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In this study, we report on the use of field-portable gas chromatography-mass spectrometry (GC-MS) with solid-phase microextraction, purge-and-trap, thermal desorption, and heated headspace sampling techniques to provide a fast response [...]

We describe a novel radio frequency ion trap mass analyzer based on toroidal trapping geometry and micro-fabrication technology. The device, called the halo ion trap, consists of two parallel ceramic plates, the facing surfaces of which are imprinted with sets of concentric ring electrodes. Radii of the imprinted rings range from 5 to 12 mm, and the spacing between the plates is 4 mm. Unlike conventional ion traps, in which hyperbolic metal electrodes establish equipotential boundary conditions, electric fields in the halo ion trap are established by applying different radio frequency potentials to each ring. The potential on each ring can be independently optimized to provide the best trapping field. The halo ion trap features an open structure, allowing easy access for in situ ionization. The toroidal geometry provides a large trapping and analyzing volume, increasing the number of ions that can be stored and reducing the effects of space-charge on mass analysis. Preliminary mass spectra show resolution (m/[DELTA]m) of 60-75 when the trap is operated at 1.9 MHz and 500 [V.sub.p-p].

A new electron ionization source was developed for orthogonal acceleration time-of-flight mass spectrometry (TOFMS) based on the superimposition of a magnetic field around a radio frequency-only (rf-only) ion guide. The cylindrically symmetric magnetic field compresses the electron beam from the electron source into a long narrow volume along the ion guide axis. The magnetic field also helps to maintain a narrow energy distribution of electrons that penetrate the full length of the ion guide despite the influence of the radial rf field. Ionization occurs inside the ion guide with improved efficiency resulting from efficient use of electrons, prolonged interaction time, and nontradifionally large ionization volume. At the same time, the rf field effectively focuses ions radially and confines them to the axis of the ion guide by collisional focusing, leading to high ion transmission efficiency. Furthermore, the source can also be operated in a trap-and-pulse mode to improve the ion sampling duty cycle of orthogonal acceleration TOFMS. To validate the design concept of this new ion source, a simple prototype using a single set of cylindrical rods was constructed and retrofitted to an orthogonal acceleration TOFMS. A significant increase in ion signal intensity was observed by operating the source in a pulsed ion extraction mode. Low detection limits (for example, 12 fg for toluene) were determined at 12.5 spectra [s.sup.-1] in the full spectrum mode.

An improved design of a novel electron ionization source for orthogonal acceleration time-of-flight mass spectrometry is described, based on the superimposition of an axial magnetic field with cylindrical symmetry around a radio frequency-only quadrupole. A tubular permanent magnet was designed to generate the required strong magnetic field and field profile. An axial electric field along the ion guide for efficient ion extraction was introduced using segmented quadrupole rods. Details of the source design and the effects of various operating parameters are described. The source produces high-quality mass spectra with regard to fragmentation, relative abundances, and isotopic ratios. Preliminary results have shown excellent sensitivity, with limits of detection in the subfemtogram range (octafluoronaphthalene, full spectrum acquisition) in gas chromatography/mass spectrometry operation.

A method of predicting reduced ion mobility values, [K.sub.0], for use in ion mobility spectrometry is described. While the method is very similar to a previously reported method based on a neural network, the method described in this paper uses a purely statistical regression approach. Furthermore, it has been applied to a wider class of compounds, including chemical agents. Various molecular parameters were evaluated in the predictive model to determine the qualitative dynamics that have the greatest effect on [K.sub.0]. An [R.sup.2] value of 80.1% was obtained when calculated [K.sub.0] values were plotted against measured [K0.sub.] values for 162 compounds for which experimental [K.sub.0] values were available. However, when chloroacetophenone and 3-xylyl bromide (3-methylbenzyl bromide) were removed from the set due to their large residual values, the predictability increased to an R2 value of 87.4%. This compares well with the value of 88.7%, which was obtained in a regression step of a previous neural network study for a less diverse set of 168 compounds.

