PERFORMANCE OF THE HPLC FLUORESCENCE SO2 DETECTOR DURING THE GASIE INSTRUMENT INTERCOMPARISON EXPERIMENT/

Sulfur dioxide (SO2) in synthetic air and diluted ambient air was meas ured as part of the Gas-Phase Sulfur Intercomparison Experiment (GASIE ) using the high performance liquid chromatography (HPLC)/fluorescence technique. SO2 was analyzed by equilibrating the gaseous sample with aqueous SO2, sulfite, and bisulfite, then converting the aqueous S(IV) to an isoindole derivative. The derivative was separated by reversed phase HPLC and detected via fluorescence. The system was calibrated wi th mixtures of SO2 in zero air prepared from an SO2 permeation device through a two-stage dilution system. The instrument has a 4-min. sampl e integration time and a measurement period of 9-min. During the GASIE intercomparison the lower limit of detection averaged 3.6 parts per t rillion by volume (pptv). The precision of replicate measurements over the entire intercomparison period was better than 5% at the 20 pptv l evel. Instrument performance was unaffected by the interferent gases i ncluded in the GASIE protocol (H2O, O-3, NOx, DMS, CO, CO2, and CH4). During diluted ambient air tests, the HPLC/fluorescence technique exhi bited an approximately 10% reduction in response relative to some othe r techniques. The cause of this apparent calibration change is not und erstood.