GB2432711A

GB2432711A - Gas mixing system for an ion source

Info

Publication number: GB2432711A
Application number: GB0520599A
Authority: GB
Inventors: Simon Meffan-Main; Howard Read; Patrick James Turner
Original assignee: GV Instruments Ltd
Current assignee: GV Instruments Ltd
Priority date: 2005-10-11
Filing date: 2005-10-11
Publication date: 2007-05-30
Anticipated expiration: 2025-10-11
Also published as: EP1949069A2; WO2007042746A3; GB0520599D0; WO2007042746A2; GB2432711B

Abstract

A gas mixing system is used to mix an analyte gas with a carrier gas before ionization of the mixed gas. The ionized mixed gas may then be supplied to a mass spectrometer. A discrete volume 21 of a sample gas is supplied at a first, relatively low pressure to a mixing chamber 37. A mixer gas 18 at a higher pressure is mixed with the sample gas in the mixing chamber 37. The output of the mixing chamber is a mixed gas at a pressure higher than the first pressure and is supplied to an ionization device 50. After supplying a sample to the ionisation device, the mixing chamber can be purged using a vacuum system 32, 35. The system is particularly suited for use with uranium hexafluoride as the sample gas and an inert gas such as argon as the mixer gas.

Description

ION SOURCE PREPARATION SYSTEM

The present invention relates to a method and a system for preparing a sample for an ion source, and apparatus incorporating such systems. Embodiments of the present invention are particularly suitable for, but not limited to, preparing samples for isotopic analysis in mass spectrometers.

One method of determining the relative proportions of the isotopes of a chemical element present in a material is to subject the material to analysis by mass spectrometry. Mass spectrometers typically consist of three main components: an ion source, a mass analyser or selector, and an ion detector. The ion source is arranged to generate a beam of ions which are characteristic of the element(s) in the sample for which the isotopic analysis is required. The mass selector is typically (but is not limited to) a magnetic field at right angles to the direction of motion of the ions, arranged to deflect the ion beams so that ions of different mass to charge ratios follow different trajectories. The ion detector typically takes the form of one or more electrodes, and is arranged to produce a signal indicative of the number of ions incident upon the detector. One example of such a mass spectrometer is described within US 4,524,275.

A sample preparation system may also be provided, arranged to provide the sample to be ionised in an appropriate form so it can be efficiently ionised in the ion source. To promote efficient ionisation, sample preparation systems are typically arranged to provide a disperse distribution of the sample material within a gaseous dispersion medium.

For example, a number of different techniques for the sample preparation and subsequent isotopic analysis of UF6 (uranium hexafluoride) are known. UF6 is a compound utilised in the enrichment of uranium. Enrichment typically utilises UF6 in a gaseous state. Uranium is a naturally occurring element containing uranium-234, uranium-235 and uranium-238 isotopes. However, only the uranium-235 isotope is fissionable. Enrichment is the process of increasing the relative concentration of uranium-235. It is desirable to be able to quickly and efficiently determine the isotopic composition of UF6, in order to determine the success of the enrichment process.

Commonly, a liquid sample is prepared by hydrolysing UF6 from gaseous or solid UF6 prior to mass spectrometry. Multiple collector thermal ionisation mass spectrometry (TIMS) and multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) are two known techniques for isotopic analysis of hydrolysed UF6.

However, hydrolysing UF6 requires manual handling of UF6, which may introduce contamination. Further, hydrolysing UF6 yields an aggressive solution (hydrofluoric acid), which requires careful handling. Pre-concentration of the hydrolysed UF6 may also be required prior to TIMS analysis.However, the largest problem with hydrolysing samples such as UF6 is the time and labour required. The fact that the hydrolysing is completed manually means that sample intervals tend to relatively long, and online monitoring of the production plant (e.g. the enrichment process quality) is not possible.

