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Spectrophotometric determination of uranium with anthranilic acid and rhodamine 6G
Tahra Vol 27. pp. 442 to 444 0 Rrg~c~ Ras Ltd 1980. Printed
@x9-9140/80/0541-0442$02.00/0 in Gml
Britain
SPECTROPHOTOMETRIC DETERMINATION OF URANIUM WITH ANTHRANILIC ACID AND RHODAMINE 6G T. V. RAMAKR~SHNA and R. S. SHREEDHARAMURTHY Department of Cheniistry, Indian Institute of Technology. Madras 600036. India (Received
3 May
1979. Rebised
16 October
1979. Accepted
26 October
1979)
Sumnmry--The reaction of the uranium-anthranilic acid complex to form an ion-association complex with Rhodamine 6G provides a means for its estimation. The anionic primary complex is suggested to be a mixed-ligand complex of uranium with anthranilic acid and its oxidation products. The method is at 575 nm) and fairly selective. and obeys Fker’s law for sensitive (r: = 6.25 x 10. I.mole-‘.cm-’ 0.04400 ppm of uranium. It has been applied to analysis of monazite sand.
A number of ion-association methods involving the use of basic dyes for the determination of uranium have been reported. I-’ Although these methods are more sensitive than those based on many of the binary systems, they all require extraction of the complex into an organic phase. Recently. Rhodamine 6G has been used in a highly selective spectrophotometric method (in aqueous medium) for the estimation of mercury6 as its tetraiodo complex. A similar approach has resulted in the development of the procedure (presented here) for the estimation of uranium with anthranitic acid and Rhodamine 6G. EXPERIMENTAL Reagents Uranium solution (500 ppm). Dissolve 0.1055 g of UOt(NO& .6H10 in 100 ml of distilled water containing
1 ml of cont. nitric acid. Dilute to give a 20-ppm solution. Anthranilic acid reagent. Dissolve 2.0 g of recrystallized anthranilic acid in the minimum of sodium hydroxide solution and dilute to about 50 ml with water. Add 2.0 ml of hydrogen peroxide (IOO-vol.) ancj heat on a water-bath for 30 min. After cooling add hydrochloric acid to neutralize the alkali and dissolve the separated anthranilic acid as the hydrochloride. Dissolve 8.0 g of pure anthranilic acid in the minimum of 6M hydrochloric acid. mix this with the oxidized anthranilic acid solution and dilute to 500 mi with distilled water. This procedure produces the optimum concentration of oxidized products in the anthranilic acid solution. Rhodamine 6G solution (0.1%). Acetic acid-sodium acetate /w&r
(I M. pH 4.5).
Procedure
Transfer 5 ml of sample solution, containing not more than 100 pg of uranium, into a dry or well-drained 25-ml standard flask. Add, with mixing, I.0 ml of 0.1 M EDTA. 5.0 ml of anthranilic acid reagent. 1.0 ml of acetate buffer. 1.0 ml of Rhodamine 6G solution and 1.0 ml of 0.5% gelatin solution. Dilute to the mark after 15 min and read the absorbance at 575 nm ifl a I@mm Ceil agaiIISt a reagent blank carried through the procedure. Establish the concentration of uranium by reference lo a calibration graph prepared for IO- 100 pg of uranium by the same procedure. 442
_ RESULTS AND DISCUSSION
Preliminary studies were carried out with a commercial sample of anthranilic acid by the procedure described, but with the pH adjusted to various values. The optimum pH for the reaction was found to be 3.8-4.7. When the reagent concentrations were varied at pH 4.5. the absorbance increased with increase in anthranilic acid concentration. This behaviour was attributed to the presence of impurities in the anthranilic acid and hence a recrystallized sample was tested. Though EDTA had had no effect on the uranium reaction with the commercial anthranilic acid (absorbance 0.210). the absorbance obtained with the recrystallized anthraniiic acid in the absence of EDTA was 0.130 and in the presence of EDTA was 0.080. This suggested that the