Control of gas flow

Abstract

The invention relates to a gas inlet system for providing gas into an analytical apparatus, comprising at least a first and a second flow restriction that are arranged on a gas inlet line, a gas flow control line connected to the gas inlet line, a gas flow controller on the gas control line, and valves for controlling gas flow in the gas inlet line and the gas control line. Also provided is a method of controlling gas flow into an analytical apparatus.

Claims

1. A gas inlet system for providing gas into an analytical apparatus operating under vacuum, the system comprising (a) a plurality of gas inlet lines fluidly connected to the apparatus, for introducing gas into the apparatus; (b) at least one valve arranged on the plurality of gas inlet lines downstream of at least one gas inlet junction, for controlling flow of gas in the plurality of inlet lines; (c) a plurality of gas flow control lines each fluidly connected to a respective gas inlet line of the plurality of gas inlet lines through the a respective gas inlet junction, wherein the plurality of gas flow control lines merge into a single gas flow control line; (d) at least one first flow restriction and at least one second flow restriction arranged on each gas inlet line, upstream from and downstream from the gas inlet junction, respectively; (e) at least one gas flow controller arranged on the single gas flow control line, such that the plurality of gas flow control lines merge into the single gas flow control line upstream from the at least one gas flow controller, to control pressure at the gas inlet junctions; (f) at least one valve for controlling flow of gas in the plurality of gas flow control lines; and (g) at least one vacuum pump or exhaust that is fluidly connected to the gas flow control lines, downstream from the gas flow controller.

2. The gas inlet system of claim 1, wherein the first flow restriction and/or the second flow restriction, when provided as a plurality of restrictions, are arranged in a parallel arrangement on the gas inlet line, and wherein the gas inlet line optionally further comprises at least one valve for selectively directing flow through the plurality of restrictions.

3. The gas inlet system of claim 1, wherein the second flow restriction is provided as a plurality of flow restrictions that are arranged in a parallel arrangement.

4. The gas inlet system of claim 1, comprising a first flow restriction and at least one second flow restriction on each of the at least one gas inlet lines, and wherein the restrictions are structured such that the ratio of gas flow through the first and the at least one second flow restriction, for the same pressure difference across both restrictions, is in the range of 1:10 to 10:1.

5. The gas inlet system of claim 1, comprising a first flow restriction and at least one second flow restriction on each of the at least one gas inlet lines, and wherein the restrictions are structured such that the ratio of gas flow through the first and the at least one second flow restriction, at a fixed gas pressure in the gas inlet line is, depending on flow controller settings, in the range of 1:1 to 1000:1.

6. The gas inlet system of claim 1, wherein each of the plurality of gas control lines is fluidly connected to a single gas flow controller.

7. The gas inlet system of claim 1, further comprising at least one flow restriction that is arranged on the gas control line.

8. The gas inlet system of claim 7, wherein the at least one flow restriction is provided as a switchable restriction that is provided as one or more restrictions on separate lines that are arranged in parallel with the gas control line and that connect to the gas control line at a first and a second junction, and wherein at least one valve is further provided for selectively directing gas flow through the one or more restrictions.

9. The gas inlet system of claim 7, wherein the at least one flow restriction is provided on a vent line that is fluidly connected to the at least one gas flow control line, between the at least one valve for controlling gas flow and the gas flow controller.

10. The gas inlet system of claim 9, wherein the vent line is open to atmosphere.

11. The gas inlet system of claim 9, wherein the vent line is connected to a gas reservoir.

12. The gas inlet system of claim 1, wherein the at least one vacuum pump is provided as a single vacuum pump.

13. The gas inlet system of claim 1, wherein the at least one vacuum pump is provided as a plurality of vacuum pumps that are sequentially arranged.

14. The gas inlet system of claim 1, further comprising at least one gas supply.

15. The gas inlet system of claim 14, wherein each of the least one gas supply, when provided as a plurality of gas supplies, is connected to a respective gas inlet line.

