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Selective complexometric determination of bismuth with mercaptans as masking agents, and its estimation in alloys
Tolanta, Vol. 32, No. 10, pp. 1011-1012, 1985 Printed
in
Great Britain.All rights reserved
Copyright 0
0039-9140/m $3.00 + 0.00 1985 Pergamon Press Ltd
SELECTIVE COMPLEXOMETRIC DETERMINATION OF BISMUTH WITH MERCAPTANS AS MASKING AGENTS, AND ITS ESTIMATION IN ALLOYS SARALA RAOOT
and K. N.
RAOOT
Defence Metallurgical Research Laboratory Kanchanbagh, (Received
22 February
1985. Accepted
Hyderabad-500 258, India
9 May
1985)
Summary-A method is proposed for selective complexometric determination of bismuth. To a solution containing bismuth and other cations, excess of EDTA is added and the surplus is back-titrated at pH 5-6 with lead nitrate (Xylenol Orange as indicator). Thioglycollic or mercaptopropionic acid is then added to decompose the bismuth-EDTA complex and the liberated EDTA is titrated with lead nitrate. The interference of various cations has been studied and the method employed to determine bismuth in a variety of alloys.
Bismuth can be titrated with EDTA at pH as low as 1,’ but cations forming comparably strong EDTA complexes, such as iron(III), thorium, zirconium, tin(IV) and titanium(IV), will interfere. This interference can be dealt with by titrating the total metal content, then treating the titrated solution with a releasing agent which will form a more stable complex with bismuth than EDTA does. The EDTA released from its bismuth complex can then be titrated with a suitable metal solution. Mercaptopropionic acid,2 2,3-mercaptopropane-1-sulphonic acid,3,4 2,3-dimercaptopropan-l-01,’ mercaptoacetic acid6 and thioglycollic acid’ have all been recommended for masking bismuth in acid medium, so should be useful as releasing agents. In our recent work on use of thioglycollic acid and mercaptopropionic acid as selective releasing agents for copper’ and tin,’ we found that bismuth caused serious interference, which might be expected from the earlier work quoted above. We therefore examined these two acids as agents for releasing bismuth from its EDTA complex. EXPERIMENTAL
Reagents Bismuth nitrate solution. Prepared by dissolving 1.0 g of high-purity bismuth in 20 ml of concentrated nitric acid, making up to 1 litre and standardizing. EDTA solution, O.OIM. Lead nitrate solution, 0.01 M. Xylenol Orange, 0.1% aqueous solution. Thioglycollic acid and mercaptopropionic tions. Hexamine, 30% solution.
acid, 20% solu-
Solutions of various metal ions (1 mgjml) were prepared from suitable salts. All chemicals used were of analytical reagent grade. Determination
of bismuth in presence of other cations
To a solution containing 5-50 mg of bismuth and various amounts of other metal ions, add excess of O.OlM EDTA, dilute to about 100 ml with water, adjust the pH to 54 with hexamine solution, add a few drops of Xylenol Orange
indicator and back-titrate the excess of EDTA with O.OlM lead nitrate. Add 2-l 5 ml of thioglycollic or mercaptopropionic acid solution, heat to boiling and boil for 4-S min, cool, adjust the pH to 5-6 with hexamine and titrate and liberated EDTA with O.OlM lead nitrate. Application
to alloys
Dissolve 0.2-0.5g of alloy in the minimum amount of aqua regiu necessary and make up to volume in a lOOmI standard flask containing sufficient potassium chloride solution to give an overall KC1 concentration of 2%. Analyse a suitable aliquot as described above. RESULTS AND DISCUSSION
