Diffusive sampling of methyl isocyanate using 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole (NBDPZ) as derivatizing agent

Abstract

A diffusive sampling method for the determination of methyl isocyanate (MIC) in air is introduced. MIC is collected using a glass fiber filter impregnated with 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole (NBDPZ). The urea derivative formed is desorbed from the filter with acetonitrile and analyzed by means of high-performance liquid chromatography (HPLC) using fluorescence detection (FLD) with λ_ex = 471 nm and λ_em = 540 nm. Additionally, a method was developed using tandem mass spectrometric (MS-MS) detection, which was performed as selected reaction monitoring (SRM) on the transition [MIC–NBDPZ + H]⁺ (m/z 307) to [NBDPZ + H]⁺ (m/z 250). The diffusive sampler was tested with MIC concentrations between 1 and 35 µg m⁻³. The sampling periods varied from 15 min to 8 h, and the relative humidity (RH) was set from 20% up to 80%. The sampling rate for all 15 min experiments was determined to be 15.0 mL min⁻¹ (using HPLC-FLD) with a relative standard deviation of 9.9% for 56 experiments. At 80% RH, only 15 min sampling gave acceptable results. Further experiments revealed that humidity did not affect the MIC derivative but the reagent on the filter prior to and during sampling. The sampling rate for all experiments (including long term sampling) performed at 20% RH was found to be 15.0 mL min⁻¹ with a relative standard deviation of 6.3% (N = 42). The limit of quantification was 3 µg m⁻³ (LC-MS-MS: 1.3 µg m⁻³) for 15 min sampling periods and 0.2 µg m⁻³ (LC-MS-MS: 0.15 µg m⁻³) for 8 h sampling runs applying fluorescence detection.