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Photometric titrations-IV:1 The chelometric titration of cadmium in the presence of zinc
Short communications
76
the coulometric titration of ceriumr?’ ion and iodine used the potentiometric method and that of bromine used the amperometric method. In the amperometric detection, the indicating current was expressed with the voltage drop measured through the definite resistance, when the voltage 0.3 - 0.4 V was applied between the two platinum electrodes through 100 kR resistance. In conclusion, the coulometric method with tinu ion is considered to be more versatile using a solid electrode such as platinum than that with titaniumm or chromiumu ions in which cases the mercury electrode is forced to be employed in place of the solid electrode. TAKW TAKAHASHI Institute of Industrial Science HIROSHISAKURAI University of Tokyo, Japan Summary-The coulometric method of electrogenerated tin rr ion using the platinum electrode as a generating cathode has been investigated. The electrolytic solution comprising 3Mpotassium chloride and 0+3M tinrv chloride has been found to be satisfactory for the determination of ceriumrV ion, iodine and bromine with an error of only a few percent provided suitable conditions are employed. Zusammenfassung-Coulometrie mit Zinn(II)-ionen (an einer Platinelektrode erzeugt) wurde untersucht. Eine elektrolyt welcher 3M in Kaliumchlorid und 0,3M in Stannichlorid ist wurde fur die Titration von Cer(IV), Jod und Brom geeignet gefunden. R&&--Les auteurs ont ttudie la coulometrie a l’aide de l’ion stanneux prepare par electrolyse, en utilisant une cathode de platine. 11s ont trouvC qu’une solution contenant du chlorure de potassium 3 M et du chlorure stannique 0,3 M convenait pour le dosage du cerium (IV), de l’iode et du brome. REFERENCES IP. Arthur and J. E. Donahue, Analyt. Chem., 1952,24, 1612. a W. Oelsen and P. Gobbels, Stahl u. Eisen, 1949, 69, 33. s I. Sakai and S. Yuki, Japan Analyst, 1958, 7, 33. * W. D. Shults, P. F. Thomason and M. T. Kelley, Analyt. Gem., 1955,27, 1750. 5 D. J. Meier, R. J. Meyers and E. H. Swift, J. Amer. Chem. Sot., 1949, 71, 2340. BA. J. Bard and J. J. Lingane, Anulyt. Chim. Acta, 1959, 20, 463. ’ T. Takahashi, K. Kimoto and H. Sakurai, Rep. Inst. Ind. Sci., Univ. of Tokyo, 1955, 5, 121.
Photometric titrations-IV:* The chelometric titration of cadmium in the presence of zinc (Received 30 May 1961. Accepted 7 June 1961) SWEETSERand BRICKER~described the EDTA titration of cadmium in the presence of zinc, with a photometric end-point at 236 mp. The titration is performed in strongly alkaline medium where zinc is present as unreactive zincate, and cadmium is kept in solution by the addition of a small amount of cyanide. The disadvantages of this procedure are: operating at a very short wavelength, the high alkalinity, and the fact that the amount of cyanide added is critical. It therefore seemed worthwhile to search for a possibility of performing such a determination under more favourable conditions. The numerical values of the stability constants of cadmium-chelonates are always very close to those of the corresponding zinc complexes with only one remarkable exception, namely, EGTA [ethyleneglycol-bis(aminoethyl)-tetra-acetic acid]. The logarithms of the stability constants of the EGTA complexes of cadmium and zinc are 16.7 and 128, respectively.a This difference of 3.9 logarithmic units refers to the absolute constants. In a practical titration the apparent stability constants have to be taken into account, and their difference can be increased by the use of an appropriate medium, such as an ammonia buffer. The logarithms of the /?-factors of cadmium and zinc in an ammonia-ammonium chloride buffer pH 10 (total concentration O.lM) are 3.9 and 8.6 respectively.s Hence the difference in the apparent stability constants under these conditions is 4.7 logarithmic units. This difference should be sufficient to permit the potentiometric titration of * Part III-see
Talanta, 1961, 8, 885.
