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An improved colorimetric determination of vanadium in geochemical prospecting samples
1070
Short communications REFERENCES
:: 3. 4. 5. ;: 8. 9. 10.
J. R. Partington, A Textbook of Inorganic Chemistry, 6th Ed. Macmillan, London, 1950. M. D. Lyutaya, T. N. Nazarchuk and K. D. Modylevskaya, USSR Putent 142805, Dec. 28,1961, Appl. Mar. 20, 1961. H. Blumenthal, Anal. Chern., 1951,23,992. 0. H. Kriege, The Analyses of Refractory Rortdes, Carbides, Nitrides, and Silicates, Los Alamos Scientific Laboratory Report, LA 2306, 1959. A. S. Lapteva, E. S. Bondarevskaya and E. N. Merkulova, Znd. Lab., USSR (English Trans.), 1968,34,1310. B. Ormont and A. Samoilov, z. Anal. Chem., 1935,102,20. I. G. Shafran and R. A. Levinson, J. Appl. Chem., USSR (English Trans.), 1940,13,1885. M. V. Kharitonova, Tr. Vses. Nauchn.-Issled. Inst. Abrazivov Shlefovaniya (English Trans)., 1967, No. 4,58. E. W. Berter, R. H. Wynne, W. F. Harris, M. I. Mistrik and F. P. Byre, paper presented at the Pittsburgh Conference of Anal. Chem., 4-8 March 1957. B. T. Kerma, personal communication, 1969.
Tahnta,
1971, Vol. 18, pp. 1070 to 1072.
An
Persamon Press. Printed in Northern Ireland
improved calorimetric determination of vanadium in geochemical prospecting samples (Received 15 March 1971. Accepted 25 March 1971)
IN THE COURSE of a geochemical survey, rapid determinations of vanadium may be required on large numbers of samples, and a precision of &I25‘A at the 95 ‘A confidence level is adequate. The colorimetric phosphotungstate method employed by the U.S. Geological Survey’ can be used over the range lOO4000 ppm vanadium. In some cases the yellow solutions obtained by following the recommended procedure are difficult to compare with standards, owing to suspensions of potassium phosphotungstate?~” or to the presence of other coloured cations. This paper describes how the sensitivity and selectivity of the method can be improved by substituting sodium hydrogen sulphate for the potassium compound during fusion of the sample, and by extracting the phosphotungstovanadic acid complex into isobutyl methyl ketone (IBMK).
EXPERIMENTAL Reagents Use distilled water and analytical-grade reagents throughout the procedure. Sodium hydrogen sulphate, fused and powdered. Nitric acid, sp. gr. 1.42. Diluted nitric acid (1 + 3). Orthophosphoric acid, sp. gr. 1.75. Sodium tungstate dihydrate solution, 5 % w/v. Standard vanadium solution, 100 pg/ml. Dissolve 0.2296 g of dried ammonium metavanadate in a mixture of 100 ml of water with 30 ml of diluted nitric acid (1 + 3). Dilute to 1 litre with water and llliX.
Isobutyl methyl ketone. Procedure Transfer 0.20-g portions of -100 mesh samples into a series of borosilicate test-tubes. Peats, certain soils and materials rich in organic matter should be ignited at 450” overnight so that residual tars or stable humic compounds do not interfere with the determination at a later stage. Add 1 g of powdered sodium hydrogen sulphate to each portion of sample, mix, heat to melt the flux then continue heating at dull red heat for 3 min. Allow the tube to cool, then leach the melt with 6 ml of diluted nitric acid (1 + 3), warming as necessary until the melt is reduced to powder. Dilute the solution to 10 ml, mix, and allow sediment to settle. Transfer 2*0-ml aliquots of each solution to another series of stoppered tubes. Add 1 ml of concentrated nitric acid to each aliquot and heat to boiling for 5 sec. Add O-3 ml of orthophosphoric
Short communications
1071
acid and mix, then 2 ml of sodium tungstate. solution and mix. Dilute the mixture to 10 ml with water, mix, and heat in a boiling-water bath for 10 min. Cool the tubes, add 1 ml of IBMK to each, shake them vigorously for 20 set, then allow the phases to separate. Prepare a series of standard tubes, using known volumes of standard vanadium solution. To each tube add 1 ml of concentrated nitric acid and heat to boiling for 5 sec. Continue as with the samples, extracting the wloured complex into IBMK as described. Compare the colours of the organic phases in the sample tubes with those of the standard series. For samples with vanadium contents greater than 0*1x, use smaller weights of sample or smaller aliquots of sample solution. RESULTS
