Determination of airborne isocyanate exposure: considerations in method selection

To assess worker isocyanate exposures in a variety of processes involving the manufacture and use of surface coatings, polyurethane foams, adhesives, resins, elastomers, binders, and sealants, it is important to be able to measure airborne reactive isocyanate-containing compounds. Choosing the correct methodology can be difficult. Isocyanate species, including monomers, prepolymers, oligomers, and polyisocyanates, are capable of producing irritation to the skin, eyes, mucous membranes, and respiratory tract. The most common adverse health effect is respiratory sensitization, and to a lesser extent dermal sensitization and hypersensitivity pneumonitis. Furthermore, isocyanate species formed during polyurethane production or thermal degradation may also produce adverse health effects. Isocyanate measurement is complicated by the fact that isocyanates may be in the form of vapors or aerosols of various particle size; the species of interest are reactive and therefore unstable; few pure analytical standards exist; and high analytical sensitivity is needed. There are numerous points in the sampling and analytical procedures at which errors can be introduced. The factors to be considered for selecting the most appropriate methodology for a given workplace include collection, derivatization, sample preparation, separation, identification, and quantification. This article discusses these factors in detail and presents a summary of method selection criteria based on the isocyanate species, its physical state, particle size, cure rate, and other factors.