Determination of 1-(2-methoxyphenyl)-piperazine derivatives of airborne diisocyanates by packed capillary liquid chromatography with pre-column large-volume enrichment

A reliable, sensitive, and robust two-valve column-switching temperature-programmed packed capillary liquid chromatography method with on-column ultraviolet detection has been developed and validated for the simultaneous determination of 2,4-toluene-diisocyanate, 2,6-toluene-diisocyanate, hexamethylene-diisocyanate, and 4,4-methylene-bisphenyl-diisocyanate in workroom air, based on an established 1-(2-methoxyphenyl)-piperazine derivatization filter sampling method. The isocyanate derivatives were enriched on a 0.32 x 30 mm 5 mum Inertsil C-8 pre-column using a non-eluting solvent composition of acetonitrile-10 mM ammonium formate (pH 4.0) (4:96, v/v) at a flow rate of 50 muL/min, prior to back-flushing on a 0.32 x 250 mm 3-mum Hypersil ODS column, using a mobile phase composition of acetonitrile-10 mM ammonium formate (pH 6.0) (40:60, v/v) at a flow rate of 5 muL/min. Injection volumes up to 1.0 mL were loaded onto the pre-column. An initial temperature of 80degreesC provided beneficial selectivity effects as compared to ambient temperature, providing baseline separation of the 2,6-toluene-diisocyanate and hexamethylene-diisocyanate derivatives. Temperature programming from 80 to 95degreesC provided efficient elution of late eluting 4,4-methylene-bisphenyl-diisocyanate. The method was validated using spiked filters with 5 to 250 ng of the 2,4-toluene-diisocyanate derivative, yielding a coefficient of correlation of 0.997 when using an injection volume of 1.0 mL. The within-assay (n = 4) and between-assay [...]