Comparison of denuder and impinger sampling for determination of gaseous toluene dilsocyanate (TDI)

An air-sampling method employing denuders coated inside with a chemisorptiv e stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precisi on of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limi t of determination (LOD) of the method, including LC-APCI-MS-MS analysis, w as found to be 1.9 mug m(-3) and 1.2 mug m(-3) for 2,4- and 2,6-TDI, respec tively, for short-term measurements (15 min). Significant lower LOD was obt ained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 mug m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampli ng with no loss in performance. The contents of denuders should, on the oth er hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.