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A note on successive complexometric determination of thorium and rare earths
Short communications
1448 10. 11. 12. 13. 14. 15. 16. 17.
I. M. Kolthoff, and E. B. Sandell, Ind. Eng. Chem., Anal. Ed., 1930, 2, 140. Z. G. Szabo and L. Csanyi, Anal. Chem., 1949,21,1144. E. H. Swift, J. Am. Chem. Sot., 1930,52,894. A. I. Vogel, Quantitative Inorganic Analysis, 2nd Ed., Longmans, London, 1951. I. M. Kolthoff and T. S. Lee. Znd. EIW. Chem.. Anal. Ed.. 1946.18.452. I. M. Kolthoff and J. J. Lingane, J. irn. Chem. Sot., 1933,55,‘1871. N. H. Furman and W. M. Murray, ibid., 1936,58,1689. I. M. Kolthoff, Rev. Trav. Chim., 1926, 45, 745.
Talanta, 1972, Vol. 19, pp. 1448 to 1450. Persamon Press.
A note on successive
complexometric
Printed in Northern
determination
Ireland
of thorium
and rare earths
(Received 2 March 1972. Accepted 25 March 1972) KNOWN’ that in spite of a sutBcient difference between the stability constants of the thoriumEDTAcomplex and the rare-earth complexes (log &hY = 23.2, log KLaY = 15.50, log KnvY = 17*9), the rare earths (RE) cannot be titrated at pH 5-5.5 after thorium, when Xylenol Orange (X0), Pyrocatechol Violet, Methylthymol Blue etc. are used as indicators, because of the formation of coloured ternary complexes such as Th-EDTA-X0, at pH 4. EDTA does not saturate all the co-ordination sites of thorium. A few years ago we proposed’ as titrants diethylenetriaminepentaacetic acid (DTPA) and triethylenetetraminehexaacetic acid (TTHA) for these successive titrations. DTPA and TTHA complexes of thorium do not react with Xylenol Orange (the best indicator for this purpose) at higher pH. Because of shortage of material at that time we studied only the first lanthanides, from lanthanum to neodymium. Later this procedure was extended to all RE bv Mukherji.” Gupta and Powell3 confirmed the original procedure and in addition for the titration of RE replaced DTPA by N-Hydroxyethylethylenediaminetriacetic acid (HEDTA). In all these procedures Xylenol Orange was used as indicator. Because these volumetric reagents, especially TTHA and HEDTA, might not always be available, we have tried to improve the EDTA method. In principle the formation of the coloured Th-EDTAX0 complex has to be prevented by addition of another complex-forming compound. We have found that acetylacetone (acac) is very suitable for this reaction. We assume that the colourless ternary complex TH-EDTA-acac is formed instead of Th-EDTA-X0. This makes possible a reliable determination of RE after thorium titration. The whole procedure is very simple, as described below. IT IS WELL
EXPERIMENTAL Reagents EDTA, O.OSM. Standardized with O.OSM lead nitrate, with Xylenol Orange as indicator. A 0.02M solution was made by appropriate dilution. Rare earth solutions, 0.05M. Prepared by dissolving the nitrates in water or the oxides in nitric acid, and standardized by EDTA titration at pH 5-5.5, with Xylenol Orange as indicator. Acetylacetone-acetone
mixture (1: 1).
Saturated hexamine solution. Xylenol Orange solution, 0.5%. Procedure Dilute the sample solution, containing not more than 35 mg of thorium and 40-50 mg of RE, to 250-300 ml. Adjust the pH carefully to 2 & 0.1, with sodium hydroxide or nitric acid. (Chloroacetic acid buffer is not suitable for thorium titration.) Add a few drops of Xylenol Orange indicator and titrate slowly with 0.02-0.05&f EDTA to the colour change from the intense red colour to lemon yellow. Then warm the solution to 35-40”, add 20 ml of acetylaceton+acetone mixture and mix thoroughly (magnetic stirrer). Add saturated hexamine solution dropwise till an intensely red-violet colour appears and add a few drops of hexamine in excess. Titrate slowly with EDTA to a pure yellow or slightly orange-yellow. The amounts of EDTA used correspond to the thorium and the total RE respectively. Typical results are summarized in Table I.
Short communications
1449
TABLEL-DETERMINATIONOF THORIUM AND RAREEARTHS.
