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Hg2Cl2 electrode
Water Research Vol. 9, pp. 663 to 665. Pe rgamon Press 1975. Printed in Great Britain.
DETERMINATION OF CHLORIDE IN WATER WITH A HgS/HgECI: ELECTRODE IVAN SEKERKA, JOSEPH F. LECHNER and RICHARD WALES Canada Centre for Inland Waters, Burlington, Ontario, Canada (Received 28 November 1974) Abstract--The application of a new type of solid state chloride ion sensitive electrode, based on HgS/Hg2C12 has been investigated for manual and automated measurements of chloride in natural, industrial and waste water. The electrode displays Nerstian response for the range 0.05-3.500 ppm of chloride and can be used for concentrations down to 0.05 ppm (5 x 10-v M). Achieved values of standard deviation, recovery and comparative tests from a variety of water samples are highly satisfactory. Inherent simplicity and sensitivity together with obtained results demonstrate the usefulness of the proposed method in routine analyses.
INTRODUCTION Methods based on gravimetry and titrimetry for the determination of small amounts of chloride generally lack precision and are not suitable for serial routine analysis. Many instrumental methods, including chloride ion-sensitive electrodes, are available (ASTM Standards, 1970; Pungor, 1967; Van Loon, 1968 and 1970; Katz and Mukherji, 1968; Mascini and Liberti, 1969; Ruzicka and Lamm, 1971; Torrance, 1974), but these have not the desired precision and accuracy especially at very low chloride levels. Furthermore, there exists a definite need for improvcment of the detection limit, since a good percentage of natural water samples show low to sub-ppm levels of chloride. The level of chloride in many industrial waters has to be kept minimal since it is an index of the corrosive potential of the water, Butler and Ison (1966). Recently, a new solid state chloride ion-selective electrode with overall better characteristics was introduced, Lechner and Sekerka (1974). The electrode consists of a pellet formed from a mixture of HgS and Hg2CI: by pressing at elevated temperature and sealing into a heat shrinkable tube. The electrode can be used over the range 3.500-0.005 ppm chloride, the linear portion of the standard curve occurring down to 0.05 ppm. The response time is significantly faster than with electrodes based on AgCI precipitate. In this work the electrode is evaluated for the determination of chloride in a variety of synthetic, natural, industrial and waste water samples. The results are compared to those obtained by the conventional, automated colorimetric method, Traversy (1971). EXPERIMENTAL Reaffents and standards Reagent-grade chemicals and deionized, double-distilled water were used for all solutions. A saturated KNO3 solution adjusted to pH 2 with HNO3 was the ionic strength adjusting buffer (ISAB). All standards solutions were prepared according to the basic analytical methods. 663
Apparatus The equipment used in this study included a HgS! HgzCl2 electrode and a double junction reference electrode (Orion 90-02-00). The outer filling solution (10% KNO3) of the reference electrode was renewed daily, to prevent contamination of the sample by chloride from the inner filling solution. This was found to be necessary in the case of measurements at low chloride levels. The results reported were obtained in part by manual procedure, using an Orion 801 millivoltmeter with Orion 751 digital printer. Automated determinations were carried out v/a a computerized apparatus for direct potentiometry and known addition techniques described by Sekerka and Lechner (1974). Procedures Manual direct potentiometry. To provide constant ionic strength and pH adjustment, 5 ml of Ionic Strength Adjusting Buffer (ISAB) was added to 50 ml aliquots of all standards and water samples. Thereafter, all consecutive millivolt readings of stirred solutions were taken after waiting for electrode equilibrium. The chloride levels were obtained by converting millivolt readings to sample activity, using a calibration curve. Automated known addition-known dilution technique. A standard solution (50.0 ml in a 200-ml beaker) of known amount of chloride (e.g. 35 ppm) was placed in the first position of the turntable, followed by water samples (50.0ml). The programmable apparatus carried out automatically all functions necessary for known additionknown dilution technique: i.e. the mechanical actions of immersions with withdrawing of the electrodes, additions of ISAB, stirring, 1: 1 dilutions with distilled water, rinsing of the electrodes before each immersion and changing of samples, and all electronic functions of accepting data at predetermined steps during the measurement cycle, followed by computation, indexing, and printout of the results expressed as ppm of chloride. A sampling rate of 20 samples per hour was found to be optimal. Potentiometric titrations. Some waste water samples, containing high levels of chloride, were titrated with a standard solution of 0.01 M mercurous nitrate at pH 2 and monitored by the HgS/HgzC12 electrode. RESULTS AND DISCUSSION Electrode characteristics Sensitivity. The electrode exhibits a Nerstian response for the range of 1 x 10-~M to 2 x 10-6M
664
1VAN SEKERKA, JOSEPH F. LECHNER a n d RICHARI) WALES
Table 2. Comparison of electrode and Standard Methods IOO
mg 1 ~C1added
20-0-l
mg 1- ~CI- found by electrode standard method
0.01 0.10 1.0 10.0 100.0
/
0.14 011 0.99 9.9 98.o
<0.1 0.15 I. l 10.1 101.0
E those obtained by conventional colorimetric thiocyanate method (Table 2).