An alternative technique is to utilise electron bombardment (EB) mass spectrometry of pure UF6 gas. Electron bombardment is particularly suitable for ionisation of UF6, as electron bombardment requires a relatively low pressure gas sample, with UF6 forming a gas at a relatively low pressure at room temperature via sublimation from the solid. However, within the electron bombardment ionising device, complex moleculars can form from lighter gases, which interfere with the analyte peaks of interest (and thus decrease the measurement accuracy). Consequently, to obtain an accurate measurement, the sample needs to be pure UF6 with no light gas contamination. Whilst only a few micrograms of UF6 are required to be introduced into the low pressure ionisation portion of the ion source to provide sufficient ions for isotopic analysis, approximately two grams of UF6 sample needs to be cleaned to achieve the desired purity for reasonable measurement accuracy. Thus, sample preparation is relatively lengthy due to the required cleaning process. Further, a relatively large amount of undesirable waste UF6 is produced. Additionally, the EB source has significant sample memory i.e. the ions output from the ion source for a sample can be contaminated with ions originating from an earlier sample, thus leading to measurement errors.

It is an aim of embodiments of the present invention to address one or more of the problems of the prior art, whether referred to herein or otherwise. It is an aim of particular embodiments to provide an improved UF6preparation system for an ion source.

According to a first aspect of the present invention there is provided an apparatus for providing an ionised sample, comprising a sample preparation system comprising: at least one mixing chamber; a sample input arranged to provide a discrete volume of gaseous sample to said mixing chamber at a first, relatively low pressure; a mixer input arranged to provide a mixer gas at a second, higher pressure to said mixing chamber for mixing with the gaseous sample; and an outlet arranged to provide a flow of gas from said chamber to an ionising device.

Such a sample preparation system allows a low pressure gaseous sample (e.g. UF6) to be introduced into a higher pressure ionising portion of an ion source. For example, using such a sample preparation system, UF6 gas can be introduced into an inductively coupled plasma ionising device. No exposed sample handling is required, minimizing the associated hazards and decreasing the likelihood of sample contamination. Further, in higher pressure ionising devices such as those utilising plasma, due to the "harder" ionisation of the device, the formation of complex moleculars from lighter gases is relatively unlikely. Thus, the undesirable cleaning of the UF6 sample prior to ionisation is not required i.e. very little sample need be wasted during the sample analysis.

The sample preparation system may comprise a vacuum system arranged to pump out residual gas from at least a portion of the sample preparation system for cleaning thereof.

The sample input may comprise a pipette for provision of said discrete volume of gaseous sample.

The sample input may comprise a sample inlet manifold coupled to said pipette, comprising a plurality of sample attachment points for selectively connecting any single sample connected to a sample attachment point to the pipette for sampling thereof The sample preparation system may comprise a vacuum system arranged to pump out gas from at least a predetermined portion of the sample input for cleaning thereof.

Said at least one mixing chamber may comprise a plurality of mixing chambers each formed as bellows and connected in series such that gas can be pushed between chambers for promoting mixing of the gaseous sample and the mixer gas.

Said at least one mixing chamber may comprise a mixing chamber containing a mixing device for promoting mixing of the gaseous sample and the mixer gas.

The apparatus may further comprise a flow controller coupled to the outlet for controlling the mass flow of gas to said ionising device.

The apparatus may comprise the ionising device.

The ionising device may be an inductively coupled plasma ionising device.

According to a second aspect of the present invention there is provided a mass spectrometer comprising the above apparatus.

According to a third aspect of the present invention there is provided a sample preparation system for an ion source, comprising: at least one mixing chamber; a sample input arranged to provide a discrete volume of gaseous sample to said mixing chamber at a first; relatively low pressure; a mixer input arranged to provide a mixer gas at a second, higher pressure to said mixing chamber for mixing with the gaseous sample; and an outlet arranged to provide a flow of gas from said chamber to an ionising device.

According to a fourth aspect of the present invention there is provided a method of preparing an ion sample, comprising mixing a discrete volume of gaseous sample at a first, relatively low pressure with a mixer gas at a second, higher pressure to form a mixed gas at a pressure greater than said first pressure; and providing the mixed gas to an ionising device for ionisation of the mixed gas.

The method may comprise the step of obtaining said gaseous sample by holding a solid of the sample at a temperature and pressure such that at least a portion of the solid sample sublimes.

Said gaseous sample may comprise UF6.

The method may comprise ionising the mixed gas to form ionised particles, and analysing the ionised particles.

