Magnetic Mass Spectrometer Research Articles

Detecting singly charged ions during field evaporation of tantalum at high temperatures

The field evaporation of tantalum from point emitters in a broad range of temperatures from T = 300 to 2500 K was studied using a static magnetic mass spectrometer equipped with a special field ion source. The room-temperature mass spectrum of field-evaporated particles displayed only the peaks of triply charged ions (Ta3+). As the temperature was increased, the charge of field-evaporated ions exhibited a decrease: at T ∼ 1000 K, the peaks of doubly charged ions (Ta2+) prevailed. The peaks of singly charged ions (Ta+) were detected for the first time at temperatures in the interval 1900 K < T < 2500 K. The rate of evaporation of singly charged tantalum ions was several orders of magnitude lower than that of doubly charged ions.

Hydration of gas-phase protonated alkylamines, amino acids and dipeptides produced by electrospray

Abstract An electrospray ionization ion source is described that produces ions continuously at 1 atm and introduces them into a temperature-variable reaction chamber in the pulsed mode where the ion–molecule equilibria can be determined in the gas phase at 10 mbar. Technical aspects and operating parameters of the technique are presented. The equilibrium constants for the hydration reactions B + (H 2 O) n −1 + H 2 O = B + (H 2 O) n , where B + = (CH 3 ) 2 NH 2 + , C 2 H 5 NH 3 + , n -C 4 H 9 NH 3 + , GluH + , MetH + , ValH + , (Glu-Met)H + and (Met-Glu)H + , were determined with a magnetic mass spectrometer, and the thermochemical properties, Δ H n − 1 , n ∘ , Δ S n − 1 , n ∘ and Δ G n − 1 , n ∘ , for these reactions were determined and discussed. The results obtained with the present technique for protonated alkylamines are compared with previously published values, demonstrating the usefulness of this technique for quantitative measurements of the gas phase ion thermochemistry based on ion–molecule equilibria. A correlation between the free energy changes for the attachment of the first water molecule to the protonated amino acids and the corresponding gas-phase basicities is obtained.

High-resolution mass spectra of the residual gas in a metallic vacuum system

The mass spectra of the residual gas in a metallic vacuum chamber of capacity 3 l are studied with an MI-9303 high-resolution magnetic resonance mass spectrometer in the mass range 1–140 u. The experiments are carried out under four evacuation conditions in the pressure range P = 10−8–10−10 Torr, and almost all the mass peaks forming multiplets are resolved. It is shown that the multiplets with mass numbers M≤80 have, as a rule, a multicomponent structure and hydrogen is the basic component responsible for the total pressure in the chamber irrespective of evacuation conditions. Next in order of intensity in the mass spectra are, CH4+, H2O+, CO+, and CO2+ peaks. Other lines in the residual gas spectra are largely due to various C-, H-, N-, and O-based compounds. In addition, the background mass spectrum involves Cl-and F-based compounds and noble gas isotopes. The multiplets with M > 80 often degenerate into a single hydrocarbon line.

Absolute Total (Counting) and Charge-Separated Partial Cross-Sections for Electron Impact Ionization of La, Pr, Ho, Tm, and Lu Atoms

Electron impact ionization of La, Pr, Ho, Tm, and Lu Atoms has been studied through measurements of absolute total (apparent σ a and counting σ c ) and charge-separated partial cross sections σ q + ( q =1–4) from the single ionization thresholds to 900 eV. The absolute and partial measurements were done using an electron–atom crossed beam apparatus and a magnetic deflection mass spectrometer, respectively. After a brief discussion on the present results, an overall discussion is made in more compact form on the cross-section results for 13 lanthanide-atom species including those for the 8 species treated in our previous studies. It is confirmed that the atoms having a 5 d electron (La, Gd, and Lu) provide larger single-ionization cross sections and thereby larger σ c values and larger population of singly-charged ions. It is also confirmed that resonance-like feature starting around the 4 d limits is observed in the σ 3+ curves for lighter lanthanide atoms. This phenomenon, observed for the first time for...

Endohedral Encapsulation of Lithium in C&lt;sub&gt;70&lt;/sub&gt;

A new diatomic molecule-containing endohedral fullerenes were prepared by ion implantation technique (introducing negatively charged C70 into a low temperature lithium plasma column by a strong exial magnetic field).The species prepared were Li@C70 and Li2@C70 and ionized by surface ionization. Their existance was demonstrated through high sensitivity, magnetic mass spectrometer. The corresponding endohedral ions undergo the Rice shrinkwrap mechanism: a mass –analyzed ion spectrum demonstrates the loss of a C2 unit from the cage. The observed ionization energies of endohedral molecules were 5.1 " 0.1 eV and 5.3 " 0.1 eV, respectively.