Th
Taken, mg RE
6.02 12.04 24.07 36.11 60.18 12.04 12.04 12.04 6.02 6.02 2407 Il.90 35.71 5.95 11.90 11.90 59.71 5.95 41.66 5.95 23.80 11.90
35.71
Th
7.44 37.20 52.07 74.39 35.91 35.91 41.09 4.11 34.49 7.62 38.09 76.18 38.95 3.90 41.80 8.36 37.35 3.74
La La La La Ce Ce Sm Sm Gd Tb Tb Tb Dy Dy Er Er Yb Yb
Found, mg RE
5.92* 12.06* 24.02 * 36.08* 6@33t 11.95 11.95 12.07 5.92 5.92 24.04 11.83 35.62 6.26 11.95 12.41 60.91: 5.92 41.65 8.70: 24.02? 235: 37.01:
7.43 Lag 36.26 La 52.23 La 72.9-73 61 La 36.43 Ce 36.50 Ce 41.05 Sm 4.20 Sm 34.67 Gd 7.71 Tb 38.54 Tb 75.17 Tb 39.16 Dy 4.06 Dy 39.64 E; 8.11 Er
-
2.88
Difference, mg Th RE -t-h10
+0*02 -0.05 -0.03 +@25 -0.09 -0*09 +0.03 -0.10 -0.10 -0.03 -0.07 -0.09 +0.31 +0.05 +0.51 7L1.20 -0.03 -O*Ol +1.75 +0.22
+11*10 +1.30
Stability constants log KT~Y - log&~y
-0.01 -0.94 +0.16 -1.49-0.79 i-O.52 +0.59 -0@4 +0*09 +@18 +0*09 +0.45 -0.99 +0.21 $-O-16 -1.16 -0.25
-
7.7 7.22 6.10 5.83 5.30
4.9 4.35 3.70
-0.86
* After the titration, acac was added and pH adjusted with hexamine: no colour appeared. t On addition of acac and adjustment of pH, slight formation of Th-EDTA-X0 complex. § End-point from violet to pink not sharp. Insticient amount of acac (see Remarks). $ Co-titration of RE, end-point sluggish and not sharp. Remarks The amount of thorium is limited to 3540 mg in the volume stated. Higher concentrations of Th-EDTA complex need larger amounts of acac for suppressing the Th-EDTA-X0 complex formation and this interferes with the subsequent titration of RE. Use of a higher temperature (40”) accelerates the dissolution of the acac-acetone mixture and makes the indicator colour change sharper. Methylthymol Blue or Byrocatechol Violet are not suitable for this procedure because of indistinct and sluggish end-points. DISCUSSION The proposed method is suitable for the determination of thorium and those rare earths haying a sufficiently lower stability constant for their EDTA-complexes [lathanum up to erbium (log KBrY = lS.SS)J. Thulium (log KTmy = 19.51) and lutetium (log KL”~ = 19-83) were not available, but we can assume that both will be partly co-titrated with thorium. As an auxiliary complex-forming compound for RE titration, and masking of alummium, iron, etc, Chernikhov et aI.* proposed sulphosalicylic acid and titrated thorium with EDTA at pH 1.5 and then RE at pH 4.5, using Xylenol Orange as indicator. The method is limited to smaller amounts of thorium (up to 15 mg) and smaller amounts of RE. The colour change of Xylenol Orange is much less sharp than in the method described above. Analyrical Laboratory J. Heyrovskj Polarographic Institute Czechoslovak Academy of Sciences Prague 1, Jilskd 16, Czechoslovakia
RUDOLFP&BE vLADIMfR w!.SEL*
1450
Short communications S--An improved method for successive determination of thorium and rare earths is described. It is based on the EDTA titration of thorium at pH 2 (Xylenol Orange as indicator) followed by addition of acetylacetone+acetone mixture, adjustment of the pH to S-55 with hexamine, and by further EDTA titration of rare earths with the same indicator. Zusanunenfassung-Ein verbessertes Verfahren zur Bestimmung von Thorium und seltenen Erden nacheinander wird beschrieben. Es beruht auf der EDTA-Titration von Thorium bei pH 2 (Indikator Xylenolorange), anschlieBender Zugabe eines Acetylaceton-AcetonGemisches, Einstellung des pH auf 5-5,5 mit Hexamethylentetramin und Weitertitration der seltenen Erden mit EDTA und dem selben Indikator. R&aun&C)n de&t une methode amelior&e pour le dosage successif du thorium et des terms rares. Elle est ba&e sur le titrage ir.I’EDTA du thorium ii pH 2 (Orange Xylenol comme indicateur), suivi de l’addition d’un melange ac&ylac&one-a&one, ajustement du pH ii 5-5,5 par l’hexamine, et nouveau titrage a I’EDTA des terres rares avec le meme indicateur. REFERENCES
1. 2. 3. 4.
