Abstract: A data acquisition system and method are described that may be used with various spectrometers. The data acquisition system may include an ion detector and a processing circuit. The processing circuit may include an initial processing module and a spectra processing module. According to one embodiment, the spectra processing module generates stick spectra and supplies the stick spectra to an external processor. The stick spectra comprise a peak intensity, resolution, and a location in the spectra for each detected peak. The stick spectra may be generated in real time.

Abstract: Ions and charged droplets move from the nozzle (6) towards the orifice (22) of a charged-particle transport device or the desolvation pipe (7). This particle motion is governed by the distribution of the pseudo-potential along particle trajectories. There are RF-voltages applied to neighboring electrodes (241-246) of the electrode array (24) cause the charged particles to substantially hover above the electrode array (24). Right before the ions come to the electrode array (24) they thus experience a repelling force “F” perpendicular to the surface of the electrode array (24). This force “F” causes an effective barrier (B) right before the electrode array (24) and consequently a pseudo-potential well (A) where the charged particles stop their motion parallel to the plume axis (D). Thus they accumulate around the center line (C) of this well (A).

Abstract: Disclosed are methods, apparatus, systems, processes and other inventions relating to: ion sources with controlled electro-pneumatic superposition, ion source synchronized to RF multipole, ion source with charge injection, optimized control in active feedback system, radiation supported charge-injection liquid spray, ion source with controlled liquid injection as well as various embodiments and combinations of each of the foregoing.

Abstract: An ion mobility spectrometer comprises a drift tube defining a drift tube inlet configured to receive ions and a drift tube outlet. The drift tube is configured to separate ions in time as a function of ion mobility. The drift tube defines a first ion activation region between the drift tube inlet and the drift tube outlet. The first ion activation region is configured to selectively induce structural changes in at least some of the ions.

Abstract: An ion mobility spectrometer is described which makes use of a pulsed flow pump to draw gas through an ion filter in pulsed operation. A gas counterflow may also be provided, in some embodiments this may also be a pulsed counterflow.

Abstract: Methods and systems are provided for detecting analytes in a gas phase sample. An ion mobility spectrometer is provided for detecting analytes having an excess amount of dopant in its separation region. In an embodiment, the dopant is added directly to the separation region, such as with a drift gas or by diffusion, thereby providing excess dopant that dominates subsequent cluster formation and maintenance. Excess dopant in the separation region minimizes or reduces interfering signals associated with unwanted substances, such as water vapor, that are introduced to the IMS. In an aspect, the invention provides IMS systems and methods having increased sensitivity and reliability for analyte detection.

Abstract: A filter for a mass- or mobility-spectrometer that bars gases or vapors of a high-pressure ion source, as well as ions of high mobility and charged droplets, from entering an evacuated mass spectrometer or a mobility spectrometer at a lower pressure than the filter. The buffer gas of the high pressure ion source is blown into the volume of this filter directly or through tubes from where buffer gas and embedded ions are sucked through the aperture of a diaphragm or through an aperture of a capillary mainly from an “extraction volume” filled with a separately supplied clean gas, into which ions of interest are pushed by electric fields formed by electrodes that are substantially rotational symmetric around the “extraction volume” and a substantially flat electrode with respect to an axis of ion extraction and the end of the capillary and the end of a coaxial tube surrounding the capillary.

Abstract: A method and apparatus for performing time of flight mass spectrometry wherein the number of sums of transients taken for generating a given spectra is determined as a function of a characteristic of the incoming data for that spectrum. For instance, the number of transient measurements taken for a given spectrum output can be determined as a function of the abundance of ions in the sample or the abundance of ions corresponding to a base peak or another selected peak. In yet another embodiment, the collection of transients is terminated when a threshold signal to noise ratio is attained.

Abstract: This invention relates to mass spectrometry that includes ion trapping in at least one of the stages of mass analysis. In particular, although not exclusively, this invention relates to tandem mass spectrometry where precursor ions and fragment ions are analysed. A method of mass spectrometry is provided comprising the sequential steps of: accumulating in an ion store a sample of one type of ions to be analysed; accumulating in the ion store a sample of another type of ions to be analysed; and mass analysing the combined samples of the ions; wherein the method comprises accumulating the sample of the one type of ions and/or the sample of another type of ions to achieve a target number of ions based on the results of a previous measurement of the respective type of ions.

