EVALUATION OF CAPILLARY GAS-CHROMATOGRAPHY FOR THE MEASUREMENT OF C2-C10 HYDROCARBONS IN URBAN AIR SAMPLES FOR AIR-POLLUTION RESEARCH

A method for the determination of speciated non-methane hydrocarbons ( C2-C-10 range) in ambient air samples was evaluated. The method involv es a two-step cryogenic procedure: preconcentration (air sample volume s of 100-1000 cm3) and prefocusing combined with capillary GC with fla me ionization detection. GC columns were used under optimized temperat ure programming conditions (GC oven starting at above ambient temperat ure). Two systems were used to monitor hydrocarbon concentrations in u rban air. The first system uses a megabore capillary column with a thi ck film of bonded non-polar silicone stationary phase (5 mum, SPB-1), which was found to,be suitable for the chromatographic separation of h ydrocarbons in ambient air samples without removing the moisture. To o btain a reasonable separation of volatile hydrocarbons in the C2-C5 ra nge, a methylsilicone column was connected in series with a megabore m ethylphenylsilicone column. Better resolution of C2-C6 hydrocarbons wa s achieved on the latter system using an Al2O3-KCl porous-layer open t ubular (PLOT) column. A dry-ice-cooled water trap was devised to remov e moisture from ambient air samples. The PLOT column was not suitable for alpha- and beta-pinene owing to decomposition. The reproducibility of GC performance (i.e., retention time and peak-area integration) is discussed in detail. Both systems showed good long-term stability and gave good results for the determination of hydrocarbon concentrations ranging from several ppt to 100 ppb by volume in air samples from the Toronto urban area.