WO2021224613A1

WO2021224613A1 - A control system

Info

Publication number: WO2021224613A1
Application number: PCT/GB2021/051080
Authority: WO
Inventors: Steven ROCHA; William Ngo; Nicola LUMLEY; David DOUCE
Original assignee: Micromass Uk Ltd
Priority date: 2020-05-05
Filing date: 2021-05-05
Publication date: 2021-11-11

Abstract

A control system for an ion source, the ion source comprising a heater including a gas source and a heating element, the heater for directing heated gas onto a capillary insertable into the ion source in use, the control system comprising: a pressure sensor for measuring the pressure of gas supplied by the gas source; and a controller operatively associated with the pressure sensor and configured to disable the heating element if the measured pressure is less than a predetermined threshold pressure.

Description

Title: A control system

Description of Invention

The present invention relates to a control system for an ion source, a flow regulator and a heater arrangement.

Background of the invention

The invention generally relates to an atmospheric solids analysis probe (ASAP). Such probes, and the associated instrument for use with ASAP, are provided by several manufacturers, including Waters Corporation, Milford, MA, U.S.A.

ASAP is a useful and relatively cheap tool for use in the direct analysis of volatile and semi-volatile, solid and liquid samples and may be used in the analysis of speciality chemicals, synthetic polymers, energy sources and food.

A sample is introduced into an ion source housing (e.g. an API source), in which the sample is volatilised using a heated gas, such as nitrogen, and the sample is then ionised using, for example, a corona discharge pin. The ionised sample may subsequently be analysed in a mass spectrometer.

The sample is introduced into the source by loading it onto the tip of a capillary. The capillary may comprise a conventional glass capillary. The capillary may be a solid rod, or a tube, with open ends.

When the capillary is arranged in the ion source housing, the distal end of the capillary is arranged adjacent the outlet of a heater for directing heated gas onto the capillary. The heater contains a heating element, which is used to heat the gas passing through the heater from a gas source, over the heating element. If a significant amount of the sample is not adequately heated by the heated gas exiting the heater, it may subsequently not be effectively volatilised into the gas phase and hence would not be ionised by the corona discharge pin. This may then reduce the speed and accuracy of the subsequent measurement. Ineffective volatilisation through incomplete heating of the sample may result in extended analysis times, with high mass high boiling point compounds being volatilised over such an extended period that it may manifest as undesirable background in the mass spectrum and subsequent analyses. There is therefore a need to ensure that the heated gas flow exiting the heater is sufficient to cause adequate heating of the sample on the capillary.

In use, there may a requirement for the temperature of the heated gas exiting the heater to be reduced for a subsequent analysis. In such instances, a user may need to wait until the temperature of the heating element has reduced sufficiently through convection with the surrounding air. This may increase the cycle time of the instrument.

Furthermore, in use, a user may wish to open the door to the chamber of the ion source, to access components therein. As they do so, there is a risk that the user may inadvertently contact the hot end of the heater, potentially burning their hand.

The present invention seeks to address at least one of the aforementioned problems. Accordingly, the present invention provides a control system for an ion source, the ion source comprising a heater including a gas source and a heating element, the heater for directing heated gas onto a capillary insertable into the ion source in use, the control system comprising: a pressure sensor for measuring the pressure of gas supplied by the gas source; and a controller operatively associated with the pressure sensor and configured to disable the heating element if the measured pressure is less than a predetermined threshold pressure.

In at least one embodiment, the predetermined threshold pressure is 6.5 Bar.

In at least one embodiment, the predetermined threshold pressure is configured to be one which causes heated gas to exit the heater with a predetermined threshold flow rate.

In at least one embodiment, the predetermined threshold flow rate is 2.5 litres per minute. The present invention further provides a flow regulator for connection to a gas source of an ion source, the flow regulator selectively configurable between: a first mode in which the flow regulator is configured to deliver gas within a first predetermined flow rate range; and a second mode in which the flow regulator is configured to deliver gas within a second predetermined flow rate range, which is higher than the first predetermined flow rate range.

