Source Mass Spectrometer Research Articles

Recombination of O2+in the ionosphere

In spite of the excellent agreement between various laboratory measurements of the recombination rate of O2(+) with electrons, it is still questionable whether the laboratory results apply in the ionosphere, because although the radiative lifetime of vibrating O2(+) is not well known, indications are that it may be very long. Whether the laboratory results apply in the atmosphere depends on whether the recombination rate is dependent on the vibrational state of the O2(+) ion and on whether the ions are deactivated (or not) in both the laboratory experiments and the atmosphere prior to recombination. To obtain reliable answers to these questions, the present study was carried out to determine the recombination of O2(+) in the ionosphere from in situ measurements of the relevant temperatures and densities made by the open source mass spectrometer carried by the AE-C satellite. The photochemistry involved is discussed. The results show that the ionospheric determination of the recombination rate of O2(+) with electrons agrees with the laboratory measurements of Walls and Dunn (1974) for electron temperatures between 1200 and 2000 K.

Direct measurements of neutral wave characteristics in the thermosphere

The elliptical and circular phases of the Atmosphere Explorer-C satellite have provided the basis for a study of the neutral wave characteristics in the thermosphere using data collected by the open source mass spectrometer used to measure both reactive (O,N) and nonreactive (O2, N2, He, Ar) constituents. The phase relationships between the constituents are discussed and the results of a wave occurrence and amplitude survey covering 338 despun orbits in which the local time and latitude characteristics of the waves are presented are discussed. Conclusions based on this survey are tested in a study of waves measured at high latitudes during a geomagnetic storm.

Temperature compensation of a Hall probe for double focusing spark source mass spectrometer

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTemperature compensation of a Hall probe for double focusing spark source mass spectrometerE. F. VozenilekCite this: Anal. Chem. 1976, 48, 11, 1654–1656Publication Date (Print):September 1, 1976Publication History Published online1 May 2002Published inissue 1 September 1976https://doi.org/10.1021/ac50005a064RIGHTS & PERMISSIONSArticle Views35Altmetric-Citations1LEARN 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 (348 KB) Get e-Alerts Get e-Alerts

Vacuum lock-sample changer for a mass spectrometer

A sequentially operating vacuum lock-samples changer for use with a thermal ionization source mass spectrometer has been designed and fabricated. Insertion of removal of samples filaments, preconditioning of the sample and analysis can be carried out simultaneously, saving considerably on the total time of analysis per sample. It has been in continuous operation for a period of more than two years without any servicing.

Application of mass spectrometry to the sequencing of proteins.

SUMMARYMass spectrometry is now established as a viable method for determing the sequence of amino acids in proteins. The approach involves chemical and enzymic digestion of the protein (as in classical methods) to small peptides (ten residues) which are then chemically modified to increase their volatility. The chemical modifications are (i) acetylation of basic nitrogen sites and (ii) Permethylation. The derivatives so obtained may be sequenced in the mass spectrometer as mixtures of several peptides. This is achieved by a temperature gradient in the mass spectrometer source, which effects partial, or total separation of the derivatized peptides according to their volatilities. In this way, much tedious separation work (sometimes the rate‐determining factor in classical approaches) may be avoided. The sequencing process is carried out from the N‐terminal residue, utilizing the preferential cleavage of the ionized petide at the amide bonds; each amino acid is associated with a characteristic mass increment and thus the sequence can be determined. Mass spectrometry is especially useful in the detection and characterization of novel amino acids which might otherwise be difficult to identify. Although almost all work to date has used electron impact mass spectrometery, in the future it is possible that newer methods of ionization, such as field desorption and chemical ionization, might be profitably used.

Use of metal dendrites for aromatisation in field ionisation mass spectrometry

Samples held in the mass spectrometer source during a field ionisation experiment aromatise on the new nickel and cobalt emitters.

