Abstract: A method of mass spectrometry is disclosed wherein ions are trapped for a period of time T within an AC or RF ion guide maintained at a pressure P wherein the product P×T is at least 1 mbar-ms. The effect of trapping the ions according to a preferred embodiment is that singly charged ions which may, for example, comprise unwanted background ions are substantially lost from the trap whereas multiply charged analyte ions are maintained within the ion trap and can then be released for subsequent mass analysis.

Abstract: A mass spectrometer includes a multipole having a main RF field for radially containing ions generally on a central axis. The multipole has first and second axial DC fields in opposite first and second direction along a length of the multipole. The first and second axial DC fields approach or add substantially to zero on the central axis. The multipole has an excitation voltage applied thereto for selectively exciting the ions of desired m/z ratios off the central axis. The excitation voltage thus causes excursion of the ions into a region where either the first or second axial DC field is strong. Thus, excitation of the ions and the DC fields cause ion drift toward a front end or a back end of the multipole. Further excitation moves the ions into regions of the DC fields that overcome barriers and causes axial ejection of the ions from the multipole.

Abstract: The present invention relates to an ion trap with a large trap capacity. A mass spectrometer comprises a first linear ion trap that performs mass selective ejection, and a second linear ion trap that accumulates and then mass selectively ejects ions ejected from the first linear ion trap. Directions of resonant excitation of ions of the first linear ion trap and of the second linear ion trap are orthogonal. Compared to conventional art, sensitivity is significantly improved.

Abstract: The invention describes a system and method to separate ions (and charged particles) suspended in gas based on their ion electrical mobility. Most common ion mobility analyzers involve two parallel plate (or concentric cylinder) elements (electrodes) between which is imposed an electrical field perpendicular to a sheath gas flow field between the cylinders. Separation occurs because high mobility ions tend to follow the electrical field while low mobility ions tend to follow the flow field. This invention describes various configurations of electrical elements and sheath gas flow fields for ion mobility separation devices with unique performance characteristics. These characteristics include devices in which: the ion inlet and outlet are on the same element; the inlet and outlet are at the same voltage; the outlet is upstream from the inlet; the outlet is on the axis; the inlet is on the axis; and the ions are focused on the outlet.

Abstract: A method of operating a mass spectrometer system having an ion trap is provided. The method comprises encoding a selected characteristic in at least one of the first group of precursor ions and the first plurality of fragments, wherein the encoding operation is applied to at least one of the first group of precursor ions and the first plurality of fragments without being applied to other ions such that the first plurality of fragment ions has the first selected characteristic and the other ions lack the first selected characteristic.

Abstract: A mass spectrometer is disclosed comprising an ion mobility spectrometer or separator (3) arranged upstream of a collision or fragmentation cell (5). Ions are separated according to their ion mobility within the ion mobility spectrometer or separator (3). The kinetic energy of the ions exiting the ion mobility spectrometer or separator (3) is increased substantially linearly with time in order to optimize the fragmentation energy of ions as they enter the collision or fragmentation cell (5).

Abstract: The invention provides an ion extraction pulser. The ion extraction pulser may be used independently or in conjunction with a mass spectrometry system. The mass spectrometry system includes an ion source for producing ions, an ion optics system downstream from the ion source for selecting and directing ions, and a detector down stream from the ion optics system for detecting the ions selected and directed by the ion optics system. The ion optics system includes one or more ion extraction pulsers.

Abstract: Method and apparatus for high field asymmetric waveform ion mobility spectrometry in an electronic chip assembly, including an input section, an ion filter and detection section and a control section, in which ion filtering proceeds in a planar chamber under influence of high field asymmetric periodic signals, with detection integrated into the flow path, for producing accurate, real-time, data for identification of a broad range of chemical compounds.

Abstract: A charged particle reaction cell of the present invention has a serially-arranged plurality of ring electrodes, wherein a modulated radio frequency voltage obtained by modulating the amplitude of a radio frequency voltage is applied, whereby ions are captured at the bottom of the ups and downs of a formed pseudopotential and are transferred with the move of the pseudopotential. In the charged particle reaction cell, the time required for the charged particle reaction can be secured and also the problem of the decrease of the throughput or the mass resolution can be solved, and the speed of the structure analysis of a measurement sample can be accelerated.

