Mass spectrometer

Details Mass spectrometer Mass spectrometer

2002-07-23

2004-08-24

Lee, John R. (Department: 2881)

Radiant energy

Ionic separation or analysis

Reexamination Certificate

active

06781116

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mass spectrometer.
2. Discussion of the Prior Art
Conventionally, mass spectrometers utilize an ion optical mass filter/analyser such as a quadrupole. However, ion optical devices must normally be operated at low pressures (high vacuum) which requires the use of expensive vacuum pumps and related equipment.
EP-1001450 discloses a centrifugal mass filter for separating low and high mass ions. Crossed electric and magnetic fields are provided which act upon ions within a chamber. The crossed fields cause ions to move through the chamber on helical paths about a central axis. The electric, magnetic and centrifugal forces acting upon the ions are arranged so that ions having a mass to charge ratio greater than a cut-off value have unconfined (loss) orbits. Such ions move radially outward until they strike the wall of the chamber. Lighter ions however, will be contained within the chamber and can be collected at the exit of the device. There is no teaching or suggestion that the mass filter is suitable for operation at relatively high pressures, and indeed the assumption in the art is that mass filters must be operated at low pressures e.g. <10
−3
mbar.
SUMMARY OF THE INVENTION
It is desired to provide an improved mass spectrometer. A significant advantage of the preferred mass filter/analyser over conventional ion optical mass filters/analysers and the mass filter disclosed in EP-1001450 is that the preferred mass filter/analyser is intended to be operated at much higher pressures than is known in the art, up to and even above atmospheric pressure. The preferred mass filter/analyser therefore represents a significant advance in the art.
In contrast to the centrifugal mass filter disclosed in EP-1001450, the preferred embodiment relates to a vortex mass filter/analyser. In a centrifuge the tangential velocity of a particle in the rotating fluid increases with radius, whereas in a vortex the tangential velocity of a particle in the rotating fluid decreases with radius.
According to a particularly preferred embodiment, the vortex mass filter/analyser may operate as a mass analyser. The term “mass analyser” is used in the present application to describe a mass to charge ratio selective device which has a high mass to charge ratio resolution (m/z)/&Dgr;(m/z). For example, the mass to charge ratio resolution (m/z)/&Dgr;(m/z) of the mass analyser according to the preferred embodiment may be 500:1 or more (i.e. it can select ions to within one mass to charge ratio unit over a range of 500 mass to charge ratio units). For reference, a conventional quadrupole mass analyser may, in certain circumstances, be considered to have a comparable mass to charge ratio resolution of up to 5000:1.
The term “mass filter” is intended to describe a mass to charge ratio selective device which operates either in a low-pass, broad band-pass or high-pass mode, and typically but not necessarily always has a relatively low mass resolution. For example, a low pass mass filter such as is disclosed in EP-1001450 which transmits ions having a mass to charge ratio <100 mass to charge ratio units could be considered to have a mass to charge ratio resolution (m/z)/&Dgr;(m/z) of 100:100. The mass filter disclosed in EP-1001450 is not therefore intended to constitute a “mass analyser” within the meaning of the present application.
Mass separators are known which separate particles on the basis of their mass rather than mass to charge ratio. Such mass separators are not intended to constitute a “mass filter” or a “mass analyser” within the meaning of the present application.
A further distinction of the preferred embodiment over the arrangement disclosed in EP-1001450 is that a magnetic field is not required and is therefore preferably not used. The preferred embodiment is therefore much simpler than the mass filter disclosed in EP-1001450.
Preferably, the vortex mass analyser comprises a chamber having a sample inlet and a hollow rotatable shaft arranged within the chamber, the interior of the shaft being in fluid communication with the chamber, wherein the interior of the shaft is connected to a pressure reducing means so that in use a vortex is created within the chamber, and wherein in use a potential difference is maintained between the wall of the chamber and the shaft.
Preferably, the shaft comprises one or more holes or apertures.
Preferably, the pressure reducing means comprises a pump.
Preferably, the potential difference is capable of being varied so that particles having a certain mass to charge ratio are arranged to be in equilibrium at a desired radius in the chamber.
Preferably, the chamber further comprises an inlet for a drying gas.
Preferably, the sample inlet and/or the inlet for a drying gas are arranged so as to generally or substantially tangentially inject a sample and/or drying gas into the chamber.
Preferably, the chamber comprises an outlet through which, in use, ions are extracted.
Preferably, ions having substantially similar mass to charge ratios are preferentially extracted from the chamber via the outlet.
Preferably, the mass spectrometer further comprises an ion source selected from the group comprising: (i) an Atmospheric Pressure Chemical Ionisation (“APCI”) ion source; (ii) an electrospray ion source; and (iii) a Matrix Assisted Laser Desorption Ionisation (“MALDI”) ion source. The MALDI ion source is preferably operated at or around atmospheric pressure. Alternatively, other atmospheric pressure ion sources may be used.
Preferably, the mass analyser comprises a chamber and ions are generated: (i) in the chamber; or (ii) externally to the chamber.
Preferably, the mass analyser is arranged and adapted to be operated at a pressure selected from the group consisting of: (i)≧1 mbar; (ii)≧2 mbar; (iii) ≧5 mbar; (iv)≧10 mbar; (v)≧20 mbar; (vi)≧50 mbar; (vii)≧100 mbar; (viii)≧150 mbar; (ix)≧200 mbar; (x)≧250 mbar; (xi)≧300 mbar; (xii)≧350 mbar; (xiii)≧400 mbar; (xiv)≧450 mbar; (xv)≧500 mbar; (xvi)≧550 mbar; (xvii)≧600 mbar; (xviii)≧650 mbar; (xix)≧700 mbar; (xx)≧750 mbar; (xxi)≧800 mbar; (xxii)≧850 mbar; (xxiii)≧900 mbar; (xxiv)≧950 mbar; (xxv)≧1000 mbar; (xxvi) approximately atmospheric pressure; and (xxvii) above atmospheric pressure.


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