METHOD FOR THE DETERMINATION OF SOME SOLUBLE ATMOSPHERIC CARBONYL-COMPOUNDS

A technique was developed for the measurement of soluble atmospheric carbonyl compounds, which uses a pyrex coil gas-liquid scrubber sampler in conjunction with a high-performance liquid chromatograph (HPLC) equipped with a UV-visible detector for separation and identification following derivatization with 2,4-dinitrophenylhydrazine (DNPH). Carbonyls exhibiting a Henry's law solubility similar to or greater than that of formaldehyde (FA) can be determined by this method; these include FA, glycolaldehyde (GA), glyoxal (GL), and methylglyoxal (MG). The typical sampling and analysis conditions are as follows: gas and liquid flow rates through the coil 2.3 L min-1 and 0.30 mL min-1, respectively; derivatization time 4 h at [DNPH] = 0.10 mM and pH 2.4; HPLC sample injection volume 1.2 mL; 6-mm path-length flow cell (360 nm for FA and GA; 400 nm for GL and MG). Based on liquid standards and field-developed chromatographic characteristics, the limits of detection are approximately 0.005 ppb (in the gas phase) for MG, approximately 0.01 ppb for GL, and approximately 0.02 ppb for FA and GA. Because of the short air-liquid contact time in the coil sampler (less-than-or-equal-to 10 s), interferences from aqueous-phase reactions of O3 are insignificant. Also, at the low pH of the scrubbing solution, interference resulting from reactions of carbonyls with S(IV) is unimportant. A number of other potential interferences were examined and found to be unimportant. This technique was employed in a field measurement at a rural site in Georgia as part of the Southern Oxidants Study in summer 1991. The concentrations of FA, GA, GL, and MG observed ranged up to 8, 0.6, 0.1, and 0.2 ppb, respectively.