Ion Source Housing Research Articles

Gas-phase dopant flow to modify nanoLC-MS and nanoESI protein charge

A miniature permeation device is used to add controlled amounts of gas-phase dopant to the air around two types of atmospheric pressure nanoflow electrospray source: a pulled glass capillary needle in a custom mount, and for the first time a commercial nano-liquid chromatography emitter in a commercial ion source housing. Intact proteins sprayed at 300 nL/min are charge-reduced by the addition of nitrogen doped with diethylamine, and the reaction is assisted by adjusting flow rate, positioning, and enclosure of the nanoflow emitter. Charge distribution is shifted to lower charge states with increasing amounts of dopant. The maximum signal of the most abundant charge state and the total signal abundance are increased to an extent dependent on the mass and isoelectric point of the protein.

Atmospheric pressure chemical ionization mass spectrometry at low flow rates: Importance of ion source housing.

Hyphenation of atmospheric pressure chemical ionization (APCI) mass spectrometry with capillary and micro high-performance liquid chromatography (HPLC) is attractive for many applications, but reliable ion sources dedicated to these conditions are still missing. There are a number of aspects to consider when designing such an ion source, including the susceptibility of the ionization processes to ambient conditions. Here we discuss the importance of ion source housing for APCI at low flow rates. Selected compounds dissolved in various solvents were used to study ionization reactions at 10 μL/min flow rate. APCI spectra were generated using the Ion Max-S source (Thermo Fisher Scientific) operated with or without the ion source housing. The APCI spectra of most compounds measured in the open and enclosed ion sources were markedly different. The differences were explained by water and oxygen molecules that entered the plasma region of the open ion source. Water tended to suppress charge transfer processes while oxygen diminished electron capture reactions and prevented the formation of acetonitrile-related radical cations useful for localizing double bonds in lipids. The effects associated with the ion source housing were significantly less important for compounds that are easy to protonate or deprotonate. The use of ion source housing prevented alternative ionization channels leading to unwanted or unexpected ions. Compared with the conventional flow rate mode (1 mL/min), the effects of ambient air components were significantly higher at 10 μL/min, emphasizing the need for ion source housing in APCI sources dedicated to low flow rates.

Comparison of a jet separator and an open splitter as an interface between a multi-capillary gas chromatographic column and a time-of-flight mass spectrometer

A gas chromatographic/time-of-flight mass spectrometric (GC/TOFMS) interface is being developed for fast on-line analysis utilizing multi-capillary column technology. A variable gap-distance jet separator has been constructed and its performance compared with that of a commercially supplied post-column open splitter recommended for use between the multi-capillary column and a mass spectrometer. Both interfaces were found to be compatible with the GC/TOFMS system at high carrier gas flow-rates, facilitating high-speed and high-resolution separations. The systems were investigated and tested with a mixture of volatile organic compounds (VOCs) with molecular masses from 85 to 166: dichloromethane, toluene, m-dichlorobenzene, o-dichlorobenzene and tetrachloroethylene. The optimum tip-to-tip gap distance corresponding to the highest efficiency of the jet separator was found to be 0.030 mm for each compound at carrier gas flow-rates of 20, 40 and 60 ml min−1 giving, in the ion source housing, ion gauge pressure readings of 1.6 × 10−6, 5.0 × 10−6 and 5.8 × 10−6 mbar, respectively. The efficiency of the jet separator (10–30% yields) was significantly higher than that of the open splitter (6–9% yields). The observation that the open splitter did not provide a constant flow-rate to the ion source was not in agreement with the manufacturer's specifications. A method for measuring the gas flow-rates in all parts of the equipment is described. The correlation between yield in the jet separator and molecular mass for the heterogeneous set of compounds studied was found to be less linear than usually reported for homologous series of compounds in jet separator studies. The result suggests that the pressure conditions in the jet may be sufficient for the separation process to be partly controlled by diffusion rather than predominately by effusion. Copyright © 2000 John Wiley & Sons, Ltd.

