LABORATORY AND FIELD INVESTIGATION OF THE DNPH CARTRIDGE TECHNIQUE FOR THE MEASUREMENT OF ATMOSPHERIC CARBONYL-COMPOUNDS

The DNPH-coated cartridge technique for measuring carbonyl compounds was evaluated using large volume silica gel cartridges and Sep-Pak C-18 silica gel and silica gel cartridges. The silica gel Sep-Pak cartridge was found to be the best of the three types evaluated for determinations in relatively clean ambient air. At concentrations of HCHO and O-3 typical of clean ambient air (2 and 40 ppb, respectively), it was determined that for all three cartridge types there was a significant negative interference from O-3. Determined acetaldehyde concentrations were also low in the presence of this concentration of O-3, but acetone was not affected. This technique can only be used to accurately measure carbonyl compounds if O-3 is first removed. NO2 and NO at concentrations typical of both rural and urban ambient air are not interferences when sampling with these cartridges. Use of both KI traps and titration with NO was found to effectively remove O-3 while allowing quantitative determination of HCHO. Intercomparison of HCHO concentrations measured simultaneously using 2,4-nitrophenylhydrazine (DNPH)-coated silica gel Sep-Pak cartridges and tunable diode laser absorption spectroscopy (TDLAS) showed that when O-3 was removed (unlike the case where O-3 was present) by KI traps or NO titration, the HCHO concentrations obtained by the DNPH and TDLAS techniques were not significantly different.