Apparatuses and methods for ion injection in mass spectrometry

Abstract

In some examples, an apparatus may include an ion injector including an ion injector entrance and an ion injector exit, and a capillary cap disposed at the ion injector exit. The capillary cap may include a capillary cap exit opening that is shaped and sized to reduce gas turbulence after the ion injector exit and improve ion signal stability.

Description

APPARATUSES AND METHODS FOR ION INJECTION IN MASS SPECTROMETRYBACKGROUND

[0001] In some cases, ionization techniques in mass spectrometry (MS) operate at atmospheric pressure. In order to detect and measure mass-to-charge ratios of the ionized species with atmospheric pressure (AP) ion sources, ions generated at atmospheric pressure may be transported from atmospheric pressure to a vacuum region of a MS system. In some cases, the MS system may generally include an ion injector, an electrodynamic ion funnel, and ion desolvation components.BRIEF DESCRIPTION OF DRAWINGS

[0002] Features of the present disclosure are illustrated by way of example and not limited in the following figure(s), in which like numerals indicate like elements, in which:

[0003] Figure 1 illustrates an atmospheric pressure to vacuum interface, in accordance with an example of the present disclosure;

[0004] Figure 2 illustrates a singlebore resistive glass capillary (hereinafter also referred to as “ion injector”), in accordance with an example of the present disclosure;

[0005] Figure 3 illustrates a round capillary cap and a slot exit capillary cap, in accordance with an example of the present disclosure;

[0006] Figure 4 illustrates examples of slot, cross, star, and muzzle-brake shaped exit capillary caps, in accordance with an example of the present disclosure;

[0007] Figure 5 illustrates various views of a slot exit capillary cap, in accordance with an example of the present disclosure;

[0008] Figure 6 illustrates a cross section of a first part of the muzzle-brake shaped exit capillary cap, in accordance with an example of the present disclosure;

[0009] Figure 7 illustrates various views of a second part of the muzzle-brake shaped exit capillary cap, in accordance with an example of the present disclosure;

[0010] Figure 8 illustrates various views including cross sectional views of an ion injector with an entrance round bore and slot exit capillary cap, in accordance with an example of the present disclosure;

[0011] Figure 9 illustrates a various views including a cross sectional view of an ioninjector with an entrance round bore and a muzzle exit capillary cap and an entrance cap, in accordance with an example of the present disclosure;

[0012] Figure 10 illustrates multiple reaction ion monitoring (MRM) ion signal stability, without application of a smoothing function to the ion signal, in accordance with an example of the present disclosure;

[0013] Figure 11 A illustrates a cross section of the slot exit capillary cap of Figure 5 and an ion injector together with an ion funnel and ion desolvation components including an atmospheric pressure to vacuum interface, in accordance with an example of the present disclosure;

[0014] Figure 11 B illustrates another example of a cross section of the slot cap of Figure 5 including an entrance cap and ion desolvation components, in accordance with an example of the present disclosure;

[0015] Figure 12 illustrates cross sectional areas of singlebore (SB) capillaries (hereinafter also referred to as “ion injectors”) and various exit cap shapes sorted based on the cross sectional area, in accordance with an example of the present disclosure;

[0016] Figure 13 illustrates an ion funnel pressure with various exit cap shapes and sizes, and reduction in ion funnel pressure as an indication of gas flow restriction, in accordance with an example of the present disclosure;

[0017] Figure 14 illustrates a principal component analysis (PCA) score plot obtained from ion signal relative standard deviation (RSD) analysis of various rotation angles of a slot exit capillary cap relative to an ion injector axis, in accordance with an example of the present disclosure;

[0018] Figure 15 illustrates a PCA score plot obtained from ion signal RSD analysis of various inlet configurations, in accordance with an example of the present disclosure; and

[0019] Figure 16 illustrates liquid chromatography-mass spectrometry / mass spectrometry (LC / MS / MS) MRM chromatographic peak area versus RSD obtained for a mixture of pesticides, in accordance with an example of the present disclosure.DETAILED DESCRIPTION

[0020] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

[0021] Throughout the present disclosure, the terms "a" and "an" are intended to denote at least one of a particular element. As used herein, the term "includes" means includes but not limited to, the term "including" means including but not limited to. The term "based on" means based at least in part on. The term “entrance” refers to the entrance end of an ion injector where gas molecules and ions enter an ion injector from an ion source. The term “exit” refers to the exit end of an ion injector where gas molecules and ions exit the ion injector to MS.

