Ion Source Of Mass Spectrometer Research Articles

Ionization dynamics within the high pressure electron capture mass spectrometer; the unusual spectra of derivatized polycyclic aromatic amines and perchlorinated unsaturated hydrocarbons

A kinetic model for chemical events occurring within the high pressure electron capture mass spectrometer (HPECMS) ion source is developed which includes four different pathways by which unconventional negative ions can be produced. These routes to unusual ions include reactions of gas phase free radicals, surface-assisted reactions, ion-electron and ion-ion recombination reactions, and ion-wall neutralization. The model developed here provides a diagnostic tool useful for the elucidation of unusual HPEC spectra. Such spectra for two environmentally important classes of compounds are explained by use of the model. These compound classes include the trifluoroacetic derivatives of polycyclic aromatic amines, which have been shown to be present in materials derived from liquified coal, and the derivatives of hexachlorocyclopentadiene, which are used as pesticides. It is shown in this study that several processes, in addition to electron capture, can be operative in the typical HPECMS ion source, and that these processes can be used advantageously for the generation of informative and sensitive mass spectral signals.

Analysis of commercial waxes using capillary supercritical fluid chromatography—mass spectrometry

Supercritical fluid chromatography—mass spectrometric analyses of several commercial waxes including beeswax, bayberry wax, microcrystalline wax, Fischer-Tropsch wax, and montan wax have been performed using direct introduction of the capillary column effluent into the ion source of a Hewlett-Packard 5985B mass spectrometer. The individual wax components: high-molecular-weight esters, di- and triglycerides, carboxylic acids, alcohols, and alkanes, showed good chromatographic peak shape without requiring derivatization. Methane chemical ionization mass spectrometery yielded pseudomolecular ions and characteristic fragmentation patterns which allowed individual wax components ranging in molecular weight from ca. 300 to 1000 a.m.u. to be identified.

Investigation of the spark erosion process in spark-source mass spectrometry with an electron microprobe

The spark erosion process in the ion source of the spark-source mass spectrometer is investigated by examining particles generated from aluminium and zinc alloys in an automated electron probe microanalyzer. For the element with the lowest melting point, selective evaporation was observed. Cross-sections of the sparked surface were examined. The thickness of the molten layer was found to be of the order of a few micrometers; the layer is locally homogeneous in chemical composition.

Mass distribution of chemical species in a polydisperse aerosol: Measurement of sodium chloride in particles by mass spectrometry

A continuous, real-time method for measurement of the mass distribution of chemical species in aerosol particles by mass spectrometry is described. Individual particles of sodium chloride from a polydisperse aerosol are introduced in the form of a beam into a miniature oven (∼28 mm 3 volume) placed in the ion source of a quadrupole mass spectrometer. The oven is made from rhenium metal sheet (0.018 mm thick) and maintained at 1600 K. The intensities of sodium ions resulting from individual particles by thermal volatilization and surface ionization inside the oven are measured with the quadrupole mass spectrometer. Masses of sodium chloride particles are obtained from these intensities using a predetermined calibration curve of the mass spectrometer signal with mass. The results are corrected for the particle transmission efficiency of the beam generator used for sample introduction into the ion source, and also for inhomogeneity im radial distribution of different size particles across the beam. The number versus mass distribution is in good agreement with the distribution determined from electron microscopy of the aerosol sample collected on a nucleopore filter. The application of mass distribution measurements to the design of nebulizers and other spray devices for the dispersion of drugs and diagnostic agents is discussed.

The electron affinity of perfluorobenzene, C 6F 6

Electron transfer equilibria (1): C 6F − 6 + B = C 6F 6 + B − were determined by measuring the time dependence of C 6F − 6 and B − after a short electron pulse in a high-pressure ion source mass spectrometer. B were reference compounds with known electron affinity. Determination of the equilibrium constants K 1 leads to Δ G 0 1 and Δ H 0 1 and these, via the known EA(B), to EA(C 6F 6) = 0.52±0.1 eV. This value is much lower than the literature value due to Lifshitz et al., i.e., EA(C 6F 6) ⩾ 1.8 eV.

ChemInform Abstract: Reactions of Sputtered Copper Cluster Ions.

AbstractThe gas‐phase ion/molecule reaction products are formed by the reaction of copper Cluster ions (sputtered from metal foil) with isobutane in a novel combination highpressure/particle‐indq‐ 1 ced emission mass spectrometer ion source.

