Formation of a Liquid Organic Ion Associate in Aqueous Solution and Its Application to the GF-AAS Determination of Trace Cadmium in Environmental Water as a Complex with 2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol

Abstract

The formation of a liquid organic ion associate in an aqueous sample was applied to the concentration and determination of cadmium in environmental water samples. Cadmium was converted into a complex with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS) in a 40-mL sample solution, and was extracted into a liquid ion associate of phenolsulfonate and benzethonium during phase formation. More than 400-fold enrichment was easily attained by this technique, because the volume of the liquid organic phase formed was very small, ca. 2 µL. After dilution of the organic phase with a small volume of 2-methoxyethanol, the cadmium in the solution was determined by GF-AAS. The detection limit was 0.09 ng/L (3σ_b). This method was applied to the determination of cadmium in river water and seawater.