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 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-mu l samples, the detection limit is 1 mu g 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 mu g 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.