Ion guide with improved gas dynamics and combined noise reduction device

Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of charged particles. It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and other chemical compounds. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass-to-charge ratios.

In a typical MS procedure, a sample is loaded onto the MS instrument and undergoes vaporization. The components of the sample are ionized by one of a variety of methods (e.g., by impacting them with an electron beam), which results in the formation of charged particles (ions). The ions are separated according to their mass-to-charge ratio in a mass analyzer by electromagnetic fields. The ions are detected, usually by a quantitative method. The ion signal is processed into mass spectra.

FIG. 1 shows a block diagram of prior art MS instrument. The mass spectrometer comprises an ion source that generates and supplies ions to be analyzed to a set of ion optics including an ion guide are used to send the ions to the analyzer. Ion optics may be located adjacent to the ion guide so that mass spectra may be taken, under the direction of the controller. The mass spectrometer, as a whole, is operated under the direction of the controller. The mass spectrometer is generally located within a vacuum chamber provided with one or more pumps to evacuate its interior.

Ion storage devices that use RF fields for transporting or storing ions have become standard in mass spectrometers. One ion guide is the humpbacked ion guide, shown in FIG. 2 and FIG. 2B , is efficient in blocking neutrals/particles to prevent ion spikes due to debris. The elongate electrodes extend along a curved axis, the electrodes being paired in the x and y axes, e.g. 0°, 90°, 180°, and 270°. Unfortunately, there is accumulation of contaminants on rising section of the curved ion guide, e.g. the surface of electrode at 270° that tends to degrade the performance of the device over time. As the device does not allow for a good pumping out of the gas flow coming from the previous chamber, downstream optics, e.g. the ion optics can also become contaminated.

FIG. 3A and FIG. 3B shows an alternate arrangement of four electrodes in a curved ion guide device that confines and transfers ions using a combination of DC, RF, and AC fields. The elongate electrodes extend along a curved axis, the electrodes being paired in the x and y axes, e.g. 0°, 90°, 180°, and 270°. In addition to the ions, the ion optics are contaminated by additional debris, e.g. neutrals, particles, or charged droplets. The static charge from the debris builds up on the ion optics thereby degrading performance of the device over time.

In one embodiment, a mass spectrometry system arrangement that includes a bent ion guide, where the bend of the ion guide is positioned such that a portion of the ion optics are visible from at the ion guide entrance, e.g. line of sight or longitudinal axis. There are four electrodes parallel with each other and the central curved axis. Each electrode is equally radially spaced from the curved central axis. For each cross section of the ion guide, the central curved axis being positioned at the origin, the curved electrodes being radially positioned at 45°, 135°, 225°, and 315°.

A removable blocking device is positioned external to the ion guide but within the “line of sight” of the ion optics.

The removable blocking device is a physical barrier large enough to collect the debris that could reenter the ion guide and accumulate on the ion optics or generate spikes.

In another embodiment, a mass spectrometry system that includes an alternate bent ion guide. The gas stream moves tangentially along a portion of the ion guide. The removable blocking device is positioned external to the ion guide.

FIG. 1 illustrates a mass spectrometry system arrangement of the prior art.

FIG. 2A and FIG. 2B illustrate a humpback ion guide used in the prior art.

FIG. 2A illustrates a device view while FIG. 3B shows the cross-sectional view of the device.

FIGS. 3A and 3B illustrate a curved ion guide used in the prior art. FIG. 3A illustrates a device view while FIG. 3B shows the cross-sectional view of the device.

FIG. 4 illustrates an embodiment of the mass spectrometry system according to the invention.

FIG. 5A and FIG. 5B illustrate a bent ion guide of the present invention. FIG. 5A illustrates a device view while FIG. 5B shows the cross-sectional view of the device.

FIG. 6A-C illustrate embodiments of the removable blocking device shown in FIG. 6 .

FIG. 7 illustrates an alternate embodiment of the removable blocking device shown in FIG. 6A-C .

FIG. 8 illustrates another embodiment of the mass spectrometry system according to the invention.

FIG. 9A and FIG. 9B illustrate a curved ion guide of the embodiment of FIG. 8 . FIG. 9A illustrates a device view while FIG. 9B shows the cross-sectional view of the device.

FIG. 4 shows a block diagram of mass spectrometer of the present invention. An ion source that generates and supplies ions to be analyzed to a set of ion optics, including an ion guide. The ion guide is used to send the ions to the analyzer. Ion optics may be located adjacent to the ion guide so that mass spectra may be taken, under the direction of the controller (not shown). The mass spectrometer, as a whole, is operated under the direction of the controller. The mass spectrometer is generally located within a vacuum chamber (not shown) provided with one or more pumps to evacuate its interior.

The bend of the ion guide 12 is positioned such that the ion optics 20 are visible from the ion guide entrance, e.g. line of sight or z-axis, through the spaces between the electrodes of the ion guide 12 . A removable blocking device 22 is positioned external to the ion guide 12 but along the “line of sight” of the ion optics 20 .

