Gas Chromatographic Detector for Selective and Sensitive Detection of Atmospheric Organic Nitrates

A highly selective and sensitive detector for measuring organic nitrates in atmospheric air samples has been developed. This detector is based on the luminol chemiluminescence-based detection of NO2 produced by postcolumn thermal decomposition of organic nitrates. Determination of the relative detector sensitivities to C3-C6 alkyl nitrates, α,β-hydroxy nitrates, α,β- dinitrates, and several mono- and multinitro aromatic compounds as well as N-nitrosodimethylamine has been conducted. The detector is shown to produce one NO2 per molecule at a pyrolysis temperature of 350 °C, yielding identical sensitivities for alkyl and hydroxy nitrates, consistent with the known thermal decomposition pathway and thermal lifetimes at this temperature. As expected, the alkyl dinitrate studied yielded a calibration slope equal to twice those of the mononitrates. At sufficiently high temperatures, the detector also responds to a variety of nitroaromatics and to N-nitrosodimethylamine. However, a yield of 50% NO2 was obtained from the thermal decomposition of N-nitrosodimethylamine and all mononitroaromatic compounds, except 1-nitronaphthalene, which yielded a slope similar to those of the alkyl nitrates. NO2 yields of 0.70 and 0.90 were obtained for 2,4-DNT and 2,4,6-TNT, respectively. The detection system is found to exhibit a linear response for all N-containing compounds studied. The significant selectivity advantage of the chemiluminescence detector is demonstrated through comparison with the ECD for both laboratory standard and ambient samples. The detection limit for determination of organic nitrates was found to be ∼0.05 pmol.