In at least one embodiment, the first flow rate range is between 1 and 4 litres per minute. In at least one embodiment, the first flow rate range is between 2.3 and 2.7 litres per minute.

In at least one embodiment, the second flow rate range is between 15 and 25 litres per minute.

In at least one embodiment, the second flow rate is 20 litres per minute.

In at least one embodiment, the flow regulator is configured to operate in the second mode in response to a door of the ion source being opened.

In at least one embodiment, the flow regulator further comprises: an inlet; an outlet; a first path fluidly connected between the inlet and outlet, and a first flow restrictor arranged in the first path configured to restrict flow therethrough to within said first predetermined flow rate range; and a second path fluidly connected between the inlet and outlet, and a valve arranged in the second path, to selectively open or close the second path.

In at least one embodiment, the second path is configured to allow a greater flow rate than the first predetermined flow range of the first path. In at least one embodiment, the flow regulator further comprises: a flow combiner, wherein the first path and second path are connected between the input and the flow combiner ; and a second flow restrictor arranged between the flow combiner and the outlet, configured to restrict flow therethrough to within said second predetermined flow rate range. The present invention further provides an ion source comprising a control system embodying the invention and a flow regulator embodying the invention.

The present invention further provides a heater arrangement comprising: a heater including a gas source and a heating element, the heater for directing heated gas onto a capillary insertable into the ion source in use, a pressure sensor for measuring the pressure of gas supplied by the gas source; and a flow regulator in fluid connection with the gas source and selectively configurable between: a first mode in which the flow regulator is configured to deliver gas within a first predetermined flow rate range; and a second mode in which the flow regulator is configured to deliver gas within a second predetermined flow rate range, which is higher than the first predetermined flow rate range; and a controller operatively associated with the pressure sensor and configured to disable the heating element if the measured pressure is less than a predetermined threshold pressure, the controller further configured to select one of the first and second modes of the flow regulator.

Embodiments of the present invention will now be described, by way of non limiting example only, with reference to the figures, in which:

Figure 1a shows an ion source with which the control system or flow regulator of the present invention may be used;

Figure 1 b shows an enlarged view of detail C in Figure 1 a:

Figure 2 shows a flow regulator embodying the present invention; Figure 3 schematically illustrates a flow regulator embodying the present invention as part of an ion source arrangement;

Figure 4 schematically illustrates a control system embodying the present invention; and

Figure 5 schematically illustrates a heater arrangement for an ion source.

Figure 1 shows an atmospheric pressure ionisation source 1. The source 1 comprises a housing 2 which defines an ionisation chamber 3 therein. The ionisation chamber 3 comprises (best seen in Figure 1b) an inlet 4 for receiving at least the distal end 5a of a capillary 5 into the chamber 3 in use.

The source 1 further comprises a desolvation heater 10. The desolvation heater 10 comprises a nozzle 11. As shown schematically in Figures 4 and 5, the desolvation heater 10 comprises a heating element 16 and a gas source 12. A power supply 13 is connected to the heating element 16 and the supply of power to the heating element 16 causes the heating element 16 to produce heat. A gas from the gas source 12 is passed over the heating element 16 and the gas is caused to heat up and exit the nozzle 11 of the desolvation heater 10 at a temperature which is related to the temperature of the heating element 16. The temperature of the gas exiting the nozzle 11 may be less than the temperature of the heating element 16. Correspondingly, the temperature of the gas as it flows over the capillary tip 5a may be lower than the temperature of the gas as it exits the nozzle 11.

The desolvation heater 10 and inlet 4 are configured such that when a capillary 5 is inserted into the ionisation chamber 3, the heated gas exiting the nozzle 11 of the desolvation heater 10 serves to heat up the distal end 5a of the capillary 5, and volatilise any sample which may be provided on the distal end 5a of the capillary 5. The ionisation source 1 further comprises a corona discharge device 20 which may comprise a corona pin 21. The corona discharge device 20 serves to ionise the volatilised sample on the distal end 5a of the capillary 5 receivable in the ionisation chamber 3.