Abstract: The invention relates to methods for the measurement of fragment ion spectra in ion trap mass spectrometers in which fragment ions below a cut-off mass cannot normally be measured. The invention consists in measuring mass spectra including light fragment ions by briefly conducting the collisionally induced fragmentation—which is always brought about by a large number of collisions—at an unusual high RF storage voltage, which produces collisions more energetically than by conventional fragmentation, and then switching the RF voltage to a low RF voltage in a fast but controlled procedure. In this way light fragment ions are produced by double cleavages from metastable fragment ions with a certain half-life time. Since the cut-off mass for the storage capability is proportional to the RF storage voltage, reducing the RF storage voltage means that the light fragment ions can also be kept and measured in the ion trap.

Abstract: The invention provides a two-dimensional ion trap, comprising a plurality of elongate electrodes positioned between first and second end electrodes, the plurality of electrodes and first and second end electrodes defining a trapping volume. A controller in electrical communication with the plurality of elongate electrodes and the first and second end electrodes is configured to progressively vary a periodic voltage applied to at least one of the plurality of elongate electrodes to cause ions to be radially ejected from the ion trap in order of their mass to charge ratios. Concurrently, the controller is configured to progressively vary a DC offset of least one of the first and second end electrodes with respect to the plurality of elongate electrodes.

Abstract: A superconducting magnet configuration (4; 14) for generating a homogeneous magnetic field B0 in an examination volume (4b), has an interior radial superconducting main field coil (1) which is disposed rotationally symmetrically about an axis (z-axis) and an oppositely driven coaxial radially exterior superconducting shielding coil (2) is characterized in that the magnet configuration (4; 14) consists of the main field coil (1), the shielding coil (2), and a ferromagnetic field formation device (3; 18), wherein the ferromagnetic field formation device (3; 18) is located at the radially inside of the main field coil (1), the main field coil (1) consisting of an unstructured solenoid coil or of several radially nested unstructured solenoid coils (15, 16) which are driven in the same direction, the axial extent Labs of the shielding coil (2) being smaller than the axial extent Lhaupt of the main field coil (1), wherein the axial magnetic field profile (5) generated by the main field coil (1) and the shielding co

Abstract: A rectilinear ion trap includes a first pair of spaced planar RF electrodes, mounted in parallel and a second pair of spaced planar electrodes, mounted in parallel and orthogonal to the first pair of electrodes. The configuration of the pairs of electrodes define an axial direction and a radial direction. The trap further includes an RF source that applies an RF voltage to at least one of the pairs of RF electrodes to generate RF fields to trap ions in the axial and radial directions.

Abstract: A compact, low-cost, and simple ion trap capable of operating at a low vacuum level is provided along with technology for utilizing that ion trap to perform mass spectroscopy and analyzing ion mobility without a drop in measurement accuracy. Ions are trapped in a one dimensional potential formed by a potential comprised of a direct current voltage and a potential comprised of an alternating current voltage. The trapped ions are made to collide with an electrode by changing at least the applied direct current voltage or alternating current voltage, and are detected as an electrical current value.

Abstract: A method of operating a mass spectrometer having a rod set is provided. The rod set has a first end, a second end opposite to the first end, and a longitudinal axis extending between the first end and the second end.

Abstract: An API source for mass spectrometry which is configured such that all or a portion of its vacuum assembly, including ion focusing and transport electrostatic lenses and ion guides, and two or more vacuum stages can be removed from the source or system vacuum housing as a complete assembly. The API source may be an ES, APCI or ICP source, or any other ion source which operates at substantially atmospheric pressure. The insert assembly can be electrically isolated from the grounded vacuum housing to enable the delivery of kilovolt potential ions into a magnetic sector mass analyzer from the API source. The insert assemblies can be configured to interface to quadrupole, Time-Of-Flight, ion trap, Fourier Transform, and magnetic sector mass analyzers. Electrical connections can be configured internally to make and break automatically when said insert assembly is inserted or removed from the surrounding vacuum housing.

Abstract: In a system for analyzing samples by mass spectrometry, analyte ions are analyzed first by field asymmetric ion mobility spectrometry (FAIMS) before being analyzed by a mass analyzer. The analyte ions are produced in an ion source operating at near atmospheric pressure and transferred via a dielectric capillary into the vacuum system of the mass analyzer. While passing through the capillary, the ions are analyzed by FAIMS via electrodes on the interior wall of the capillary.

Abstract: The invention provides, in various embodiments, systems and methods relating to controlling ion behavior in an ion-based analysis system.

