Speciation, separation and enrichment of Cr(III) and Cr(VI) in environmental samples by ion-pair solvent extraction using a beta-diketone ligand

A simple speciation, separation and enrichment method has been developed for the determination of Cr(III) and Cr(VI) ions in different samples by ion-pair solvent extraction with a beta-diketone ligand, 2-(4-methoxybenzoyl)-N'-benzylidene-3-(4-methoxyphenyl)-3-oxo-N-phenyl-propono hydrazide (MBMP). Cr(III) was separated from Cr(VI) as Cr(III)-(MBMP)-perchlorate ternary ion-pair complex. The influences of various analytical parameters including pH, amount of reagent, shaking time, sample volume and ionic strength on the recovery of Cr(III) and/or Cr(VI) were investigated. Total chromium was obtained after reducing Cr(VI) to Cr(III) with NH(2)OH center dot HCl. Recoveries were found to be higher than 95% and the relative standard deviation (RSD) was less than 2%. The method detection limit based on 3 sigma criterion for Cr(III) was found to be 0.32 mu g L(-1). The formed ternary ion-pair complex, Cr(III) : MBMP: 2ClO(4), has a molar ratio of 1 : 1 : 2. The developed method has been applied successfully to the speciation of chromium in various natural water, soil, sediment and hair samples with satisfactory results.