Evaluation of lower carbonyls and photochemical oxidants by HPLC-UV and HRGC-MS

Formaldehyde, acetaldehyde, acetone, ozone and nitrogen dioxide were measured in ambient air after having simultaneously collected them on a pair of silica gel cartridges coated with 2,4-dinitro-phenylhydrazine (DNPH) and 1-methyl-1-(2,4-dinitro)-phenylhydrazine (MDNPH), respectively. By reaction with DNPH, the three carbonyls were derivatized to hydrazones and NO2 converted into 2,4-dinitrophenylazide (DNPA), whilst both NO2 and O3 produced N-methyl-2,4-dinitroaniline (MDNA) on MDNPH coating, which was also able to fast react with formaldehyde. The different derivatives were then separated, identified and quantified by HPLC-UV and HRGC-MS. The limits of detection (LOD) for Ox (O3+NO2), NO2, HCHO, CH3CHO and CH3COCH3 were 1.5, 0.4, 0.7, 0.7 and 0.7 ppbv, respectively, for 30 l (1 h) air sampled. When compared with ozone photometric and nitrogen dioxide chemiluminescent analysers, the proposed chromatographic methods, especially HPLC, demonstrated good accuracy (14% for Ox in the 20–100 ppbv range and 21% for NO2 in the 3–14 ppbv range) under field sampling conditions. The comparison between DNPH and MDNPH cartridges about lower carbonyls showed that only HCHO was efficiently collected on MDNPH cartridges, whilst CH3CHO and CH3COCH3 were partly and almost completely lost, respectively. However, significant differences in HCHO mixing ratios (39% on average) were observed with the two types of cartridges.