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CRER-1068
Details of the procedures are given in the appendices.
EVALUATION OF THE PROCEDURES
1.
Standardization of the Calcium Oxalate Method
Although consistent and reproducible results for calcium
were obtained by the oxalate method, it was not certain that the
absolute content of calcium was known with sufficient accuracy.
|
Early attempts,to verify the analyses by an independent method,
such as flame photometry, were unsuccessful.
It was decided,
therefore, to check chemical yields and stoichiometry of the:
wo
-
oxalate precipitate by means of a radiochemical technique, using
4.7 d calcium-47 (510, 810, 1300 keV Y) as a tracer.
A known
quantity of the tracer was added to a solution of the sample prior
to the removal of silica, and following the separation procedure
described in Appendix 3,
weighed and counted.
the calcium oxalate precipitate was
Calcium-47 losses averaged less than 0.1%.
The oxalate was dissolved in dilute nitric acid and
calcium was re-precipitated twice with 85% fuming nitric acid.
The precipitate of calcium nitrate was then dried and extracted ©
twice with 10 ml of a one to one ethanol-ether mixture.
Calcium
nitrate is readily soluble. in this solvent but barium and strontium
nitrates are not.
Rare-earths and other elements were removed by
scavenging with ferric hydroxide.
;
The calcium was then re-precipit-
ated as oxalate for weighing and counting.
Throughout the procedure, the calcium-47 activity per
gram of oxalate, i.e. the specific activity, remained unchanged,
Showing that two precipitations were sufficient to obtain pure