Abstract: An electron capture dissociation device to implement a combination of electron capture dissociation and collision dissociation and a mass spectrometer with the use thereof are provided. This device includes a linear ion trap provided with linear multipole electrodes applied with a radio frequency electric field and wall electrodes that are arranged on both ends in the axis direction of the linear multipole electrodes, have holes on the central axis thereof, and generate a wall electric field by being applied with a direct-current voltage, a cylindrical magnetic field-generating unit that generates a magnetic field parallel to the central axis of the linear multipole electrodes and surrounds the linear ion trap, and an electron source arranged opposite to the linear multipole electrodes with sandwiching one of the wall electrodes. The electron generation site of the electron source is placed in the inside of the magnetic field generated by the magnetic field-generating unit.

Abstract: The invention provides a two-dimensional ion trap, comprising a plurality of elongate electrodes positioned between first and second end electrodes, the plurality of electrodes and first and second end electrodes defining a trapping volume. A controller in electrical communication with the plurality of elongate electrodes and the first and second end electrodes is configured to progressively vary a periodic voltage applied to at least one of the plurality of elongate electrodes to cause ions to be radially ejected from the ion trap in order of their mass to charge ratios. Concurrently, the controller is configured to progressively vary a DC offset of least one of the first and second end electrodes with respect to the plurality of elongate electrodes.

Abstract: Disclosed is an ion trap mass spectrometer for MSn analysis, which comprises a frequency-driven ion trap section operable to trap sample ions and isolate a precursor ion from the sample ions, while setting an ion-trapping RF voltage waveform at a first frequency providing a first low-mass cutoff (LMCO) value, and, then after setting the ion-trapping RF voltage waveform at a second frequency greater than the first frequency to provide a second LMCO value less than the first LMCO value, without changing an amplitude of the ion-trapping RF voltage waveform, to irradiate the precursor ion in a trapped state with light so as to photodissociate the precursor ion into fragment ions; and an analyzer section operable to subject the fragment ions ejected from the ion trap section, to mass spectrometry so as to obtain information about a molecular structure of the precursor ion. The ion trap mass spectrometer of the present invention can maximize a mass range coverable in one cycle of MSn analysis.

Abstract: An imbalanced radio frequency (RF) field creates a retarding barrier near the exit aperture of a multipole ion guide, in combination with the extracting DC field such that the barrier provides an m/z dependent cut of ion sampling. Contrary to the prior art, the mass dependent sampling provides a well-conditioned ion beam suitable for other mass spectrometric devices. The mass selective sampling is suggested for improving duty cycle of o-TOF MS, for injecting ions into a multi-reflecting TOF MS in a zoom mode, for parallel MS-MS analysis in a trap-TOF MS, as well as for moderate mass filtering in fragmentation cells and ion reactors. With the aid of resonant excitation, the mass selective ion sampling is suggested for mass analysis.

Abstract: An ultra compact ion mobility based analyzer in a multilayered chip assembly employing various features such as a ion flow generator to propel ions through an ion mobility based filter and, thereby, reduce analyzer size, cost, and power requirements.

Abstract: A system for guiding an ion beam along an axis (Z), comprises at least one section having upper flat plate strip electrodes (Iu, 2u, 3u, 4u and 5u) and lower flat plate strip electrodes (Id, 2d, 3d, 4d and 5d) for producing at least one electric field of substantially symmetric in a parallel direction and substantially antisymmetric in a perpendicular direction with respect to a plane including a beam axis and a fringe-field boundary that is located at the end of the at least one section.

Abstract: A method for reducing the energy spread of ions over a specific and limited mass to charge ratio range is disclosed, along with an ion deceleration arrangement for implementing such a method. An electric field, having an electric field strength E is generated by a deceleration electrode arrangement (250). Ions of a specific and limited mass to charge ratio range, but having a spread of energies, are directed into the decelerating electric field generated by the deceleration electrode arrangement (250). The decelerating electric field is then removed, once substantially all of the ions of the specific mass to charge ratio range have entered the decelerating electric field. By matching the electric field strength E to the energy spread of the ions upon entry into the electric field, the energy spread of the said ions is reduced. Preferred embodiments of the invention employ energy dispersion upstream of the ion deceleration arrangement.