Abstract: An improved electrospray ion source for increasing the current generated from the electrospray process and of the type having a needle (10), a counter-electrode (20), a saddle or outer electrode (30), and concurrent flow of gas (92). A method and device is disclosed that utilizes a controlled electrospray nebulizer where an aerosol comprised of charged droplets and gas-phase ions is sprayed into a field-free or near field-free desolvation or reaction region (120).

Abstract: An automatic gain control (AGC) technique and apparatus is introduced herein for any temporally non-uniform ion beam, such as, for example, an ion beam produced by a MALDI ion source so as to minimize space charge effects. The disclosed configurations and techniques can be achieved by using an ion optical gating element and applying a desired signal waveform (e.g., a square wave) having a predetermined duty cycle. The applied voltage amplitude of such a signal can be configured to switch between a voltage which fully transmits the ions, and a voltage which does not transmit any ions. The frequency is chosen to result in a period which is significantly lower than the smallest non-uniformity period. Techniques of the present invention can also be extended to methods of AGC which can use a single ion injection event from the ion source to avoid variations in ion numbers from an unstable ion source.

Abstract: An ion mobility spectrometer instrument has a drift tube that is partitioned into a plurality of cascaded drift tube segments. A number of electric field activation sources may each be coupled to one or more of the plurality of drift tube segments. A control circuit is configured to control operation of the number of electric field activation sources in a manner that sequentially applies electric fields to the drift tube segments to allow only ions having a predefined ion mobility or range of ion mobilities to travel through the drift tube. The drift tube segments may define a linear drift tube or a closed drift tube with a continuous ion travel path. Techniques are disclosed for operating the ion mobility spectrometer to produce highly resolved ion mobility spectra.

Abstract: Disclosed is an ion mobility spectrometer.

Abstract: A leak detection system has: a test chamber connected to a vacuum pump; a filling device for filling a test piece with helium gas; a transfer device for transferring the test piece between a ready-for-detection position in which the test piece is ready to be carried into the test chamber and a filling-operation position in which the operation of filling helium gas by the filling device is performed; a carrying device for carrying the test piece from the ready-for-detection position to a detection position inside the test chamber; a sealing device for hermetically sealing the test chamber in a state in which the helium-gas-filled test piece is in the detection position; and a leak detector for detecting helium to be leaked out of the test piece when, after having sealed the test chamber by the sealing device, the test chamber is evacuated by the vacuum pump to a predetermined pressure.

Abstract: This invention describes an ion mobility spectrometer system for chemical detection in the field. The system allows: a high throughput operation, an interface to new ionization methods, and an interface to a mass spectrometer.

Abstract: A mass spectrometer is disclosed comprising a FAIMS device comprising two parallel electrodes (9a, 9b) in series with an ion mobility separator (12) forming part of a mass spectrometer. Ions are separated in the FAIMS device (9a, 9b) according to their rate of change of ion mobility with electric field strength. The ions which are onwardly transmitted from the FAIMS device (9a, 9b) are then passed to an ion separator device (12) comprising a plurality of electrodes (12) and an optional ion trapping region (33). Ions are radially confined with the ion separator by application of an AC or RF voltage to the electrodes (12) and ions are separated according to their ion mobility by applying an axial DC voltage gradient which may remain constant as a function of time or which may vary with time.

Abstract: A mass spectrometer includes a pulsed ion source that generates an ion beam comprising a plurality of ions. A first timed ion selector passes a first group of ions. A first ion mirror generates a reflected ion beam comprising the first group of ions that at least partially compensates for an initial kinetic energy distribution of the first group of ions. A second timed ion selector passes a second group of ions. A second ion mirror generates a reflected ion beam comprising the second group of ions that at least partially compensates for an initial kinetic energy distribution of the second group of ions. A timed ion deflector deflects the second group of ions to a detector assembly comprising at least two ion detectors which detects the deflected ion beam.

