Active single-drop microextraction for the determination of gaseous diisocyanates

This paper presents a novel application of active single-drop microextraction (SDME) for the determination of mixtures of four gaseous diisocyanates: 2,4- and 2,6-toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and methylene diphenyl diisocyanate (MDI). The optimised simultaneous extraction, preconcentration and derivatization method utilizes a 2.3-μL Milli-Q water drop containing dibutylamine (DBA) as a derivatization reagent and phenylisocyanate (PHI) as an injection standard. A type III screening design, combined with Box-Behnken surface modelling and Simplex optimisation was applied to optimise the method. Several SDME approaches – standard SDME, automatic organic solvent film (OSF) and use of a supported-drop (SD) device – were compared with solid-phase microextraction (SPME) in terms of sensitivity and robustness under varied conditions. Of these SDME alternatives, SD proved to be the most suitable for diisocyanate sampling. The detection limits using SDME followed by UPLC–MS–MS analysis were 0.9 and 0.8 μg m−3 for 2,4- and 2,6-TDI, respectively, 1.0 μg m−3 for HDI and 0.2 μg m−3 for MDI.