WO2006034530A1

WO2006034530A1 - A time of flight mass spectrometer

Info

Publication number: WO2006034530A1
Application number: PCT/AU2005/001461
Authority: WO
Inventors: Andrew J Edgecombe; Andrew M Uhe
Original assignee: Gbc Scientific Equipment Pty Ltd
Priority date: 2004-09-30
Filing date: 2005-09-22
Publication date: 2006-04-06

Abstract

A time of flight spectrometer is disclosed which includes a time of flight chamber (10) an ion source (16) for producing ions for travel through the chamber (10) and a detector (38) for detecting the ions. The ions are accelerated into the chamber (10) by an orthogonal accelerator (36). A blanker (34) is provided for blanking plasma gases and also for preventing predetermined ions from being detected by the spectrometer. A processor (12) controls the blanker so as to blank those ions and to check that the blanker is working properly by allowing blank specific ions and selectively allow those specific ions to reach the detector (38).

Description

A TIME OF FLIGHT MASS SPECTROMETER

Field of the Invention

This invention relates to a time of flight mass spectrometer and, in particular, to such a spectrometer which is able to restrict specific sample ions from being detected by the spectrometer.

Background of the Invention In some instances it is desirable to provide an analysis instrument which is able to detect certain substances but is restricted from detecting other such substances. One example of such an instrument is a time of flight mass spectrometer which is used to analyse sample substances to provide an indication of the nature of the constituents of the sample substance. In order to restrict the instrument from detecting predetermined constituents of the sample substance, it is necessary to ensure that the instrument is first capable of doing this and can reliably be prevented from modification to detect such constituents.

Summary of the Invention

The object of this invention is to provide a time of flight mass spectrometer which is restricted from detecting certain substances.

The invention may be said to reside in a time of flight mass spectrometer comprising: a time of flight chamber; an ion source for supplying ions from a sample for travel through the time of flight chamber; a detector for receiving the ions after travel through the time of flight chamber to enable the ions which are detected to be identified so that the constituents of the sample can be determined; _M O _

a blanker for blanking ions travelling through the time of flight chamber so that blanked ions do not reach the detector; and a processor for controlling the blanker to: (a) blank predetermined ions so those ions are not received by the detector so the detector is not able to provide an indication of those ions in the sample during analysing of the sample; and the processing being for performing a blanking check to:

(b) selectively blank specific ions other than the predetermined ions at a time when the specific ions are expected to arrive at the blanker so that those specific ions are not able to reach the detector; (c) selectively control the blanker to allow the specific ions to reach the detector; and (d) wherein the blanking of the specific ions and the detection of the specific ions is used to provide an indication that the blanking of the predetermined ions will operate correctly to prevent the predetermined ions from being detected by the detector.

Thus, in order to prevent the detection of certain ions and therefore the indication of certain constituents in the sample substance, the blanker is controlled to blank those ions so they are not received by the detector. To ensure that the blanking takes place correctly and the blanking timing of the spectrometer has not been tampered with so as to change the blanking time to allow those predetermined ions to pass the detector, the blanking of the specific ions and the detection of the specific ions is used to ensure that blanking is correctly occurring and there has been no relative time shift of the blanking period which would allow the predetermined ions to reach the detector. In other words, the blanker is closed at the time the specific ions should be present, thereby _wm O _mm

preventing them from reaching the detector, and is opened when the specific ions should be present so those ions can then reach the detector. Thus, if the specific ions were not detected during the first phase of blanking and were detected during the second phase of blanking, it is assumed that the blanker is operating correctly. Thus, the spectrometer can reliably prevent the predetermined ions from reaching the detector so the instrument cannot be used to detect the constituents to which those ions relate, and also to ensure that blanking is operating properly.

Preferably the processor is also for shutting down the spectrometer in the event that it is determined that blanking is not operating properly to prevent the predetermined ions from reaching the detector.

Preferably the processor is for performing the blanking check by selectively blanking the specific ions at a time when the specific ions are expected to arrive at the blanker so that those ions do not reach the detector, and operating the blanker so that the blanker is opened at the time when the specific ions are expected to arrive at the blanker, so that only the specific ions reach the detector.

Thus, the blanker is operated in a first phase to open the blanker to the specific ions and in a second phase to close the blanker to the specific ions.

In one embodiment the shut down may simply be a control to the software of the instrument to prevent the software from analysing data produced by the detector and presenting that data.

