Determination of complex mixtures of airborne isocyanates and aminesPart 5.† Determination of low molecular weight aliphatic isocyanates as dibutylamine derivatives

Abstract

A method is presented for the determination of low molecular weight aliphatic isocyanates, methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC) and butyl isocyanate (BIC), as their dibutylamine (DBA) derivatives. The method is based on sampling in midget impinger flasks containing 10 ml of 0.01 mol l^–1 DBA in toluene (as in Parts 1–4 in this series). The samples are analysed using liquid chromatography–electrospray mass spectrometry (LC–ESP–MS) or gas chromatography– mass spectrometry using chemical ionisation with ammonia, monitoring positive ions (GC–PCI). Quantification was effected by monitoring the molecular ions MH⁺. Aliquots of 10 ml of toluene solutions containing 0.01 mol l^–1 DBA were spiked with 0.03–0.85 µg of MIC–, EIC–, PIC– and BIC–DBA. The correlation coefficients for LC–ESP–MS were in the range 0.9952–0.9999 (n = 14). The repeatability (RSD) was in the range 0.37–1.2% (0.12–0.34 µg ml^–1, n = 10). The instrumental detection limit for MIC was about 15 µg l^–1, which corresponds to about 0.5 µg m^–3 in a 15 l air sample. The correlation coefficients for GC–PCI were in the range 0.9913–0.9990. The repeatability (RSD) was in the range 1.1–4.9% (0.12–0.34 µg ml^–1, n = 10). The instrumental detection limit for MIC was about 0.2

µg l^–1, which corresponds to about 0.05 µg m^–3 in a 15 l

air sample. Using electron ionisation, the instrumental detection limit for MIC was about 10 µg l^–1. No derivatisation reaction losses were seen when the derivatization reaction between PIC and DBA took place in the presence of morpholine, propylamine, ethanol, phenol and water. When mineral wool with a phenol–formaldehyde–urea resin was thermally degraded, 0.1% m/m of MIC was released. In air samples taken on top of a new electric oven insulated with mineral wool, MIC was found in the range 0.1–3 mg m^–3. No MIC in air was found from a pre-heated oven.