Short communications
77
cadmium in the presence of zinc employing the mercury drop electrode.4 This approach is at present under investigation in the authors’ laboratory. The difference of barely five lo~t~ic units represents a border-line case for a visual titration when a complex-forming indicator is employed. In addition to this, there is no indicator known which reacts specifically with cadmium, and the hope of ever finding one seems to be very slight. The difference of 4.7 log-units is more than sufficient for a photometric end-point, provided that either of the two metal-systems is self-indicating .O This, however, is not the case, since all species involved are colourless. A possibility may exist in the ultraviolet region, but this has not been investigated. Theoretical considerations indicate the possibility of placing a se~-~~~t~g system having an appropriate stability constant between that of the cadmium and zinc. For example, Underwood used copper as photometric indicator in the EDTA titration of bismuth.6 Copper is especially suitable for this purpose because of the relatively large difference of the extinction Thestabilityconstant coefficients of the free copper ion or its amino complexand anycheloncomplex. of the copper-EGTA complex has not yet been reported in the literature. It is, however, reasonable to assume that it will be of the same order as, or even somewhat greater than, that of the cadmium complex. Fortunately the logarithm of the p-factor for copper in an ammonia buffer as specified above is 8*3.$ This makes it possible to arrange the apparent stability constants in the order Cd > Cu > Zn. Experiments verified this assumption, Thus, a titration of cadmium in the presence of zinc is possible with copper as the photometric indicator. EXPERIMENTAL Apparatus The photometric titrator used was described in an earlier paper in this series7 Cuvettes with a light path of 3 and 10 cm and a capacity of about 100-200 ml were employed. A Sargent automatic burette was used. Reagents
Solutions of metals ions and complexing reagent were prepared from Reagent Grade material and standardised according to well-established chelometric procedures.8~s The buffer, pH 10, was prepared by dissolving 70 g of ammonia chloride and 570 ml of cone. ammonia in de-ionised water and diluting to I litre. Absorbance curves of copper in solutions containing buffer (pH 10) in the absence of EGTA and in the presence of excess EGTA show that the most suitable wavelength for the titration is between 700 and 750 m,u. A 742-m,u interference filter was used.
Accurately measured amount of cadmium and zinc solutions were pipetted into the titration cell, 10 ml of buffer, pH IO (the amount of buffer is not critical), and 5 ml of O-l&f solution of copper sulphate were added, and diluted to about 150 ml with de-ionised water. The cell was placed in the phototitrator, and the titration was performed in the usual manner. The transmittance readings were plotted on semi-log paper or, in the case of small changes, more conveniently transformed to absorbance and plotted on linear paper. RESULTS A representative curve is shown in Fig. 1. The results of some titrations are presented in Table I. When the concentration of zinc is not exceedingly high the titration can be extended to a second, but less sharp, end-point thus permitting the determination of cadmium and copper in the presence of zinc. Iron and aluminium in moderate amounts, when masked with tartrate, do not interfere. Magnesium can be present in considerable quantities. Most of the other ions interfere as in other chelometric procedures; they are either co-titrated, e.g., lead and calcium, or cause a decrease in the slope difference, e.g., nickel. This, however, is no serious drawback, since the separation of cadmium and zinc from most other elements can readily be effected by ion-exchange methodsI On the other hand, some multicomponent systems can be resolved by chelometric titrations involving operation with aliquots and employing different masking reagents, titrants and indicators. Where up till now the sum of cadmium plus zinc has been determined, the cadmium may be determined in a further step incorporating the new method.
18
Short communications 0.090
O.lM Zn (total voltune about 150 ml; cell length 10 cm; 742 m,&
0.0401
t 0.1
0
, o-2
1 O-4
I 0.3 Id
M
EGTA.
I 05
I 0.6
1 0.7
ml
FIG. 1.-Titration
curve for the determination of 2*00ml of 5 x lO-3M Cd in the presence of 50 ml of O-1M Zn (total volume about 150 ml; cell length 10 cm; 742 mp).
TABLE I. TITRATIONOF
CADMIUM
WITH
O*lMEGTA
-
I
Cd
4,OO 9.90 4.00 4.00 203 1000 2.03 3.56 1.01 2.03
4*00 9.94 4.02 3.95 2.06 1000 2.00 364 1.04 2.08
OF ZINC. 742 rnb
Zn, ml
Pound, ml
Taken, ml
INTHEPRESENCE
0
O.lM 3-cm cell
25 5 100 I o O.lM
5 x 10-3M lo-cm cell
10 50 15 I 25 50 0.2M
Cd:Zn Ratio 1:25 1: 1.25 1:25 1:50 1:lOO 1:260 1:300 1:500
The following example may show the principle of this approach. The sample contained the following ions: Pb, Zn, Cd and Cu. In the first aliquot Pb was titrated with EDTA (Eriochrome Black T as indicator) in thepresenceof tartrate and cyanide. After selective demasking of Zn and Cd with formaldehyde, the titration was continued to obtain the sum Zn + Cd. In a second aliquot the sum Pb + Cd was obtained employing the new method. In a third aliquot the sum of all metals present was obtained by an EDTA titration at pH 6 using PAN as indicator. The following results were obtained; the tirst figure is the calculated value, the second figure the experimental one. Cu: 2.18; 2.26. Zn: 5,45; 540. Pb: 3.82; 3.80. Cd: 1.05; 1.08. Acknowledgement-The work was performed the aid is gratefully acknowledged. School of Chemistry Georgia Institute of Technology Atlanta, Georgia, U.S.A.
under a grant of the National
Science Foundation; H. FLAXHKA J. GANCHOFF
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.
