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The spectrophotometric determination of mercury in selenium
1548
Short communications
4 J. Korbl, R. PPibil and A. Emr, Chem. Listy, 1956, 50, 1440; Coil. Czech. Chem, Comm., 22, 961. 5 R. Piibil and V. Veseli, Tulunta, 1963, 10,383.
The spectrophotometric (Received
determination
7 May 1964. Accepted
1957,
of mercury in selenium 16 August 1964)
IN the determination
of high purity selenium, mercury is an important impurity. At the level of 1 ppm, the precision of the blanks becomes most important. This paper discusses a dithizoner-” procedure with low consistent blanks, in which the other impurities, normally found in selenium, are non-interfering. EXPERIMENTAL Reagents Standard mercury solution: 1 pg per ml in 0.5M sulphuric acid. Dissolve 0.1354 g of HgCl, in exactly 1000 ml of 0.5M sulphuric acid. Dilute 5 ml of this solution to exactly 500 ml with 0.5M sulphuric acid. Selenium: 99.999 % purity. Dithizone: Chloroform solution (8.0 mg per 500 ml of chloroform). Dissolve 0.160 g of dithizone in 200 ml of chloroform. Dilute a lo-ml aliquot to 500 ml with chloroform. B@kring and complexing solution: Dissolve 100 g of sodium acetate, 10 g of EDTA and 20 g of sodium thiocyanate in 500 ml of water. Sulphuric acid: 0.5M Aqueous ammonia : Procedure Sample dissolution procedure : Dissolve the sample of selenium in a minimum amount of nitric acid (1: l).O Transfer the solution to a volumetric flask such that aliquots containing 0.5 g of selenium will be contained in 25 ml or less. If the volume is less than 25 ml, adjust it with water. To the aliquot of sample, add 20 ml of buffering solution and immediately adjust the pH to 4.5-5.0 with sulphuric acid (0.5M). Transfer the solution to separatory funnel A, and add 10 ml of the dithizone-chloroform solution. Shake for 2 min and allow the layers to separate. Reserve the lower layer in a second separatory funnel, B. Add lOm1 of chloroform to the aqueous layer of separatory funnel A, and shake for 0.5 min. Drain the lower layer into separatory funnel B. Discard the aqueous layer. To separatory funnel B add 50-60ml of water and 13-15 drops of aqueous ammonia. Extract for 30 set, allow the layers to separate, and drain the chloroform layer into separatory funnel A. Discard the aqueous layer. To separatory funnel A add 50-60 ml of water and 13-15 drops of aqueous ammonia. Extract for 30 set and reserve the chloroform layer in a dry 25-ml volumetric flask. Make to volume with absolute ethanol. Determine the absorbance in a Beckman DU Spectrophotometer in 5-cm cells at a wavelength of 495 rnp.
RESULTS TABLE L-PRECISION
Blank
Absorption
OF BLANK SOLUTIONS
(495 mp/5 cm) vs. water
0.012 0.012 0.011 0.012 0.018 0.020 0.011 0.012 Average = 0.013
Deviation from average 0.003 -0GO1 -0.002 -0+)01 + 0.005 + 0.007 -0GO2 -0@01 Average = &OGI3
1549
Short communications TABLE II.-STANDARD
Hg, Icg
Absorption
0
(495 rnp/S cm) 0.011 0.012 0.018 0.020 0.318 0.320 0.610 0.614 0.935 0.930
5 10 15
TABLE III.-STANDARD Hg* ccg 0
10 15
Sample, g
0.0604 0.0608 0.0594 0.0598 0.0613 0.0609 Average = 0.0604 Factor = 16.7 ,~g of Hg/lGOO
Ai B
1OpgofHg
Absorption
0.054
0.304 0.300 0605 0.600 0.914 0.906
0.0608 0.0600 0.0605 0.0600 0.0609 0.0604 Average = 0.0603 Factor = 16.7 ,ug of Hg/lGIO
Absorption
0.500 0.500 0.500 0.500 0.500 0.500
a Corrected for absorbance
METHOD WITH 0.5gor SELENIUM
Corrected absorption
OF MERCURY IN SELENIUM SAMPLE
(495 rnp/S cm)
8:;;; A
,~g of Hg
0.302 0.304 0.594 0.598 0.919 0.914
TABLE IV.-DETERMINATION
Sample
Absorption/l
Average 0.016
(495 mp/5cm) 0.054 0.057 0.053 0.054 0.358 0.354 0.659 0.654 0.968 0.960
5
Corrected absorption for 0.016 average blank
CURVE BY MONO-COLOUR
Absorption
METHOD’
CURVE BYMONO-COLOUR
of Sample A.