Ion/molecule reaction between sulphur hexafluoride negative ion and water under atmospheric pressure ionization mass spectrometric conditions

Reaction between SF 6 − and water to form SF 4O −1 has been observed in the ion source of an atmospheric pressure ionization mass spectrometer.

DE‐2 mass spectrometer observations relevant to the shuttle glow

A comparison of satellite mass spectrometer data from Dynamics Explorer‐2 and Atmosphere Explorer‐C and ‐D provides new evidence supporting the hypothesis that NO2 is the source of the observed continuum glow near ram‐facing surfaces of the space shuttle. Surface reactions of thermospheric N and O in mass spectrometer ion sources produce NO and NO2 in amounts highly dependent on surface temperature and composition, with direct exposure of ion source surfaces to rammed gas a necessary condition for the production of large amounts of NO2. Initial orbit data indicate that a period of surface conditioning is necessary before these odd nitrogen molecules can be produced efficiently.

Mass spectrometry with an inductively coupled plasma as an ion source: the influence on ultratrace analysis of background and matrix response

An outline is provided of the mode of operation of the atmospheric pressure inductively coupled plasma (ICP) when used as a mass spectrometer ion source. The generation of doubly charged ions and molecular peaks is discussed for the author's system in relation to the limitations they impose on trace element detection limits and on the analysis of samples with high matrix concentrations. Detection limits obtained under compromise operating conditions are shown for a range of elements in both single ion and multielement detection modes.

Real-time measurement of sodium chloride in individual aerosol particles by mass spectrometry

The method of particle analysis by mass spectrometry has been applied to the quantitative measurement of sodium chloride in individual particles on a real-time basis. Particles of known masses are individually introduced, in the form of a beam, into a miniature Knudsen cell oven (1600 K). The oven is fabricated from rhenium metal sheet (0.018 mm thick) and is situated in the ion source of a quadrupole mass spectrometer. A particle once inside the oven is trapped and completely volatilized; this overcomes the problem of partial volatilization due to particles bouncing from the filament surface. Individual particles are thermally volatilized and ionized inside the rhenium oven, and produce discrete sodium ion pulses whose intensities are measured with the quadrupole mass spectrometer. An ion pulse width of several milliseconds (4-12 ms) is found for particles in the mass range 1.3 x 10 to the -13th to 5.4 x 10 to the -11th g. The sodium ion intensity is found to be proportional to the particle mass to the 0.86-power. The intensity distribution for monodisperse aerosol particles possesses a geometric standard deviation of 1.09, showing that the method can be used for the determination of the mass distribution function with good resolution in a polydisperse aerosol.

Characterization of Bacteria by Particle Beam Mass Spectrometry

A technique is described for detecting and characterizing bacteria on a single-particle basis by mass spectrometry. The method involves generation of a particle beam of single whole cells which are rapidly volatilized and ionized in vacuum in the ion source of a quadrupole mass spectrometer. The particle beam can be generated, with minimal sample handling, from a naturally occurring aerosol or from a solution of bacteria that can be dispersed as an aerosol. The mass spectrum is generated by successively measuring the average intensities of different mass peaks. The average intensity is obtained by measuring the ion intensity distribution at the particular mass (m/e) for ion pulses from more than 1,000 bacteria particles. Bacillus cereus, Bacillus subtilis, and Pseudomonas putida samples were analyzed to test the capability of the instrument for differentiating among species of bacteria. Significant ion-intensity information was produced over the m/e range of 50 to 300, an improvement over previous pyrolysis-mass spectrometry results. The complex mass spectra contained a few unique peaks which could be used for the differentiation of the bacteria. A statistical analysis of the variations in peak intensities among the three bacteria provided a quantitative measure of the reproducibility of the instrument and its ability to differentiate among bacteria. The technique could lead to a new rapid method for the analysis of microorganisms and could be used for the detection of airborne pathogens on a continuous, real-time basis.

