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Some observations on a new adiphenine-selective plastic membrane electrode based on adipheninium tetraphenylborate
MICROCHEMICAL
JOURNAL
42, 267-273 (1990)
Some Observations on a New Adiphenine-Selective Membrane Electrode Based on Adipheninium Tetraphenylborate Y. M. ISSA, HOSNY IBRAHIM,’ Department
of Chemistry,
Plastic
A. F. SHOUKRY, AND 0. A. EL-RASHIEDY
Faculty
of Science, Cairo University,
Giza, Egypt
Received April 21, 1990; accepted May 25, 1990 A new adiphenine (Ad) ion-selective PVC membrane electrode based on the ion-pair complex of Ad with sodium tetraphenylborate was prepared and its performance characteristics were studied. The electrode exhibited a linear response with a good Nemstian slope over a relatively wide range of concentration. Up to 24 h continuous soaking, the calibration graph slope was constant at 53.0 mV/concentration decade, at 25”C, then it decreased gradually as the time of soaking increases reaching 41 mV/decade after 11days. The changes in pH did not affect the electrode performance within the range 2.2-7.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The electrode showed very good selectivity for Ad with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were used to determine Ad in pure solutions and in a pharmaceutical preparation. 6 1990 Academic Press, IIIC.
INTRODUCTION
Adiphenine hydrochloride (Ad+Cl-), 2-diethylaminoethyl diphenylacetate hydrochloride, is an important pharmaceutical compound. It has weak parasympatholytic actions without the effects of atropine on the central nervous system, heart, eye, and salivary glands. It has been used for the symptomatic relief of visceral systems. Several techniques have been used to determine AdCl including spectrophotometry (Z-3) complexometry (4), GC (5), and HPLC (6-9). The compound has been identified qualitatively by IR spectroscopy (10) and thin-layer chromatography (II). Evstratova and Kochegina (12) analyzed mixtures of salts including AdCl potentiometrically. The sample is dissolved in dimethylformamide and titrated with a solution of KOH in an ethanol-benzene mixture, in a cell containing platinum and calomel electrodes. So far, no adiphenine-responsive electrode has been reported for the potentiometric determination of adiphenine in aqueous medium. In the present work, a plastic membrane electrode selective for adipheninium cation was constructed and its performance characteristics were studied. The electrode is based on incorporation of the adipheninium tetraphenylborate (Ad’TPB-) ion pair in a polyvinyl chloride (PVC) membrane plasticized with ’ To whom correspondence should be addressed. 267 0026265X&O $1.50 Copyright 0 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
268
ISSA ET AL.
dioctylphthalate (DOP). The electrode is used successfully as a sensor to determine AdCl in pure solutions and in Spasmo-Cibalgin ampules (CIBA). EXPERIMENTAL METHODS Reagents and materials. All chemicals used were of analytical grade. Distilled water was used throughout all experiments. Pure grade AdCl was supplied by Misr Co. Pharm. Ind. S.A.A., Egypt. The pharmaceutical preparation of SpasmoCibalgin ampules (220 mg aminophenazone + 30 mg diallylbarbituric acid + 25 mg AdWml) was provided by CIBA. The ion pair, Ad+TPB-, was precipitated by mixing AdCl with NaTPB solution. The white precipitate obtained was filtered, washed thoroughly with distilled water, and dried at room temperature. The electrodes. The