Abstract: An ion mobility sensor system including an ion mobility spectrometer and a differential mobility spectrometer coupled to the ion mobility spectrometer. The ion mobility spectrometer has a first chamber having first end and a second end extending along a first direction, and a first electrode system that generates a constant electric field parallel to the first direction. The differential mobility spectrometer includes a second chamber having a third end and a fourth end configured such that a fluid may flow in a second direction from the third end to the fourth end, and a second electrode system that generates an asymmetric electric field within an interior of the second chamber. Additionally, the ion mobility spectrometer and the differential mobility spectrometer form an interface region. Also, the first end and the third end are positioned facing one another so that the constant electric field enters the third end and overlaps the fluid flowing in the second direction.

Abstract: A method and apparatus for time-of-flight (TOF) mass spectrometry. The apparatus improves the ion focusing properties in an orthogonal direction and permits connection with an orthogonal-acceleration ion source for improvement of sensitivity. The apparatus comprises an ion source for emitting ions in a pulsed manner, an analyzer for realizing a helical trajectory, and a detector for detecting the ions. The analyzer is composed of plural laminated toroidal electric fields to realize the helical trajectory.

Abstract: An inexpensive mass spectrometer system is provided. This mass spectrometer is capable obtaining structural information of a substance at an improved efficiency, and the time required for the analysis and identification of the substance has been reduced. Identification precision has also been improved. More specifically, this invention provides a tandem mass spectrometer system in which the sample is ionized at the desired polarity, fragment ions obtained by dissociating the ion is analyzed in first or second mass spectrometer section, polarity of the second mass spectrometer is determined based on the result of the analysis, and the mass spectroscopy is carried out. A method for the mass spectroscopy is also provided.

Abstract: A method for determining elemental composition of ions from mass spectral data, comprising obtaining at least one mass measurement from mass spectral data; obtaining a search list of candidate elemental compositions whose exact masses fall within a given mass tolerance range from the accurate mass; reporting a probability measure based on a mass error; calculating an isotope pattern for each candidate elemental composition from the search list; constructing a peak component matrix including at least one of the isotope pattern and mass spectral data; performing a regression against at least one of isotope pattern, mass spectral data, and the peak component matrix; reporting a second probability measure for at least one candidate elemental composition based on the isotope pattern regression; and combining the two the probability measures into an overall probability measure. A method for determining elemental isotope ratios from mass spectral data.

Abstract: In a mass spectrometer, a dual stage axial extraction field is applied to transport ions from an accumulator with a shutter and an ion guide to a detector cell. Ions of the same mass may be transported to the detector cell or a point axially preceding the detector cell at the same time by selecting the relative strengths of a first axial electric field applied to the accumulator and a second axial electric field applied to the shutter and further by selecting relative axial lengths of the accumulator, shutter, and an ion guide. A dual stage decelerating field may also be applied to slow ion down prior to and after entering the detector cell.

Abstract: The invention relates generally to ion mobility based systems, methods and devices for analyzing samples and, more particularly, to sample pre-separation and amplification.

Abstract: A device 6 for separating ions according to differences in their ion mobility as a function of electric field strength is disclosed. The device 6 comprises an upper electrode 7a, a lower electrode 7b and a plurality of intermediate electrodes 8. An asymmetric voltage waveform is applied to the upper electrode 7a and a DC compensating voltage is applied to the lower electrode 7b.

Abstract: Techniques for measuring energy contamination using time-of-flight (TOF) sensor are disclosed. In one particular exemplary embodiment, the techniques may be realized as a method for detecting energy contamination in an ion beam using time-of-flight comprising directing an ion beam towards an entrance of a sensor, wherein the ion beam may include charged particles and neutral particles, blocking the ion beam periodically from entering the sensor and allowing a pulse of the ion beam to enter the sensor periodically using a gate mechanism, separating the charged particles and the neutral particles of the ion beam pulse based at least in part upon different transit times over a distance caused by variations in at least one of mass and energy associated with the charged particles and the neutral particles, and detecting at least one of the charged particles and the neutral particles separately at a detector based at least in part upon the different transit times.

