Abstract

An on-line inorganic (InHg) and organomercury (OrHg) species separation, preconcentration and determination system consisting of cold vapor atomic absorption spectrometry (CV-AAS) coupled to a flow injection (FI) method was studied. The inorganic mercury species was retained on a column (id, 3 mm; length, 80 mm) charged with a Dowex 1X-8 resin (particle size 50–100 mesh) as the anionic complex formed with Methylthymol Blue (MTB), at pH 6.3. Previous oxidation of the organomercurial species permitted the determination of total mercury. Therefore, the separation of mercury species was obtained with the combined use of on-line selective formation of the InHg–MTB complex and the retention of this anionic compound on the anion exchange resin. The difference between total and inorganic mercury determined the organomercury content in the samples. The inorganic mercury was removed on-line from the micro-column with 3 M nitric acid. The mercury cold vapor generation was performed in an on-line system with 7.0% (w/v) SnCl₂ and 20% (v/v) HCl as reducing solution. A preconcentration factor of 180 was obtained for the preconcentration of 250 ml of aqueous solution. The detection limit for InHg and OrHg was 0.8 ng l⁻¹. The precision for ten replicate determinations at the 15 ng l⁻¹ Hg level was 4.4% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the separation and preconcentration system for mercury species was linear, with a correlation coefficient of 0.9994 at levels near the detection limit up to at least 100 µg l⁻¹. The accuracy of the method was evaluated by the analysis of a certified reference material QC Metal LL3 Mercury in Water. The method was successfully applied to the speciation of mercury in water samples.