76
the coulometric titration of ceriumr?’ ion and iodine used the potentiometric method and that of bromine used the amperometric method. In the amperometric detection, the indicating current was expressed with the voltage drop measured through the definite resistance, when the voltage 0.3 - 0.4 V was applied between the two platinum electrodes through 100 kR resistance. In conclusion, the coulometric method with tinu ion is considered to be more versatile using a solid electrode such as platinum than that with titaniumm or chromiumu ions in which cases the mercury electrode is forced to be employed in place of the solid electrode. TAKW TAKAHASHI Institute of Industrial Science HIROSHISAKURAI University of Tokyo, Japan Summary-The coulometric method of electrogenerated tin rr ion using the platinum electrode as a generating cathode has been investigated. The electrolytic solution comprising 3Mpotassium chloride and 0+3M tinrv chloride has been found to be satisfactory for the determination of ceriumrV ion, iodine and bromine with an error of only a few percent provided suitable conditions are employed. Zusammenfassung-Coulometrie mit Zinn(II)-ionen (an einer Platinelektrode erzeugt) wurde untersucht. Eine elektrolyt welcher 3M in Kaliumchlorid und 0,3M in Stannichlorid ist wurde fur die Titration von Cer(IV), Jod und Brom geeignet gefunden. R&&--Les auteurs ont ttudie la coulometrie a l’aide de l’ion stanneux prepare par electrolyse, en utilisant une cathode de platine. 11s ont trouvC qu’une solution contenant du chlorure de potassium 3 M et du chlorure stannique 0,3 M convenait pour le dosage du cerium (IV), de l’iode et du brome. REFERENCES IP. Arthur and J. E. Donahue, Analyt. Chem., 1952,24, 1612. a W. Oelsen and P. Gobbels, Stahl u. Eisen, 1949, 69, 33. s I. Sakai and S. Yuki, Japan Analyst, 1958, 7, 33. * W. D. Shults, P. F. Thomason and M. T. Kelley, Analyt. Gem., 1955,27, 1750. 5 D. J. Meier, R. J. Meyers and E. H. Swift, J. Amer. Chem. Sot., 1949, 71, 2340. BA. J. Bard and J. J. Lingane, Anulyt. Chim. Acta, 1959, 20, 463. ’ T. Takahashi, K. Kimoto and H. Sakurai, Rep. Inst. Ind. Sci., Univ. of Tokyo, 1955, 5, 121.
Photometric titrations-IV:* The chelometric titration of cadmium in the presence of zinc (Received 30 May 1961. Accepted 7 June 1961) SWEETSERand BRICKER~described the EDTA titration of cadmium in the presence of zinc, with a photometric end-point at 236 mp. The titration is performed in strongly alkaline medium where zinc is present as unreactive zincate, and cadmium is kept in solution by the addition of a small amount of cyanide. The disadvantages of this procedure are: operating at a very short wavelength, the high alkalinity, and the fact that the amount of cyanide added is critical. It therefore seemed worthwhile to search for a possibility of performing such a determination under more favourable conditions. The numerical values of the stability constants of cadmium-chelonates are always very close to those of the corresponding zinc complexes with only one remarkable exception, namely, EGTA [ethyleneglycol-bis(aminoethyl)-tetra-acetic acid]. The logarithms of the stability constants of the EGTA complexes of cadmium and zinc are 16.7 and 128, respectively.a This difference of 3.9 logarithmic units refers to the absolute constants. In a practical titration the apparent stability constants have to be taken into account, and their difference can be increased by the use of an appropriate medium, such as an ammonia buffer. The logarithms of the /?-factors of cadmium and zinc in an ammonia-ammonium chloride buffer pH 10 (total concentration O.lM) are 3.9 and 8.6 respectively.s Hence the difference in the apparent stability constants under these conditions is 4.7 logarithmic units. This difference should be sufficient to permit the potentiometric titration of * Part III-see
Talanta, 1961, 8, 885.
