Method optimization for the determination of four mercury species by micro-liquid chromatography-inductively coupled...

A method based on the coupling microHPLC-microneb-ICPMS has been developed for Hg(II), MeHg+, EtHg+ and PhHg+ species. Gradient elution using methanol and l-cysteine at pH 3.0 allowed the chromatographic separation of all species in less than 13 min (total analysis time 15 min). The direct coupling of microLC to ICPMS through a Micromist nebulizer permits the analysis of environmental water without sample pretreatment and derivatization steps. Nebulizer type, organic modifier and column length were the main parameters tested. The methanol content and pH of the mobile phase greatly affected the retention time and sensitivity of the method. Key factors to obtain high signal to noise ratio, at concentrations below 1 microg L(-1), were found to be the nebulization step and traces of Hg present in the complexing agent. A detailed optimization of carrier and make up gas flow rates have enabled the nebulization of the methanol gradient elution with good mass transport efficiency, low organic solvent loading into the plasma and excellent precision. The performance of the microHPLC-microneb-ICPMS method developed was evaluated on a surface water sample filtered (0.22 microm) and spiked with 0.5 microg L(-1) (as Hg) of each species. Precision (R.S.D., n=6) for all species of Hg varied from 0.5 to 2.1%. Detection limit, defined as three times the standard deviation (n=6), ranged from 8 ng L(-1) for EtHg+ to 32 ng L(-1) for PhHg+ and was noticeably lower than those reported in previous LC-based methods. Accuracy was suitable with recoveries ranging from 85 to 100% when tested at two levels (0.5 and 10 microg L(-1)) in groundwater samples. Recovery was matrix affected when water samples of high salinity (depurated wastewater and seawater) were used.