EVALUATION OF ISOPRENE OXIDATION AS AN INTERFERENCE IN THE CARTRIDGE SAMPLING AND DERIVATIZATION OF ATMOSPHERIC CARBONYL-COMPOUNDS

The heterogeneous oxidation of isoprene by ozone and radicals formed in the reaction of ozone with the hydrazine derivatization reagent, either 2,4-dinitrophenylhydrazine (DNPH) or dansylhydrazine (DNSH), is shown to be a serious interference in the cartridge sampling and derivatization of atmospheric aldehydes and ketones. Positive artifact peaks of formaldehyde, methacrolein, methyl vinyl ketone, and several larger carbonyl compounds are formed, presumably through the oxidation of isoprene and its polymerization products. Formation of artifact peaks is nonlinear with respect to sampling time, with longer sampling times resulting in a greater proportion of ozone/isoprene reaction products. These previously unreported interferences are potentially significant for other atmospheric alkene species, which also may react with ozone on sorbent surfaces to generate carbonyl compounds in situ. Artifact peaks for methyl vinyl ketone and methacrolein are minimized by acidifying octadecyl silica (C-18) cartridges prior to sampling, but in this case high molecular weight aldehydes are produced by the reaction of ozone with the C-18 stationary phase. Data obtained through cartridge sampling of air masses containing isoprene or other alkenes and moderate levels of ozone (greater than or equal to 50 ppbv) should be carefully evaluated with respect to this interference.