Drift Gas Research Articles

Qualitative and quantitative evaluation of deconvolution for ion mobility spectrometry

Using deconvolution, ion mobility peak shape was found to be dependent upon the nature of the compound, moisture of the drift gas, and acquisition temperature (water clustering) over processes such as ion scavenging and diffusion. Under low moisture conditions, the nature of the compound had greater impact upon peak shape than experimental variables such as temperature. When coeluting compounds were introduced into the mobility spectrometer, peak shape and deconvolution performance were dependent upon the above factors as well as relative concentrations, proton affinities, and differences in the drift times of the mobility peaks of individual components. Deconvolution coupled with atmospheric pressure chemical ionization mass spectrometry was employed for interpretation of mixed component mobility spectra.

Results from the SLD barrel CRID detector

We report on operational experience with and experimental performance of the SLD barrel Cherenkov Ring Imaging Detector from the 1992 and 1993 physics runs. The liquid (C/sub 6/F/sub 14/) and gas (C/sub 5/F/sub 12/) radiator recirculation systems have performed well, and the drift gas supply system has operated successfully with TMAE for three years. Cherenkov rings have been observed from both the liquid and gas radiators. The number and angular resolution of Cherenkov photons have been measured, and found to be close to design specifications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Long-term, efficient RICH detector operation with TMAE

The efficient, long-term operation of the largest RICH detectors — using a TMAE vapor photocathode in long drift time projection imaging chambers with many square meters of quartz window area — is a remarkable achievement, particularly when their geometry and performance is compared with antecedent photomultipliers. Their detection efficiency can however be rapidly compromised, particularly by electronegative contamination in the TMAE-laden drift gas. This report reviews the techniques for maintaining long electron lifetime, including automated on-line monitoring, which allows more time for remedial action before a major degradation in performance. The TMAE compatibility of chamber and fluid system materials is reviewed, and large-scale techniques for TMAE purification are described.

The fluid systems for the SLD Cherenkov Ring Imaging Detector

The design and operation of the fluid delivery, monitor, and control systems for the SLD barrel Cherenkov Ring Imaging Detector (CRID) are described. The systems deliver drift gas (C/sub 2/H/sub 6/+TMAE), radiator gas (C/sub 5/F/sub 12/+N/sub 2/), and radiator liquid (C/sub 6/F/sub 14/). Measured critical quantities such as electron lifetime in the drift gas and ultraviolet (UV) transparencies of the radiator fluids, together with the operational experience, are reported. >

Radial wire drift chambers with fast gases for tracking at future supercolliders

We report on progress in the development of wire-based tracking in the forward region of experiments at future supercolliders. Results are presented from experimental studies of candidate fast drift gases in crossed electric and magnetic fields, and on the operation of a prototype “wedge” of a radial wire drift chamber cell.

The mobility and ion structure of protonated aminoazoles

The reduced mobility of protonated pyrazole derivatives was measured by ion mobility spectrometry (IMS) in air, nitrogen, and carbon dioxide, at temperatures between 150 and 250°C. It was found that the mobility of protonated 5-amino-1-phenylpyrazole was higher than that of its 3- and 4-isomers. This was attributed to the fact that in the 5-isomer the preferred site of protonation is on the endocyclic nitrogen, which leads to delocalization of the ionic charge, and thus to a diminished interaction with the drift gas molecules. On the other hand, protonated 5-amino-1-methylpyrazole has a slightly lower mobility than its isomers, which is indicative of a different protonation mechanism.

Photoemissive ionisation source for ion mobility detectors

A combination of a photoemissive ionisation source coupled to an ion mobility detector has been developed which utilises a pulsed light source thereby eliminating the need for an ion injection gate. Factors influencing the performance of this negative ion detector have been investigated. With air as the sample and drift gas streams, the performance of the detector is comparable to conventional designs employing radioactive ionisers.

Measurement of spatial resolutions and drift velocities in a drift-chamber filled with a helium-DME mixture

We have measured spatial resolutions in a quadratic drift cell using as drift gas pure DME or a mixture of 70% He and 30% DME at atmospheric pressure. For a maximum drift distance of 5 mm we obtained in the He-DME mixture a resolution σ r = 80 μ m over 60% of the drift cell and for pure DME σ r = 40 μ m over 80% of the drift cell. The drift velocity of electrons is approximately three times faster in this mixture than in pure DME. A systematic study of the electric field dependence of the drift velocities in various He-DME mixtures is also presented.