impurity in the anthranilic acid was also involved in the reaction. This impurity was thought to be a product of oxidation of anthranilic acid. As the concentration of the oxidized product in the commercial sample was very low, it was increased by oxidation with peroxide. A black product. soluble only in alkali. acetone and methanol to give an intense red solution, was obtained. The compound could not be characterized, however. An extremely low concentration of this product was found to increase the absorbance obtained with recrystallized anthranilic acid. even in the presence of EDTA. No reaction was obtained with the same concentration of oxidized product alone. Also, low concentrations of azo compounds such as diazotized anthranilic acid self-coupled or coupled with salicylic acid produced. along with pure anthranilic acid. ionassociation complexes which were more stable to EDTA. Therefore it is suggested that the oxidized product is an azo compound. by analogy with the presence of azobenzene in aerially oxidized aniline.’ and that it forms a more stable mixed-ligand complex with anthranilic acid and uranium. In order to produce anthranilic acid containing the optimum concen-
SHORT
443
COMMUNK-ATIONS
Fig. 1. Absorption spectra of uranium-anthranilic acid-Rhodamine 6G system: @H 4.5; total volume 25 ml; IO-mm cells): A. 1.0 ml of 4.3 x 10e4M Rhodamine 6G and 5.0 ml of 2% anthranilic acid solution; B.C,D, as in A. with 20, 50 and 100 pg of uranium respectively.
tration of oxidized product the procedure described above was developed. The absorption ‘spectra shown in Fig. 1 clearly show the bathochromic shift from the absorption maximum of the dye (530 nm) to that of the complex (575 nm). Beer’s law is obeyed over the range 0.04-4.0 ppm of uranium and the molar absorptivity is 6.25 x 10’ l.mole-’ .cm-i. The ratio of uranium to Rhodamine 6G is shown to be 1: 1 by the mole-ratio plot shown in Fig 2. In spite of the increased stability of the mixed-ligand primary complex, the overall stability is not high, as evident from Fig. 2 and the fact that the absorbance for a given amount of uranium and a fixed volume of reagent decreases with increase in sample volume. With sample volumes of 4, 5,6 and 10 ml the absorbances due to 20 pg of uranium were 0.230, 0.210, 0.190 and 0.140 respectively. This effect is attributed to the primary mixed-Iigand complex also having comparatively low stability, and thus being dissociated to an extent determined by the concentrations of the reactants. Thus for reproducible results, all volumes must be kept constant.
removing the interference of Zr, Hf, and MO could be found. Analysis of monazite sand
A 0.5-g sample of finely ground monazite sand was attacked by the method of Hughes and Carswell* and the solution was made up to 100 ml Then 1 ml of this solution was treated with 5 drops of saturated alhminium nitrate solution followed by addition of dilute ammonia solution tiU the precipitation of aluminium was complete. The precipitate was centrifuged, washed with dilute ammonia solution and dissolved in 8 ml of saturated aluminium nitrate solution’ (- 2.7M). The solution was transferred quanti-
Interference studies The recommended procedure was applied to solutions containing 20 /Ig of uranium and 1 mg and 0.5 mg amounts of various ions and the results are summarized in Table 1. Up to 0.5 mg of Sb(V), Cr(VI) and Ce(IV) could be masked by reduction with 1 ml of lo/’ hydroxylamine hydrochloride solution. Up to 1 mg of Fe@) or Fe(I1) was masked with 1 mi of 0.5% potassium cyanide solution. Addition of 1 ml of 5% thiourea masked 1 mg each of Pt(IV) and Pd. No method for
t
A
Od
0
2.0
4.0
4.3x 1G4M Rhodomns6G ml
Fig 2. Mole-ratio plot (pH 4.5; total volume 25 ml; IO-mm cells; 575 nm): 1.0 ml of 4.3 x IO-*&f uranium’ (100 ppm) and 5.0 ml of 2% anthranilic acid solution.