5OO
Analysis of water samples
/
/
/
J
I
6
5 - Jo0
I
4
I
3
[ct-]
Fig. 1. Calibration curves of chloride ion electrodes. 1. Commercial Ag/S/AgCI electrode as given by Orion (1967). 2. Commercial Ag2S/AgCI electrode as tested in our laboratory. 3. HgS/Hg2C12 electrode. CI-. For routine water analyses of chloride, results obtained in the non-linear portion of the calibration curve (2 x 10 -6 to 5 × 10 -7 M C1-) are satisfactory. The comparison of the calibration curves of HgS/ HgzCI 2 a n d Ag2S/AgC1 electrodes can be seen in Fig. 1.
Samples of tap, boiler, natural streams, lake, a n d waste waters from Southern O n t a r i o were analyzed for chloride by HgS/Hg2CI_, electrode, by AgzS/AgCI electrode and by colorimetric method. Comparison of these methods is given in Table 3. The recovery test was performed by analyzing a variety of natural water samples before and after known addition of chloride. The recoveries, summarized in Table 4, were very close to the theoretical values. The results of potentiometric titrations of waste water samples are included in Table 4. The proposed manual method is simple, sensitive, a n d inexpensive, fast, accurate, precise, a n d therefore it is considered to be very convenient for the analysis Table 3. Water samples analyses
Interference In agreement with selectivity constants of the HgS/ Hg2C12 electrode published by Lechner a n d Sekerka (1974), the interference of other halides was found to be in the order o f I > B r - > C N S - = C l - . C o n sequently, when a sample contains significant a m o u n t s of interfering ions, the obtained result represents total a m o u n t s of I - , Br , C N S - and C1-. Potential interference by C N a n d S z- ions was eliminated however, by the p r o t o n a t i o n of these ions at the operational p H 2. The response time, stability a n d effect o f p H were described in our previous paper, see Lechner and Sekerka (1974).
Precision and accuracy To test the precision, five replicates at five different concentrations were run. O b t a i n e d values of relative standard deviations summarized in Table 1 show a high precision. A series of various standard solutions was analyzed for chloride by the HgS/HgzCI2 electrode m e t h o d and the results were compared with Table 1. Precision of chloride determination mgl iCladded 0.01 0. I 1.0 10.0 100.0
mgl-lCl found 0.14 0.1t 0.99 9.9 98.0
Sx (n = 5) 0.45 0.14 0.15 0.13 0.14
Sample No.
HgS/Hg2CI z electrode
1 2 3 4 5 6 7 8 9 10 1I 12 13 14
0.05 0.3 0.3 0.3 1.2 1.4 3.1 5.3 5.8 23.0 27.0 71.0 74.6 103.0
mgl ~C1- found by AgS/AgCI Standard electrode method * * * * 0.5 0.5 1.0 5.0 6.0 26.0 26.0 72.0 72.0 103.0
< 0.1 0.3 0.4 0.3 1.0 1.4 3.1 5.0 5.7 24.0 26.0 75.0 73.0 105.0
* Undetectable -below lower limit of detection of AgS/ AgCI electrode. Table 4. Recovery test in water samples mgl 1 (~'l (1l = 5) Type of water
Present
Added
Found
Recovery C.)
Boiler River Lake Waste Waste* Waste*
0.05 5.9 23.0 71.0 74.6 103.0
0,1 2.0 t0,0 20,0 20,0 20.0
(1.155 8.0 33.5 89.0 93,5 120,6
110 105 105 95 99 98
* Determined by potentiometric titration with 0.01M HgNO3 solution
Determination of chloride in water of small n u m b e r s of samples a n d in situ measurements, whereas, the a u t o m a t e d system is economical for serial analysis of large n u m b e r s of industrial a n d natural water samples. Both procedures are suitable for m e a s u r e m e n t of chloride ions in the concentration range of 5 x 10-7-1 x 10-1M.
