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Gravimetric determination of caesium and potassium with sodium triphenylcyanoborate (caesignost)
Talanta, 1968, Vol. 15. PP. 185 to 188. PcrrgamonPress. Printed in Northern Ireland
GRAVIMETRIC DETERMINATION OF CAESIUM AND POTASSIUM WITH SODIUM TRIPHENYLCYANOBORATE (CAESIGNOST) ALICA BAUMAN Institute for Medical Research, Yugoslav Academy of Sciences and Arts, Zagreb, Yugoslavia (Received 21 July 1967. Accepted 20 August 1967) Sunuuary-Caesium can be determined gravimetrically with sodium triphenyl~o~ate (C~si~ost) as precipitant. The precipitation The was checked by addition of Is7Cstracer and ~-s~~me~y. foilowing ammeters were studied: temperature, digestion time, influence oFpotassium on the precipitation of caesium, and separation of caesium from bulk quantities of potassium.
triphenylcyanoborate is prepared1 by heating sodium-tetraphenylborate with sodium cyanide. The reactions of sodium t~phenylcyanoborate (C!aesignost) were studied by Havir* with special emphasis on electrometric methods. He succeeded in determining caesium qualitatively and quantitatively in small amounts. Under his experimental conditions potassium did not precipitate at all. The present investigation was undertaken to check the usefulness of Caesignost as a precipitant for caesium and potassium individually and for caesium in the presence of large quantities of potassium. It was also intended to test its app~~b~ty to radio~he~~l separation. Radioactive tracer technique was used to develop the procedure. The procedure of Ravir served as a starting point, but larger samples were used. SODIUM
EXPERIMENTAL Reagents Solutions of cae&um and tassium were prepared from CsCi, CsNO1, KC1 and KNOI. The concentration of caesium was etermined vimetricaity by precipitation as CsBi& and of potassium by pfecipitation as potassium 8” tetraphenyl K rate. Caes:gnost-sodmm triphenylcyanoborate (Hey1 8c Co., Berlin)--was prepared as a 7 % aqueous solution. If a turbidity appears, clarification by addition of 1 g of alkali-free aluminium hydroxide is recommended. If, during the clarification, the first portions passing through the filter-paper (Schleicher & Schuell SS 595) are still turbid, the solution must be refiltered several timea. Blanks were run from time to time. All the reagents used were analytical grade. I*‘Cs, fxrr= 3Oy, measured ~1426min Ia?Baby gamma-wunting at 662 keV with a 4 x 4 in, NaI(Ti) crystal and a 256-channel analyser. Procedurefor caeshn A preliminary study was undertaken to determine the appropriate concentration of Caesignost and acidity of the solution which would result in quantitative separation of a precipitate with de&able physical characteristics. The same procedure was used in ah the comparison tests. The conversion factor is 0,331. Different amotmts of caesi~ (20-30 mg) were precipitated with caesignost at room temperature. The pH of the solution was adJusted to 3, the experimentally found optimum, with hydrochloric or nitric acid. A stoichiometric excess of 7% Caestgnost solution was added, with stirring. A white precipitate was formed and allowed to stand ovemight. After collection on a porosity 4 sintered 185
ALXCA BAU~~AN
186
filter, the precipitate was washed twice with 1% Caesignost solution and twice with 2 ml of Ezs water. It was dried for 1 hr at 105”, cooled and weighed. The precipitate is most soluble in acetone. The results were evaluated statistically and given in Tables 1 and 2. The results indicate ETERMINAnON OF CABSIUM IN CXILGRIDE MEDIUM
