Determination of airborne isocyanate exposure: Considerations in method selection

To assess worker isocyanate exposures in a variety of processes involving t he manufacture and use of surface coatings, polyurethane foams, adhesives, resins, elastomers, binders, and sealants, it is important to be able to me asure airborne reactive isocyanate-containing compounds. Choosing the corre ct methodology can be difficult. Isocyanate species, including monomers, pr epolymers, oligomers, and polyisocyanates, are capable of producing irritat ion to the skin, eyes, mucous membranes, and respiratory tract. The most co mmon adverse health effect is respiratory sensitization, and to a lesser ex tent dermal sensitization and hypersensitivity pneumonitis. Furthermore, is ocyanate species formed during polyurethane production or thermal degradati on may also produce adverse health effects. Isocyanate measurement is compl icated by the fact that isocyanates may be in the form of vapors or aerosol s of various particle size; the species of interest are reactive and theref ore unstable; few pure analytical standards exist; and high analytical sens itivity 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 inclu de collection, derivatization, sample preparation, separation, identificati on, and quantification. This article discusses these factors in detail and presents a summary of method selection criteria based on the isocyanate spe cies, its physical state, particle size, cure rate, and other factors.