Abstract: A method for operating a mass spectrometer includes determining a first performance characteristic while operating the mass spectrometer with a first electron emitter, storing first information relating to the first performance characteristic, determining a second performance characteristic while operating the mass spectrometer with a second electron emitter, storing second information relating to the second performance characteristic, and thereafter switching from operation using the first electron emitter to operation using the second electron emitter. The switching includes using the first and second information to normalize performance of the second electron emitter after the switching relative to performance of the first electron emitter before the switching.

Abstract: A method for the mass-selective transport of ions, especially in a mass spectrometer, comprises the steps movement of the ions on a movement path on which a plurality of electrodes are arranged, and loading the electrodes with pulse-shaped acceleration voltages under the effect of which the ions experience a mass-dependent change of speed, wherein the electrodes are loaded with the pulse-shaped acceleration voltages such t at target ions with a pre-determined target mass are accelerated along the movement path. Furthermore, an ion conductor for mass-selective transport of ions, especially in a mass spectrometer, is described.

Abstract: A mass spectrometer includes: an ion source for ionizing a specimen to generate ions, an ion transport portion for transporting the ions, a linear ion trap portion for accumulating the transported ions by a potential formed axially, and a control portion of ejecting the ions within a second m/z range different from a first m/z range, from the linear ion trap portion, and substantially at the same timing as the timing of accumulating the ions within the first m/z range from the transport portion into the linear ion trap portion. The ion transportation portion having a mass selection means for selecting the ions in the first m/z range.

Abstract: An ion guide includes multiple stages. An electric field within each stage guides ions along a guide axis. Within each stage, amplitude and frequency, and resolving potential of the electric field may be independently varied. The geometry of the rods maintains a similarly shaped field from stage to stage, allowing efficient guidance of the ions along the axis. In particular, each rod segment of the ith of stage has a cross sectional radius ri, and a central axis located a distance Ri+ri from the guide axis. The ratio ri/Ri and is substantially constant along the guide axis, thereby preserving the shape of the field.

Abstract: An ultra compact ion mobility based analyzer in a multilayered chip assembly employing various features such as a ion flow generator to propel ions through an ion mobility based filter and, thereby, reduce analyzer size, cost, and power requirements.

Abstract: The present invention provides, inter alia, a multipole ion guide for moving and guiding ions, particularly in a mass spectrometer. The multipole ion guide comprises multiple rods with a resistive coating, and radio frequency (RF) and direct current (DC) voltages applying to the resistive coating of each rod. Devices and systems comprising the multipole ion guide, as well as methods of use thereof, are also provided.

Abstract: The present invention provides a device, system, and associated methods to actively or passively sample air by directing it onto the surface of a porous light-absorbing semiconductor, for example, a desorption/ionization on porous silicon (“DIOS”) chip. Upon adsorption of an analyte, the surface may be analyzed directly by laser desorption/ionization time-of-flight mass spectrometry. Because the process of laser desorption/ionization and subsequent mass detection does not require elevated temperatures, thermal degradation of analytes is avoided.

Abstract: Particular aspects provide novel methods for analysis of ion populations, the methods comprising filtering and selecting an ion population using a low-field dual-gate ion mobility spectrometer comprising a drift tube, the spectrometer operating at a pressure of at least 100 Torr, to provide mobility-selected ions. Certain aspects comprise: (i) subsequently accumulating the low-field selected ions in an ion trap (e.g., an MS ion trap) and mass spectrometry analysis; (ii) introducing the low-field selected ions into a high-field ion mobility spectrometer for separating thereby (optionally followed by mass spectrometry); and (iii) introducing the low-field selected ions into an ion trap mass spectrometer, and subsequently into a second low-field ion mobility spectrometer (e.g., a non-dual gate spectrometer operating at less than about 100 Torr). Additional aspects provide novel apparatus and combination thereof for performing the disclosed methods.

Abstract: A combined rf-only/FAIMS analyzer is disclosed for use in mass spectrometry and other applications. The disclosed apparatus includes a plurality of flat-plate electrodes arranged around a longitudinal axis of the apparatus so as to define generally a parallelogram in a cross section taken in a plane that is normal to the longitudinal axis. FAIMS is removed electronically when not desired by application of radio frequency (rf) waveforms to the flat-plate electrodes.

Abstract: An asymmetric field ion mobility spectrometer for filtering ions via an asymmetric electric field, an ion flow generator propulsing ions to the filter via a propulsion field.