0028 0.025 0.615 0.612 0.028 0.035
Corrected absorption
Hg, pg
) 0.011 0.017 0.014 0.589a 0.586a 0.017 0.024
0.28 0.23 9.83 9.79 0.28 040
1550
Short communications
CONCLUSIONS This procedure seems suitable for the determination of mercury in the low ppm in selenium. There is no interference from the presence of up to 25 pg each of silver, lead, or copper. EUGENEN. POLL~CK Ledgemont Laboratory Kennecott Copper Corporation Lexington 73, Mass., U.S.A.
Summary-Microgram quantities of mercury can be determined in the presence of as much as 05 g of selenium by a dithizone in chloroform extraction procedure. Common interferences are complexed by EDTA and sodium thiocyanate. Zusannnenfassung-Mikrogrammengen Hg konnen neben 0,s g Selen durch Extraktion mit Dithizon in Chloroform bestimmt werden. Haufiger auftrende Stiirungen werden mit EDTA und Natriumrhodanid maskiert. R&urn&-En presence d’une quantite de selenium pouvant atteindre 0,5 g, on peut doser des quantites de mercure de l’ordre du microgramme par une methode d’extraction a la dithizone en chloroforme. Les substances interferentes sont complex&es a I’EDTA et au thiocyanate de sodium. REFERENCES 1 E. B. Sandell, Coiorimetric Determination of Traces qf Metals. Interscience Publishers, Inc., New York. Interscience Publishers, Ltd., Third Edition. 1959, n. 621. 2 F. 0. Snell and C. T. Snell, &Corimetric Methods bf A&&is. D. Van Nostrand, Inc., Princeton, N.J., 1959, p. 33. B G. H. Morrison and H. Freiser, Solvent Extraction in Analytical Chemistry. J. Wiley and Sons, Inc., New York, 1957, p. 218. 4 V. L. Miller and F. Swanberg, Jr., Analyt. Chem., 1957, 29, 391. 6 D. Polley and V. L. Miller, ibid., 1955, 27, 1162. BR. F. Milton and J. L. Hoskins, Analyst, 1947, 72, 6. 7 0. B. Mathre and E. B. Sandell, Talanta, 1964, II, 295.
Radiochemical (Received
separation of cobalt by isotopic exchange 29 May
1964. Accepted
26 August
1964)
LANGER’in 1942 studied the exchange of silver ions between freshly precipitated silver chloride and an aqueous solution of silver nitrate, using radioactive silver tracer. He found that rapid isotopic exchange takes place between the silver atoms in the precipitate and the silver atoms in the solution. Sunderman and Meinke2 made use of this fact to develop a rapid single-step, high-decontamination procedure for the separation of trace amounts of radioactive silver from solutions containing other activities. They also applied this technique for the separation of iodine-131s and for the preparation of p-ray sources of silver-III.’ By the use of isotopic exchange it is possible to devise simple separation procedures, and to shorten the existing radiochemical procedures, without sacrificing specificity or yield. In the present paper, the technique of isotopic exchange has been applied to develop a rapid procedure for the separation of trace amounts of cobalt from aqueous solutions. If freshly precipitated cobalt(H) oxalate is agitated with an aqueous solution containing radioisotopes of cobalt, a high percentage of radioactive cobalt will, in a short time, exchange with the inactive cobalt in the precipitate. The necessary conditions of the exchange are that the concentration of inactive atoms in the precipitate should be much greater than that in the solution, and that the precipitate should have a low solubility.