Characterization of Polymers by Direct Pyrolysis/Chemical Ionization Mass Spectrometry

Abstract The characterization of polymers by pyrolysis directly in the ion source of a double focusing magnetic sector mass spectrometer, operating in the chemical ionization mode, is described. Pyrolysis is achieved by two different probe techniques. A low temperature, slow heating rate direct insertion probe (DIP) is used at 400°C, and a specifically constructed high temperature, fast heating rate, high temperature pyrolysis (HTP) probe is used at 1000°C. This probe is capable of achieving pyrolysis temperatures of 1200°C at controlled heating rates up to 20,000°C/s. The mass spectrometric analysis of the pyrolysis products was achieved under chemical ionization (CI) conditions utilizing methane, isobutane, and ammonia as reagent gases. Under CI conditions the molecular ions formed in the mass spectrometer show little tendency to fragment. The CI mass pyrograms are very simple, with each peak in the spectra ascribable to a particular component in the pyrolysis product mixture. The results of the two probe pyrolysis techniques are compared and the utility of each technique for the characterization of polymers is demonstrated using the vinyl polymers polymethyl methacrylate, polyvinyl chloride, and polystyrene.

Pyrolysis-gas chromatography-photoionization-mass spectrometry, a new approach in the analysis of macromolecular materials

A Curie-point evaporation/pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) instrument is described in which a fused-silica capillary column is coupled directly both to the pyrolysis unit and to the ion source of a photoionization mass spectrometer. Photoionization by means of a rare gas resonance lamp was used as the low-energy ionization technique. The performance of the instrument was tested with a Grob test mixture at photoionization energies of 11.8 eV (Ar I) and 10.6 eV (Kr I). Photoionization mass spectra of 1-octanol, methyl octanoate, dimethylaniline and n-dodecane obtained at these energies are discussed. Py-GC-photoionization-mass spectrometry (PIMS) and PIMS data for the (1 → 4)-α-glucan amylose are presented and compared with electron impact (EI) Py-GC-MS and Py-MS results. The cumulative Ar I photoionization mass spectrum of the GC-MS data on amylose closely resembles the 14-eV EI spectrum of amylose. The method is a promising alternative to the existing low-voltage EI ionization mass spectrometry for the pyrolysis analysis of macromolecular materials.

Micro column liquid chromatography-mass spectrometry using a capillary interface

The design and performance of a capillary interface for micro column liquid chromatography-mass spectrometry are described. The total effluent 10–40 μl/min) of the micro column is fed into the ion source of a quadrupole mass spectrometer via a desolvation chamber, whereby the mobile phase provides for chemical ionization. The interface is based on a fused-silica capillary (25 μm I.D.) fitted to a removable probe. The outlet of the capillary is brazed into a bar of brass to achieve an efficient heat transfer from the heated probe tip to the mobile phase. The temperatures of the probe tip, desolvation chamber and ion source are controlled independently. A discharge tube has been installed on the desolvation chamber as an alternative to the filament. Applications to the analysis of sugars, antioxidants and pharmaceuticals are presented.

Coupling a quadrupole mass spectrometer and a Fourier transform mass spectrometer

Experiments performed by the authors during the last year have demonstrated the feasibility of a new analytical instrument called a tandem quadrupole-Fourier transform mass spectrometer (QFT-MS). Ions made in the source of a quadrupole mass spectrometer are extracted and focused into a beam. The ion beam is then injected axially into a superconducting electromagnet where the ions are stored in an analyzer cell and detected by Fourier transform mass spectrometry (FT-MS). The goal of this project is to combine the highly developed chromatographic and sample ionization features of a quadrupole mass spectrometer with the versatility and high mass resolution that is available with Fourier transform detection. High mass resolution is possible because differential pumping separates the ion source of the quadrupole mass spectrometer from the analyzer cell of the FT-MS instrument. A novel method is described for efficiently injecting ions axially into the solenoidal magnetic field. The QFT-MS instrument has many features in common with triple quadrupole mass spectrometers but with QFT-MS, much higher mass resolution is possible. For example, a mass resolution of 140 000 is demonstrated for m/z 78 ions produced by collision-induced dissociation of bromobenzene molecular ions.