Preferably the processor is also for controlling the blanker to prevent plasma gas from reaching the detector during the analysis of the sample substance so the ions which relate to the plasma gas do not saturate the detector during analysis of the sample.

Typically the plasma gas is argon. However, other inert gases such as nitrogen can also be used.

Thus, during actual analysis, the argon ions are blanked by the blanker so they are not detected by the detector as is conventional.

The predetermined ions which are to be prevented from reaching the detector may be ions above a predetermined mass or ions within a predetermined mass range. This can therefore ensure that the predetermined ions do not reach the detector and that multiply charged ions relating to the constituent which the instrument is to be prevented from detecting, are also not received by the detector.

Preferably the specific ions comprise the plasma gas ions so that by blanking the plasma gas ions and ensuring that the plasma gas ions are not detected by the detector, and blanking other ions and ensuring that the specific ions do reach the detector, the timing of the blanking can be verified and regarded as operating correctly.

Preferably the processor controls the blanker to perform the blanking of the other ions and the blanking of the specific ions in random order.

Most preferably the processor is for causing the blanking of the other ions and the blanking of the specific ions to occur a plurality of times and in random order.

Preferably the processor comprises a timing module for supplying blanking signals to the blanker for operating the blanker, a source module for controlling the supply of ions into the time of flight chamber, and an analyser module for receiving signals from the detector for providing an indication of the ions detected by the detector and therefore the constituents of the sample.

Preferably the control of the blanker is performed by the timing module to selectively blank the specific ions 'and selectively control the blanker to allow the specific ions to reach the detector.

Preferably the said modules are coded so that the processor will allow the modules to operate, only if the coding of the modules match a predetermined requirement to prevent modules from being removed and replaced to override the operation of the blanker to allow the predetermined ions to be detected by the detector.

Preferably the processor further includes a communications interface for coupling the processor to a computer, an ion optics module for focusing ions produced by the source and a blanker module for receiving signals from the timing module and for producing blanker pulses for supply to the blanker to operate the blanker.

Preferably the source comprises an RF system for producing a plasma, a gas box for supplying a plasma gas and an accelerator for receiving the ions from the RF system and for accelerating the ions into the time of flight chamber.

Preferably the accelerator is an orthogonal accelerator.

Preferably the ion optics module focuses the ions for supply to the orthogonal accelerator.

Preferably data transmitted between the interface and the personal computer is encrypted to ensure security of the communications between the computer and the processor. Brief Description of the Drawing

A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawing which shows a schematic block diagram of a time of flight mass spectrometer in accordance with the preferred embodiment.

Detailed Description of the Preferred Embodiment The drawing shows a schematic view of a time of flight mass spectrometer which has a time of flight chamber 10 and a processor 12. The processor 12 is adapted to be connected to a computer 14, such as a person computer.

The spectrometer also includes an RF system 16 for producing a plasma from a sample and a gas box 18 for providing a plasma gas in which the sample is entrained for supply to the time of flight chamber 10.

The chamber 10 is evacuated by turbo pumps 20, 22 and 24 which are controlled by a vacuum and slide valve controller 26, which in turn is controlled by the processor 12.

The processor 12 has a serial communications interface 30 for connecting the processor 12 to the personal computer 14, a timing card 32 for controlling the timing of blanker 34 within the time of flight chamber 10, an orthogonal accelerator power board 34 for controlling an orthogonal accelerator 36 which receives ions from the plasma produced by the RF system 16 and accelerates the ions into the time of flight chamber 10 so that the ions travels through the time of flight chamber 10 for receipt by a detector 38.

In the embodiment shown, the accelerator 36 and detector 38 are at the same end of the time of flight chamber 10 and the time of flight chamber 10 would include a , reflectron (not shown) at the opposite end of the time of flight chamber for receiving the ions and reflecting them towards the detector 38. However, in other embodiments the detector 38 could simply be at the end of the time of flight chamber 10 opposite the orthogonal accelerator 36.

The processor 12 also includes an analyser power board 42 which receives a signal from the detector 38 when ions are detected so that data can be supplied which enables the nature of the ions to be determined from the time of flight of the ions through the time of flight chamber 10 to thereby enable the constituents of the sample to be determined. The board 42 also controls the power supplied to the reflectron, liner of the time of flight chamber 10, deflection plate and blanker as is conventional.

