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 w as evaluated using large volume silica gel cartridges and Sep-Pak C-18 silica gel and silica gel cartridges. The silica gel Sep-Pak cartridg e was found to be the best of the three types evaluated for determinat ions in relatively clean ambient air. At concentrations of HCHO and O- 3 typical of clean ambient air (2 and 40 ppb, respectively), it was de termined that for all three cartridge types there was a significant ne gative interference from O-3. Determined acetaldehyde concentrations w ere also low in the presence of this concentration of O-3, but acetone was not affected. This technique can only be used to accurately measu re carbonyl compounds if O-3 is first removed. NO2 and NO at concentra tions typical of both rural and urban ambient air are not interference s when sampling with these cartridges. Use of both KI traps and titrat ion with NO was found to effectively remove O-3 while allowing quantit ative determination of HCHO. Intercomparison of HCHO concentrations me asured simultaneously using 2,4-nitrophenylhydrazine (DNPH)-coated sil ica gel Sep-Pak cartridges and tunable diode laser absorption spectros copy (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 o btained by the DNPH and TDLAS techniques were not significantly differ ent.