MDHS 25 Revisited: Part 2, Modified Sampling and Analytical Procedures Applied to HDI-Based Isocyanates

The method that is probably the most commonly used worldwide for the determination of total organic isocyanates (NCO) in air is the Health and Safety Executive method, MDHS 25/3, Organic Isocyanates in Air, and its variants. This paper summarizes some of the research and development work carried out by Health and Safety Laboratory on this method since its publication in 1999 with the eventual aim of incorporating this work in an updated version of MDHS 25 (i.e. MDHS 25/4). The work falls into two main areas: use of liquid chromatography/ mass spectrometry (LC/MS) as an alternative to liquid chromatography with electrochemical and ultraviolet/visible detection (LC/EC/UV) and evaluation of ‘solid-phase’sampling techniques as an alternative to the impinger‐filter combination stated in MDHS 25/3. This paper deals primarily with HDI-based NCO but some comments regarding aromatic NCO (MDI and TDI) are included for completeness. An LC/MS/MS version of MDHS 25/3 has been developed that gives improved performance to the ‘classical’ version of MDHS 25/3 using EC/UV detection. The LC/ MS/MS offers significant advantages over the EC/UV version of MDHS 25/3 in that it is more sensitive, provides improved identification, and has been found to be easier to use. The solid-phase samplers evaluated were a double-thickness glass-fibre (GF/B) filter coated with 1-(2-methoxyphenyl)piperazine (MP) reagent in an IOM (Institute of Occupational Medicine) sampling head (‘FIN-MP’ sampler) and an MP-impregnated polyurethane foam sponge (PUF) with an MP-coated glass-fibre (GF/A) backup filter also in an IOM sampling head (‘Rudzinski’ sampler). Both samplers were found to give acceptable performance for the sampling of oligomeric HDI in workplace air and in laboratory simulations when compared to the impinger‐filter combination at levels corresponding to the UK short-term limit (70 mg m 23 ). For practical reasons, the FIN-MP sampler was the preferred alternative.