Mass spectrum is obtained when ions (usually in a beam) are separated according to the mass-to-charge (m/z) ratios of the ionic species present. This plot is a graphical representation of m/z values versus measured ion abundance information.
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The part of the spectrometer that analyzes the process by which a mixture of ionic species is separated according to the mass-to-charge ratio (m/z). The analysis may be qualitative and/or quantitative.
Time of Flight (TOF) instruments utilize the times taken by ions to pass (fly) along an evacuated tube as a means of measuring m/z values and therefore of obtaining a mass spectrum.
Quadrupole mass spectrometers consist of an ion source; ion optics to accelerate and focus the ions through an aperture into the quadrupole filter; the quadrupole filter itself, with control voltage supplies; an exit aperture, an ion detector, detection electronics, and a high-vacuum system.
Ion-trap mass spectrometers use three electrodes to trap ions in a small volume. The advantages of the ion-trap mass spectrometer include compact size and the ability to trap and accumulate ions to increase the signal-to-noise ratio of a measurement.
With single focusing analyzers, a circular beam path of 180, 90, or 60 degrees can be used. The various forces influencing the particle separate ions with different mass-to-charge ratios.
In double focusing analyzers, an electrostatic analyzer is added to separate particles with difference in kinetic energies.
Other unlisted, specialty or proprietary Mass Analyzer Design.
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The electrospray ionization (ESI) source consists of a very fine needle and a series of skimmers. A sample solution is sprayed into the source chamber to form droplets. The droplets carry charge when the exit the capillary, and as the solvent evaporates, the droplets disappear leaving highly-charged analyte molecules. ESI is particularly useful for large biological molecules that are difficult to vaporize or ionize.
In fast atom bombardment (FAB), a high-energy beam of neutral atoms, typically Xe or Ar, strikes a solid or low-vapor-pressure liquid sample causing desorption and ionization. It is used for large biological molecules that are difficult to get into the gas phase. The sample is usually dispersed in a matrix such as glycerol. FAB causes little fragmentation and usually gives a large molecular ion peak, making it useful for molecular weight determination.
Electron impact ionization (EI) source uses an electron beam, usually generated from a tungsten filament, to ionize gas-phase atoms or molecules. An electron from the beam knocks an electron off of analyte atoms or molecules to create ions.
Matrix-assisted laser desorption/ionization (MALDI) is a LIMS method of vaporizing and ionizing large biological molecules, such as proteins or DNA fragments. The biological molecules are dispersed in a solid matrix such as nicotinic acid or dihydroxybenzoic acid. A UV laser pulse ablates the matrix that carries some of the large molecules into the gas phase in an ionized form so they can be extracted into a mass spectrometer.
Other unlisted, specialty or proprietary Ionization Method.
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A channeltron is a horn-shaped, continuous dynode structure that is coated on the inside with an electron-emissive material. An ion striking the channeltron creates secondary electrons that have an avalanche effect to create more secondary electrons and finally a current pulse.
A Daly detector consists of a metal knob that emits secondary electrons when struck by an ion. The secondary electrons are accelerated onto a scintillator that produces light that is then detected by a photomultiplier tube.
Electron multiplier tubes (EMT) are similar in design to photomultiplier-tubes. They consist of a series of biased dynodes that eject secondary electrons when they are struck by an ion. They therefore multiply the ion current and can be used in analog or digital mode.
A Faraday cup is a metal cup that is placed in the path of the ion beam. It is attached to an electrometer, which measures the ion-beam current. Since a Faraday cup can only be used in an analog mode, it is less sensitive than other detectors that are capable of operating in pulse-counting mode.
A microchannel plate (MCP) consists of an array of glass capillaries (10-25 µm inner diameters) that are coated on the inside with an electron-emissive material. The capillaries are biased at a high voltage and like the channeltron, an ion that strikes the inside wall one of the capillaries creates an avalanche of secondary electrons. This cascading effect creates a gain of 103 to 104 and produces a current pulse at the output.
Other unlisted, specialty or proprietary Detector Type.
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An interface between a gas chromatograph and a mass spectrometer that provides continuous introduction of effluent gas from a gas chromatograph into a mass spectrometer ion source.
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An interface between a liquid chromatograph and a mass spectrometer that provides continuous introduction of effluent gas from a liquid chromatograph into a mass spectrometer ion source.
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The panel uses digital keypads or menus for programming.
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Serial ports or interfaces can be used for serial communication, in which only one bit is transferred at a time. Examples include RS232, RS422, RS485, USB etc.
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No integral display. Output is read and displayed remotely.
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Portable spectrometers are modular devices that are designed for ease of transport and assembly. Rugged enclosures, PC interfaces, and customizable software packages are common features for the portable device.
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This is the full required range of ambient operating temperature.
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