Probe Mass Spectrometer Research Articles

Rapid Tryptic Mapping Using Enzymically Active Mass Spectrometer Probe Tips

A method has been developed for rapid, sensitive, and accurate tryptic mapping of polypeptides using matrix-assisted laser desorption/ionization time-of-flight mass analysis. The technique utilizes mass spectrometer probe tips which have been activated through the covalent immobilization of trypsin. The enzymatically active probe tips were used for the tryptic mapping of chicken egg lysozyme and the results compared with those obtained using either free trypsin or agarose-immobilized trypsin. A significant increase in the overall sensitivity of the process was observed using the active probe tips, as well as the production of more characteristic proteolytic fragments and the elimination of background signals due to the autolysis of the trypsin. Further, probe tip digestions were found to be rapid and convenient.

Mechanisms for polycrystalline silicon defect passivation by hydrogenation in an electron cyclotron resonance plasma

An in-line mass spectrometer and Langmuir probes have been employed to examine mechanisms of plasma immersion hydrogen passivation of grain boundary defects in polycrystalline silicon thin film transistors. Relative fluxes of H+ and H+2 as well as total ion current density were measured at the substrate location in an electron cyclotron resonance hydrogen discharge. Measurements were made over a range of operating conditions over which passivation rates have been shown to vary dramatically. Data presented show a strong correlation of both H+ flux and ion bombardment energy with good transistor performance obtained at operating pressures below 1 mTorr. This suggests that discharge operating conditions that promote dissociation of H2 to form H and H+ (which may diffuse more rapidly through solid material than H2), as well as increased sheath voltages and therefore ion energy at the substrate, are important to obtaining acceptable process rates.

FALP and CRESU studies of ionic reactions

Results obtained from the study of ionic reactions at the University of Rennes are reviewed. A brief description of the apparatus available in our laboratory is given. The historical evolution of the flowing afterglow device is emphasized as it is directly connected to one of the major puzzling questions in dissociative recombination studies: what is the rate coefficient for the dissociative recombination of H 3 + in its ground state? Special attention is given to the dissociative recombination process which until recently was the main topic studied in Rennes. A compilation of our measurements of branching ratios and rate coefficients is presented. Results from other authors are also outlined with particular attention paid to H 3 +. Electron attachment and ion/molecule reactions studied with the flowing afterglow Langmuir probe mass spectrometer are presented. The first results of ion/molecule reactions at very low temperatures have been recently obtained with the CRESU apparatus available in Rennes. Comparison with measurements carried out in Meudon at lower pressures is made and discussed.

Detection of [FORMULA][F][RM]H[/RM][INF]2[/INF][ZW][SUP]18[/SUP][RM]O[/RM][/F][/FORMULA] in Jupiter

We report the detection of a single line of H218O in Jupiter at 1980.76 cm-1, the first detection of 18O in Jupiter. Models of the spectrum of Jupiter near this line imply that the Jovian isotopic abundance ratio 18O/16O is 1-3 times the terrestrial value. It is not possible to distinguish between the terrestrial ratio and highly anomalous oxygen isotope ratios of 2 or 3 times terrestrial because of the difficulties in modeling the spectrum and our reliance on a single H218O feature. Anomalous 18O in Jupiter could be caused by an intrinsic oxygen-isotope heterogeneity between solid and gaseous reservoirs in the preplanetary nebula, although given the constancy of 16O/18O in other solar system objects, such an explanation seems unlikely. Neither the isotopic anomalies in individual meteorite grains nor the differences in isotopic ratios between those in the solar system and in the interstellar medium would explain a gross enhancement of 18O in the outer solar system. The Galileo Probe Mass Spectrometer experiment may not allow a more accurate abundance determination of H218O because of the much larger amount of interfering 20Ne that may be present. It appears that no lines of H217O are detectable in the 5 μm window.

Reaction of anthracene with atomic ions of interstellar interest. A FALP measurement at room temperature

We present the results obtained on studying the reaction of anthracene with some atomic ions of interstellar interest (He + and C +) and with Ar +. Rate coefficients have been measured at room temperature (293 K) in afterglow experiments using flowing afterglow Langmuir probe-mass spectrometer apparatus. Reactions proceed with rate coefficients of respectively 5.2 × 10 −9, 3 × 10 −9, 1 × 10 −9 cm 3 s −1 for He +, C + and Ar +. The results were obtained with an uncertainty of about 30% and were found to be close to the Langevin rate. The nature of the products has also been investigated. More particularly, the evidence for carbon accretion and for the production of doubly charged species is discussed.

