Inorganic mercury and methylmercury determination in polluted waters by HPLC coupled to cold vapour atomic fluorescence spectroscopy

A systematic study of Hg2+ and CH3Hg+ (MeHg+) speciation using hyphenated techniques, was performed for high-performance liquid chromatography coupled to on-line UV irradiation and cold-vapour atomic fluorescence spectroscopy (HPLC-UV-CV-AFS). First, a comparative study of the behaviour of three mobile phase compositions (using tetrabutylammonium bromide (TBAB), L-cysteine and ammonium pyrrolidinedithiocarbamate (APDC)) is presented. The separation and detection system was optimised by considering factors that modify fluorescence signal and the separation such as, the addition of different percentages of an organic modifier (methanol (MeOH) and acetonitrile (ACN)) to the mobile phase, the type of reducing agent used (SnCl2 and NaBH4) and the potential memory effects of the material of which the injection system is made (stainless steel, PEEK). The mobile phase selected for its sensitivity was a mixture 80:20 MeOH: 0.0015 mol l(-1) APDC and 0.01 mol l(-1) NH4CH3COO (pH 5.5). The detection and quantification limits were close to 1.5 and 5 mg l(-1) for both species (as Hg), respectively. Recoveries obtained using fortified water samples of distinct origin (soft mineral, tap, river, seawater, and wastewater), ranged from 90 to 115% for concentrations about 2 and 20 times over quantification limits. Good repeatability was obtained (about 5%) independently of the concentrations, with reproducibility values about 20% at low concentrations and 5-10% at higher concentrations. Our proposed method proved to be straightforward for use by environmental laboratories for routine Hg2+ and MeHg+ determinations in polluted water samples.