The [Co(CN)6]3- complex is of interest as a basic carrier of the five different radionuclides 56Co, 57Co, 58Co, 60Co and 14C. The first four are gamma emitters while the latter is a pure beta emitter.

In actual field situations, [Co(CN)6]3- may be used in areas where 35SCN — or S14CN — have been applied simultaneously. Since the thiocyanate tracers have to be analysed by liquid scintillation counting the presence of [Co(CN)6]3-, regardless of the radiolabel, will disturb the counting of the thiocyanate. For gamma emitting labels, the analysis may be performed by gamma spectrometry, but if the label on the [Co(CN)6]3- is 14C, there will be a mutual disturbance of the two radiolabelled complexes. Therefore, there was a need to develop radiochemical procedures to separate cobalthexacyanide and thiocyanate at the tracer level in produced water and results of attempts at this separation have been reported.

A method was developed for quantitative analysis using 1000 mL of sea water (as a substitute for produced water) containing a mixture of SCN — and [Co(CN)6]3- produced by enrichment procedures and preconcentration into samples small enough to be measured by liquid scintillation counting. The sample volume for liquid scintillation counting should not exceed 8-10 mL, since this is normally the maximum water sample volume dissolved by modern scintillation cocktails (12 mL) for ordinary 22 mL scintillation vials.

The main hypothesis was to take advantage of the difference in anionic charges to obtain a separation. The test sequence involved the following:

• Screening tests used to find a selective separation procedure for [Co(CN)6]3- by the use of 60Co labelled complex as a tracer. The separation is based on either solvent extraction or ion exchange techniques.

• Testing of different stripping or elution agents in order to minimize the degree of quenching in the final counting samples.

• Checking the absorption and stripping/elution characteristics of SCN- in the [Co(CN)6]3- method.

• Performing separation experiments on an actual sample containing both tracers labelled with 60Co and 14C.

The screening experiments with 60Co were measured by gamma spectroscopy using a lead shielded, high resolution semiconductor detector and 14C was measured with a liquid scintillation counter.