CONTINUOUS AUTOMATED-DETERMINATION OF ATMOSPHERIC FORMALDEHYDE AT THE PARTS-PER-TRILLION LEVEL

1,3-Cyclohexanedione was used for automated near real-time fluorometric determination of atmospheric formaldehyde. Although previous literature reports indicate this reagent to be nonselective, adaptation of a fast flow injection technique that does not rely on the completion of the reaction provided a method with a selectivity factor of >300 for HCHO over its nearest congener, CH3CHO. The system was optimized with respect to the reagent and scrubber liquid composition, reaction temperature, and pH. The limit of detection (LOD) in the aqueous phase is similar to 6 nM (180 ng/L) HCHO for a 45-mu L, sample (270 fmol) with the linear dynamic range spanning >3 orders of magnitude, up to at least 14 mu M. The mean relative standard deviation in the 14 nM-14 mu M range is 3%. Gas-phase measurements utilized a Nafion 811 hydrophilic membrane tube based diffusion scrubber with ii ater as the scrubbing liquid carrier. At a sampling rate of 1.4 L/min, the LOD for gas-phase HCHO is 9 pptrv. The mean rsd in the 0.07-110 ppbv range is 1.5%.