The method may comprise the step of isolating the sample from the preparation line of an ongoing treatment process.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an apparatus including a sample preparation systemin accordance with an embodiment of the present invention; and Figure 2 is a schematic diagram of a mass spectrometer incorporating the apparatus shown in Figure 1.

Figure 1 is a schematic diagram of an apparatus 10 arranged to generate a beam of ions 12. The apparatus 10 includes a sample preparation system 20 and ionising device (i.e. ion source) 50.

Preferably, the ionising device is a plasma ionising device. Even more preferably, the ionising device is an inductively coupled plasma (ICP) source e.g. suitable for ICPMS (inductively coupled plasma mass spectrometry). Such an ionising device typically operates within a pressure range between 0.5 and 4 bar. More specifically, such ionising devices operate at approximately ambient (or slightly less than ambient) pressure i.e. a pressure of approximately (just less than) 1 bar or 1 atmosphere.

The sample preparation system 20 is arranged to provide a gaseous mix of the sample to the ionising device 50 at a pressure substantially equal to that of the ambient operating pressure of the ionising device. In other words, the gaseous flow into the ionising device of the sample is typically at a pressure of approximately 1 atmosphere.

The sample is a substance that is gaseous at a pressure at or slightly less than that of the operating pressure of the ionising device. Sample input (23, 24, 25, 36) is arranged to provide a discrete volume of gaseous sample (at a pressure at which the sample is still a gas) to a mixing chamber (or expansion chamber) 37. The sample input is connected to the sample source 21.

The sample source 21 can be a container containing a discrete volume of sample e.g. a sample vial. Alternatively, the sample source can be obtained directly from an ongoing treatment process e.g. the preparation line of an enrichment plant or a manufacturing facility, thus allowing online analysis of the sample via a mass spectrometer connected to the sample source.

The sample input includes a series of valves (23, 25 & 36) arranged to allow discrete samples to be isolated from the sample source 21. In the particular embodiment illustrated, the sample input includes a pipette 24, arranged to sample (measure) a predetermined volume of the gaseous sample. In this example, the pipette is arranged to sample a discrete, predetermined volume of gaseous sample of less than 10 ml, and preferably of approximately 1 ml. The predetermined volume of gaseous sample is relatively small compared with the volume of the mixing chamber (e.g. at least an order of magnitude smaller). In this particular embodiment, the mixing chamber has a volume of 500 ml.

In this particular embodiment, the sample source 21 is a vial containing solid and gaseous UF6. At room temperature and pressure, solid UF6 can sublime directly to the gaseous state, resulting in a partial pressure of approximately 0.1 bar of gaseous UF6 above the solid sample at room temperature and pressure. It will be appreciated that other temperature and pressure conditions may be utilised for sublimation (or transformation from gas to liquid) of other types of sample. The sample vial 21 is connected to the pipette 24, via a valve (in this example, via an integral valve 22 and an isolating valve 23).

A mixer input (valves 17, 36) is arranged to provide a mixer gas 18 to the mixing chamber 37. The mixer gas 18 is typically, but not exclusively, an inert gas. In this particular embodiment the mixer gas is argon. The mixer gas is provided at a higher pressure than that of the gaseous sample, such that the mixed gas formed by the mixer gas and gaseous sample within the mixing chamber 37 is at a higher pressure than the original gaseous sample (e.g. as obtained via the pipette 24 from the sample source 21). Further, the pressure of the mixed gas within the mixing chamber is arranged to be at a higher pressure than the ambient operating gaseous pressure within the ionising device 50. Thus, when the mixing chamber is coupled to the ionising device 50, the mixed gas will flow into the ionising device 50. An outlet of the mixing chamber 37 is coupled to an input of the ionising device 50 via an outlet valve 38, a flow controller input valve 39, and a flow control device 40.

The flow controller 40 is utilised to control the flow of gas from the mixing chamber 37 into the ionising device. The flow controller may direct gas straight into the ionising device. However, in this particular embodiment, the flow controller 40 directs the mixed gas from the mixing chamber into a carrier gas flow from gas supply 19. The carrier gas from supply 19 is typically, but not exlusively, an inert gas. In this particular embodiment, the carrier gas is argon. The carrier gas transports the mixed gas to the ionising device. Specifically, in this particular embodiment, the carrier gas is provided at sufficient flow rate and pressure to transport the mixed gas to the centre of the plasma in the ionising device 50.

