Mass spectrometry for on-line monitoring of perfluoro compounds using Li+ ion attachment techniques

Mass Spectrometric Characterization of the Partial Oxidation Process of a Gasoline Surrogate Induced by a Dielectric Barrier Discharge

Plasma-assisted combustion can improve the thermal efficiency and stability of internal combustion engines; based on this, among various types of discharge method, surface dielectric barrier discharge (SDBD) induced partial oxidation of hydrocarbons was investigated in this study. To demonstrate the general mechanisms of SDBD-induced partial oxidation of gasoline, we used a five-component gasoline surrogate (S5R), which consisted of a mixture of alkanes (isooctane, n-heptane, and methylcyclohexane), alkenes (trimethyl pentene isomers), and toluene, as the model. The detailed process of SDBD-induced partial oxidation of hydrocarbon was investigated by Fourier transform infrared spectroscopy, ion attachment mass spectrometry, and density functional theory calculation. SDBD irradiation of the hydrocarbon/air mixture induced dissociation of oxygen molecule through direct electron impact and collision with excited nitrogen molecules, and the resultant oxygen atom then reacted with a hydrocarbon molecule. Alkane and toluene were converted to alkyl hydroperoxide by a reaction with the oxygen atom and subsequent attachment of O₂. The resultant alkyl hydroperoxide then provided a ketone and/or aldehyde. In contrast, the alkenes underwent attachment of an oxygen atom and were either converted to fragments containing a carbonyl group or to etoposide. Regarding the analytical method, the partially oxidized products were selectively ionized from the hydrocarbon/air mixture when Na⁺ was used as the reagent ion for ion attachment mass spectrometry.

Real-time monitoring for reforming processes of liquid hydrocarbon fuel–air pre-mixtures by non-thermal plasmas using ion attachment mass spectrometry

Plasma induced reforming processes of fuel–air mixtures were investigated to understand the mechanism of the low temperature plasma-assisted combustion technique, which can improve the thermal efficiency and stability of internal combustion engines.

Mass spectrometric investigation and formation mechanisms of high-mass species in the downstream region of Ar/CF(4)/O(2) plasmas

Mass analysis has been conducted on the positive ions and neutral species in the downstream region of Ar/CF(4)/O(2) plasmas. The neutral species have been ionized by Li(+) attachment before mass analysis. The CF(2)O(+), C(2)F(5)O(+) and C(n)F(2n-1)O(+) (1 <or=n<or= 6) positive ions and the C(n)F(2n)O (1 <or=n<or= 7) neutral species have been found as the species composed of C, F and O. The intensity of C(2)F(4)O observed via the Li(+)-attachment mass spectra has been exceptionally weak in comparison to the intensities of CF(2)O and C(3)F(6)O. In addition, neither C(2)F(4) nor C(3)F(6) have been observed, although C(n)F(2n) (n>or= 4) have been observed as the species composed only of C and F. These findings suggest that C(n)F(2n)O (n>or= 3) are produced mainly through the following reactions: CF(3)(CF(2))(m)CF = CF(2) + O((3)P) --> CF(2)((3)B(1)) + CF(3)(CF(2))(m)CFO (m>or= 1) and CF(3)(CF(2))(m)CF = CF(CF(2))(n)CF(3) + O((3)P) --> CF(3)(CF(2))(m)CF + CF(3)(CF(2))(n)CFO (m, n>or= 1), where the CF(3)(CF(2))(n)- group might have side chains, as in (CF(3))(2)CF(CF(2))(n-2)-. With the help of quantum chemistry calculations of reaction enthalpies and transition states, the formation mechanisms of the observed species have been discussed in detail.

Electron capture atmospheric pressure photoionization mass spectrometry: analysis of fullerenes, perfluorinated compounds, and pentafluorobenzyl derivatives

An electron capture (EC) ionization mechanism has been found to be highly efficient in negative-ion atmospheric pressure photoionization (APPI) for the analysis of compounds with positive electron affinity (EA). Using negative-ion APPI, we first report the sensitive detection of natural electrophores with limited polarity, such as fullerenes and perfluorinated compounds, by mass spectrometry (MS). Using direct infusion on a quadrupole time-of-flight (QTOF) mass spectrometer, the limits of detection (LODs) for C(60) and perfluoromethylcyclohexane were determined to be 0.15 pg (0.2 fmol) and 1 femtoliter (fL) ( approximately 1.5 pg or 4.3 fmol), respectively. As the EA of the analyte increases, the detection sensitivity is enhanced. Making use of the accurate mass measurement capability of the QTOF mass spectrometer, we were able to investigate the elemental composition of the ions in each spectrum and attribute the observed high sensitivity to an EC-initiated ionization process. The proposed EC ionization mechanism is further supported by the observation of a dissociative EC reaction of pentafluorobenzyl (PFB)-derivatized phenols. The analysis of phenols by EC-APPI of their PFB derivatives resulted in very high sensitivity, with the lowest reported LOD of approximately 0.17 pg (0.5 fmol) being for 2,4-dinitrophenol. For future LC/EC-APPI-MS applications, the effect of additives and solvents on sensitivity was also tested and reported.

Application of Ion Attachment Mass Spectrometry to Evolved Gas Analysis for in Situ Monitoring of Porous Ceramic Processing

Ion attachment mass spectrometry was applied to evolved gas analysis-mass spectrometry (EGA-MS), generally known as thermogravimetry-mass spectrometry. Characteristic species arising from poly(vinyl alcohol) (PVA) and poly(methyl methacrylate) (PMMA) resin, used as a binder and a porogen, respectively, in the starting materials for porous ceramics, were detected in the mass spectra. The EGA curves of the characteristic mass peaks from PVA and PMMA, when plotted against the programmed temperature, successfully showed the individual pyrolysis behavior of each polymer during the firing process.