R. PEbil and V. VeselL, Talanta, 1962,10, 899. A. K. Mukherii, ibid., 1966,13, 1183. A. K. Gupta &d J. A. Powell, ibid,, 1964,11, 1339 Yu. A. Chemikhov, R. S. Tramm and K. S. Pevzner, Zavodsk. Lab., 1960,26,921; 1961,8, No. 1433.
Talaata,
1972, Vol. 19. pp. 1450 to 1454. Praamon
Anal. Abstr.,
Press. Printed in Northern IWand
Spectrophotometric study of the reaction of bismuth@)
with Xylenol Orange
(Received 16 July 1971. Accepted 16 February 1972) XYLENOL ORANGE forms complexes with bismuth(III), which can be used for spectrophotometric determination of bismuth.l-B It is generally believed that only the 1: 1 Bi:XO complex is formed, but the system has not been fully studied. Our study shows that several complexes are formed. EXPERIMENTAL Reagents Xylenol Orange solution 1.00 x 10-sM. The purity of the reagent was checked by elemental analysis. Bismuth perchlorate solution 1.00 x lO-BM. Dissolve spectrally-pure metal in nitric acid, add perchloric acid and evaporate the solution. Dilute to volume (the pH should be ~1.3). The pH of solutions was controlled with perchloric acid and sodium hydroxide. All investigations were carried out at a constant ionic strength of 1.0 maintained by the addition of the required amount of sodium perchlorate. The reagents used werepro analysi grade. RESULTS
AND
DISCUSSION
The absorption spectra of bismuth(II1) and Xylenol Orange (X0) solutions of various concentrations and pH are shown in Fig. 1. In acidic medium X0 has an absorption maximum at 440 nm (curve 8). The addition of bismuth(II1) gives rise to an absorption maximum at about 550 run (curve 7). When X0 is in excess in slightly acidic medium this maximum decreases and a new one appears at 500nm (curves 1 and 6). These changes are associated with the formation of different complexes, the composition of which was established by the isomolar series and mole-ratio methods. The complex formed over the pH interval from -0.2 to 1.0 has a 1: 1 composition, but the one formed at pH > 1.O has a 1: 2 composition.
1448 10. 11. 12. 13. 14. 15. 16. 17.
I. M. Kolthoff, and E. B. Sandell, Ind. Eng. Chem., Anal. Ed., 1930, 2, 140. Z. G. Szabo and L. Csanyi, Anal. Chem., 1949,21,1144. E. H. Swift, J. Am. Chem. Sot., 1930,52,894. A. I. Vogel, Quantitative Inorganic Analysis, 2nd Ed., Longmans, London, 1951. I. M. Kolthoff and T. S. Lee. Znd. EIW. Chem.. Anal. Ed.. 1946.18.452. I. M. Kolthoff and J. J. Lingane, J. irn. Chem. Sot., 1933,55,‘1871. N. H. Furman and W. M. Murray, ibid., 1936,58,1689. I. M. Kolthoff, Rev. Trav. Chim., 1926, 45, 745.
Talanta, 1972, Vol. 19, pp. 1448 to 1450. Persamon Press.
A note on successive
complexometric
Printed in Northern
determination
Ireland
of thorium
and rare earths
(Received 2 March 1972. Accepted 25 March 1972) KNOWN’ that in spite of a sutBcient difference between the stability constants of the thoriumEDTAcomplex and the rare-earth complexes (log &hY = 23.2, log KLaY = 15.50, log KnvY = 17*9), the rare earths (RE) cannot be titrated at pH 5-5.5 after thorium, when Xylenol Orange (X0), Pyrocatechol Violet, Methylthymol Blue etc. are used as indicators, because of the formation of coloured ternary complexes such as Th-EDTA-X0, at pH 4. EDTA does not saturate all the co-ordination sites of thorium. A few years ago we proposed’ as titrants diethylenetriaminepentaacetic acid (DTPA) and triethylenetetraminehexaacetic acid (TTHA) for these successive titrations. DTPA and TTHA complexes of thorium do not react with Xylenol Orange (the best indicator for this purpose) at higher pH. Because of shortage of material at that time we studied only the first lanthanides, from lanthanum to neodymium. Later this procedure was extended to all RE bv Mukherji.” Gupta and Powell3 confirmed the original procedure and in addition for the titration of RE replaced DTPA by N-Hydroxyethylethylenediaminetriacetic acid (HEDTA). In all these procedures Xylenol Orange was used as indicator. Because these volumetric reagents, especially TTHA and HEDTA, might not always be available, we have tried to improve the EDTA method. In principle the formation of the coloured Th-EDTAX0 complex has to be prevented by addition of another complex-forming compound. We have found that acetylacetone (acac) is very suitable for this reaction. We assume that the colourless ternary complex TH-EDTA-acac is formed instead of Th-EDTA-X0. This makes possible a reliable determination of RE after thorium titration. The whole procedure is very simple, as described below. IT IS WELL
EXPERIMENTAL Reagents EDTA, O.OSM. Standardized with O.OSM lead nitrate, with Xylenol Orange as indicator. A 0.02M solution was made by appropriate dilution. Rare earth solutions, 0.05M. Prepared by dissolving the nitrates in water or the oxides in nitric acid, and standardized by EDTA titration at pH 5-5.5, with Xylenol Orange as indicator. Acetylacetone-acetone
mixture (1: 1).
