Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Reexamination Certificate
2000-01-14
2002-10-22
Lee, John R. (Department: 2878)
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
C250S282000
Reexamination Certificate
active
06469296
ABSTRACT:
TECHNICAL FIELD
This invention relates to ion accelerators. In particular, the invention relates to an ion acceleration apparatus and method for use in mass spectrometry, such as time of flight mass spectrometry.
BACKGROUND ART
Mass spectrometry is an analytical methodology used for quantitative elemental analysis of materials and mixtures of materials. In mass spectrometry, a sample of a material to be analyzed called an analyte is broken into particles of its constituent parts. The particles are typically molecular in size. Once produced, the analyte particles are separated by the spectrometer based on their respective masses. The separated particles are then detected and a “mass spectrum” of the material is produced. The mass spectrum is analogous to a fingerprint of the sample material being analyzed. The mass spectrum provides information about the masses and in some cases quantities of the various analyte particles that make up the sample. In particular, mass spectrometry can be used to determine the molecular weights of molecules and molecular fragments within an analyte. Additionally, mass spectrometry can identify components within the analyte based on the fragmentation pattern when the material is broken into particles. Mass spectrometry has proven to be a very powerful analytical tool in material science, chemistry and biology along with a number of other related fields.
A specific type of mass spectrometer is the time-of-flight (TOF) mass spectrometer. The TOF mass spectrometer (TOFMS) uses the differences in the time of flight or transit time through the spectrometer to separate and identify the analyte constituent parts. In the basic TOF mass spectrometer, particles of the analyte are produced and ionized by an ion source. The analyte ions are then introduced into an ion accelerator that subjects the ions to an electric field. The electric field accelerates the analyte ions and launches them into a drift tube or drift region. After being accelerated, the analyte ions are allowed to drift in the absence of the accelerating electric field until they strike an ion detector at the end of the drift region. The drift velocity of a given analyte ion is a function of both the mass and the charge of the ion. Therefore, if the analyte ions are produced having the same charge, ions of different masses will have different drift velocities upon exiting the accelerator and, in turn, will arrive at the detector at different points in time. The differential transit time or differential ‘time-of-flight’ separates the analyte ions by mass and enables the detection of the individual analyte particle types present in the sample.
When an analyte ion strikes the detector, the detector generates a signal. The time at which the signal is generated by the detector is used to determine the mass of the particle. In addition, for many detector types, the strength of the signal produced by the detector is proportional to the quantity of the ions striking it at a given point in time. Therefore, the quantity of particles of a given mass often can be determined also. With this information about particle mass and quantity, a mass spectrum can be computed and the composition of the analyte can be inferred.
In a time of flight mass spectrometer (TOFMS), the ion accelerator accepts a stream of ions from an ion source and accelerates the analyte ions by applying an electric field. The velocity of a given ion when it exits the ion accelerator is proportional to the square root of the accelerating field strength, the square root of the charge of the ion, and inversely proportional to the square root of the mass of the ion. Thus, ions with the same charge but differing masses are accelerated to differing velocities by the ion accelerator.
In addition to accelerating the analyte ions, the ion accelerator pulse modulates
25
the ion stream. The term “pulse modulation” as used herein refers to breaking the ion stream into a series of ion bunches or “packets”, each packet being individually accelerated by action of the ion accelerator. The individual packets are accelerated and allowed to drift to the detector one packet at a time. To accomplish the pulse modulation, the ion accelerator collects ions produced by the ion source in an input or fill region for a period of time. The period or time interval during which ions are collected is known as the fill period or fill interval. The ion accelerator periodically releases the collected ions from the fill region into an acceleration region. The period when the ions are released from the fill region into the acceleration region is known as the pulse period or duration. The sequential fill and pulse periods produce packets of ions traveling in the drift region and striking the detector. The separation in time between the packets is designed to enable the measurement of the differential TOFs of the various analyte ions. Ion accelerators are sometimes also referred to as a “pulser” or an “ion storage modulator” due to the pulse modulation that they impart on the analyte ion stream.
A widely used, conventional ion accelerator used in mass spectrometry is based on a design first proposed by Wiley and Mclaren (W. C. Wiley and I. H. Mclaren, “Time-of-Flight Spectrometer with Improved Resolution,” The Review of Scientific Instruments, vol. 26, no. 12, December, 1955, pp. 1150-1157) incorporated herein by reference. A description of a more contemporary version of the conventional accelerator based on the Wiley-Mclaren design is provided by Dodonov et al (A. F. Dodonov, et al, “Electrospray Ionization on a Reflecting Time-of-Flight Mass Spectrometer,” in Time-of-Flight Mass Spectrometry, ed. Robert J. Cotter, ACS Symposium Series 549, American Chemical Society, Washington, D.C., 1994, Chapter 7, pp. 108-123) incorporated herein by reference. The mechanical configuration of the ion accelerator is illustrated in
FIG. 1. A
schematic of the conventional ion accelerator is illustrated in FIG.
2
.
The ion accelerator comprises a stack or sequentially located plurality of thin metal plates or electrodes separated by insulating spaces or spacers. The conventional ion accelerator further comprises a pair of high voltage pulse generators,
22
and
23
, a fixed high voltage bias source
24
and a multi-tap voltage divider
20
.
The stack of electrodes comprises a first electrode
10
, a first grid
12
, a second grid
13
, a third grid
14
, and a plurality of guard frames
16
. The first electrode
10
is a solid conductive plate called a pulser plate or pulser electrode. The grids
12
,
13
, and
14
are conductive plates each of which has a porous, conductive screen or wire mesh covering a hole or opening that penetrates from one side of the grid to the other. The guard frames
16
are also conductive plates with a hole similar to that of the grids
10
-
14
except the hole in the guard frames
16
is not covered with a screen.
In the ion accelerator, the electrodes are ordered such that the pulser electrode
10
is followed by the first and second grids
12
,
13
. The second grid
13
, in turn, is followed by a plurality of guard frames
16
that, in turn, are followed by the third grid
14
. A space between the pulser electrode
10
and the first grid
12
is called a fill region
17
. The holes in the grids
12
-
14
and the guard frames
16
are aligned in the stack to produce a channel or path from the fill region
17
to the third grid
14
. The channel is called the acceleration region
18
.
As depicted in the schematic illustrated in
FIG. 2
, the conventional ion accelerator comprises the first high voltage pulse generator
22
connected to the pulser electrode
10
and the second high voltage pulse generator
23
connected to the second grid
13
. The high voltage bias source
24
is connected to third grid
14
. The high voltage bias source
24
is also connected to an input port of the multi-tap voltage divider
20
. Each of the taps or output ports of the voltage divider
20
is connected, in turn, to one of the plurality of guard frames
16
. Each of the g
Foote James
Hansen Stuart C.
Agilent Technologie,s Inc.
Lee John R.
Quash Anthony
LandOfFree
Ion acceleration apparatus and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ion acceleration apparatus and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ion acceleration apparatus and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2982793