Abstract: A mass spectrometer and a method of operating and building same is provided in which a hexapole component is deliberately added to a substantially quadrupole field. This can result in unwanted octopole and dipole fields also being added to the substantially quadrupole field. Modifications to the mass spectrometer as well as ways of operating the mass spectrometer are provided for dealing with the unwanted octopole and dipole fields.

Abstract: An ion detection device, method and computer readable medium storing instructions for applying voltages to shutter elements of the detection device to compress ions in a volume defined by the shutter elements and to output the compressed ions to a collector. The ion detection device has a chamber having an inlet and receives ions through the inlet, a shutter provided in the chamber opposite the inlet and configured to allow or prevent the ions to pass the shutter, the shutter having first and second shutter elements, a collector provided in the chamber opposite the shutter and configured to collect ions passed through the shutter, and a processing unit electrically connected to the first and second shutter elements.

Abstract: The present invention provides a radio frequency (RF) power supply in a mass spectrometer. The power supply provides an RF signal to electrodes of a storage device to create a trapping field. The RF field is usually collapsed prior to ion ejection. In an illustrative embodiment the RF power supply includes a RF signal supply; a coil arranged to receive the signal provided by the RF signal supply and to provide an output RF signal for supply to electrodes of an ion storage device; and a shunt including a switch operative to switch between a first open position and a second closed position in which the shunt shorts the coil output.

Abstract: A system and method are disclosed for effectively compensating for an unbalanced or non-zero centerline radio-frequency potential in a quadrupolar ion trap, the unbalanced centerline potential created by a compensation feature that minimizes non-linear field components created by one or more ejection slots in the ion trap. The ion trap includes a centerline that passes longitudinally through a trapping volume inside of the ion trap, a pair of Y electrodes with inner Y electrode surfaces that are approximately parallel to the centerline, and a pair of X electrodes with inner X electrode surfaces that are approximately parallel to the centerline. The X electrodes have ejection slots through which trapped ions are ejected from the ion trap. A Y signal with a Y signal amplitude is coupled to both of the Y electrodes. An X signal with an X signal amplitude is coupled to both of the X electrodes.

Abstract: A method and apparatus for multiplexing plural ion beams to a mass spectrometer. At least two ion sources are provided with means of transporting the ions from the ion sources to separate two-dimensional ion traps. Each ion trap is used for storage and transmission of the ions and operates between the ion sources and the mass analyzer. Each ion trap has a set of equally spaced, parallel multipole rods, as well as entrance and exit sections into which and from which ions enter and exit the trap, respectively. For each ion trap, the entrance section is placed in a region where background gas pressure is at viscous flow. The pressure at the exit section drops to molecular flow pressure regimes without a break in the structure of the ion trap. Each trap alternately stores and transmits ions by way of a fast voltage switch applied to the ion trap exit lens.

Abstract: An ion trap (104) for a mass spectrometer includes an RF trapping voltage source (112) for applying an RF trapping voltage to at least one of a plurality of electrodes (102, 106, 110) of the ion trap (104) to trap at least a portion of ions in the ion trap (104); a resonance excitation voltage source (114) for applying a resonance excitation voltage pulse to the electrodes(102, 106, 110) to cause at least a portion of a selected set of ions to undergo collisions and break into ion fragments; and a computer (116) for controlling the RF trapping voltage source (112) to reduce the RF trapping voltage after a predetermined delay period following termination of the resonance excitation voltage pulse to a second amplitude for retaining a low mass ion fragments in the ion trap (104) for later analysis.

Abstract: Apparatus and method for trapping uncharged multi-pole particles comprises a bound cavity for receiving the particles, and a multiplicity of electrodes coupled to the cavity for producing an electric field in the cavity. In a preferred embodiment, the electrodes are configured to produce in the electric field potential both a multi-pole (e.g., dipole) component that aligns the particles predominantly along an axis of the cavity and a higher order multi-pole (e.g., hexapole) component that forms a trapping region along the axis. In one embodiment, the electrodes and/or the particles are cooled to a cryogenic temperature.

Abstract: A device for transporting and focusing ions in a low vacuum or atmospheric-pressure region of a mass spectrometer is constructed from a plurality of longitudinally spaced apart electrodes to which oscillatory (e.g., radio-frequency) voltages are applied. In order to create a tapered field that focuses ions to a narrow beam near the device exit, the inter-electrode spacing or the oscillatory voltage amplitude is increased in the direction of ion travel.

