Dry Sampling for Isocyanates
Measurement of the Potential Exposure to Isocyanate Monomers and Oligomers during Automotive Spray Paint Applications: A Comparison of Two Sampling Methods
By Gary Oishi
Isocyanates are the reactive component used in making polyurethane materials. Simple polyurethanes (PU) are made by reacting an isocyanate and polyol. Other forms of PU materials can be made with active hydrogen-containing compounds such as alcohols, carboxylic acids, and amines, yielding products with various characteristics. 
Isocyanates are used in numerous commercial and residential applications such as paints, coatings, and insulating foams, leading to potential exposures for many workers. The most common interactions people have with isocyanates are through exposure to paints, coatings, and insulating foams, and from polyurethane foams found in furniture. However, these materials are cured prior to use. Consequently, when these same materials are applied or thermally degraded, there is a risk for exposure not only to the monomer but also the oligomers.
Exposures During Spray Painting
Why the concern? We know isocyanates are highly reactive, powerful irritants and sensitizers to the mucous membranes of the respiratory tract, eyes, and skin. Exposures can develop into and manifest as occupational asthma or—as a worst case—even lead to death.
Numerous sampling approaches exist for isocyanates, from solution-type samplers that utilize impingers to dry-type filter samplers and even combinations of the two. The R&D team at Millipore Sigma recently undertook a study to determine whether typical sampling methods resulted in an underestimation of exposure during automotive spray-painting operations. We examined two dry-type samplers since this platform type is commonly used. Comparison sampling was performed using a 37 mm cassette (ORBO-80) containing the derivatizing reagent 1-(2-pyridyl)piperazine (1,2-PP) coated on a glass fiber filter as described in OSHA methods 42 and 47. The samples were field desorbed as described in the methods. The other sampler type was a Denuder + 13 mm cassette dry filter sampler (ASSET EZ4-NCO), which contains two glass-fiber filters coated with the derivatizing agent dibutylamine (DBA).
The automotive clear coat used in our study is commercially available and recommended by a local auto body repair shop. The two components of the coating (clear coat and activator) were mixed per the manufacturer’s instructions and thinned. The clear coat contained a mixture of both hexamethylene diisocyanate (HDI) and Isophorone Diisocyante (IPDI). A high-volume, low-pressure (HVLP) spray gun was used to apply the coating to a car hood in a ventilated spray booth. Both personal and area samples were collected simultaneously for 15 minutes.