Abstract: A mass spectrometer is disclosed wherein a z-lens upstream of an orthogonal acceleration Time of Flight mass analyser is repeatedly switched between a first mode wherein ions are transmitted to the mass analyser for subsequent mass analysis with a relatively high transmission and a second mode wherein ions are transmitted with a relatively low transmission. If it is determined that mass spectral data obtained when the mass analyser is in the first mode is suffering from saturation, then suitably scaled mass spectral data obtained when the mass analyser is in the second mode is used instead. If the saturation is severe then the mass spectral data obtained in the first mode may be replaced in its entirety with mass spectral data obtained in the second mode.

Abstract: A method is disclosed of identifying parent ions by matching daughter ions found to be produced at substantially the same time that the parent ions elute from a mixture. Ions emitted from an ion source are incident upon a collision cell which alternately and repeatedly switches between a first mode wherein the ions are substantially fragmented to produce daughter ions and a second mode wherein the ions are not substantially fragmented. Mass spectra are taken in both modes, and at the end of an experimental run parent and daughter ions are recognized by comparing the mass spectra obtained in the two different modes. Daughter ions are matched to particular parent ions on the basis of the closeness of fit of their elution times, and this enables parent ions to then be identified.

Abstract: A plasma mass spectrometer comprises a plasma torch (1) for generating ions from a sample introduced into a plasma (2), a nozzle-skimmer interface (3,5) for transmitting said ions into a first evacuated chamber (11), ion guiding means (12), an apertured diaphragm (18) dividing said first evacuated chamber (11) from a second evacuated chamber, and an ion mass-to-charge ratio analyzer in the second chamber for producing a mass spectrum. The ion guiding means comprises a multipole rod-set (13,14,15), means for applying an AC voltage between rods in the set, and means (22) for introducing into said ion guiding means an inert gas selected from the group comprising helium, neon, argon, krypton, xenon and nitrogen so that the partial pressure of said inert gas inside said rod-set is at least 10−3 torr. Interfering peaks in the spectrum, such as Ar+, are thereby reduced.

Abstract: A mass spectrometer is disclosed comprising an ion guide which spans two or more vacuum chambers. The ion guide comprises a plurality of electrodes having apertures. Preferably, one of the electrodes also forms a differential pumping aperture which separates two vacuum chambers.

Abstract: An improved method of parent ion scanning is disclosed. In one embodiment a quadrupole mass filter 3 upstream of a collision cell 4 is arranged to operate in a highpass mode. Parent ions transmitted by the mass filter 3 are fragmented in the collision cell 4 and detected by an orthogonal time of flight analyser 5 which obtains a daughter ion mass spectrum. Ions having a mass to charge ratio below the cutoff of the mass filter 3 are identified as daughter ions, and candidate parent ions may then be discovered and their identity confirmed by obtaining corresponding daughter ion spectra. In a second embodiment, the collision cell 4 alternates between high and low fragmentation and candidate parent ions can additionally be identified on the basis of the loss of a predetermined ion or neutral particle.

Abstract: A MALDI sample plate 1 is disclosed which comprises a metallic substrate 2 having a circular groove or moat 3. A hydrophobic polytetrafluoroethylene layer 4 is applied to the substrate 2 and a central portion 5 of the substrate 2 is laser etched which roughens the surface of the substrate 2. A thin polystyrene layer is then applied to the polytetrafluoroethylene layer 4 and the central portion 5.

Abstract: A time of flight mass analyzer having a drift region, an ion package generator, first and second ion reflectors and at least one ion detector. The drift region has an axis, an entrance and an exit and provides for a place wherein ions may be temporarily separated according to their mass-to-charge ratios. The ion package generator injects packets of ions into the drift region at the region's entrance from a beam of ions by intermittently applying an electrostatic field such that the packets of ions enter the drift region in an initial direction which is inclined to the direction of said beam of ions. The first ion reflector is disposed at the exit of the drift region to reflect, back towards the entrance, ions which are traveling towards the reflector in the drift region.