The carrier gas flow, together with the mixed gas flow from the mass flow controller 40, is directed into the ionising device for ionisation of the diluted sample.

In this example the flow controller 40 delivers a relatively small volume of the mixed gas per minute to the ionising device, compared with the total volume of mixed gas prepared in the mixing chamber 37. Preferably, the flow controller is arranged to provide less than 1% of the mixing chamber 37 volume per minute to the ionising device. In the particular embodiment illustrated, the flow controller is arranged to provide a flow rate of mixed gas of approximately 1 ml per minute i.e. approximately 0.2% of the mixing chamber volume. Such a small rate of depletion of the mixing chamber ensures relatively uniform molecular flow and minimises sample fractionation.

The flow controller may be a fixed flow valve, or a manual or automated variable flow valve, pin-hole leak or an electronically controlled mass flow controller. The controller can be set at a fixed flow rate, or adjusted dynamically during an analysis, to maintain the ion beam 12 from the ion source 50 at a fixed level.

To clean the sample preparation system 10, and remove residual traces of earlier samples, the sample preparation system includes at least one vacuum system (26, 27.

28, 29, 30, 31, 32, 33, 34, 35, 41). The vacuum system also enables the admittance of the (higher pressure) gaseous sample into the (lower pressure) sample preparation system.

The vacuum system includes two valves (26, 41) connecting the vacuum system to relevant portions of the sample preparation system. Further in this embodiment, the vacuum system includes two rotary pumps (31, 34) and a turbo pump (30). However, the vacuum system could consist of any kind of vacuum pump. The vacuum system includes a pressure gauge (29) for monitoring the level of vacuum achieved. The level of vacuum achieved by the vacuum system will depend upon the degree of cleanliness required within the sample preparation system (e.g. to prevent cross contamination between samples). The vacuum system is utilised to pump out residual gas between samples. Further, the vacuum system can be utilised to pump out residual air in the head space between valves 22 and 23 formed when a sample vial is attached to the system. Further, the vacuum system can be utilised to reduce the pressure in the air' space above the solid sample in the sample source 21 to the desired level, so as to achieve sublimation, if required.

In the embodiment illustrated in Figure 1, the vacuum system (26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 41) is coupled to the sample input via valve 26. The vacuum system can be utilised to remove gas from the common input (between valves 25, 36 and 17) for the sample gas and the mixer gas. Additionally, the vacuum system (26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 41) can be utilised to remove gas from the pipette 24, as well as the air space above the sample vial 21 between valves 22 and 23 if desired, by appropriate control of valves 23 and 25.

The vacuum system (26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 41) is also coupled to the conduit connecting outlet valve 38 and controller input valve 39 via vacuum control valve 41. The vacuum system (26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 41) can be used to evacuate that conduit, and can also be utilised to remove gas from the mixing chamber 37 by appropriate opening of valve 38. Closing of valve 39 and/or the flow controller 40 if appropriate whilst the evacuation is occurring, prevents interruption of the carrier gas flow 19 into the ionising device 50.

The pressure gauge 29 is used to monitor the pump out of the sample preparation system. Such monitoring is extremely useful, to control the sample "rinse" from the system, to ensure minimum carry over to the next sample.

The two parts to the illustrated vacuum system (33, 34, 35 and 28, 29, 30, 31, 32) permit a two-stage pumping out of the sample preparation system. In this embodiment, the rotary pump vacuum sub-system (33, 34, 35) permits initial pumping out of the sample preparation to low vacuum while the turbo molecular pump vacuum sub-system, (28, 29, 30, 31, 32) permits final pumping out of the sample preparation to high vacuum, through the use of control valves 33 and 28 appropriately. In some cases single stage pumping may be preferred for simplicity and cost.

A typical operation of the ion source will now be described.

The vacuum system is utilised to evacuate the sample preparation system between valves 23, 17 and 40, as well as the air space above sample vial 21. Generally, a relatively high vacuum is utilised e.g. a vacuum of approximately 1x106 bar. Valve is closed and valves 22 and 23 opened, thereby admitting a quantity of gaseous UF6 from the sample vial 21 into the pipette 24. Valves 22 and 23 are closed.