Short communications
77
cadmium in the presence of zinc employing the mercury drop electrode.4 This approach is at present under investigation in the authors’ laboratory. The difference of barely five lo~t~ic units represents a border-line case for a visual titration when a complex-forming indicator is employed. In addition to this, there is no indicator known which reacts specifically with cadmium, and the hope of ever finding one seems to be very slight. The difference of 4.7 log-units is more than sufficient for a photometric end-point, provided that either of the two metal-systems is self-indicating .O This, however, is not the case, since all species involved are colourless. A possibility may exist in the ultraviolet region, but this has not been investigated. Theoretical considerations indicate the possibility of placing a se~-~~~t~g system having an appropriate stability constant between that of the cadmium and zinc. For example, Underwood used copper as photometric indicator in the EDTA titration of bismuth.6 Copper is especially suitable for this purpose because of the relatively large difference of the extinction Thestabilityconstant coefficients of the free copper ion or its amino complexand anycheloncomplex. of the copper-EGTA complex has not yet been reported in the literature. It is, however, reasonable to assume that it will be of the same order as, or even somewhat greater than, that of the cadmium complex. Fortunately the logarithm of the p-factor for copper in an ammonia buffer as specified above is 8*3.$ This makes it possible to arrange the apparent stability constants in the order Cd > Cu > Zn. Experiments verified this assumption, Thus, a titration of cadmium in the presence of zinc is possible with copper as the photometric indicator. EXPERIMENTAL Apparatus The photometric titrator used was described in an earlier paper in this series7 Cuvettes with a light path of 3 and 10 cm and a capacity of about 100-200 ml were employed. A Sargent automatic burette was used. Reagents
Solutions of metals ions and complexing reagent were prepared from Reagent Grade material and standardised according to well-established chelometric procedures.8~s The buffer, pH 10, was prepared by dissolving 70 g of ammonia chloride and 570 ml of cone. ammonia in de-ionised water and diluting to I litre. Absorbance curves of copper in solutions containing buffer (pH 10) in the absence of EGTA and in the presence of excess EGTA show that the most suitable wavelength for the titration is between 700 and 750 m,u. A 742-m,u interference filter was used.
Accurately measured amount of cadmium and zinc solutions were pipetted into the titration cell, 10 ml of buffer, pH IO (the amount of buffer is not critical), and 5 ml of O-l&f solution of copper sulphate were added, and diluted to about 150 ml with de-ionised water. The cell was placed in the phototitrator, and the titration was performed in the usual manner. The transmittance readings were plotted on semi-log paper or, in the case of small changes, more conveniently transformed to absorbance and plotted on linear paper. RESULTS A representative curve is shown in Fig. 1. The results of some titrations are presented in Table I. When the concentration of zinc is not exceedingly high the titration can be extended to a second, but less sharp, end-point thus permitting the determination of cadmium and copper in the presence of zinc. Iron and aluminium in moderate amounts, when masked with tartrate, do not interfere. Magnesium can be present in considerable quantities. Most of the other ions interfere as in other chelometric procedures; they are either co-titrated, e.g., lead and calcium, or cause a decrease in the slope difference, e.g., nickel. This, however, is no serious drawback, since the separation of cadmium and zinc from most other elements can readily be effected by ion-exchange methodsI On the other hand, some multicomponent systems can be resolved by chelometric titrations involving operation with aliquots and employing different masking reagents, titrants and indicators. Where up till now the sum of cadmium plus zinc has been determined, the cadmium may be determined in a further step incorporating the new method.
18
Short communications 0.090
O.lM Zn (total voltune about 150 ml; cell length 10 cm; 742 m,&
0.0401
t 0.1
0
, o-2
1 O-4
I 0.3 Id
M
EGTA.
I 05
I 0.6
1 0.7
ml
FIG. 1.-Titration
curve for the determination of 2*00ml of 5 x lO-3M Cd in the presence of 50 ml of O-1M Zn (total volume about 150 ml; cell length 10 cm; 742 mp).
TABLE I. TITRATIONOF
CADMIUM
WITH
O*lMEGTA
-
I
Cd
4,OO 9.90 4.00 4.00 203 1000 2.03 3.56 1.01 2.03
4*00 9.94 4.02 3.95 2.06 1000 2.00 364 1.04 2.08
OF ZINC. 742 rnb
Zn, ml
Pound, ml
Taken, ml
INTHEPRESENCE
0
O.lM 3-cm cell
25 5 100 I o O.lM
5 x 10-3M lo-cm cell
10 50 15 I 25 50 0.2M
Cd:Zn Ratio 1:25 1: 1.25 1:25 1:50 1:lOO 1:260 1:300 1:500
The following example may show the principle of this approach. The sample contained the following ions: Pb, Zn, Cd and Cu. In the first aliquot Pb was titrated with EDTA (Eriochrome Black T as indicator) in thepresenceof tartrate and cyanide. After selective demasking of Zn and Cd with formaldehyde, the titration was continued to obtain the sum Zn + Cd. In a second aliquot the sum Pb + Cd was obtained employing the new method. In a third aliquot the sum of all metals present was obtained by an EDTA titration at pH 6 using PAN as indicator. The following results were obtained; the tirst figure is the calculated value, the second figure the experimental one. Cu: 2.18; 2.26. Zn: 5,45; 540. Pb: 3.82; 3.80. Cd: 1.05; 1.08. Acknowledgement-The work was performed the aid is gratefully acknowledged. School of Chemistry Georgia Institute of Technology Atlanta, Georgia, U.S.A.
under a grant of the National
Science Foundation; H. FLAXHKA J. GANCHOFF
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.