The volatilised and ionised sample may then pass into the inlet cone of a mass spectrometer (not shown), to which the ionisation source 1 is mounted in use. As schematically illustrated in Figure 4, the present invention provides a control system 50 comprising a pressure sensor 14 for measuring the pressure of the gas supplied by the gas source 12. The control system 50 further comprises a controller 15 which is operatively associated with the pressure sensor 14 and configured to disable the heating element 16 if the measured pressure (by the pressure sensor 14) is less than a predetermined threshold pressure. In the embodiment shown, the controller 15 is operatively associated with the power supply 13, so as to selectively disable the power supply to the heating element 16. As noted above, if a significant amount of the sample is not adequately heated by the heated gas exiting the heater 10 it may subsequently not be effectively volatilised into the gas phase and hence would not be ionised by the corona discharge pin 21. This may then reduce the speed and accuracy of the subsequent measurement.

It may therefore be important to ensure that the temperature and flow rate of the heated gas exiting the nozzle 11 are sufficient. If the flow rate is not sufficient, then inadequate heating of the sample may be experienced. The flow rate of the gas leaving the nozzle 11 may be related to the pressure of the gas supplied by the gas source 12. If the pressure of the gas supplied by the gas source 12 is not above a predetermined threshold pressure, then the flow rate of the gas over the heating element 16 may also be below a predetermined threshold flow rate. Subsequently, not only may an inadequate flow of heated gas leave the nozzle 11 , the heating element 16 may be caused to overheat, since the flow of gas over the heating element 16 is not sufficient to maintain the temperature of the heating element at the temperature directed by the controller 15. There is a risk, therefore, that the heating element 16 may burn out or at least become damaged.

Accordingly, the controller 15 of the control system 50 embodying the present invention is operatively associated with the pressure sensor 14 and is configured to disable the heating element 16 if the measured pressure is less than a predetermined threshold pressure.

In at least one embodiment, the predetermined threshold pressure may be 6.5 Bar.

In at least one embodiment, the predetermined threshold pressure is configured to be one which causes heated gas to exit the heater 10 with a predetermined threshold flow rate. In at least one embodiment, the predetermined threshold flow rate is 2.5 litres per minute.

Accordingly, a control system 50 embodying the present invention is configured to disable the heating element 16 if the measured pressure is less than a predetermined threshold pressure and/or the flow rate of the gas exiting the heater 10 is lower than a predetermined threshold flow rate.

In at least one embodiment, the gas supplied by the gas source 12 may be nitrogen. A control system 50 embodying the present invention provides a direct means of measuring inadequate gas flow to the heater 10 by directly monitoring the pressure of the gas source 12. This then provides a notification to the user that the predetermined threshold pressure is out of range to maintain the predetermined threshold flow rate of 2.5 litres per minute.

With reference to Figure 2 and 3, the present invention further provides a flow regulator 100 for connection to a gas source 12 of an ion source 1. The flow regulator 100 is selectively configurable between a first mode in which the flow regulator 100 is configured to deliver gas within a first predetermined flow rate range; and a second mode in which the flow regulator is configured to deliver gas within a second predetermined flow rate range. The second predetermined flow rate range is higher than the first predetermined flow rate range.

In at least one embodiment, the first predetermined flow rate range is one which is suitable for an “analytical mode” of the ion source. By “analytical mode” is meant the normal mode in which the ionisation source 1 operates to conduct an analysis on a sample provided on the distal end 5a of the capillary 5.

In at least one embodiment, the first flow rate range may be between 1 and 4 litres per minute. In at least one embodiment, the first flow rate range may be between 2.3 and 2.7 litres per minute.

