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Diphenic acid as a selective reagent for the amperometric determination of thorium(IV)
754 Talanta,
SHORT COMMUNICATIONS Vol
24, pp. 754-155. Pergamon Press, 1977 Prmted m Great Br~tam
DIPHENIC ACID AS A SELECTIVE REAGENT FOR THE AMPEROMETRIC DETERMINATION OF THORIUM(IV) C. L. SHARMA and P. K. JAIN Chemistry Department, University of Roorkee, Roorkee, India (Received 2 March 1911. Revised 28 June 1971. Accepted 28 August 1977)
Summary-Th(IV) has been titrated amperometrically at an applied e.m.f. of - 1.0 V (dropping mercury electrode vs. SCE) with diphenic acid (neutralized with sodium hydroxide). Th(IV) in the range 8.NO.O mg/lOU ml can be determined with an error of *OS%. A number of foreign ions including Ce(IV), Zr(IV), La(III), U(IV), U(V1) do not interfere even if present in excess, but traces of Ti(IV) do. The method is rapid and selective and has been used for the determination of Th(IV) in monazite sand.
The analytical chemistry of thorium has been studied extensively during the last few decades. A number of methods have been suggested for its detectionI and determination, but there have been few amperometric methods. The EDTA method5-9 is subject to certain interferences. Amperometric determination with reagents such as alkali metal tungstates, la,11 benzenephosphonic acid,s thoron,” potassium ferrocyanide, oxalic acid and citric acidI is also subject to interference. The indirect methods with EDTA14s15 or rotating tantalum16.17 and oxide electrodes’ 8 have been deemed unsatisfactory because of their sensitivity to variation in laboratory conditions, and possible mechanical errors. Wendlandtlg has reported on the thermolysis of thorium diphenate but its use for the determination of thorium has not been pursued. Diphenic acid provides not only a rapid and accurate method but has the advantage that there are few interferences. Zr(IV), La(III), Ce(IV), Fe(II1) etc., which are generally associated with Th(IV) in most of its minerals and ores, do not interfere in the present method. EXPERIMENTAL
Apparatus
A Toshniwal manual polarograph, type CLO-2, with Pye “Scalamp” galvanometer in the external circuit, was used. The polarographic cell was kept immersed in a water thermostat maintained at 25 + 1”. A Fischer capillary was used for the dropping mercury electrode, with a drop time of 3.5 sec. Reagents and solutions
Thorium nitrate, potassium nitrate, diphenic acid and dloxan were all of analytical grade. The solution of diphenic acid was prepared in 40% dioxan, the other solutions were made’in distilled water. DISCUSSION
Eflect of pH The most accurate results were obtained at pH 3-5 for thorium and cl0 for the diphenic acid solution. Concentration range
From 8 to 60 mg of thorium in 100 ml of solution can be titrated with diphenic acid with an error of *0.5x (Table l), Outside this concentration range, the method is less accurate and the end-points are not very sharp. Thorium in monazite was determined by the spectrophotometric Thoron method,” and found to be 6.49%. Taking this as the correct value, the present method gives more accurate and precise results than the EDTA method.
Procedure
A measured volume of standard thorium solution was placed in a lOO-ml standard flask, then 50 ml of l.OM sodium perchlorate were added and the solution was diluted to the mark with distilled water. An aliquot (10 or 20 ml) of this solution was transferred to a polarographic cell and deaerated by passage of pure nitrogen. An e.m.f. of -1.0 V (vs. SCE) was applied, with the d.m.e. as indicator electrode. This potential was found to give sharp end-points and to eliminate most interferences. Measured volumes of reagent solution were added, then stirred in by passage of nitrogen, and the changes in diffusion current were noted. The galvanometer deflection was plotted against volume of titrant added, to locate the endpoint (which occurs at a thorium: titrant ratio of 1:2 as expected). In direct titrations (thorium nitrate in the cell), the current first decreases and then shows a slight increase beyond the end-point; in reverse titrations a slight increase in current at the beginning and a sharp increase beyond the end-point is observed. Representative results for both titrations are presented in Table 1. Table 1. Amperometric determination of thormm(IV) with diphenic acid Th(IV) present, mg
Th(IV) found mg
50.0 40.5 30.8 20.0
49.8 40.3 30.9 20.1
Th(IV) present, mg*
Th(IV) found, mg*
47.5 35.8 20.0 9.50
47.6 35.9 20.1 9.54
* Reverse titrations.
