Airborne isocyanates in polyurethane spray painting: determination and respirator efficiency

The concentrations of airborne isocyanates were measured during spray painting with two-component polyurethane paint. The isocyanate component - hexamethylene-diisocyanate (HDI) and its prepolymer of the biuret type - were determined by high performance liquid chromatography after derivatization to stable urea derivatives with N-4-nitrobenzyl-N-n-propylamine. Samples were collected on reagent impregnated glassfiber filters, and the derivatives were eluted with the chromatographic eluent. An impregnation technique is reported; it facilitates the chromatographic separation and the subsequent quantitative determination. Recovery studies from filters were performed in the range of 0.05 to 30 micrograms for the HDI monomer, and 0.5 to 100 micrograms for the HDI oligomer on the same filter. Average recoveries of the monomer and the oligomer were 97 +/- 2% (standard deviation) and 92 +/- 4%, respectively. The concentrations of the isocyanate components, measured during spray painting, were very high. For example, the level of the monomer frequently exceeded the hygienic limit value of 0.07 mg/m, set by the National Board of Labour Protection in Finland. As the concentrations of the HDI oligomer were at least one order of magnitude higher, appreciable exposure to isocyanate occurred if the respiratory protection was inadequate. The filter sampling technique made it possible to measure concentrations inside respirators.