Comparison of air samplers for determination of isocyanic acid and applicability for work environment exposure assessment
Isocyanic acid (ICA) is one of the most abundant isocyanates formed during thermal decomposition of polyurethane (PUR), and other nitrogen containing polymers. Hot-work, such as flame cutting, forging, grinding, turning and welding may give rise to thermal decomposition of said polymers potentially forming significant amounts of ICA. A newly launched dry denuder sampler for airborne isocyanates using di-n-butylamine (DBA) demonstrated build-up of background ICA-DBA over time. Build-up of background ICA-DBA was not observed when stored at inert conditions (Ar atmosphere) for 84 days. Thus, freshly prepared denuders were used. The sampling efficiency of ICA using freshly prepared denuder samplers (0.2 L min−1), impinger + filter samplers (0.5 L min−1) using DBA and 1-(2-methoxyphenyl) piperazine (2MP)-impregnated filter cassette samplers (1 L min−1) was investigated. PTR-MS measurements of ICA were used as a quantitative reference. Dynamically generated standard ICA atmospheres covered the range 5.6 to 640 ppb at absolute humidities (AH) 4.0 and 16 g m−3. Recovered ICA was found to be 73–115% (denuder), 89–115% (impinger + filter) and 62–100% (2MP filter cassette). The method limit of detection (LOD) was equal to an amount of ICA of 24 ng (denuder), 8.9 ng (impinger + filter) and 9.4 ng (2MP filter cassette). The PTR-MS LOD for ICA was 1.8 and 2.8 ppb in atmospheres with an AH of 4 and 16 g m−3. Denuder samplers were used for personal (n = 176) and stationary (n = 31) air sampling during hot-work at six industrial sites (n = 23 workers). ICA was detected above method LOD in 66% and 58% of the personal and stationary samples, respectively. ICA workroom air concentrations were determined to be 1.8–320 ppb (median 12 ppb) (personal samples), and 1.5–44 ppb (median 6.6 ppb) (stationary samples).