Comparison of a jet separator and an open splitter as an interface between a multi-capillary gas chromatographic column and a time-of-flight mass spectrometer

A gas chromatographic/time-of-flight mass spectrometric (GC/TOFMS) interface is being developed for fast on-line analysis utilizing multi-capillary column technology. A variable gap-distance jet separator has been constructed and its performance compared with that of a commercially supplied post-column open splitter recommended for use between the multi-capillary column and a mass spectrometer. Both interfaces were found to be compatible with the GC/TOFMS system at high carrier gas flow-rates, facilitating high-speed and high-resolution separations. The systems were investigated and tested with a mixture of volatile organic compounds (VOCs) with molecular masses from 85 to 166: dichloromethane, toluene, m-dichlorobenzene, o-dichlorobenzene and tetrachloroethylene. The optimum tip-to-tip gap distance corresponding to the highest efficiency of the jet separator was found to be 0.030 mm for each compound at carrier gas flow-rates of 20, 40 and 60 ml min(-1) giving, in the ion source housing, ion gauge pressure readings of 1.6 x 10(-6), 5.0 x 10(-6) and 5.8 x 10(-6) mbar, respectively. The efficiency of the jet separator (10-30% yields) was significantly higher than that of the open splitter (6-9% yields). The observation that the open splitter did not provide a constant flow-rate to the ion source was not in agreement with the manufacturer's specifications. A method for measuring the gas flow-rates in all parts of the equipment is described. The correlation between yield in the jet separator and molecular mass for the heterogeneous set of compounds studied was found to be less linear than usually reported for homologous series of compounds in jet separator studies. The result suggests that the pressure conditions in the jet may be sufficient for the separation process to be partly controlled by diffusion rather than predominately by effusion. Copyright 2000 John Wiley & Sons, Ltd.

Study of sulfur oxidation products by pyrolysis high-resolution mass spectrometry

High-temperature oxidations of hydrogen sulfide and methanethiol with O2 and NO2 were investigated using a special flow probe that was coupled to the ion-source housing of a high-resolution mass spectrometer. The direct coupling permitted prompt analysis of oxi dation products effusing from the flow probe. Nominally isobaric 32 S– 16 O2 doublets were resolved at a mass resolution of >8,000, which allowed for identification of several reaction products. Under conditions of medium-low pressure (0.8–4 Torr) and long mean resi dence times (0.5 s) in the probe, the oxidations yielded mostly stable products. Hydrogen sulfide was oxidized to form SO, SO 2 ,S 2 and S2O whose relative intensities were studied as a function of temperature and reactant mixture composition. Methanethiol yielded CH3SNO, CH3SSCH3, CS2, SO2 and traces of SO3 and SO3H depending on the temperature and reactant mixture composition.

Microplasma Mass Spectrometric Detection in Capillary Gas Chromatography

A simple and miniaturized 350-kHz helium discharge for plasma mass spectrometric detection in gas chromatography (GC) has been developed. The plasma was sustained at low pressure within the end of the capillary GC column (0.32-mm i.d.) inside the ion source housing of a quadrupole mass spectrometer. This allowed direct introduction of ions from the plasma to the mass analyzer using only a repeller and electrostatic lenses to focus the ions. The plasma was sustained in only 25 mL min(-)(1) of helium, which was accepted by the mass spectrometer vacuum system. This low gas flow also served to enhance the energy density of the discharge and to produce a narrow spray of ions toward the mass analyzer. Due to the miniaturized nature of the plasma, it was operated at a low power level (2.0 W), and traces of oxygen were added to avoid deposition of carbon. With this new concept for GC plasma mass spectrometric detection, chlorine was successfully monitored down to the 2.2 pg s(-)(1) level without interference from elements like C, S, P, O, F, and N.

‘Underflow’ introduction system for solid and liquid samples in bench‐top gas chromatographic/mass spectrometric systems

AbstractA simple, inexpensive inlet system was developed for the introduction of liquid and solid samples, to be employed in commercial gas chromatographic/mass spectrometric instruments, and not requiring sample injection through the chromatographic column. The system does not need any modifications of the ion source housing and pumping system and is based on admitting the sample vapour as an underflow to the normal helium flow through the chromatographic column at a location near the transfer line.

