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Potentiometric titration of cyanide and chloride, using the silver specific-ion electrode as an indicator
952
Short communications R&um&Une lame de platine recouverte d’un film de mercure et de sulfure de mercure est recommand& comme &&ode pour les titrages potentiom&iques au thioac&amide. REFERENCES
1. 2. 3. 4.
G. Bush, C. W. Zuehlke and A. E. Ballard, Anal. Chem., 1959,31,1369. M. Pryszczewska, Talanta, 1%3,10,135. T. M. Hseu and G. A. Rechnitz, Anal. Chem., 1968,40,1054. R. Cecil, Biochim. Biophys. Actu, 1955,18,154.
Talanta, 1971,Vol. 18,pp. 952to 955. PersamonPress. Printed in Northern Ireland
Potentiometric titration of cyanide and chloride, using the silver specific-ion electrode as an indicator* (Received 24 August 1970. Accepted 10 January 1971) SEVERALmethods are available for the titration of cyanide in solutions. The most common visual method is that of Liebig.’ Gerchman and Rechnitzs used a glass electrode as an indicator for the potentiometric titration of cyanide in solutions. However, these titrations were not performed in the presence of chloride. For mixtures of cyanide and chloride, the usual procedure is to determine thecyanideconcentration by Liebig’s method and then to add an excess of standard silver nitrate, tilter off the precipitate of AgCl and AgCN, and titrate an aliquot of the filtrate for the excess of silver nitrate.* Ikeda et al.’ described an amperometric titration for the simultaneous determination of cyanide and chloride, methanol and gelatin being added. Souse5 has reported a complexometric procedure for the determination of cyanide and chloride in a mixture. Iwasaki et a1.Odescribed a calorimetric procedure for cyanide and chloride, using thiocyanate. However, all of these methods suffer from at least one of the following disadvantages; they are time-consuming, the analysis must be performed on aliquots of the sample, or additional reagents must be added in the analysis. In solutions of cyanide containing large amounts of chloride, it is difficult to determine the visual end-point accurately because a small residual precipitate of silver cyanide appears which obscures the end-point. However, the potentiometric end-point is precise and accurate and is denoted by a large potential change (approximately 500 mV). This paper describes a method for titrating cyanide and chloride in a single solution and quantitatively determining the concentration of each with one continuous titration. EXPERIMENTAL Apparatus Magnetic stirring motor and Teflon-covered bar. Orion “Ionanalyzer” Model 801 pH meter. Orion silverlsulphide specific-ion electrode, Model 94-16. Reagents Potassium cyanide, --O*lM. Potassium chloride, O*lOOOM. Silver nitrate, 0~1000M. Procedure Aliquots of the O.lM solutions of cyanide and chloride in a single solution were titrated with the O.lM silver nitrate, the silver specific-ion electrode vs. calomel electrode system being used for the potential measurements. The potentials obtained were plotted against the volume of titrant for determination of the end-points. RESULTS AND DISCUSSION Figure 1 shows a typical titration curve for a mixture of cyanide and chloride. equivalence point of equation (1). Ag+ + 2CN- = Ag(CN),-. * This work was supported by the United States Atomic Energy Commission.
Point A is the (1)
Short communications
953
Point A precedes Liebig’s visual end-point by an amount approximately equivalent to the amount of excess of Ag+ needed to form the visible precipitate. A value of twice the volume of titrant at point A +5ca
+400
+3w
+200
+loo
%
0
-100
-200
-300 -400
-500
-600
/
I
I
I
I
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28
-700
I
I
I
I
I
I
I
I
,I
ml OF Ag NO3 FIG. l.-Titration
curve of a mixture of cyanide and chloride with 0~1000M silver nitrate. Point A is the tirst end-point of the cyanide titration. Point B is the second end-point of the cyanide titration. Point C is the chloride end-point.
[equation (1)] was used to calculate the total cyanide concentration. Point B is the equivalence point indicated by equation (2), or the point at which all the cyanide is converted into insoluble AgCN. Ag(CN),-
f Ag+ = 2AgCN.
(2)
In a solution containing a large amount of chloride, point B is difficult to distinguish because the rate of potential change at the end-point is small compared to that at point A. As a result of the difficulty of reading point B, it was not used in the calculations of total cyanide concentration. Point C is the end-point of the titration of the chloride: Cl- + Ag+ = AgCl.