16. The gas inlet system of claim 1, wherein the analytical apparatus is a mass spectrometer.

17. The gas inlet system of claim 16, wherein the at least one gas inlet line is fluidly connected to a collision cell of the mass spectrometer.

18. The gas inlet system of claim 16, wherein the vacuum pump connected to the gas control line is part of a vacuum pumping system of the mass spectrometer.

19. An analytical apparatus with a gas inlet system according to claim 1.

20. A method of controlling gas flow into an analytical apparatus operating under vacuum, the method comprising steps of flowing gas from at least one gas supply into a plurality of gas inlet lines for providing gas into an analytical apparatus; splitting away a portion of the gas flow in each gas inlet line into a respective one of a plurality of gas control lines that is arranged on the gas inlet line and that meets the gas inlet line at a respective gas inlet junction, such that a portion of the gas flow in the gas inlet line flows through the respective gas control line, and wherein gas flow in each gas control line is controlled by means of a gas flow controller that regulates pressure at the gas inlet junction, wherein the plurality of gas control lines merge into a single gas control line upstream of the gas flow controller, and a vacuum pump or exhaust that fluidly connected to the plurality of gas control lines, downstream from the gas flow controller; whereby the portion of gas that is not split away from the gas inlet line into the gas control line is delivered into the apparatus and the flow rate into the analytical apparatus is determined by the difference in gas pressure between the gas inlet junction and the analytical apparatus.

21. The method of claim 20, wherein the portion of gas that is split away from the gas inlet line ranges from about 0.0001% to 99.99%.

22. The method of claim 20, further comprising (i) using the gas flow controller to set a first back pressure in the gas control line and thereby a first gas flow rate into the analytical apparatus, followed by (ii) using the gas flow controller to set a second back pressure in the gas control line, different to the first back pressure, and thereby a second gas flow rate into the analytical apparatus, different to the first flow rate.

23. The method of claim 22, wherein at least one of the first and second back pressures is less than 1 bar.

24. The method of claim 22, wherein the first and second flow rates differ by a factor of at least 10.

25. The method of claim 24, wherein the first and second flow rates differ by a factor that is up to up to 100.

26. The method of claim 20, wherein the flow through the gas control line is sufficiently high that no back diffusion into the gas inlet line occurs.

27. The method of claim 20, further comprising controlling flow of gas from the gas supply to the gas inlet junction by means of a first flow restriction and controlling flow of gas from the gas inlet junction into the analytical apparatus by means of at least one second flow restriction.

28. The method of claim 27, wherein the at least one second flow restriction is provided as a plurality of flow restrictions that are arranged in a parallel arrangement.

29. The method of any one of the claim 20, wherein gas from a plurality of gas supplies is flowed into separate gas inlet lines, and wherein the flow of gas in each of the gas inlet lines is controlled by splitting away a portion of the gas flow in each of the gas inlet lines.

30. The method of claim 20, wherein the analytical apparatus is a mass spectrometer.

31. The gas inlet system of claim 1, wherein the gas flow controller is selected from a back pressure regulator, a mass flow controller, or a volume flow controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The skilled person will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the present teachings in any way.

(2) FIG. 1 shows a gas inlet system according to the invention.

(3) FIG. 2 shows a gas inlet system that further includes a vacuum pump on the gas control line.

(4) FIG. 3 shows a configuration of the gas inlet system that has two gas inlet lines, each connected to a gas control line.

(5) FIG. 4 shows a configuration having a switchable second restriction on the gas inlet line.

(6) FIG. 5 shows a configuration having a bleed restriction on the gas control line.

(7) FIG. 6 shows different flow rates achievable by the gas inlet system according by the system for different values of gas inlet pressure, P.sub.in, pressure at the gas inlet junction, P.sub.i; (A) P.sub.in set at 2000 mbar and P.sub.i at 100 mbar; (B) P.sub.in set at 2000 mbar and P.sub.i at 1069 mbar(ambient pressure); (C) P.sub.in set at 5000 mbar and P.sub.i at 4050 mbar. Restrictions are shown in arbitrary units.

