DETERMINATION OF COMPLEX-MIXTURES OF AIRBORNE ISOCYANATES AND AMINES - PART 4 - DETERMINATION OF ALIPHATIC ISOCYANATES AS DIBUTYLAMINE DERIVATIVES USING LIQUID-CHROMATOGRAPHY AND MASS-SPECTROMETRY

An LC-MS method is presented for the determination of aliphatic isocya nate [hexamethylene diisocyanate] (HDI), isophorone diisocyanate (IPDI ), biuret and isocyanurate] adducts of HDI as their dibutylamine (DBA) derivatives, The method is based on sampling in midget impinger flask s containing 10 ml of 0.01 mol l(-1) DBA in toluene (see parts 1-3 of this series dagger). The excess reagent and the solvent are removed by evaporation, The enriched samples are then analysed using LC-electros pray MS, Quantification of HDI-DBA and IPDI-DBA was effected by monito ring the molecular ion [MH](+). Linear calibration graphs were obtaine d in the range 50-500 nmol l(-1) with correlation coefficients of 0.99 65-0.9997. The RSD for samples spiked at a concentration of 1 nmol l(- 1) was 1.7 and 2.9% for the two IPDI-DBA isomers (n = 8) and 1.2% for HDI-DBA (n = 8), On injecting 4 mu l of the 0.5 ml sample, the instrum ental detection limit was about 20 nmol l(-1), which corresponds to ab out 0.1 mu g m(-3) for HDI and 0.2 mu g m(-3) for IPDI for a 15 l air sample. No degradation was observed after storage of the derivatives f or up to 4 months in acetonitrile or toluene, No losses were seen when the derivatization reaction took place in the presence of interferent s such as morpholine, hexamethylenediamine, isophoronediamine and phen ol corresponding to concentrations of 10 ppm in air for a 15 l air sam ple, The influence of water was studied by spiking with volumes corres ponding to a relative humidity of 80% at 30 degrees C in 15 l of air, The reaction rates of HDI and IPDI with DBA mere found to be 2-3 times faster than those for 1-(2-methoxyphenyl)piperazine.