The mixture of hydrazones formed from the reactions of the set of carbonyl compounds commonly found in air can then be separated using HPLC and detected using light absorption at 254 or ~365 nm (e.g., see Kuntz et al., f 980; Lipari and Swarin, 1982; and Kuwata et al., 1983).

The aldehydes and ketones can be collected in several different ways. One of the most common is the use of solid sorbents such as silica gel, Florisil, or C18 cartridges that are coated with DNPH (e.g., see Lipari and Swarin, 1985; Arnts and Tejada, 1989; Zhou and Mopper, 1990; Sirju and Shepson, 1995; and Kleindienst et al., 1998). Some care must be taken to avoid artifacts due to reactions of 03, which has been shown to give positive interferences for C18 cartridges but negative interferences when silica gel is used as the sorbent (e.g., see Arnts and Tejada, 1989; Rodler et al., 1993; Sirju and Shepson, 1995; Kleindienst et al., 1998; Gilpin et al., 1997; and Apel et al., 1998b). The DNPH technique has also been used in passive samplers for HCHO (e.g., see Levin et al., f989; and Grosjean and Williams, 1992). However, with care, concentrations in the 30- to 500-ppt range (depending on the particular carbonyl) can be measured using this technique and a 156-L air sample (Grosjean et al., f996a).

Other approaches to collection of the carbonyl compounds include the use of impingers containing the DNPH in a solvent such as acetonitrile (e.g., Grosjean and Fung, 1982; Lipari and Swarin, 1982), scrubbers (e.g., Dasgupta et al., 1988, 1990; Lee and Zhou, 1993), mist chambers (e.g., Cofer and Edahl, 1986; Munger et al., 1995; Khare et al., 1997), and condensation collectors (Dawson and Farmer, 1988).

Alternate derivatization techniques have also been used. These include dansylhydrazine with fluorescence or chemiluminescence detection of the hydrazone (e.g., Nondek et al., 1992; Rodler et al., 1993), 3-methyl-2-

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