Development and application of a dichotomous vapor/aerosol sampler for HDI-derived total reactive isocyanate group

A dichotomous vapor/aerosol sampler was developed for measurement of HDI (1 ,6-hexamethylene diisocyanate)-derived total reactive isocyanate group (TRI G). The sampler consisted of an impactor or cyclone inlet, followed by an a nnular diffusional denuder, and a glass-fiber filter backup. The denuder wa lls and backup filter were each coated with 20 mg tributylphosphate and 1 m g MAMA reagent (9-N-methylamino-methylanthracene). After collection, MAMA-d erivatized isocyanates were desorbed from the sampler and determined by hig h-performance liquid chromatography with dual-wavelength ultraviolet absorb ance and fluorescence detection. Test atmospheres of HDI vapor and of HDI/H DI-biuret aerosols were generated in the laboratory and sampled with the op timized dichotomous sampler. Vapor phase HDI was completely collected by th e diffusional denuder. When a mixture of HDI-biuret and HDI (similar to 30 ppb) was nebulized and collected with the dichotomous sampler, approximatel y 78% of the HDI was in the vapor phase, whereas about 22% was associated w ith the aerosol fraction. The dichotomous sampler was then used to measure vapor and condensed phase TRIG in a paint spray booth during application of a polyurethane paint. Measured levels of TRIG during the spraying operatio n averaged 391 +/- 154 mu g/m(3). Concentrations of HDI monomer averaged on ly 14 +/- 6.5 mu g/m(3). HDI-biuret was the largest component of TRIG found in these samples and was completely in the condensed aerosol phase. In con trast, the majority of the HDI was in the vapor phase, but significant (15- 26%) amounts were measured in the aerosol fraction of the paint overspray. Thus, significant partitioning of HDI between vapor and condensed phases wa s demonstrated in both the laboratory and field, even when its concentratio n was well below the vapor saturation point.