Abstract: The invention relates to a multi-sensor laser system for the selective trace analysis of organic material, the multi-sensor system having at least one laser ion mobility spectrometer, an absorption spectrometer and a fluorescent measuring device. The system is characterized in that it is equipped with a device for the simultaneous generation of a common laser beam with different wavelengths and pulses for the simultaneous operation of the laser ion mobility spectrometer, the absorption spectrometer and the fluorescent measuring device. This avoids the disadvantages of the known solutions in prior art and provides an improved solution for the highly sensitive and highly selective trace analysis of organic material, in particular hazardous substances such as explosives and warfare agents in the air.

Abstract: Apparatuses and method are provided. For example, in one embodiment, a ring electrode includes a plurality of sub-rings adapted to provide an electric field inside a spectrometer. The sub-rings have an internal sub-ring radius. There is a ring insulator between adjacent sub-rings. Each said ring insulator has substantially the same internal radius as the sub-rings. In another embodiment, a method is provided for insertion of the ring electrode inside the spectrometer.

Abstract: The present invention provides a method of reflecting ions in a multireflection time of flight mass spectrometer comprising providing an ion mirror having a plurality of electrodes, the ion mirror having a cross section with a first, minor axis (Y) and a second, major axis (X) each perpendicular to a longitudinal axis (Z) of the ion mirror which lies generally in the direction of time of flight separation of the ions in the mirror; guiding ions towards the ion mirror; applying a voltage to the electrodes so as to create an electric field which: (a) causes the mean trajectory of the ions to intersect a plane of symmetry of the ion mirror which contains the longitudinal (Z) and major axes (X) of the mirror; (b) causes the ions to reflect in the ion mirror; and (c) causes the ions to exit the ion mirror in a direction such that the mean trajectory of ions passing through the ion mirror has a component of movement in a direction (Y) perpendicular to and diverging from the said plane of symmetry thereof.

Abstract: Chemical sampling systems and methods that can inexpensively and efficiently provide accurate chemical sampling in dusty environments are disclosed. The system can include a chemical detector, an elastomeric membrane, and a support structure for the elastomeric membrane. The gas chromatograph can have a sample inlet through which chemicals from the gaseous environment can enter the gas chromatograph. The sample inlet can be covered with the elastomeric membrane, the elastomeric membrane being configured to extract chemicals from the gaseous environment while excluding dust and other particles from passing into the gas chromatograph. The support structure can be disposed between the elastomeric membrane and the sample inlet and can provide mechanical support to the elastomeric membrane.

Abstract: The concept underlying the invention is the development of a generic method for the detection and identification of gases in airplane interior spaces and an associated device, which is small and manageable, has a simple design, and allows the immediate and simultaneous detection and identification of the gases to be examined. This is achieved in that the supply air of the airplane interior space (20) is fed to a measuring device (1) and the measurement results of the measuring device (1) are analyzed by means of mathematical methods. Such methods and the associated devices for the detection and identification of gases in airplane interior spaces are used in order to spot and verify gases, particularly odors and explosive gases and/or gases harmful to people's health.

Abstract: In a time-of-flight mass spectrometer having an ion source with a first accelerating electrode, a distance between the surface of a sample and the first accelerating electrode is maintained at a predetermined distance which is critical for determining the mass and quantity of ions generated by the ion source. A digital image of the sample surface is obtained with a digital camera and a predetermined characteristic of the digital image is determined. The predetermined characteristic is then used to compute an adjustment amount by which the sample surface is moved to maintain the predetermined distance. Determining the predetermined characteristic can be simplified by projecting a light pattern onto the sample surface at an angle and determining the predetermined characteristic from the digital image of the pattern.

Abstract: A substance detection device, including a chemical substance analyzer, including an ion mobility spectrometer (IMS), a desorber, a conduit, and a membrane. The membrane extends across a cross-section of the conduit, and the membrane is positioned to have a desorber side in gas communication with the desorber and an analysis side opposite the desorber side. The substance detection device can be configured to direct a portion of a chemical substance to the desorber through the conduit so that at least a portion of the entrained chemical substance is transferred to the membrane by interacting with the desorber side of the membrane. The membrane is adapted to diffuse at least a portion of the chemical substance transferred to the membrane through the membrane to the analysis side. The device also includes a particle separator including a protuberance extending into a collection chamber of the particle separator.