adipheninium-responsive electrode based on the Ad-TPB ion-pair complex was constructed as previously described (13). Five membrane compositions were tried (Table 1). The electrode bodies were filled with a solution that was 10-l M in NaCl and lop3 M in AdCl and preconditioned by soaking in lo-* M AdCl solution. Potentiometric studies and electrochemical system. Potentiometric measurements were carried out with a Chemtrix Type 62 digital pWmV meter. A Techne circulator thermostat, Model C-100, was used to control the temperature of the test solution. The electrochemical system was as follows: Ag/AgCl/filling solution/membrane/test solution //KC1 salt bridge//saturated calomel electrode. Selectivity. The selectivity coefficients, Kp*z+,JZt , of the electrode toward different cationic species, J”+, were determined by the separate solutions method described previously (24). Potentiometric determination of AdCl. AdCl has been determined potentiometrically using the investigated electrode by the extrapolation and standard addition methods (15) and by potentiometric titration with a standard solution of NaTPB. RESULTS AND DISCUSSION Composition of the membrane. Five membrane compositions were investigated (Table 1). For each composition, the electrode was repeatedly prepared four times. The relative standard deviation values of slopes obtained (Table 1) show that the preparation process is highly reproducible. The results also reveal that composition V having the 14.5% ion pair leads to a hard membrane with poor physical properties. This is most probably due to oversaturation of the ion pair in the solvent mediator inside the PVC network. Electrodes made by using membrane II exhibited the best performance characteristics [slope 56.3 mV/ concentration decade, at 25°C; usable concentration range 1.2 x 10A5-3.2 x IO-* M AdCl; response time ~20 s]. In all subsequent studies, electrodes made of membrane II were used. Effect of soaking. Calibration plots (pAd vs E,mV) were obtained after the electrode was soaked continuously in lo-* M AdCl for 15 min; 1.5, 3, and 24 h;
ADIPHENINE-SELECTIVE
MEMBRANE
269
ELECTRODE
TABLE 1 Composition of the Membrane and Slope of the Calibration Graphs at 25 k 0. 1°C” Composition % (w/w) Membrane
Ion pair
DOP
PVC
Slope (mV/decade)
I II III IV V
5.5 8.0 10.0 12.5 14.5
51.0 49.5 49.0 47.0 46.0
43.5 42.5 41.0 40.5 39.5
43.0 56.3 48.0 47.3 -
s* m 0.1 -
a 1M h of soaking in 10m3M AdCI. * Relative standard deviation (four preparations).
and 2, 4, 5, 6, 9 and 11 days (Fig. 1). Up to 24 h of continuous soaking, the calibration graph slope is constant at 56.3 mV/decade, at 25°C then it decreases slightly to 50.0 mV/decade at 2-4 days, to 49 mV/decade at 5-6 days, to 48 mV/decade at 9 days, and to 41 mV/decade after 11 days of continuous soaking. The above results show that the electrode should be kept in a closed vessel and stored in a refrigerator while not in use. From Fig. 1 it is also clear that the lower limit of the Nernstian part of the calibration graph has not been significantly affected by the time of soaking ranging between 1.58 x 10P5 and 3.98 x 10m5M AdCl. 200
150 z w
100
50
4 3 I I , 6L,GJ‘l" , I 6543210
2 I 1
IO I ^ I
I .
, II I
(b) I
(cl
FIG. 1. Calibration graphs obtained, at 2X, after soaking the Ad electrode for (a) 15 min; (b) 1% and (c) 3 h; and (d) 1, (e) 2, (f) 4, (g) 5, (h) 6, (i) 9, and (i) 11 days.
270
ISSA ET AL.
PAd FIG. 2. Electrode potentialpAd plots at (a) 20, (b) 25, (c) 30, (d) 35, (e) 40, (0 45, (g) 50, and(h) 55°C.
