Validation of a Solvent-Free Sampler for the Determination of Low Molecular Weight Aliphatic Isocyanates Under Thermal Degradation Conditions

Abstract

During the thermal degradation of 1,6-hexamethylenediiso- cyanate-based (HDI) car paint, the eight most abundant isocyanates generated are isocyanic acid, methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, pentyl isocyanate, hexyl isocyanate, and 1,6-hexamethylenediisocyanate. For the first time, a method using solvent-free samplers is proposed and validated for the simultaneous sampling of all these isocyanates. The sampling efficiency during thermal degradation of car paint can be affected by the formation of dust and aerosols and by the emission of many chemicals, such as isocyanic acid, anhydrides, amines, and alcohols that consume the reagent or interfere in the derivatization procedure. Sampling was performed using cassettes containing two 1-(2-methoxyphenyl)piperazine (MOPIP)-coated glass fiber filters (MFs) (∼4.9 mg per filter) and compared with bubblers containing 15 mL of MOPIP solution in toluene (1.0 mg/mL−1) and with bubblers backed with MFs. A DIN 53436 laboratory scale furnace was used to generate the isocyanates under thermal degradation conditions. For an aliphatic isocyanate concentration of approximately 42 μ g(NCO) m−3, no significant difference in sampling efficiency was observed between the three techniques studied, thus confirming the sampling efficiency of the MFs. The samples were analyzed using high-performance liquid chromatography coupled with electrospray/tandem mass spectrometry. Quantification was performed in daughter mode monitoring (MOPIP+H)+ fragments. For concentrations between 0.013 μ g(NCO) mL−1 and 0.52 μ g(NCO) mL−1 for the monoisocyanates, and between 0.026 μg(NCO) mL−1 and 1.04 μg(NCO) mL−1 for the HDI, the correlation coefficients were in the 0.9974–0.9996 range (n = 18). Analytical reproducibility and precision were better than 95.4% and 94.9%, respectively, for all the isocyanates. The instrumental detection limits, defined as three times the standard deviation measured at the lowest point on the calibration curve were in the 1.8–3.0 ng(NCO) mL−1 range (n = 8), which corresponds to about 0.37–0.60 μg(NCO) m−3 for a 15-L air sample when the filters are desorbed in 3 mL.