Electrospray ionization has grown to be one of the most commonly used ionization techniques for mass spectrometry, and efforts continue to improve its performance. Typically, the sprayer tip must be very close to the entrance orifice of the mass spectrometer in order to maximize the conduction of ions from the sprayer into the mass spectrometer. However, because of space-charge repulsion, most ions never reach the sampling orifice. In this work, an industrial air amplifier, for which the working mechanism is based on venturi and coanda effects, was added between an electrospray ionization source and a time-of-flight mass spectrometer. When a series of reserpine solutions (0.5, 1.0, 5.0, and 10.0 [micro]M) were monitored using mass spectrometry, an over 5-fold increase in m/z 609.3 ion intensity was measured for a separation distance of 14 mm between the electrospray tip and interface capillary inlet, as compared to when the electrospray tip was in its normal position 1 mm in front of the inlet without the amplifier. When a voltage was applied to the air amplifier to further assist in focusing the electrosprayed ions, an ~18-fold increase in m/z 609.3 ion intensity was obtained. In addition, a 34-fold reduction in method detection limit was observed.

The interfacing of capillary column supercritical fluid chromatography (SFC) to time-of-flight mass spectrometry (TOFMS) through atmospheric pressure chemical ionization (APCI) was investigated. An ion source chamber and a new, flexible, and efficient transfer line from the SFC to the TOFMS system were designed to accommodate the requirements of this study. Ionization of analytes was performed using a corona discharge needle. The interface was equipped with two multiple-axis translation stages for positioning of the transfer line tip and the discharge needle inside the ion chamber. The investigations were oriented toward the optimization of parameters which have a strong effect on the intensity and stability of the analyte signal, including background stability, corona discharge needle positioning in the ion source, transfer line tip and discharge needle relative positioning, curtain gas and makeup gas flow interactions, ion chamber temperature, and elution pressure of analytes from the SFC system.

The design and use of a solid-phase injector for open tubular column supercritical fluid chromatography (SFC) are reported. For sample introduction, a liquid sample was loaded on a platinum wire. After the solvent had evaporated, the wire was inserted into, and sealed in, the injector. The chromatographic run was started by introducing the supercritical mobile phase into the injector. Absolute and relative peak area reproducibilities, as well as retention time reproducibility, of the injection method were evaluated. The relative standard deviations (% RSDs) of absolute and relative peak areas were 2.0-4.5 and 0.4-1.8%, respectively, for both 1- and 2-[micro]L injections. Larger deviations were observed for compounds that had high vapor pressures. The % RSDs of retention times from six subsequent injections were 0.04-0.06., A model of a solid-phase injector for open tubular column supercritical fluid chromatography was evaluated. Experiments involved the introduction of a liquid sample for evaporation on a platinum injector. A supercritical mobile phase was used to commence the chromatographic run. Measurements of absolute and relative peak area reproducibilities, retention time reproducibility and their relative standard deviations demonstrated the utility of the injection method.

The various different processes taking place in the type-2-diabetes-related peptide, IAPP (Islet Amyloid Polypeptide) are discussed. The analysis shows that the sequences that are responsible for the formation of amyloid fiber and membrane disruption occur independently in two distinct regions of the peptide.

Ferroptosis is a form of programmed cell death associated with inflammation, neurodegeneration, and ischemia. Vitamin E (alpha-tocopherol) has been reported to prevent ferroptosis, but the mechanism by which this occurs is controversial. To elucidate the biochemical mechanism of vitamin E activity, we systematically investigated the effects of its major vitamers and metabolites on lipid oxidation and ferroptosis in a striatal cell model. We found that a specific endogenous metabolite of vitamin E, alpha-tocopherol hydroquinone, was a dramatically more potent inhibitor of ferroptosis than its parent compound, and inhibits 15-lipoxygenase via reduction of the enzyme’s non-heme iron from its active Fe3+ state to an inactive Fe2+ state. Furthermore, a non-metabolizable isosteric analog of vitamin E which retains antioxidant activity neither inhibited 15-lipoxygenase nor prevented ferroptosis. These results call into question the prevailing model that vitamin E acts predominantly as a non-specific lipophilic antioxidant. We propose that, similar to the other lipophilic vitamins A, D and K, vitamin E is instead a pro-vitamin, with its quinone/hydroquinone metabolites responsible for its anti-ferroptotic cytoprotective activity. [ABSTRACT FROM AUTHOR]