REFERENCES
American Society for Testing and Materials (1970) ASTM Standards 23, D 512, Philadelphia. Butler G. and Ison H. C. K. (1966) Corrosion and its Prevention in Waters. pp. 14 and 174, Leonard Hill, London. Katz D. A. and Mukherji A. K. (1968) Determination of halides with ion-selective electrodes. Microchem. J. 13, 604-615. Lechner J. F. and Sekerka I. (1974) Chloride ion-selective electrode based on Hg/Hg2C12. J. Electroanal. Chem. (in press). Mascini M. and Liberti A. (1969) An analytical study of a new type of halide sensitive electrode prepared from silver halides and thermoplastic polymers. Anal. Chim. Acta. 47, 33%345.
665
Orion Research Inc. (1967) Instruction Manual, Halide Ion Electrode, p. 6. Pungor E. (1967) Theory and application of anion selective membrane electrodes. Anal. Chem. 39, No 13, 28A-45A. Ruzicka J. and Lamm C. G. (1971) Selectrode--The universal ion-selective solid state electrode. Part I. Halides. Anal. Chim. Acta. 54, 1-12. Sekerka I. and Lechner J. F. (1974) Automated simultaneous determination of water hardness, specific conductance and pH. Anal. Letters. 7(6), 39%408. Torrance K. (1974) A potentiometric method for the determination of chloride in boiler waters in the range 0.110#g ml- of chloride. Analyst. 99, 203 210. Traversy W. J. (1971) Methods for Chemical Analysis of Waters and Wastewaters. pp. 23-26. Water Quality Division, Department of Fisheries and Forestry, Ottawa, Canada. Van Loon J. C. (1968) Determination of chloride in chloride-containing materials with a chloride membrane electrode. Analyst. 93(12), 788 791. Van Loon J. C. (1970) Laboratory construction and laboratory and field evaluation of thermoplastic chlorideselective electrodes with liquid filling solution and soli& solid connections. Anal. Chim. Acta. 54, 23-28.
DETERMINATION OF CHLORIDE IN WATER WITH A HgS/HgECI: ELECTRODE IVAN SEKERKA, JOSEPH F. LECHNER and RICHARD WALES Canada Centre for Inland Waters, Burlington, Ontario, Canada (Received 28 November 1974) Abstract--The application of a new type of solid state chloride ion sensitive electrode, based on HgS/Hg2C12 has been investigated for manual and automated measurements of chloride in natural, industrial and waste water. The electrode displays Nerstian response for the range 0.05-3.500 ppm of chloride and can be used for concentrations down to 0.05 ppm (5 x 10-v M). Achieved values of standard deviation, recovery and comparative tests from a variety of water samples are highly satisfactory. Inherent simplicity and sensitivity together with obtained results demonstrate the usefulness of the proposed method in routine analyses.