Recent results from the DELPHI barrel ring imaging Cherenkov counter

The DELPHI detector installed in the LEP (Large Electron-Positron Collider) is equipped with RICH (ring imaging Cherenkov) counters. The barrel part incorporates a liquid (C/sub 6/F/sub 14/) and a gaseous (C/sub 5/F/sub 12/) radiator, providing particle identification up to 20 GeV/c. The Cherenkov photons of both radiators are detected by TPC (time projection chamber)-like photon detectors. The drift gas (75% CH/sub 4/+25% C/sub 2/H/sub 6/) is doped with TMAE (tetrakis-dimethylamine-ethylene) by which the ultraviolet Cherenkov photons are converted into single free photoelectrons. These are drifted towards multiwire proportional chambers at the end of the drift tubes, and the space coordinates of the conversion point are determined. One half of the barrel RICH is now equipped with drift tubes and has provided results from the liquid radiator since spring 1990. The gas radiator has been tested with C/sub 2/F/sub 6/ as a preliminary filling since August 1990. The data obtained demonstrate the good particle identification potential. For the liquid radiator, the number of detected photons per ring in hadron jets is N=8, whereas for muon pairs (single tracks) N=10 has been obtained. For the gas radiator, 2.1 photons per track were observed, which demonstrates good functioning of the focussing mirrors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Current neutralization of nanosecond risetime, high-current electron beams

Methods of achieving current neutralization in fast-risetime (<3 ns) electron beams propagating in low-pressure gas are described. For this investigation, a 3-MV, 30-kA intense beam was injected into a drift cell containing gas pressures form 0.10 to 20 torr. By using a fast net current monitor (100-ps risetime), it was possible to observe beam front gas breakdown phenomena and to optimize the drift cell gas pressure to achieve maximum current neutralization. Experimental observations have shown that by increasing the drift gas pressure (P approximately=12.5 torr) to decrease the mean time between secondary electron gas collisions, the beam can propagate with 90% current neutralization for the full beam pulsewidth (16 ns).

Performance of small-radius thin-wall drift tubes in an SSC radiation environment at the MIT Research Reactor

Drift tubes of 1.9-mm radius and 25- mu wall thickness were exposed to neutrons and associated gamma radiation from uranium fission at the MIT Research Reactor. In 45 hours of irradiation, the drift tubes received a neutron fluence with energy greater than 0.5 MeV of 1.1*10/sup 13/ cm/sup -2/ And accumulated a charge per wire length of 0.08 coul cm/sup -1/, about that expected for three years of operation at the SSC for a lead scintillator calorimeter at a 1-m radius and for drift tubes at a distance of several tens of centimeters from the beam axis. Measurement of the pulse height, pulse shape, counting rates, andcurrents showed no degradation in drift tube performance. Fast (few nanosecond rise time), sharp (20-ns width) pulses were observed at counting rates of 5 MHz using CF/sub 4/ as the drift gas. >

Electron capture ion mobility spectrometry for the selective detection of chlorinated and brominated species after capillary gas chromatography

AbstractThis paper reports the first investigation of electron capture ion mobility spectrometry as a detection method for capillary gas chromatography. In previous work with negative ion mobility detection after gas chromatography, the principal reactant ion species were O2− or hydrated O2− due to the presence of oxygen in the drift gas. These molecular reactant ions have a mobility similar to chloride and bromide ions, which are the principal product ions formed by most halogenated organics via dissociative ion‐molecule reactions. Oxygenated reactant ions thus interfere with the selective detection of chloride and bromide product ions. A recently described ion mobility detector design efficiently eliminated ambient impurities, including oxygen, from infiltrating the ionization region of the detector; consequently, in the negative mode of operation, the ionization species with N2 drift gas were thermalized electrons. Thermalized electrons have a high mobility and their drift time occupies a region of the ion mobility spectrum not occupied by chloride, bromide, or other product ions. The result was improved selectivity for halogenated organics which ionize by dissociative electron capture. This was demonstrated by the selective detection of 4,4′‐dibromobiphenyl from the components of a polychlorinated biphenyl mixture (Aroclor 1248).

The effects of saturation and substitution on the mobility of protonated cyclic compounds

The mobility in air of protonated cyclic compounds was measured by ion mobility spectrometry techniques. From the mobility measurements it was found that the collisional cross-sections of saturated ions were much larger than those of their unsaturated analogs. This was attributed to elongation of bonds on saturation and to the additional hydrogen atoms. On substitution of CH 2 by NH in saturated compounds, or of CH by N in unsaturated compounds, the mobility of the protonated compounds decreased. This was attributed to changes in the internal charge distribution: in the monosubstituted analogs the charge is localized mainly on the site of the heteroatom, while in the hydrocarbons the ionic charge is largely delocalized in the ring. Thus, the interaction of the ion with the drift gas molecules is stronger in the heterocyclic ions, leading to larger collision cross-sections and lower mobilities. Subsequent substitution had little or no further effect. Ions possessing a cyclic structure were observed to have higher mobilities than their noncyclic isomers.