SHORT COMMUNICATIONS
Table I. Interference studies Interferent
Remarks
Cu(lII, Ca. Mg, Ba Sr. Zn, Pb. Ni, Mn(l1). Co(H), AI, Hg(llh V(V), Tb, Dy. Pr, Sm. Ho, PO:AsO:-, AsO:-. B.O$- (1 mg each)
No interference
Th. La, N4 G4 Y, Cd Be, S@‘) and W(V1) (0.5 mg each)
No interference Interfere
Fe(l1) and (Ill), Pt(lV), Pd. Cr(Vr). Ce4lV), Zr, Hf. Mo(Vl), Sb(VX F-, ClO;, SCN- and oralatc (0.5 mg each)
Table 2. Analysis of monazite sand
Reported
Uranium added per gram of sample
Sample
Us01 %’
(“/. as U3W
: 3 4
0.35 0.35 0.35
l
UsOs found. “/; Arsenazo Ill Proposed method method
1 mg (0.115%)
0.3% 0.35.0.34.0.33 0x.0.34 0.46 0.57
2 mg (0.23%)
0.35,0.35, 0.36. 0.35.0.33 0.36
By Bhabha Atomic Research Centre, Bombay.
tatively into a 60-ml scparatory funnel with 1 ml of saturated aluminium nitrate solution for rinsing pur-
poses. and shaken with 5 ml of methyl isobutyl ketone for 3 min. The aqueous phase was discarded. The uranium was stripped from the organic phase with two portions of 0.1M hydrochloric acid The acid phase was treated with loo/, ammonium carbonate solution till the precipitation of aluminium was complete. Uranium was held in solution as the c~wcw,l l - compkx. lo The precipitate was digested, centrifuged, washed with 1004 ammonium carbonate solution and discarded. The solution and washings were combined. evaporated to dryness, and heated to sublime the ammonium salts. The residue was dissolved in 5 ml of 0.M hydrochloric acid and the det&nination of uranium was completed as described above. Table 2 shows that similar results were obtained when the same two sample solutions were repeatedly analysed by the proposed method and by the arsenazo III procedure ” after separation of the uranium by the method described above. ConcIusions The present paper establishes the feasibility of developing an aqueous procedure for the estimation of uranium with basic dyes. Owing to the instability of the primary complex, there is need to use a high con-
centration of reagents and rigorous control of conditions. If a suitable water-solubk ligand which forms a more stable compkx with uranium could be found. this approach is very promising, as it combines the ease of colour development in the aqueous phase with the sensitivity attainable with the use of basic dyes. Acknowledgemmt-One of us (RSSM) is grateful NCERT. New Delhi for financial assistance.
to
REFERENCES
1. N. R. Andersen and D. M. Hercules. Anal. Chum.. 1964.
36. 2138. 2. H. H. Ph. Moeken and W. A. H. Van Neste. Anal. Chim. Acru. 1967. 37. 480. 3. L. S. Sokolova G. G. Shchemeleva and P. N. Kovalenko, Tr. Novocherk. Politekh. Inst.. 1969. 220, 83. 4. V. M. Tarayan, E. N. Ovsepyan and A. A. Petrosyan. 5.
Arm Khim. Zh, 1970.23, Yu. V. Stepanenko and Lab., 1974,40. 263.
1085.
G. G. Shchemeleva.
Zuvodsk.
6. T. V. Ramakrishna, G. Aravamudan and M. Vijayakumar, Anal. Chim. Acre 1976, 84, 369. 7. H. Zollinger, Azo Md Diazo Chemisrry, p, 192. lnterscience. New York. 1961. 8. K. C. Hughes and D. J. Carswell, Analysr, 1970. 95, 302. 9. 0. A. Nietzel and M. A. De Sesa. Anul. Chem., 1957, 29,756.