Table 2. Determination of thorium in monazite (thorium present* = 6.49%) Thorium found (A), %
Thorium found (B), %
6.50 6.48 6.47 6.49
6.66 6.59 6.62 6.64
* Thoron as calorimetric reagent.” (A) amperometric method. (B) EDTA method using Xylenol Orange as indicator.
SHORT
Determination of thorium in monazite
REFERENCES
Monazite powder (lOGmesh) was mixed with 5 times its weight of CaCl, and then heated at 1CKKl”for about 5 hr. The cooled reaction product was extracted with water and hot dilute hydrochloric acid. The hydroxides were preclpitated from the acid extract with sodium hydroxide solution, filtered off, washed, dissolved in hydrochloric acid and evaporated to dryness to render the silica insoluble. The residue was again extracted with hot hydrochloric acid and then the solution was treated with oxalic acid. The oxalate precipitate was collected and washed, then extracted with sodium carbonate solution, and the extract heated with perchloric acid to remove the carbonate. The solution was then diluted with distilled water and thorium determined as usual. The results were compared with those for the complexometric determination of thorium(IV), with Xylenol Orange as indicator (Table 2). Interference
Vol
24. pp
755-157
1. C. E. White and C. S. Lowe, Ind. Eng. Chem., Anal. Ed. 1941, 13, 809. 2. V. I. Kuznetsov, J. Gen. Chem. (U.S.S.R.), 1944, 14, 914. 3. J. S. Fritz and E. C. Bradford, Anal. Chem. 1958, 30, 1021. 4. S. K. Dutta and S. N. Saha, 2. Anal. Chem. 1960, 174,
38. 5. F. Vydra and J. Vorlic’ek, Collection Czech. Chem. Commun., 1966, 31, 51. 6. A. H. Zhdanov and M. M. Umarova, Tr. Tashkent Gos. Uniu. 1964, No. 264, 40. 7. V. A. Khadeev and L. S. Maslova, ibid., 1967, No. 288, 12. 8. A. K. Mukherji, J. Electroanal. Chem. 1961, 13, 425.
9. A. M. Gerorgyam, S. T. Talipor and V. A. Khadeev, Uzb. Khim. Zh., 1973, 23, 1714.
studies
Interferences were studied by taking an aliquot of the thorium solution. adding a 55lo-fold amount of the foreign ion and titrating as de&bed above. Li+, K+, Rb+, Cal>, SrZf Ba’+, Zn’+, Hg2+, Mn’+, A13+, Zr4+, La3+, Nd3+, Ce3’, Ce4+, U(IV), U(VI), Cl-, Br-, I-, SO:-, S2- do not interfere. The following species do not interfere at the Cr(II1) < 4.0, given: Fe(II1) < 4.5, M:Th ratios Pd(II) C 4.5, CH,COO- < 4.0, SO;- < 4.0, S,O:- < 3.0, NO; < 1.5, SCN- < 1.0. The interferences due to the following ions can be removed by the addition of the reagents given in parentheses: Sb(II1) (I-); As(II1) (Sz-); Cu(II) (ascorbc acid), Co(I1) (CN-); Ni(I1) dimethylglyoxime; PMII) and Cd(H) (2-mercaptobenzothiazole). F- and Pd:’ [Zr(IV)]; ‘P;O$- [Mg(iI)], MOO:- (ascorbic acid). The interferences due to CO:- and C,Oi- ions can be eliminated by heating the solution with perchloric acid. However, Ti(IV) was found to interfere. Thorium should be separated from titanium by oxalate precipitation before the estimation. The precipitate is ignited and then treated with cont. sulphuric acid to convert it into the sulphate. The thorium is then estimated by the method described.
Talonto.
155
COMMUNICATIONS
Pergamon
Press.