Effect of temperature of the test solution. Figure 2 represents calibration graphs (electrode potential, Eelec,versus PAd) constructed at test solution temperature 20, 25, 30, 35, 40, 45, 50, and 55°C. The slope, usable concentration range, and response time of the electrode at each temperature are given in Table 2. The results show that within the temperature range investigated, the electrode responds, practically, to AdCl concentration with a nearly constant usable concenTABLE 2 Selectivity Coefficients, ~~+‘+J’+, for Adiphenine-Responsive Electrode Using the Separate Solution Method Interferent Li+ Na+ K+ NH; Mg* + Ca*+ Ba*’ S?’ Cd*+ Mn’+ Fe*+ co*+ Ni*+ CU*+ Zn Hg*+ Pb2+
e;+ ,J’ + 5.17 x 7.30 x 8.50 x 6.81 x 7.65 x 5.93 x 6.21 x 5.67 x 6.97 x 5.75 x 5.53 x 5.41 x 5.36 x 6.21 x 5.41 x 6.21 x 6.36 x
10-4 10-4 10-4 1O-4 10V5 10-3 lo-’ lo-’ lo-’ 10-s 10-5 10-T 1O-5 1O-5 1o-5 1O-4 1O-5
Interferent
e;+,J’+
Glycine Alanine Phenylalanine Methionine Tetramethylammonium bromide
6.21 6.45 6.21 6.66 6.21
x x x x x
1O-4 1O-4 1O-4 10-4 1O-4
Tetrabutylammonium iodide
9.80 x 10-l
Triethylbenzylammonium chloride
1.71 x lo-*
Cetyltrimethylammonium bromide
The electrode surface is poisoned
ADIPHENINE-SELECTIVE
MEMBRANE
-1ooc ,
,
,
1
2
3
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271
ELECTRODE
,
,
,
,
,
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5
6
7
8
9
10
11
P”
3. Effect of pH of the test solution on the potential reading (a) 4.80 X 1O-5, (b) 3.27 and (c) 4.54 x 10m3M AdCI. FIG.
x
10e3,
tration range of about 1.5 x 10-5-3.0 x IO-* M. Nevertheless, within the temperature range 30-45”C, the calibration graph slopes obtained are closer to the theoritical Nernstian values than those outside this range, reflecting better thermodynamic ionic exchange at the membrane-solution interface. For the determination of the isothermal coefficient of the electrode (dE”/dT), the standard electrode potentials (E”) were determined, at different temperatures, from Fig. 2 as the intercepts of the calibration graphs at pAd = 0 (Table 2) and plotted versus (t - 29, where c is the temperature of the experiment. A straight line plot is obtained according to (16) I (b)
loo -
50 > E. w
o-
-50 -
-100
r 0
12
3
k-i---+3
4
5
6
LI
, I I1 01234567
7 5I
I I 01234567
6I
7I(b)
i
I
I
,[C)
1
I
I
I
I
,(d)
I 0
I 12
1
I 3
I 4
I 5
I 6
,(e) 7
mL- NaTPB ( 1c2M)
4. Potentiometric titration of 50 ml solution, containing (a) 13.92, (b) 10.44, (c) 6.96, (d) 3.48, and (e) 1.74 mg AdCl using lo-* M standard NaTPB solution. FIG.
272
ISSA ET AL. TABLE 3 Potentiometric Determination of AdCl in Pure Solution and in Spasmo-Cibalgin Injections Extrapolation method
Standard addition method
Potentiometric titration
mg
Recovery
S*
Recovery
Recovery
Sample
taken
m
(%)
m
(W
Pure solution Spasmo-Cibalgin ampules
0.87-35.0
101.3
0.7
99.4
1.1
1.25-25.0
-
98.5
2.1
102 99.7
0.5 1.9
* Relative standard deviation (four determinations).
I? = E;, + (dE”/dT)(t
- 25).
The slope of the straight line obtained represents the isothermal coefficient of the electrode, it is 0.00055 VPC, revealing a fairly good thermal stability of the electrode within the temperature range investigated. EfSect of PH. The effect of pH of the test solution (4.80 x lop5 to 4.54 X 10e3 M AdCl) on the electrode potential was investigated by following the variation in potential with change in pH by the addition of very small volumes of hydrochloric acid and/or sodium hydroxide (0. l-l M each). Representative curves are shown in Fig. 3. It is evident that the change in pH has a negligible effect in the pH range 2.2-7.5. At 2.2 > pH > 7.5 the potential readings decrease sharply. This is attributed to penetration of chloride and hydroxide ions, respectively. SeZectivity. The intluence of some inorganic cations, sugars, amino acids, and large organic cations on the Ad electrode was investigated, the selectivity coefficients being determined by the separate solution method (Table 2). None of the investigated species were found to interfere as shown by the very small values of Pi;+ ,J” + . This reflects a very high selectivity of the investigated electrode toward the adipheninium cation. Analytical application. The investigated electrode was shown to be useful in the potentiometric determination of AdCl in pure solutions by the extrapolation and standard addition methods and by potentiometric titration. Representative titration curves are shown in Fig. 4. The adiphenine-containing pharmaceutical preparation (Spasmo-Cibalgin ampules) has been assayed by the standard addition method and by potentiometric titration using the investigated electrode. Collective results are given in Table 3. From the table it is evident that the present electrode is very useful for the microdetermination of AdCl in its solutions. ACKNOWLEDGMENT The authors express their deep thanks to Misr Co. for Pharm. Ind., Mataria, Cairo, Egypt, for providing the pharmaceutical compound investigated in this work.