The ions produced by the RF system 16 are conditioned by ion optics (not shown) controlled by ion optics board 44 so as to focus the ions to produce a narrow beam and ion package for supply to the orthogonal accelerator 36 so that a bundle of ions can be concurrently pushed out from the accelerator 36 for travel along the time of flight chamber 10. The accelerator 36 is controlled by a signal on line 35 from timing card 34.

The data received from the detector 38 by the board 42 is supplied to bus 50 which in turn supplies the data to the personal computer 14 for analysis.

In normal operation, sample ions are supplied from the RF system 16 to the orthogonal accelerator 36. The orthogonal accelerator power board 34 receives a power command from the PC 14 via the bus 50 and outputs a pulse timing signal on line 33 to the timing card 32. The timing card 32 controls the blanking timer by way of supply of a signal on line 45 to a blanker smart gate module 46 which simply receives the timing signal and produces the blanking pulse which is supplied to the blanker 34. An ion signal is supplied from the chamber 10 on line 48 to the personal computer 14 and the blanking pulse and signal on the line 48 and 45 are synchronised so that a predetermined time after the ions are pushed out of the accelerator 36 into the chamber 10, the blanking pulse activates the blanker 34 so that ions formed from the plasma gas supplied by the gas box 18 are blanked and do not reach the detector 38. The reason for this blanking is to ensure that the detector 38 is not saturated by the high proportion of plasma gas ions which entrain the sample ions and which, if received by the detector 38, would greatly reduce the sensitivity of the detector 38 and saturate the signals relating to the specific ions produced by the sample material.

The operation of the time of flight mass spectrometer as described above is conventional and therefore, a further explanation of the operation and components of the spectrometer is not needed.

In the preferred embodiment of the invention, predetermined ions are to be prevented from reaching the detector 38 so that the spectrometer cannot be used to analyse a sample to see whether those specific ions, and therefore the constituent to which those ions relate is present in a sample material. The predetermined ions which are to be excluded are blanked by the blanker 34 by supplying a timing signal on line 45 to the module 46 so that a further blanking pulse is supplied to the blanker 34 at the time those predetermined ions are expected to arrive at the blanker 34 so that the blanker 34 prevents those ions from being received by the detector 38.

Most typically the blanker comprises a gate in the form of a plurality of electrodes generally in the form of grids which produce magnetic fields which merely deflect the ions, or extract the ions from the ion beam produced by the orthogonal accelerator 36 so those ions do not arrive at the detector 38.

Thus, by timing the blanking pulse to the blanker 34 the predetermined ions can be prevented from reaching the detector 38. Similarly, if the predetermined ions can be multiply charged, they are also blanked by determining the time when the multiply charged ions would arrive at the blanker 34, and producing a further blanking pulse to operate the blanker 34 to ensure that those ions are also extracted. Thus, the predetermined ions, whether singly or multiply charged, are prevented from reaching the detector 38 and therefore cannot be detected by the spectrometer. Thus, the spectrometer cannot be used to determine whether such constituents are present in the sample.

As is apparent from the above description, the timing of the blanking pulse which extracts the predetermined ions is critical to ensure that the ions are in fact extracted. If the timing of the blanking pulse which is intended to extract the predetermined ions can be altered, then it may be possible for those ions to reach the detector 38. The timing of the blanking pulse could be altered possibly by increasing the length of the line 45 to delay by a small amount the time of the timing signal on the line 45 to in turn delay the time of the blanking pulse. This may well allow the predetermined ions to reach the detector 38 because they may travel past the blanker 34 before the blanking pulse is received by the blanker 34 to activate the blanker. This change in timing may also move the blanking pulse which removes the argon. However, if the predetermined ions are sufficiently heavier than the argon ions, it is likely that the predetermined ions could well be detected, notwithstanding the fact that a large population of argon ions may also reach the detector 38 because of the different time at which the argon ions and the heavier ions would arrive at the detector 38.

