Both solvent extraction and ion exchange procedures may be used for entrapment, enrichment and separation of [Co(CN)6]3- and SCN- tracers from saline waters (sea water or formation water). It seems, however, that the ion exchange procedures are the least labour intensive.

The results reported indicate a higher solvent extraction yield for [Co(CN)6]3- with strong basic extractants rather than weak ones for the prevailing experimental conditions. This is valid both for the liquid extraction agents and for the solid anion exchangers tested. In the ion exchange processes, it is found that [Co(CN)6]3- is more strongly absorbed by Dowex 1 x 2 than by Dowex 2 x 8, although the absorption yields are close to 100% for both under the prevailing conditions. Their relative absorption strengths appear through their ability to release the tracer again by various elution agents.

The difference in the degree of cross-linking between the Dowex 1 x 2 and Dowex 2 x 8 resins would favour the kinetics of the x2 resin. However, for reasonable flow rates, the kinetics is not an issue. Since the Dowex 2 x 8 resin shows the highest elution yield (which was previously concluded to be due to the difference in the functional groups), use of the Dowex 2 x 8 resin is recommended for the actual separation process.

The remaining SCN — on the Dowex 2 x 8 ion exchanger after sample loading may be eluted selectively and with high elution efficiency by 10 mL of 0.1M NaClO4. This eluate may be added to the raffinate after the sample loading process and used as a feed to the BioRad AG1 column for separation and enrichment of the SCN- tracer along the lines already outlined.

From a 1000 mL sample, the total recovery (chemical yield) is >65%. Since the volume is reduced by a factor of 100, the enrichment factor is >65. By optimizing the process, it is probably possible to double this figure, especially by selecting carefully only the elution volume containing the bulk of the tracer peak. In this way, the volume may perhaps be reduced by a factor of 2-3 with a slight reduction in chemical yield.

The [Co(CN)6]3- complex may be stripped from Dowex 2 x 8 by, for instance, 10 mL 5M NH4NO3 (acceptable for modern scintillation cocktails) with an efficiency of 75%. The overall chemical yield will, therefore, be >75%. From the same sample size as for SCN-, the volume reduction will amount to a factor of 100 and the corresponding enrichment factor to >75. It is also possible to improve this figure by optimization of the procedure along the same lines as described for SCN-.

Appendix I