Saturated hexamine solution. Xylenol Orange solution, 0.5%. Procedure Dilute the sample solution, containing not more than 35 mg of thorium and 40-50 mg of RE, to 250-300 ml. Adjust the pH carefully to 2 & 0.1, with sodium hydroxide or nitric acid. (Chloroacetic acid buffer is not suitable for thorium titration.) Add a few drops of Xylenol Orange indicator and titrate slowly with 0.02-0.05&f EDTA to the colour change from the intense red colour to lemon yellow. Then warm the solution to 35-40”, add 20 ml of acetylaceton+acetone mixture and mix thoroughly (magnetic stirrer). Add saturated hexamine solution dropwise till an intensely red-violet colour appears and add a few drops of hexamine in excess. Titrate slowly with EDTA to a pure yellow or slightly orange-yellow. The amounts of EDTA used correspond to the thorium and the total RE respectively. Typical results are summarized in Table I.
Short communications
1449
TABLEL-DETERMINATIONOF THORIUM AND RAREEARTHS.
Th
Taken, mg RE
6.02 12.04 24.07 36.11 60.18 12.04 12.04 12.04 6.02 6.02 2407 Il.90 35.71 5.95 11.90 11.90 59.71 5.95 41.66 5.95 23.80 11.90
35.71
Th
7.44 37.20 52.07 74.39 35.91 35.91 41.09 4.11 34.49 7.62 38.09 76.18 38.95 3.90 41.80 8.36 37.35 3.74
La La La La Ce Ce Sm Sm Gd Tb Tb Tb Dy Dy Er Er Yb Yb
Found, mg RE
5.92* 12.06* 24.02 * 36.08* 6@33t 11.95 11.95 12.07 5.92 5.92 24.04 11.83 35.62 6.26 11.95 12.41 60.91: 5.92 41.65 8.70: 24.02? 235: 37.01:
7.43 Lag 36.26 La 52.23 La 72.9-73 61 La 36.43 Ce 36.50 Ce 41.05 Sm 4.20 Sm 34.67 Gd 7.71 Tb 38.54 Tb 75.17 Tb 39.16 Dy 4.06 Dy 39.64 E; 8.11 Er
-
2.88
Difference, mg Th RE -t-h10
+0*02 -0.05 -0.03 +@25 -0.09 -0*09 +0.03 -0.10 -0.10 -0.03 -0.07 -0.09 +0.31 +0.05 +0.51 7L1.20 -0.03 -O*Ol +1.75 +0.22
+11*10 +1.30
Stability constants log KT~Y - log&~y
-0.01 -0.94 +0.16 -1.49-0.79 i-O.52 +0.59 -0@4 +0*09 +@18 +0*09 +0.45 -0.99 +0.21 $-O-16 -1.16 -0.25
-
7.7 7.22 6.10 5.83 5.30
4.9 4.35 3.70
-0.86
* After the titration, acac was added and pH adjusted with hexamine: no colour appeared. t On addition of acac and adjustment of pH, slight formation of Th-EDTA-X0 complex. § End-point from violet to pink not sharp. Insticient amount of acac (see Remarks). $ Co-titration of RE, end-point sluggish and not sharp. Remarks The amount of thorium is limited to 3540 mg in the volume stated. Higher concentrations of Th-EDTA complex need larger amounts of acac for suppressing the Th-EDTA-X0 complex formation and this interferes with the subsequent titration of RE. Use of a higher temperature (40”) accelerates the dissolution of the acac-acetone mixture and makes the indicator colour change sharper. Methylthymol Blue or Byrocatechol Violet are not suitable for this procedure because of indistinct and sluggish end-points. DISCUSSION The proposed method is suitable for the determination of thorium and those rare earths haying a sufficiently lower stability constant for their EDTA-complexes [lathanum up to erbium (log KBrY = lS.SS)J. Thulium (log KTmy = 19.51) and lutetium (log KL”~ = 19-83) were not available, but we can assume that both will be partly co-titrated with thorium. As an auxiliary complex-forming compound for RE titration, and masking of alummium, iron, etc, Chernikhov et aI.* proposed sulphosalicylic acid and titrated thorium with EDTA at pH 1.5 and then RE at pH 4.5, using Xylenol Orange as indicator. The method is limited to smaller amounts of thorium (up to 15 mg) and smaller amounts of RE. The colour change of Xylenol Orange is much less sharp than in the method described above. Analyrical Laboratory J. Heyrovskj Polarographic Institute Czechoslovak Academy of Sciences Prague 1, Jilskd 16, Czechoslovakia