[0022] Apparatuses for ion injection in mass spectrometry (MS), and methods for ion injection in MS are disclosed herein.

[0023] With respect to the apparatuses and methods disclosed herein, as disclosed herein, ionization techniques in MS operate at atmospheric pressure. In order to achieve a highest possible sensitivity with atmospheric pressure (AP) ion sources, ions generated at atmospheric pressure may be transported from atmospheric pressure to a vacuum region of an MS system using, for example, round bore ion injector capillaries or apertures. Generally, these ion injector capillaries and apertures may be separated from the main vacuum stage of MS by conductance limits, and differentially pumped ion opticsand interfaces.

[0024] In some examples, one of the atmospheric pressure to vacuum interfaces used with high gas flow into MS systems includes an electrodynamic ion funnel. One advantage of the ion funnel interface is its capability for efficient ion collection and guiding.

[0025] With respect to the atmospheric pressure to vacuum interface, in some cases, the ion flux may be increased by using wider bore ion injector capillaries to increase the sensitivity for MS systems equipped with ion funnels. In this regard, in order to utilize wider bore capillaries, it can be technically challenging to control neutral gas flow into an ion funnel for more efficient pumping and a stable ion beam.

[0026] In order to address the aforementioned technical challenges, in some cases, long slotted ion injectors may be used with ion funnel interfaces to achieve higher ion flux and improved pumping efficiency of the MS system. However, ion signal stability may not be addressed with such ion injectors. Moreover, the manufacturing process for machining of such ion injectors can be technically challenging.

[0027] The apparatuses and methods disclosed herein address the aforementioned technical challenges by accomplishing ion injection from atmospheric pressure to vacuum of MS systems by using a round bore capillary (e.g., “ion injector” as disclosed herein). In one example, the ion injector may include an inner diameter of 1 .2 mm, a length of 90 mm and a slot capillary cap with a width of 0.6 mm. Other ion injectors with different slot widths as well as of cross, star, and muzzle-brake shaped capillary caps may also be utilized with different capillary inner diameters.

[0028] The apparatuses and methods disclosed herein provide for a reduction in gasturbulence and recirculation in an atmospheric-to-vacuum interface such as an ion funnel.This results in improved ion signal reproducibility and precision, and therefore reduced MS detection limits.

[0029] For the apparatuses and methods disclosed herein, the exit capillary caps may be manufactured separately from the ion injector to thus provide a desired exit pattern to disrupt the neutral gas jet entering the ion funnel.

[0030] According to examples disclosed herein, an apparatus may include an ion injector including an ion injector entrance and an ion injector exit, and a capillary cap disposed at the ion injector exit. The capillary cap may include a capillary cap exit opening that is shaped and sized to reduce gas turbulence after the ion injector exit (e.g., in the ion funnel) and improve ion signal stability.

[0031] In some examples, the capillary cap exit opening may include a rectangular slot shape. In this regard, the rectangular slot shape may include curved portions. Alternatively, the capillary cap exit opening may include a cross slot shape, a star slot shape, or a muzzle brake configuration including a circular capillary cap exit opening and elongated slots along a side wall of the capillary cap. The capillary cap may include a concave area on an opposite side of an exit face of the capillary cap.

[0032] According to examples disclosed herein, a capillary cap may be disposable at an ion injector exit of an ion injector that includes an ion injector entrance and the ion injector exit. The capillary cap may include a capillary cap exit opening that is shaped and sized to reduce gas turbulence after the ion injector exit (e.g., in the ion funnel) and improve ion signal stability.

[0033] According to examples disclosed herein, a method may include attaching a capillary cap to an ion injector including an ion injector entrance and the ion injector exit. The capillary cap may include a capillary cap exit opening that is shaped and sized to reduce gas turbulence after the ion injector exit (e.g., in the ion funnel) and improve ion signal stability.

[0034] Figure 1 illustrates an atmospheric pressure to vacuum interface 100, in accordance with an example of the present disclosure.

[0035] Referring to Figure 1 , the atmospheric pressure to vacuum interface 100 may include an ion injector 102 that includes an entrance capillary cap 104 and an exit capillary cap 106. The atmospheric pressure to vacuum interface 100 may further include an ion funnel 108, with the pressure zones of the atmospheric pressure to vacuum interface 100 being separated into an atmospheric pressure zone 110, a low vacuum zone 112, and a high vacuum zone 114 by means of differential pumping.