Atomic nitrogen densities in the thermosphere

Recently atomic nitrogen densities of ∼106cm−3 were measured at 400 km by the open source mass spectrometer on the Atmosphere Explorer‐C satellite (AE‐C). Daytime N densities ∼5 × 107cm−3 at 160 km have also been inferred from airglow and other measurements on AE‐C. We show that atomic nitrogen densities of this magnitude result in significantly lower values for the O2+ concentration than those measured on AE‐C over the altitude range to 160 to 200 km, because of the removal process O2+ + N k3 → NO+ + O. We show that the discrepancy can be explained in terms of latitudinal variations in both the N and O2 densities. We also present evidence which indicates that k3 could be as low as 1 × 10−10cm−3 at ionospheric temperatures.

ChemInform Abstract: STABILITY AND STRUCTURE OF H3CO(+) FORMED FROM COH(+) + H2 AT LOW TEMPERATURE

Chemischer InformationsdienstVolume 6, Issue 44 Physical Organic Chemistry ChemInform Abstract: STABILITY AND STRUCTURE OF H3CO(+) FORMED FROM COH(+) + H2 AT LOW TEMPERATURE KENZO HIRAOKA, KENZO HIRAOKASearch for more papers by this authorPAUL KEBARLE, PAUL KEBARLESearch for more papers by this author KENZO HIRAOKA, KENZO HIRAOKASearch for more papers by this authorPAUL KEBARLE, PAUL KEBARLESearch for more papers by this author First published: November 4, 1975 https://doi.org/10.1002/chin.197544060AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume6, Issue44November 4, 1975 RelatedInformation

Stability and structure of H3CO+ formed from COH++H2 at low temperature

The gas phase equilibrium (1) HCO++H2 = H3CO+ was studied in the temperature range −100 to −165 °C with a pulsed electron beam high pressure ion source mass spectrometer. Van’t Hoff plots of K1 led to ΔH °1 = −3.9 kcal/mole and ΔS °1 = −20.5 e.u. (stand. state 1 atm). This ΔH1 and standard thermochemical data lead to ΔHf(H3CO+) = 196.8 kcal/mole. Thus the H3CO+ formed by (1) is not protonated formaldehyde H2COH+ whose ΔHf = 169.8 kcal/mole. The reactivity of H3CO+ observed in ion molecule reactions and the theoretically predicted charge distribution in HCO+ suggest that the structure of H3CO+ is an HCO+ in which the partially positive hydrogen forms a weak three center bond with an H2. This bond is similar to, but weaker than the bond occurring between H3+ and H2 in the H5+ molecule.

Temperature dependence of bimolecular ion molecule reactions. The reaction C2H5++CH4 = C3H7++H2

The reaction C2H5++CH4 = C3H7++H2 [Reaction (1)] was observed in pure methane in a pulsed electron beam high pressure ion source mass spectrometer. The rate constants k1 determined in the temperature range 250–650 °K were found to increase with temperature. An Arrhenius plot of k1 gave a straight line which yields 6×10−13 cm3 molecule−1⋅sec−1 for the preexponential factor and 2.5 kcal/mole for the activation energy E1. At temperatures below 250 °K, Reaction (1) was gradually replaced by (8): C2H5++2CH4 = C3H9++CH4. It is concluded that both (1) and (8) proceed by the excited intermediate (C3H9+) * which may back react to C2H5++CH4, decompose to C3H7++H2, or be stabilized to C3H9+. The positive temperature dependence of (1) arises from an internal energy barrier B between the three center bonded structures: x x x x The lowest energy structure IV is formed by the addition of C2H5+ to CH4. The H2 elimination from C3H9+ must proceed via structure III. The barrier B = ΔH8+Ea(1) = 6.6+2.5 kcal/mole is larger than the barrier A for back dissociation of C3H9+ to C2H5++CH4, where A = ΔH8 = 6.6 kcal/mole. Thus at low temperature back dissociation predominates, while at higher temperatures H2 elimination becomes competitive.

Distribution function data and the electronic states for parent ion fragmentation of some simple organic compounds

Equations based on those originally derived by Hills, Futrell and Wahrhaftig are solved to evaluate the first fragmentation rate constant in the mass spectrometer source. The results so obtained are related to the distribution function for the parent ion in the source, and thus are also related to photoelectron spectra of the compound. Hence, some identification of which energy states are leading to the fragmentation at a given energy can be made. This is applied to carbon disulfide, acetone and several simple alcohols, and distribution function data curves are given for those.

