Abstract

This paper evaluates the performance of the NIOSH draft method 5525 for analysis of monomeric and TRIG aliphatic isocyanates in autobody repair shops. It was found that an optimized pH gradient enhanced noticeably the resolution and, therefore, identification of aliphatic isocyanates. Samples proved to be very stable for at least a year when stored at −13 °C in the freezer, and no major stability problems were found for the MAP reagent. The detector response factor RSD for selected MAP ureas was 40% in the fluorescence (FLD), 3% in the UV at 254 nm (UV₂₅₄), and 1% in the UV at 370 nm (UV₃₇₀). The mean FLD/UV₂₅₄ and UV₂₅₄/UV₃₇₀ detector response ratios of standards were 31.7 (RSD = 37.8) and 17.1 (RSD = 5.4), respectively. The FLD/UV₂₅₄ ratio in bulks varied from 0.41 to 1.97 times the HDI monomer ratio. The mean UV₂₅₄/UV₃₇₀ ratio in bulks was 16.1 (range 14.1 to 19.2, N = 38). Mean (range) recovery of 92 (91.2–93.2)% was found for the N3300 (isocyanurate) spiked on 25 mm quartz fiber filters in the range 0.07 to 2.2 µg NCO ml⁻¹. Mean (range) recovery for impingers was 100.7 (91.7–106.0)% for N3300 in the concentration range of 0.018 to 2.5 µg NCO ml⁻¹ and 81.0 (76.1–89.1)% for IPDI in the concentration range of 0.016 to 1.87 µg NCO ml⁻¹. Analytical method precision was 3.4% and mean bias 7.4% (range = 0–25%). The NIOSH draft method 5525 provides flexibility, enhanced sensitivity and specificity, powerful resolution, and very small compound-to-compound variability in the UV₂₅₄, resulting in a more reliable identification and quantification of aliphatic isocyanates.