Continuous Determination of Atmospheric Ammonia by an Automated Gas Chromatographic System

A highly sensitive gas chromatographic system has been developed for continuous measurement of trace levels of ammonia concentrations in the atmosphere. The method is based on preconcentration using an collection tube packed with an adsorbent (alkalized Porasil B), thermal desorption, and analysis by a gas chromatograph equipped with a flame thermionic detector. The air sample was first preconcentrated by passing air through the collection tube at ambient temperature. The collected samples were thermally released for gas chromatographic analyses into the analytical column by use of a Curie-point thermal desorption device. Ammonia concentrations were quantitatively determined using this system. The detection limit for ammonia was approximately 30 pg, which allowed up to 20 pptv with a 2-L air sample, and the relative standard deviation was better than 5% in the range of 2-106 ppbv of ammonia. The results of the field tests demonstrated a unique combination of a short time resolution (15- or 30-min cycle) and a high sensitivity that allowed the monitoring of diurnal variations. The measurement procedure was automated for sampling and analysis.