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Semimicro determination of strontium and calcium in mixtures
Short communications
79
Summary_--A new method for the photometric titration of cadmium in the presence of zinc using ethylene~y~i-bis(~~tbyl~~~a-a~~c acid is described. Copper ion in ammonical solution serves as photome~c indicator. One ml of O-01Cd solution in a total volume of about 150 ml was determined in the presence of a SOO-foIdexcess of zinc. Zusammeufassnug--Eine neue Methode zur photometrischen Titration von Cadmium neben Zink mit Athylenglocol-bis(aminoatbyl) tetressigs&re wird beschrieben. Kupferion in ammoniakalischer Losung dient als photometrischer Indicator. 1 ml 0.01 m Cd-Ltjsung in 150 ml Titrationsvolum konnte neben der 500 fachen Menge Zink bestimmt werden. R&um&-Les auteurs decrivent une nouvelle m&ode de dosage photometrique du cadmium, en presence de ziuc, par I’acide ethylene-glycol-bis(atnino&hyl) tetrac&ique. L’ion cuivre en solution ammoniacale sert d’indicateur photometrique. Un ml de solution de cadmium 0,Ol M dam un volume total d’environ 150 ml a et6 dose en presence dun exc& de zinc 500 fois plus important. REFERENCES r P. S. Sweetser and C. E. Bricker, Analyt. Chem., 1954,26, 195. * A. Ringbom, G. Pensar and E. Warn&en, Anulyt. Chim. Acta, 19X$19,525. a E. Wanninen, Acta Acad. Abonensis, 1960,21,104. 4 C. N. Reilley and R. S&mid, Analyt. Chem., 1958,30,947. 6 H. Flaschka, Talanta, 1961, 8, 381. BA. L. Underwood, Analyf. Chem., 1954,26,1322. 7 H. Flaschka and P. 0. Sawyer, Tuianta, 1961. 8, 521. 8 G. Schwarzenbach, Die komp~exometrische Titration. F. Encke, Stuttgart, 1956. @H. Flaschka, EDTA Titrations, Pergamon Press, London, 1959. lo K. H. Kraus and G. E. Moore, J. Amer. Chem. Sot., 1953,7S, 1960.
Semimicro determhtion
of strontium and cakiam in mixtares*
(Received 23 June 1961. Accepted 27 August 1961)
INTRODUCTION THEdete~ation of strontium and calcium in a mixture is one of the most ditl’icult and troublesome problems in analytical chemistry, because of the similarity of their properties. The gravimetric. procedures described are not free from co-precipitation and therefore if a quantitative determination is needed, several precipitations must be effected. The commonly used procedure is by precipitating strontium nitrate in a mixture of alcohol-ether1 thus separating it from calcium, followed by the gravimetric determination of the strontium as sulphate, or oxide, and the determination of calcium as oxide, or titrimetrically. Weiss and Shipma$ used potassium rhodizonate in a gravimetric method for the separation of s~onti~-~ from calcium. According to their paper, about 80 to 90 % stronti~ can be recovered when the ratio Ca:Sr is as high as SO,using a four-fold excess of rhodizonate. Lieser and HiidS determined the solubility of strontium rhodizonate in solution. Their results show that under appropriate conditions the separation between calcium and strontium cau be effected quantitatively by this reagent. In the present study we attempted to find suitable conditions for (a) a quantitative separation of strontium and calcium by rhodizonate; (6) a rapid determination of both ions, without using radiochemical techniques. Calcium and s~onti~ were determined by a ~mplexome~c method.4 To permit this the rhodizonate had to be eliminated, because its presence interfered in the titrations. The conditions for this elimination were also studied. * This investigation was initiated and sponsored by the Israel Atomic Energy Commission, and is published with their permission. A full version of this paper is published as a report in the Israel Atomic Energy Bulletin, No. 695 1961.
