Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Reexamination Certificate
1997-03-14
2001-11-13
Nguyen, Kiet T. (Department: 2878)
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
Reexamination Certificate
active
06316768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to improved system and sub-system components for time of flight mass spectrometers which are used for detecting, recording and displaying time of flight mass spectrometry data.
2. State of the Art
For the purposes of this invention, time of flight (TOF) mass spectrometry will be defined as the conversion of an electrically recorded mass spectra into a chemically recognizable form. Useful background information about time of flight mass spectrometers and improvements made therein is taught in U.S. patent application Ser. No. 08/751,509 which is herein incorporated by reference.
A common time of flight mass spectrometer architecture exists which will serve as a basis for the present invention. However, it should be remembered that while the present invention is particularly applicable to the systems of a mass spectrometer, the technology is also applicable to other industries.
FIG. 1
is a block diagram which is provided to show some components of a mass spectrometer as known to those skilled in the art. The components identified as
12
are the electronics associated with mass spectrometer which function either as a transient digitizer or a time to digital converter. The electronics
12
are thus electrically coupled to a time of flight mass spectrometer, also known as a waveform recorder, which is generally indicated at
10
. A time of flight mass spectrometer
10
is typically constructed of a chamber having an outer vacuum housing
14
and an inner flight tube
16
shown in cross-section.
FIG. 1
shows the inner flight tube
16
along its length. The cross section of the inner flight tube
16
can be circular, square or other appropriate tube shapes as known to those skilled in the art of time of flight mass spectrometry. An input port
18
enables particles (ions) to be injected into the flight tube
16
and accelerated down the length of the flight tube
16
by a combination of a pulser
20
(a.k.a. a pulsed repeller plate) and a series of field defining electrodes
22
which are disposed so as to define a pathway
24
within the vacuum housing
14
for the ions to travel. A particle is accelerated down the flight tube
16
toward a microchannel plate
26
and an anode detector
28
(single or multiple anodes). Particles striking the microchannel plate
26
are then detected as an electrical pulse on the anode detector
28
, which in turn causes the anode detector
28
to generate an electrical signal which is processed by the electronics
12
associated with the anode detector
28
.
An explanation of the mass spectrometer
10
is incomplete without looking at what subsystems precede and follow the mass spectrometer
10
. Specifically, these subsystems include the transportation of particles to the mass spectrometer in a transport subsystem
30
, and a data system
32
which receives information from the mass spectrometer
10
.
The transportation subsystem of particular interest is an ion transport system
30
for directing ions to the mass spectrometer
10
. The ion transport system
30
typically includes a series of RF quadrapoles
52
constructed of individual differential pumping units
50
. The differential pumping units
50
are typically required because ions are being transported from a pressurized area to the vacuum housing
14
. The pressure surrounding the ions is decreased in stages so that a much larger single pumping unit does not have to be used. Consequently, two differential pumping units
50
are shown to illustrate the concept of gradually decreasing pressure.
To provide additional background information, this application incorporates by reference the information taught in U.S. patent application Ser. No. 08/814,898 filed Mar. 12, 1997, with the title TAPERED OR TILTED ELECTRODES TO ALLOW THE SUPERPOSITION OF INDEPENDENTLY CONTROLLABLE DC FIELD GRADIENTS TO RF FIELDS.
In summary, the above-referenced patent application shows state of the art ion transport systems which include the system shown in
FIG. 2A. A
system
40
is comprised of four electrodes
42
, where one electrode
42
is obscured by another in this view. In
FIG. 2A
, the path
44
an ion
46
travels is shown as indicated to be generally along with and parallel to a lengthwise quadrapole axis
48
of the electrodes
42
. The electrodes
42
are charged with an RF component. The RF component is provided so that ions are confined in the radial direction relative to the lengthwise axis
48
of the quadrapole system
40
.
The system
40
shown in
FIG. 2A
is known as an RF quadrapole
52
because of the four electrodes
42
which generate the RF field for confining ions in the radial direction. However, other multipole electrode configurations are also present in the state of the art, such as six (hexapole) or eight (octapole) electrode systems. All function similarly in that the systems provide confinement in the radial direction. However, for an ion
46
traveling near the axis of the system
40
, the effect of higher order RF fields created by a greater number of electrodes is minimal.
FIG. 2B
is provided to show that the electrodes
42
(
FIG. 2A
) are arranged such that they are generally positioned at four corners of a square. This means that the distance from any electrode
42
to the nearest two electrodes is generally equidistant for each of the electrodes.
Generating a DC axial field gradient is useful when it is desirable to accelerate ions axially along the quadrapole axis
48
. The DC field gradient is also useful in overcoming drag forces arising from the presence of background gas which may be present along the ion path.
An improvement to the RF quadrapole system
40
described above is the creation of quadrapole pairs which are tilted and/or tapered. This effectively doubles the number of electrodes
42
used in the system
40
, as will be explained later.
With the above background in mind, some of the problems with state of the art systems for a time of flight mass spectrometer will now be addressed. This will focus attention on the improvements made to the entire system by the present invention. Beginning with the ion transport system
30
, it is often necessary to introduce electrical signals into chambers which are pressurized or have a vacuum therein. Chamber walls are typically constructed of discrete insulating materials interspersed with discrete metallic components which are sometimes used for propagating electrical signals. The opposite is also true that the walls are primarily formed of metal and interspersed with insulating material.
Therefore, it would be an advantage to provide a chamber wall which is comprised of materials which are relatively so much easier to fabricate than the chamber walls of the prior art that the costs of the system are significantly reduced.
In a related system shown in
FIG. 3
, discrete non-insulating material is typically used in the construction of a vacuum flange comprised of a seal
34
and an O-ring
36
for closing a vacuum chamber
38
. Furthermore, if electrical signals are to be introduced into the vacuum chamber
38
, metallic, glass or ceramic feedthroughs must be provided as conduits through the seal
34
. Without the feedthroughs, any electrical signals applied to the seal would be dispersed and insulated from the vacuum chamber by the O-ring which is typically a rubber-like material. The result is that it is difficult and costly to propagate electrical signals into the vacuum chamber
38
.
It would therefore be an improvement over the prior art to provide a vacuum seal which would not disperse electrical signals with which it comes into contact. Furthermore, it would be an advantage to provide a seal which did not require the use of a specialized feedthrough which is costly and might require modification of the seal to install.
Another related problem in the prior art is when a skimmer cone is coupled to chamber walls. A skimmer cone shown generally at
51
in
FIG. 1
is utilized for the purpose of preserving a supersonic beam in a d
Davis Larry J.
Jones Jeffrey L.
Lee Edgar D.
Rockwood Alan L.
Leco Corporation
Nguyen Kiet T.
Thorpe North & Western LLP
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