By opening valves 25 and 36 with valves 26, 17 and 38 closed, the gaseous sample in the pipette is transferred, in part, to the mixing chamber 37. Valve 25 is now closed and valve 17 opened, such that mixer gas 18 flows in to the mixing chamber 37. The pressure of the mixer gas 18 is regulated using a pressure regulator and thus the pressure of the mixed gas in the mixing chamber 37 is raised to the (predetermined) regulated pressure. Valves 17 and 36 are then closed. The mixing chamber 37 is now isolated by valves 36 and 38. The gases within the chamber can then mix.

Valve 41 is closed, and valves 38 and 39 are opened, such that gas from the mixing chamber 37 flows through the flow controller 40 (which controls the flow of the mixed gas) into the ionising device 50. The flow control 40 may control either the mass flow rate or volume flow rate of the mixed gas.

The ionising device then ionises the mixed gas, to provide an ion beam for analysis.

This ion beam 12 can be analysed using a spectrometer e.g. a multiple collector single or double focussing mass spectrometer (with or without a collision reaction cell) can be employed for the simultaneous analysis of all isotopes of uranium. Alternatively, any other kind of optical or mass spectrometer (e.g. a time-of-flight or quadrupole mass spectrometer) may be utilised to analyse the ion beam.

It will be appreciated that the above sample preparation system is described by way of example only. Various alternative embodiments will be understood as falling within the scope of the present invention.

For example, the device 10 illustrated in Figure 1 is illustrated as having a connection to a single sample source 21. It will be appreciated that a multi-port manifold (configured to connect to a number of sample sources) can also be utilised as a sample input. Such a multi-port sample inlet manifold could be connected directly to the pipette 24. Alternatively, the multi-port inlet manifold could be connected directly (via appropriate valving) to a mixing chamber 37, with a volume measurement device (e.g. pipette) connected in series at each input port of the manifold, for measuring the desired predetermined volume of each sample prior to input to the mixing chamber 37. As mentioned above, the sample source 21 could be a discrete sample (e.g. a vial) or a production line (e.g. a tap off a production line in an enrichment plant). The sample source is arranged to provide a gaseous sample with a pressure at or below the operating pressure of the ionising device (e.g. atmospheric pressure).

Preferably, the sample preparation system is also arranged to provide one or more standards (e.g. materials of known isotopic abundance) for calibration of the ion beam 12 within the analysing device (e.g. calibration of the operation of the mass spectrometer). Preferably, such a standard input (or inputs) is configured in a similar manner to the sample input. If a multi-port manifold is utilised as the sample input, then one or more of the ports may be coupled to standards.

In the above embodiment, the mixing chamber is described as a single chamber.

However, it will be appreciated that the mixing chamber can take the form of two or more chambers. Such chambers may be formed as bellows, connected in series, such that the gas can be pushed between chambers to ensure adequate mixing of the gaseous sample and the mixer (diluting) gas. A mixing device can be located within the mixing chamber, to facilitate mixing of the gases.

The mixing device can be arranged to promote mixing of the gaseous sample and the mixer gas using a variety of techniques. For example, the mixer device can be arranged to provide a turbulent flow into the mixing chamber of one or more of the gases. Such a turbulent flow can be induced by an arrangement of baffles located within the mixing chamber and/or the input to the mixing chamber. Equally, the mixer device could take the form of a mechanical mixer utilising a rotor located within the mixing chamber. Equally, the mixing device could be arranged to mix the gases via agitation of elements located within the mixing chamber, via either internal or external means (e.g. manipulation of the elements using electromagnetism, or simple shaking of the mixing chamber containing the elements).

Multiple sample preparation systems 20 could be coupled to a single ion source 50, having separate flow controllers, or sharing a common flow controller 40.

Preferably, the sample preparation system (and indeed, preferably the complete ion source and analysis equipment e.g. mass spectrometer) are fully automated.

Preferably, the system is integrated with a lab management system or operated remotely.