1971 Prmted
m Great
10. R. S. Saxena and 0. P. Sharma, Experientia, 1966, 22, 104.
11. C. M. Gupta, Bull. Chem. Sot. Japan, 1966, 39, 807. 12. I. A. Tserkovnitskaya and In-Chiu Yeh, Vestn. Leningr. Univ., Ser. Fiz. Khim. 1963, 3, 135. 13. V. A. Khadeev and L. S. Masalova, Tr. Tashkent Gos. univ., 1967, No. 288, 3. 14. J. R. Dean and W. E. Harris, Anal. Lett., 1969, 2, 93. 15. V. A. Khadeev and S. A. Kochergina, Uzb. Khim. Zh., 1967, 11, 15. 16. A. K. Zhdanov and I. A. Markhavaev, Zh. Vses. Khim. Obshchest. 1971, 585, 1615. 17. A. K. Zhdanov. I. A. Markhabaev and N. P. Muminov, Uzb. Khim Zh., 1974, 18, 15. 18. K. G. Mueller and A. Hermam, Z. Anal. Chem., 1971, 256, 345. 19. W. W. Wendlandt, Anal. Chim. Acta, 1958, 18, 316. 20. M. H. Fletcher, F. S. Grimaldi and L. B. Jenkins, Anal. Chem., 1957, 29, 963.
Bntam
SENSITIVITY ENHANCEMENT IN FLAMELESS ATOMIZATION SYSTEMS BY USE OF A RIGID TUNGSTEN COLLAR Metropolitan
c. D. WALL Police Forensic Science Laboratory, 109, Lambeth Road, London SEl, England
(Received 21 April 1977. Accepted 26 May 1977)
Summary-Sensitivity enhancement was achieved in a flameless atomization system by the insertion of a rigid tungsten “collar” 1 cm long and 0.5 mm thick. With such a collar the electrical and thermal properties of the furnace were essentially those of the original tube, and the existing power pack could be used without modification. A significant improvement in sensitivity was found for the majority of the sixteen elements studied. The system did not appear to suffer from the deformation problems associated with other systems of atomization from metal surfaces.
It has been known since the inception of graphite atomization systems that graphite has a number of distinct disadvantages due to its porosity and reactivity with certain elements. Its many advantages have meant that most of the attempts to overcome these problems have been associated with modifications to the graphite itself, particularly by pyrolytic coating.lp4 Some attempts have been made to atomize samples from metal surfaces. A tantalum liner
has been produced from thin foil,5 as have tantalum ribbons6 Devices using thin metal do, however, tend to deform at higher temperatures and the use of a rigid system would appear to offer distinct advantages. The entire graphite rod of a carbon filament system has been replaced by a tungsten rod of similar dimensions.’ This resulted in signal enhancement and a substantial improvement in freedom from matrix effects, but owing to the large bulk
SHORT COMMUNICATIONS Vol
24, pp. 754-155. Pergamon Press, 1977 Prmted m Great Br~tam
DIPHENIC ACID AS A SELECTIVE REAGENT FOR THE AMPEROMETRIC DETERMINATION OF THORIUM(IV) C. L. SHARMA and P. K. JAIN Chemistry Department, University of Roorkee, Roorkee, India (Received 2 March 1911. Revised 28 June 1971. Accepted 28 August 1977)
Summary-Th(IV) has been titrated amperometrically at an applied e.m.f. of - 1.0 V (dropping mercury electrode vs. SCE) with diphenic acid (neutralized with sodium hydroxide). Th(IV) in the range 8.NO.O mg/lOU ml can be determined with an error of *OS%. A number of foreign ions including Ce(IV), Zr(IV), La(III), U(IV), U(V1) do not interfere even if present in excess, but traces of Ti(IV) do. The method is rapid and selective and has been used for the determination of Th(IV) in monazite sand.
The analytical chemistry of thorium has been studied extensively during the last few decades. A number of methods have been suggested for its detectionI and determination, but there have been few amperometric methods. The EDTA method5-9 is subject to certain interferences. Amperometric determination with reagents such as alkali metal tungstates, la,11 benzenephosphonic acid,s thoron,” potassium ferrocyanide, oxalic acid and citric acidI is also subject to interference. The indirect methods with EDTA14s15 or rotating tantalum16.17 and oxide electrodes’ 8 have been deemed unsatisfactory because of their sensitivity to variation in laboratory conditions, and possible mechanical errors. Wendlandtlg has reported on the thermolysis of thorium diphenate but its use for the determination of thorium has not been pursued. Diphenic acid provides not only a rapid and accurate method but has the advantage that there are few interferences. Zr(IV), La(III), Ce(IV), Fe(II1) etc., which are generally associated with Th(IV) in most of its minerals and ores, do not interfere in the present method. EXPERIMENTAL
Apparatus
A Toshniwal manual polarograph, type CLO-2, with Pye “Scalamp” galvanometer in the external circuit, was used. The polarographic cell was kept immersed in a water thermostat maintained at 25 + 1”. A Fischer capillary was used for the dropping mercury electrode, with a drop time of 3.5 sec. Reagents and solutions
Thorium nitrate, potassium nitrate, diphenic acid and dloxan were all of analytical grade. The solution of diphenic acid was prepared in 40% dioxan, the other solutions were made’in distilled water. DISCUSSION
Eflect of pH The most accurate results were obtained at pH 3-5 for thorium and cl0 for the diphenic acid solution. Concentration range
From 8 to 60 mg of thorium in 100 ml of solution can be titrated with diphenic acid with an error of *0.5x (Table l), Outside this concentration range, the method is less accurate and the end-points are not very sharp. Thorium in monazite was determined by the spectrophotometric Thoron method,” and found to be 6.49%. Taking this as the correct value, the present method gives more accurate and precise results than the EDTA method.