TASL~I.-D
cs added, “g
cs found, * mg
Standard deviation, mg
20.0 30.0 40.0 JO.0
19.72 29.70 39.80 49~60
I.41 1.71 1.95 1.99
Coefficient of vaiiation, % 7.1 5.6 ;:;
* Mean value of 10 results. TABLE II.-DETERMINATION OF CAESIUM IN NITRATE MEDIUM
cs added, mg
cs found, W
20.0 30.0 40.0 50.0
Coefficient of variation, %
Standard deviation mg
l
1960 2990 39.75 49.80
140 1.73 1.98 2.24
7.1 ;:; 4.5
* Mean value of 10 results. little or no difference in the precipitation in chloride and nitrate media. As shown in Tables I and II satisfactory results can be obtained with 20-50 mg of caesium, though the relative error is large. Larger amounts up to 4OOmg were also determined, with similar results. A difference in the precipitation yield due to variations in room temperature was observed. Therefore the next objective of investigation was to tind the optimal temperature range for the precipitation. TABLE III.--PRECIPITATION OF CAESIUM AT DIFFERFiNTTEMPERATURES
cs
cs
Temperature, OC
taken, W
found,* q
Standard deviation W
15-25 30
20.0 20.0
19.72 16.40
*140 h3.41
+ Mean value of 20 results The standard deviation of the results obtained at 30” was very large. It is therefore suggested that the precipitation should be made at room temperatures not exceeding 25”. Caesium was then precipitated at room temperature but the time of digestion was limited to 30 min. The results are given in Table IV, and are much improved. TABLE IV.PRECIPITATION OF CAESIUM AFIER 30-MIN DIGESTION cs
cs
added, “g 20.0 50.0
found, mg 19.90 49.80
Standard deviation, mg *0.19 fO.22
Gravimetric determination of caesium irlld potassium
187
Procedure for potassium Since Havir’ got no precipitate with limited quantities of potassium, his experiments were repeated and extended by precipnating 10-50 mg and 50-1000 mg of potassium under the same conditrons as for caesium. In both cases precitation kained incomplete. The results are given in Table V.
TABLEV.-D~ERIUNA-~~ON OF POTAsXUM Time of digestion,
K added,
kr
mg
12
K found, v
JO.0
@5
1z DO 1%
157 136.0 298.0 nil n$
Procedure for c(lcpskm in the presence of potassium $0 determine the behaviour of caesium in solution in the presence of various amounts of different
salts of potassium, a synthetic model with rough resemblance to vegetation or biological material was prepared and used throughout the experiment. The composition of the synthetic model was NH, = 10 mg; Ca*+ = 140 mg; Cl- = 330 mg; K+ = 200 mg; F@+ = 7 mg; SO,*- = 20 mg; Na+ = 130 mg; Mg*+ = 10 mg; PG&*-= 60 mg; in 100 ml of den&era&d water. Each sample had 20 mg of caesium added and was spiked with 2 x I@ pCi of lWs. The separation was camed out according to the scheme: 100 ml of model solution + 20 mg of Cs-carrier -i- 2CO0pCi of ra7Cs -i- KC1
add 10 % NH, solution i hydroxides precipitated
+ filtrate: Cs, Mg, K, Na, Ca
1 Jcarbonates precipitated
add Na,CO,
4 lIltrate: Cs, Na, K add HCl 1
From the y-ray spectrum and weight of the precipitate no contamination with potassium was evident. The fInal precipitate was dissolved in acetone and the caesium was reprecipitated, The results are presented in Table VI. TABLEVI,-PREC~P~~AT~ON OF ~AE.WJM IN THE PREZNCE OF LARGEQUANTITIES OF PoTAssrUM KC1 added, g
Yield, % Gamma-spectrometry
0
98-8
5 10
59.6 59.4
GravimetriC
Potassium co-precipitated, %
98.3 59.4 59.4
-
The necessary conditions were obtained by shortening the maximum time of digestion to 30 min, B
188
ALXA
thus avoiding co-precipitation of potassium. influence on the precipitation.