Mass spectrometric and electrostatic probe measurements of N2/O2 plasma flow

Plasma wind tunnels are used at the Laboratoire d'Aerothermique at Meudon to simulate the different parameters of the gas surrounding the surface of space vehicles during hypersonic flight in the upper atmosphere. In the present work, mass spectrometric and double electrostatic probe measurements in a stagnation point are performed in N2/O2 plasmas. Axial distributions of electron density and temperature are obtained from the fit between experimental data and Laframboise expression for the double cylindrical probe current. Neutral and ion distributions are measured by mass analysis for different axial positions, and are then compared with a chemical model for air, in order to evaluate the dominant reactions in the plasma flow.

Micropore membrane inlet mass spectrometer probes suitable for measurement of tissue surface gas tensions

AbstractNew membrane inlet mass spectrometer (MIMS) probes are described that feature a micropore in a flat metal surface filled with a polymer membrane (Krytox high‐vacuum fluorinated grease). In vitro assessment of spatial resolution, time response, stirring effect and calibration are reported. The small membrane area for this MIMS results in spatial resolution of about 30 μm, adequate for measuring gas tensions at an exposed tissue surface in experimental studies of tissue oxygenation and tissue gas exchange. These probes offer a unique combination of minimal stirring effect and rapid response speed for measurements of gas partial pressures in the per cent range in aqueous solutions. Several gases, including oxygen, carbon dioxide, helium, sulfur hexafluoride and argon, permeate the polymer membrane to give a detectable signal, and the membrane is highly impermeable to water. Membrane dimensions were calculated from time response characteristics and the measured gas sample rate for argon. The membrane area was independently confirmed by direct assessment of spatial resolution. This MIMS is highly linear, has an excellent signal‐to‐noise ratio and offers practical advantages over electrode approaches to the measurement of gas tensions in aqueous solution.

Direct Mass Spectrometric Analysis of Glycosphingolipid Transferred to a Polyvinylidene Difluoride Membrane by Thin-Layer Chromatography Blotting

A simple, rapid method for the analysis of glycosphingolipid that combines "thin-layer chromatography (TLC) blotting" and mass spectrometry is reported. Glycosphingolipids developed by TLC were transferred to a polyvinylidene difluoride membrane by TLC blotting, after which the glycosphingolipid band on the membrane was excised and placed on a mass spectrometer probe tip, and a few microliters of triethanolamine was added as the matrix. The sample was analyzed by secondary ion mass spectrometry. About 1 μg of glycosphingolipid subjected to TLC can be analyzed. The major advantage of this method is that glycosphingolipid can be analyzed structurally without purification by repeated column chromatography.

Peptide characterization using bioreactive mass spectrometer probe tips

A method has been developed for the rapid and sensitive mass spectrometric characterization of peptides. The approach uses bioreactive mass spectrometer probe tips, incorporating covalently bound enzymes, which are capable of modifying biomolecules for analytical purposes. In the demonstrated cases, enzymatic proteolysis is initiated upon application of analyte to the probe tips, time is allowed for digestion, and the products are analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The probe tips have been used for proteolytic mapping and partial sequence determination of picomole quantities of peptide. Analysis times were approximately 30 min. Two methods of database search were utilized. The first used limited peptide sequence information and parent molecular weight, while the second used exclusively the molecular weights of a number of endoproteolytic fragments. A simple method of comparing the match of experimental data for a tryptic digest with the results of a search is described.

Electron attachment to anthracene. A FALP measurement of the rate coefficient at room temperature

The rate coefficient β for electron attachment to anthracene has been measured at room temperature using a flowing afterglow Langmuir probe mass spectrometer. A value of 1 × 10 −9 cm 3 s −1 (30% uncertainty) was found, indicating that an activation energy barrier might exist.

Intra-vascular oxygen sensors for neonatal monitoring

The following topics are discussed: clinical background; catheter-tip sensors; transport of O/sub 2/ in blood; principles and construction of O/sub 2/ sensors; electrochemical O/sub 2/ measurement; mass spectrometer probes; optical O/sub 2/ sensors; in vivo use; clinical experience; problems of sensors in clinical use; hemocompatibility (blood-polymer interactions); future prospects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Atomic-Level Studies of Processes on Metal Surfaces

An atomic-level understanding of surface phenomena is becoming increasingly important as materials scientists and engineers begin to fabricate new materials by controlling their growth at the nanometer or subnanometer scale. Recent advances in molecular beam epitaxy and chemical vapor deposition make it possible to assemble a crystalline solid or epitaxial overlayer literally one atomic layer at a time. The need to characterize the structure and composition of these complex materials in finer and finer detail has forced the traditional analytical tools (e.g., electron microscopy) to strive for better and better spatial resolution. It has also generated a virtual explosion in the proliferation of scanning probe microscopies inherently capable of viewing surface structure at the atomic level. This same need has recently rekindled an interest in the technique that first allowed scientists to view a solid surface in atomic detail: the field ion microscope (FIM). The unique attributes of this instrument and its successor, the atom probe mass spectrometer, make it possible to observe individual atoms on a solid surface, to remove atoms from the surface one atomic layer at a time, and to determine the chemical identity of the atoms as they are removed. The close match between these capabilities and the requirements of modern-day materials analysis have stimulated renewed efforts to use the FIM to gain fundamental insight into materials problems. This article discusses a few selected applications of the FIM, individually and combined with the atom probe, to phenomena occurring at the surface of solid materials.