Procedure
A measured volume of standard thorium solution was placed in a lOO-ml standard flask, then 50 ml of l.OM sodium perchlorate were added and the solution was diluted to the mark with distilled water. An aliquot (10 or 20 ml) of this solution was transferred to a polarographic cell and deaerated by passage of pure nitrogen. An e.m.f. of -1.0 V (vs. SCE) was applied, with the d.m.e. as indicator electrode. This potential was found to give sharp end-points and to eliminate most interferences. Measured volumes of reagent solution were added, then stirred in by passage of nitrogen, and the changes in diffusion current were noted. The galvanometer deflection was plotted against volume of titrant added, to locate the endpoint (which occurs at a thorium: titrant ratio of 1:2 as expected). In direct titrations (thorium nitrate in the cell), the current first decreases and then shows a slight increase beyond the end-point; in reverse titrations a slight increase in current at the beginning and a sharp increase beyond the end-point is observed. Representative results for both titrations are presented in Table 1. Table 1. Amperometric determination of thormm(IV) with diphenic acid Th(IV) present, mg
Th(IV) found mg
50.0 40.5 30.8 20.0
49.8 40.3 30.9 20.1
Th(IV) present, mg*
Th(IV) found, mg*
47.5 35.8 20.0 9.50
47.6 35.9 20.1 9.54
* Reverse titrations.
Table 2. Determination of thorium in monazite (thorium present* = 6.49%) Thorium found (A), %
Thorium found (B), %
6.50 6.48 6.47 6.49
6.66 6.59 6.62 6.64
* Thoron as calorimetric reagent.” (A) amperometric method. (B) EDTA method using Xylenol Orange as indicator.
SHORT
Determination of thorium in monazite
REFERENCES
Monazite powder (lOGmesh) was mixed with 5 times its weight of CaCl, and then heated at 1CKKl”for about 5 hr. The cooled reaction product was extracted with water and hot dilute hydrochloric acid. The hydroxides were preclpitated from the acid extract with sodium hydroxide solution, filtered off, washed, dissolved in hydrochloric acid and evaporated to dryness to render the silica insoluble. The residue was again extracted with hot hydrochloric acid and then the solution was treated with oxalic acid. The oxalate precipitate was collected and washed, then extracted with sodium carbonate solution, and the extract heated with perchloric acid to remove the carbonate. The solution was then diluted with distilled water and thorium determined as usual. The results were compared with those for the complexometric determination of thorium(IV), with Xylenol Orange as indicator (Table 2). Interference
Vol
24. pp
755-157
1. C. E. White and C. S. Lowe, Ind. Eng. Chem., Anal. Ed. 1941, 13, 809. 2. V. I. Kuznetsov, J. Gen. Chem. (U.S.S.R.), 1944, 14, 914. 3. J. S. Fritz and E. C. Bradford, Anal. Chem. 1958, 30, 1021. 4. S. K. Dutta and S. N. Saha, 2. Anal. Chem. 1960, 174,
38. 5. F. Vydra and J. Vorlic’ek, Collection Czech. Chem. Commun., 1966, 31, 51. 6. A. H. Zhdanov and M. M. Umarova, Tr. Tashkent Gos. Uniu. 1964, No. 264, 40. 7. V. A. Khadeev and L. S. Maslova, ibid., 1967, No. 288, 12. 8. A. K. Mukherji, J. Electroanal. Chem. 1961, 13, 425.