Ionic fragmentation of deep core-level (Cl1s) excited chloroform molecule

The ionic fragmentation of the chloroform (CHCl 3 ) molecule has been studied along the Cl1s edge, using synchrotron radiation and a magnetic mass spectrometer. The following cations were observed: Cl + , Cl 2+ , CCl + , CCl 2 + , CHCl + , Cl 3+ , H + and C + . While all ions are seen to be formed at the intense resonance which dominates the photoabsorption spectrum below the chlorine 1s edge (taken to occur at 2828.6 eV), the probability of observation of the CHCl + , C + and Cl 3+ cations is seen to significantly decrease above the ionization edge.

Lead isotope ratio measurements in geological glasses by laser ablation-sector field-ICP mass spectrometry (LA-SF-ICPMS)

We have tested the capabilities of LA-SF-ICPMS for in situ Pb isotopic work on geological glasses using a 213 nm Nd:YAG laser system and a double focusing magnetic sector field ICP mass spectrometer. Experiments were done with the MPI-DING and USGS reference glasses, USGS rock powders molten as glass beads and basaltic glasses from Hawaii. In particular, the precision and accuracy of 208 Pb/ 206 Pb and 207 Pb/ 206 Pb ratios were investigated for three-spot analyses of glasses with different Pb contents (0.4–40 μg/g) at spot sizes of 12–160 μm. Using the fast and precise electrical scan mode, we obtained for samples with Pb concentration >1 μg/g in-run precisions (1 R.S.E.) of better than 0.1% and 0.2% for spot diameters of 120 and 40 μm, respectively. The LA-SF-ICPMS isotope ratios agree with the high-precision TIMS and MC-ICPMS data within the external precision (R.S.D. = 0.1–0.2%). The LA-SF-ICPMS results for 208 Pb/ 204 Pb, 207 Pb/ 204 Pb and 206 Pb/ 204 Pb are less precise (about 0.5–1%) due to the low abundance of 204 Pb and correction from the 204 Hg interference. In this paper, we present the first LA-SF-ICPMS Pb isotope data for the MPI-DING (KL2-G, ATHO-G) and USGS reference glasses (BCR-2G, BHVO-2G) which may be useful for microanalytical in situ Pb isotope analysis. The findings of small (<2%), but significant differences in Pb isotope ratios of Hawaiian glasses of different ages, demonstrate that LA-SF-ICPMS is a suitable tool for geochemical research.

The possibilities of a mass spectrometer equipped with a Llewellyn inlet system in the analysis of air and water samples

The design of a multimembrane inlet system, in which the method proposed by Llewellyn for enriching gases (through the addition of volatile organic components and certain other gases) for purposes of chromatography/mass spectrometry is described. A mechanism that enables one to obtain an enrichment effect of ∼106 for a considerable group of compounds in the process of analyzing air and water samples, supplied to the mass spectrometer through the proposed inlet system, is considered. The results are given from the experimental verification of the inlet system operating as part of a portable magnetic mass spectrometer.

Characterization of ion species mix of the TEXTOR diagnostic hydrogen beam injector with a rf and arc-discharge plasma box

The ion specie fractions of the diagnostic hydrogen beam of TEXTOR tokamak have been determined by making use of a Hα-light Doppler shift spectroscopy and alternatively by a magnetic mass spectrometer. The measurements were done for the fixed beam energy of 50 keV and beam current variable up to 2.5 A. According to the measurements, the full energy beam component is for a radio frequency plasma box ∼50% by the particle density and more than 75% for an arc-discharge plasma box.

Integration test of a miniature ExB mass spectrometer with a gas chromatograph for development of a low-cost, portable, chemical-detection system

We present preliminary test results for the integration of a miniature crossed electric and magnetic field mass spectrometer (MS) and a small commercial gas chromatograph (GC). We targeted the experiments to identify design variables for the next generation of field-portable low-cost micro-GC–MS instruments to be developed at Lawrence Livermore National Laboratory for identification of chemical warfare agents (CWAs) and, specifically, to evaluate the potential usage of the commercial version of the compact double-focusing MS (CDFMS) as the detector component.