DESCRIPTION OF VARIOUS EMBODIMENTS

(8) In the following, exemplary embodiments of the invention will be described, referring to the figures. These examples are provided to provide further understanding of the invention, without limiting its scope.

(9) In the following description, a series of steps are described. The skilled person will appreciate that unless required by the context, the order of steps is not critical for the resulting configuration and its effect. Further, it will be apparent to the skilled person that irrespective of the order of steps, the presence or absence of time delay between steps, can be present between some or all of the described steps.

(10) It should be appreciated that the invention is applicable for gas inlet systems in analytical systems general, including mass spectrometers and in particular in collision cells for use in mass spectrometers. In general, therefore, the gas that is being delivered in the system will be variable. Further, the system and method according to the invention is illustrated in the embodiments that follow with a preferred embodiment of collision cell, but it should be appreciated that the invention is also applicable to other analytical systems that include or involve gas delivery components.

(11) Referring to FIG. 1, there is schematically shown a gas inlet system 1, for delivering gas from a gas supply 10 into a collision cell 9, having a gas inlet line 2 and a gas control line 11, that are connected at a gas line junction 6. A first flow restriction 3 and a second flow restriction 4 are arranged on the gas inlet line 2. Valves 5, 7 are arranged on the gas inlet line and the gas control lines, respectively. A flow controller (back pressure regulator) 8 is arranged on the gas control line, downstream from the valve 7. In this embodiment, the flow controller is not pumped and simply exhausts to atmosphere through exhaust 12.

(12) If the gas is not to be used in the collision cell, valves 5, 7 are kept closed. Opening the valves results in gas flowing through the restriction 3 towards the gas inlet junction 6. If the system uses a back pressure regulator, the pressure at this point in the system (P.sub.i) is regulated by the back pressure regulator 8. Gas flow through the restriction 3 is therefore defined by P.sub.in, the pressure from the gas supply, and the pressure P.sub.i at the gas inlet junction 6. Gas then flows from the gas inlet junction and through the second restriction 4, into the collision cell 9. Since the pressure in the collision cell is very low, e.g. 0.01 mbar or less, the flow rate through the second restriction is controlled by P.sub.i, in accordance with the Poisseuille formula.

(13) Flow rates in the system can be adjusted by altering P.sub.in and/or P.sub.i, and/or by changing the flow restrictions 3, 4. For example, doubling P.sub.i results in a roughly 4-fold increase in flow rate through the restriction 4, a five-fold increase in P.sub.i results in more than a 20-fold increase in flow rate, and so on. However, due to the fact that the lowest value of P.sub.i achievable in this setup (ambient pressure) is 1 bar, P.sub.i would have to set to almost 5 bar to achieve a 20-fold change in flow rate.

(14) Although feasible, it might be advantageous to operate the system at lower pressure, for example due to valve ratings. Further, a larger range in pressure and therefore a larger range in achievable flow rates, would be advantageous.

(15) Accordingly, turning to FIG. 2, an alternative embodiment of the system includes a vacuum pump 13 that is arranged on the gas control line 11 downstream of the flow controller. In this configuration, P.sub.i can be set as appropriate to achieve any desired flow rate into the collision cell 9. As an example, by arranging appropriate restrictions 3, 4 on the gas inlet line 2, and control P.sub.i between 100 mbar and 1 bar, gas flow that differs by a factor of 100 is achievable.

(16) Care must be taken when configuring the system that the flow rate through the control line 11 is always high enough so that no back diffusion into the gas inlet line 2 occurs. However, this is achievable by adjusting the pressure and restrictions in the system, and by adjusting the restriction of the gas control line.

(17) The vacuum pump 13 can have an exhaust that is open to atmosphere. However, multiple vacuum pumps can also be used with the system, for example pumps that are sequentially arranged. The vacuum pump can also be a part of, or be connected to, the vacuum pump system of a mass spectrometer.

(18) The system can be set up so that gas flow of multiple gases can be individually controlled using a single flow controller. An example of a set up for 2 gases is shown in FIG. 3, although the skilled person will appreciate that this setup can be equally applied for any number of gases, through additional gas lines.

