillilitre volumes.
HALIDE-SELECTIVE ELECTRODES
437
T h e p o t e n t i a l - d e t e r m i n i n g m e c h a n i s m for these electrodes involves an ione x c h a n g e process b e t w e e n the test s o l u t i o n a n d the surface layer o f the active
precipitate p h a s e , w i t h c a r b o n acting as an inert e l e c t r o n collector or d o n o r
(el. Ru~i~ka et al. 12.14). T h e ion-selective c a r b o n paste e l e c t r o d e d i p p e d into a solution o f an oxidizing a g e n t showed a c e r t a i n p o t e n t i a l in the e s t a b l i s h m e n t of
w h i c h the c a r b o n itself has no part. T h e m o r e strongly oxidizing the solution
(Fe 3 +, K M n O 4 , Ce 4 +, etc.), the m o r e positive was the potential. C o m p o u n d s having
a s t r o n g oxidizing a c t i o n interfered a n d s h o u l d therefore be r e d u c e d o r complexed
beforehand.
SUMMARY
T h e b e h a v i o u r o f a simple type of ion-selective e l e c t r o d e for h a l o g e n s a n d
silver has b e e n studied. T h e e l e c t r o d e consists of a plastic b o d y filled with c a r b o n
paste, the surface of w h i c h c a n be easily renewed. T h e p a s t e c o m p o s i t i o n is based o n
c a r b o n - n u j o l (5 : 1, w/v) or c a r b o n - p a r a f f i n wax (3 : 1, w / w ) c o n t a i n i n g a p r e p a r e d
m i x t u r e of silver h a l i d e - s i l v e r sulphide (1-307/o). T h e electrodes h a v e low o h m i c
resistance a n d s h o w a r a p i d N e r n s t i a n r e s p o n s e ( w i t h i n 2 - 5 mV) for halide a n d
silver ions d o w n to 5- 10 -5 M chloride, 1- 10 -5 M b r o m i d e a n d 5- 10 -7 M iodide
with the respective electrodes. Ions f o r m i n g very stable c o m p l e x e s w i t h halide or
silver a n d t h o s e h a v i n g strong oxidizing or r e d u c i n g a c t i o n interfere.
RI~SUMI~
U n e 6tude est effectu6e sur le c o m p o r t e m e n t d ' u n e 61ectrode s61ective ionique,
de t y p e simple, p o u r halog~nes et argent. L'61ectrode est c o n s t i t u t e d ' u n corps de
plastique r e m p l i d ' u n e pate de c a r b o n e , d o n t la surface peut ~tre facilement
r~nouvel~e. L a c o m p o s i t i o n de la pate est ~ base de c a r b o n e - n u j o l (5:1 poids/
v o l u m e ) ou de c a r b o n e - p a r a f f i n e (3:1 p o i d s / p o i d s ) a v e c 1 /L 3 0 ~ d ' u n m~lange
h a l o g ~ n u r e d ' a r g e n t - s u l f u r e d'argent. L'61ectrode pr~sente u n e faible r6sistance
o h m i q u e et u n e r~ponse n e r n s t i e n n e rapide. Les ions f o r m a n t des c o m p l e x e s tt'~s
stables avec h a l o g 6 n u r e o u argent, et ceux a y a n t une a c t i o n f o r t e m e n t o x y d a n t e ou
r~ductrice g~nent.
ZUSAMMENFASSUNG
D a s V e r h a l t e n eines einfachen M o d e l l s einer ionenselektiven E l e k t r o d e fiir
H a l o g e n e u n d Silber w u r d e untersucht. D i e E l e k t r o d e b e s t e h t aus einer Kunststoffhiille, die m i t einer K o h l e p a s t e gefiillt ist, d e r e n O b e r f l a c h e leicht e r n e u e r t w e r d e n
k a n n . Die P a s t e enth~ilt K o h l e n s t o f f - N u j o l (5:1, G / V ) o d e r Kohlenstoff-Paraffinw a c h s (3:1, G / G ) , d e m 1-307/o Silberhalogenid--Silbersulfid beigemischt sind. Die
E l e k t r o d e n h a b e n einen niedrigen O h m s c h e n W i d e r s t a n d u n d zeigen ein schnelles
N e r n s t s c h e s A n s p r e c h v e r h a l t e n gegeniiber H a l o g e n i d - u n d Sflberionen. Die unteren
K o n z e n t r a t i o n s g r e n z e n far die e n t s p r e c h e n d e n E l e k t r o d e n sind 5 . 1 0 - 5 M Chlorid,
1-10 - s M B r o m i d u n d 5-10 -7 M Jodid. Ionen, die mit H a l o g e n i d o d e r Silber
sehr stabile K o m p l e x e bilden o d e r stark o x i d i e r e n d o d e r r e d u z i e r e n d wirken, st~ren.
438
~. MESARIC, E. A. M. F. D A H M E N
REFERENCES
1 M. F r a n t a n d J. W. Ross, Science, 154 (1966) 1553.
2 (3. J. M o o d y a n d J. D. R. Thomas, Selective Ion-Sensitive Electrodes, Merrow Technical Library,
Watford, 1971.
3 R. A. Durst (Editor), Io~-Selective Electrodes, NBS Spee. Publ. No. 314, 1969.
4 E. P u n g o r a n d K. Toth, ,4nalyst, 95 (1970) 625.
5 W. Simon, H. R. W u h r r n a n n , M. Vasak, L. A. Pioda, R. D o h n e r a n d Z. ~tefana¢, Angew. Chem.,
82 (1970) 437.
6 R. B. Fischer a n d R. F. Babcook, Anal. Chem., 30 (1958) 1732.
7 S. Morazzani-Pelletier a n d M. A. Baffler, J. Chim. Phys., 62 (1965) 429.
8 A. Shatkay, Anal. Chem., 39 (1967) 1059.
9 R. G e y e r a n d W. Syring, Z. Chem., 6 (1966) 92.
10 E. Pungor, J. Havas a n d K. Toth, Z. Chem., 5 (1965) 9.
11 E. Pungor, Anal. Chem., 39 (1967) 28A.
12 J. Ru~.i~ka a n d A. G. L a m m , Anal. CI, im. Acta, 54 (1971) 1.
13 J. Ru~.i~ka, J. Chr. Tjell a n d C. (3. Lamm, Patent Appl. P. 20 34 686.5, 1970, The Federal
Republic of G e r m a n y .
14 E. H. Hahsen, C. G. Latnrh a n d J. Ru~i~ka, Anal. Chim. Acta, 59 (1972) 403.
15 S. P. Perone, Anal. Chem., 35 (1963) 2091.
16 E. P u n g o r a n d E. Szepesvary, Anal. Chim. Acta, 43 (1968) 289.
17 C. O l s o n a n d R. N. Adams, Anal. Chim. A'cta, 22(1960) 582.
18 L. (3. Sill6n a n d A. E. Martell, Stability Constants o f Ion Complexes, Chem. Sot., L o n d o n , Publ. No. 17,
1967.
19 A . J . Martin, Anal. Cller~., 30(1958) 233.