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Measurements of C1−C15 alkyl nitrates, perchloroethylene, and bromoform at two different sampling sites near Santa Cruz, CA, were conducted in 1995. The halocarbons were used as marker molecules to differentiate the air parcels collected into marine and continental groups. The average concentration of ∑n/i-C3−C12 alkyl nitrates at the California Coast (19.3 pptv) was lower than the levels obtained in the coastal mountains (53.9 pptv). This difference was shown to be most significant for the long chain n/i-C6−C12 alkyl nitrates. It is concluded that the ≥C6 alkyl nitrates in continental air can contribute 1−2% to the total NO y . The results are summarized together with earlier data sets to give a picture of contemporary levels and of the global occurrence of C3−C12 alkyl nitrates. In comparison with South Atlantic air (3.5 pptv), pattern analysis of n-alkyl nitrates suggests a marine source of primary n-alkyl nitrates. It is also shown that liquid chromatographic preseparation of the air sample extracts leads to a fraction that contains more polar organic nitrates. Several alkyl dinitrates and benzyl nitrate are detected in air samples from California, the South Atlantic region, and Europe. The vicinal alkyl dinitrates show increased abundance in a nighttime sample. The relative abundance of benzyl nitrate compared to alkyl (mono) nitrates is used as a tool for global air mass characterization.

High-resolution gas chromatographic separation of all diastereomeric monomethyl-substituted cyclohexyl nitrates is shown on a nonpolar methylpolysiloxane stationary phase, and the first application of this procedure to the environmental diastereomeric analysis of alkyl nitrates is presented. Two characteristic signals in the achiral analysis of atmospheric samples could be assigned to the smallest alkyl nitrate containing two asymmetric carbon atoms, 3-methyl-2-pentyl nitrate. Retention indices in the temperature-programmed separation based on the n-alkanes were determined. The homologous series of 1-alkyl nitrates were found to be useful as ECD-visible n-alkanes. Enantiomeric separation of alkyl nitrates was achieved on heptakis(3-O-acetyl,-2,6-di-O-pentyl)-β-cyclodextrin (LIPODEX-D). The influence of the nitrooxy group and the alkyl chain length on the chiral discrimination on LIPODEX-D is discussed for 25 chiral alkyl nitrates. The absolute configurations of some alkyl nitrates were assigned by asymmetric synthesis of enantiomerically pure references. The complexity of the alkyl nitrate mixtures present in air samples does not allow a direct chiral separation as the alkyl nitrates partly coelute on the LIPODEX-D column. Column coupling of LIPODEX-D with a polar achiral stationary phase like polyalkylenglycol (PAG) was successfully applied to solve this problem, and the chiral alkyl nitrates present in a typical air sample were separated. A systematic nomenclature for alkyl nitrates is introduced to handle the steadily growing number of branched and long-chain alkyl nitrates detected in environmental analysis.

Abstract. Column selectivity is examined for a series of smectic liquid crystalline columns and is compared with methyl and C,, polysiloxane columns for the separation of polycyclic aromatic hydrocarbon (PAH) isomers. A set of extended and condensed solute probes is described that provides a sensitive indication of variations in column shape selectivity. Examples of shape selectivity differences are presented for smectic liquid crystalline columns and 5% phenyl polysiloxane columns using various PAH isomer sets. Variations in selectivity have been observed among different smectic liquid crystalline columns, and this problem appears more significant than for methyl polysiloxane columns. The selectivity ratio for tetraphenylmethane and p-terphenyl provides a sensitive indication of column shape selectivity, with a change in elution order occurring between ordered (smectic liquid crystalline) columns and non-ordered (methyl polysiloxane) columns. Shape selectivity differences indicated by this test mixture are apparent for more complex PAH isomer mixtures. Despite stationary phase selectivity variability, smectic liquid crystalline columns offer considerable potential for solving difficult separation problems involving structured solutes.