Separation and preconcentration system based on ultrasonic probe-assisted ionic liquid dispersive liquid–liquid microextraction for determination trace amount of chromium(VI) by electrothermal atomic absorption spectrometry

A novel method of ultrasonic probe-assisted ionic liquid dispersive liquid–liquid microextraction combined with electrothermal atomic absorption spectrometry (ETAAS) was developed for the determination of chromium(VI) species in water samples. In this procedure, the hydrophobic chelate of chromium(VI) with ammonium pyrrolidinedithiocarbamate (APDC) was extracted into the fine droplets of 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF6]), which was dispersed into the aqueous sample solution by ultrasonication using an ultrasonic probe. Several variables such as the volume of [Hmim][PF6], sample pH, concentration of APDC, and extraction time were investigated in detail. Under the optimum conditions, the limit of detection of the proposed method was 0.07 ng mL−1 for Cr(VI) and the relative standard deviation for five-replicated determination of 2.0 ng mL−1 Cr(VI) was 9.2%. The proposed method has been also successfully applied to the determination of chromium(VI) species in lake and tap water samples.