AND
DISCUSSION
The proposed procedure was applied to some hundreds of stream sediment and soil samples from various localities, with results ranging from 25 to 1000 ppm of vanadium. Some of the higher and lower values were compared with spectrographic estimates of total vanadium in the samples. These comparisons, together with results on standard samples are recorded in Table I. TASL~ I.--RESULTS
OF DETERMINATIONS OF VANADIUM IN GEOLGGICAL SAMF’LJS
Vanadium, ppm Sample
Published results Mean Range
Spectrographic estimate
Syenite rock-l * Sulphide ore-l * Granadiorite GSP-1 t Andesite AGV-1 t Peridotite PCC-1 f
87 192 52 121 31.2
5&150 90-262 38-67 70-171 21-55
-
Dunite DTS-1 t Basalt BCR-1 t
18.9 384
6-52 120-700
-
Stream sediments: Locality A Locality B Locality B Locality B Locality B
-
-
-
-
200 60 500 100 300
Proposed method 75, 50 200,250 100,50 125, 125 50, 25, 50, 50 50, 50, 50 50.25 375,375, 325 375,375,375,350 250,250 50,50 400,400 200,100 125,200,400 250, 125
* C.A.A.S. standard sample, described by Webber.4 t U.S.G.S. standard sample, described by Flanagan6 Standard deviations of 10 ppm about a mean value of 47 ppm and 20 ppm about a mean of 364 ppm were obtained when using the proposed method to determine the vanadium contents of standard samples PCC-1 and BCR-1. The method is suitable for use in a field laboratory by relatively unskilled operators. Accuracy may be improved in a central laboratory by modifying the sample attack and by making more precise measurements of weight, volume, and wlour intensity. The coloured vanadium complex was extracted more cleanly into IBMK than into isobutanol as used by Sherwood and Chapman.6 Up to lOO-fold amounts (relative to vanadium) of copper, nickel, chromium, and cobalt either present in the samples or added as solutions were not extracted into the organic phase under the conditions given. The coloured complex in IBMK is stable for at least a week in a glass-stoppered tube. Acknowledgements-Thanks are due to the Director, Institute of Geological Sciences, London, for permission to publish. X-ray examinations of the potassium phosphotungstate were carried out within the Mineralogy Unit, and spectrographic estimates of vanadium within the Analytical and Ceramics Unit of the Geochemical Division. Institute of Geological Sciences Geochemical Division 64-78 Gray’s Inn Road London W.C.l. 6
J. L.
ROBERTS
1072
Short communications Summary_-The calorimetric method employed by the U.S. Geological Survey for the determination of vanadium in large numbers of geochemical prospecting samples has been examined. Use of sodium hydrogen sulphate for fusing the samples avoids precipitation of potassium phosphotungstate during colour development. Sensitivity and selectivity of the method are enhanced by extracting the phosphotungstovanadic acid into isobutyl methyl ketone. Zusanuneufassong--Das vom U.S. Geological Survey verwendete Verfahren zur Be&imrnung von Vanadium in goBen Anzahlen geochemischer Prospektierungsproben wurde untersucht. Die Verwendung von Natrium-hydrogensulfat zum Schmelzaufschlu8 der Probe vermeidet das Ausfallen von Kaliumphosphorwolframat w%hrend der Farbentwicklung. Die EmpBndlichkeit und die Selektivittit des Verfahrens werden verbessert, wenn man die Phosphorwolframvanadiumslure in Isobutyl-methylketon extrahiert. RCum&-Gn a examine la methode colorim&rique employee par le U.S. Geological Survey pour le dosage du vanadium dam des nombres importants d’6chantillon.s de prospection geochimique. L’emploi de sulfate acide de sodium pour la fusion de 1’8chantillon evite la prt+cipitation de phosphotungstate de potassium durant le developpement de la coloration. La sensibilite et la sdlectivite de la m6thode sont accrues en extrayant l’acide phosphotungstovanadique en methylisobutylc&one. REFERENCES
1. F. N. Ward, H. W. Lakin, F. C. Canney et al., U.S. Geol. Surv. Bull., 1963, No. 1152,87. 2. E. R. Wright and M. G. Mellon, Znd. Eng. Chem., Anal. Ed., 1937,9,251. 3. W. F. Linke, Solabilities of Inorganic and Metal-Organic Compounds, 4th Ed., Vol. II, p. 292. American Chemical Society, Washington, D.C., 1965. 4. G. R. Webber, Geochim. Cosmochim. Acta, 1965,29, 229. 5. F. J. Flanagan, ibid., 1969,33,81. 6. R. M. Sherwood and F. R. Chapman Jr., Anal. Chem., 1955,27,88.