(3)
954
Short communications
The volume of titrant indicated at point C minus twice the volume of titrant at point A is the volume of titrant for the chloride titration. The precision and accuracy of this method were determined by analysing a series of sample solutions containing specific amounts of potassium cyanide and potassium chloride. The results are reported in Table I. TABLE I.-SAMPLES OF CYANIDE AND -RIDE
Sample No.
mnwle taken
mmole found
CN-
CI-
0.0 5.0 10.0 25.0 10.0 25.0 25.0 25.0
25.0 25.0 25.0 25.0 10.0 10.0 5.0 0.0
CN-
CI-
10.0 2498 0.96 2498 2494 2496
25.05 25.1 25.05 25.01 10.04 10.02 5.01 0.0
The results in Table I show that for both cyanide and chloride, the maximum deviation is O-4% with an average deviation of 0.2% from the true value. All the chloride values in Table I show positive deviations from the true values. This is explained by a slight leakage of the potassium chloride from the calomel electrode during the titration. An investigation was made to determine the possible application of this method to pollution studies. The use of specific-ion electrodes in pollution studies has been reported by Weber’ and also by Riseman The lowest detectable limit of cyanide in distilled water was 20 ppb. In solutions containing small amounts of chloride (20 ppm), the lower detectable limit for cyanide was 0.3 ppm which agrees with reported values. In solutions containing amounts of chloride similar to those in sea-water (19 g chloride/l. of solution, representing approximately a lo6 excess of chloride relative to cyanide), the lower detectable limit for cyanide was also 0.3 ppm. This low detectable limit for cyanide shows that this method is applicable for determining cyanide in river and sea-water, assuming the interferences are small. Acknowledgement-The author wishes to thank J. C. Russell and B. T. Kenna, Sandia Laboratories, Albuquerque, New Mexico, for consultations. Sandia Laboratories Albuquerque, New Mexico, U.S.A.
FRANKJ.CQNRAD
Summa~-Conditions are given for consecutive potentiometric titration of cyanide and chloride in mmole amounts, a silver-specific electrode being used as indicator electrode. Zusammeafasstnu-Die Arbeitsbedingungen zur potentiometrischen Titration von Cyanid und Chlorid in Millimolmengen nacheinander werden angegeben; eine fiir Silber spezifische Elektrode dient als Indikatorelektrode. R&sum&On donne les conditions pour le titrage potentiometrique consecutif de cyanure et de chlorure en quantites de l’ordre de la mmole, une electrode sp&fique de l’argent &ant utilide comme electrode indicatrice. REFERENCES 1, N. H. Furman, Standard Methodr of Chemical Analysis, p, 761. Van Nostrand, 2. L. L. Gerchman and G. A. Rechnitz, Z. Anal. Chem., 1967,230,265.
New York, 1962.
955
Short communications
3. N. H. Furman, StandardMerhodr of Chemical Ana[ysis, p. 339. Van Nostrand, New York, 1962. 4. S. Ikeda, G. Nishida and T. Yoshida, Bunseki Klgaku, 1964,13,690; Chem. Abstt., 1964,61, 10043. 5. A. Sousa, Inform. Quim. Anal. (Madrid), 1961,15,61; Chem. Abstr., 1961,57,4032e. 6. I. Iwashaki, S. Utsumi, T. Oxawa and R. Hasegawa, Nippon Kagaku Zasshi, 1957, 78, 468; Chem. Abstr., 1958,52,10794c. 7. S. J. Weber, Am. Laboratory, p. 15, July 1970. 8. J. M. Riseman, Am. Laboratory, p. 32, July 1969.