INTRODUCTION Methods based on gravimetry and titrimetry for the determination of small amounts of chloride generally lack precision and are not suitable for serial routine analysis. Many instrumental methods, including chloride ion-sensitive electrodes, are available (ASTM Standards, 1970; Pungor, 1967; Van Loon, 1968 and 1970; Katz and Mukherji, 1968; Mascini and Liberti, 1969; Ruzicka and Lamm, 1971; Torrance, 1974), but these have not the desired precision and accuracy especially at very low chloride levels. Furthermore, there exists a definite need for improvcment of the detection limit, since a good percentage of natural water samples show low to sub-ppm levels of chloride. The level of chloride in many industrial waters has to be kept minimal since it is an index of the corrosive potential of the water, Butler and Ison (1966). Recently, a new solid state chloride ion-selective electrode with overall better characteristics was introduced, Lechner and Sekerka (1974). The electrode consists of a pellet formed from a mixture of HgS and Hg2CI: by pressing at elevated temperature and sealing into a heat shrinkable tube. The electrode can be used over the range 3.500-0.005 ppm chloride, the linear portion of the standard curve occurring down to 0.05 ppm. The response time is significantly faster than with electrodes based on AgCI precipitate. In this work the electrode is evaluated for the determination of chloride in a variety of synthetic, natural, industrial and waste water samples. The results are compared to those obtained by the conventional, automated colorimetric method, Traversy (1971). EXPERIMENTAL Reaffents and standards Reagent-grade chemicals and deionized, double-distilled water were used for all solutions. A saturated KNO3 solution adjusted to pH 2 with HNO3 was the ionic strength adjusting buffer (ISAB). All standards solutions were prepared according to the basic analytical methods. 663
Apparatus The equipment used in this study included a HgS! HgzCl2 electrode and a double junction reference electrode (Orion 90-02-00). The outer filling solution (10% KNO3) of the reference electrode was renewed daily, to prevent contamination of the sample by chloride from the inner filling solution. This was found to be necessary in the case of measurements at low chloride levels. The results reported were obtained in part by manual procedure, using an Orion 801 millivoltmeter with Orion 751 digital printer. Automated determinations were carried out v/a a computerized apparatus for direct potentiometry and known addition techniques described by Sekerka and Lechner (1974). Procedures Manual direct potentiometry. To provide constant ionic strength and pH adjustment, 5 ml of Ionic Strength Adjusting Buffer (ISAB) was added to 50 ml aliquots of all standards and water samples. Thereafter, all consecutive millivolt readings of stirred solutions were taken after waiting for electrode equilibrium. The chloride levels were obtained by converting millivolt readings to sample activity, using a calibration curve. Automated known addition-known dilution technique. A standard solution (50.0 ml in a 200-ml beaker) of known amount of chloride (e.g. 35 ppm) was placed in the first position of the turntable, followed by water samples (50.0ml). The programmable apparatus carried out automatically all functions necessary for known additionknown dilution technique: i.e. the mechanical actions of immersions with withdrawing of the electrodes, additions of ISAB, stirring, 1: 1 dilutions with distilled water, rinsing of the electrodes before each immersion and changing of samples, and all electronic functions of accepting data at predetermined steps during the measurement cycle, followed by computation, indexing, and printout of the results expressed as ppm of chloride. A sampling rate of 20 samples per hour was found to be optimal. Potentiometric titrations. Some waste water samples, containing high levels of chloride, were titrated with a standard solution of 0.01 M mercurous nitrate at pH 2 and monitored by the HgS/HgzC12 electrode. RESULTS AND DISCUSSION Electrode characteristics Sensitivity. The electrode exhibits a Nerstian response for the range of 1 x 10-~M to 2 x 10-6M
664
1VAN SEKERKA, JOSEPH F. LECHNER a n d RICHARI) WALES
Table 2. Comparison of electrode and Standard Methods IOO
mg 1 ~C1added
20-0-l
mg 1- ~CI- found by electrode standard method
0.01 0.10 1.0 10.0 100.0
/
0.14 011 0.99 9.9 98.o
<0.1 0.15 I. l 10.1 101.0
E those obtained by conventional colorimetric thiocyanate method (Table 2).
5OO
Analysis of water samples
/
/
/
J
I
6
5 - Jo0
I
4
I
3
[ct-]
Fig. 1. Calibration curves of chloride ion electrodes. 1. Commercial Ag/S/AgCI electrode as given by Orion (1967). 2. Commercial Ag2S/AgCI electrode as tested in our laboratory. 3. HgS/Hg2C12 electrode. CI-. For routine water analyses of chloride, results obtained in the non-linear portion of the calibration curve (2 x 10 -6 to 5 × 10 -7 M C1-) are satisfactory. The comparison of the calibration curves of HgS/ HgzCI 2 a n d Ag2S/AgC1 electrodes can be seen in Fig. 1.
Samples of tap, boiler, natural streams, lake, a n d waste waters from Southern O n t a r i o were analyzed for chloride by HgS/Hg2CI_, electrode, by AgzS/AgCI electrode and by colorimetric method. Comparison of these methods is given in Table 3. The recovery test was performed by analyzing a variety of natural water samples before and after known addition of chloride. The recoveries, summarized in Table 4, were very close to the theoretical values. The results of potentiometric titrations of waste water samples are included in Table 4. The proposed manual method is simple, sensitive, a n d inexpensive, fast, accurate, precise, a n d therefore it is considered to be very convenient for the analysis Table 3. Water samples analyses
Interference In agreement with selectivity constants of the HgS/ Hg2C12 electrode published by Lechner a n d Sekerka (1974), the interference of other halides was found to be in the order o f I > B r - > C N S - = C l - . C o n sequently, when a sample contains significant a m o u n t s of interfering ions, the obtained result represents total a m o u n t s of I - , Br , C N S - and C1-. Potential interference by C N a n d S z- ions was eliminated however, by the p r o t o n a t i o n of these ions at the operational p H 2. The response time, stability a n d effect o f p H were described in our previous paper, see Lechner and Sekerka (1974).