80
Short communications EXPERIMENTAL
Reagents The reagents used were all of analytical grade. The aqueous rhodizonate solution (0.2%) was always freshly prepared from the sodium rhodizonate salt (B.D.H.). The EDTA solution was standardised by titration against a standard solution of strontium or calcium nitrate. The complexometric indicator, which was not stable for more than 2-3 days, was prepared by dissolving 0.1 g of o-cresolphthaleincomplexone (B.D.H.), O-05 g of methyl red and 0.05 g of bromocresol green in a few drops of concentrated ammonia and diluting to 100 ml with water.&
(a) Separation of strontium and calcium: The pH of the solutions with appropriate contents of calcium and strontium is adjusted to a value between 6-7. If the solutions to be analysed are acid, neutralisation can only be effected by potassium hydroxide. The volume of the solution should be about 15 ml. A two-fold excess of rhodizonate to strontium is added, with continuous stirring. After 5 min standing, the precipitate is filtered through Whatman No. 42 filter paper. The precipitate is washed on the filter with small amounts of water (10-15 ml) and dissolved in 15 ml of 0+5N HNO,. This solution is used for the determination of strontium after the elimination of the rhodizonate. The rhodizonate must also be removed from the filtrate for the determination of calcium. (6) Elimination of rhodizonate: The acid solution of strontium and rhodizonate is neutralised with a few drops of 1N NaOH until a brown-reddish colour appears. The solution is passed through a column, 16 mm in diameter and 180 mm long, filled to 3/4 of its length with the anion-exchange resin Amberlite IRA 410 Cl-technical, and the resin is then washed with 50 ml of water, the washings being added to the eluate. The solution of calcium is passed through the same column without neutralisation. To save time, the precipitate of strontium rhodizonate is filtered through a filter funnel which is placed directly above the ion-exchange column. By this procedure, the filtrate containing the calcium has the rhodizonate removed immediately. (c) Complexometric titrations: (i) Titration of calcium: 15-20 ml of saturated NH&I, 5 ml of cont. NH,OH, 10-15 ml of alcohol and 5-6 drops of the indicator are added to the solution. The solution is titrated with 0.02N EDTA until the red colour disappears abruptly. (ii) Titration of strontium: 5 ml of cont. NH,OH, 40-50 ml of alcohol and 5-6 drops of the indicator are added to the solution. The titration is carried out with 0.05N EDTA, to the same end-point. RESULTS
AND
DISCUSSION
The conditions for the quantitative precipitation of strontium rhodizonate without the coprecipitation of calcium were studied. As the presence of sodium and ammonium ions interfere with the precipitation by rhodizonate, acid solutions can only be brought to the required pH by neutralisation with potassium hydroxide. As can be seen from the results (Table I) the greatest accuracy was obtained with mixtures containing about 5 mg of strontium and O-5 mg of calcium in about l&15 ml solution. Only a twofold excess of rhodizonate to the strontium was needed, and the precipitate obtained could be filtered after a few min. Under these conditions the coprecipitation of calcium was avoided. The rhodizonate could be eliminated in two different ways : (a) heating to dryness, (b) ion exchange. The first procedure prolonged the time needed for the determination by 3-12 hr, and therefore, the ion-exchange method was used. It was found that by using a small column, filled with anionexchanger in the chloride form, the rhodizonate from the solutions was removed in about 15 min. The optimum pH for the exchange was found to be 6, and acid solutions of strontium rhodizonate were adjusted to this pH with a sodium hydroxide solution. It was also found that the removal of rhodizonate occurred more easily when the precipitate was dissolved in nitric acid than in hydrochloric acid. The solutions containing calcium and strontium were titrated with EDTA after the addition of alcohol, ammonia, ammonium chloride and o-cresolphthaleincomplexone. The quantity of alcohol It was found that 40-50 ml of alcohol added influenced the end-point in the case of strontium.