Combined 13C NMR- and mass-spectrometry for non-invasive monitoring of metabolism

A method for the long-term incubation of cell suspensions at measured dissolved gas concentrations during acquisition of NMR spectra is described: a mass spectrometer probe in the cell suspension provides continuous monitoring of gases. Its usefulness is shown for Trichomonas vaginalis where fermentation products from glucose in 72 μM O2 are different from those under strictly anaerobic conditions.

Rapid analysis of occluded Pr2NH in the AlPO4-11 and VPI-5 molecular sieves by direct mass spectrometry

The aluminophosphate molecular sieves AlPO4-11 and VPI-5 have been prepared in the presence of dipropylamine (Pr2NH), a structure-directing organic incorporated into their synthesis gels. The AlPO4-11 molecular sieve's unidimensional channel system contains occluded Pr2NH, detected by TG, in its straight channel structural voids; VPI-5 contains no significant amount of Pr2NH (also determined via TG). The as-synthesized Pr2NH-AlPO4-11 was placed in a mass spectrometer probe (ca. 0.1 mg), which was evacuated to ca. 10–6 mbar and heated at 2 °C s–1, and its cracking pattern analysed with time. The Pr2NH cracking pattern was observed from ca. 275 °C and above, peaking at ca. 350 °C. This is assigned as Pr2NH removed from the AlPO4-11 channel system during the direct mass-spectrometric analysis. Trace amounts of Pr2NH were also observed from the as-synthesized VPI-5. For each material, the above results also indicated that the Pr2NH was unprotonated. Thus, temperatureprogrammed mass spectrometry proves to be a rapid method for the qualitative analysis of guest molecules in molecular-sieve hosts.

Galileo Probe Mass Spectrometer experiment

The Galileo Probe Mass Spectrometer (GPMS) is a Probe instrument designed to measure the chemical and isotopic composition including vertical variations of the constituents in the atmosphere of Jupiter. The measurement will be performed by in situ sampling of the ambient atmosphere in the pressure range from approximately 150 mbar to 20 bar. In addition batch sampling will be performed for noble gas composition measurement and isotopic ratio determination and for sensitivity enhancement of non-reactive trace gases.

Mass spectrometric study of simple olefinic flames: Comparison with laser diagnostics of C2H4/O2/Ar flames at 20 torr

AbstractA new research apparatus for characterization of low‐pressure premixed flames has been developed. This instrument incorporates several spectral techniques in one apparatus so that various diagnostic techniques can be quantitatively compared and the usable detection range expanded. Features include detection by mass analysis with a triple quadrupole mass spectrometer and by laser techniques such as laser‐induced fluorescence. Temperature profiles of the flame both with and without the mass spectrometer probe were obtained by thermocople. Concentration profiles of the highly reactive flame species H˙, O, and OH˙ were obtained and compared.

Rate measurements for the reaction of H-atoms with the xenon and krypton fluoride molecules.

Elementary strongly exothermic reactions of H-atoms with the F 2, KrF 2, XeF 2, XeF 4, XeF 6 molecules useful for chemical lasers have been investigated by mass-spectrometric probing of the diffusion cloud in flow [1] . Some ionisation and appearance potentials were defined [2] from experimental ionization efficiency curves. Arrhenius expressions were obtained for the rate constants between 298–505 K. They correspond to an activation energy of 8.9± 0.6; 11.3±0.2; 21.8±2; 22.6±5; 28.5±3.8 kj/mol for the H + F 2, KrF 2, XeF 2, XeF 4, XeF 6 reactions respectively, with the preexponential factor near 10 −10cc/molec-c for all rate constants. It was established that HF product of the H+F 2 “model” reaction is excited up to 8-th vibrational level while such one of the H+ KrF 2 reaction is not vibrationally excited. Thus a second product of H+KrF 2 reaction may be eximer KrF(B 2Σ) with the energy excitation 481.3 kJ/mol which corresponds to sum of the reaction heat and activation energy.