REFERENCES 1. Zal’tsberg, V. Kh.; Zhivopistsev, V. P.; Bogoslovskaya, 0. N. Farmatsiya 86-87. 2. Adeishvili, L. V. Khim-Farm. Zh., 1979, 13, 49-101.
(Moscow),
1977, 26,
ADIPHENINE-SELECTIVE 3. 4. 5. 6. 7. 8. 9. 10. II. 12. 13. II. IS. 16.
MEMBRANE
ELECTRODE
273
Sane, R. T.; Shinde, B. R.; Parikh, A. K.; Tikekar, S. P. Indian Drugs, 1984, 21, 257-260. Gileva, L. N. Farmatsiya (Moscow), 1979, 28, 4044. Pawelczyk, E.; Wachowiak, R. Farm. Pal., 1977, 33, 413417. Brown, N. D.; Scovill, J. P.; Sleeman, H. K.; Doctor, B. P. J. Chromatogr., 1980,200,267-270. Ghilardelli, G.; Rotilio, F.; Zaccheo, F., Nannetti, M. Boll. Chim. Farm., 1980, 119, 483-186. Michelot, J.; Moreav, M. F.; Madelmont, J. C. ; Labarre, P.; Meyniel, G. J. Chromatogr., 1983, 257, 395-399. Facchini, G.; Zaccheo, F.; Nanetti, M. Boil. Chim. Farm., 1983, 122, 405411. Adeishvili, L. V. Farmatsiya (Moscow), 1980, 29, 32-35. Slepova, L. N.; Salivanova, L. I. Farmatsiya (Moscow), 1981, 30, 63-64. Evstratova, K. I.; Kochegina, A. A. Farmatsiya (Moscow), 1976, 25, 25-29. Shoukry, A. F.; Badawy, S. S.; Issa, Y. M. Anal. Chem., 1987, 59, 1078-1081. Badawy, S. S.; Shoukry, A. F.; Issa, Y. M. Analyst (London), 1986, 111, 1363-1365. Peter, D. G.; Hayes, J. M.; Hieftje, G. M. Chemical Separafion and Measuremenrs. Saunders, Philadelphia, 1974. Antropov, L. I. Theoreticai Electrochemistry. Mir, Moscow, 1972.
JOURNAL
42, 267-273 (1990)
Some Observations on a New Adiphenine-Selective Membrane Electrode Based on Adipheninium Tetraphenylborate Y. M. ISSA, HOSNY IBRAHIM,’ Department
of Chemistry,
Plastic
A. F. SHOUKRY, AND 0. A. EL-RASHIEDY
Faculty
of Science, Cairo University,
Giza, Egypt
Received April 21, 1990; accepted May 25, 1990 A new adiphenine (Ad) ion-selective PVC membrane electrode based on the ion-pair complex of Ad with sodium tetraphenylborate was prepared and its performance characteristics were studied. The electrode exhibited a linear response with a good Nemstian slope over a relatively wide range of concentration. Up to 24 h continuous soaking, the calibration graph slope was constant at 53.0 mV/concentration decade, at 25”C, then it decreased gradually as the time of soaking increases reaching 41 mV/decade after 11days. The changes in pH did not affect the electrode performance within the range 2.2-7.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The electrode showed very good selectivity for Ad with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were used to determine Ad in pure solutions and in a pharmaceutical preparation. 6 1990 Academic Press, IIIC.
