Development of a new approach for total isocyanate determination using the reagent 9-anthracenylmethyl1-piperazinecarboxylate

Diisocyanates and polyisocyanates are widely used in the manufacture of polyurethane materials and coatings. Exposure to airborne isocyanate species is known to cause respiratory disorders. Measurement of isocyanate exposure levels has traditionally involved collection and derivatization of isocyanate species in an air sample followed by reversed-phase HPLC analysis. HPLC analysis of isocyanate samples is complicated for several reasons. Air samples may contain isocyanate species of very different reversed-phase retention (e.g., monomeric and polymeric isocyanates) and some species may not even be chromatographable. Also, pure analytical standards are available only for monomeric isocyanates, so non-monomeric isocyanate species are typically quantified based on the response of monomer standards, which assumes that the non-monomeric species have the same response factor as the monomer. Finally, the analysis of the raw chromatographic data containing many peaks is labor intensive. The method described here would circumvent many of the limitations of traditional methods. In this method, isocyanate species are derivatized with 9-anthracenylmethyl 1-piperazinecarboxylate (PAC) upon collection. At this point, a portion of the sample can be analyzed for individual components of interest (such as monomers) and/or a portion can be treated with a reagent that converts all PAC derivatives to a single analyte. Quantification of this analyte gives a measure of total isocyanate group. This paper examines the reactivity of PAC, the separation of PAC derivatives from excess PAC reagent, the conversion of PAC derivatives to a single analyte and the HPLC determination of this analyte and PAC derivatives of several monomeric isocyanates.