A methodology for workplace air monitoring of aromatic and aliphatic, mono- and polyisocyanates by derivatisation with di-n-butylamine (DBA) is presented. Air sampling was performed using midget impinger flasks containing 10 ml of 0.01 mol l(-1) DBA in toluene and a glass-fibre filter in series after the impinger flask, thereby providing the possibility of collecting and derivatising isocyanates in both the gas and particle phases. Quantification was made by LC-MS, monitoring the molecular ions [MH]+. Air samples taken with this method in car repair shops showed that many different isocyanates are formed during thermal decomposition of polyurethane (PUR) coatings. In addition to isocyanates such as hexamethylene (HDI), isophorone (IPDI), toluene (TDI) and methylenediphenyl diisocyanate (MDI), monoisocyanates such as methyl (MIC), ethyl (EIC), propyl (PIC), butyl (BIC) and phenyl isocyanate (PhI) were found. In many air samples the aliphatic monoisocyanates dominated. During cutting and welding operations, the highest levels of isocyanates were observed. In a single air sample from a welding operation in a car repair shop, the highest concentrations found were: MIC, 290; EIC, 60; PIC, 20; BIC, 9; PhI, 27; HDI, 105; IPDI, 39; MDI, 4; and 2,4-TDI and 2,6-TDI 140 microg m(-3). Monitoring the particle size distribution and concentration during grinding, welding and cutting operations showed that ultrafine particles (< 0.1 microm) were formed at high concentrations. Isocyanates with low volatility were mainly found in the particle phase, but isocyanates with a relatively high volatility such as TDI, were found in both the particle and gas phases.

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An LC-MS method is presented for the determination of thermal decomposition products of polyurethane. The method is based on the collection of air samples in midget impinger flasks containing 0.01 moll-1 dibutylamine (DBA) dissolved in toluene. DBA reacts with isocyanates to give urea derivatives. The amines simultaneously collected were derivatized with ethyl chloroformate (ET) to give urethane derivatives. Two isomers of toluene diisocyanate (2,4-and 2,6-TDI), toluene-2,4-and -2,6-diamine (TDA), three isomers of toluene aminoisocyanates and oligomers with two and three aromatic rings were determined in air containing thermal decomposition products of TDI-polyurethane. LC with gradient elution, at 0.5 ml min-l starting with acetonitrile-water (46 + 54) and ending after 14 min with acetonitrile-water (77.5 + 22.5) and atmospheric pressure ionization monitoring of positive ions demonstrated highly sensitive and selective determinations. Quantification was performed by monitoring the molecular ion [M + 1]+ of TDI-DBA and TDA-ET derivatives. The instrumental detection limit was 1 nmol 1-1 of TDI-DBA and 2 nmol l-l of TDA-ET. Linear calibration curves were obtained and the correlation coefficient was 0.9981-0.9996 for 50-500 nmol 1-1 (n = 14). The over-all precision for samples spiked at a concentration of 500 nmol 1-l of 2,4and 2,6-TDA-ET and 2,4-and 2,6-TDI-DBA was 1.7, 1.6, 1.8 and 1.9% (n = l l ) , respectively.

An LC-MS method is presented for the determination of aliphatic isocyanate [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 flasks containing 10 ml of 0.01 mol l 21 DBA in toluene (see parts 1-3 of this series † ). The excess reagent and the solvent are removed by evaporation. The enriched samples are then analysed using LC-electrospray MS. Quantification of HDI-DBA and IPDI-DBA was effected by monitoring the molecular ion [MH] + . Linear calibration graphs were obtained in the range 50-500 nmol l 21 with correlation coefficients of 0.9965-0.9997. The RSD for samples spiked at a concentration of 1 nmol l 21 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 ml of the 0.5 ml sample, the instrumental detection limit was about 20 nmol l 21 , which corresponds to about 0.1 mg m 23 for HDI and 0.2 mg m 23 for IPDI for a 15 l air sample.No degradation was observed after storage of the derivatives for up to 4 months in acetonitrile or toluene. No losses were seen when the derivatization reaction took place in the presence of interferents such as morpholine, hexamethylenediamine, isophoronediamine and phenol corresponding to concentrations of 10 ppm in air for a 15 l air sample. The influence of water was studied by spiking with volumes corresponding to a relative humidity of 80% at 30 °C in 15 l of air. The reaction rates of HDI and IPDI with DBA were found to be 2-3 times faster than those for 1-(2-methoxyphenyl)piperazine.

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