INTRODUCTION
Adiphenine hydrochloride (Ad+Cl-), 2-diethylaminoethyl diphenylacetate hydrochloride, is an important pharmaceutical compound. It has weak parasympatholytic actions without the effects of atropine on the central nervous system, heart, eye, and salivary glands. It has been used for the symptomatic relief of visceral systems. Several techniques have been used to determine AdCl including spectrophotometry (Z-3) complexometry (4), GC (5), and HPLC (6-9). The compound has been identified qualitatively by IR spectroscopy (10) and thin-layer chromatography (II). Evstratova and Kochegina (12) analyzed mixtures of salts including AdCl potentiometrically. The sample is dissolved in dimethylformamide and titrated with a solution of KOH in an ethanol-benzene mixture, in a cell containing platinum and calomel electrodes. So far, no adiphenine-responsive electrode has been reported for the potentiometric determination of adiphenine in aqueous medium. In the present work, a plastic membrane electrode selective for adipheninium cation was constructed and its performance characteristics were studied. The electrode is based on incorporation of the adipheninium tetraphenylborate (Ad’TPB-) ion pair in a polyvinyl chloride (PVC) membrane plasticized with ’ To whom correspondence should be addressed. 267 0026265X&O $1.50 Copyright 0 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
268
ISSA ET AL.
dioctylphthalate (DOP). The electrode is used successfully as a sensor to determine AdCl in pure solutions and in Spasmo-Cibalgin ampules (CIBA). EXPERIMENTAL METHODS Reagents and materials. All chemicals used were of analytical grade. Distilled water was used throughout all experiments. Pure grade AdCl was supplied by Misr Co. Pharm. Ind. S.A.A., Egypt. The pharmaceutical preparation of SpasmoCibalgin ampules (220 mg aminophenazone + 30 mg diallylbarbituric acid + 25 mg AdWml) was provided by CIBA. The ion pair, Ad+TPB-, was precipitated by mixing AdCl with NaTPB solution. The white precipitate obtained was filtered, washed thoroughly with distilled water, and dried at room temperature. The electrodes. The adipheninium-responsive electrode based on the Ad-TPB ion-pair complex was constructed as previously described (13). Five membrane compositions were tried (Table 1). The electrode bodies were filled with a solution that was 10-l M in NaCl and lop3 M in AdCl and preconditioned by soaking in lo-* M AdCl solution. Potentiometric studies and electrochemical system. Potentiometric measurements were carried out with a Chemtrix Type 62 digital pWmV meter. A Techne circulator thermostat, Model C-100, was used to control the temperature of the test solution. The electrochemical system was as follows: Ag/AgCl/filling solution/membrane/test solution //KC1 salt bridge//saturated calomel electrode. Selectivity. The selectivity coefficients, Kp*z+,JZt , of the electrode toward different cationic species, J”+, were determined by the separate solutions method described previously (24). Potentiometric determination of AdCl. AdCl has been determined potentiometrically using the investigated electrode by the extrapolation and standard addition methods (15) and by potentiometric titration with a standard solution of NaTPB. RESULTS AND DISCUSSION Composition of the membrane. Five membrane compositions were investigated (Table 1). For each composition, the electrode was repeatedly prepared four times. The relative standard deviation values of slopes obtained (Table 1) show that the preparation process is highly reproducible. The results also reveal that composition V having the 14.5% ion pair leads to a hard membrane with poor physical properties. This is most probably due to oversaturation of the ion pair in the solvent mediator inside the PVC network. Electrodes made by using membrane II exhibited the best performance characteristics [slope 56.3 mV/ concentration decade, at 25°C; usable concentration range 1.2 x 10A5-3.2 x IO-* M AdCl; response time ~20 s]. In all subsequent studies, electrodes made of membrane II were used. Effect of soaking. Calibration plots (pAd vs E,mV) were obtained after the electrode was soaked continuously in lo-* M AdCl for 15 min; 1.5, 3, and 24 h;
ADIPHENINE-SELECTIVE
MEMBRANE
269
ELECTRODE
TABLE 1 Composition of the Membrane and Slope of the Calibration Graphs at 25 k 0. 1°C” Composition % (w/w) Membrane
Ion pair
DOP
PVC
Slope (mV/decade)
I II III IV V
5.5 8.0 10.0 12.5 14.5
51.0 49.5 49.0 47.0 46.0
43.5 42.5 41.0 40.5 39.5
43.0 56.3 48.0 47.3 -
s* m 0.1 -
a 1M h of soaking in 10m3M AdCI. * Relative standard deviation (four preparations).