Talanta, 1971, Vol. 18. PP. 1072 to 1074.
Perpamon Press. Printed in Northem
Ireland
Rapid dissolution of sulphide ore for the determination of copper (Received 9 February 1971. Accepted 16 March 1971)
THATPERCHLORIC ACIDcan be used effectively for the dissolution of sulphide ores for the determination of copper was pointed out by Goetx, Diehl and Hach. 1 Not only is the dissolution more rapid and the need to eliminate nitric acid by evaporation avoided, but in contrast to the nitric acid dissolution no bead of elemental sulphur is formed; such sulphur interferes in the subsequent iodometric determination of copper and requires prolonged boiling with nitric acid plus sulphuric acid for removal. We have no evidence that the perchloric acid dissolution method has found acceptance in commercial laboratories but the method has been used for 20 years without incident by the undergraduates studying uantitative analysis at Iowa State University. I We have now found that a mixture of equal volumes o9 70% perchloric acid and 85 % phosphoric acid is even more efficacious for the dissolution of sulphide ores, than is perchloric acid alone. Such a mixture of perchloric and phosphoric acids was used by Goetz and Wadsworth8 to dissolve iron ores. Even those ores most recalcitrant to attack by hydrochloric acid are dissolved in 90 sec. by this mixture. Again the method has been used by the undergraduates at Iowa State University for 20 years without incident.& The method was extended to the dissolution of manganiferous ores by Knoeck and Diehl,6 the process providing in addition a convenient oxidation of the manganese to the tervalent state, ready for titrimetric or spectrophotometric determination.
Short communications REFERENCES
:: 3. 4. 5. ;: 8. 9. 10.
J. R. Partington, A Textbook of Inorganic Chemistry, 6th Ed. Macmillan, London, 1950. M. D. Lyutaya, T. N. Nazarchuk and K. D. Modylevskaya, USSR Putent 142805, Dec. 28,1961, Appl. Mar. 20, 1961. H. Blumenthal, Anal. Chern., 1951,23,992. 0. H. Kriege, The Analyses of Refractory Rortdes, Carbides, Nitrides, and Silicates, Los Alamos Scientific Laboratory Report, LA 2306, 1959. A. S. Lapteva, E. S. Bondarevskaya and E. N. Merkulova, Znd. Lab., USSR (English Trans.), 1968,34,1310. B. Ormont and A. Samoilov, z. Anal. Chem., 1935,102,20. I. G. Shafran and R. A. Levinson, J. Appl. Chem., USSR (English Trans.), 1940,13,1885. M. V. Kharitonova, Tr. Vses. Nauchn.-Issled. Inst. Abrazivov Shlefovaniya (English Trans)., 1967, No. 4,58. E. W. Berter, R. H. Wynne, W. F. Harris, M. I. Mistrik and F. P. Byre, paper presented at the Pittsburgh Conference of Anal. Chem., 4-8 March 1957. B. T. Kerma, personal communication, 1969.
Tahnta,
1971, Vol. 18, pp. 1070 to 1072.
An
Persamon Press. Printed in Northern Ireland
improved calorimetric determination of vanadium in geochemical prospecting samples (Received 15 March 1971. Accepted 25 March 1971)
IN THE COURSE of a geochemical survey, rapid determinations of vanadium may be required on large numbers of samples, and a precision of &I25‘A at the 95 ‘A confidence level is adequate. The colorimetric phosphotungstate method employed by the U.S. Geological Survey’ can be used over the range lOO4000 ppm vanadium. In some cases the yellow solutions obtained by following the recommended procedure are difficult to compare with standards, owing to suspensions of potassium phosphotungstate?~” or to the presence of other coloured cations. This paper describes how the sensitivity and selectivity of the method can be improved by substituting sodium hydrogen sulphate for the potassium compound during fusion of the sample, and by extracting the phosphotungstovanadic acid complex into isobutyl methyl ketone (IBMK).