Talanta, 1971,Vol. 18,PP. 955to 960. PersamonPress. Printedin NorthernIreland
AAS-mung
von Rhenium in Wolfram, Molybdh
und Tantal
(Eingegangen am 21 Dezember 1970. Angenommen am 24 Februar 1971)
DIE MBCHANISCHBN und elastischen Eigenschaften der hochschmelxenden %qargsmetalle werden in starkem AusmaB schon durch geringe Rheniumbeimengungen beeintlusst.l Die analytische Bestimmung kleinster Rheniummengen in diesen Materialien ist daher in letzter Zeit von mannigfachem Interesse. Die Bestimmung von Rhenium in Gegenwart von Molybdiin ist dartiberhinaus bedeutsam, da die einzige Quelle xur kommerxiellen Gewinnung d&es Metalles Molybdtiite unterschiedlichster Provenienz, mit einem Rheniumgehalt der Erxe in der Gri%senordmmg von 0,Ol bis 0,2%, ist. Die Bestimmung von Rhenium in diesen Elementen ist daher hauptsiichlich eine Frage der Spumnanalyse. In der Literatur* sind zahlreiche analytische Methoden zur Bestimmung von Rhenium beschrieben. Die Verfahren sind jedoch wenig xufiiedenstellend; hauptaiichlich wegen der durch die Matrixelemente verursachten St&ungen, die oft xeitlich recht aufwendige Trenu- und Am-eicherungsverfahren notwendig machen. Dabei sind diese Storungen von besonderer Bedeutung in Gegenwart grbsserer Mengen der Matrixelemente. Die Atom-Absorption+Spektroskopie hat sich in vielen Fiillen als Analysen-Schnellmethode bewlhrt, da sie seltener durch andere Begleitelemente gestiirt wird. Es sollte daher versucht werden diese Methode auf die Bestimmung von Rheniumspuren in Wolfram, MolybdHn und Tantal anzuwenden und unter Vermeidung aufwendiger Trenn- und Anreicherungsprozeduren em Schnellverfahren hierxu auszuarbeiten. EXPERIMENTELLER
TEIL
Apparatur
Die Untersuchungen wurden mit emem kommerziellen Atom-Absorptions-Spektralphotometer Model1 303 der Fa. Perkin-Elmer durchgefilhrt. Die Versuchsdaten sind im einzemen in der Tabelle I zusammengestellt. Die Flammeneinstelhmg sol1 dabei nach Biechlep so sein, dalJ der rote Flammensaum etwa 10-20 mm hoch ist, werm keine Lbsung angeaaugt wird. TABELLE I.-VERWCXSBEDINGIJNGEN
Spektrometer Schreiber Hohlkathodenlampe Wellenhinge Spaltbreite Spektrale Bandbreite Brenngas Druck Striimungsgeschw. Oxydans Druck Strismungsgeschw. Sprtlhgeschwindigkeit
Perkm-Elmer 303 Hitachi 165 Intensitron 4 = 346,04 mn & = 346,47 mn a, = 345,79 nm 0,3 mm 0,235 mn Acetylen 0,55 atii 2,5 Liter/min. Lachgas 1,7 atti 12 - 14 Liter/m&. 2,5 ml/min
Short communications R&um&Une lame de platine recouverte d’un film de mercure et de sulfure de mercure est recommand& comme &&ode pour les titrages potentiom&iques au thioac&amide. REFERENCES
1. 2. 3. 4.
G. Bush, C. W. Zuehlke and A. E. Ballard, Anal. Chem., 1959,31,1369. M. Pryszczewska, Talanta, 1%3,10,135. T. M. Hseu and G. A. Rechnitz, Anal. Chem., 1968,40,1054. R. Cecil, Biochim. Biophys. Actu, 1955,18,154.
Talanta, 1971,Vol. 18,pp. 952to 955. PersamonPress. Printed in Northern Ireland
Potentiometric titration of cyanide and chloride, using the silver specific-ion electrode as an indicator* (Received 24 August 1970. Accepted 10 January 1971) SEVERALmethods are available for the titration of cyanide in solutions. The most common visual method is that of Liebig.’ Gerchman and Rechnitzs used a glass electrode as an indicator for the potentiometric titration of cyanide in solutions. However, these titrations were not performed in the presence of chloride. For mixtures of cyanide and chloride, the usual procedure is to determine thecyanideconcentration by Liebig’s method and then to add an excess of standard silver nitrate, tilter off the precipitate of AgCl and AgCN, and titrate an aliquot of the filtrate for the excess of silver nitrate.* Ikeda et al.’ described an amperometric titration for the simultaneous determination of cyanide and chloride, methanol and gelatin being added. Souse5 has reported a complexometric procedure for the determination of cyanide and chloride in a mixture. Iwasaki et a1.Odescribed a calorimetric procedure for cyanide and chloride, using thiocyanate. However, all of these methods suffer from at least one of the following disadvantages; they are time-consuming, the analysis must be performed on aliquots of the sample, or additional reagents must be added in the analysis. In solutions of cyanide containing large amounts of chloride, it is difficult to determine the visual end-point accurately because a small residual precipitate of silver cyanide appears which obscures the end-point. However, the potentiometric end-point is precise and accurate and is denoted by a large potential change (approximately 500 mV). This paper describes a method for titrating cyanide and chloride in a single solution and quantitatively determining the concentration of each with one continuous titration. EXPERIMENTAL Apparatus Magnetic stirring motor and Teflon-covered bar. Orion “Ionanalyzer” Model 801 pH meter. Orion silverlsulphide specific-ion electrode, Model 94-16. Reagents Potassium cyanide, --O*lM. Potassium chloride, O*lOOOM. Silver nitrate, 0~1000M. Procedure Aliquots of the O.lM solutions of cyanide and chloride in a single solution were titrated with the O.lM silver nitrate, the silver specific-ion electrode vs. calomel electrode system being used for the potential measurements. The potentials obtained were plotted against the volume of titrant for determination of the end-points. RESULTS AND DISCUSSION Figure 1 shows a typical titration curve for a mixture of cyanide and chloride. equivalence point of equation (1). Ag+ + 2CN- = Ag(CN),-. * This work was supported by the United States Atomic Energy Commission.
