acidity in the buffer region between the first and second hydrogen is due to the common ion effect of the tetrabutylammonium ion on the dissociation of tetrabutylammonium bimalonate. The reaction of tetrabutylammonium ion with the malonate ion to increase the acidity could not be expected to be extensive in this case since the titrant cation is shielded ( 1 ) . The addition of a large amount of
tetrabutylammonium bromide in the titration of a very weak acid would appear to be a useful technique for increasing the acidity and obtaining better titration curves when titrating with tetrabutylammonium hydroxide. While it is recognized that some estimation of the dissociation constant of the tetrabutylammonium salt of the acid is necessary for successful application, this is not believed to be a serious limitation.
LITERATURE CITED
( 1 ) Harlow, G. A., ANAL. CHEM. 34,
1482 (1962). (2) Marple, L. W.,Fritz, J. S., ANAL. CHEM.34, 796 (1962). (3) Ibid., p. 1223.
RECEIVED for review Xovember 13, 1962. Accepted June 26, 1963. Contribution No. 1242. Work performed in the Ames LaboratoFy of the U. S. Atomic Energy Commission.
Chlorostannate Method for Separation of Radiocesium C. F. GOEKING, C. L. GHANN, and E. I. WYATT Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b A rapid and reliable method was developed for the separation of radiocesium from fission-product mixtures. Stannic chloride is used to precipitate cesium selectively as cesium chlorostannate, CszSnCle, from a 50 (v./v.) % solution of concentrated HCI in ethyl alcohol. Usually, the major portion of contaminants is removed by one scavenging step followed by two precipitations of cesium. The method is comparable with the perchloric acid and tetraphenylboron precipitation methods for cesium with respect to decontamination factors, carrier yields, analytical time, and accuracy. It has been applied satisfactorily to a variety of samples.
T
rapid and accurate radiochemical separation of radiocesium is of great importance in the analysis of fission-product mixtures. The long half life (30 years) of Cs13’ and the high vield (67J from the fissioning of make this isotope one of the more reliable fission products for use in measuring the burnup of reactor fuel. Numerous precipitation methods have been used to isolate radiocesium. Of these, the perchloric acid method (1, 8 ) and the tetraphenylboron method ( I , 3 ) are used most often. Both, however, are time-consuming. B chlorostannate method is described herein which require3 not longer than one hour for each complete determination in duplicate. Precipitation of ccsium as cesium chlorostannate, C&kiCI,, from a 50 (v./v.)% solution of concentrated HC1 in C2HrOHhas long been used to separate cesium from sodium and potassium ( 4 ) . Any rubidium present will be precipitated with the cesium. However, in a fission-product solution the HE
1434
ANALYTICAL CHEMISTRY
principal rubidium radioisotopes usually present are short-lived. If the sample has been out of the reactor for several hours, the amounts of these activities will be negligible. Except for special cases, discussed later, the radiochemical chlorostannate method consists in scavenging with Zr+4 and Fe+3 to form a mixed precipitate of zirconium iodate, Zr(Io~)d, and ferric iodate, Fe(IOJd. The scavenge step is followed by two precipitations of CszSnClb from a 50 (v./v.)% solution of HC1 in CzHjOH by addition of SnCL. The final precipitate is air-dried, weighed, and counted. This method is suggested as an alternate means for the separation of radiocesium. It has the advantages of being rapid and utilizing nonhazardous reagents; in addition, it effects good decontamination and high carrier yields that are comparable with those characteristic of the perchloric acid and tetraphenylboron methods. REAGENTS
Standard Solution of Cesium Carrier. Prepare by dissolving -10 grams of CsCl in 1 liter of distilled water. Standardize the solution as follows. Pipet six 5-ml. portions into separate beakers. Treat each as follows: add 35 nil. of a 50 (v./v.) yo solution of concentrat,ed HC1 in C 2 H 5 0 H ; then add 15 ml. of SnCL reagent. Stir the solution well t o ensure complete precipitation of the cesium. Filter the C&3nCle through a tared, medium-fine, sintered-glass filter. Wash the precipitate twice with a 4 (v./v.)% solution of concentrated HC1 in CzH60H; dry it with diethyl ether washes. Desiccate the filter in a vacuum desiccator for 10 to 15 minutes; then remove it and weigh it. The carrier yield should be 10 to 15 mg. of CszSnCIBper milliliter of cesium carrier
solution. The six results should agree within &l%. Hydrochloric Acid-Ethyl Alcohol Solutions. A. 50 (v./v.)% Solution of Concentrated HC1 in CzH50H. Prepare by adding 1 volume of concentrated HC1 to 1 volume of 95% CzH50H. B. 4 (v./v.)% Solution of Concentrated HC1 in C2H60H. Prepare by adding 1 volume of concentrated HC1 to 24 volumes of 95% C&OH. Stannic Chloride Reagent. Prepare by saturating a 50 (v./v.)% solution of concentrated HC1 in CzH,OH with analytical reagent grade SnCl4. Zirconium(1V) Solution, -10 mg. of Zr+4 per ml. Prepare by dissolving 35 grams of ZrOC12.8Hz0in 1 liter of discfiled mater. Iron(1II) Solution, -5 mg. of Fe+8 per ml. Prepare by dissolving 24 grams of FeCl3.6H20 in 1 liter of dist’llled water. Ruthenium(II1) Holdback Solution, -10 mg. of Ruf3 per ml. Prepare by dissolving 30 grams of R u C l ~ z H 2 0in 1 liter of distilled water. Iodic Acid Solution, 0.35M Prepare by dissolving 62 grams of H I 0 3 in 1 liter of distilled water. PROCEDURE
Formation of Zirconium IodateFerric Iodate Precipitate. Into a 50-ml. centrifuge tube, pipet 2 ml. of standard solution of cesium carrier and a predetermined volume of the sample. Add 3 drops of Zr+4 solution and 2 drops of Fe+3 solution. Adjust the p H of the solution t o 2; then add 5 ml. of 0.36M HIOs. Stir the solution, centrifuge the mixture, and decant the supernate into a second 50-ml. centrifuge tube. To the decanted supernate repent the addition of Zr+4 and Fe+S solutions. Stir the solution, centrifuge the mixture, and decant the supernate into a third 50-ml. centrifuge tube.