81
Short comrmmications TABLE I.-ANALYSIS OF ~rxruass
-
-
Found, mg
Taken, v -F
Deviation, mg
Sr
Sr 4.99 499 5.00 9.99 4.99
OF CALCIUM
AND
1
STRONTIUM
Deviation,
%
Ca
Sr
Ca
Sr
Ca
510 2.53 4.88 4.70 0.56
+0*01 +0*01 f@lO +0*99 +@05
-0.08 +@OZ -0.14 -0.45
0.2 0.2 2.0 10.0 1.0
-
-- ~I___ 5.00 500 5.10 10.98 5.04
5.02 2.51 502 5.15 -@6
-
No. of
I-
-,-
I
-
1.5 0.8
2.8 8-O -
were necessary for reproducible results. Titration effected with O*OlN EDTA showed no clear end-points. It was found that for calcium 0~02_0*1N EDTA could be used, while for strontium the smallest usable no~a~ity was 0.05. ~omplexometric titrations with other indicators were attempted but the best results were obtained by the u-cresoiphth~eincompiexo~e mixture described above although the end-point was not very sharp. Summary-A method is described for the quantitative separation and determination of about 5 mg of strontium and 0.5-5 mg of calcium, by precipitation of strontium at pH N 6 with sodium rhodizonate, and dete~ination of both ions by complexometric titrations. Zusammenfassung-Eine Methode zur quantitativen Trennung und Bestimmung von etwa 5 mg Strontium und 05-5 mg Calcium durch Flllung von Strontium mit Natrium-Rhodizonat bei pH -6 und komplexometrische Titrierung der beiden Ionen wird beschrieben. R&am&--Les auteurs decrivent une methode de separation et de dosage d’environ 5 mg strontium et de 0,5-S mg calcium par p~ip~~tion du stronti~ par le rhodizonate de sodium a pH ~6 et dosage des deux ions par titrages complexometriques. C. HEITNER-WIRCXJIN A. ALsu Department of Inorganic and Analytical Chemistry Hebrew University, Jerusalem, Israel REFERENCES 1 W. W. Scott, ~t~dard method of Chemical Analysis. D. Van Nostrand Company, Inc., Vol. I, p. 123. * H. V. Weiss and W. H. Shipman, Anafyt. Chem., 1957,29,1764. * K. H. Lieser and W. Hild, 2. Naturforsch., 1960, 1!5b,62. rl G. Anderegg, H. Flaschka, R. Sallmann and G. Schwarzenbach, Helv. Chim. Acta, 1954, 37, 113. 5 Frank J. Welcher, The Analytical Uses of Ethylenediaminetetra-acetic acid. D. Van Nostrand Co., 1958, pp, 106, 115, 143.
A spot test for uraniumvI with resacetophenone-oxime (Received 6 Jane 1961. Accepted 17 JaIy 1961) R~ACETOF~NONE-0~~ was recommended by Neelakantam and co-workers1.B for the colorhnetric determination of iron’u and uraniumv’. A reddish-brown wlour was developed on the addition of the reagent to uraniumvr m . a weak mineral acid medium. The intensity of the colour was found to increase with an increase in pH of the solution. This paper presents the results of the experiments carried out to establish the limit of identification of uraniumv’ using resacetophenone-oxime.
79
Summary_--A new method for the photometric titration of cadmium in the presence of zinc using ethylene~y~i-bis(~~tbyl~~~a-a~~c acid is described. Copper ion in ammonical solution serves as photome~c indicator. One ml of O-01Cd solution in a total volume of about 150 ml was determined in the presence of a SOO-foIdexcess of zinc. Zusammeufassnug--Eine neue Methode zur photometrischen Titration von Cadmium neben Zink mit Athylenglocol-bis(aminoatbyl) tetressigs&re wird beschrieben. Kupferion in ammoniakalischer Losung dient als photometrischer Indicator. 1 ml 0.01 m Cd-Ltjsung in 150 ml Titrationsvolum konnte neben der 500 fachen Menge Zink bestimmt werden. R&um&-Les auteurs decrivent une nouvelle m&ode de dosage photometrique du cadmium, en presence de ziuc, par I’acide ethylene-glycol-bis(atnino&hyl) tetrac&ique. L’ion cuivre en solution ammoniacale sert d’indicateur photometrique. Un ml de solution de cadmium 0,Ol M dam un volume total d’environ 150 ml a et6 dose en presence dun exc& de zinc 500 fois plus important. REFERENCES r P. S. Sweetser and C. E. Bricker, Analyt. Chem., 1954,26, 195. * A. Ringbom, G. Pensar and E. Warn&en, Anulyt. Chim. Acta, 19X$19,525. a E. Wanninen, Acta Acad. Abonensis, 1960,21,104. 4 C. N. Reilley and R. S&mid, Analyt. Chem., 1958,30,947. 6 H. Flaschka, Talanta, 1961, 8, 381. BA. L. Underwood, Analyf. Chem., 1954,26,1322. 7 H. Flaschka and P. 0. Sawyer, Tuianta, 1961. 8, 521. 8 G. Schwarzenbach, Die komp~exometrische Titration. F. Encke, Stuttgart, 1956. @H. Flaschka, EDTA Titrations, Pergamon Press, London, 1959. lo K. H. Kraus and G. E. Moore, J. Amer. Chem. Sot., 1953,7S, 1960.