Point A is the (1)
Short communications
953
Point A precedes Liebig’s visual end-point by an amount approximately equivalent to the amount of excess of Ag+ needed to form the visible precipitate. A value of twice the volume of titrant at point A +5ca
+400
+3w
+200
+loo
%
0
-100
-200
-300 -400
-500
-600
/
I
I
I
I
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28
-700
I
I
I
I
I
I
I
I
,I
ml OF Ag NO3 FIG. l.-Titration
curve of a mixture of cyanide and chloride with 0~1000M silver nitrate. Point A is the tirst end-point of the cyanide titration. Point B is the second end-point of the cyanide titration. Point C is the chloride end-point.
[equation (1)] was used to calculate the total cyanide concentration. Point B is the equivalence point indicated by equation (2), or the point at which all the cyanide is converted into insoluble AgCN. Ag(CN),-
f Ag+ = 2AgCN.
(2)
In a solution containing a large amount of chloride, point B is difficult to distinguish because the rate of potential change at the end-point is small compared to that at point A. As a result of the difficulty of reading point B, it was not used in the calculations of total cyanide concentration. Point C is the end-point of the titration of the chloride: Cl- + Ag+ = AgCl.
(3)
954
Short communications
The volume of titrant indicated at point C minus twice the volume of titrant at point A is the volume of titrant for the chloride titration. The precision and accuracy of this method were determined by analysing a series of sample solutions containing specific amounts of potassium cyanide and potassium chloride. The results are reported in Table I. TABLE I.-SAMPLES OF CYANIDE AND -RIDE
Sample No.
mnwle taken
mmole found
CN-
CI-
0.0 5.0 10.0 25.0 10.0 25.0 25.0 25.0
25.0 25.0 25.0 25.0 10.0 10.0 5.0 0.0
CN-
CI-
10.0 2498 0.96 2498 2494 2496
25.05 25.1 25.05 25.01 10.04 10.02 5.01 0.0
The results in Table I show that for both cyanide and chloride, the maximum deviation is O-4% with an average deviation of 0.2% from the true value. All the chloride values in Table I show positive deviations from the true values. This is explained by a slight leakage of the potassium chloride from the calomel electrode during the titration. An investigation was made to determine the possible application of this method to pollution studies. The use of specific-ion electrodes in pollution studies has been reported by Weber’ and also by Riseman The lowest detectable limit of cyanide in distilled water was 20 ppb. In solutions containing small amounts of chloride (20 ppm), the lower detectable limit for cyanide was 0.3 ppm which agrees with reported values. In solutions containing amounts of chloride similar to those in sea-water (19 g chloride/l. of solution, representing approximately a lo6 excess of chloride relative to cyanide), the lower detectable limit for cyanide was also 0.3 ppm. This low detectable limit for cyanide shows that this method is applicable for determining cyanide in river and sea-water, assuming the interferences are small. Acknowledgement-The author wishes to thank J. C. Russell and B. T. Kenna, Sandia Laboratories, Albuquerque, New Mexico, for consultations. Sandia Laboratories Albuquerque, New Mexico, U.S.A.
FRANKJ.CQNRAD
Summa~-Conditions are given for consecutive potentiometric titration of cyanide and chloride in mmole amounts, a silver-specific electrode being used as indicator electrode. Zusammeafasstnu-Die Arbeitsbedingungen zur potentiometrischen Titration von Cyanid und Chlorid in Millimolmengen nacheinander werden angegeben; eine fiir Silber spezifische Elektrode dient als Indikatorelektrode. R&sum&On donne les conditions pour le titrage potentiometrique consecutif de cyanure et de chlorure en quantites de l’ordre de la mmole, une electrode sp&fique de l’argent &ant utilide comme electrode indicatrice. REFERENCES 1, N. H. Furman, Standard Methodr of Chemical Analysis, p, 761. Van Nostrand, 2. L. L. Gerchman and G. A. Rechnitz, Z. Anal. Chem., 1967,230,265.