Precipitation of Cesium as CszSnC16. T o t h e second decanted supernate, add 10 nil. of a 50 (v./v.)% solution of concentrated HC1 i n C2H50H, 4 drops of Fe+3 solution, and 3 ml. of SnC14 reagent. Stir the solution t o ensure the complei e precipitation of cesium a s Cs~SnCls, centrifuge the mixture, and discard the supernate. K a s h the precipitate once with 10 ml. of 50 (v./v.)% solution of concentrated HCl in CzHsOH, centrifuge the mixture, and discard the wash. Dissolve the precipitate in a minimum of hot diqtilled n a t e r (not more than 3 ml.); then add 10 ml. of a 50 (v./v) % solution of concentrated HC1 in CZHsOH. (For samples of high ruthenium activity, a drop of Ru+3 holdback carrier added at this point will aid in the complete removal of the ruthenium activity.) Add 3 ml. of SnC14 reagent. Stir the solution, centrifuge the mixture, and discard the supernate. Raqh the preciFitate with a few niilliliters of a 50 (v./v.)% solution of concentrated HCl in C2H5011,centrifuge the mixture, and discard the wash. Csing a 4 (v./v.)% solution of roncentrated HC1 in CzHjOH, slurry the precipilate onto a previously tared filter disk placed in a Hirsch funnel. K a s h the precipitate twice with a 4 (v./r.)70solution ci concentrated HC1 in C2H50H, and dIy it mith diethyl ether washes. Measurement of Radiocesium. IVeigh t h e precipit,ite and determine the per cent raciocheniical yield. Transfer t h e preciritate t o a culture tube a n d measure t i e gamma activity u i t h a well-type gamma scintillation counter. The radioisotope of cesium most commonly sought is Csl37, 15 liich decays bj; the emission of two beta particles, 0.01- (927,) and 1.17-m.e.v. (8%). The 0.51-m.e.v. bet2 decays to Ra137m, which undergoes isomeric transition t o Ba137 by emission of 0.662-m.e.v. photons. Other rad oisotopes of cesium sometimes prment in fission products are Cs1j4 and Cs13G Cesium-134 (tl = 2.07 years) decays n i t h 0.083(32'%), 0.31- (5%), 0.655- (SO%,, and 0.683-m.e.v. (13%) beta activities and 0.473-, 0.569-, 0.605-, 0.796-, 1.038-, 1.168-, 1.367-m.e.v.. and other gamma activities (6). Cesium-136 (tl 2 = 12.9 days) decays with t h ? emission of 0.341(9370) and 0.657-m.c .v. (iyc) betas and 0.0672-, 0.153-, 0.102-, 0.265, 0.335-, 0.822-, 1.04-, 1.25- and 1.41-m.e.v. gammas ( 5 ) . If either Cs114or Csl36 IS present, it become, >iecessary to resort to y-rav spectrometry to determine C.13'. RESULTS AND DISCUSSION
Accuracy and Precision of Method. For t h e chlorostaniiate method, the t.ttent ul t h e interchauge uf the cesium radioisotopw present in a sample with t h e noni adioactive cesium carrier added was determined accurately, by initially adding a known amount of Cs137to tl-e sample, carrying out the procedure given above, and
Table 1. Recovery of Cesium Activity Sample. Solution of of 4.15 X 106 c.p.m. activity Test
portion of sample
Carrier yield, yo i9.4 60.8 63.4 70.1 84.6 80.0
Table 11.
Xethod Chlorostannate Perchloric acid Tetraphenylboron
Counts corrected for yield, c.p.m. X
Recovery of Cs137 t CP /G
4.18 4.14 4 04 4.15 4.10 4.08
Specific activity of CszSnCls, c.p.m./mg.
x
100.7 99.8 97.3 100.0 98.8 98.3
10-6
1.38 1.3T 1.33 1.37 1.35 1.35
Comparison of Precipitation Methods Time required for duplicate analyses, hr.
Average carrier yield, yo
Cs137 in sample, c.p.m./ml. x 10-6
1.0 2.3 2.5
60.0 64.5 66.6
1.41 1.45 1.43
measuring the C'sl37 recovered in the final precipitate. The results are shown in Table I. After all activity measur?meat? were corrected for background counts and to 100yG carrier yield, an average value of 4.12 X 10a c.p.m. per ml. was obtained as compared n i t h 4.15 X lo5 c.p.m. per ml. added initially, which is 99.3% recovery of the CsI37. The greatest deviation from the initial value mas S O X . The experimentally determined specific activity of the precipitate showed a maximum deviation of
