Determination of Complex Mixtures of Airborne Isocyanates and Amines.Part 3. Methylenediphenyl Diisocyanate, Methylenediphenylamino Isocyanate and Methylenediphenyldiamine and Structural Analogues after Thermal Degradation of Polyurethane

Abstract

A method is presented for the determination of isocyanates in polymeric methylenediphenyl diisocyanate (MDI) and related compounds formed during the thermal decomposition of polyurethane (PUR). Derivatization of isocyanates was performed in impinger flasks containing dibutylamine (DBA) with the formation of urea derivatives. Compounds containing amine groups were then derivatized with ethyl chloroformate (ET) to give urethane derivatives. Reversed-phase liquid chromatography, with a gradient flow rate of 40 µl min^-1and mass spectrometry in the electrospray mode monitoring positive ions was studied. Injection volumes of up to 10 µl of the sample were made possible by using column focusing. 1,5-Naphthyldiisocyanate–DBA and 1,5-naphthyldiamine–ET derivatives were used as internal standards. Virtually linear calibration curves were obtained for 4,4′-MDI–DBA and 4,4′-methylenediphenyl-diamine–ET (MDA–ET) and the correlation coefficients were 0.9952–0.9964 (n = 14). The precision for five injections of samples spiked with 4,4′-MDA–ET, and 4,4′-MDI–DBA at concentrations of 50 nmol ml^-1 was 2.76 and 2.55%, respectively. The instrumental detection limit, defined as three times the noise, was 4 fmol of MDI–DBA and 50 fmol of MDA–ET injected. In chromatograms of polymeric MDI derivatized with diethylamine, dipropylamine and DBA, the presence of several structural isomers and analogues in polymeric MDI was demonstrated. In the chromatograms of thermal decomposition products of MDI–PUR, in addition to isocyanates, related amino isocyanates and amines were also observed.

References

1. A. L. Kennedy and W. E. Brown, Occup. Med., 1992, 7, 301.
2. G. Skarping, M. Dalene, B.-G. Svensson, M. Littorin, B. Åkesson, H. Welinder and S. Skerfving, Occup. Environ. Med., 1996, 53, 180.
3. C. Sangö and E. Zimerson, J. Liq. Chromatogr., 1980, 3, 971.
4. G. Skarping, M. Dalene and P. Brunmark, Chromatographia, 1994, 39, 619.
5. G. Skarping and M. Dalene, J. Chromatogr. B, 1995, 663, 209.
6. L. Renman, C. Sangö and G. Skarping, Am. Ind. Hyg. Assoc. J., 1986, 47, 621.
7. M. Spanne, H. Tinnerberg, M. Dalene and G. Skarping, Analyst, 1996, 121, 1095.
8. H. Tinnerberg, M. Spanne, M. Dalene and G. Skarping, Analyst, 1996, 121, 1101.
9. A. Tiljander, G. Skarping and M. Dalene, J. Liq. Chromatogr., 1990, 13, 803.