The utilisation of such a sample preparation system allows relatively rapid sampling times e.g. the sampling times are only limited by the time taken to clean the previous sample from the inlet system. If desired, a plurality of such sample preparation systems could be utilised, such that whilst one system is operating, the other system is being cleaned to further reduce the sampling times. Analysis times can be relatively short, particularly if the sample preparation system is coupled with a multi-collector ICPMS system.

The system may be utilised for discrete sample analysis. Alternatively, the system may be utilised for on-line process control sample analysis. Typically, this would take the form of discrete snapshots of the on-line process (e.g. discrete snap shots of the uranium isotope composition in an enrichment plant). However, in an alternative embodiment, a continuous flow (injection) of gaseous sample is made into a diluting (mixer) gas, prior to injection into the ionising device.

Although the preferred embodiment has been described in relation to isotopic composition measurements of UF6, the system could be utilised to analyse impurities (for example Tc, Ru, and/or Np in the UF6 product andlor feed). In the prior art, such analysis is believed to be done exclusively by hydrolysing the UF6 sample, with subsequent analysis by magnetic sector or quadrupole ICPMS. Such a prior art technique will have the same drawbacks as hydrolysis of UF6 samples for isotopic analysis. However, such an analysis of impurities could be performed by utilising the sample preparation system as described herein for sample preparation, assuming suitable standardisation/calibration of the mass spectrometer.

Although the preferred embodiment is described in relation to utilising UF6 as a sample for ICPMS, it will be appreciated that the invention is not restricted for use with UF6. In particular, the sample preparation system may be utilised for preparation of any gas at or below atmospheric pressure that is to be introduced into an ICP system (ionising device). For example, Chlorine isotope measurements could be made from gases such as CH3C1.

Although the above embodiments have been described in relation to providing an ion beam for mass spectrometry, it will be appreciated that other analysis techniques/apparatus may be utilised instead of a mass spectrometer. For example, the ion beam output from the ion source could be fed into an optical ICP spectrometer allowing chemical composition to be determined using the optical emission spectrum from the ICP source.

However, Figure 2 shows a schematic diagram of a typical mass spectrometer 100 including such a sample preparation system. The mass spectrometer 100 comprises three main components: an ion source 50 (coupled to a sample preparation system 20 as described above with reference to Figure 1), a mass analyser 51 and an ion detector 60.

The ion source 10 ionises the sample material, and as an output produces a beam of ions 12.

The mass analyser (or mass selector) 51 receives the ions 12 from the ion source 50, and separates the ions according to their mass-to-charge ratios. For a magnetic sector analyser, this is usually accomplished by using electric and magnetic fields. The mass analyser 51 shown in Figure 2 is arranged to provide a magnetic field at right angles to the direction of motion of the ions 12. The ion beam 12 is deflected so that ions of different mass-to-charge ratios follow different beam trajectories 52a, 52b, 52c.

These trajectories 52a, 52b, 52c can be altered by varying the strength of the magnetic

field which deflects the ion beam 12.

Each ion detector 60 produces an electrical signal related to the number of ions incident from the detector. Ion detectors 60 are placed in the optical output path of the mass analyser 51. An entrance aperture 62 (termed the collector slit) is positioned in front of each ion detector so that ions of only one particular mass-to-charge ratio can fall on the iondetector i.e. so that the beam corresponding to only one trajectory passes through the entrance aperture.

The mass spectrometer 100 in Figure 2 comprises a plurality of ion detectors 60. The slits 62 and detectors 60 are positioned such that each detector receives ions of a different mass-to-charge ratio. The mass analyser 51 is generally arranged to focus each of the ion beams 52a, 52b, 52c to a respective focal point. These points define a plane, termed the focal plane. Each of the entrance apertures 62 is normally positioned at a respective focal point of an ion beam trajectory 52a, 52b, 52c. The position of the entrance apertures 62 (and the corresponding detectors 60) can normally be controlled, along with the magnetic field of the mass analyser 51, to provide optimum alignment of the different ion beams with the detectors 60.

The enclosure 108 is typically maintained at a relatively high vacuum e.g. at a pressure of 1 08 Ton or less, to minimise contamination and interference effects.

It will be appreciated that the sample preparation system as described herein provides a number of advantages.