Flow reactor and triple quadrupole mass spectrometer investigations of negative ion reactions involving nitric acid: Implications for atmospheric HNO3 detection by chemical ionization mass spectrometry

Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO3-(H2O)n and NO3-(H2O)n with HNO3. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N2-buffer (1–3 hPa) at room temperature. The reaction rate coefficients of OH-, O2-, O3-, CO4-, CO3-, CO3-H2O, NO3-, and NO3-H2O were measured relative to the known rate k=3.0×10-9 cm3 s-1 for the reaction of O- with HNO3. The main product ion of the reaction of CO3-H2O with HNO3 was found to be (CO3HNO3)- supporting a previous suggestion made on the basis of balloon-borne ACIMS measurements. For the reaction of bare CO3- with HNO3 three product ions were observed, namely NO3-, (NO3OH)-, and (CO3HNO3)-. The reaction rate coefficients for CO3-H2O (1.7×10-9 cm3 s-1) and NO3-H2O (1.6×10-9 cm3 s-1) were found to be close to the collision rate. The measured k values for bare CO3- (1.3×10-9 cm3 s-1) and NO3- (0.7×10-9 cm3 s-1) are somewhat smaller. The collisional dissociations of CO3-(H2O)n, NO3-(H2O)n (n=1, 2), (CO3HNO3)- and (NO3HNO3)-, occasionally influencing ACIMS measurements, were also studied. Fragment ion distributions were measured using a triple quadrupole mass spectrometer. The results showed that previous stratospheric nitric acid measurements were unimpaired from collisional dissociation processes whereas these processes played a major role during previous tropospheric measurements leading to an underestimation of nitric acid concentrations. Previous ACIMS HNO3 detection was also affected by the conversion of CO3-(H2O)n to NO3-(H2O)n due to ion source-produced neutral radicals. A novel ACIMS ion source was developed in order to avoid these problems and to improve the ACIMS method.

Troposphere-stratosphere interactions in a one-dimensional model of Jovian photochemistry

A simple one-dimensional model of the Jovian atmosphere including the coupling between a rapidly mixed troposphere and a stagnant stratosphere is presented. We treat analytically the case of a chemically unreactive species flowing downward through the stratosphere and troposphere with a constant flux. The calculated concentration profile has a maximum value approximately one atmospheric scale height above the tropause. The corresponding mixing ratio rapidly decreases in the lower stratosphere. The contrast between the peak stratosphere and tropopause concentrations reflects the variation between the lower stratosphere and upper troposphere eddy diffusion coefficients. Numerical simulations of unreactive CO and C 2H 6, considering high-altitude photochemical sources (yielding downward fluxes to the troposphere) and deep troposphere thermochemical sources, demonstrate that upper troposphere abundances may have a large photochemical contribution Recent observations of CO near 5 bar can be reproduced by a model using any one of three different tropospheric eddy diffusion profiles: a constant value of ∼ 10 8 cm 2 sec −1, a constant value of ⪷10 4 cm 2 sec −1 , or a two-layer model with a rapidly mixed (10 8 cm 2 sec −1) layer below 20 bar and a slower mixing layer (10 4 cm 2 sec −1) between 100 mbar and 20 bar. In the latter two scenarios, the photochemical source is an important and/or dominant source of upper tropospheric CO. However, the upper tropospheric C 2H 6 abundances are distinctly different among the three cases. These calculations suggest objectives for higher spectral resolution observations, critical vertical scales for planning experiments on future missions to Jupiter, and predictions that can be tested with the Galileo probe mass spectrometer.

Hydrogen Production by Rumen Holotrich Protozoa: Effects of Oxygen and Implications for Metabolic Control by In Situ Conditions

Experiments with washed suspensions of holotrich protozoa (Isotricha spp. and Dasytricha ruminantium) showed that both organisms have an efficient O2-scavenging capability (apparent Km values 2.3 and 0.3 microM, respectively). Reversible inhibition of H2 production increased almost linearly with increasing O2 up to 1.5 microM; higher levels of O2 gave irreversible inhibition. In situ determinations of H2, CH4, O2 and CO2 in ovine rumen liquor, using a membrane inlet mass spectrometer probe, indicated that O2 was present before feeding at 1-1.5 microM and decreased to undetectable levels (less than 0.25 microM) within 25 min after feeding. A transient increase in O2 concentration after feeding occurred only in defaunated animals and resulted in suppression of CH4 and CO2 production. The presence of washed holotrich protozoa decreases the O2 sensitivity of CH4 production by suspensions of a cultured methanogenic bacterium Methanosarcina barkeri. It is concluded that holotrich protozoa play a role in ruminal O2 utilization as well as in the production of fermentation end products (especially short-chain volatile fatty acids) utilized by the ruminant and H2 utilized by methanogenic bacteria. These hydrogenosome-containing protozoa thus both control patterns of fermentation by influencing O2 levels, and are themselves regulated by the low ambient O2 concentrations they experience in the rumen.