The formation constant for the bismuth-EDTA complex’ is variously reported as 1023-1026. The stability constants for the complexes of bismuth with thioglycollic and mercaptopropionic acid are not known, but because these acids release EDTA from its bismuth complex, their stability constants must be higher than that for the EDTA complex. We have found that 5 ml of 20% thioglycollic or mercaptopropionic acid solution quantitatively releases EDTA from its complex with 20 mg of bismuth, on boiling for 4-5 min. The treatment with these acids lowers the pH from that at the end of the first titration, and to ensure a correct end-point in the second titration with lead, it is necessary to adjust the pH back to 5-6. Table 1 shows that the method is selective for bismuth in the presence of nickel, zinc, cadmium, cobalt, lead, manganese, aluminium, iron(III), indium, yttrium, lanthanum, samarium, cerium(III), titanium(IV) and zirconium, but manganese gives some trouble in the end-point detection in both titrations when more than 5 mg of it is present. Copper(I1) and tin(IV) are also quantitatively released from their EDTA complexes by means of mercaptans 8,9and cause interference, but this can be prevented by masking copper with ascorbic acid and thioureaiOz” and tin with tartaric acid’* before the
1011
1012
SHORT
COMMUNlCATlONS
Table 1. Determination of bismuth in presence of foreign metal ions
Table 2. Determination
of bismuth in solid and synthetic alloy samples
Bi’+, mg
Bi found, %
Found Foreign ion, mg
Taken
MPA
TGA
cu2+
12.00 50.0 8.00 45.0 10.00 40.0 35.00 45.0 5.00 45.0 15.00 8.00 40.0 12.00 18.00 50.0 10.00 18.00 5.00 30.0 15.00 25.0 12.00 30.0 8.00 40.0 12.00 45.0 20.00 35.0 10.00 50.0 15.00 25.0 10.00 45.0 8.00 40.0
12.07 49.9 7.94 44.7 10.03 39.8 34.9 45.1 5.02 44.9 14.94 8.05 40.1 11.97 17.97 49.9 10.08 17.87 4.96 30.1 15.05 24.9 11.91 30.1 8.05 39.9 12.07 45.2 20.06 34.9 9.93 50.2 15.05 24.9 10.03 44.9 8.05 39.7
12.07 50.2 8.05 45.1 10.03 40.1 34.9 45.2 4.96 45.1 15.05 7.94 40.2 11.97 18.13 50.1 9.93 18.13 4.96 29.9 15.10 25.1 11.97 29.9 7.94 40.2 12.02 44.9 19.91 35.1 10.03 49.9 15.05 25.1 9.98 45.2 7.94 39.9
NP+ Zn2+ Cd2+ car+ Pd2+ Hg2+ Pb2+ Mn2+ Al’+ Fe”+ In’+ Yr+ Las+ Sm’+ Ce’+ Ti4+ zl-.++ Sn4+
40.4a 10.1” 40.3 10.1 50.6 10.1 40.5 20.3 20.4 10.2 18.0b 6.0b 40.4s 10.lb 30.8 15.4 5.0 3.0 25.0’ 5.0’ 25.8 12.9 25.8 12.9 28.4 7.1 30.5 5.1 28.4 14.2 40.2 10.1 20.4 10.2 40.1 10.3 50.5d 25.3d
MPA = Mercaptopropionic acid. TGA = Thioglycollic acid. *Ascorbic acid and thiourea added to mask copper. bThiourea added to mask palladium and mercury. “Excess of EDTA added, pH adjusted to 3, solution boiled for 3 min. dTartaric acid added to mask Sn(IV). titration.
Thiourea
will likewise
mask
palladium’3
and mercuryI which would also otherwise interfere. A notable feature of the method is its capability to determine bismuth in presence of metals such as iron,
Alloy Sn-Bi Pb-Bi Cd-Bi Wood’s metal* Pb (25.0); Sn (12.5); Cd (12.5); Bi (50.0) Bismuth solder Pb (40.0); Sn (15.1); Bi (44.9) Eutectic fusible alloy Pb (32.0); Sn (14.8); Bi (53.2)
a
b
59.9 56.1 40.0 50.0
59.7b 55.gb 40.2s 50.2b
44.9
44.7b 45.2
53.2
53.0s 53.5
C
60.0 56.4 40.0 49.7
PGravimetric values by bismuth oxychloride precipitation.” bValues by mercaptopropionic acid release. ‘Values by thioglycollic acid release. *Synthetic mixture.
