Evaluation of a thermionic detector for capillary supercritical fluid chromatography of nitrated polycyclic aromatic compounds

Abstract

Abstract A thermionic detector was evaluated for capillary supercritical fluid chromatography of polar nitro‐containing polycyclic aromatic compounds (nitro‐PAC). Three modes of detector operation were studied. The best performance was obtained using a nitro‐selective mode of detection. Although linearity was confined to a narrow range for a given source current, the sensitivity was excellent; 20 pg injected for p ‐nitrophenol gave a signal‐to‐noise ratio of 3. Conventional thermionic detection also produced good sensitivity; however, serious baseline drift was observed at high operating temperatures using density programming. A third mode, flame thermionic detection, was not acceptable because of low sensitivity. A number of nitro‐PAC were successfully chromatographed using density programming at 101°C. Hydroxynitropyrenes, nitropyrene quinones, and 9‐hydroxy‐2‐nitrofluorene, which could not be eluted in capillary gas chromatography, were successfully chromatographed here. Retention of these compounds increased sequentially on 50% n ‐octyl‐, 5% phenyl‐, and 25% biphenyl polysiloxane stationary phases, respectively. Stationary phase interactions appeared to be more a function of the polar functional groups on the aromatic rings than of the hydrocarbon character of the compounds. Solute solubility in the mobile phase and volatility were additional factors contributing to the elution of these molecules. Finally, these results were used to identify a number of nitro‐PAC in a polar subfraction of a diesel particulate extract.