Mass spectrometer ion source

Figure Bl.7.4. Schematic diagram of a reverse geometry (BE) magnetic sector mass spectrometer ion source (1) focusing lens (2) magnetic sector (3) field-free region (4) beam resolving slits (5) electrostatic sector (6) electron multiplier detector (7). Second field-free region components collision cells (8) and beam deflection electrodes (9).

Continuous inlet. An inlet in which sample passes continuously into the mass spectrometer ion source, as distinguished from a reservoir inlet or a direct-inlet probe. 

Direct GC/MS interface. An interface in which all the effluent from a gas chromatograph passes into the mass spectrometer ion source during an analysis, without any splitting of the effluent. 

GC/MS interface. An interface between a gas chromatograph and a mass spectrometer that provides continuous introduction of effluent gas from a gas chromatograph to a mass spectrometer ion source. 

Nonfractionating continuous inlet. An inlet in which gas flows from a gas stream being analyzed to the mass spectrometer ion source without any change in the conditions of flow through the inlet or by the conditions of flow through the ion source. This flow is usually viscous flow, such that the mean free path is very small in comparison with the smallest dimension of a traverse section of the channel. The flow characteristics are determined mainly by collisions between gas molecules, i.e., the viscosity of the gas. The flow can be laminar or turbulent. 

Sample introduction system. A system used to introduce sample to a mass spectrometer ion source. Sample introduction system, introduction system, sample inlet system, inlet system, and inlet are synonymous terms. 

Solvent-divert system. Used in conjunction with an interface, it permits temporary interruption of the flow from a chromatograph to a mass spectrometer by briefly opening a valve to a pumping line. Thus effluent present at a high concentration (usually solvent) does not enter the mass spectrometer ion source. 

Vacuum-lock inlet. An inlet through which a sample is first placed in a chamber the chamber is then pumped out, and a valve is opened so that the sample can be introduced to the mass spectrometer ion source. A vacuum-lock inlet commonly uses a direct-inlet probe, which passes through one or more sliding seals, although other kinds of vacuum-lock inlets are also used. 

The interface in GC/MS is a device for transporting the effluent from the gas chromatograph to the mass spectrometer. This must be done in such a manner that the analyte neither condenses in the interface nor decomposes before entering the mass spectrometer ion source. In addition, the gas load entering the ion source must be within the pumping capacity of the mass spectrometer. 

Figure 9. Dependence of the ratio of CH + ions to total ions in the methane mass spectrum on the pressure of methane in the mass spectrometer ion source for different values of source repeller voltage...

Direct insertion probe pyrolysis mass spectrometry (DPMS) utilises a device for introducing a single sample of a solid or liquid, usually contained in a quartz or other non-reactive sample holder, into a mass spectrometer ion source. A direct insertion probe consists of a shaft having a sample holder at one end [70] the probe is inserted through a vacuum lock to place the sample holder near to the ion source of the mass spectrometer. The sample is vaporized by heat from the ion source or by heat from a separate heater that surrounds the sample holder. Sample molecules are evaporated into the ion source where they are then ionized as gas-phase molecules. In a recent study, Uyar et al. [74] used such a device for studying the thermal stability of coalesced polymers of polycarbonate, PMMA and polylvinyl acetate) (PVAc) [75] and their binary and ternary blends [74] obtained from their preparation as inclusion compounds in cyclodextrins. 

C content [Stevenson (99) Anderson and Avery (24) ]. If no skeletal rearrangements occur in the mass spectrometer ion source, it is very easy to see how the position of the l3C atom can be obtained from the relative... 

Penning ionization occurs with the (trace) gas M having an ionization energy lower than the energy of the metastable state of the excited (noble gas) atoms A. The above ionization processes have also been employed to construct mass spectrometer ion sources. [21,24] However, Penning ionization sources never escaped the realm of academic research to find widespread analytical application. 

The oldest but obviously old-fashioned way to introduce solids into a mass spectrometer ion source is by directly placing them inside an ion source which is mounted to the instrument thereafter and heated. [37] The use of a micro sample vial or crucible containing some 0.1-2 pg of the analyte that can be directly... 

Fock, W. Design of a Mass Spectrometer Ion Source Based on Computed Ion Trajectories. Int. J. Mass Spectrom. Ion Phys. 1969,5,285-291. 

Swingle, D.L. Mass Spectrometer Ion Source with High Yield. J. Appl. Phys. 1970,47, 1496-1499. 

A number of excellent reviews and books have included consideration of the fundamental electron impact ionization process, and the attention afforded the experimental measurement of ionization potentials and Augment ion appearance energies over the years is reflected in the comprehensive database of ionization potentials and gas phase ion enthalpies of formation published through the National Bureau of Standards in printed and electronic forms. In contrast, few absolute ionization cross sections have been measured. The most comprehensive compilation of molecular ionization cross sections are relative values measmed with a modified commercial electron impact mass spectrometer ion source using the cross section for Ar as a reference. ... 

Several recent reviews can provide the reader with an historical perspective and information about additional applications of chemical ionization mass spectrometry. (7-10) Under normal conditions, electron impact mass spectrometry is carried out by bombarding sample molecules with 70 eV electrons in a mass spectrometer ion source... 

Chemical ionization (Cl) sources (48, 49) use electron bombardment of a reagent gas at higher pressures than normally found in a mass spectrometer ion source, i.e., torr. Sample ionization follows via an ion-molecule reaction, often accompanied by a proton transfer to yield a quasi-molecular ion ... 

Derivatized polyethers such as polyether sulfate have been investigated for both positive- and negative-ion calibration [11]. Although poly ether sulfates are not commercially available, they are easily synthesized. Lauryl sulfate ethoxy-lates were also used as calibrants for negative-ion ESI. Polyether amines and quaternary ammonium salts were used as positive-ion calibration solutions [11]. These commercially available compounds do not exhibit significant sodium or potassium adducts, and they are more easily flushed out of the mass spectrometer ion source than are nonderivatized polyethers. In addition, doubly charged poly ether diamines can produce reference peaks at low m/z values. 

The mass spectrometer ion source can impose an additional time dependence on the decay of a reactant or the growth of a product if the species being detected resides in the source for a period of time that is comparable... 

Since APCI and ESI interfaces operate at atmospheric pressure and do not depend upon vacuum pumps to remove solvent vapor, they are compatible with a wide range of HPLC flow rates. HPLC methods that have been developed using conventional detectors such as UV/VIS, IR, or fluorescence are usually transferable to LC/MS systems without adjustment. However, the solvent system should contain only volatile solvents, buffers, or ion-pair agents to reduce fouling of the mass spectrometer ion source. In the case of chlorophyll solvent systems, isocratic and gradient combinations of methanol, acetonitrile, water, acetone, and/or ethyl acetate have been used for APCI or ESI LC/MS. Unlike continuous-flow FAB/LSIMS, no sample matrix is necessary. 

In contrast, both gas and liquid chromatography enable the samples of interest to be separated into individual components prior to introduction into the mass spectrometer ion source. Gas chromatography involves sample introduction with the requisite that the sample components must be volatilized prior to separation, and results in a gas sample being introduced to the mass spectrometer (i.e. El, Cl). Figure 5-2 shows the chromatogram obtained after a mixture of three simple phenolic compounds - phenol,... 

A LMI emitter s smallness makes it possible to attach it to the ion source of almost any magnetic sector or quadrupole mass spectrometer. Ion sources which have already been designed for fast atom bombardment (FAB) or field desorption (FD) are ideally suited to modification for LMI/SIMS operation. 

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