Coupled column liquid chromatography for the trace determination of polar pesticides in water using direct large-volume injection: method development strategy applied to methyl isothiocyanate

The potential of coupled column liquid gas chromatography (LC) for the trace determination of a single polar compound by direct large-volume injection of aqueous samples was studied and a general approach to method development for this class of compound is discussed. As a new application, the determination of methyl isothiocyanate (MITC) by means of reversed-phase (RP) LC column switching and UV detection at 237 nm is reported. With direct injection of 770-μl samples, the detection limit is 1 μg l −1 and the time of analysis is about 10 min. For a further increase in selectivity and detectability (down to a level of about 0.1 gmg l −1), a rapid liquid-liquid extraction followed by an organic-aqueous phase switch on a silica cartridge is required prior to RPLC. No residues of MITC were found in over 200 surface water samples investigated.