BAUMAN It seems that further addition of potassium has no
DISCUSSION
Caesignost undergoes a decomposition which has not yet been explained. In a period varying from a few hours to several weeks the solution may become turbid, progressively developing a strong phenolic odor. It also appears that the presence of the decomposition products may speed further deterioration. As mentioned before, the first portions of filtered reagent are usually turbid and must be refiltered several times. By analogy with sodium tetraphenylborate4 the filtrate was clarified by addition of a trace of a caesium salt. The precip itate serves as a carrier for the very fine particles causing the turbidity, and in the process the filtrate is saturated with caesium triphenylcyanoborate. A pH higher than 7 should be avoided. The alumina treatment yields a solution of pH 4-5. The precipitation of caesium is complete under the chosen conditions. The gravimetric technique was used because of its simplicity and convenience. The coarseness of the precipitate was found to depend on the pH of the solution. The precipitation of potassium does not occur immediately, even on stirring, as it does in the case of caesium, but starts after 1 hr, which is an advantage when separating caesium in the same solution. The white precipitate of potassium triphenylcyanoborate is not as coarse as that of caesium triphenylcyanoborate. The precipitation of caesium in the presence of small amounts of potassium up to 200 mg is not impeded if the time of digestion is limited to 30 min. Larger quantities of potassium (up to 5-Og) do not co-precipitate, but interfere with quantitative precipitation of caesium. Addition of ammonia does not interfere with the precipitation of caesium. Sodium triphenylcyanoborate can be recommended as a precipitant for caesium in radiochemical analysis, especially for the separation of ls7Cs in fall-outs in the presence of negligible amounts of potassium, and in samples of vegetation and seawateP where the ratio K: Cs-carrier may exceed 200. Zusammenfw-Cum kann gravimetrisch mit Natriumtriphenylcyanoborat (Caesignost) als F%lhmgsmittel bestimmt werden. Die F&lhmg wurde durch Zusatz von la7Cs als Tracer und GammaSpektrometrie geprtift. Folgende Parameter wurden untersucht: Temperatur, Absitzzeit, EinfluI3 von Ralium auf die Caesiumf~lhmg und Abtrennung von Caesium von grol3en Kaliumtiberschtissen. R&sum&-On peut doser le caesium gravimetriquement en utilisant le triphenylcyanoborate de sodium (Caesignost) comme agent de precipitation. On a contr81e la precipitation par addition de traceur rrrCs et par spectrom&rie gamma. On a etudie les parametres suivants: temperature, temps de digestion, influence du potassium sur la pr& cipitation du caesium, et separation du caesium de quantitb considerables de potassium. REFERENCES 1. 2. 3. 4.
G. Witting and P. Raff, Ann., 1951, 573, 195. S. Havir, Collection Czech. Chern. Commun., 1961, 26, 1775. A. Bauman, Thesis, University of Zagreb, 1965. C. N. Reilley, Advances in Analytical Chemistry and Instrumentation, Vol. I, p. 16. Interscience, New York, 1960. 5. A. Bauman and V. Popovic, II Yugoslav Congress of Pure and Applied Chemistry, .Beograd, 1966.
GRAVIMETRIC DETERMINATION OF CAESIUM AND POTASSIUM WITH SODIUM TRIPHENYLCYANOBORATE (CAESIGNOST) ALICA BAUMAN Institute for Medical Research, Yugoslav Academy of Sciences and Arts, Zagreb, Yugoslavia (Received 21 July 1967. Accepted 20 August 1967) Sunuuary-Caesium can be determined gravimetrically with sodium triphenyl~o~ate (C~si~ost) as precipitant. The precipitation The was checked by addition of Is7Cstracer and ~-s~~me~y. foilowing ammeters were studied: temperature, digestion time, influence oFpotassium on the precipitation of caesium, and separation of caesium from bulk quantities of potassium.
triphenylcyanoborate is prepared1 by heating sodium-tetraphenylborate with sodium cyanide. The reactions of sodium t~phenylcyanoborate (C!aesignost) were studied by Havir* with special emphasis on electrometric methods. He succeeded in determining caesium qualitatively and quantitatively in small amounts. Under his experimental conditions potassium did not precipitate at all. The present investigation was undertaken to check the usefulness of Caesignost as a precipitant for caesium and potassium individually and for caesium in the presence of large quantities of potassium. It was also intended to test its app~~b~ty to radio~he~~l separation. Radioactive tracer technique was used to develop the procedure. The procedure of Ravir served as a starting point, but larger samples were used. SODIUM