Reactions of ions in excited electronic states: (N2+·)* + N2 → N3++N

The formation of N3+ ions from N2+· ions in an excited electronic state has been studied using ion cyclotron resonance (ICR) spectroscopy. By analysis of the ICR data is was possible to determine the rate constant for formation of N3+ to be k3 = 5.5±1.0×10−11 cm3 sec−1·molecule−1, the lifetime of the precursor N2+· excited state to be 1/k4>10−2 sec, and the ratio of active N2+· excited states to the remainder of the N2+· formed in the electron beam to be k2/k1 = 10±1×10−3. Comparison with previously published single source work and with optical studies of Holland and Maier indicate that at least two excited states of N2+· may be responsible for the formation of N3+ in the single source instruments, the A 2Π state (τ ≃ 6×10−6 sec) and a quartet state (τ ≥ 10−2 sec). The onset of N3+ formation in the ICR is at 22.6±0.6 eV, about 1.5 eV above the onset in the single source mass spectrometer. It is suggested the ICR onset corresponds to the onset of the active quartet state and the mass spectrometer onset to the thermodynamical onset of the N3+ ion. This analysis yields Δ Hf (N3+)=372± 4 kcal/mole.

A combined electron impact, chemical ionization, field ionization and field desorption mass spectrometer source

Detailed information about the construction and design of a combined ion source is given. By the use of an exchangeable ion exit slit for the ionization chamber the source is constructed to operate either at a source pressure of about 1 Torr for chemical ionization or at lower source pressures for electron impact ionization, field ionization or field desorption. The potentialities of this source are demonstrated by the mass spectra of a peptide as obtained with the different ionization modes.

The characteristics of an open source mass spectrometer under conditions simulating upper atmosphere flight

The characteristics of an open-source mass spectrometer designed for use on the Atmosphere Explorer satellites C, D and E were determined in a high speed molecular beam simulating upper atmosphere flight. In its normal mode of operation it was found that for CO 2 and Ar beams having speeds as great as 3.9 km sec −1 the performance closely matched that of an idealized closed source instrument. When operated in a “fly-through” mode, one in which no drawing out fields were applied to ions formed in the electron beam, the mass spectrometer rejected either residual gases or molecules which had reflected from the instrument's surfaces, and passed only incident beam molecules or ion fragments acquiring kinetic energy in the ionization process. The application as a gas analysis tool is discussed, as is the application to analyses of an ambient atmosphere by an instrument carried on a fast-moving spacecraft such as an earth satellite or planetary probe.

Micro-sample analysis by spark source mass spectrometry

The abundances of the neodymium isotopes in a 1 microgram sample of neodymium oxide have been determined using the AEI MS702R spark source mass spectrometer in order to evaluate the precision of analysis for small samples. Gold was used as the support material for the sample. Three different modes of analysis have been evaluated, namely (1) simultaneous detection of all masses on the photographic plate, (2) magnetic scanning, with electrical detection of the individual and total ion currents and recording of the individual/total ion current ratio, and (3) electrical switching between masses, with electrical detection as in (2). It is shown that satisfactory results are obtained for all three modes of analysis. The time required for acquiring the data and subsequent evaluation is discussed for each mode. The neodymium isotope abundances are calculated and compared with published values for natural neodymium.

Major and trace elements in the Allende meteorite

WE have determined major and trace element abundances for seven Ca,Al-rich aggregates, ten melilite chondrules, and an olivine chondrule and two olivine-rich aggregates from the Allende meteorite, a type III carbonaceous chondrite. Major element abundances were determined with the electron microprobe technique described by Reed and Ware1. An MS7 spark source mass spectrometer was used for the determination of trace element abundances. The technique used was that described by Taylor2 but with improved and extended data reduction techniques. The precision is about ±5% for the rare earth elements (REEs) and the accuracy about ±10%, but varies somewhat, being poorer for elements below mass number 105 than for those with higher mass numbers.

