Bruker Daltonik Gmbh

Other

Claus Köster

Jochen Franzen

Karsten Michelmann

The present invention provides a method for acquiring fragment ion mass spectra with a time-of-flight mass spectrometer, whereby mixed mass spectra with fragment ions of different parent ion species are acquired and compared with each other in such a way that the signals of those fragment ions which originate from the same parent ion species are determined. The time-of-flight mass spectrometer contains an ion source, a flight path, a reflector and an ion detector. The flight path is preferably field-free and is positioned before the reflector, and the reflector preferably has a quadratically increasing reflection potential.

Fragment ion mass spectra measured with tandem time-of-flight mass spectrometers

The invention relates to embodiments of high-resolution time-of-flight (TOF) mass spectrometers with special reflectors. The invention provides reflectors with ideal energy and solid angle focusing, based on Cassini ion traps, and proposes that a section of the flight path of the TOF mass spectrometers takes the form of a Cassini reflector. It is particularly favorable to make the ions fly through this Cassini reflector in a TOF mass spectrometer at relatively low energies, with kinetic energies of below one or two kiloelectronvolts. This results in a long, mass-dispersive passage time in addition to the time of flight of the other flight paths, without increasing the energy spread, angular spread or temporal distribution width of ions of the same mass. It is also possible to place several Cassini reflectors in series in order to extend the mass-dispersive time of flight. Several TOF mass spectrometers for axial as well as orthogonal ion injection with Cassini reflectors are presented.

Time-of-flight mass spectrometers with cassini reflector

The invention relates to the voltage supply of mass spectrometers, particularly electrostatic Kingdon ion analyzers, requiring extremely noise-free operating voltages. The invention proposes the use of passive charge storage devices, which operate without any feedback control and display no measurable noise or ripple if they are well shielded, instead of the usual actively operating high-voltage generators. Chemical charge storage devices or capacitors with good insulation can be used for this purpose. These may display slight voltage decreases due to continuous discharge, depending on their quality, but these decreases can be mathematically compensated.

Voltage supplies for mass spectrometers

The geometry of a Kingdon ion trap, in which harmonic ion oscillation in a potential well in a longitudinal direction is completely decoupled from ion oscillation in a direction transverse to the longitudinal direction, is arranged so that the oscillating ions introduced through the entrance tube cannot return to the entrance tube until they have performed several longitudinal oscillations during which time heavier ions can be introduced into the trap. In one embodiment, ions enter the trap via an entrance tube extending through, but electrically insulated from, one of the Kingdon trap housing electrodes and located outside the minimum of the potential well in the longitudinal direction.

Introduction of ions into kingdon ion traps

Ions are introduced into a Kingdon ion trap in which the ions can oscillate harmonically in a potential well in the longitudinal direction, essentially decoupled from their transverse motion by a Kingdon ion guide, which can consist of a drill-hole through the wall of the ion trap housing electrodes and a central wire. An injection potential is first applied to the wire, but once the heaviest ions of interest have been injected into the trap, the potential of the wire is switched to the potential of the housing electrodes, to trap the ions in the trap. The ions introduced into the Kingdon ion trap may come from a small ion cloud, located in a Paul trap.

Introduction of ions into electrostatic ion traps

An electrostatic Kingdon ion trap in which ions can oscillate harmonically in the longitudinal direction, decoupled from their motions in the transverse direction is formed from at least three inner electrodes located inside a hollow outer housing electrode. The inner surface of the housing electrode and the outer surfaces of the inner electrodes are formed so that when a potential is applied between the housing and the inner electrodes, the potential distribution inside the housing contains not only a term for a harmonic potential well in the axial direction, but also a term for the potential distribution in the radial direction, that contains, independent of the axial coordinate, the equations for a family of Cassini curves of at least the third order.

