On the Determination of Reactive Compounds in Aerosols

Abstract: Many sources of airborne contaminants have always been present in various work environments. With the development of thermosetting plastic systems, the use of reactive chemical compounds was greatly increased and thus also the risk of exposure to reactive and potentially hazardous compounds. Exposure can occur in many situations, not only at the workplace where the raw materials are handled. The finished products may emit unreacted or excess compounds, like in furniture made of particleboard with phenol-formaldehyde resin that may emit formaldehyde for a long time. Another emission source can arise when some thermosetting plastics like polyurethane and phenol-formaldehyde-urea resins are heated, intentionally or by accident. Many different types of isocyanates in a complex mixture are released at such occasions. In an effort to characterise those emissions in more detail, a new analytical method for the derivatisation and analysis of isocyanates was developed. The new derivatisation reagent, di-n-butylamine, was found to be suitable for the determination of many types of isocyanates even when complicated mixtures of air pollutants were present in the work environment. However, it was found that the used standard sampler, the midget impinger, had almost negligible collection efficiency for particles with an aerodynamic diameter smaller than 1.5 µm. In the work operations where polyurethane products were heated and decomposed, leading to the emission of isocyanate-containing aerosols, the particles were found to be mainly in the sub-micron range and thus not collected by the impinger sampler. In car repair shops, very high concentrations of airborne isocyanates found to be emitted at common work operations as welding and cutting in polyurethane painted vehicles. As an initial solution, a glass-fibre filter was connected in series after the impinger to collect the particles that otherwise would have escaped sampling. The relatively volatile reagent dibutylamine proved to be well suited for this sampling technique as the reagent evaporates from the sampling liquid and impregnates particles collected on the filter. In air samples taken with this method in car repair shops, very high concentrations of isocyanates were found to be emitted during operations such as welding and cutting in vehicles. In order to avoid undesirable reactions that can take place between the studied compound and other compounds present in the work environment, it is desirable to supply the reagent at the earliest possible moment in the sampling process. The ideal might be to supply the reagent to the sample even before collection. Using the aerosol particles as condensation nuclei for a condensing reagent vapour, this can be done. A new method to supply a large excess of liquid reagent to particles in an aerosol before collection of the particles was presented. This new type of sampler may become useful in the investigation of the actual chemical composition of reactive air contaminants at workplaces.