EXPERIMENTAL Reagents Use distilled water and analytical-grade reagents throughout the procedure. Sodium hydrogen sulphate, fused and powdered. Nitric acid, sp. gr. 1.42. Diluted nitric acid (1 + 3). Orthophosphoric acid, sp. gr. 1.75. Sodium tungstate dihydrate solution, 5 % w/v. Standard vanadium solution, 100 pg/ml. Dissolve 0.2296 g of dried ammonium metavanadate in a mixture of 100 ml of water with 30 ml of diluted nitric acid (1 + 3). Dilute to 1 litre with water and llliX.
Isobutyl methyl ketone. Procedure Transfer 0.20-g portions of -100 mesh samples into a series of borosilicate test-tubes. Peats, certain soils and materials rich in organic matter should be ignited at 450” overnight so that residual tars or stable humic compounds do not interfere with the determination at a later stage. Add 1 g of powdered sodium hydrogen sulphate to each portion of sample, mix, heat to melt the flux then continue heating at dull red heat for 3 min. Allow the tube to cool, then leach the melt with 6 ml of diluted nitric acid (1 + 3), warming as necessary until the melt is reduced to powder. Dilute the solution to 10 ml, mix, and allow sediment to settle. Transfer 2*0-ml aliquots of each solution to another series of stoppered tubes. Add 1 ml of concentrated nitric acid to each aliquot and heat to boiling for 5 sec. Add O-3 ml of orthophosphoric
Short communications
1071
acid and mix, then 2 ml of sodium tungstate. solution and mix. Dilute the mixture to 10 ml with water, mix, and heat in a boiling-water bath for 10 min. Cool the tubes, add 1 ml of IBMK to each, shake them vigorously for 20 set, then allow the phases to separate. Prepare a series of standard tubes, using known volumes of standard vanadium solution. To each tube add 1 ml of concentrated nitric acid and heat to boiling for 5 sec. Continue as with the samples, extracting the wloured complex into IBMK as described. Compare the colours of the organic phases in the sample tubes with those of the standard series. For samples with vanadium contents greater than 0*1x, use smaller weights of sample or smaller aliquots of sample solution. RESULTS
AND
DISCUSSION
The proposed procedure was applied to some hundreds of stream sediment and soil samples from various localities, with results ranging from 25 to 1000 ppm of vanadium. Some of the higher and lower values were compared with spectrographic estimates of total vanadium in the samples. These comparisons, together with results on standard samples are recorded in Table I. TASL~ I.--RESULTS
OF DETERMINATIONS OF VANADIUM IN GEOLGGICAL SAMF’LJS
Vanadium, ppm Sample
Published results Mean Range
Spectrographic estimate
Syenite rock-l * Sulphide ore-l * Granadiorite GSP-1 t Andesite AGV-1 t Peridotite PCC-1 f
87 192 52 121 31.2
5&150 90-262 38-67 70-171 21-55
-
Dunite DTS-1 t Basalt BCR-1 t
18.9 384
6-52 120-700
-
Stream sediments: Locality A Locality B Locality B Locality B Locality B
-
-
-
-
200 60 500 100 300
Proposed method 75, 50 200,250 100,50 125, 125 50, 25, 50, 50 50, 50, 50 50.25 375,375, 325 375,375,375,350 250,250 50,50 400,400 200,100 125,200,400 250, 125
* C.A.A.S. standard sample, described by Webber.4 t U.S.G.S. standard sample, described by Flanagan6 Standard deviations of 10 ppm about a mean value of 47 ppm and 20 ppm about a mean of 364 ppm were obtained when using the proposed method to determine the vanadium contents of standard samples PCC-1 and BCR-1. The method is suitable for use in a field laboratory by relatively unskilled operators. Accuracy may be improved in a central laboratory by modifying the sample attack and by making more precise measurements of weight, volume, and wlour intensity. The coloured vanadium complex was extracted more cleanly into IBMK than into isobutanol as used by Sherwood and Chapman.6 Up to lOO-fold amounts (relative to vanadium) of copper, nickel, chromium, and cobalt either present in the samples or added as solutions were not extracted into the organic phase under the conditions given. The coloured complex in IBMK is stable for at least a week in a glass-stoppered tube. Acknowledgements-Thanks are due to the Director, Institute of Geological Sciences, London, for permission to publish. X-ray examinations of the potassium phosphotungstate were carried out within the Mineralogy Unit, and spectrographic estimates of vanadium within the Analytical and Ceramics Unit of the Geochemical Division. Institute of Geological Sciences Geochemical Division 64-78 Gray’s Inn Road London W.C.l. 6