[0036] Figure 2 illustrates a singlebore resistive glass capillary (hereinafter also referred to as “ion injector”), in accordance with an example of the present disclosure.

[0037] Referring to Figure 2, views that include an end view, a side view, a section view, and an enlarged section view are respectively shown at 200, 202, 204, and 206. In the example shown, the ion injector 102 may include a bore 220 including an inner diameter of 1.2 mm as shown at 208, and a length of 90 mm as shown at 210. Yet further, various additional dimensions are shown for the example of Figure 2. However, other ion injectors with different dimensions may also be utilized as needed with different capillary inner diameters. A fire polish may be applied to area 212 to smooth out ground surfaces and to blend sharp edges. Ends of the ion injector 102 may be plated as shown at 214,with a resistive surface being removed at 216.

[0038] Figure 3 illustrates a round capillary cap and a slot exit capillary cap, in accordance with an example of the present disclosure.

[0039] Referring to Figure 3, a round capillary cap 300 is shown and includes an entrance inner diameter (ID), for example, of 4.2 mm. However, other IDs may also be utilized as needed for the round capillary cap 300. Further, a rectangular slot exit capillary cap 302 is shown and includes a slot length, for example, of 4.0 mm and a slot width, for example, of 0.6 mm. However, other slot lengths and widths may also be utilized as needed for the rectangular slot exit capillary cap 302. In the example of Figure 3, the rectangular slot may include curved portions as shown at 304. The configuration of the rectangular slot exit capillary cap 302 as shown may disrupt gas flowing through the constant diameter ion injector 102 and exiting the rectangular slot exit capillary cap 302.

[0040] The round capillary cap 300 may be used at both the entrance and the exit of an ion injector. However, as disclosed herein, a slot (or another shaped) capillary cap may be used at the exit of the ion injector, and thus a more stable ion signal may be obtained as opposed to using a round capillary cap. An example of a configuration of the ion injector may include a round bore entrance capillary cap, a singlebore ion injector, and a round bore exit capillary cap. Another example of a configuration of the ion injector may include a round bore entrance capillary cap, a singlebore ion injector, and a shaped (e.g., slot, cross, star, or muzzle brake) exit capillary cap, to thus improve ion signal stability as disclosed herein.

[0041] Figure 4 illustrates examples of slot, cross, star, and muzzle-brake shaped exit capillary caps, in accordance with an example of the present disclosure.

[0042] Referring to Figure 4, compared to the example of Figure 3, rectangular slot exit capillary caps are shown at 400 and 402, and include different slot widths, for example, of 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, and 0.8 mm. A cross exit capillary cap is shown at 404, a star exit capillary cap is shown at 406, and a muzzle-brake shaped exit capillary cap is shown at 408. The cross exit capillary cap shown at 404 may include two orthogonal slots as shown at 410. The star exit capillary cap shown at 406 may include three slots disposed in a star pattern as shown at 412. Further, the muzzle-brake shaped exit capillary cap shown at 408 may include first and second parts 418 and 420, respectively. First part 418 is shown in further details in Figure 6. Second part 420 is shown in further detail in Figure 7, and may include a circular capillary cap exit opening 414 and elongated slots 416 along a side wall of the capillary cap. In this regard, gas may exit the circular capillary cap exit opening 414, as well as the elongated slots 416.

[0043] Figure 5 illustrates various views of a slot exit capillary cap, in accordance with an example of the present disclosure.

[0044] Referring to Figure 5, another example of a rectangular slot exit capillary cap 500 is shown. In this regard, various views that include top, front, side, bottom, and isometric views are shown, respectively, at 502, 504, 506, 508, and 510. The rectangular slot exit capillary cap 500 may include a concave area 512 on an opposite side of an exit face 514 of the capillary cap. Referring to Figures 2 and 5, the concave area 512 may provide a gap between exit face 218 of the ion injector 102, and inner area 516 of the capillary cap. In this regard, since slot 520 of the rectangular slot exit capillary cap 500, which may include a dimension in the range of 0.3 mm to 0.8 mm, may partially cover bore 220, which may include a dimension of approximately 1.2 mm, the gap provided bythe concave area 512 may permit un-blocked flow of gas through the bore 220 of the ion injector 102, further through the concave area 512, and out through the slot 520. In other examples, the slot 520 of the rectangular slot exit capillary cap 500 may include a width dimension that is equal to or greater than a diameter of the bore 220. Further, the rectangular slot exit capillary cap 500 may include openings 518, for example, for providing electrical contact to ion injector 102 via a canted coil spring.

