Microwave-assisted derivatization and single-drop microextraction for gas chromatographic determination of chromium(III) in water

A rapid and efficient sample preparation method combining microwave-assisted derivatization (MAD) and single-drop microextraction (SDME) for the gas chromatographic (GC) determination of trace Cr(III) in water was developed. Aqueous Cr(III) was first converted to the volatile chromium trifluoroacetylacetonate (Cr(tfa)3) by reaction with 1,1,1-trifluoroacetylacetone (Htfa) under the irradiation of microwave. Derivatization of Cr(III) at ng ml−1 level could be completed in less than 1 min. The formed Cr(tfa)3 was then extracted into a small droplet (2 μl) of toluene suspended at the tip of a microsyringe needle. The optimal extraction time was 30 min. The solvent drop was directly injected into a GC equipped with a flame photometric detector (FPD) for analysis. The two Cr(tfa)3 isomers extracted could be efficiently separated in 2 min. Linearity (r > 0.99) over the concentration range 2–300 ng ml−1 Cr was obtained and the limit of detection was 0.5 ng ml−1 Cr. The relative standard deviation was 7.8% at 20 ng ml−1 Cr (n = 5). Applicability of this method to water analysis was examined by analyzing the chromium content in a reference standard water sample and an industrial effluent.