Evaluation of 9-Methylamino-Methylanthracene as a Chemical Label for Total Reactive Isocyanate Group: A Comparison of Mono- and Di-Isocyanate Monomers

Abstract

9-Methylamino-methylanthracene (MAMA) is a secondary amine compound commonly used for derivatization and quantitation of specific commercial isocyanate compounds by HPLC with detection by fluorescence and ultra-violet light absorbance. The determination of airborne total reactive isocyanate group (TRIG) compounds arising from partially polymerized polyurethanes and thermal decomposition products of fully cured polyurethanes is of interest in industrial hygiene. The potential application of MAMA to the measurement of TRIG has been evaluated using a series of 11 model isocyanate compounds, including aliphatic and aromatic, mono-, and diisocyanates. After synthesis, purification, and characterization, the 11 isocyanate-MAMA urea derivatives were analyzed by reversed phase HPLC using three detection / quantitation modes: fluorescence with excitation at 245 nm and emission at 414 nm, and UV absorbance at 245 and 370 nm. ANOVA of the observed response factors showed statistically significant differences among the isocyanates for each of the detection modes. The most variable was fluorescence with an overall coefficient of variation of 55%. whereas absorbance at 245 nm and at 370 nm showed coefficients of variation of only 14% and 8.6%, respectively. The ratios of response factors for absorbance at 245 nm and at 370 nm were relatively constant across isocyanates, with a mean of 10.46 and standard deviation of 0.87 (8.3%). Certain structure / response relationships were observed, particularly the enhancement of UV absorbance by aromatic isocyanate derivatives and a general decrease in fluorescence by derivatives containing unhindered aromatic rings conjugated to the urea group. These results suggest that the ratio of UV absorbance at 245 nm to that at 370 nm may be used for reliable identification of unknown MAMA-derivatized TRIG and that quantitation of MAMA-derivatized TRIG may be achieved with satisfactory accuracy using absorbance detection at 370 nm.