GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF ULTRA-TRACE LEVELS OF COBALT AFTER SOLVENT-EXTRACTION USING W/O/W EMULSIONS AS LIQUID SURFACTANT MEMBRANES

A high-enrichment method by liquid-liquid extraction using liquid surfactant membranes was developed for the determination of cobalt at pgcm_3 levels by graphite furnace atomic absorption spectrometry (GF-AAS). Two cubic centimeters of w/o [water in oil, in this case dilute hydrochloric acid in kerosene (1:1) containing 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (PC-88A)] emulsion droplets coated with sorbitan monooleate are dispersed in a resulting volume of 1000 cm3 of an aqueous sample solution (pH 4.7 - 5.8) containing less than 1 mg of cobalt(II). The analyte is extracted into the organic phase to form a complex with PC-88A and successively back-extracted into the inner acidic aqueous phase. After the w/o emulsion phase is separated from the outer aqueous phase, the emulsions are demulsified into the organic and inner aqueous phases. The cobalt content is then determined by GF-AAS with an injection volume of 10 mm3 of the inner aqueous phase. By this procedure, a concentration factor of 550 was achieved for cobalt(II). As a result, the detection limit of cobalt was 10 pg cnr3, and the calibration graph was linear up to 1 mg cm? of cobalt(II). The relative standard deviation for ten replicate measurements of 50 pg cm-3 cobalt(II) was 7.1%. The results of an analysis oi simulated nuclear reactor coolant water are given. © 1990, The Japan Society for Analytical Chemistry. All rights reserved.