Time-resolved sampling of isocyanate peak exposure-chamber validation of a prototype sampler

A prototype sampler for time-resolved monitoring of toluene diisocyanate (TDI) exposure peaks was developed. The sampler contained multiple sampling tubes arranged in a manifold equipped with an internal valve and a step motor, enabling automatic switching of the sampling flow between the tubes, allowing a sequence of up to 10 samples to be collected automatically. The inlet part of the sampling tubes contained a glass wool plug, impregnated with equimolar amounts of di-n-butyl amine (DBA) and acetic acid, to ensure efficient collection and derivatisation of the diisocyanates. The diisocyanate-DBA derivatives were analysed using liquid chromatography tandem mass spectrometry. A streamlined workup procedure was introduced, consisting of a single extraction step combined with the addition of a deuterium-labelled internal standard. The streamlined workup procedure was validated against a reference method (ISO 17734). The sampler tubes were validated by monitoring concentrations from a TDI standard atmosphere and through comparative measurements with a reference method. During short-term sampling (<5 min) at flow rates of up to 2.0 L/min, the sampler tubes exhibited minimal breakthrough and high precision, with a relative standard deviation below 5%. At lower flow rates (0.5 L/min), the tubes were suitable for long-term sampling of up to 4 h. The prototype TR-sampler was successfully validated for monitoring of high TDI exposure peaks (≈2 mg/m3 [280 ppb v/v] for a 1-min sample) as well as monitoring of concentrations down to 0.25 µg TDI/m3 [0.036 ppb] for a 1-min sample with an accuracy of > 90% compared to the reference sampler.