Short communications
4 J. Korbl, R. PPibil and A. Emr, Chem. Listy, 1956, 50, 1440; Coil. Czech. Chem, Comm., 22, 961. 5 R. Piibil and V. Veseli, Tulunta, 1963, 10,383.
The spectrophotometric (Received
determination
7 May 1964. Accepted
1957,
of mercury in selenium 16 August 1964)
IN the determination
of high purity selenium, mercury is an important impurity. At the level of 1 ppm, the precision of the blanks becomes most important. This paper discusses a dithizoner-” procedure with low consistent blanks, in which the other impurities, normally found in selenium, are non-interfering. EXPERIMENTAL Reagents Standard mercury solution: 1 pg per ml in 0.5M sulphuric acid. Dissolve 0.1354 g of HgCl, in exactly 1000 ml of 0.5M sulphuric acid. Dilute 5 ml of this solution to exactly 500 ml with 0.5M sulphuric acid. Selenium: 99.999 % purity. Dithizone: Chloroform solution (8.0 mg per 500 ml of chloroform). Dissolve 0.160 g of dithizone in 200 ml of chloroform. Dilute a lo-ml aliquot to 500 ml with chloroform. B@kring and complexing solution: Dissolve 100 g of sodium acetate, 10 g of EDTA and 20 g of sodium thiocyanate in 500 ml of water. Sulphuric acid: 0.5M Aqueous ammonia : Procedure Sample dissolution procedure : Dissolve the sample of selenium in a minimum amount of nitric acid (1: l).O Transfer the solution to a volumetric flask such that aliquots containing 0.5 g of selenium will be contained in 25 ml or less. If the volume is less than 25 ml, adjust it with water. To the aliquot of sample, add 20 ml of buffering solution and immediately adjust the pH to 4.5-5.0 with sulphuric acid (0.5M). Transfer the solution to separatory funnel A, and add 10 ml of the dithizone-chloroform solution. Shake for 2 min and allow the layers to separate. Reserve the lower layer in a second separatory funnel, B. Add lOm1 of chloroform to the aqueous layer of separatory funnel A, and shake for 0.5 min. Drain the lower layer into separatory funnel B. Discard the aqueous layer. To separatory funnel B add 50-60ml of water and 13-15 drops of aqueous ammonia. Extract for 30 set, allow the layers to separate, and drain the chloroform layer into separatory funnel A. Discard the aqueous layer. To separatory funnel A add 50-60 ml of water and 13-15 drops of aqueous ammonia. Extract for 30 set and reserve the chloroform layer in a dry 25-ml volumetric flask. Make to volume with absolute ethanol. Determine the absorbance in a Beckman DU Spectrophotometer in 5-cm cells at a wavelength of 495 rnp.
RESULTS TABLE L-PRECISION
Blank
Absorption
OF BLANK SOLUTIONS
(495 mp/5 cm) vs. water
0.012 0.012 0.011 0.012 0.018 0.020 0.011 0.012 Average = 0.013
Deviation from average 0.003 -0GO1 -0.002 -0+)01 + 0.005 + 0.007 -0GO2 -0@01 Average = &OGI3
1549
Short communications TABLE II.-STANDARD
Hg, Icg
Absorption
0
(495 rnp/S cm) 0.011 0.012 0.018 0.020 0.318 0.320 0.610 0.614 0.935 0.930
5 10 15
TABLE III.-STANDARD Hg* ccg 0
10 15
Sample, g
0.0604 0.0608 0.0594 0.0598 0.0613 0.0609 Average = 0.0604 Factor = 16.7 ,~g of Hg/lGOO
Ai B
1OpgofHg
Absorption
0.054
0.304 0.300 0605 0.600 0.914 0.906
0.0608 0.0600 0.0605 0.0600 0.0609 0.0604 Average = 0.0603 Factor = 16.7 ,ug of Hg/lGIO
Absorption
0.500 0.500 0.500 0.500 0.500 0.500
a Corrected for absorbance
METHOD WITH 0.5gor SELENIUM
Corrected absorption
OF MERCURY IN SELENIUM SAMPLE
(495 rnp/S cm)
8:;;; A
,~g of Hg
0.302 0.304 0.594 0.598 0.919 0.914
TABLE IV.-DETERMINATION
Sample
Absorption/l
Average 0.016
(495 mp/5cm) 0.054 0.057 0.053 0.054 0.358 0.354 0.659 0.654 0.968 0.960
5
Corrected absorption for 0.016 average blank
CURVE BY MONO-COLOUR
Absorption
METHOD’
CURVE BYMONO-COLOUR
of Sample A.
