Evaluation of capillary gas chromatography for the measurement Of C 2–C 10 hydrocarbons in urban air samples for air pollution research

Abstract

A method for the determination of speciated non-methane hydrocarbons (C 2–C 10, range) in ambient air samples was evaluated. The method involves a two-step cryogenic procedure: preconcentration (air sample volumes of 100–1000 cm 3) and prefocusing combined with capillary GC with flame ionization detection. GC columns were used under optimized temperature programming conditions (GC oven starting at above ambient temperature). Two systems were used to monitor hydrocarbon concentrations in urban air. The first system uses a megabore capillary column with a thick film of bonded non-polar silicone stationary phase (5 μm, SPB-1), which was found to be suitable for the chromatographic separation of hydrocarbons in ambient air samples without removing the moisture. To obtain a reasonable separation of volatile hydrocarbons in the C 2–C 5, range, a methylsilicone column was connected in series with a megabore methylphenylsilicone column. Better resolution of C 2–C 6, hydrocarbons was achieved on the latter system using an Al 2, O 3-KCl porous-layer open tubular (PLOT) colunm. A dry-ice-cooled water trap was devised to remove moisture from ambient air samples. The PLOT column was not suitable for α- and β-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.