Flow tube studies of reactions of cyanogen with ions selected from cyanogen

The selected-ion flow tube (SIFT) technique has been applied at 296±2 K to a study of the ion chemistry of cyanogen, C 2N 2, initiated by the ionization of C 2N 2. The ions are derived from C 2N 2 in a separate source and are then allowed to react with C 2N 2 essentially in isolation. All of the ions N +, N 2 +, C +, C 2 +, CN +, C 2N + and C 2N 2 + were observed to react rapidly with C 2N 2 with nearly unit efficiency. The reaction paths were of a varied nature and led to the product ions C 2N +, C 2N 2 +, C 3N +, C 4 +, N 3 + and CN 2 +. Addition of C 2N 2 was a predominant feature of the secondary ion chemistry which established polymeric ions of the type (C 2 n N 2 n−4 ) + with n = 2 and 3, (C n+2 N n ) + with n = 2 to 5, (C 2 n N 2 n−1 ) + with n = 2 and 3, and (CN) n + with n = 3 to 6. The results are compared with previous mass spectrometer ion source measurements at lower pressures and with mass spectra obtained for the electron-induced radiolytic polymerization of C 2N 2. Their relevance to the ion chemistry in the atmosphere of Titan is also discussed briefly.

Chemical ionization mass spectrometric determination of boron-10 in enriched boron

A chemical ionization mass spectrometric method determination /sup 10/B in enriched boron was developed and investigated. Boric acid and methanol were reacted to form volatile methyl borate which was directly introduced into the ion source of a quadrupole mass spectrometer. Methyl borate was ionized by reaction with methane and methanol ions. The /sup 10/B content was determined for the measured /sup 11/B//sup 10/B ratio by using the (CH/sub 3/O)/sub 3/BH/sup +/ ion and a mass spectrometer calibration factor based on the National Bureau of Standards (NBS) SRM 952 boron isotope standard. The precision of the chemical ionization mass spectrometric method is comparable to thermionic emission methods. The relative standard deviation on replicate samples did not exceed 0.009% for the 95% enriched /sup 10/B samples. The analytical results from 96 enriched boron powder samples were compared by using both thermionic emission and chemical ionization mass spectroscopy. The standard error of the difference between paired samples was less than 0.097 across the range of 96 samples. The analysis time is typically less than 10 min per sample. 28 references, 9 figures, 2 tables.

Improvements of a shock tube coupled with a mass spectrometer for reaction studies

A pressure relief valve has been constructed which improves the ability to study fast reactions behind reflected shock waves, using a shock tube coupled with a time-of-flight mass spectrometer. This possibility is interesting, especially in order to study different reaction mechanisms depending on the pressure range. The valve, installed on the shock tube, allows a fast pressure decrease in the shock tube and, consequently, in the mass spectrometer ion source, after the observation of the concentration changes of the reacting mixture. A study has been made with this apparatus of the oxidation reaction of the stoichiometric mixture of methane and oxygen diluted in argon over a wide temperature range. Some results of this preliminary study are reported, in order to confirm the reliability of this original apparatus.

Photodissociation of Cl 2+, Br 2+ and I 2+

The photodissociation spectra of Cl 2 +, Br 2 + and I 2 + have been recorded over the range 1.80–2.55 eV. Vibrational structure resolved in the photodissociation spectra indicates that a predissociation mechanism is involved in the dissociation of these ions. The most likely pathway involves population of vibrational levels of the B̃ 2 Σ g + state via photoinduced transitions from vibrational levels of the à 2Π u state, which are in turn populated by electron impact ionization of the corresponding molecules in the mass spectrometer ion source. The B̃ 2 Σ g + state levels then predissociate, probably by curve crossing, giving rise to electronic predissociation. Based on sensitivity factors and the estimated transit time for ions formed in the mass spectrometer ion source to reach the photon interaction region, the lifetime of the à 2Π u state must be approximately 1–10μs.

An improved high-pressure, temperature-variable ion source with coaxial electron beam/ion exit slit

A new mass spectrometer ion source has been developed to study high-pressure ion molecule kinetics and equilibria as a function of temperature. Unlike conventional mass spectrometer sources, the present source has coaxial electron entrance and ion exit apertures. Ions move through the source at a constant velocity due to the presence of a constant drift potential gradient. Low drift fields are used to minimize non-thermal conditions. The effect of the field on ion energy is discussed. As both a demonstration and a test of the source operation, mobilities of ions in gases were studied as a function of drift field, pressure and temperature. Good agreement was obtained with previously reported mobility measurements. The ternary association reaction N 2 + + 2N 2 → N 4 + + N 2 and the equilibrium CO 2 + + 2CO 2 ⇆ (CO 2) 2 + + CO 2 were also investigated as a function of temperature and pressure. Again, good agreement between literature values and these experiments was obtained.