WO2003058673A2

WO2003058673A2 - Adaptive mounting

Info

Publication number: WO2003058673A2
Application number: PCT/EP2003/000041
Authority: WO
Inventors: Jan Axelsson
Original assignee: Amersham Biosciences Ab
Priority date: 2002-01-10
Filing date: 2003-01-06
Publication date: 2003-07-17
Also published as: AU2003202541A8; WO2003058673A3; GB0200469D0; AU2003202541A1

Abstract

An element (9) in the path of ions (18) in a mass spectrometer is adaptively mounted so that variations in the path ions take can be compensated for in order to improve the resolution of the mass spectrometer. Preferably the element is mounted on at least one variable shape mounting element (37) which can vary its length in response to signals from remote control means (21).

Description

ADAPTIVE MOUNTING

Field of the Invention

The present invention relates to devices and methods of the type mentioned in the preambles of the independent claims for improving the resolution of mass spectrometers.

Prior Art

Mass spectrometers can be used to determine the composition of samples. In some time-of- flight mass spectrometers (TOF MS) a sample is ionised in the first end of a mass spectrometer, accelerated by an electrical field towards the second end of the mass spectrometer at a certain time and the arrival time of ions at a detector mounted at the second end is recorded. The time between an ion being accelerated and it being detected at the detector is known as the time of flight for the ion and is dependent on, amongst others, the length of the flight path and the mass to charge ratio of the ion. The resolution of a TOF MS is dependent on the spread of the flight times of ions of the same type. One of the main reasons for the spread of flight times is the difference in the lengths of the flight paths that the individual ions take. One of the variations in the length of the flight path is caused by the different radial positions of the ions when they are accelerated to the mass spectrometer detector surface. When mass spectrometers are assembled the manufacturer provides detectors with adjustable mountings which can be manually adjusted in an attempt to align the detector surfaces so that the total flight time of ions from the source to the detector surface is independent of radial position and the resolution is optimised. This is no easy task as errors in alignment of the order of micro-meters cause substantially decreased resolution. Additionally, often no provision is made for realigning the detector surfaces in the field to compensate for misalignments which may occur during use of the device. The flight tube and the electrodes are examples of other elements of the mass spectrometer the positions of which may influence the resolution of the mass spectrometer.

Summary of the Invention According to the present invention, at least some of the problems with the prior art are solved by means of a device having the features present in the characterising part of claim 1 and a method having the features mentioned in the characterising part of claim 5. Brief Description of the Figures

Figure 1 shows schematically a cross-section through a mass spectrometer provided with an adaptive mounting device in accordance with a first embodiment of the present invention;

Figure 2 shows schematically in perspective an ion-detector supported by an adaptive mounting device in accordance with a second embodiment of the present invention.

Detailed Description of Embodiments Illustrating the Invention

Figure 1 shows a simplified schematic drawing (not to scale) of a time-of-flight mass spectrometer (TOF MS) 1 provided with an adaptive mounting device in accordance with the present invention in which some parts of the mass spectrometer which are not related to the present invention are omitted in order to facilitate illustration of the present invention. TOF MS 1 comprises an sample plate 3 mounted at a first end 5 of a flight tube 7 and an ion detector 9 mounted at the second end 11 of the flight tube 7. Ionisation means such as a laser 13 are directed onto the sample plate 3 and can be operated to ionise a sample 15 positioned on the sample plate 3. Electrical field generating accelerating grids 17 are positioned between the sample plate 3 and the ion detector 9 and can be energised in order to accelerate ions 18 from the sample plate 3 towards the ion detector 9. Ion detector 9 can be arranged to produce an output signal whenever ions 18 (represented by dashed lines in the figures) of sufficient energy hit its detector surface 19. Laser 13, accelerating grids 17 and ion detector 9 are preferably all connected to an automated remote control means such as a computer 21 which is programmable to operate the laser 13, to energise the accelerating grids 17 at an appropriate time to accelerate ions towards the ion detector 9, and to record the ion arrival signals from the ion detector 9.

Ion detector 9 is mounted to the flight tube by means of an adaptive mounting device 23 in accordance with a first embodiment of the present invention.

Circular ion detector 9 is attached to, and held at a short distance from, said a support surface 25, which is rigidly attached to, or is an integral part of, the second end 11 of the mass spectrometer 1, by mounting means in the form of two legs 27 A, 27 B and adaptive mounting device 23. Legs 27 A, 27B are each fixed at one end 29A, 29B to said support surface 25 and are pivotally joined by joints (only one of which, 31A, is shown in fig. 1) at their opposite ends (only one of which, 33A, is shown in fig. 1) to the rim 35 of ion detector 9.

Adaptive mounting device 23 comprises at least one variable shape mounting element 37 which is attached at a first end 39 to the support surface 25 and is pivotally attached by a joint 41 at a second end 43 to the rim 35 of ion detector 9 that it is intended to align. Preferably legs 27 A, 27B and adaptive mounting device 23 are spaced equidistantly around the rim 35 of ion detector 9. Variable shape mounting element 37 is able to vary its length in response to control signals provided remotely from a control means, preferably the same computer 21 which controls the laser 13, accelerating grids or plates 15 and ion detector 9. In this first embodiment of the present invention variable shape mounting element 37 is a linear piezoelectric actuator which can vary its length in response to an electrical voltage applied to it from the remote control means 21. If variable shape mounting element 37 increases in length from 1 to L then the part of the rim 35 to which it is attached is pushed towards the first end of flight tube 7 and the ion detector 9 is pivoted about the joints connecting legs 27 A, 27B to the rim 35. This causes ion detector 9 to pivot from the position shown in solid lines to the position shown in dotted lines in fig 1. The opposite movement occurs if variable shape mounting element 37 decreases in length.