Minor and trace element distribution in melilite and pyroxene from the Allende meteorite

Melilite and pyroxene were separated from a coarsely crystalline chondrule in the Allende meteorite and analysed by microprobe and spark source mass spectrometer techniques. Elemental abundances in the bulk chondrule are consistent with a mixture of equal amounts of the two minerals, as observed microscopically. The lanthanide distributions are markedly different in the two minerals; relative to chondrite abundances, melilite shows progressive depletion of the lanthanides La-Sm, a positive Eu anomaly, and relatively constant abundances of the heavier lanthanides (Gd-Yb, and Y), whereas pyroxene shows progressive enrichment towards the heavier lanthanides, on which is superimposed a negative Eu anomaly. Both minerals, and the bulk chondrule, show unusual concentrations of the platinum metals, but the crystallographic site or sites of these metals remains to be determined.

Determination of plasma testosterone by combined gas chromatography-mass spectrometry

A rapid quantitative method has been developed for the estimation of testosterone in human male peripheral plasma using the technique of combined gas chromatography-mass spectrometry. Plasma samples are submitted to a simple extraction procedure and after forming the bromomethyldimethylsilyl ether derivative are analysed without further purification on a 50 cm 2.0% OV-1 column. Deuterium-labelled testosterone is added to the plasma as an internal standard and quantitation effected by multiple peak monitoring at low resolving power. The standard deviation of the method is 7.2% of the mean value for a determination at the level of 0.81 μg/100 ml plasma. In addition, it is shown that the method has sufficient inherent sensitivity to be applicable to the estimation of testosterone in female plasma. In an alternative technique, after a preliminary thin-layer separation, the same samples are introduced directly into the mass spectrometer source and analysed at a higher resolving power. An analysis of the limitations imposed by the purity of the stable isotope-labeled compound used as internal standard in multiple peak monitoring methods is also presented.

Gas Phase Solvation of the Ammonium Ion by NH3 and H2O and Stabilities of Mixed Clusters NH4+ (NH3)n(H2O)w

The gas phase equilibria[Formula: see text]and those leading to mixed clusters like[Formula: see text]were measured with a pulsed electron beam high pressure ion source mass spectrometer. The ion source contained pure ammonia or mixtures of ammonia and water vapor at pressures in the Torr range. Determination of the temperature dependence of the equilibrium constants led to the evaluation of ΔG0, ΔH0, and ΔS0 values for the equilibria from n = 1 to 4 and w = 1 to 5. The ΔG0 values for the NH4+(NH3)n equilibria were in good agreement with previous determinations from this laboratory. Fair agreement was observed for the ΔH0 and ΔS0 values. Comparison with the corresponding results for NH4+(H2O)w showed that the ΔHn,n−1 and ΔG0n,n−1 were larger than ΔHw,w−1 and ΔG0w,w−1. The difference was largest for the first step (1,0) and decreased progressively until a reversal with water values becoming larger occurred at the (5,4) step. The stronger hydrogen bonds of NH3 to NH4+ for low ligand numbers is explained by the greater basicity of NH3. As the ionic charge becomes dispersed and more distant stronger interactions are obtained with water which gives stronger H bonds in the absence of positive ionic charge. Breaks in the ΔHn,n−1 values indicate existence of a relatively stable NH4+(NH3)4 symmetric ion. A much smaller and less distinct break is observed with pure water ligands.The mixed ammonia–water clusters show similar effects. The addition of a NH3 molecule to a pure water ligand complex gives the strongest interaction. The addition of H2O to a pure ammonia cluster gives the weakest interaction. The above effect is strongest at lowest ligand numbers. The difference decreases gradually and becomes reversed for more than four ligands.

Ion-molecule condensation reactions in the mass spectra of arenechromium tricarbonyl derivatives

The reactions of substituted arenechromium tricarbonyl derivatives in a mass spectrometer source have been studied, and the existence of secondary ions of the types [Ar 2Cr 2(CO) 3] + and [Ar 2Cr 3(CO) 6] + confirmed. Such ions are shown to arise from ion-molecule reactions at pressures of 5 × 10 −6 to 2 × 10 −5 mmHg. Appearance potentials have been measured and used to confirm the reactant ions, and also to provide information on the fragmentation pathways of the secondary ions.