Abstract: A plasma mass spectrometer comprises a plasma torch (1) for generating ions from a sample introduced into a plasma (2), a nozzle-skimmer interface (3,5) for transmitting said ions into a first evacuated chamber (11), ion guiding means (12), an apertured diaphragm (18) dividing said first evacuated chamber (11) from a second evacuated chamber, and an ion mass-to-charge ratio analyzer in the second chamber for producing a mass spectrum. The ion guiding means comprises a multipole rod-set (13,14,15), means for applying an AC voltage between rods in the set, and means (22) for introducing into said ion guiding means an inert gas selected from the group comprising helium, neon, argon, krypton, xenon and nitrogen so that the partial pressure of said inert gas inside said rod-set is at least 10−3 torr. Interfering peaks in the spectrum, such as Ar+, are thereby reduced.

Abstract: A method of determining the sequence of amino acids that constitute peptides, polypeptides or proteins by mass spectrometry and especially by tandem mass spectrometry is disclosed without the use of any additional data concerning the nature of the peptide and without any limit to the number of possible sequences considered. The method can be implemented on a personal computer typically used for data acquisition on the tandem mass spectrometer even in the case of peptides comprising 10 or more amino acids. The method does not rely on exhaustive comparison of the spectra predicted from every possible amino acid sequence with any molecular weight constraint, but instead uses mathematical techniques to simulate the effect of such a complete search without actually carrying it out.

Abstract: A method of identifying a protein, polypeptide or peptide by means of mass spectrometry and especially by tandem mass spectrometry is disclosed. The method preferably models the fragmentation of a peptide or protein in a tandem mass spectrometer to facilitate comparison with an experimentally determined spectrum. A fragmentation model is used which takes account of all possible fragmentation pathways which a particular sequence of amino acids may undergo. A peptide or protein may be identified by comparing an experimentally determined mass spectrum with spectra predicted using such a fragmentation model from a library of known peptides or proteins. Alternatively, a de novo method of determining the amino acid sequence of an unknown peptide using such a fragmentation model may be used.

Abstract: An electrospray and/or atmospheric pressure ionization mass spectrometer includes an evacuated chamber, a sampling region within which is maintained a pressure greater than in the evacuation chamber, a sampling orifice that communicates between the sampling region and the evacuation chamber, and a mass analyzer that receives charged particles along a first axis through the sampling orifice from the sampling region into the evacuated chamber. A plurality of charged-particle jet generators, each having an associated jet axis, are adapted to be alternatively, selectively aligned such that a respective jet axis intersects with the first axis associated with the mass analyzer. This alignment is performed through the use of a hollow member which functions to guide charged particles through the sampling orifice to the evacuated chamber and, subsequently, to the mass analyzer.

Abstract: A method of correcting mass-spectral data acquired using a time-of-flight mass spectrometer (1) is disclosed comprising recognizing in an observed mass spectrum the mass peaks and determining the observed peak area and mass centroid. Then, using a correction table, the observed mass centroid is corrected for the effect of detector dead-time. The correction table is generated using a Monte Carlo simulation.

Abstract: The invention comprises a mass spectrometer 1 and a method of mass spectrometry that is especially useful for the measurement of the isotopic composition of hydrogen in the presence of a helium carrier gas. Interference to the accurate measurement of the small HD+ peak at mass-to-charge ratio 3 by the much larger He+ peak at mass-to-charge ratio 4 is reduced by provision of an energy filter 35 in the ion detector assembly used to collect HD+ ions. This prevents ions of He+ which have lost energy through scattering, etc giving rise to a signal from the HD+ detector and distorting the deuterium hydrogen isotopic ratio measurement. Such a mass spectrometer 1 is typically used in conjunction with a continuous flow inlet system 4 based on an elemental analyzer that converts hydrogen present in a sample to gaseous hydrogen in a flow of helium carrier gas.

Abstract: A plasma mass spectrometer comprises a plasma torch (1) for generating ions from a sample introduced into a plasma (2), a nozzle-skimmer interface (3, 5) for transmitting said ions into a first evacuated chamber (11), ion guiding means (12), an apertured diaphragm (18) dividing said first evacuated chamber (11) from a second evacuated chamber, and an ion mass-to-charge ratio analyzer in the second chamber for producing a mass spectrum. The ion guiding means comprises a multipole rod-set (13, 14, 15), means for applying an AC voltage between rods in the set, and means (22) for introducing into said ion guiding means an inert gas selected from the group comprising helium, neon, argon, krypton, xenon and nitrogen so that the partial pressure of said inert gas inside said rod-set is at least 10−3 torr.

