A large (ca 0.7 L) wire-cylinder benchtop reactor was developed and tested for DC corona processing of VOC (volatile organic compound)-contaminated air at room temperature and pressure. The aim of our research is the identification and rationalization of the chemical reactions responsible for VOC removal. Model hydrocarbons, n-hexane and 2,2,4-trimethylpentane (i-octane), were used to characterize the process and compare the effects of DC corona polarity and of humidity on its energy efficiency and products. n-Hexane and i-octane behave very similarly. For both, the energy efficiency is significantly better with negative than with positive DC corona, especially in humid air. The effect of humidity is most interesting. Thus, while with -DC corona the process efficiency is significantly better in humid air, a slight inhibition is observed with +DC corona. Differences between +DC and -DC corona are also found in the amounts of volatile products formed, which include CO2, CO, and minor quantities of organic byproducts (aldehydes, ketones, alcohols, and lower hydrocarbons). A significant fraction of the carbon originally present as VOC is, however, unaccounted for by the analysis of gaseous and volatile organic products and must, therefore, end up as nonvolatile materials and aerosols.

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A mechanistic study is reported on i‐octane and hexane processing with +DC and −DC corona in air at room temperature and pressure. Current/voltage profiles are matched with the ion analysis data obtained by APCI mass spectrometry. With a −DC corona, the hydrocarbons do not modify the negative ion population with respect to uncontaminated air. In contrast, with a +DC corona many hydrocarbon‐derived positive ions form. O(3P) and •OH were also investigated using chemical probes (ozone formation and CO oxidation, respectively). The results, combined with efficiency and product data, suggest that with −DC corona radical initiation steps occur, whereas with +DC corona ionic reactions prevail.

Underivatized oligosaccharides were analyzed by electrospray ionization (ESI) using a linear ion trap mass spectrometer in the negative ion mode with post-column addition of an aqueous solution of formic acid. Under these conditions all oligosaccharides showed the presence of the corresponding formate adduct [M + HCOO](-) with high intensity and easy subsequent low-energy collision-induced dissociation (CID) fragmentation using successive MS(n) experiments. A careful examination of the mass spectra obtained from these MS(n) experiments pointed out some significant differences useful to identify and quantify the single components in mixtures of coeluted disaccharides. This new sensitive and rapid method was successfully applied to the quantification of oligosaccharides in some juices minimizing sample handling.

Cover: The picture shows current/voltage profiles for DC coronas in pure air (green) and in air doped with i‐octane (blue) or hexane (red). Hydrocarbons have no effect on –DC but strongly reduce +DC corona current. Ion analysis provides a rationale for these macroscopic observations: Numerous hydrocarbon‐derived positive ions but no negative ions are detected in the plasma. Further details can be found in the article by E. Marotta, A. Callea, X. Ren, M. Rea, and C. Paradisi* on page 146.