EXPERIMENTAL Reagents Solutions of cae&um and tassium were prepared from CsCi, CsNO1, KC1 and KNOI. The concentration of caesium was etermined vimetricaity by precipitation as CsBi& and of potassium by pfecipitation as potassium 8” tetraphenyl K rate. Caes:gnost-sodmm triphenylcyanoborate (Hey1 8c Co., Berlin)--was prepared as a 7 % aqueous solution. If a turbidity appears, clarification by addition of 1 g of alkali-free aluminium hydroxide is recommended. If, during the clarification, the first portions passing through the filter-paper (Schleicher & Schuell SS 595) are still turbid, the solution must be refiltered several timea. Blanks were run from time to time. All the reagents used were analytical grade. I*‘Cs, fxrr= 3Oy, measured ~1426min Ia?Baby gamma-wunting at 662 keV with a 4 x 4 in, NaI(Ti) crystal and a 256-channel analyser. Procedurefor caeshn A preliminary study was undertaken to determine the appropriate concentration of Caesignost and acidity of the solution which would result in quantitative separation of a precipitate with de&able physical characteristics. The same procedure was used in ah the comparison tests. The conversion factor is 0,331. Different amotmts of caesi~ (20-30 mg) were precipitated with caesignost at room temperature. The pH of the solution was adJusted to 3, the experimentally found optimum, with hydrochloric or nitric acid. A stoichiometric excess of 7% Caestgnost solution was added, with stirring. A white precipitate was formed and allowed to stand ovemight. After collection on a porosity 4 sintered 185
ALXCA BAU~~AN
186
filter, the precipitate was washed twice with 1% Caesignost solution and twice with 2 ml of Ezs water. It was dried for 1 hr at 105”, cooled and weighed. The precipitate is most soluble in acetone. The results were evaluated statistically and given in Tables 1 and 2. The results indicate ETERMINAnON OF CABSIUM IN CXILGRIDE MEDIUM
TASL~I.-D
cs added, “g
cs found, * mg
Standard deviation, mg
20.0 30.0 40.0 JO.0
19.72 29.70 39.80 49~60
I.41 1.71 1.95 1.99
Coefficient of vaiiation, % 7.1 5.6 ;:;
* Mean value of 10 results. TABLE II.-DETERMINATION OF CAESIUM IN NITRATE MEDIUM
cs added, mg
cs found, W
20.0 30.0 40.0 50.0
Coefficient of variation, %
Standard deviation mg
l
1960 2990 39.75 49.80
140 1.73 1.98 2.24
7.1 ;:; 4.5
* Mean value of 10 results. little or no difference in the precipitation in chloride and nitrate media. As shown in Tables I and II satisfactory results can be obtained with 20-50 mg of caesium, though the relative error is large. Larger amounts up to 4OOmg were also determined, with similar results. A difference in the precipitation yield due to variations in room temperature was observed. Therefore the next objective of investigation was to tind the optimal temperature range for the precipitation. TABLE III.--PRECIPITATION OF CAESIUM AT DIFFERFiNTTEMPERATURES
cs
cs
Temperature, OC
taken, W
found,* q
Standard deviation W
15-25 30
20.0 20.0
19.72 16.40
*140 h3.41
+ Mean value of 20 results The standard deviation of the results obtained at 30” was very large. It is therefore suggested that the precipitation should be made at room temperatures not exceeding 25”. Caesium was then precipitated at room temperature but the time of digestion was limited to 30 min. The results are given in Table IV, and are much improved. TABLE IV.PRECIPITATION OF CAESIUM AFIER 30-MIN DIGESTION cs
cs
added, “g 20.0 50.0
found, mg 19.90 49.80
Standard deviation, mg *0.19 fO.22
Gravimetric determination of caesium irlld potassium
187
Procedure for potassium Since Havir’ got no precipitate with limited quantities of potassium, his experiments were repeated and extended by precipnating 10-50 mg and 50-1000 mg of potassium under the same conditrons as for caesium. In both cases precitation kained incomplete. The results are given in Table V.