tin, titanium and zirconium, which seriously interfere in the direct titration at low pH. Table 2 gives results obtained for bismuth in alloys and these are in good agreement with those obtained by a standard procedure,15 the relative error in no case exceeding 1%. Besides being selective and accurate, the method is simple and rapid. A suite of three alloy samples can be analysed in 1 hr. Acknowledgement-Grateful thanks are due to Dr P. Rama Rao, Director, Defence Metallurgical Research Laboratory, Hyderabad, for permission to communicate this paper. REFERENCES
1. R. Piibil, Applied Complexometry, Pergamon Press, Oxford, 1982. 2. K. Yamaguchi and K. Ueno, Talanfa, 1963, 10, 1195. 3. L. A. Volf, ZavorLFk. Lab., 1960, 26, 1353. 4. Yu. V. Morachevskii and L. A. Volf, Zh. Analit. Khim., 1960, 15, 656.
5. R. Piibil and Z. Roubal, Collection Czech. Chem. Commun., 1954, 19, 1162. 6. R. Piibil and Vesely, Chemist-Analyst, 1965, 54, 12. 7. Idem, Talanta, 1961, 8, 880. 8. S. Raoot, K. N. Raoot and N. R. Desikan, Indian J. Technol., 1983, 21, 39.
9. K. N. Raoot and S. Raoot, Talanta, 1984, 31, 469. 10. 0. B. Budevsky and L. Simova, ibid., 1962, 9, 769. 11. K. N. Raoot, S. Raoot, B. V. Rao and D. P. Lahiri, Indian J. Technol., 1976, 14, 254.
12. S. Raoot and K. N. Raoot, ibid., 1983, 21, 442. 13. K. N. Raoot, S. Raoot and V. L. Kumari, Talanta, 1983, 30, 611.
14. R. P. Singh, ibid., 1969, 16, 1447. 15. N. H. Furman, Standard Methods of Chemical Analysis, 6th Ed., Vol. I, p. 195. Van Nostrand, New York, 1962.
in
Great Britain.All rights reserved
Copyright 0
0039-9140/m $3.00 + 0.00 1985 Pergamon Press Ltd
SELECTIVE COMPLEXOMETRIC DETERMINATION OF BISMUTH WITH MERCAPTANS AS MASKING AGENTS, AND ITS ESTIMATION IN ALLOYS SARALA RAOOT
and K. N.
RAOOT
Defence Metallurgical Research Laboratory Kanchanbagh, (Received
22 February
1985. Accepted
Hyderabad-500 258, India
9 May
1985)
Summary-A method is proposed for selective complexometric determination of bismuth. To a solution containing bismuth and other cations, excess of EDTA is added and the surplus is back-titrated at pH 5-6 with lead nitrate (Xylenol Orange as indicator). Thioglycollic or mercaptopropionic acid is then added to decompose the bismuth-EDTA complex and the liberated EDTA is titrated with lead nitrate. The interference of various cations has been studied and the method employed to determine bismuth in a variety of alloys.
Bismuth can be titrated with EDTA at pH as low as 1,’ but cations forming comparably strong EDTA complexes, such as iron(III), thorium, zirconium, tin(IV) and titanium(IV), will interfere. This interference can be dealt with by titrating the total metal content, then treating the titrated solution with a releasing agent which will form a more stable complex with bismuth than EDTA does. The EDTA released from its bismuth complex can then be titrated with a suitable metal solution. Mercaptopropionic acid,2 2,3-mercaptopropane-1-sulphonic acid,3,4 2,3-dimercaptopropan-l-01,’ mercaptoacetic acid6 and thioglycollic acid’ have all been recommended for masking bismuth in acid medium, so should be useful as releasing agents. In our recent work on use of thioglycollic acid and mercaptopropionic acid as selective releasing agents for copper’ and tin,’ we found that bismuth caused serious interference, which might be expected from the earlier work quoted above. We therefore examined these two acids as agents for releasing bismuth from its EDTA complex. EXPERIMENTAL
Reagents Bismuth nitrate solution. Prepared by dissolving 1.0 g of high-purity bismuth in 20 ml of concentrated nitric acid, making up to 1 litre and standardizing. EDTA solution, O.OIM. Lead nitrate solution, 0.01 M. Xylenol Orange, 0.1% aqueous solution. Thioglycollic acid and mercaptopropionic tions. Hexamine, 30% solution.