0028 0.025 0.615 0.612 0.028 0.035
Corrected absorption
Hg, pg
) 0.011 0.017 0.014 0.589a 0.586a 0.017 0.024
0.28 0.23 9.83 9.79 0.28 040
1550
Short communications
CONCLUSIONS This procedure seems suitable for the determination of mercury in the low ppm in selenium. There is no interference from the presence of up to 25 pg each of silver, lead, or copper. EUGENEN. POLL~CK Ledgemont Laboratory Kennecott Copper Corporation Lexington 73, Mass., U.S.A.
Summary-Microgram quantities of mercury can be determined in the presence of as much as 05 g of selenium by a dithizone in chloroform extraction procedure. Common interferences are complexed by EDTA and sodium thiocyanate. Zusannnenfassung-Mikrogrammengen Hg konnen neben 0,s g Selen durch Extraktion mit Dithizon in Chloroform bestimmt werden. Haufiger auftrende Stiirungen werden mit EDTA und Natriumrhodanid maskiert. R&urn&-En presence d’une quantite de selenium pouvant atteindre 0,5 g, on peut doser des quantites de mercure de l’ordre du microgramme par une methode d’extraction a la dithizone en chloroforme. Les substances interferentes sont complex&es a I’EDTA et au thiocyanate de sodium. REFERENCES 1 E. B. Sandell, Coiorimetric Determination of Traces qf Metals. Interscience Publishers, Inc., New York. Interscience Publishers, Ltd., Third Edition. 1959, n. 621. 2 F. 0. Snell and C. T. Snell, &Corimetric Methods bf A&&is. D. Van Nostrand, Inc., Princeton, N.J., 1959, p. 33. B G. H. Morrison and H. Freiser, Solvent Extraction in Analytical Chemistry. J. Wiley and Sons, Inc., New York, 1957, p. 218. 4 V. L. Miller and F. Swanberg, Jr., Analyt. Chem., 1957, 29, 391. 6 D. Polley and V. L. Miller, ibid., 1955, 27, 1162. BR. F. Milton and J. L. Hoskins, Analyst, 1947, 72, 6. 7 0. B. Mathre and E. B. Sandell, Talanta, 1964, II, 295.
Radiochemical (Received
separation of cobalt by isotopic exchange 29 May
1964. Accepted
26 August
1964)
LANGER’in 1942 studied the exchange of silver ions between freshly precipitated silver chloride and an aqueous solution of silver nitrate, using radioactive silver tracer. He found that rapid isotopic exchange takes place between the silver atoms in the precipitate and the silver atoms in the solution. Sunderman and Meinke2 made use of this fact to develop a rapid single-step, high-decontamination procedure for the separation of trace amounts of radioactive silver from solutions containing other activities. They also applied this technique for the separation of iodine-131s and for the preparation of p-ray sources of silver-III.’ By the use of isotopic exchange it is possible to devise simple separation procedures, and to shorten the existing radiochemical procedures, without sacrificing specificity or yield. In the present paper, the technique of isotopic exchange has been applied to develop a rapid procedure for the separation of trace amounts of cobalt from aqueous solutions. If freshly precipitated cobalt(H) oxalate is agitated with an aqueous solution containing radioisotopes of cobalt, a high percentage of radioactive cobalt will, in a short time, exchange with the inactive cobalt in the precipitate. The necessary conditions of the exchange are that the concentration of inactive atoms in the precipitate should be much greater than that in the solution, and that the precipitate should have a low solubility.