Graphite Furnace Atomic Absorption Spectrometric Determination of Ultra-Trace Levels of Cobalt after Solvent Extraction Using W/O/W Emulsions as Liquid Surfactant Membranes

Abstract

A high-enrichment method by liquid-liquid extraction using liquid surfactant membranes was developed for the determination of cobalt at pg cm-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 (l:l) 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 cm-3 , and the calibration graph was linear up to 1 mg cm-3 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 of simulated nuclear reactor coolant water are given.

Atomic absorption, atomic emission, and flame emission spectrometry

“…It was then applied to the determination of several trace metals in seawater with a preconcentration factor of 50-60 times (559). A 550-fold enrichment of Co was obtained (560,561) by a liquid-liquid extraction procedure in which the analyte was extracted from water into a small volume of a water/oil emulsion. The emulsion was removed and broken, and the aqueous phase was analyzed by ETAAS.…”

Chemiluminescence from the reaction of chloroauric acid with luminol in reverse micelles

“…As some organic solvents have a suppressing effect on the luminol CL reaction (3, 4), a relatively tedious procedure, like back-extraction into the aqueous phase (5) or evaporation of the solvent (6), is required to use conventional aqueous solutions for CL measurements after solvent extraction. To avoid such lengthy processes, we have reported the use of reversed micellar solution (7) and developed an on-line method based on the combination of CL Numerous recent publications and research articles are evidence to the popularity of micelles and microemulsions and their applications in routine analysis (9)(10)(11). However, the use of a reversed micellar system in CL analysis is of singular importance.…”