[0045] In some examples, the slot 520 (as well as other slots and exit openings as disclosed herein) of the rectangular slot exit capillary cap 500 may be positioned centrally along a central longitudinal axis of bore 220 of the ion injector 102. In other examples, the slot 520 (as well as other slots and exit openings as disclosed herein) of the rectangular slot exit capillary cap 500 may be offset radially relative to the central longitudinal axis of bore 220 of the ion injector 102. In other examples, as shown in Figure 1 , the ion injector 102 may be disposed in a radially offset position relative to a central longitudinal axis 116 of ion funnel 118. This offset may minimize the possibility of large droplets exiting from the ion injector 102, exiting straight through the ion funnel 118, and reaching downstream ion optics, and therefore minimizing optics contamination and chemical noise.

[0046] Figure 6 illustrates a cross section of the first part of the muzzle-brake shaped exit capillary cap, in accordance with an example of the present disclosure;

[0047] Referring to Figure 6, with respect to the first part 418 of the muzzle-brake shaped exit capillary cap 408, a sectional view similar to section B-B of Figure 5 is shown. The first part 418 of the muzzle-brake shaped exit capillary cap 408 may include a curved space 602 on an opposite side of a face 604 of the capillary cap. Referring to Figures 2and 6, the curved space 602 may provide a gap between exit face 218 of the ion injector 102, and inner area 606 of the first part 418. The first part 418 may include openings 608, similar to openings 518 of the rectangular slot exit capillary cap 500 for providing electrical contact to the ion injector 102 via a canted coil spring. Further, the first part 418 may include an indented region 610 at the face 604.

[0048] Figure 7 illustrates various views of the second part of the muzzle-brake shaped exit capillary cap, in accordance with an example of the present disclosure.

[0049] Referring to Figures 4 and 7, as disclosed herein, the second part 420 of the muzzle-brake shaped exit capillary cap shown at 408 may include a circular capillary cap exit opening 414 and elongated slots 416 along a side wall of the second part 420. The elongated slots 416 may provide a spring force action to grab the first part 418 of the muzzle-brake shaped exit capillary cap shown at 408, and openings for gas release. In this regard, various views of the second part 420 are shown and include top, side, bottom, and first and second isometric views, respectively, at 700, 702, 704, 706, and 708. The second part 420 may include a cave-shaped area 710 on an opposite side of an exit face 712. Referring to Figures 6 and 7, the cave-shaped area 710 may provide a gap between face 604 (e.g., by means of the indented region 610) and inner area 714 of the second part 420. Referring to Figures 6, 7, and 9, the gap 906 defined by the indented region 610 and the inner area 714 is shown with the first and second parts 418 and 420, respectively, disposed in an engaged configuration. The gap 906 may be further defined by spacers 716 that separate the indented region 610 and the inner area 714.

[0050] Figure 8 illustrates various views including cross sectional views of an ion injector with an entrance round bore and slot exit capillary cap, in accordance with anexample of the present disclosure.

[0051] Referring to Figure 8, an example of the ion injector 102 may include a 1.2 mm inner diameter (ID) capillary with a 2.0 mm ID entrance capillary cap 104. The ion injector 102 may further include the exit capillary cap 106, which may include a slot exit capillary cap. Left side, right side, top, two bottom, and isometric views of the ion injector 102 are shown, respectively, at 800, 802, 804, 806, 808, and 810.

[0052] Figure 9 illustrates a various views including a cross sectional view of an ion injector with an entrance round bore and a muzzle exit capillary cap and an entrance cap, in accordance with an example of the present disclosure.

[0053] Referring to Figure 9, another example of the ion injector 102 may include a 1.2 mm inner diameter (ID) capillary with a 2.0 mm ID entrance capillary cap 104. The ion injector 102 may further include the exit capillary cap 106, which may include the first and second parts 418 and 420, respectively, of the muzzle-brake shaped exit capillary cap shown at 408. Left side, isometric, and cross-sectional views of the ion injector 102 are shown, respectively, at 900, 902, and 904.

[0054] Figure 10 illustrates multiple reaction ion monitoring (MRM) ion signal stability, without application of a smoothing function to the ion signal, in accordance with an example of the present disclosure.