I 0. P. Blanquet. Anal. Chim. Acta. 1957. 11. S. B. Savvin, Talunta, 1961. g, 673.
16. 44.
@x9-9140/80/0541-0442$02.00/0 in Gml
Britain
SPECTROPHOTOMETRIC DETERMINATION OF URANIUM WITH ANTHRANILIC ACID AND RHODAMINE 6G T. V. RAMAKR~SHNA and R. S. SHREEDHARAMURTHY Department of Cheniistry, Indian Institute of Technology. Madras 600036. India (Received
3 May
1979. Rebised
16 October
1979. Accepted
26 October
1979)
Sumnmry--The reaction of the uranium-anthranilic acid complex to form an ion-association complex with Rhodamine 6G provides a means for its estimation. The anionic primary complex is suggested to be a mixed-ligand complex of uranium with anthranilic acid and its oxidation products. The method is at 575 nm) and fairly selective. and obeys Fker’s law for sensitive (r: = 6.25 x 10. I.mole-‘.cm-’ 0.04400 ppm of uranium. It has been applied to analysis of monazite sand.
A number of ion-association methods involving the use of basic dyes for the determination of uranium have been reported. I-’ Although these methods are more sensitive than those based on many of the binary systems, they all require extraction of the complex into an organic phase. Recently. Rhodamine 6G has been used in a highly selective spectrophotometric method (in aqueous medium) for the estimation of mercury6 as its tetraiodo complex. A similar approach has resulted in the development of the procedure (presented here) for the estimation of uranium with anthranitic acid and Rhodamine 6G. EXPERIMENTAL Reagents Uranium solution (500 ppm). Dissolve 0.1055 g of UOt(NO& .6H10 in 100 ml of distilled water containing
1 ml of cont. nitric acid. Dilute to give a 20-ppm solution. Anthranilic acid reagent. Dissolve 2.0 g of recrystallized anthranilic acid in the minimum of sodium hydroxide solution and dilute to about 50 ml with water. Add 2.0 ml of hydrogen peroxide (IOO-vol.) ancj heat on a water-bath for 30 min. After cooling add hydrochloric acid to neutralize the alkali and dissolve the separated anthranilic acid as the hydrochloride. Dissolve 8.0 g of pure anthranilic acid in the minimum of 6M hydrochloric acid. mix this with the oxidized anthranilic acid solution and dilute to 500 mi with distilled water. This procedure produces the optimum concentration of oxidized products in the anthranilic acid solution. Rhodamine 6G solution (0.1%). Acetic acid-sodium acetate /w&r
(I M. pH 4.5).
Procedure
Transfer 5 ml of sample solution, containing not more than 100 pg of uranium, into a dry or well-drained 25-ml standard flask. Add, with mixing, I.0 ml of 0.1 M EDTA. 5.0 ml of anthranilic acid reagent. 1.0 ml of acetate buffer. 1.0 ml of Rhodamine 6G solution and 1.0 ml of 0.5% gelatin solution. Dilute to the mark after 15 min and read the absorbance at 575 nm ifl a I@mm Ceil agaiIISt a reagent blank carried through the procedure. Establish the concentration of uranium by reference lo a calibration graph prepared for IO- 100 pg of uranium by the same procedure. 442
_ RESULTS AND DISCUSSION
Preliminary studies were carried out with a commercial sample of anthranilic acid by the procedure described, but with the pH adjusted to various values. The optimum pH for the reaction was found to be 3.8-4.7. When the reagent concentrations were varied at pH 4.5. the absorbance increased with increase in anthranilic acid concentration. This behaviour was attributed to the presence of impurities in the anthranilic acid and hence a recrystallized sample was tested. Though EDTA had had no effect on the uranium reaction with the commercial anthranilic acid (absorbance 0.210). the absorbance obtained with the recrystallized anthraniiic acid in the absence of EDTA was 0.130 and in the presence of EDTA was 0.080. This suggested that the impurity in the anthranilic acid was also involved in the