(19) In FIG. 3, two gas supplies 10, 10 are shown, each being connected to a gas inlet line 2, 2 that feed into a collision cell 9. Each gas inlet line is connected to a respective gas control line 11, 11 that merge at a gas control line junction 14. Valves 7, 7 control gas flow through the gas control lines. In an alternative configuration, a single switch valve can be arranged at the control line junction 14. A single flow controller 8 is connected on the gas control line, downstream from the control line junction 14.

(20) Thus, in this configuration, a single flow controller can be used to regulate gas flow in the two gas inlet lines 2, 2. By configuring the restrictions 3, 3 and 4, 4, on each respective gas inlet line, and gas pressure P.sub.in and P.sub.i, the latter through the back pressure regulator 8, flow rates in each gas inlet line can be independently set to any desired value. Thereby, individual flow rates for different gases, each fed through separate gas inlet lines, is possible. The gas flows from each gas supply 10, 10 could be flowed into the cell 9 simultaneously or, more typically, at different times. Appropriate operation of valves 5, 7 and 5, 7 permit either one or both of the gas supplies to be connected to the cell at one time.

(21) The gas inlet system can be arranged to include switchable flow restriction, to further expand the capabilities of the system. In FIG. 4, an example of such a setup is provided. Here, two second flow restrictions 4, 4 are arranged on a single gas inlet line 2. The restrictions are switchable through two valves 5, 5 that are arranged between the restrictions and the collision cell 9.

(22) By having switchable restrictions on the gas inlet lines, further possibilities for adjusting flow rates are possible. Thus by having different restrictions, the range of flow rates can be expanded for any given configuration of the gas control line 11.

(23) It should be appreciated that additional parallel restrictions can be arranged in the same manner on the gas inlet line as appropriate, and additional valves included so as to be able to selectively direct gas flow through any one restriction.

(24) Further, a similar arrangement of restrictions can be arranged on the gas control line. Such restrictions are arranged between the valve 7 and the flow controller 8. Through such an arrangement of restrictions, the flow rate in the gas control line can be adjusted. This can be especially important at low flow rates when there is an increased risk of back flow. Another advantage of this position of the switchable restriction would be that gas flowing through these switchable restrictions is not introduced into the analyzer; therefore, the demands on cleanness, low dead volume etc are very relaxed, and the relaxation time after switching the restrictions are minimized.

(25) Flow controllers, for example when provided as a back pressure regulator, can have problems when operating at very low flow rates. One way of handling low flow rates is to make the restriction 3 in the system less restrictive, thereby increasing flow rate into the gas control line without affecting other parameters in the system. However, this has the drawback that gas consumption in the system is increased.

(26) In FIG. 5, an alternative arrangement is shown that provides a solution to this dilemma, in which a bleed restriction 15 is provided on a vent or bleed line 16 that is arranged between the valve 7 and controller 8. The vent line can be open atmosphere, or alternatively it can be open to a gas reservoir. In this configuration, the controller 8 can handle even very low flow rates in the gas control line, since additional flow through the controller will be provided by the bleed vent. Care must be taken in this setup to maintain flow through the control line high enough so that there is no back flow of gas in the gas control line, since the bleed is open to atmospheric pressure. The restriction 15 can be adjusted so as to provide adequate flow of gas into the controller while minimizing risk of back flow.

(27) As should be appreciated by the foregoing description of particular embodiments of the system according the invention, the system is highly adaptable, and can be configured to provide a large range of flow rates at different pressures. A few exemplary arrangements of the system, showing how flow rates can vary based on different configurations and pressures, will now be described.

