Ultrasound-assisted emulsification microextraction combined with graphite furnace atomic absorption spectrometry for the chromium speciation in water samples.

A simple method was proposed by ultrasound-assisted emulsification microextraction (UAEME) combined with GF AAS for Cr speciation in water samples using tributhylphosphate (TBP) as extractor solvent and dispersion with ultrasound, without disperser solvent. The selective separation and pre-concentration of Cr(VI) species in an aqueous medium with HCl and NaCl was optimized with Rotatable Central Composite Design. Total Cr was determined after oxidation of Cr(III) to Cr(VI) by KMnO4. This method resulted in detection limits of 0.85 ng L-1 for Cr(VI) and 1.82 ng L-1 for Cr(total), as well as enrichment factors around 77. The accuracy was evaluated with mineral, tap and natural water. The recovery ranged from 90% to 114%. A case study was carried out with Brazilian commercial mineral water and the total concentrations ranged from 0.47 ± 0.01 µg L-1 to 3.9 ± 0.19 µg L-1. The Cr(VI) values ranged from 0.02 ± 0.01 µg L-1 to 2.3 ± 0.13 µg L-1.