reaction. This impurity was thought to be a product of oxidation of anthranilic acid. As the concentration of the oxidized product in the commercial sample was very low, it was increased by oxidation with peroxide. A black product. soluble only in alkali. acetone and methanol to give an intense red solution, was obtained. The compound could not be characterized, however. An extremely low concentration of this product was found to increase the absorbance obtained with recrystallized anthranilic acid. even in the presence of EDTA. No reaction was obtained with the same concentration of oxidized product alone. Also, low concentrations of azo compounds such as diazotized anthranilic acid self-coupled or coupled with salicylic acid produced. along with pure anthranilic acid. ionassociation complexes which were more stable to EDTA. Therefore it is suggested that the oxidized product is an azo compound. by analogy with the presence of azobenzene in aerially oxidized aniline.’ and that it forms a more stable mixed-ligand complex with anthranilic acid and uranium. In order to produce anthranilic acid containing the optimum concen-
SHORT
443
COMMUNK-ATIONS
Fig. 1. Absorption spectra of uranium-anthranilic acid-Rhodamine 6G system: @H 4.5; total volume 25 ml; IO-mm cells): A. 1.0 ml of 4.3 x 10e4M Rhodamine 6G and 5.0 ml of 2% anthranilic acid solution; B.C,D, as in A. with 20, 50 and 100 pg of uranium respectively.
tration of oxidized product the procedure described above was developed. The absorption ‘spectra shown in Fig. 1 clearly show the bathochromic shift from the absorption maximum of the dye (530 nm) to that of the complex (575 nm). Beer’s law is obeyed over the range 0.04-4.0 ppm of uranium and the molar absorptivity is 6.25 x 10’ l.mole-’ .cm-i. The ratio of uranium to Rhodamine 6G is shown to be 1: 1 by the mole-ratio plot shown in Fig 2. In spite of the increased stability of the mixed-ligand primary complex, the overall stability is not high, as evident from Fig. 2 and the fact that the absorbance for a given amount of uranium and a fixed volume of reagent decreases with increase in sample volume. With sample volumes of 4, 5,6 and 10 ml the absorbances due to 20 pg of uranium were 0.230, 0.210, 0.190 and 0.140 respectively. This effect is attributed to the primary mixed-Iigand complex also having comparatively low stability, and thus being dissociated to an extent determined by the concentrations of the reactants. Thus for reproducible results, all volumes must be kept constant.
removing the interference of Zr, Hf, and MO could be found. Analysis of monazite sand
A 0.5-g sample of finely ground monazite sand was attacked by the method of Hughes and Carswell* and the solution was made up to 100 ml Then 1 ml of this solution was treated with 5 drops of saturated alhminium nitrate solution followed by addition of dilute ammonia solution tiU the precipitation of aluminium was complete. The precipitate was centrifuged, washed with dilute ammonia solution and dissolved in 8 ml of saturated aluminium nitrate solution’ (- 2.7M). The solution was transferred quanti-
Interference studies The recommended procedure was applied to solutions containing 20 /Ig of uranium and 1 mg and 0.5 mg amounts of various ions and the results are summarized in Table 1. Up to 0.5 mg of Sb(V), Cr(VI) and Ce(IV) could be masked by reduction with 1 ml of lo/’ hydroxylamine hydrochloride solution. Up to 1 mg of Fe@) or Fe(I1) was masked with 1 mi of 0.5% potassium cyanide solution. Addition of 1 ml of 5% thiourea masked 1 mg each of Pt(IV) and Pd. No method for
t
A
Od
0
2.0
4.0
4.3x 1G4M Rhodomns6G ml
Fig 2. Mole-ratio plot (pH 4.5; total volume 25 ml; IO-mm cells; 575 nm): 1.0 ml of 4.3 x IO-*&f uranium’ (100 ppm) and 5.0 ml of 2% anthranilic acid solution.