(28) Thus, turning to FIG. 6, results of simulations showing the effects of different setups are shown. The simulations were done for a configuration of the system that contain a single first restriction and a single second restriction. In a first setup, P.sub.in is set to 2 bar(a). Restrictions are shown in arbitrary units, and flow rates in the control line for different values of P.sub.i are shown in (A) and (B), respectively. Thus, when P.sub.i is set at 100 mbar(a) by the back pressure regulator, (A), the flow rate from the gas supply is 39.9 mL/min, the flow rate through the second restriction to the collision cell is 0.25 mL/min, and the flow rate in the control line is 39.65 mL/min. Accordingly, a majority of the gas is delivered through the control line to atmosphere. In (B), P.sub.i has been set to 1069 mbar(a) (ambient pressure), which results in a flow rate through the second restriction to the collision cell of 28.6 mL/min, while the flow rate through the control line is now very low, or about 0.003 mL/min. As a consequence, through a 10-fold decrease in P.sub.i more than a 100 fold change in flow rate through the second restriction, into the analytical system, is achieved.

(29) A simultaneous increase in the restrictions by a factor of 10 would result in flow rates that range between 0.025 and 3 mL/min, i.e. the flow rate is linear with respect to the restriction. As will be noted, gas consumption in this setup is highest when the flow rate into the analytical apparatus is lowest, due to the fact that most of the gas is released to atmosphere through the control line.

(30) If there is no vacuum pump in the system, P.sub.i can never be lower than ambient pressure (1 bar(a)). In the configuration shown in (C), P.sub.in has been set to 5000 mbar(a), and P.sub.i is set at 4050 mbar(a). The restrictions are 1000 and 2000, respectively, resulting in a flow rate of 8.2 mL/min into the analytical apparatus, with a flow rate from the gas supply of 8.60 mL/min and a flow rate in the control line of 0.40 mL/min. Increasing the inlet pressure P.sub.in to 6000 mbar(a), a flow rate of 12 mL/min into the analytical apparatus is achievable, while a reduction to 1000 mbar(a) at the junction point (P.sub.i) results in a flow rate of 0.5 mL/min. Accordingly, for this configuration, a 24-fold range in flow rates is achievable.

(31) As should be appreciated based on the foregoing description of the invention and some of its embodiments, the invention provides distinct advantages over gas inlet systems that are known in the art. Some of these advantages include: a single flow controller can be used for switching between multiple gases switching time between gases is minimal cost savings, compared with use of multiple flow controllers a very high range of flow rates are possible, in particular when using a vacuum pump in the system providing switchable restrictions increases the flow rate range to values not achievable with a conventional positioning of a flow controller gas consumption can be fairly low use of bleed restriction facilitates regulation of flow rates gas passing through the flow controller is not introduced into the analytical apparatus, which has several distinct advantages: impurities from the flow controller therefore not contaminating no risk of particles from flow controller entering analytical apparatus even on first use, flushing time is minimal

(32) As used herein, including in the claims, singular forms of terms are to be construed as also including the plural form and vice versa, unless the context indicates otherwise. Thus, it should be noted that as used herein, the singular forms a, an, and the include plural references unless the context clearly dictates otherwise.

(33) Throughout the description and claims, the terms comprise, including, having, and contain and their variations should be understood as meaning including but not limited to, and are not intended to exclude other components.

(34) The present invention also covers the exact terms, features, values and ranges etc. in case these terms, features, values and ranges etc. are used in conjunction with terms such as about, around, generally, substantially, essentially, at least etc. (i.e., about 3 shall also cover exactly 3 or substantially constant shall also cover exactly constant).

(35) The term at least one should be understood as meaning one or more, and therefore includes both embodiments that include one or multiple components. Furthermore, dependent claims that refer to independent claims that describe features with at least one have the same meaning, both when the feature is referred to as the and the at least one.

(36) It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention can be made while still falling within scope of the invention. Features disclosed in the specification, unless stated otherwise, can be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed represents one example of a generic series of equivalent or similar features.

(37) Use of exemplary language, such as for instance, such as, for example and the like, is merely intended to better illustrate the invention and does not indicate a limitation on the scope of the invention unless so claimed. Any steps described in the specification may be performed in any order or simultaneously, unless the context clearly indicates otherwise.

(38) All of the features and/or steps disclosed in the specification can be combined in any combination, except for combinations where at least some of the features and/or steps are mutually exclusive. In particular, preferred features of the invention are applicable to all aspects of the invention and may be used in any combination.