Precision and accuracy To test the precision, five replicates at five different concentrations were run. O b t a i n e d values of relative standard deviations summarized in Table 1 show a high precision. A series of various standard solutions was analyzed for chloride by the HgS/HgzCI2 electrode m e t h o d and the results were compared with Table 1. Precision of chloride determination mgl iCladded 0.01 0. I 1.0 10.0 100.0
mgl-lCl found 0.14 0.1t 0.99 9.9 98.0
Sx (n = 5) 0.45 0.14 0.15 0.13 0.14
Sample No.
HgS/Hg2CI z electrode
1 2 3 4 5 6 7 8 9 10 1I 12 13 14
0.05 0.3 0.3 0.3 1.2 1.4 3.1 5.3 5.8 23.0 27.0 71.0 74.6 103.0
mgl ~C1- found by AgS/AgCI Standard electrode method * * * * 0.5 0.5 1.0 5.0 6.0 26.0 26.0 72.0 72.0 103.0
< 0.1 0.3 0.4 0.3 1.0 1.4 3.1 5.0 5.7 24.0 26.0 75.0 73.0 105.0
* Undetectable -below lower limit of detection of AgS/ AgCI electrode. Table 4. Recovery test in water samples mgl 1 (~'l (1l = 5) Type of water
Present
Added
Found
Recovery C.)
Boiler River Lake Waste Waste* Waste*
0.05 5.9 23.0 71.0 74.6 103.0
0,1 2.0 t0,0 20,0 20,0 20.0
(1.155 8.0 33.5 89.0 93,5 120,6
110 105 105 95 99 98
* Determined by potentiometric titration with 0.01M HgNO3 solution
Determination of chloride in water of small n u m b e r s of samples a n d in situ measurements, whereas, the a u t o m a t e d system is economical for serial analysis of large n u m b e r s of industrial a n d natural water samples. Both procedures are suitable for m e a s u r e m e n t of chloride ions in the concentration range of 5 x 10-7-1 x 10-1M.
REFERENCES
American Society for Testing and Materials (1970) ASTM Standards 23, D 512, Philadelphia. Butler G. and Ison H. C. K. (1966) Corrosion and its Prevention in Waters. pp. 14 and 174, Leonard Hill, London. Katz D. A. and Mukherji A. K. (1968) Determination of halides with ion-selective electrodes. Microchem. J. 13, 604-615. Lechner J. F. and Sekerka I. (1974) Chloride ion-selective electrode based on Hg/Hg2C12. J. Electroanal. Chem. (in press). Mascini M. and Liberti A. (1969) An analytical study of a new type of halide sensitive electrode prepared from silver halides and thermoplastic polymers. Anal. Chim. Acta. 47, 33%345.
665
Orion Research Inc. (1967) Instruction Manual, Halide Ion Electrode, p. 6. Pungor E. (1967) Theory and application of anion selective membrane electrodes. Anal. Chem. 39, No 13, 28A-45A. Ruzicka J. and Lamm C. G. (1971) Selectrode--The universal ion-selective solid state electrode. Part I. Halides. Anal. Chim. Acta. 54, 1-12. Sekerka I. and Lechner J. F. (1974) Automated simultaneous determination of water hardness, specific conductance and pH. Anal. Letters. 7(6), 39%408. Torrance K. (1974) A potentiometric method for the determination of chloride in boiler waters in the range 0.110#g ml- of chloride. Analyst. 99, 203 210. Traversy W. J. (1971) Methods for Chemical Analysis of Waters and Wastewaters. pp. 23-26. Water Quality Division, Department of Fisheries and Forestry, Ottawa, Canada. Van Loon J. C. (1968) Determination of chloride in chloride-containing materials with a chloride membrane electrode. Analyst. 93(12), 788 791. Van Loon J. C. (1970) Laboratory construction and laboratory and field evaluation of thermoplastic chlorideselective electrodes with liquid filling solution and soli& solid connections. Anal. Chim. Acta. 54, 23-28.