SHORT COMMUNICATIONS
Table I. Interference studies Interferent
Remarks
Cu(lII, Ca. Mg, Ba Sr. Zn, Pb. Ni, Mn(l1). Co(H), AI, Hg(llh V(V), Tb, Dy. Pr, Sm. Ho, PO:AsO:-, AsO:-. B.O$- (1 mg each)
No interference
Th. La, N4 G4 Y, Cd Be, S@‘) and W(V1) (0.5 mg each)
No interference Interfere
Fe(l1) and (Ill), Pt(lV), Pd. Cr(Vr). Ce4lV), Zr, Hf. Mo(Vl), Sb(VX F-, ClO;, SCN- and oralatc (0.5 mg each)
Table 2. Analysis of monazite sand
Reported
Uranium added per gram of sample
Sample
Us01 %’
(“/. as U3W
: 3 4
0.35 0.35 0.35
l
UsOs found. “/; Arsenazo Ill Proposed method method
1 mg (0.115%)
0.3% 0.35.0.34.0.33 0x.0.34 0.46 0.57
2 mg (0.23%)
0.35,0.35, 0.36. 0.35.0.33 0.36
By Bhabha Atomic Research Centre, Bombay.
tatively into a 60-ml scparatory funnel with 1 ml of saturated aluminium nitrate solution for rinsing pur-
poses. and shaken with 5 ml of methyl isobutyl ketone for 3 min. The aqueous phase was discarded. The uranium was stripped from the organic phase with two portions of 0.1M hydrochloric acid The acid phase was treated with loo/, ammonium carbonate solution till the precipitation of aluminium was complete. Uranium was held in solution as the c~wcw,l l - compkx. lo The precipitate was digested, centrifuged, washed with 1004 ammonium carbonate solution and discarded. The solution and washings were combined. evaporated to dryness, and heated to sublime the ammonium salts. The residue was dissolved in 5 ml of 0.M hydrochloric acid and the det&nination of uranium was completed as described above. Table 2 shows that similar results were obtained when the same two sample solutions were repeatedly analysed by the proposed method and by the arsenazo III procedure ” after separation of the uranium by the method described above. ConcIusions The present paper establishes the feasibility of developing an aqueous procedure for the estimation of uranium with basic dyes. Owing to the instability of the primary complex, there is need to use a high con-
centration of reagents and rigorous control of conditions. If a suitable water-solubk ligand which forms a more stable compkx with uranium could be found. this approach is very promising, as it combines the ease of colour development in the aqueous phase with the sensitivity attainable with the use of basic dyes. Acknowledgemmt-One of us (RSSM) is grateful NCERT. New Delhi for financial assistance.
to
REFERENCES
1. N. R. Andersen and D. M. Hercules. Anal. Chum.. 1964.
36. 2138. 2. H. H. Ph. Moeken and W. A. H. Van Neste. Anal. Chim. Acru. 1967. 37. 480. 3. L. S. Sokolova G. G. Shchemeleva and P. N. Kovalenko, Tr. Novocherk. Politekh. Inst.. 1969. 220, 83. 4. V. M. Tarayan, E. N. Ovsepyan and A. A. Petrosyan. 5.
Arm Khim. Zh, 1970.23, Yu. V. Stepanenko and Lab., 1974,40. 263.
1085.
G. G. Shchemeleva.
Zuvodsk.
6. T. V. Ramakrishna, G. Aravamudan and M. Vijayakumar, Anal. Chim. Acre 1976, 84, 369. 7. H. Zollinger, Azo Md Diazo Chemisrry, p, 192. lnterscience. New York. 1961. 8. K. C. Hughes and D. J. Carswell, Analysr, 1970. 95, 302. 9. 0. A. Nietzel and M. A. De Sesa. Anul. Chem., 1957, 29,756.
I 0. P. Blanquet. Anal. Chim. Acta. 1957. 11. S. B. Savvin, Talunta, 1961. g, 673.
16. 44.