Direct immersion dual-drop microextraction for simultaneous separation and enrichment of Cr(III) and Cr(IV) in food samples prior to graphite furnace atomic absorption spectrometry detection

Non-chromatographic speciation methods generally involve speciation conversion, which may cause sample contamination, analysis errors and tedious operations. In this work, a direct immersion dual-drop microextraction (DIDDME) was firstly developed for separation and preconcentration of Cr(III) and Cr(VI). In DIDDME, two organic drops on needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent for reacting with a specific species. Thus, Cr(III) and Cr(VI) were selectively extracted into different drops. This method afforded detection limits of 3.0 and 4.1 ng/L, quantification limit of 10 ng/L and 14 ng/L, linear range of 0.01-30 ng mL(-1) and enrichment factors of 354-fold and 326-fold for Cr(III) and Cr(VI), respectively. Precisions like repeatability and reproducibility were assessed by calculating relative standard deviations, which were lower than 5.4 % and 6.9 %, respectively. This procedure was used successfully for quantification of Cr(III) and Cr(VI) in food samples.

Automated summary

A direct immersion dual-drop microextraction (DIDDME) method was developed for the separation and preconcentration of Cr(III) and Cr(VI). Using two organic drops on needle tips of microsyringes, each containing a specific chelating reagent, Cr(III) and Cr(VI) were selectively extracted into different drops. The method showed low detection limits, wide linear range, high enrichment factors, and good precision, and was successfully applied to quantify Cr(III) and Cr(VI) in food samples.