and 2, 4, 5, 6, 9 and 11 days (Fig. 1). Up to 24 h of continuous soaking, the calibration graph slope is constant at 56.3 mV/decade, at 25°C then it decreases slightly to 50.0 mV/decade at 2-4 days, to 49 mV/decade at 5-6 days, to 48 mV/decade at 9 days, and to 41 mV/decade after 11 days of continuous soaking. The above results show that the electrode should be kept in a closed vessel and stored in a refrigerator while not in use. From Fig. 1 it is also clear that the lower limit of the Nernstian part of the calibration graph has not been significantly affected by the time of soaking ranging between 1.58 x 10P5 and 3.98 x 10m5M AdCl. 200
150 z w
100
50
4 3 I I , 6L,GJ‘l" , I 6543210
2 I 1
IO I ^ I
I .
, II I
(b) I
(cl
FIG. 1. Calibration graphs obtained, at 2X, after soaking the Ad electrode for (a) 15 min; (b) 1% and (c) 3 h; and (d) 1, (e) 2, (f) 4, (g) 5, (h) 6, (i) 9, and (i) 11 days.
270
ISSA ET AL.
PAd FIG. 2. Electrode potentialpAd plots at (a) 20, (b) 25, (c) 30, (d) 35, (e) 40, (0 45, (g) 50, and(h) 55°C.
Effect of temperature of the test solution. Figure 2 represents calibration graphs (electrode potential, Eelec,versus PAd) constructed at test solution temperature 20, 25, 30, 35, 40, 45, 50, and 55°C. The slope, usable concentration range, and response time of the electrode at each temperature are given in Table 2. The results show that within the temperature range investigated, the electrode responds, practically, to AdCl concentration with a nearly constant usable concenTABLE 2 Selectivity Coefficients, ~~+‘+J’+, for Adiphenine-Responsive Electrode Using the Separate Solution Method Interferent Li+ Na+ K+ NH; Mg* + Ca*+ Ba*’ S?’ Cd*+ Mn’+ Fe*+ co*+ Ni*+ CU*+ Zn Hg*+ Pb2+
e;+ ,J’ + 5.17 x 7.30 x 8.50 x 6.81 x 7.65 x 5.93 x 6.21 x 5.67 x 6.97 x 5.75 x 5.53 x 5.41 x 5.36 x 6.21 x 5.41 x 6.21 x 6.36 x
10-4 10-4 10-4 1O-4 10V5 10-3 lo-’ lo-’ lo-’ 10-s 10-5 10-T 1O-5 1O-5 1o-5 1O-4 1O-5
Interferent
e;+,J’+
Glycine Alanine Phenylalanine Methionine Tetramethylammonium bromide
6.21 6.45 6.21 6.66 6.21
x x x x x
1O-4 1O-4 1O-4 10-4 1O-4
Tetrabutylammonium iodide
9.80 x 10-l
Triethylbenzylammonium chloride
1.71 x lo-*
Cetyltrimethylammonium bromide
The electrode surface is poisoned
ADIPHENINE-SELECTIVE
MEMBRANE
-1ooc ,
,
,
1
2
3
, ‘
271
ELECTRODE
,
,
,
,
,
(
,
5
6
7
8
9
10
11
P”