TABLEV.-D~ERIUNA-~~ON OF POTAsXUM Time of digestion,
K added,
kr
mg
12
K found, v
JO.0
@5
1z DO 1%
157 136.0 298.0 nil n$
Procedure for c(lcpskm in the presence of potassium $0 determine the behaviour of caesium in solution in the presence of various amounts of different
salts of potassium, a synthetic model with rough resemblance to vegetation or biological material was prepared and used throughout the experiment. The composition of the synthetic model was NH, = 10 mg; Ca*+ = 140 mg; Cl- = 330 mg; K+ = 200 mg; F@+ = 7 mg; SO,*- = 20 mg; Na+ = 130 mg; Mg*+ = 10 mg; PG&*-= 60 mg; in 100 ml of den&era&d water. Each sample had 20 mg of caesium added and was spiked with 2 x I@ pCi of lWs. The separation was camed out according to the scheme: 100 ml of model solution + 20 mg of Cs-carrier -i- 2CO0pCi of ra7Cs -i- KC1
add 10 % NH, solution i hydroxides precipitated
+ filtrate: Cs, Mg, K, Na, Ca
1 Jcarbonates precipitated
add Na,CO,
4 lIltrate: Cs, Na, K add HCl 1
From the y-ray spectrum and weight of the precipitate no contamination with potassium was evident. The fInal precipitate was dissolved in acetone and the caesium was reprecipitated, The results are presented in Table VI. TABLEVI,-PREC~P~~AT~ON OF ~AE.WJM IN THE PREZNCE OF LARGEQUANTITIES OF PoTAssrUM KC1 added, g
Yield, % Gamma-spectrometry
0
98-8
5 10
59.6 59.4
GravimetriC
Potassium co-precipitated, %
98.3 59.4 59.4
-
The necessary conditions were obtained by shortening the maximum time of digestion to 30 min, B
188
ALXA
thus avoiding co-precipitation of potassium. influence on the precipitation.
BAUMAN It seems that further addition of potassium has no
DISCUSSION
Caesignost undergoes a decomposition which has not yet been explained. In a period varying from a few hours to several weeks the solution may become turbid, progressively developing a strong phenolic odor. It also appears that the presence of the decomposition products may speed further deterioration. As mentioned before, the first portions of filtered reagent are usually turbid and must be refiltered several times. By analogy with sodium tetraphenylborate4 the filtrate was clarified by addition of a trace of a caesium salt. The precip itate serves as a carrier for the very fine particles causing the turbidity, and in the process the filtrate is saturated with caesium triphenylcyanoborate. A pH higher than 7 should be avoided. The alumina treatment yields a solution of pH 4-5. The precipitation of caesium is complete under the chosen conditions. The gravimetric technique was used because of its simplicity and convenience. The coarseness of the precipitate was found to depend on the pH of the solution. The precipitation of potassium does not occur immediately, even on stirring, as it does in the case of caesium, but starts after 1 hr, which is an advantage when separating caesium in the same solution. The white precipitate of potassium triphenylcyanoborate is not as coarse as that of caesium triphenylcyanoborate. The precipitation of caesium in the presence of small amounts of potassium up to 200 mg is not impeded if the time of digestion is limited to 30 min. Larger quantities of potassium (up to 5-Og) do not co-precipitate, but interfere with quantitative precipitation of caesium. Addition of ammonia does not interfere with the precipitation of caesium. Sodium triphenylcyanoborate can be recommended as a precipitant for caesium in radiochemical analysis, especially for the separation of ls7Cs in fall-outs in the presence of negligible amounts of potassium, and in samples of vegetation and seawateP where the ratio K: Cs-carrier may exceed 200. Zusammenfw-Cum kann gravimetrisch mit Natriumtriphenylcyanoborat (Caesignost) als F%lhmgsmittel bestimmt werden. Die F&lhmg wurde durch Zusatz von la7Cs als Tracer und GammaSpektrometrie geprtift. Folgende Parameter wurden untersucht: Temperatur, Absitzzeit, EinfluI3 von Ralium auf die Caesiumf~lhmg und Abtrennung von Caesium von grol3en Kaliumtiberschtissen. R&sum&-On peut doser le caesium gravimetriquement en utilisant le triphenylcyanoborate de sodium (Caesignost) comme agent de precipitation. On a contr81e la precipitation par addition de traceur rrrCs et par spectrom&rie gamma. On a etudie les parametres suivants: temperature, temps de digestion, influence du potassium sur la pr& cipitation du caesium, et separation du caesium de quantitb considerables de potassium. REFERENCES 1. 2. 3. 4.
G. Witting and P. Raff, Ann., 1951, 573, 195. S. Havir, Collection Czech. Chern. Commun., 1961, 26, 1775. A. Bauman, Thesis, University of Zagreb, 1965. C. N. Reilley, Advances in Analytical Chemistry and Instrumentation, Vol. I, p. 16. Interscience, New York, 1960. 5. A. Bauman and V. Popovic, II Yugoslav Congress of Pure and Applied Chemistry, .Beograd, 1966.