9. A. M. Gerorgyam, S. T. Talipor and V. A. Khadeev, Uzb. Khim. Zh., 1973, 23, 1714.
studies
Interferences were studied by taking an aliquot of the thorium solution. adding a 55lo-fold amount of the foreign ion and titrating as de&bed above. Li+, K+, Rb+, Cal>, SrZf Ba’+, Zn’+, Hg2+, Mn’+, A13+, Zr4+, La3+, Nd3+, Ce3’, Ce4+, U(IV), U(VI), Cl-, Br-, I-, SO:-, S2- do not interfere. The following species do not interfere at the Cr(II1) < 4.0, given: Fe(II1) < 4.5, M:Th ratios Pd(II) C 4.5, CH,COO- < 4.0, SO;- < 4.0, S,O:- < 3.0, NO; < 1.5, SCN- < 1.0. The interferences due to the following ions can be removed by the addition of the reagents given in parentheses: Sb(II1) (I-); As(II1) (Sz-); Cu(II) (ascorbc acid), Co(I1) (CN-); Ni(I1) dimethylglyoxime; PMII) and Cd(H) (2-mercaptobenzothiazole). F- and Pd:’ [Zr(IV)]; ‘P;O$- [Mg(iI)], MOO:- (ascorbic acid). The interferences due to CO:- and C,Oi- ions can be eliminated by heating the solution with perchloric acid. However, Ti(IV) was found to interfere. Thorium should be separated from titanium by oxalate precipitation before the estimation. The precipitate is ignited and then treated with cont. sulphuric acid to convert it into the sulphate. The thorium is then estimated by the method described.
Talonto.
155
COMMUNICATIONS
Pergamon
Press.
1971 Prmted
m Great
10. R. S. Saxena and 0. P. Sharma, Experientia, 1966, 22, 104.
11. C. M. Gupta, Bull. Chem. Sot. Japan, 1966, 39, 807. 12. I. A. Tserkovnitskaya and In-Chiu Yeh, Vestn. Leningr. Univ., Ser. Fiz. Khim. 1963, 3, 135. 13. V. A. Khadeev and L. S. Masalova, Tr. Tashkent Gos. univ., 1967, No. 288, 3. 14. J. R. Dean and W. E. Harris, Anal. Lett., 1969, 2, 93. 15. V. A. Khadeev and S. A. Kochergina, Uzb. Khim. Zh., 1967, 11, 15. 16. A. K. Zhdanov and I. A. Markhavaev, Zh. Vses. Khim. Obshchest. 1971, 585, 1615. 17. A. K. Zhdanov. I. A. Markhabaev and N. P. Muminov, Uzb. Khim Zh., 1974, 18, 15. 18. K. G. Mueller and A. Hermam, Z. Anal. Chem., 1971, 256, 345. 19. W. W. Wendlandt, Anal. Chim. Acta, 1958, 18, 316. 20. M. H. Fletcher, F. S. Grimaldi and L. B. Jenkins, Anal. Chem., 1957, 29, 963.
Bntam
SENSITIVITY ENHANCEMENT IN FLAMELESS ATOMIZATION SYSTEMS BY USE OF A RIGID TUNGSTEN COLLAR Metropolitan
c. D. WALL Police Forensic Science Laboratory, 109, Lambeth Road, London SEl, England
(Received 21 April 1977. Accepted 26 May 1977)
Summary-Sensitivity enhancement was achieved in a flameless atomization system by the insertion of a rigid tungsten “collar” 1 cm long and 0.5 mm thick. With such a collar the electrical and thermal properties of the furnace were essentially those of the original tube, and the existing power pack could be used without modification. A significant improvement in sensitivity was found for the majority of the sixteen elements studied. The system did not appear to suffer from the deformation problems associated with other systems of atomization from metal surfaces.
It has been known since the inception of graphite atomization systems that graphite has a number of distinct disadvantages due to its porosity and reactivity with certain elements. Its many advantages have meant that most of the attempts to overcome these problems have been associated with modifications to the graphite itself, particularly by pyrolytic coating.lp4 Some attempts have been made to atomize samples from metal surfaces. A tantalum liner
has been produced from thin foil,5 as have tantalum ribbons6 Devices using thin metal do, however, tend to deform at higher temperatures and the use of a rigid system would appear to offer distinct advantages. The entire graphite rod of a carbon filament system has been replaced by a tungsten rod of similar dimensions.’ This resulted in signal enhancement and a substantial improvement in freedom from matrix effects, but owing to the large bulk