Using dimethylether as a drift gas in a high precision drift tube detector

Excellent spatial resolution (34 μm) has been obtained using dimethylether ((CH 3) 2O) at 1 atm in a small drift tube detector. This is better by at least a factor of 2 compared to previous work (∼ 80 μ m) with a conventional gas (a 50-50 argon-ethane mixture) in the same detector. The Lorentz angle and the gas amplification have been measured over a wide range of electric and magnetic fields.

An ion mobility spectrometry/mass spectrometry (IMS/MS) study of the site of protonation in anilines

Ion mobility spectrometry (IMS) and IMS/MS techniques were used to differentiate between nitrogenprotonated and carbon-protonated anilines, both of which coexist under the conditions of the IMS. Analysis of the results led to the conclusion that the former species had lower mobilities than the latter. This was attributed mainly to charge delocalization in the ring-protonated species, which results in a weaker interaction with the drift gas molecules. Furthermore,meta-alkyl substitution enhanced ring protonation, while in 2-chloroaniline the nitrogenprotonated species was predominant, as expected.

Long electron drift in TMAE-doped gas in the barrel rich detector

The DELPHI Barrel RICH (ring-imaging Cherenkov) detector is based on the principle of the drift of single electrons over distances up to 1.5 m in TPC-like drift tubes made of quartz. The drift is performed in a longitudinal electric field of 0.53 kV/cm and in a gas mixutre of 80% CH 4, 20% C 2H 6 and ≈ 1000 ppm of TMAE as photosensitive additive. The electron loss during the drift has been measured for different TMAE concentrations and different TMAE qualities. It will be shown that an absorption length λ > 10 m can be obtained even for high TMAE concentrations. This could only be achieved by taking extreme care in the purity of the TMAE and the drift gas. We will also report on the systematic errors in the reconstruction of the photon conversion point due to distortions in the electron drift. Small focusing effects have been observed close to the walls.

Effects of temperature and clustering on mobility of ions in carbon dioxide

The effects of temperature and clustering on the mobility of ions drifting in CO{sub 2} at ambient pressure were studied by ion mobility spectrometry (IMS). A semiempirical procedure for obtaining quantitative data on the size of the cluster was applied. At 90{degree}C, about three CO{sub 2} molecules, on average, clustered around protonated amine core ions. As the temperature was raised, the number of clustered molecules decreased, and above 200{degree}C, it was practically zero. A clear mass-mobility correlation was observed in the protonated aliphatic amines even at 90{degree}C. Protonated pyridine, picoline, lutidine, and collidine were unresolved at this temperature, but as the temperature was raised, resolution improved. On the whole, use of CO{sub 2} as a drift gas in IMS, although inferior in some cases, should not be precluded.

Effect of temperature on the mobility of ions

The effect of temperature, between 87 and 250{degree}C, on the mobility of protonated amines in helium, air, CO{sub 2}, and SF{sub 6} was studied by ion mobility spectrometry. In helium, the reduced mobility was found to decrease as the temperature was raised, due to an increase in the collision cross section, and was approximately proportional to T{sup {minus}1/2}. In CO{sub 2}, where clustering takes place at low temperatures, raising the temperature led to an increase in the reduced mobility, mainly due to breakdown of the clusters and a decrease in the effective mass of the ion. In air, where only little clustering was observed, the reduced mobility of light ions increases with the temperature, while for heavy ions the opposite was found. In SF{sub 6}, like in CO{sub 2}, the increase of the reduced mobility with temperature was attributed to breakdown of clusters. An expression for the temperature dependence of the reduced mobility in each of these drift gases was determined semiempirically.

Effect of drift gas on mobility of ions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of drift gas on mobility of ionsZeev Karpas and Zvi BerantCite this: J. Phys. Chem. 1989, 93, 8, 3021–3025Publication Date (Print):April 1, 1989Publication History Published online1 May 2002Published inissue 1 April 1989https://doi.org/10.1021/j100345a030RIGHTS & PERMISSIONSArticle Views295Altmetric-Citations45LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (573 KB) Get e-Alerts

Lorentz angle studies for the SLD endcap Cherenkov Ring Imaging detector

In the endcaps of the Cherenkov Ring Imaging Detectors for SLD, photoelectrons drift under the influence of crossed electric and magnetic fields. The geometry of the encap design is closely coupled to the Lorentz angle in the chosen drift gas. In this report, we present recent measurements of Lorentz angles and drift velocities in gases suitable for the CRID photon detectors. We compare these measurements to predictions from a theoretical model; good agreement is observed. Based on our results we present a design for detectors operating in a 0.6 T transverse magnetic field.