Semimicro determhtion
of strontium and cakiam in mixtares*
(Received 23 June 1961. Accepted 27 August 1961)
INTRODUCTION THEdete~ation of strontium and calcium in a mixture is one of the most ditl’icult and troublesome problems in analytical chemistry, because of the similarity of their properties. The gravimetric. procedures described are not free from co-precipitation and therefore if a quantitative determination is needed, several precipitations must be effected. The commonly used procedure is by precipitating strontium nitrate in a mixture of alcohol-ether1 thus separating it from calcium, followed by the gravimetric determination of the strontium as sulphate, or oxide, and the determination of calcium as oxide, or titrimetrically. Weiss and Shipma$ used potassium rhodizonate in a gravimetric method for the separation of s~onti~-~ from calcium. According to their paper, about 80 to 90 % stronti~ can be recovered when the ratio Ca:Sr is as high as SO,using a four-fold excess of rhodizonate. Lieser and HiidS determined the solubility of strontium rhodizonate in solution. Their results show that under appropriate conditions the separation between calcium and strontium cau be effected quantitatively by this reagent. In the present study we attempted to find suitable conditions for (a) a quantitative separation of strontium and calcium by rhodizonate; (6) a rapid determination of both ions, without using radiochemical techniques. Calcium and s~onti~ were determined by a ~mplexome~c method.4 To permit this the rhodizonate had to be eliminated, because its presence interfered in the titrations. The conditions for this elimination were also studied. * This investigation was initiated and sponsored by the Israel Atomic Energy Commission, and is published with their permission. A full version of this paper is published as a report in the Israel Atomic Energy Bulletin, No. 695 1961.
80
Short communications EXPERIMENTAL
Reagents The reagents used were all of analytical grade. The aqueous rhodizonate solution (0.2%) was always freshly prepared from the sodium rhodizonate salt (B.D.H.). The EDTA solution was standardised by titration against a standard solution of strontium or calcium nitrate. The complexometric indicator, which was not stable for more than 2-3 days, was prepared by dissolving 0.1 g of o-cresolphthaleincomplexone (B.D.H.), O-05 g of methyl red and 0.05 g of bromocresol green in a few drops of concentrated ammonia and diluting to 100 ml with water.&
(a) Separation of strontium and calcium: The pH of the solutions with appropriate contents of calcium and strontium is adjusted to a value between 6-7. If the solutions to be analysed are acid, neutralisation can only be effected by potassium hydroxide. The volume of the solution should be about 15 ml. A two-fold excess of rhodizonate to strontium is added, with continuous stirring. After 5 min standing, the precipitate is filtered through Whatman No. 42 filter paper. The precipitate is washed on the filter with small amounts of water (10-15 ml) and dissolved in 15 ml of 0+5N HNO,. This solution is used for the determination of strontium after the elimination of the rhodizonate. The rhodizonate must also be removed from the filtrate for the determination of calcium. (6) Elimination of rhodizonate: The acid solution of strontium and rhodizonate is neutralised with a few drops of 1N NaOH until a brown-reddish colour appears. The solution is passed through a column, 16 mm in diameter and 180 mm long, filled to 3/4 of its length with the anion-exchange resin Amberlite IRA 410 Cl-technical, and the resin is then washed with 50 ml of water, the washings being added to the eluate. The solution of calcium is passed through the same column without neutralisation. To save time, the precipitate of strontium rhodizonate is filtered through a filter funnel which is placed directly above the ion-exchange column. By this procedure, the filtrate containing the calcium has the rhodizonate removed immediately. (c) Complexometric titrations: (i) Titration of calcium: 15-20 ml of saturated NH&I, 5 ml of cont. NH,OH, 10-15 ml of alcohol and 5-6 drops of the indicator are added to the solution. The solution is titrated with 0.02N EDTA until the red colour disappears abruptly. (ii) Titration of strontium: 5 ml of cont. NH,OH, 40-50 ml of alcohol and 5-6 drops of the indicator are added to the solution. The titration is carried out with 0.05N EDTA, to the same end-point. RESULTS
AND
DISCUSSION
The conditions for the quantitative precipitation of strontium rhodizonate without the coprecipitation of calcium were studied. As the presence of sodium and ammonium ions interfere with the precipitation by rhodizonate, acid solutions can only be brought to the required pH by neutralisation with potassium hydroxide. As can be seen from the results (Table I) the greatest accuracy was obtained with mixtures containing about 5 mg of strontium and O-5 mg of calcium in about l&15 ml solution. Only a twofold excess of rhodizonate to the strontium was needed, and the precipitate obtained could be filtered after a few min. Under these conditions the coprecipitation of calcium was avoided. The rhodizonate could be eliminated in two different ways : (a) heating to dryness, (b) ion exchange. The first procedure prolonged the time needed for the determination by 3-12 hr, and therefore, the ion-exchange method was used. It was found that by using a small column, filled with anionexchanger in the chloride form, the rhodizonate from the solutions was removed in about 15 min. The optimum pH for the exchange was found to be 6, and acid solutions of strontium rhodizonate were adjusted to this pH with a sodium hydroxide solution. It was also found that the removal of rhodizonate occurred more easily when the precipitate was dissolved in nitric acid than in hydrochloric acid. The solutions containing calcium and strontium were titrated with EDTA after the addition of alcohol, ammonia, ammonium chloride and o-cresolphthaleincomplexone. The quantity of alcohol It was found that 40-50 ml of alcohol added influenced the end-point in the case of strontium.