The second predetermined flow rate range of the second mode may be one which is configured so as to have a cooling effect on the heating element 16. As noted above, in use, there may be a requirement for the temperature of the heated gas exiting the heater 10 to be reduced. In such instances, a user may need to wait until the temperature of the heating element 16 has reduced sufficiently through convection with the surrounding air. This may increase the cycle time of the instrument.

By providing a flow regulator 100 embodying the present invention, which is operable in a second mode in which the flow regulator 100 is configured to deliver gas within the second predetermined flow rate range, the temperature of the heating element 16 may be reduced within a suitable time frame so as to allow the subsequent operation of the ion source 1. In at least one embodiment, the second predetermined flow rate range is between 15 and 25 litres per minute. In at least one embodiment, the second predetermined flow rate is 20 litres per minute.

There may also be a requirement to rapidly cool the heating element 16, and thus the heater 10, when there is risk of a user touching the heater 10 or the nozzle 11. For example, the ion source 1 may be opened, allowing the user access into the ionisation chamber 3. In such instances, there may be a need to rapidly cool the heating element 16. Accordingly, a flow regulator 100 embodying the present invention may be configured to operate in said second mode, configured to deliver gas within the second predetermined flow rate range, when a door of the ion source 1 is detected as having been opened.

As shown in cross-section in Figure 2, and schematically in Figure 3, the flow regulator 100 may comprise an inlet 101 and an outlet 102. The inlet 101 is for connection to the gas source 12. The flow regulator 100 defines a first path 110 and a second path 120. Both the first 110 and second 120 paths are fluidly connected between the inlet 101 and outlet 102, in parallel. As schematically shown in Figure 3, the flow regulator 100 may comprise a flow splitter 103 which is fluidly connected between the inlet 101 and both the first 110 and second 120 paths. The flow regulator 100 may comprise a flow combiner 104, fluidly connected between both the first 110 and second 120 paths and the outlet 102. The flow splitter 103 serves to split the flow from the inlet 101 into both the first 110 and second 120 paths. The flow combiner 104 serves to combine the flow from the first 110 and second 120 paths, before passing the combined flow to the outlet 102.

The first path 110 further comprises a first flow restrictor 111 arranged in the first path 110 and configured to restrict flow through the first path 110 to within the first predetermined flow rate range. Furthermore, there may be a pressure sensor 14 in communication with the first path 110.

The second path 120 further comprises a valve 121 arranged in the second path 120, to selectively open or close (block) the second path 120. Accordingly, when the valve 121 is configured to close the second path 120, any gas passing through the flow regulator 100 will be directed through the first path 110, and therefore subject to the first flow restrictor 111. The valve 121 may comprise a solenoid actuator.

When the valve 121 is configured to open the second path 120, any gas flowing through the flow regulator 100 will flow through the second path 120, since there is, in at least one embodiment, no restriction on the flow of gas through the second path 120 (or at least less restriction than the first path 110). In at least one embodiment, the flow regulator 100 is configured such that when the valve 121 is configured to open the second path 120, the flow regulator 100 delivers gas within the second predetermined flow rate range.

In at least one embodiment, the flow regulator 100 further comprises a second flow restrictor 122, configured to restrict flow therethrough to within the second predetermined flow rate range. In the embodiment schematically shown in Figure 3, the second flow restrictor 122 is shown as being fluidly connected between the flow combiner 104 and the outlet 102 of the flow regulator 100. Alternatively, the second flow restrictor 122 could be provided within the second path 120 (i.e. between the flow splitter 103 and the flow combiner 104).

The control system shown in Figure 3 may further comprise a gas source isolation valve 130 in communication with the gas source 12. There may further be provided a filter 131 in line with the gas source 12. As schematically shown in Figure 3, there may further be a supply of gas 132 to the inlet cone of the mass spectrometer. In Figure 3, the control system 15 is shown connected to the pressure sensor 14, the valve 121 and the isolation valve 130.

