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The use of pervaporation as an alternative to headspace is proposed. The analytical system involves the speciation of organomercury compounds in solid samples using pervaporation, which has been coupled for the first time to gas chromatography. The speciation of mercury as Me(2)Hg, Et(2)Hg, and MeHgCl has been carried out without any derivatization of the analytes, which, after separation from the solid matrix, are preconcentrated on a Tenax minicolumn prior to desorption and chromatographic separation on a semicapillary column (HP-1) prior to atomic fluorescence detection. No column degradation was observed. Linear ranges and detection limits slightly better than those obtained by headspace GC were observed for mercury species in solid samples. Excellent recoveries (between 95 and 107%) for mercury species added to complex solid samples were obtained by this extremely simple and easily automated setup.

Two methods based on flow injection atomic fluorescence have been developed in order to speciate Se as Se'"-SeV'. Both methods use hydride generation of Sew with atomic fluorescence detection as the derivatization-detection step. In the first method, two sample plugs are injected simultaneously in series, so that the first plug passes straight to the detector to determine Se'". The second plug passes through a focused microwave device where Se"' is reduced to Sew prior to its conversion into the hydride. The Se"' content is then given as the difference between the two results. In the second method a mini-column is used to retain both the Se species; Sew and Sen are then eluted sequentially with formic and hydrochloric acids, respectively. The columns can be used for preconcentration of the analytes as well as for sampling. Both methods show exceptional sensitivity [limits of detection (3s) of 0.04 pg 1-'1 and wide linear range up to 50 pg I-', with excellent linearity (9 = 0.999), and reproducibility (relative standard deviation<5%). The methods have been used in an intercomparison exercise for the Measurements and Testing Programme and have been applied to the determination of the analytes in tap water and haemodialysis samples.

Digestion programmes for different types of samples (milk, sausage and lyophilized pig kidney certified reference material) have been developed using a focused microwave digestor prior to the determination of selenium. The digestion step does not alter the oxidation state of the analyte; thus, the speciation of the target analyte is also achieved with the help of the microwave digestor, which facilitates a subsequent on-line reduction step in a flow injection (F'I) manifold before determination by FI cathodic stripping voltammetry. Excellent recoveries for the spiked and certified values were obtained using digestion programmes which varied from 2 0 4 5 min. The on-line microwave procedure for the reduction of Sew affords good sensitivity and linearity (S120 yg 1-1, r = 0.994) of the over-all determination method, and dramatically reduces the time necessary for Sen reduction.