To ensure that the timing of the blanking pulse to prevent the predetermined ions from reaching the detector 38 is not adjusted, the preferred embodiment of the invention provides for the timing card to perform a blanker timing check. The check is performed under the control of the timing card before the timing card can be controlled by the personal computer 14, for example, when the spectrometer is turned on to analyse sample. To perform the check, the timing module 32 outputs a timing signal on line 45 to the module 46 to cause the module 46 to produce a blanking pulse to operate the blanker 34 so as to remove the argon ions from sample ions accelerated into the chamber 10 by the orthogonal accelerator 36. The ions are detected by the detector 38 and the signal produced from the detector 38 is received by the computer 14 so that the computer 14 can determined whether there are ions present at the time that one would expect to see the argon ions. The computer 14 resupplies this information back to the timing card 32 to indicate to the timing card 32 whether the argon ions were present or were not present. The timing card also produces a timing pulse on line 45 so that the blanker module 46 produces a blanker pulse to the blanker 34 to blank all ion species, except for the argon species, so that the argon species are able to arrive at the detector 38 but no other species are able to arrive at the detector 38. Once again, the output from the detector 38 is received by the computer 14 and the computer 14 resupplies that information back to the timing card to indicate whether the argon is or is not present. If the argon is not present when the blanker was controlled to prevent the argon ion from reaching the detector 38, and the argon was present when the blanker 34 was controlled to allow the argon ions to reach the detector 38, the blanker timing produced by the timing module 32 to the blanker 34 is operating correctly. Thus, it can be assumed that the blanking pulse which is to remove the predetermined ions is also operating correctly, and the predetermined ions will in fact be removed and will not reach the detector 38 when the instrument is actually making measurements and analysing the sample material.

In the preferred embodiment of the invention, it is the timing module 32 which controls the argon check to determine that the blanker 34 is operating properly. The timing module 32 can be initially prompted to perform the check by the data station software loaded into the computer 14 and will not operate to allow proper analysis of material until such time as the check has been made. However, at no time does the data station software know the nature of the phases of the argon check, but simply returns to the timing card information to show whether the argon is or is not present. The timing card knows which phase of the test it performed, and therefore can match the results supplied by the computer with the particular phase to ensure that argon is present when it was expected and not present when it was not expected. This in turn ensures that the timing of the blanking pulses is operating correctly and the timing has not been manipulated to try to override the blanking of the predetermined ions.

To ensure that the processor cannot be tampered with, or the PC used to control the timing card 38 to provide incorrect results in an attempt to fool the timing card into believing that the blanking timing is correct, the computer 14 does not know whether the timing card is producing the blanket timing signal to allow the argon to reach the detector 38 or to prevent the argon from reaching the detector 38. Thus, the computer 14 is simply only able to supply a signal back to the timing card 32 indicating whether the argon is present or was not present, and the timing card 32 can then determine whether this matches the particular timing signal which was produced to then enable the timing card 32 to ensure that the blanker timing is operating correctly. Furthermore, to prevent the possibility of a simply random correct data being supplied from the processor 14 back to the timing card 32, the pairs of blanking timing signals which either allow the argon to be received by the detector or prevent the argon from reaching the detector 38 are randomly ordered and are supplied a plurality of times such as 20 times. The timing card therefore determines for each of the 20 events whether the data received back from the computer 14 matches that which the timing card would expect to receive having regard to the timing signal which was supplied by the timing card to thereby ensure that the timing of the blanking pulses received by the blanker 34 are correct.

If the timing card 32 determines that the blanking timing is working properly, the timing card can allow the personal computer 14 to load into the timing card particular blanking timings which may be desired for usual operation of the spectrometer so that measurements can be taken and analysis of sample material provided.

If the timing card indicates that the blanker timing is not operating correctly, then the timing card effectively shuts down the instruments by preventing the instrument from analysing sample so that data is not analysed by the board^* 42 or the computer 14 until the instrument has been corrected.

To further secure the device, communications between the computer 14 and the processor 12 are encrypted to maintain the security of the information and data which is supplied to and from the processor 12. Furtherstill, according to the preferred embodiment of the invention, the orthogonal accelerator power board 34, the timing card 32 and the analyser board 42 are effectively matched in the instrument so that each of those boards match one another or a predetermined criteria for the instrument to operate, otherwise the instrument will shut down. The reason for this is to prevent various modules from being taken out of the restricted spectrometer and replaced by other modules in an attempt to override the blanking signals which prevent the predetermined ions from reaching the detector 38. In the preferred embodiment, this is done by providing a code to each of the aforesaid modules so that when the device is operating, the codes are supplied from the modules to the computer 14 and must match in order for the computer 14 and the processor 12 to continue operation. If there is no match, indicative of the fact that one of the modules may have been replaced, the instrument is shut down to prevent data from being analysed.

In the preferred' embodiment of the invention, the vacuum controller 26 may also include a code which needs to match the other codes of the board 34, the card 32 and the board 42 in order for the time of flight spectrometer to operate.

