DETERMINATION OF COMPLEX-MIXTURES OF AIRBORNE ISOCYANATES AND AMINES .3. METHYLENEDIPHENYL DIISOCYANATE, METHYLENEDIPHENYLAMINO ISOCYANATE AND METHYLENEDIPHENYLIDIAMINE AND STRUCTURAL ANALOGS AFTER THERMAL-DEGRADATION OF POLYURETHANE

A method is presented for the determination of isocyanates in polymeri c methylenediphenyl diisocyanate (MDI) and related compounds formed du ring the thermal decomposition of polyurethane (PUR). Derivatization o f isocyanates was performed in impinger flasks containing dibutylamine (DBA) with the formation of urea derivatives. Compounds containing am ine groups were then derivatized with ethyl chloroformate (ET) to give urethane derivatives. Reversed-phase liquid chromatography, with a gr adient flow rate of 40 mu l min(-1) and mass spectrometry in the elect rospray mode monitoring positive ions was studied. Injection volumes o f up to 10 mu l of the sample were made possible by using column focus ing. 1,5-Naphthyldiisocyanate-DBA and 1,5-naphthyldiamine-ET derivativ es were used as internal standards, Virtually linear calibration curve s were obtained for 4,4'-MDI-DBA and 4,4'-methylenediphenyldiamine-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 2.5 5%, respectively. The instrumental detection limit, defined as three t imes the noise, was 4 fmol of MDI-DBA and 50 fmol of MDA-ET injected. In chromatograms of polymeric MDI derivatized with diethylamine, dipro pylamine and DBA, the presence of several structural isomers and analo gues in polymeric MDI was demonstrated. In the chromatograms of therma l decomposition products of MDI-PUR, in addition to isocyanates, relat ed amino isocyanates and amines were also observed.