The control system 50 and flow regulator 100 disclosed herein may be used in combination with one another, for use in a heater arrangement for an ion source.

With reference to the schematic illustration of Figure 5, the isolation valve 130 may be in fluid communication with the gas source 12. The output of the isolation valve 130 is fed to the input of the flow regulator 100. The pressure sensor 14 forms part of the flow regulator 100. The controller 15 communicates with the flow regulator 100 (namely the pressure sensor 14 and the valve 121), receiving and sending signals thereto. The flow regulator then feeds gas to the heater 10, to be heated by the heating element 16 which is controlled by the controller 15.

In figure 5, the ‘cone gas’ connection 132 between the isolation valve 130 and the inlet cone is not shown. The connection 132 is not essential to the invention. When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

1. A control system for an ion source, the ion source comprising a heater including a gas source and a heating element, the heater for directing heated gas onto a capillary insertable into the ion source in use, the control system comprising: a pressure sensor for measuring the pressure of gas supplied by the gas source; and a controller operatively associated with the pressure sensor and configured to disable the heating element if the measured pressure is less than a predetermined threshold pressure.

2. A control system according to claim 1 , wherein the predetermined threshold pressure is 6.5 Bar.

3. A control system according to claim 1 , wherein the predetermined threshold pressure is configured to be one which causes heated gas to exit the heater with a predetermined threshold flow rate.

4. A control system according to claim 3, wherein the predetermined threshold flow rate is 2.5 litres per minute.

5. A flow regulator for connection to a gas source of an ion source, the flow regulator selectively configurable between: a first mode in which the flow regulator is configured to deliver gas within a first predetermined flow rate range; and a second mode in which the flow regulator is configured to deliver gas within a second predetermined flow rate range, which is higher than the first predetermined flow rate range.

6. A flow regulator according to claim 5, wherein the first flow rate range is between 1 and 4 litres per minute.

7. A flow regulator according to claim 5, wherein the first flow rate range is between 2.3 and 2.7 litres per minute.

8. A flow regulator according to any of claims 5 to 7, wherein the second flow rate range is between 15 and 25 litres per minute.

9. A flow regulator according to any of claims 5 to 7, wherein the second flow rate is 20 litres per minute.

10. A flow regulator according to any of claims 5 to 9, configured to operate in the second mode in response to a door of the ion source being opened.

11. A flow regulator according to any of claims 5 to 10, comprising: an inlet; an outlet; a first path fluidly connected between the inlet and outlet, and a first flow restrictor arranged in the first path configured to restrict flow therethrough to within said first predetermined flow rate range; and a second path fluidly connected between the inlet and outlet, and a valve arranged in the second path, to selectively open or close the second path.

12. A flow regulator according to claim 11 , wherein the second path is configured to allow a greater flow rate than the first predetermined flow range of the first path.

13. A flow regulator according to any of claims 11 and 12, further comprising: a flow combiner, wherein the first path and second path are connected between the input and the flow combiner ; and a second flow restrictor arranged between the flow combiner and the outlet, configured to restrict flow therethrough to within said second predetermined flow rate range.

14. An ion source comprising a control system according to any of claims 1 to 4 and a flow regulator according to any of claim 5 to 13.

15. A heater arrangement comprising: a heater including a gas source and a heating element, the heater for directing heated gas onto a capillary insertable into the ion source in use, a pressure sensor for measuring the pressure of gas supplied by the gas source; and a flow regulator in fluid connection with the gas source and selectively configurable between: a first mode in which the flow regulator is configured to deliver gas within a first predetermined flow rate range; and a second mode in which the flow regulator is configured to deliver gas within a second predetermined flow rate range, which is higher than the first predetermined flow rate range; and a controller operatively associated with the pressure sensor and configured to disable the heating element if the measured pressure is less than a predetermined threshold pressure, the controller further configured to select one of the first and second modes of the flow regulator.