acid, 20% solu-
Solutions of various metal ions (1 mgjml) were prepared from suitable salts. All chemicals used were of analytical reagent grade. Determination
of bismuth in presence of other cations
To a solution containing 5-50 mg of bismuth and various amounts of other metal ions, add excess of O.OlM EDTA, dilute to about 100 ml with water, adjust the pH to 54 with hexamine solution, add a few drops of Xylenol Orange
indicator and back-titrate the excess of EDTA with O.OlM lead nitrate. Add 2-l 5 ml of thioglycollic or mercaptopropionic acid solution, heat to boiling and boil for 4-S min, cool, adjust the pH to 5-6 with hexamine and titrate and liberated EDTA with O.OlM lead nitrate. Application
to alloys
Dissolve 0.2-0.5g of alloy in the minimum amount of aqua regiu necessary and make up to volume in a lOOmI standard flask containing sufficient potassium chloride solution to give an overall KC1 concentration of 2%. Analyse a suitable aliquot as described above. RESULTS AND DISCUSSION
The formation constant for the bismuth-EDTA complex’ is variously reported as 1023-1026. The stability constants for the complexes of bismuth with thioglycollic and mercaptopropionic acid are not known, but because these acids release EDTA from its bismuth complex, their stability constants must be higher than that for the EDTA complex. We have found that 5 ml of 20% thioglycollic or mercaptopropionic acid solution quantitatively releases EDTA from its complex with 20 mg of bismuth, on boiling for 4-5 min. The treatment with these acids lowers the pH from that at the end of the first titration, and to ensure a correct end-point in the second titration with lead, it is necessary to adjust the pH back to 5-6. Table 1 shows that the method is selective for bismuth in the presence of nickel, zinc, cadmium, cobalt, lead, manganese, aluminium, iron(III), indium, yttrium, lanthanum, samarium, cerium(III), titanium(IV) and zirconium, but manganese gives some trouble in the end-point detection in both titrations when more than 5 mg of it is present. Copper(I1) and tin(IV) are also quantitatively released from their EDTA complexes by means of mercaptans 8,9and cause interference, but this can be prevented by masking copper with ascorbic acid and thioureaiOz” and tin with tartaric acid’* before the
1011
1012
SHORT
COMMUNlCATlONS
Table 1. Determination of bismuth in presence of foreign metal ions
Table 2. Determination
of bismuth in solid and synthetic alloy samples
Bi’+, mg
Bi found, %
Found Foreign ion, mg
Taken
MPA
TGA
cu2+
12.00 50.0 8.00 45.0 10.00 40.0 35.00 45.0 5.00 45.0 15.00 8.00 40.0 12.00 18.00 50.0 10.00 18.00 5.00 30.0 15.00 25.0 12.00 30.0 8.00 40.0 12.00 45.0 20.00 35.0 10.00 50.0 15.00 25.0 10.00 45.0 8.00 40.0
12.07 49.9 7.94 44.7 10.03 39.8 34.9 45.1 5.02 44.9 14.94 8.05 40.1 11.97 17.97 49.9 10.08 17.87 4.96 30.1 15.05 24.9 11.91 30.1 8.05 39.9 12.07 45.2 20.06 34.9 9.93 50.2 15.05 24.9 10.03 44.9 8.05 39.7
12.07 50.2 8.05 45.1 10.03 40.1 34.9 45.2 4.96 45.1 15.05 7.94 40.2 11.97 18.13 50.1 9.93 18.13 4.96 29.9 15.10 25.1 11.97 29.9 7.94 40.2 12.02 44.9 19.91 35.1 10.03 49.9 15.05 25.1 9.98 45.2 7.94 39.9
NP+ Zn2+ Cd2+ car+ Pd2+ Hg2+ Pb2+ Mn2+ Al’+ Fe”+ In’+ Yr+ Las+ Sm’+ Ce’+ Ti4+ zl-.++ Sn4+
40.4a 10.1” 40.3 10.1 50.6 10.1 40.5 20.3 20.4 10.2 18.0b 6.0b 40.4s 10.lb 30.8 15.4 5.0 3.0 25.0’ 5.0’ 25.8 12.9 25.8 12.9 28.4 7.1 30.5 5.1 28.4 14.2 40.2 10.1 20.4 10.2 40.1 10.3 50.5d 25.3d
MPA = Mercaptopropionic acid. TGA = Thioglycollic acid. *Ascorbic acid and thiourea added to mask copper. bThiourea added to mask palladium and mercury. “Excess of EDTA added, pH adjusted to 3, solution boiled for 3 min. dTartaric acid added to mask Sn(IV). titration.
