Isocyanates are important in industrial hygiene and workplace monitoring. Owing to their severe acute toxicity and sensitizing properties, analytical methods with high sampling efficiency and sensitivity in the low ppb to ppt range are required. The reactivity of isocyanates necessitates initial derivatization with nucleophilic agents--usually amines--for stabilization and enrichment; this is often followed by chromatographic separation with spectroscopic, electrochemical, or mass spectrometric detection. Sampling strategies for airborne isocyanates comprise active, i.e. pumped, or passive, i.e. diffusive, methods; the method selected depends on the application. Whereas active methods rely mainly on impingers, reagent-coated filters, or sampling tubes, passive samplers make use of reagent-coated filters, the surface of which is connected to the air sample by diffusion channels. Because airborne isocyanates are prone to occur in different forms, i.e. as vapors, as aerosols, or adsorbed on particulate matter, denuder sampling has been introduced, thus enabling simultaneous collection of gaseous and aerosol isocyanates. The first part of this review summarizes chemical methods and reagents which have been introduced for derivatization of airborne isocyanates. The advantages and drawbacks of the individual derivatization procedures and their combination with different detection principles are evaluated. In the second part, the most recent developments in air sampling for isocyanates, with special focus on diffusive sampling, are reviewed and critically discussed.

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 lambdaex = 471 nm and lambdaex = 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 microg 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 microg m(-3) (LC-MS-MS: 1.3 microg m(-3)) for 15 min sampling periods and 0.2 microg m(-3) (LC-MS-MS: 0.15 microg m(-3)) for 8 h sampling runs applying fluorescence detection.

Ferrocenoyl piperazide is introduced as a new pre-column derivatizing agent for the analysis of various isocyanates in air samples using reversed-phase liquid chromatographic separation, electrochemical oxidation/ionization, and mass spectrometry. The nonpolar derivatives can be separated well using a phenyl-modified stationary phase and a formic acid/ammonium formate buffer of pH 3, which yields excellent separations, especially for one problematic group of isocyanates consisting of 2,4-and 2,6-toluylenediisocyanate (2,4-and 2,6-TDI) and hexamethylenediisocyanate (HDI). Electrochemical oxidation at low potentials (0.5 V versus Pd/H 2 ) leads to formation of charged products, which are nebulized in a commercial atmospheric pressure chemical ionization (APCI) source, with the corona discharge operated only at low voltage. Limits of detection between 6 and 20 nmol/L are obtained for the isocyanate derivatives, and calibration is linear over at least two decades of concentration. The method is applied for the analysis of air after thermal degradation of a polyurethane foam, and it is demonstrated that it is suitable as well for the analysis of carboxylic acid chlorides and of

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The first passive sampling device for the determination of airborne peroxyacetic acid (PAA) is presented. 2-([3-{2-[4-Amino-2-(methylsulfanyl)phenyl]-1-diazenyl}phenyl]sulfonyl)-1-ethanol (ADS) is used to impregnate glass fiber filters, and the reagent is oxidized by PAA to the corresponding sulfoxide ADSO. After elution of the filters, ADS and ADSO are separated by reversed-phase HPLC and detected by UV/visible absorbance. Limit of detection is 30 ppb, limit of quantification is 90 ppb (for 30 min sampling), and the linear range comprises 2 orders of magnitude. Thorough investigations were carried out with respect to the selectivity of the method toward hydrogen peroxide, and air samples were analyzed successfully after disinfection of a laboratory area.