Surface ionization of the lanthanides

Abstract The surface ionization of Lanthanides: Ce, Pr, Nd, Sm and Eu, and its fluctuations (noises) have been studied using a double filament ion source in a 90° magnetic mass spectrometer. Using the Saha-Langmuir equation there were measured ionization potentials of LnO molecules as the dissociation products of the oxides Ln 2 O 3 (the Ln symbol denotes the arbitrary rare earth elements: Ce, Pr, Nd, Sm, Eu). Ionic desorption energies of LnO molecules were determined using the fluctuation (noise) method.

Sputtering with polyatomic ions: revisiting kinetic energy distributions of secondary ions

Anew more accurate data processing procedure for calibration of kinetic energies of secondary ions measured in magnetic sector secondary ion mass spectrometers has been developed. The procedure was applied to reprocessing of raw data from previously published measurements of kinetic energy spectra of secondary atomic and cluster ions sputtered from Ta by 6 keV/atom Au � ,Auand Auprojectiles. Absolute energies of the sputtered Ta þ ions were determined more accurately, which permitted a fairer comparison of energy spectra for the same secondary ions measured under bombardment with different primary ions. Most probable and mean energies were determined for the sputtered ions, and their energy spectra were converted into distributions over inverse velocities. The reprocessed experimental results revealed strong differences between results for atomic and diatomic ions and those for larger cluster ions (consisting of more than seven atoms). In particular, the comparison of atomic and polyatomic bombardment showed that there are strong differences between atomic and diatomic sputtered species, while there were almost no changes between larger sputtered clusters. Results are discussed in terms of observed enhancements under polyatomic ion bombardment for the total sputtering efficiency and the ionization of sputtered species.

Field gas chromatography–mass spectrometry for fast analysis

The objective of this presentation is to demonstrate the original device and procedure for fast gas chromatography-mass spectrometry (GC-MS) analysis of gaseous and liquid samples and to discuss its features and capabilities. The concept was developed in order to expand the range of compounds suitable for GC separation and to reduce the time of analysis. Field GC-MS, consisting of original "concentrator-thermodesorber" (CTD) unit, multiple module GC system and compact magnetic mass spectrometer with powerful two-stage vacuum system and multicollector ion detector, is represented. The whole weight of the device is 90 kg. Power consumption is 250 W. The device and analytical procedures allow high speed screening of toxic substances in air and extracts within 100 s per sample. The examples of applications are described, including fast screening of tributyl phosphate (TBP) in air at low ppt level at the rate 1 sample/min.

Intercomparison study on accurate mass measurement of small molecules in mass spectrometry

The results from an intercomparison of accurate mass measurement of a small molecule (molecular weight 475 Da) across a broad range of mass spectrometers are reported. The intercomparison was designed to evaluate the relative capabilities and the optimum methodology of the diverse range of mass spectrometers currently used to record accurate mass measurements. The data will be used as a basis for developing guidance on accurate mass measurement. The need for guidance has resulted from the continued growth in the use of accurate mass measurements for assignment of elemental formula in the chemical and biochemical industries. This has been fuelled by a number of factors and includes the rapid pace of instrument development, which has enabled accurate mass measurements to be made in a less costly, yet robust fashion. The data from the intercomparison will allow us to compare those protocols that produced excellent accuracy and precision with those that produced poorer accuracy and/or precision for each type of mass spectrometer. The key points for best practice will then be established from this comparison for each type of mass spectrometer and accurate mass measurement technique. A compound was sent to the participating laboratories (in the UK, Europe, and USA), the identity of which was not revealed. Each laboratory was asked to record a minimum of five repeat mass measurements of the molecular species using their local protocols and their preferred ionization technique or techniques. To the best of our knowledge there were no interfering (unresolved) ions that originated from the sample. A questionnaire was also completed with the experimental work. The information from the questionnaires was used to evaluate the protocols used to record the measurements. Forty-five laboratories have reported their results. To summarize the performance of mass spectrometers in the intercomparison, magnetic sector field mass spectrometers used in peak matching mode and FTMS reported the highest mean mass measurement accuracy (88 and 83%, respectively, achieved < or =1 ppm). Magnetic sector field mass spectrometers used in voltage scanning produced 60% of the mean mass measurements with accuracy < or =1 ppm. Magnetic sector field mass spectrometers used in magnet scanning modes, quadrupole-TOF and TOF instruments generally achieved mean mass measurement accuracy between 5 and 10 ppm. The two low resolution triple quadrupoles used in the inter-comparison produced mean mass measurement accuracy of <2 ppm. The precision of the data from each instrument and experiment type is an important consideration when evaluating their relative capabilities. Using both the precision and accuracy, it will be possible to define the uncertainty associated with the elemental formulae derived from accurate mass measurements. Therefore, a thorough statistical evaluation of the data is underway and will be presented in a subsequent publication.