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 method of scanning a sample plate surface mask in an area adjacent to a conductive area using mass spectrometry is disclosed. The method comprises the steps of providing a sample plate including a mask applied with a rough surface to the electrically conductive surface to produce a sample site comprising a central portion formed from the electrically conductive surface and a marginal portion of the mask, preparing an analyte comprising mixing a biomolecule with an organic solvent, an aqueous solution, and a matrix selected from the group of ?-cyano-4-hydroxycinnamic acid and3,5-dimethoxy-4-hydroxycinnamic acid; applying the analyte to the sample site; forming at least one crystal of the analyte in an area on the mask adjacent to the conductive area, and scanning the area on the mask adjacent to the conductive area with a laser beam.

Abstract: Disclosed are ion cyclotron resonance (ICR) cells and other ion-trapping cells with plural groups of multiple trapping electrodes for shaping (e.g., flattening) the radial electric field within the ICR cell. Also disclosed are methods for controlling the electric field to diminish effects of de-phasing. The diminished effects are achieved by decreasing space-charge contributions by increasing the length of the ion-oscillation path along the z-axis of the ICR cell. The methods and devices enhance the time-domain signal of a Fourier-transform ion-cyclotron resonance mass spectrometer (FTICR-MS) and provide enhanced resolution and accuracy of mass measurements.

Abstract: A substance detection device including a chemical substance analyzer, including, a conduit, and a membrane, wherein the membrane extends across a cross-section of the conduit, wherein the membrane is positioned to have one side and an analysis side opposite the one side, wherein the substance detection device is adapted to direct a portion of a chemical substance to the one side through the conduit, the substance detection device further including a particle separation apparatus, including a particle collection device having a collection chamber containing a first fluid and including an outlet, wherein the outlet is in fluid communication with the conduit such that particles directed through the outlet travel through the conduit and chemical substances which may be on those particles directed through the outlet are transferred to the membrane by interacting with the one side of the membrane.

Abstract: The invention relates to determining the masses from the time-of-flight values of ions in time-of-flight mass spectrometers where the accelerating voltage for the ions is not applied permanently, but is switched on at a certain time, resulting in a temporally changing acceleration for a short time after the voltage has been switched on. An aspect of the invention includes formally describing the effect of the temporally changing acceleration on the calibration curve—an effect which cannot be subjected to a strict mathematical-analytical calculation—by introducing a “reduced mass” m?m0 instead of the mass m. The mass reduction factor m0 does not describe a real mass difference, but a mass-dependent shortfall in the final kinetic energy after the ions have passed through the acceleration, a shortfall which can be observed with the temporally changing acceleration.

Abstract: A Matrix Assisted Laser Desorption Ionization ion source or ion imaging device is disclosed comprising a laser (1) and a zoom lens (3, 4, 5). The zoom lens (3, 4, 5) is arranged to be able to vary the magnification of a laser beam which is directed onto a target region, sample surface or target plate (13) of the ion source or ion imaging device.

Abstract: A method for analyzing a mixture of components includes forming precursor ions from the components, alternately causing the precursor ions to pass to and to by-pass a fragmentation device, to form product ions from the precursor ions that pass to the device and to form substantially fewer product ions from precursor ions that by-pass the device, and obtaining mass spectra from product ions received from the device and from precursor ions that by-passed the device. An apparatus for analyzing a sample includes an ion source for forming precursor ions from the components of the sample, a fragmentation device for forming product ions from the precursor ions, a by-pass device disposed upstream of the fragmentation device for switchable by-pass of the fragmentation device, and a mass analyzer.

Abstract: A high field asymmetric waveform ion mobility spectrometer (FAIMS) includes at least two focusing electrodes that are separated one from the other by a gap, which decreases in width along a direction of ion flow. Within the gap is disposed an electrode assembly including a first electrode and a second electrode, approximately flat surfaces of the first and second electrodes facing one another so as to define a space of approximately uniform thicknesses therebetween. During use electrical signals are applied via an electrical contact on at least one of the first electrode and the second electrode, and on each one of the at least two focusing electrodes. The electrical signals are for establishing electrode electric field conditions within the space between the first electrode and the second, for selectively transmitting ions therethrough and for directing the selectively transmitted ions in a direction away from one of the at least two focusing electrodes and toward a central portion of the space.