81
Short comrmmications TABLE I.-ANALYSIS OF ~rxruass
-
-
Found, mg
Taken, v -F
Deviation, mg
Sr
Sr 4.99 499 5.00 9.99 4.99
OF CALCIUM
AND
1
STRONTIUM
Deviation,
%
Ca
Sr
Ca
Sr
Ca
510 2.53 4.88 4.70 0.56
+0*01 +0*01 f@lO +0*99 +@05
-0.08 +@OZ -0.14 -0.45
0.2 0.2 2.0 10.0 1.0
-
-- ~I___ 5.00 500 5.10 10.98 5.04
5.02 2.51 502 5.15 -@6
-
No. of
I-
-,-
I
-
1.5 0.8
2.8 8-O -
were necessary for reproducible results. Titration effected with O*OlN EDTA showed no clear end-points. It was found that for calcium 0~02_0*1N EDTA could be used, while for strontium the smallest usable no~a~ity was 0.05. ~omplexometric titrations with other indicators were attempted but the best results were obtained by the u-cresoiphth~eincompiexo~e mixture described above although the end-point was not very sharp. Summary-A method is described for the quantitative separation and determination of about 5 mg of strontium and 0.5-5 mg of calcium, by precipitation of strontium at pH N 6 with sodium rhodizonate, and dete~ination of both ions by complexometric titrations. Zusammenfassung-Eine Methode zur quantitativen Trennung und Bestimmung von etwa 5 mg Strontium und 05-5 mg Calcium durch Flllung von Strontium mit Natrium-Rhodizonat bei pH -6 und komplexometrische Titrierung der beiden Ionen wird beschrieben. R&am&--Les auteurs decrivent une methode de separation et de dosage d’environ 5 mg strontium et de 0,5-S mg calcium par p~ip~~tion du stronti~ par le rhodizonate de sodium a pH ~6 et dosage des deux ions par titrages complexometriques. C. HEITNER-WIRCXJIN A. ALsu Department of Inorganic and Analytical Chemistry Hebrew University, Jerusalem, Israel REFERENCES 1 W. W. Scott, ~t~dard method of Chemical Analysis. D. Van Nostrand Company, Inc., Vol. I, p. 123. * H. V. Weiss and W. H. Shipman, Anafyt. Chem., 1957,29,1764. * K. H. Lieser and W. Hild, 2. Naturforsch., 1960, 1!5b,62. rl G. Anderegg, H. Flaschka, R. Sallmann and G. Schwarzenbach, Helv. Chim. Acta, 1954, 37, 113. 5 Frank J. Welcher, The Analytical Uses of Ethylenediaminetetra-acetic acid. D. Van Nostrand Co., 1958, pp, 106, 115, 143.
A spot test for uraniumvI with resacetophenone-oxime (Received 6 Jane 1961. Accepted 17 JaIy 1961) R~ACETOF~NONE-0~~ was recommended by Neelakantam and co-workers1.B for the colorhnetric determination of iron’u and uraniumv’. A reddish-brown wlour was developed on the addition of the reagent to uraniumvr m . a weak mineral acid medium. The intensity of the colour was found to increase with an increase in pH of the solution. This paper presents the results of the experiments carried out to establish the limit of identification of uraniumv’ using resacetophenone-oxime.