Determination of airborne methyl isocyanate as dibutylamine or 1-(2-methoxyphenyl)piperazine derivatives by liquid and gas chromatography

Abstract

The usefulness of a glass fibre filter method to collect airborne methyl isocyanate (MIC) was studied in laboratory experiments and in a workplace during manufacture of mineral wool insulation material. Filter collection was based on derivatisation in situ with 1-(2-methoxyphenyl)piperazine (2MP). 2MP impinger sampling was also evaluated in the workplace. Impinger sampling with dibutylamine (DBA) was used as an independent method. The samples were analysed by liquid and gas chromatography using various detection techniques: mass spectrometry, ultraviolet and electrochemical detection (LC-MS, LC-UV, LC-EchD and GC-MS). The sampling efficiency of 2MP filters for MIC varied with the origin of the glass fibre filter. Two Whatman filters (diameter 25 mm) with altogether 21 μmol of 2MP collected 100% of 9.8 μg of MIC during 30 min at an airflow rate of 1 l min⁻¹. The workplace measurements were performed at two concentration levels, 0.003 and 0.09 mg m⁻³. The theoretical amounts of derivatisation reagent were 42 μmol (2MP filter), 52 μmol (2MP impinger) and 100 μmol (DBA). MIC concentrations were 20% lower by the 2MP methods compared with the DBA method (statistically significant difference). Breakthrough was 6% for the DBA method and 9% for the 2MP impinger method. To trap both MIC and isocyanic acid, which was also present in the workplace samples, a tenfold molar amount of 2MP reagent was used. The precision of sample preparation, expressed as relative standard deviation, was 3.5% (0.17 μg ml⁻¹, n = 6). The precision of sampling in the workplace was 15% (0.002 mg m⁻³, n = 6). The limit of quantification was 0.0006 mg m⁻³ for 30 l of air by the 2MP impinger method and 0.03–0.05 mg m⁻³ by the 2MP filter method. Hence, airborne MIC can be determined using 2MP as derivatisation reagent. Impinger sampling is preferable when low concentration levels are expected.