Versatile Gas/Particle Ion Chromatograph

摘要

A new,compact gas/particle ion chromatograph has been developed for measuring ionic constituents in PM_(2.5) (particulate matter of aerodynamic diameter <=2.5 mum) and water-soluble ionogenic gases.The instrument has separate sampling channels for gases and particles.In one,a membrane denuder collects soluble gases for precon-centration and analysis.In the other,a cyclone removes larger particles,a membrane denuder removes soluble gases,and a continuously wetted hydrophilic filter collects particles.A single,multiport,syringe pump handles liquid transport,and one conductivity detector measures anions and ammonium for both channels.Electrodialytically generated gradient hydroxide eluent permits 20 min chromatographic runs.Gas/particle samples are each collected for 40 min,but the sampling intervals are staggered by 20 min.Liquid samples from the gas denuder and particle collector are aspirated and preconcentrated on sequential cation and anion concentrators and transferred respectively to an ammonia transfer device and an anion separation column.The flow configuration results in an ammonium peak before anion peaks in the chromatogram.The system measures ammonia,organic acids (such as acetic,formic,and oxalic acids),HCl,HONO,SO_2,HNO_3,and the corresponding ions in the aerosol phase.Low ng/m~3 to sub-ng/m~3 limits of detection (LODs) are attained for most common gases and paniculate constituents,the LODs for gaseous SO_2 to NH_3 range,for example,from sub parts per trillion by volume (sub-pptv) to approx 5 pptv.