Abstract: An ion mobility spectrometer does not require a physical aperture grid to prevent premature ion detector response. The last electrodes adjacent to the ion collector (typically the last four or five) have an electrode pitch that is less than the width of the ion swarm and each of the adjacent electrodes is connected to a source of free charge, thereby providing a virtual aperture grid at the end of the drift region that shields the ion collector from the mirror current of the approaching ion swarm. The virtual aperture grid is less complex in assembly and function and is less sensitive to vibrations than the physical aperture grid.

Abstract: A device (6) for separating ions according to differences in their ion mobility as a function of electric field strength is disclosed. The device (6) comprises an upper electrode (7a), a lower electrode (7b) and a plurality of intermediate electrodes (8). An asymmetric voltage waveform is applied to the upper electrode (7a) and a DC compensating voltage is applied to the lower electrode (7b).

Abstract: The present invention combines ionization modes produced by, for example, electrospray (ESI), atmospheric pressure chemical ionization (APCI), and thermospray for analysis of molecules. Specifically, this invention relates to the creation of a new source apparatus combining APCI and ESI which will interface with existing mass spectrometers, as well as the creation of new mass spectrometers where the present invention would be the ionization source.

Abstract: An apparatus for detecting chemical substances which is high in sensitivity and selectivity is provided. An organic acid or an organic acid salt is used to generate an organic acid gas from an organic acid gas generator 3 to be mixed with a sample gas for introduction into an ion source 4 for ionization, thereby obtaining a mass spectrum by a mass analysis region 5. A data processor 6 determines the detection or non-detection of a specific m/z of an organic acid adduct ion obtained by adding a molecule generated from the organic acid to a molecule with specific m/z generated from a target chemical substance to be detected based on the obtained mass spectrum. When there is an ion peak with the m/z of the organic acid adduct ion, the presence of the target chemical substance to be detected is determined, and an alarm is sounded. False detection can be prevented.

Abstract: A mass spectrogram employs a set of controllable electrodes to produce a time varying axially inhomogenous electric field and enhance separation of charged particles by exposing the charged particles to different electric field strengths based on their spatial positions. The fields may be tailored to provide a traveling wave that expands portions of a spectrographic plot of the particles and/or to provide focusing or other effects.

Abstract: An ion mobility spectrometer and method thereof are disclosed. The ion mobility spectrometer comprises an electrode and an ion source arranged adjacent to the electrode, wherein the ion mobility spectrometer further comprises: a single or a group of focusing guide electrodes arranged on the side of the ion source far away from the electrode and shaped as a funnel to output ions from the ion source; and a storage section arranged on the ion-outputting side of the focusing guide electrode for storing ions generated from the ion source. With the scheme of separating the ion source and the storage region, the present invention can facilitate exchange of different ion sources, so that a source can be replaced with another different source without any change in the subsequent configuration. The storage section can be made very thin in the direction of ion movement, its diameter can be very large, and the internal electric field is almost zero.

Abstract: A mass spectrometer is disclosed comprising a first storage ion trap (2) arranged upstream of a high performance analytical ion trap (3). According to an embodiment ions are simultaneously scanned from both the first and second ion trap (2, 3). At any instant in time the quantity of charge present within the second ion trap (3) is limited or restricted so that the second ion trap (3) does not suffer from space charge saturation effects and hence the performance of the second ion trap (3) is not degraded.

Abstract: Time-of-flight mass spectrometer instruments are disclosed for monitoring fast processes with large dynamic range using a multi-threshold TDC data acquisition method or a threshold ADC data acquisition method. Embodiments using a combination of both methods are also disclosed.

Abstract: LC/MS data generated by an LC/MS system is analyzed to determine groupings of ions associated with originating molecules. Ions are grouped initially according to retention time, for example, using retention time or chromatographic peaks in mass chromatograms. After initial groupings are determined based on retention time, ion peak shapes are compared to determine whether ions should be excluded. Ions having peak shapes not matching other ions, or alternatively a reference peak shape, are excluded from the group.

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.