[0055] Referring to Figure 10, at 1000, MRM ion signal stability is illustrated at dwell time = 0.5 ms using capillary inner diameter (ID) of 1 .2 mm, exit caps round bore (R = 4.2 mm), and slot (W = 0.6 mm) by delivering a constant liquid flow of a constant calibrant concentration to an atmospheric pressure (AP) ion source. The MRM ion signal stabilityis determined without application of smoothing to the ion signal. The MRM ion signal stability shows greater stability for the slot exit capillary cap as compared to the round bore exit capillary cap. In this regard, the characteristic dimension (e.g., width of the slot) of slot exit capillary cap 302 results in faster settlement of the supersonic expansion compared to the round bore exit cap, thus resulting in more stable ion signal in the ion funnel downstream of the ion injector 102.

[0056] Figure 11 A illustrates a cross section of the slot exit capillary cap of Figure 5 and an ion injector together with an ion funnel and ion desolvation components including an atmospheric pressure to vacuum interface, in accordance with an example of the present disclosure.

[0057] Referring to Figure 11 A, a cross section of the slot exit capillary cap of Figure 5 and a 1.2 mm ion injector is shown at 1100. The example of Figure 11 A further shows an ion funnel 1102 and ion desolvation components 1104 including an atmospheric pressure to vacuum interface, such as the atmospheric pressure to vacuum interface 100 of Figure 1 .

[0058] Figure 11 B illustrates another example of a cross section of the slot cap of Figure 5 including an entrance cap and ion desolvation components, in accordance with an example of the present disclosure.

[0059] Referring to Figure 11 B, another example of a cross section of the slot cap of Figure 5 including a 2 mm inner diameter (ID) entrance capillary cap is shown at 1106. The example of Figure 11 B further shows ion desolvation components 1108.

[0060] Figure 12 illustrates cross sectional areas of singlebore (SB) capillaries (alsoreferred to herein as “ion injector”) and various exit cap shapes sorted based on the cross sectional area, in accordance with an example of the present disclosure.

[0061] Referring to Figure 12, cross sectional areas of SB capillaries and various exit cap shapes are shown. In this regard, as shown, a slot width (W) = 0.3 mm with a smaller cross section than SB capillary ID = 1 .2 mm restricts the gas flow. Ion signal stability may also be improved by reducing ion funnel pressure via restricting gas flow into the ion funnel or using higher pumping capacity. In this regard, the data of Figure 12 shows that the cross sectional areas of all of the shaped exit capillary caps except for slot width (W) = 0.3 mm are bigger than the cross sectional area of SB capillary ID = 1.2 mm, and do not result in gas flow restriction and cannot result in improved ion signal stability if decrease in ion funnel pressure is considered.

[0062] Figure 13 illustrates an ion funnel pressure with various exit cap shapes and sizes, and reduction in ion funnel pressure as an indication of gas flow restriction, in accordance with an example of the present disclosure.

[0063] Referring to Figure 13, an ion funnel pressure using an ion injector inner diameter (ID) of 1 .2 mm with various exit cap shapes is shown. In this regard, the table of Figure 13 shows reduction in ion funnel pressure for slot width (W) = 0.3 mm as an indication of gas flow restriction. The data of Figure 13 demonstrate that improving ion signal stability may be accomplished by using shaped exit capillary caps (except for slot width (W) = 0.3 mm), as opposed to gas flow reduction or using higher pumping capacity.

[0064] Figure 14 illustrates a principal component analysis (PCA) score plot obtained from ion signal relative standard deviation (RSD) analysis of various rotation angles of a slot exit capillary cap relative to an ion injector axis, in accordance with an example of thepresent disclosure.

[0065] Referring to Figure 14, the PCA score plot obtained from ion signal RSD analysis of various rotation angles of a slot exit capillary cap relative to an ion injector axis is shown at 1400. In this regard, negative scores indicate improvement in ion signal RSD. A major variance of the data is along the PC1 axis. Further, different rotation angles of the slot exit capillary cap as shown at 1402 show minimal impact on ion signal RSD as shown at the PCA score plot 1400.

[0066] Figure 15 illustrates a PCA score plot obtained from ion signal RSD analysis of various inlet configurations, where negative scores indicate improvement in ion signal RSD, in accordance with an example of the present disclosure.