Kingdon ion traps with higher-order cassini potentials

Charged droplets are guided along a defined path from a droplet source to a droplet sink. A focusing pseudopotential distribution generated by audio frequencies on electrodes of a guiding device guide the charged droplets from the droplet source to the droplet sink with low loss. The droplets can be driven along the droplet guide by a gas flow, an axial electric field or a combination of both. For example, charged droplets from a spray capillary of an electrospray ion source at atmospheric pressure may be introduced into the inlet capillary leading to the vacuum system of ion analyzers, a procedure similar to that used up to now in nanoelectrospraying, but with substantially higher flow rates. In the guiding device, the droplets can be manipulated in different ways, for example evaporated down to a desired size. The introduction of small droplets into gas-aspirating capillaries is of interest because it is possible to keep the droplets on axis by Bernoulli focusing and to guide them in large quantities and with low loss through the capillary. The ability to guide the droplets makes it also possible to install a segmented inlet capillary with intermediate pumping, which allows pumping capacity to be saved. Advantageously, the sensitivity of ion analyzers such as mass spectrometers or ion mobility spectrometers by at least one order of magnitude.

Guiding spray droplets into an inlet capillary of a mass spectrometer

In a Kingdon ion trap in which harmonic ion oscillation in a potential well in a longitudinal direction is completely decoupled from ion oscillation in a direction transverse to the longitudinal direction, ions enter the trap via an entrance tube extending through, but electrically insulated from, one of the Kingdon trap housing electrodes and located outside the minimum of the potential well in the longitudinal direction. The geometry of the Kingdon trap is arranged so that the oscillating ions introduced through the entrance tube cannot return to the entrance tube until they have performed several longitudinal oscillations during which time heavy ions can be introduced into the trap.

Introduction of ions into Kingdon ion traps

In a mass spectrometer with an electrostatic ion trap, the electrostatic ion trap has an outer electrode with an ion-repelling electric potential applied to it and a plurality of inner electrodes with ion-attracting potentials applied to each inner electrode. The outer electrode and the inner electrodes are shaped and arranged in such a way that a harmonic electric potential is formed in one spatial direction and, perpendicular to this spatial direction, an electric potential is formed in which ions move in stable, radial trajectories.

Mass spectrometer with an electrostatic ion trap

Fragment ion spectra are acquired in Kingdon ion traps that have a potential well for harmonic oscillations of the ions in the longitudinal direction and in which the ions can oscillate radially in a plane between two or more inner electrodes. Metastable ions, preferably produced by laser desorption, are introduced into the Kingdon ion trap close to the minimum of the longitudinal potential well and stored there locally for a predetermined time period. Excess internal energy in the metastable ions causes most of the ions to decompose ergodically to fragment ions. Then the fragment ions and any remaining analyte ions are excited to execute harmonic oscillations in the longitudinal potential well. The harmonic oscillations are measured as image currents, from which a high-resolution mass spectrum of the fragment ions can be calculated.

Fragmentation of ions in Kingdon ion traps

The invention relates to the evaluation of mass spectra from mass spectrometers in which ions are excited to mass-specific oscillating or orbiting motions, and the ion motion is recorded as a time signal. The invention provides methods to detect parameter drift that occurs during the recording of a time signal in such a 'frequency mass spectrometer' by analyzing the instantaneous frequency or the phase spectrum of a frequency component, and provides a method to correct for influence of the frequency drift on the mass spectrum correspondingly. In one embodiment a Fourier transformation converts a measured time signal into a frequency spectrum and examines the phase spectrum of a frequency component to establish whether this phase spectrum deviates from the phase spectrum of a harmonic time signal. The phase spectrum of a harmonic time signal is either linear or constant. In another embodiment the time domain signal is processed using a Short Time Fourier Transformation function to determine an instantaneous frequency, which can be used to correct the parameter drift, yielding a corrected time signal. From the corrected time signal a mass spectrum with better mass resolution can be derived, as can be seen from corrected mass signal profile compared with uncorrected mass signal profile.

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Lilienthal, Germany

Claus Köster