The application of tryptamine to derivatize airborne isocyanates has been evaluated and adopted by the National Institute for Occupational Safety and Health (NIOSH) as the latest isocyanates regulatory method (Method 5522) in the USA. Method 5522 uses dimethyl sulfoxide (DMSO) as the impinger solvent in which tryptamine is dissolved to sample isocyanates for analysis. Since DMSO is both extremely hygroscopic and corrosive, it is not a satisfactory solvent for impinger air sampling of isocyanates. The high boiling and freezing points also present some distinct drawbacks. In a search for a suitable impinger solvent, the efficiencies of various solvents, which all were potentially more suitable for sampling isocyanates viz., N,N'-dimethylformamide, butyl acetate, isobutyl acetate, sec-butyl acetate, tert-butyl acetate and octane, were investigated. Simulated air sampling was conducted on two commonly used isocyanates in industry, hexamethylene diisocyanate (HDI) and toluene diisocyanate (TDI), which were vaporized and sampled into impingers containing dissolved tryptamine. Butyl acetate and octane were found to be most suitable for using as impinger solvents. Recoveries of isocyanates at two concentration levels of HDI and TDI were 93.4-108% in comparison with those of using DMSO.