Thiourea
will likewise
mask
palladium’3
and mercuryI which would also otherwise interfere. A notable feature of the method is its capability to determine bismuth in presence of metals such as iron,
Alloy Sn-Bi Pb-Bi Cd-Bi Wood’s metal* Pb (25.0); Sn (12.5); Cd (12.5); Bi (50.0) Bismuth solder Pb (40.0); Sn (15.1); Bi (44.9) Eutectic fusible alloy Pb (32.0); Sn (14.8); Bi (53.2)
a
b
59.9 56.1 40.0 50.0
59.7b 55.gb 40.2s 50.2b
44.9
44.7b 45.2
53.2
53.0s 53.5
C
60.0 56.4 40.0 49.7
PGravimetric values by bismuth oxychloride precipitation.” bValues by mercaptopropionic acid release. ‘Values by thioglycollic acid release. *Synthetic mixture.
tin, titanium and zirconium, which seriously interfere in the direct titration at low pH. Table 2 gives results obtained for bismuth in alloys and these are in good agreement with those obtained by a standard procedure,15 the relative error in no case exceeding 1%. Besides being selective and accurate, the method is simple and rapid. A suite of three alloy samples can be analysed in 1 hr. Acknowledgement-Grateful thanks are due to Dr P. Rama Rao, Director, Defence Metallurgical Research Laboratory, Hyderabad, for permission to communicate this paper. REFERENCES
1. R. Piibil, Applied Complexometry, Pergamon Press, Oxford, 1982. 2. K. Yamaguchi and K. Ueno, Talanfa, 1963, 10, 1195. 3. L. A. Volf, ZavorLFk. Lab., 1960, 26, 1353. 4. Yu. V. Morachevskii and L. A. Volf, Zh. Analit. Khim., 1960, 15, 656.
5. R. Piibil and Z. Roubal, Collection Czech. Chem. Commun., 1954, 19, 1162. 6. R. Piibil and Vesely, Chemist-Analyst, 1965, 54, 12. 7. Idem, Talanta, 1961, 8, 880. 8. S. Raoot, K. N. Raoot and N. R. Desikan, Indian J. Technol., 1983, 21, 39.
9. K. N. Raoot and S. Raoot, Talanta, 1984, 31, 469. 10. 0. B. Budevsky and L. Simova, ibid., 1962, 9, 769. 11. K. N. Raoot, S. Raoot, B. V. Rao and D. P. Lahiri, Indian J. Technol., 1976, 14, 254.
12. S. Raoot and K. N. Raoot, ibid., 1983, 21, 442. 13. K. N. Raoot, S. Raoot and V. L. Kumari, Talanta, 1983, 30, 611.
14. R. P. Singh, ibid., 1969, 16, 1447. 15. N. H. Furman, Standard Methods of Chemical Analysis, 6th Ed., Vol. I, p. 195. Van Nostrand, New York, 1962.