Abstract: An adjustable, low mass-to-charge (m/z) filter is disclosed employing electrospray ionization to block ions associated with unwanted low m/z species from entering the mass spectrometer and contributing their space charge to down-stream ion accumulation steps. The low-mass filter is made by using an adjustable potential energy barrier from the conductance limiting terminal electrode of an electrodynamic ion funnel, which prohibits species with higher ion mobilities from being transmitted. The filter provides a linear voltage adjustment of low-mass filtering from m/z values from about 50 to about 500. Mass filtering above m/z 500 can also be performed; however, higher m/z species are attenuated. The mass filter was evaluated with a liquid chromatography-mass spectrometry analysis of an albumin tryptic digest and resulted in the ability to block low-mass, “background” ions which account for 40-70% of the total ion current from the ESI source during peak elution.

Abstract: A mass spectrometer according to one embodiment can include first and second endcap electrodes, first and second outer ring electrodes, and a central ring electrode. The first outer ring electrode can be positioned downstream of the first endcap electrode. The central ring electrode can be positioned downstream of the first outer ring electrode. The second outer ring electrode can be positioned downstream of the central ring electrode. The second endcap electrode can be positioned downstream of the second outer ring electrode. The mass spectrometer can also include a radio frequency (RF) signal supply operable to apply an RF signal to the first and second outer ring electrodes to thereby generate a substantially octapolar field for trapping charged particles.

Abstract: This invention relates to tandem mass spectrometry and, in particular, to tandem mass spectrometry using a linear ion trap and a time of flight detector to collect mass spectra to form a MS/MS experiment. The accepted standard is to store and mass analyze precursor ions in the ion trap before ejecting the ions axially to a collision cell for fragmentation before mass analysis of the fragments in the time of flight detector. This invention makes use of orthogonal ejection of ions with a narrow range of m/z values to produce a ribbon beam of ions that are injected into the collision cell. The shape of this beam and the high energy of the ions are accommodated by using a planar design of collision cell. Ions are retained in the ion trap during ejection so that successive narrow ranges may be stepped through consecutively to cover all precursor ions of interest.

Abstract: The invention provides a multipole device for a mass spectrometer system. In general, the multipole device contains a plurality of conductive rods each comprising a conductive layer, a resistive layer, and an insulative layer between the conductive and resistive layers. The invention finds use in a variety of applications, including ion transport, ion fragmentation and ion mass filtration. Accordingly, the invention may be employed in a variety of mass spectrometer systems.

Abstract: A mass analyser (2) is provided comprising a plurality of electrodes having apertures through which ions are transmitted in use. A plurality of seudo-potential corrugations are created along the axis of the mass analyser (2). The amplitude or depth of the pseudo-potential corrugations is inversely proportional to the mass to charge ratio of an ion. One or more transient DC voltages are applied to the electrodes of the mass analyser (2) in order to urge ions along the length of the mass analyser (2). The amplitude of the transient DC voltages applied to the electrodes is increased with time and ions are caused to be emitted from the mass analyser (2) in reverse order of mass to charge ratio.

Abstract: A high pressure collision cell for use in a mass spectrometer. The high pressure collision cell has a cell length L selected to be in a range such that upon application of voltages to a pair of opposed elongate electrically conducting electrodes there is produced an electric field of sufficient strength across the collision cell length L in to aid in directing ions entering the collision cell to along a transverse flow axis. The pressure in the collision cell is maintained in a range from about 50 mTorr to 1000 mTorr and wherein the collision cell length L and the pressure are selected such that a target thickness, defined as a product of the collision cell length L and the pressure, is maintained in a range from about 0.2 to about 2 mm-Torr.

Abstract: In the ion storage device 10 according to the present invention, an LC resonant circuit 40 for generating an RF voltage for trapping ions is connected to at least one of the electrodes 11, 12 and 13 surrounding the ion storing space 14. The LC resonant circuit 40 includes switching devices 46, 47 and resistances 48, 49 for stopping the RF voltage when the ions stored in the ion storing space 14 are ejected. The inductance L, the capacitance C and the resistance R of the LC resonant circuit are set to substantially satisfy the critical damping condition, which means that R=X/2 where X=?0L=(?0C)?1. According to this configuration, the RF voltage damps fast when the RF voltage is stopped by the switching devices 46, 47, and the deterioration of the mass resolution of the mass analyzer or the peak shift in the mass spectrum is prevented.