For example, no exposed sample handling is required, nor any hydrolysing reactions.

Potential sample contamination can be minimised by using relatively dilute samples, thus also minimising contamination of the analysis device and memory between samples. The sample preparation system allows the elimination of any human exposure to UF6, since the sample preparation system can be a completely contained system. The sample preparation system is designed to be fully automated if desired (e.g. under computer control), and can be integrated into a lab management system.

Gas flow rate and hence sample (e.g. UF6) concentration can be dynamically adjusted to optimise sample analysis. A highly sensitive mass spectrometer can be employed, thus allowing the sample to be very dilute upon entry to the mass spectrometer, thus minimising the contamination of mass spectrometry apparatus. Further, utilising plasma ionising devices allows complete fragmentation and high ionisation efficiency, thus simplifying the resulting mass spectrum, and enhancing the precision of the analysis. Further, mass fractionation can be corrected automatically by standards admitted via the sample preparation system.

Claims

CLAIMS

1. An apparatus for providing an ionised sample, comprising a sample preparation system comprising: at least one mixing chamber; a sample input arranged to provide a discrete volume, of gaseous sample to said mixing chamber at a first, relatively low pressure; a mixer input arranged to provide a mixer gas at a second, higher pressure to said mixing chamber for mixing with the gaseous sample; and an outlet arranged to provide a flow of gas from said chamber to an ion ionising device.

2. An apparatus as claimed in claim 1, wherein the sample preparation system further comprises a vacuum system arranged to pump out residual gas from at least a portion of the sample preparation system for cleaning thereof.

3. An apparatus as claimed in claim 1 or claim 2, wherein the sample input comprises a pipette for provision of said discrete volume of gaseous sample.

4. An apparatus as claimed in claim 3, wherein the sample input comprises a sample inlet manifold coupled to said pipette, comprising a plurality of sample attachment points for selectively connecting any single sample connected to a sample attachment point to the pipette for sampling thereof.

5. An apparatus as claimed in any one of the above claims, wherein the sample preparation system comprises a vacuum system arranged to pump out gas from at least a predetermined portion of the sample input for cleaning thereof.

6. An apparatus as claimed in any one of the above claims, wherein said at least one mixing chamber comprises a plurality of mixing chambers each formed as bellows and connected in series such that gas can be pushed between chambers for promoting mixing of the gaseous sample and the mixer gas.

7. An apparatus as claimed in any one of the above claims, wherein said at least one mixing chamber comprises a mixing chamber containing a mixing device for promoting mixing of the gaseous sample and the mixer gas.

8. An apparatus as claimed in any one of the above claims, further comprising a flow controller coupled to the outlet for controlling the mass flow of gas to said ionising device.

9. An apparatus as claimed in any one of the above claims, further comprising the ionising device.

10. An apparatus as claimed in claim 9, wherein the ionising device is an inductively coupled plasma ionising device.

11. A mass spectrometer comprising an apparatus as claimed in any one of claims ito 10.

12. A sample preparation system for an ion source, comprising: at least one mixing chamber; a sample input arranged to provide a discrete volume of gaseous sample to said mixing chamber at a first, relatively low pressure; a mixer input arranged to provide a mixer gas at a second, higher pressure to said mixing chamber for mixing with the gaseous sample; and an outlet arranged to provide a flow of gas from said chamber to an ionising device.

13. A method of preparing an ion sample, comprising: mixing a discrete volume of gaseous sample at a first, relatively low pressure with a mixer gas at a second, higher pressure to form a mixed gas at a pressure greater than said first pressure; and providing the mixed gas to an ionising device for ionisation of the mixed gas.

14. A method as claimed in claim 13, further comprising the step of obtaining said gaseous sample by holding a solid of the sample at a temperature and pressure such that at least a portion of the solid sample sublimes.

15. A method as claimed in claim 13 or claim 14, wherein said gaseous sample comprises UF6.

16. A method as claimed in any one of claims 13 to 15, further comprising: ionising the mixed gas to form ionised particles; and analysing the ionised particles.

17. A method as claimed in any one of claims 13 to 16, further comprising the step of isolating the sample from the preparation line of an ongoing treatment process.