FIG. 5A and FIG. 5B illustrate a bent ion guide of the present invention. FIG. 5A shows the plan view while FIG. 5B illustrates a cross-sectional view. The ion guide includes N curved electrodes, where N 2 . In this illustrative embodiment, N is 4.

The ion guide 12 includes 4 curved electrodes 24 A-D. The ion guide 12 has a central curved axis being co-extensive with an arc of a circular section having a radius of curvature and the x-axis extending between the ion guide entrance and the ion guide exit. A portion of the z-axis is external to the ion guide 12 . In operation, the particulate matter travels along the longitudinal axis.

As shown in FIG. 5B , the four electrodes are parallel with each other and the central curved axis. Each electrode is equally radially spaced from the curved central axis. For each cross section of the ion guide, the central curved axis being positioned at the origin, the curved electrodes being radially positioned at 45°, 135°, 225°, and 315°.

In the prior art, the plane including the curved central axis is coincident with the x-axis, the ion optics are blocked by the rising section of the ion guide. This rising section of the ion guide collects the neutrals, particulants, and charged droplets. This debris increases the build up to static charges that affects the speed of ion transmission. As the debris is enclosed within the ion guide, the debris travels and collects on the ion optics.

FIG. 6A-C illustrates an embodiment of the removable blocking device shown in FIG. 4 . FIG. 6A shows a blocking device that includes a flat surface facing the ion source that prevents particles from bouncing back into the ion guide. The surface is positioned such that the normal is away from the ion guide. FIG. 6B shows a block device that includes a concave surface that “captures or collects” the particles. FIG. 6C shows a blocking device that includes a vertex that deflects particles and gas stream away from the ion guide. Each surface is positioned such that the particle stream moves tangential to the surface or has a normal away from the ion guide. The aforementioned concepts may be combined to create a blocking device that deflects and collects particles.

The blocking device may be insulative or conductive. When the blocking device is conductive, the blocking device is a conductive metal post to allow grounding or being tied to a power supply. FIG. 7 further shows an optional cap positioned over the tip of the post to facilitate quick and efficient cleaning.

FIG. 7 illustrates an alternate embodiment of the removable blocking device shown in FIG. 4 . In this embodiment, the blocking device is an optional cap sheathing the tip of the post. The sheath is a physical barrier that prohibits reentry of particulant matter and debris into the ion guide. The sheath may consist of tape, plastic, cardboard, etc.

For the embodiments shown in FIG. 6 and FIG. 7 , the post is external to the ion guide while blocking a portion of the ion optics.

FIG. 8 illustrates a mass spectrometry system that includes an alternate bent ion guide. The ion guide is positioned between the ion source and a mass analyzer. The mass analyzer is further connected to downstream analysis devices, e.g. detector optics. A removable blocking device is positioned external to the ion guide but within the “line of sight” along the z-axis.

The “gas stream” travels tangential to the rising section of the curved axis. The ion optics are not exposed to the gas stream. FIG. 9A and FIG. 9B illustrates a curved ion guide 12 of the present invention. FIG. 9A shows the plan view while FIG. 9B illustrates a cross-sectional view. The ion guide 12 includes four curved electrodes 24 A-D. The ion guide 12 has a central curved axis being co-extensive with an arc of a circular section having a radius of curvature and the z-axis extending between the ion guide entrance and the ion guide exit. A portion of the z-axis is external to the ion guide 12 . In operation, the particulate matter travels along the z-axis.

As shown in FIG. 9B , the four electrodes 24 A-D define a curved ion guide region arranged about the curved central axis and between the four electrodes. The curved ion guide region has a rising section and a falling section. The four electrodes are parallel with each other and the central curved axis. Each electrode is equally radially spaced from the curved central axis. For each cross section of the ion guide, the central curved axis being positioned at the origin, the curved electrodes being radially positioned at 45°, 135°, 225°, and 315°.

In the prior art, the plane including the curved central axis is coincident with the y-axis, the ion optics are blocked by the rising section of the ion guide. This rising section of the ion guide collects the neutrals, particulants, and charged droplets. This debris increases the build up to static charges that can affect the speed of ion transmission. As the debris is enclosed within the ion guide, the debris can also travel and collects on the ion optics.

In the present invention, the ion optics are not shielded by the rising section of the ion guide but shielded by the blocking device. In operation, the ions travel within the ion guide while the “gas stream” passes between the electrodes of the ion guide along the “line of sight” from the ion source to the ion optics. The debris exits the ion guide and collects on the blocking device before it can reenter the ion guide or is deflected by the blocking device.

While the ion guide has been illustratively described using curved electrodes, the concept can be extended to any ion guide, i.e. stacked ring ion guide, having an ion stream where particulate matter could reenter the ion guide and contaminate the ion optics.