Abstract
An aqueous scrubber liquid is pumped through a filament-filled narrow bore microporous hydrophobic membrane tube while sample air flows around it. A constant fraction of the analyte gas, dependent on its diffusion coefficient and the effective mass accommodation coefficient in the scrubber liquid and on the diffusion scrubber dimensions and sampling rate, is collected in the liquid. One or more reagents are added to the effluent liquid for specific determination of the gas of interest. The Hantzsch reaction, peroxidase-mediated oxidation of p-hydroxyphenylacetic acid by peroxide, and bisulfite addition to 9- N-acridinylmaleimide, all direct adaptations of previously described continuous flow aqueous analytical procedures, are used for the determination of HCHO, H 2O 2 and SO 2, respectively. A permeation-based SO 2 source and previously described Henry's Law-based porous membrane sources of HCHO and H 2O 2 are integral to the respective instruments for calibration. Programmed inert valves allow the instruments to perform any sequence of zero, calibrate and sample functions. Each instrument occupies a standard two-tier (50×100 cm) laboratory cart and has been successfully field tested. With a filter fluorometer as detector, LODs are 100 pptv HCHO, 30 pptv H 2O 2 and 175 pptv SO 2. There is no significant dependence on relative humidity. Specific interference testing ( SO 2 O 3 for HCHO and H 2O 2, O 3 H 2O 2H 2SCH 3SH for SO 2) reveals no major interferences.
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