Determination of radioactive strontium in seawater

This paper describes the procedures of isolating strontium and yttrium from seawater that enable the determination of ^89,90Sr. In one procedure, strontium is directly isolated from seawater on the column filled with Sr resin by binding of strontium to the resin from 3 M HNO₃ in a seawater, and successive elution with HNO₃. In others, strontium is precipitated from seawater with (NH₄)₂CO₃, followed by isolation on a Sr column or an anion exchange column. It is shown that strontium precipitation is optimal with concentration of 0.3 M (NH₄)₂CO₃ at pH = 11. In these conditions, 100% Y, 78% Sr, 80% Ca and 50% Mg are precipitated. Strontium is bound on to Sr column from 5 to 8 M HNO₃, separated from other elements by elution with 3 M HNO₃ and 0.05 M HNO₃. Strontium and yttrium are bound on to anion exchange column from alcoholic solutions of nitric acid. The optimum mixture of alcohols for sample binding is a mixture of ethanol and methanol with the volume ratio 1:3. Strontium and yttrium are separated from Mg, Ca, K, and other elements by elution with 0.25 M HNO₃ in the mixture of ethanol and methanol. After the separation, yttrium and strontium are eluted from the column with water or methanol.In the procedure of direct isolation from 1 l of the sample, the average recovery of 50% was obtained. In the remaining two procedures, the strontium recovery was about 60% for the Sr column and 65% for anion exchange column. Recovery of yttrium is about 70% for the anion exchange column. It turned out that the procedure with the Sr resin (direct isolation and isolation after precipitation) is simpler and faster in the phase of the isolation on the column in comparison with the procedure with the anion exchanger. The procedure with the anion exchanger, however, enables the simultaneous isolation of yttrium and strontium and rapid determination of ^89,90Sr. These procedures were tested by determination of ^89,90Sr on liquid scintillation counter and Cherenkov counting in 5 M HNO₃. Obtained results showed that activity of 50 mBq l⁻¹ of ^89,90Sr and higher can be simultaneously determined.