J. L.
ROBERTS
1072
Short communications Summary_-The calorimetric method employed by the U.S. Geological Survey for the determination of vanadium in large numbers of geochemical prospecting samples has been examined. Use of sodium hydrogen sulphate for fusing the samples avoids precipitation of potassium phosphotungstate during colour development. Sensitivity and selectivity of the method are enhanced by extracting the phosphotungstovanadic acid into isobutyl methyl ketone. Zusanuneufassong--Das vom U.S. Geological Survey verwendete Verfahren zur Be&imrnung von Vanadium in goBen Anzahlen geochemischer Prospektierungsproben wurde untersucht. Die Verwendung von Natrium-hydrogensulfat zum Schmelzaufschlu8 der Probe vermeidet das Ausfallen von Kaliumphosphorwolframat w%hrend der Farbentwicklung. Die EmpBndlichkeit und die Selektivittit des Verfahrens werden verbessert, wenn man die Phosphorwolframvanadiumslure in Isobutyl-methylketon extrahiert. RCum&-Gn a examine la methode colorim&rique employee par le U.S. Geological Survey pour le dosage du vanadium dam des nombres importants d’6chantillon.s de prospection geochimique. L’emploi de sulfate acide de sodium pour la fusion de 1’8chantillon evite la prt+cipitation de phosphotungstate de potassium durant le developpement de la coloration. La sensibilite et la sdlectivite de la m6thode sont accrues en extrayant l’acide phosphotungstovanadique en methylisobutylc&one. REFERENCES
1. F. N. Ward, H. W. Lakin, F. C. Canney et al., U.S. Geol. Surv. Bull., 1963, No. 1152,87. 2. E. R. Wright and M. G. Mellon, Znd. Eng. Chem., Anal. Ed., 1937,9,251. 3. W. F. Linke, Solabilities of Inorganic and Metal-Organic Compounds, 4th Ed., Vol. II, p. 292. American Chemical Society, Washington, D.C., 1965. 4. G. R. Webber, Geochim. Cosmochim. Acta, 1965,29, 229. 5. F. J. Flanagan, ibid., 1969,33,81. 6. R. M. Sherwood and F. R. Chapman Jr., Anal. Chem., 1955,27,88.
Talanta, 1971, Vol. 18. PP. 1072 to 1074.
Perpamon Press. Printed in Northem
Ireland
Rapid dissolution of sulphide ore for the determination of copper (Received 9 February 1971. Accepted 16 March 1971)
THATPERCHLORIC ACIDcan be used effectively for the dissolution of sulphide ores for the determination of copper was pointed out by Goetx, Diehl and Hach. 1 Not only is the dissolution more rapid and the need to eliminate nitric acid by evaporation avoided, but in contrast to the nitric acid dissolution no bead of elemental sulphur is formed; such sulphur interferes in the subsequent iodometric determination of copper and requires prolonged boiling with nitric acid plus sulphuric acid for removal. We have no evidence that the perchloric acid dissolution method has found acceptance in commercial laboratories but the method has been used for 20 years without incident by the undergraduates studying uantitative analysis at Iowa State University. I We have now found that a mixture of equal volumes o9 70% perchloric acid and 85 % phosphoric acid is even more efficacious for the dissolution of sulphide ores, than is perchloric acid alone. Such a mixture of perchloric and phosphoric acids was used by Goetz and Wadsworth8 to dissolve iron ores. Even those ores most recalcitrant to attack by hydrochloric acid are dissolved in 90 sec. by this mixture. Again the method has been used by the undergraduates at Iowa State University for 20 years without incident.& The method was extended to the dissolution of manganiferous ores by Knoeck and Diehl,6 the process providing in addition a convenient oxidation of the manganese to the tervalent state, ready for titrimetric or spectrophotometric determination.