The control means 21 may be programmed to remotely control the adjustment of the length of variable shape mounting element 37 in order to move ion detector 9 to a position which gives the best resolution. Preferably this adjustment is achieved using a feedback system for finding the shape, e.g. length, of the variable shape mounting element that gives the best resolution. This could be a system in which an adjustment is made in one direction, the effect of the adjustment on the resolution is determined and further adjustments made in the same direction until a deterioration in the resolution occurs. Adjustments are then made in the reverse direction until the best resolution is achieved. This could be achieved by producing a series of beams of ions of known mass/charge ratio from a sample and adjusting the length of the variable shape mounting element 37 in stages until the width of the resulting peak detected by the ion detector 9 is reduced to a minimum. For example, the length of the variable shape mounting element 37 could be increased in length under the control of control means 21 with increments which are 1% or 5% or 10% of its shortest length or any other suitable increment and the resolution of the mass spectrometer checked by control means 21 after each increment. The control means 21 could be programmed to set the length of the variable shape mounting element at the length which gave the best resolution.

Alternatively, the length of variable shape mounting element 37 may be adjusted by an operator who remotely adjusts the length of variable shape mounting element 37 by varying the voltage applied to it while watching a monitor showing an image displaying the width of the detected peak. The operator could identify by eye the variable shape mounting element 37 length which gives the ion detector position which gives the narrowest peak width and control the variable shape mounting element 37 to stay at that length.

In a second embodiment of the present invention, an element in a mass spectrometer such as an ion detector 9 is supported by a plurality of variable shape mounting elements. In a preferred embodiment of the present invention shown schematically in figure 2, an ion detector is supported by three variable shape mounting elements 37A, 37, B, 37C which are preferably spaced equally around its perimeter. Variable shape mounting elements are preferably attached to the rim of ion detector 9 by joints such as ball and socket joints 41A, 41B, 41C which allow ion detector to tilt with respect to variable shape mounting elements 37A-37C. The tilt of the ion detector with respect to its supporting surface 25 in a plane which passes through a straight line R connecting the mounting points 41 A, 41B of two variable shape mounting elements 37A, 37 B can be adjusted by varying the length of variable shape element 37C. Similarly the tilt of the ion detector with respect to its supporting surface 25 in a plane which passes through a straight line S connecting the mounting points 41B, 41 C of two variable shape mounting elements 37B, 37 C can be adjusted by varying the length of variable shape element 37A and the tilt of the ion detector with respect to its supporting surface 25 in a plane which passes through a straight line T connecting the mounting points 41 A, 41 C of two variable shape mounting elements 37A, 37 C can be adjusted by varying the length of variable shape element 37B. Additionally, it is possible to not only adjust the tilt of the ion detector 9 towards the ion source but also to adjust the distance between the ion detector and the ion source by extending or retracting all of the variable shape mounting elements 37A-37C the same distance. Using this embodiment of the present invention it is possible to find the position of the ion detector 9 which gives the best resolution by varying in turn the length of each variable shape element 37A-37C while observing the effect of the change in length on the resolution of the output from the mass spectrometer. Preferably the resolution is adjusted before the mass spectrometer is used for analysing a sample. Further adjustment of the resolution may take place hourly, daily, weekly, monthly, etc. or as required.

The variable shape mounting element may be made of any suitable material or components, for example hydraulic or pneumatic actuators, an electrical motor moving a supporting arm or bending a flexible supporting beam or operating a screw jack, etc. The variable shape element does not have to be mounted by means of hinges to the component which it is intended to adjust the position of- it is sufficient to design the mounting arrangement to be flexible enough such that the force exerted by the variable shape mounting element is able to move the component.

The present invention has been illustrated by examples in which an ion-detector is moved but it is conceivable to adjust other components to improve the resolution of a device such as a mass spectrometer. For example, electrodes could be mounted on tiltable or movable mountings, or the ion detector could be rigidly mounted on the flight tube and the whole flight tube tilted or moved and bellows provided between the flight tube and its mounting in order to maintain the vacuum in the flight tube.

The above mentioned embodiments are intended to illustrate the present invention and are not intended to limit the scope of protection claimed by the following claims.

Claims

1. Device for improving the resolution of a mass spectrometer comprising elements (7, 9, 17) able to influence the resolution of the mass spectrometer characterised in that it comprises at least one variable shape mounting element (37) arranged for adjusting the position of an element (7, 9, 17) wherein the shape of said variable shape mounting element (37) is controllable remotely.

2. Device in accordance with claim 1 characterised in that said variable shape mounting element (37) is a piezo-electric actuator.

3. Device in accordance with any of the previous claims characterised in that said element (9) is an ion-detector (9) or electrode (17) or flight tube (7).

4. Device in accordance with any of the previous claims characterised in that said variable shape mounting element (37) is controllable remotely by automated remote control means such as a computer (21).

5. Device in accordance with any of the previous claims characterised in that it has at least two variable shape mounting elements (37A, 37B).

6. Method for improving the resolution of a mass spectrometer characterised by the steps of: mounting an element (7, 9, 17) in the ion path by means of at least one remotely controllable variable shape mounting element (37): providing remote control means for adjusting the shape of said variable shape mounting element (37).

7. Method in accordance with claim 5 characterised by the further step of providing said remote control means (21) with a feedback system for finding the shape, e.g. length, of the variable shape mounting element which gives the best resolution.

8. Method in accordance with claim 7 characterised in that said feedback system comprises the steps of measuring the resolution of the mass spectrometer, adjusting the shape of the variable shape mounting element in one direction, determining the effect of the adjustment on the resolution, making further adjustments made in the same direction until a deterioration in the resolution occurs and making adjustments in the reverse direction until the best resolution is achieved.

9. A mass spectrometer provided with a device or method in accordance with any of the previous claims.