Matrix-assisted laser desorption/ionization with an external ion source Fourier-transform mass spectrometer.

Mass spectra of several model oligopeptides (substance P, [Arg8]-vasopressin, tyrothricin, and the B-chain of bovine insulin) have been obtained with a matrix-assisted laser desorption/ionization (MALDI) source and a custom-designed Fourier-transform mass spectrometer (FTMS). The MALDI source is outside the magnetic field in a separately pumped external chamber, and ions are injected through the fringing fields of the magnet and into the FTMS analyzer cell by a long quadrupole mass filter that is operated in the RF-only mode. A large window on the ion source housing makes it easy to point and focus the laser beam onto the sample probe tip. A good quality mass spectrum is achieved for 0.5 pmol of substance P, and the mass resolution for the B-chain of bovine insulin is 19,000.

Direct coupling of micro high-performance liquid chromatography with fast atom bombardment mass spectrometry : II. Application to gradient elution of bile acids

A new system without a moving belt has been developed for direct coupling of micro high-performance liquid chromatography with fast atom (xenon or argon) bombardment mass spectrometry. The structure of the interface was basically the same as used previously, but the mass spectrometer was modified by adding both a liquid nitrogen trap between the ion source housing and the diffusion pump, and a position adjuster for the interface.Stable ionization of the solute in a glycerol matrix is achieved at flow-rates below 2 μl/min. The system was applied to the analysis of bile acids by gradient elution chromatography. Steady baselines were observed in the mass chromatograms.

Improved Bevatron Local Injector Ion Source Performance

Performance tests of the improved Bevatron Local Injector PIG Ion Source using particles of Si 4+, Ne 3+, and He 2+ are described. Initial measurements of the 8.4 keV/nucleon Si 4+ beam show an intensity of 100 particle microamperes with a normalized emittance of .06 ? cm-mrad. A low energy beam transport line provides mass analysis, diagnostics, and matching into a 200 MHz RFQ linac. The RFQ accelerates the beam from 8.4 to 200 keV/nucleon. The injector is unusual in the sense that all ion source power supplies, the A.C. distribution network, vacuum control equipment, and computer control system are contained in a four bay rack mounted on insulators which is located on a floor immediately above the ion source. The rack, transmission line, and the ion source housing are raised by a D.C. power supply to 80 kilovolts above earth ground. All power supplies, which are referenced to rack ground, are modular in construction and easily removable for maintenance. A.C. power is delivered to the rack via a 21 kVA, 3-phase transformer.

Precision abrasion mass spectrometry: Instrumental method for determination of the quantitative distribution of volatile compounds trapped in polymeric materials

An instrument to mass spectrometrically analyze volatile compounds trapped or formed in an intractable solid matrix such as a polymer or resin-fiber composite is described. Samples are precisely abraded inside the ion-source housing of a time-of-flight mass spectrometer, and the evolved compounds are mass analyzed. By use of appropriate data acquisition and analysis techniques, either qualitative or quantitative information about the indigenous volatile compounds can be obtained. In the latter case, distribution profiles of the trapped compound(s) can be measured. Typical results for water in an epoxy resin and the pertinent experimental variables in obtaining accurate distribution profiles are discussed.

An atmospheric pressure ionization (api) source for a magnetic sector mass spectrometer

An Atmospheric Pressure Ionization (API) source has been built for a magnetic sector mass spectrometer. The ionization reactions, initiated by electrons from a Nickel-63 source are carried out in a flowing gas stream at atmospheric pressure. The reaction chamber is separated from the mass analyzer high vacuum region by a 50 μm aperture. The API mass spectrometer is being differentially pumped in order to maintain a pressure of 10 −6 torr in the analyzer region. This is being achieved by a 6 in. high speed pumping system connected to the ion source housing. The API source is electrically isolated from ground and connected to the accelerating high voltage of the mass spectrometer.