Abstract: An ion detector (27) for use in a time-of-flight mass spectrometer (1) is disclosed. The ion detector (27), which has an extended dynamic range, comprises collection electrodes (36, 38; 39) of different surface areas. In one embodiment the collection electrodes (36, 38; 39) are formed in an array consisting of a larger plate-like collection electrode (36, 38) and a smaller plate-like collection electrode (39). Microchannel multiplier plates (31, 32) may be arranged in front of the collection electrodes (36, 38; 39). In an alternative embodiment the collection electrodes consist of a grid (42) or, more preferably, a wire electrode (50) disposed in front of a plate-like electrode (43).

Abstract: A plasma mass spectrometer comprises a plasma torch (1) for generating ions from a sample introduced into a plasma (2), a nozzle-skimmer interface (3,5) for transmitting said ions into a first evacuated chamber (11), ion guiding means (12), an apertured diaphragm (18) dividing said first evacuated chamber (11) from a second evacuated chamber, and an ion mass-to-charge ratio analyzer in the second chamber for producing a mass spectrum. The ion guiding means comprises a multipole rod-set (13,14,15), means for applying an AC voltage between rods in the set, and means (22) for introducing into said ion guiding means an inert gas selected from the group comprising helium, neon, argon, krypton, xenon and nitrogen so that the partial pressure of said inert gas inside said rod-set is at least 10−3 torr. Interfering peaks in the spectrum, such as Ar, are thereby reduced.

Abstract: The invention provides methods and apparatus for tandem mass spectrometry (MS/MS) in which parent ions generated from a sample are passed through a mass filter (2) and are fragmented into daughter ions in fragmentation means (3), the daughter ions being passed through a discontinuous output mass analyser, such as a time-of-flight analyzer (16) or an ion storage device (29). The range of possible parent mass-to-charge ratios is split into a plurality of smaller ranges, and the mass filter (2) is set to pass ions of each smaller range in turn. A flag is set for each smaller range which produces daughter ions of interest, and the mass filter (2) is set to pass each mass-to-charge ratio of the flagged ranges so that the mass-to-charge ratios of the fragmented ions produced for each of the mass-to-charge ratios passed may be determined using the discontinuous analyser (16, 29). The flagged ranges may be themselves split into a plurality of still smaller ranges, which are correspondingly flagged.

Abstract: A Faraday Cup charged-particle detector for use in an isotopic ratio mass spectrometer is provided with a charged-particle collector substrate being at least partially composed of carbon produced by burning wood or other grained or cellular organic material so that the substrate surface has an open cellular structure and wherein the cells are of elongated tubular form. The detector is economic to manufacture, reliable and has an increased lifetime.

Abstract: A continuous flow method of determining the quantitative isotopic composition of hydrogen comprised in a compound is disclosed, together with apparatus for carrying out the method. The method involves introducing the sample to be analysed into a flow of carrier gas which does not contain hydrogen, the carrier gas then being arranged to flow through a heated catalytic reactor which contain a chromium-based catalyst. The sample is pyrolysed in the catalytic reactor so as to form molecular hydrogen which is then analysed mass-spectrometrically. Preferably a gas chromatrograph is disposed before the catalytic reactor so that one or more components or a mixture may be separately analysed.

Abstract: Atmospheric Pressure Chemical Ionization (APCI) and electrospray ionization sources for the mass spectrometric analysis of solutions, and associated methods. The apparatus and methods are characterised in that ions generated by APCI or electrospray are directed such that their directions of travel immediately on formation can be resolved into two perpendicular components, one of which is aligned with a linear first trajectory which passes through an entrance orifice, an extraction chamber and into an evacuation port through which the extraction chamber is evacuated. The direction of travel is such that the component of velocity so aligned is smaller than the component perpendicular to it. Ions leave the chamber along a second trajectory which is inclined at an angle between 30.degree. and 150.degree. to the linear first trajectory and may pass into a mass analyzer.