RUDOLFP&BE vLADIMfR w!.SEL*
1450
Short communications S--An improved method for successive determination of thorium and rare earths is described. It is based on the EDTA titration of thorium at pH 2 (Xylenol Orange as indicator) followed by addition of acetylacetone+acetone mixture, adjustment of the pH to S-55 with hexamine, and by further EDTA titration of rare earths with the same indicator. Zusanunenfassung-Ein verbessertes Verfahren zur Bestimmung von Thorium und seltenen Erden nacheinander wird beschrieben. Es beruht auf der EDTA-Titration von Thorium bei pH 2 (Indikator Xylenolorange), anschlieBender Zugabe eines Acetylaceton-AcetonGemisches, Einstellung des pH auf 5-5,5 mit Hexamethylentetramin und Weitertitration der seltenen Erden mit EDTA und dem selben Indikator. R&aun&C)n de&t une methode amelior&e pour le dosage successif du thorium et des terms rares. Elle est ba&e sur le titrage ir.I’EDTA du thorium ii pH 2 (Orange Xylenol comme indicateur), suivi de l’addition d’un melange ac&ylac&one-a&one, ajustement du pH ii 5-5,5 par l’hexamine, et nouveau titrage a I’EDTA des terres rares avec le meme indicateur. REFERENCES
1. 2. 3. 4.
R. PEbil and V. VeselL, Talanta, 1962,10, 899. A. K. Mukherii, ibid., 1966,13, 1183. A. K. Gupta &d J. A. Powell, ibid,, 1964,11, 1339 Yu. A. Chemikhov, R. S. Tramm and K. S. Pevzner, Zavodsk. Lab., 1960,26,921; 1961,8, No. 1433.
Talaata,
1972, Vol. 19. pp. 1450 to 1454. Praamon
Anal. Abstr.,
Press. Printed in Northern IWand
Spectrophotometric study of the reaction of bismuth@)
with Xylenol Orange
(Received 16 July 1971. Accepted 16 February 1972) XYLENOL ORANGE forms complexes with bismuth(III), which can be used for spectrophotometric determination of bismuth.l-B It is generally believed that only the 1: 1 Bi:XO complex is formed, but the system has not been fully studied. Our study shows that several complexes are formed. EXPERIMENTAL Reagents Xylenol Orange solution 1.00 x 10-sM. The purity of the reagent was checked by elemental analysis. Bismuth perchlorate solution 1.00 x lO-BM. Dissolve spectrally-pure metal in nitric acid, add perchloric acid and evaporate the solution. Dilute to volume (the pH should be ~1.3). The pH of solutions was controlled with perchloric acid and sodium hydroxide. All investigations were carried out at a constant ionic strength of 1.0 maintained by the addition of the required amount of sodium perchlorate. The reagents used werepro analysi grade. RESULTS
AND
DISCUSSION
The absorption spectra of bismuth(II1) and Xylenol Orange (X0) solutions of various concentrations and pH are shown in Fig. 1. In acidic medium X0 has an absorption maximum at 440 nm (curve 8). The addition of bismuth(II1) gives rise to an absorption maximum at about 550 run (curve 7). When X0 is in excess in slightly acidic medium this maximum decreases and a new one appears at 500nm (curves 1 and 6). These changes are associated with the formation of different complexes, the composition of which was established by the isomolar series and mole-ratio methods. The complex formed over the pH interval from -0.2 to 1.0 has a 1: 1 composition, but the one formed at pH > 1.O has a 1: 2 composition.