Kinetic-energy release in Coulomb explosion of metastable C3H52+

C 3 H 5 2+ , formed by electron impact ionization of propane, undergoes metastable decay into C2H2++CH3+. We have monitored this reaction in a magnetic mass spectrometer of reversed geometry that is equipped with two electric sectors (BEE geometry). Three different techniques were applied to identify the fragment ions and determine the kinetic-energy release (KER) of spontaneous Coulomb explosion of C3H52+ in the second and third field free regions of the mass spectrometer. The KER distribution is very narrow, with a width of about 3% [root-mean square standard deviation]. An average KER of 4.58±0.15 eV is derived from the distribution. High level ab initio quantum-chemical calculations of the structure and energetics of C3H52+ are reported. The activation barrier of the reverse reaction, CH3++C2H2+ (vinylidene), is computed. The value closely agrees with the experimental average KER, thus indicating that essentially all energy available in the reaction is partitioned into kinetic energy.

Collision efficiency in an electrospray source interfaced with a magnetic mass spectrometer

The collision efficiency in two distinct areas of an electrospray ion source has been compared on the basis of diagnostic ion intensities related to the voltages applied on three different lenses. The dissociation of covalent or non-covalent bonds and the shift of the charge state distribution of multiple-charged protein ions were used as indicators of the internal energy amount acquired by collisional activation. The results show that, for a given voltage difference between two successive lenses on the ion beam axis, the more efficient collision-induced dissociation processes are observed after the skimmer and not before. Although the enhancement of the fragmentation rate by increasing the skimmer voltage could be accompanied by a loss of sensitivity, this procedure should be of interest for analytical purposes.

Methods for Estimating Theoretically the Influence of Ion Scattering and Reflection on the Isotopic Sensitivity of Static Magnetic Mass-Spectrometers

For purposes of optimizing ion-optical systems, analyzer construction, and pump placement in static magnetic mass-spectrometers for isotopic analysis of uranium compounds, a comparative analysis is made and a review is given of methods described in the literature for theoretical estimates of the influence of scattering and reflection of ions on the isotopic sensitivity. Conclusions which make it possible to solve the problem are drawn.

The LEDA512 integrated circuit anode array for the analog recording of mass spectra

This article describes two generations of a novel integrated circuit multi-anode electron detector chip (LEDA512). This chip is designed for usage as an analog ion detector in magnetic mass spectrometers, in combination with a stack of two micro channel plates. The first generation chip is applied in a positive ion mass spectrometer on-board the ESA ROSETTA cometary mission. The detector chip comprises two identical and redundant parts, each consisting in a row of 512 rectangular anodes for electron collection, and in an anode multiplexer followed by a charge amplifier. A second-generation of the chip is scheduled. It will implement additional features, such as: radiation hard MOS transistors and shift registers and improved output drive capabilities.

The Ion-optical scheme of a portable mass spectrometer

An ion-optical scheme for a portable magnetic double-focusing mass spectrometer that makes it possible to analyze several components simultaneously over a wide mass range (the mass-spectrograph operating mode) is proposed. This scheme effectively solves the research and technological problems involving the analysis of rapidly varying compositions.

Definitive characterization of some C 5H 5N ·+ and C 6H 7N ·+ radical cations by associative ion–molecule reactions

Abstract Isomeric C 5 H 5 N ·+ and C 6 H 7 N ·+ radical cations were allowed to interact with various neutral reagents in the quadrupole collision chamber of a six sector magnetic deflection type tandem mass spectrometer. Using CH 3 SSCH 3 , CH 3 OH, or H 2 O, iso-C 3 H 7 I, and tert-C 4 H 9 NC as substrates, specific associative ion–molecule reactions occur whose products were analyzed in a subsequent high energy collision induced dissociation experiment. Differentiation between ionized pyridine and its 1,2-H shift isomer is readily achieved with each of the four substrates as the latter C 5 H 5 N ·+ ion exhibits a radical-type reactivity characteristic of its distonic character. An unambiguous structure characterization of the C 6 H 7 N ·+ ions, namely ionized 2-methylpyridine, the N -methylene pyridinium ylide ion, the 2-methylene-1-hydropyridine ion, and the N -methyl-2-dehydropyridine radical cation, is realized when all of the above substrates are used in the analysis.