Direct analysis of saturated hydrocarbons using glow discharge plasma ionization source for mass spectrometry.

The ionization source based on glow discharge plasma using ambient air is driven by a pulsed direct-current voltage for soft plasma ionization (SPI). The novelty of this work is that molecular ions [M+13]+ related to the analyte species (M), which may be formed by numerous oxidation, can be dominantly detected as a base peak with little or no fragmentation of them in an air plasma at a pressure of several kPa. The unique ion [M+13]+ was assigned to the oxidation product, [M+O-3H]+, which was confirmed as a deuterated ion [M+O-3D]+ ([M+10]+) by using a deuterated solvent. The ionization reactions were suggested that the product ion [M+O-3H]+ may arise from hydride abstraction reaction of M with O2+•, dehydrogenation reaction of [M-H]+• and subsequently oxidation reaction of [M-3H]+ with O3. n-Alkane mixtures was also measured to evaluate the intermolecular interaction in this system. The limits of detection (LOD) were in the range of 0.126-1.68 ppmv and the relative standard deviation (RSD) for repeatability was approximately 10.0% at the lowest concentration. To our knowledge, this is the first report demonstrating that the spectrum pattern of saturated hydrocarbons could be directly determined without any complicated fragmentation.

Removal of gaseous elemental mercury by hydrogen chloride non-thermal plasma modified biochar.

Hydrogen chloride (HCl) non-thermal plasma was applied to introduce Cl active sites on biochar prepared from sorghum straw in this study. Surface modified biochar was then placed in flue gas with typical components to investigate its elemental mercury (Hg0) capture ability. To elucidate the adsorption mechanism & binding properties, samples were characterized by N2 adsorption, scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) and X-ray absorption near edge structure (XANES) analysis of Hg LIII-edge, Cl K-edge and S K-edge. Experimental results showed that HCl plasma modification successfully increased Cl active sites on biochar and greatly increased its mercury removal efficiency. Both HCl treatments (w/without plasma involvement) altered biochar's surface structure and layered structure generated. XANES spectra revealed that adsorbed-Hg on HCl-treated biochars mainly in the form of Hg+. Gaseous Hg0 was believed to heterogeneously react with chlorinated sites through electron-transfer and formed Hg2Cl2 compounds. With the presence of NO or SO2 in the system, adsorbed mercury existed on biochar mainly as Hg+. SO2 competed and inhibited the adsorption of Hg0; while NO promoted Hg0 removal capacity by increasing the active sites and enhancing the adsorption kinetics of adjacent Cl-containing sites.