C.S. Leasure

Proton affinity equilibria for polycyclic aromatic hydrocarbons at atmospheric pressure in ion mobility spectrometry

Proton affinity equilibria for 5 polycyclic aromatic hydrocarbons (PAH) and 2 oxygenated polycyclic aromatic hydrocarbons (oxy-PAH) were measured at atmospheric pressure using ion mobility spectrometry. In spectra for pure compounds, values for reduced mobilities (cm2 V−1 s−1) for MH+ with percent deviations from literature values were: pyrene, 1.58 (4.6%); anthracene, 1.68 (4.3%); phenanthrene, 1.64 (5.8%); naphthalene, 1.92 (2.7%); benzene, 2.34 (3.1%); benzophenone, 1.64 (8.6%); and acetophenone, 1.82 (0%). Gas phase proton transfer occurred at 660–670 torr with binary mixtures of PAH and oxy-PAH. Product ion equilibria in binary mixtures were shifted towards compounds with greater gas phase basicity. For example, a concentration ratio of 7:1 for pyrene to anthracene was necessary for near equal intensity in product ions, while almost 50:1 for phenanthrene to pyrene was necessary for equal intensity in product ions. The order of proton affinities for PAH and oxy-PAH relative to pyrene was determined as anthracene > phenanthrene > acetophenone > naphthalene > benzene and was consistent with basicity values measured using high-vacuum techniques. Ternary mixtures were prepared through addition of a third PAH to binary mixtures. Product ion intensities were also controlled for PAH and oxy-PAH in ternary mixtures at atmospheric pressure through gas phase basicity.

Sensing of Petrochemical Fuels in Soils Using Headspace Analysis with Photoionization-Ion Mobility Spectrometry

Abstract Photoionization-Ion Mobility Spectrometry (PI-IMS) was used to distinguish among common petrochemical fuels including leaded gasoline, unleaded gasoline, kerosene, and diesel fuel through sampling of headpsace vapors over liquid samples. Positive ion mobility spectra obtained in air at ambient pressure were comprised of 3 to 5 peaks which were tentatively identified as benzene, alkylated benzenes, naphthalene and alkylated naphthalenes. The simple mobility spectra from PI-IMS analysis, due to selective ionization of aromatic hydrocarbons. were contrasted with the complex chromatographic patterns for the same fuels from scanning GC/MS analysis. Discrimination between unleaded gasoline and diesel fuel in fuel mixtures was possible using PI-IMS across a broad range of gas-phase concentration ratios. Fuels were also detected in soil using PI-IMS analysis of headspace vapors at 25[ddot]C. Unleaded gasoline in soil was detected from 0.16 to 16 mg/kg for only 0.1 g of sample with nearly linear response....

Flow characteristics in a segmented closed-tube design for ion-mobility spectrometry

Abstract Closed-tube design with unidirectional flow of drift gas in ion-mobility spectrometry (i.m.s) was found to provide residence times for analyte from 10 s to 10 min based on drift gas flow rate. The volume of drift gas necessary to restore reactant ions completely to the original intensity, after addition of excess (>900 mg l −1 ) of analyte to the ion source, was three times the inner volume of the tube, regardless of flow rate. Contamination of the i.m.s. tube from analyte in the external atmosphere occurred readily in the open-tube design and in the closed-tube design with or without a slight vacuum attached to the tube. Rates of migration of analyte from outside to inside the tube were similar in all designs and the present closed-tube design was largely non-resistant to external contamination. Product-ion intensities for aromatic and polynuclear aromatic hydrocarbons were independent of drift flow rate from 100 to 800 ml min −1 in the closed-tube design with no formation of artifacts. Plots of ion intensity vs. concentration of o -xylene were linear int wo ranges, 0.05–0.08 μg l −1 and 0.1–2 μg l −1 , with slopes of 1.2 × 10 −9 A l μg −1 in the first range and 1.0 × 10 −11 A l μg −1 in the second range. No changes in mobility of aromatic product-ion peaks were seen with increases in concentration when the analyte was added to the drift gas rather than near the reaction region in unidirectional flow.

Characterization of Discharge Water from Hydrostatic Testing of Natural Gas Pipelines Using High Resolution Gas Chromatography/Mass Spectrometry

Abstract Hydrostatic testing of natural gas pipelines may lead to production of water which is contaminated with organic compounds in a highly complex mixture. Present in this complex mixture are benzene, C 3 to C 5 alkylated benzenes, dimethyl disulfide, C 3 to C 5 alkylated disulfides, saturated alkanes, and branched/unsaturated alkanes. Estimated minimum concentrations of benzene were 25 to 38mg/L. Composition of discharge water was not uniform throughout the dewatering process but varied as a function of extent of discharge. While chemical oxygen demand decreased uniformly in discharge water with increased extent of dewatering, selected toxic organic compounds showed less consistent variations. Other similar examinations of discharge waters from natural gas pipelines have not been previously reported.

Instrument review: performance of the applescope system in laboratory signal collection and averaging

Effects of pulse width using external triggering on performance of modified Apple IIe computer were investigated. Regular synchronous collection of signal using digital signal averaging with commercially available hardware and software (Applescope/sup R/) was dependent upon characteristics of external triggering including pulse width. Minimum width of trigger pulses for acceptable performance was determined to be a function of user-specified time base and was thoroughly characterized. Frequency response as a function of signal amplitude was also characterized. 6 references, 5 figures.

Signal generator for diagnosing chromatographic and mass spectrometric data systems

An electronic test circuit has been designed, constructed and characterized for production of signals which have peak shapes and widths similar to those obtained in gas chromatography, mass spectrometry, and ion mobility spectrometry. Operation of the circuit is based on operational amplifiers and monostable multivibrators. In this circuit design, variables including peak height, peak width, retention times, and number of peaks in a signal can be independently controlled by the analyst. Both repetitive and single sweep signals may be generated with amplitudes from 0.5 to 18 V and with peak widths from 1 nsec. to 20 minutes. Behavior in each major section of the circuit has been characterized and limitations in signal parameters were defined. The circuit was applied to a computer-based digital signal averager and a reporting integrator to demonstrate flexibility and usefulness.