Whilst in the preferred embodiment the blanker timing check is performed when the instrument is initially switched on for each measurement, the check could also be performed at random times throughout the measurement. This embodiment is less preferred because it may slow down the taking of actual measurements.

Furthermore, if the timing check fails, the timing card 32 can merely restrict its operation so that it is only able to perform timing checks until it receives an acceptable number of pass scans. Furtherstill, the spectrometer, even if the timing fails, may still be able to perform argon present checks so that a user can use the spectrometer to see only the argon peaks, as this may assist in diagnosing problems with the spectrometer if the timing check fails, not because of any tampering but merely because of some problem with the spectrometer.

The preferred embodiment of the invention has a specific example that all of the checking is performed by the spectrometer itself and, in particular, by the timing card and not by end front end software which is loaded into the processor 14. This greatly reduces the likelihood of tampering or manipulating data by the processor 14 to provide incorrect data to the processor 12 which could be used to cause the processor to believe that the spectrometer is operating properly to restrict the predetermined ions when it is in fact not.

Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise", or variations such as "comprises" or "comprising", is used in an inclusive sense, ie. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMS :

1. A time of flight mass spectrometer comprising: a time of flight chamber; an ion source for supplying ions from a sample for travel through the time of flight chamber; a detector for receiving the ions after travel through the time of flight chamber to enable the ions which are detected to be identified so that the constituents of the sample can be determined; a blanker for blanking ions travelling through the time of flight chamber so that blanked ions do not reach the detector; and a processor for controlling the blanker to: (a) blank predetermined ions so those ions are not received by the detector so the detector is not able to provide an indication of those ions in the sample during analysing of the sample; and the processing being for performing a blanking check to:

2. The spectrometer of claim 1, wherein the processor is also for shutting down the spectrometer in the event that it is determined that blanking is not operating properly to prevent the predetermined ions from reaching the detector.

3. The spectrometer of claim 1, wherein the processor is for performing the blanking check by selectively blanking the specific ions at a time when the specific ions are expected to arrive at the blanker so that those ions do not reach the detector, and operating the blanker so that the blanker is opened at the time when the specific ions are expected to arrive at the blanker, so that only the specific ions reach the detector.

4. The spectrometer of claim 1, wherein the processor is also for controlling the blanker to prevent plasma gas from reaching the detector during the analysis of the sample substance so the ions which relate to the plasma gas do not saturate the detector during analysis of the sample.

5. The spectrometer of claim 1, wherein the specific ions comprise plasma gas ions so that by blanking the plasma gas ions and ensuring that the plasma gas ions are not detected by the detector, and blanking other ions and ensuring that the specific ions do reach the detector, the timing of the blanking can be verified and regarded as operating correctly.

6. The spectrometer of claim 1, wherein the processor controls the blanker to perform the blanking of the other ions and the blanking of the specific ions in random order.

7. The spectrometer of claim 1, wherein the processor is for causing the blanking of the other ions and the blanking of the specific ions to occur a plurality of times and in random order.

8. The spectrometer of claim 1, wherein the processor comprises a timing module for supplying blanking signals to the blanker for operating the blanker, a source module for controlling the supply of ions into the time of flight chamber, and an analyser module for receiving signals from the detector for providing an indication of the ions detected by the detector and therefore the constituents of the sample.

9. The spectrometer of claim 8, wherein the control of the blanker is performed by the timing module to selectively blank the specific ions and selectively control the blanker to allow the specific ions to reach the detector.

10. The spectrometer of claim 8, wherein the said modules are coded so that the processor will allow the modules to operate, only if the coding of the modules match a predetermined requirement to prevent modules from being removed and replaced to override the operation of the blanker to allow the predetermined ions to be detected by the detector.

11. The spectrometer of claim 8, wherein the processor further includes a communications interface for coupling the processor to a computer, an ion optics module for focusing ions produced by the source and a blanker module for receiving signals from the timing module and for producing blanker pulses for supply to the blanker to operate the blanker.

12. The spectrometer of claim 1, wherein the source comprises an RF system for producing a plasma, a gas box for supplying a plasma gas and an accelerator for receiving the ions from the RF system and for accelerating the ions into the time of flight chamber.

13. The spectrometer of claim 8, wherein the accelerator is an orthogonal accelerator.

14. The spectrometer of claim 8, wherein the ion optics module focuses the ions for supply to the orthogonal accelerator.

15. The spectrometer of claim 11, wherein data transmitted between the interface and the personal computer is encrypted to ensure security of the communications between the computer and the processor.