Automated headspace single-drop microextraction via a lab-in-syringe platform for mercury electrothermal atomic absorption spectrometric determination after in situ vapor generation

摘要

A novel fully automated headspace single drop microextraction system based on a programmable lab-in-syringe platform hyphenated to electrothermal atomic absorption spectrometry (ETAAS) for in situ vapor generation assays, was developed. Mixing of precise metered volumes of sample and stannous chloride solutions along with generation of mercury vapor were accomplished inside the microsyringe under reduced pressure environment in a closed manner excluding the possibility of analyte losses. The released of Hg~0 vapor was trapped on the surface of a 25 μL aqueous microdrop consisting of finely dispersed Pd~0 via amalgamation process. Reduced pressure conditions during the preconcentration step increased the extraction rates, resulting in a shorter cycle of analysis and higher sampling frequency. The proposed preconcentration system was fully characterized through optimization of the relevant parameters affecting the generation and sequestration of the vapor of mercury. For 3.5 mL sample, an enhancement factor of 75 was obtained. The detection limit and the precision expressed as relative standard deviation (RSD) were 0.48 μg L~(-1) and 4.2% (at 5.0 μg L~(-1) Hg(Ⅱ) concentration level) respectively. The proposed LIS-SH-SDME-ETAAS method was evaluated by analyzing the IAEA-350 and BCR 278-R certified reference materials as well as environmental water samples.