3. Effect of pH of the test solution on the potential reading (a) 4.80 X 1O-5, (b) 3.27 and (c) 4.54 x 10m3M AdCI. FIG.
x
10e3,
tration range of about 1.5 x 10-5-3.0 x IO-* M. Nevertheless, within the temperature range 30-45”C, the calibration graph slopes obtained are closer to the theoritical Nernstian values than those outside this range, reflecting better thermodynamic ionic exchange at the membrane-solution interface. For the determination of the isothermal coefficient of the electrode (dE”/dT), the standard electrode potentials (E”) were determined, at different temperatures, from Fig. 2 as the intercepts of the calibration graphs at pAd = 0 (Table 2) and plotted versus (t - 29, where c is the temperature of the experiment. A straight line plot is obtained according to (16) I (b)
loo -
50 > E. w
o-
-50 -
-100
r 0
12
3
k-i---+3
4
5
6
LI
, I I1 01234567
7 5I
I I 01234567
6I
7I(b)
i
I
I
,[C)
1
I
I
I
I
,(d)
I 0
I 12
1
I 3
I 4
I 5
I 6
,(e) 7
mL- NaTPB ( 1c2M)
4. Potentiometric titration of 50 ml solution, containing (a) 13.92, (b) 10.44, (c) 6.96, (d) 3.48, and (e) 1.74 mg AdCl using lo-* M standard NaTPB solution. FIG.
272
ISSA ET AL. TABLE 3 Potentiometric Determination of AdCl in Pure Solution and in Spasmo-Cibalgin Injections Extrapolation method
Standard addition method
Potentiometric titration
mg
Recovery
S*
Recovery
Recovery
Sample
taken
m
(%)
m
(W
Pure solution Spasmo-Cibalgin ampules
0.87-35.0
101.3
0.7
99.4
1.1
1.25-25.0
-
98.5
2.1
102 99.7
0.5 1.9
* Relative standard deviation (four determinations).
I? = E;, + (dE”/dT)(t
- 25).
The slope of the straight line obtained represents the isothermal coefficient of the electrode, it is 0.00055 VPC, revealing a fairly good thermal stability of the electrode within the temperature range investigated. EfSect of PH. The effect of pH of the test solution (4.80 x lop5 to 4.54 X 10e3 M AdCl) on the electrode potential was investigated by following the variation in potential with change in pH by the addition of very small volumes of hydrochloric acid and/or sodium hydroxide (0. l-l M each). Representative curves are shown in Fig. 3. It is evident that the change in pH has a negligible effect in the pH range 2.2-7.5. At 2.2 > pH > 7.5 the potential readings decrease sharply. This is attributed to penetration of chloride and hydroxide ions, respectively. SeZectivity. The intluence of some inorganic cations, sugars, amino acids, and large organic cations on the Ad electrode was investigated, the selectivity coefficients being determined by the separate solution method (Table 2). None of the investigated species were found to interfere as shown by the very small values of Pi;+ ,J” + . This reflects a very high selectivity of the investigated electrode toward the adipheninium cation. Analytical application. The investigated electrode was shown to be useful in the potentiometric determination of AdCl in pure solutions by the extrapolation and standard addition methods and by potentiometric titration. Representative titration curves are shown in Fig. 4. The adiphenine-containing pharmaceutical preparation (Spasmo-Cibalgin ampules) has been assayed by the standard addition method and by potentiometric titration using the investigated electrode. Collective results are given in Table 3. From the table it is evident that the present electrode is very useful for the microdetermination of AdCl in its solutions. ACKNOWLEDGMENT The authors express their deep thanks to Misr Co. for Pharm. Ind., Mataria, Cairo, Egypt, for providing the pharmaceutical compound investigated in this work.
REFERENCES 1. Zal’tsberg, V. Kh.; Zhivopistsev, V. P.; Bogoslovskaya, 0. N. Farmatsiya 86-87. 2. Adeishvili, L. V. Khim-Farm. Zh., 1979, 13, 49-101.
(Moscow),
1977, 26,
ADIPHENINE-SELECTIVE 3. 4. 5. 6. 7. 8. 9. 10. II. 12. 13. II. IS. 16.
MEMBRANE
ELECTRODE
273
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