New York, 1962.
955
Short communications
3. N. H. Furman, StandardMerhodr of Chemical Ana[ysis, p. 339. Van Nostrand, New York, 1962. 4. S. Ikeda, G. Nishida and T. Yoshida, Bunseki Klgaku, 1964,13,690; Chem. Abstt., 1964,61, 10043. 5. A. Sousa, Inform. Quim. Anal. (Madrid), 1961,15,61; Chem. Abstr., 1961,57,4032e. 6. I. Iwashaki, S. Utsumi, T. Oxawa and R. Hasegawa, Nippon Kagaku Zasshi, 1957, 78, 468; Chem. Abstr., 1958,52,10794c. 7. S. J. Weber, Am. Laboratory, p. 15, July 1970. 8. J. M. Riseman, Am. Laboratory, p. 32, July 1969.
Talanta, 1971,Vol. 18,PP. 955to 960. PersamonPress. Printedin NorthernIreland
AAS-mung
von Rhenium in Wolfram, Molybdh
und Tantal
(Eingegangen am 21 Dezember 1970. Angenommen am 24 Februar 1971)
DIE MBCHANISCHBN und elastischen Eigenschaften der hochschmelxenden %qargsmetalle werden in starkem AusmaB schon durch geringe Rheniumbeimengungen beeintlusst.l Die analytische Bestimmung kleinster Rheniummengen in diesen Materialien ist daher in letzter Zeit von mannigfachem Interesse. Die Bestimmung von Rhenium in Gegenwart von Molybdiin ist dartiberhinaus bedeutsam, da die einzige Quelle xur kommerxiellen Gewinnung d&es Metalles Molybdtiite unterschiedlichster Provenienz, mit einem Rheniumgehalt der Erxe in der Gri%senordmmg von 0,Ol bis 0,2%, ist. Die Bestimmung von Rhenium in diesen Elementen ist daher hauptsiichlich eine Frage der Spumnanalyse. In der Literatur* sind zahlreiche analytische Methoden zur Bestimmung von Rhenium beschrieben. Die Verfahren sind jedoch wenig xufiiedenstellend; hauptaiichlich wegen der durch die Matrixelemente verursachten St&ungen, die oft xeitlich recht aufwendige Trenu- und Am-eicherungsverfahren notwendig machen. Dabei sind diese Storungen von besonderer Bedeutung in Gegenwart grbsserer Mengen der Matrixelemente. Die Atom-Absorption+Spektroskopie hat sich in vielen Fiillen als Analysen-Schnellmethode bewlhrt, da sie seltener durch andere Begleitelemente gestiirt wird. Es sollte daher versucht werden diese Methode auf die Bestimmung von Rheniumspuren in Wolfram, MolybdHn und Tantal anzuwenden und unter Vermeidung aufwendiger Trenn- und Anreicherungsprozeduren em Schnellverfahren hierxu auszuarbeiten. EXPERIMENTELLER
TEIL
Apparatur
Die Untersuchungen wurden mit emem kommerziellen Atom-Absorptions-Spektralphotometer Model1 303 der Fa. Perkin-Elmer durchgefilhrt. Die Versuchsdaten sind im einzemen in der Tabelle I zusammengestellt. Die Flammeneinstelhmg sol1 dabei nach Biechlep so sein, dalJ der rote Flammensaum etwa 10-20 mm hoch ist, werm keine Lbsung angeaaugt wird. TABELLE I.-VERWCXSBEDINGIJNGEN
Spektrometer Schreiber Hohlkathodenlampe Wellenhinge Spaltbreite Spektrale Bandbreite Brenngas Druck Striimungsgeschw. Oxydans Druck Strismungsgeschw. Sprtlhgeschwindigkeit
Perkm-Elmer 303 Hitachi 165 Intensitron 4 = 346,04 mn & = 346,47 mn a, = 345,79 nm 0,3 mm 0,235 mn Acetylen 0,55 atii 2,5 Liter/min. Lachgas 1,7 atti 12 - 14 Liter/m&. 2,5 ml/min