[0067] Referring to Figure 15, a PCA score plot obtained from ion signal RSD analysis of various capillary caps installed at the exit of ion injector capillary 102 is shown at 1500. In this regard, negative scores indicate improvement in ion signal RSD. Further, different types of capillary caps are shown at 1502. All shaped exit capillary caps outperform round exit capillary caps by providing better ion signal RSD at similar ion funnel pressure. Among the shaped exit capillary caps, a slot exit capillary cap with width (W) = 0.4 mm, 0.5 mm, 0.6 mm, and 0.7mm, and cross exit capillary cap resulted in better ion signal RSD than a slot exit capillary cap with width (W) = 0.8 mm and 0.9 mm, and the star exit capillary cap.

[0068] Figure 16 illustrates liquid chromatography-mass spectrometry / mass spectrometry (LC / MS / MS) MRM chromatographic peak area versus RSD obtained for a mixture of pesticides, in accordance with an example of the present disclosure.

[0069] Referring to Figure 16, LC / MS / MS MRM chromatographic peak area versus RSD obtained for a mixture of pesticides at extremely short MRM dwell time = 0.5 ms is shown at 1600. The dwell time may represent the duration that an ion beam is sampled for a quantitative measurement. The chromatographic peak area RSDs may be determined based on 10 replicate injections of the pesticide mixture with individual pesticides having equal concentration. Pesticides in this mixture may cover a wide range of area responses (due to their varied ionization efficiencies) corresponding to different number of ions reaching a detector. Both short dwell time and low chromatographic peak area may result in larger RSD. Using a slot exit capillary cap may generate a narrower distribution of peak area RSD for pesticides in this pesticide mixture as compared to a round exit capillary cap. Improvement in peak area RSD for the slot exit capillary cap at the exit of ion injector 102 may thus indicate that an ion beam entering the ion funnel experiences less fluctuation and noise.

[0070] What has been described and illustrated herein is an example along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the subject matter, which is intended to be defined by the following claims -and their equivalents -in which all terms are meant in their broadest reasonable sense unless otherwise indicated.

Claims

What is claimed is:1 . An apparatus comprising: an ion injector including an ion injector entrance and an ion injector exit; and a capillary cap disposed at the ion injector exit, wherein the capillary cap includes a capillary cap exit opening that is shaped and sized to reduce gas turbulence after the ion injector exit and improve ion signal stability.

2. The apparatus according to claim 1 , wherein the capillary cap includes a concave area on an opposite side of an exit face of the capillary cap.

3. The apparatus according to claim 1 , wherein the capillary cap exit opening includes a rectangular slot shape.

4. The apparatus according to claim 3, wherein the rectangular slot shape includes curved portions.

5. The apparatus according to claim 1 , wherein the capillary cap exit opening includes a cross slot shape.

6. The apparatus according to claim 1 , wherein the capillary cap exit opening includes a star slot shape.

7. The apparatus according to claim 1 , wherein the capillary cap includes a muzzle brake configuration including a circular capillary cap exit opening and elongated slots along a side wall of the capillary cap.

8. An apparatus comprising: a capillary cap disposable at an ion injector exit of an ion injector that includes an ion injector entrance and the ion injector exit, wherein the capillary cap includes a capillary cap exit opening that is shaped and sized to reduce gas turbulence after the ion injector exit and improve ion signal stability.

9. The apparatus according to claim 8, wherein the capillary cap exit opening includes a rectangular slot shape.

10. The apparatus according to claim 9, wherein the rectangular slot shape includes curved portions.11 . The apparatus according to claim 8, wherein the capillary cap exit opening includes a cross slot shape.

12. The apparatus according to claim 8, wherein the capillary cap exit opening includes a star slot shape.

13. The apparatus according to claim 8, wherein the capillary cap includes a muzzle brake configuration including a circular capillary cap exit opening and elongated slots along a side wall of the capillary cap.

14. The apparatus according to claim 8, wherein the capillary cap includes a concave area on an opposite side of an exit face of the capillary cap.

15. A method comprising: attaching a capillary cap to an ion injector exit of an ion injector including an ion injector entrance and the ion injector exit, wherein the capillary cap includes a capillary cap exit opening that is shaped and sized to reduce gas turbulence after the ion injector exit and improve ion signal stability.

16. The method according to claim 15, wherein the capillary cap exit opening includes a rectangular slot shape.

17. The method according to claim 15, wherein the capillary cap exit opening includesa smaller width compared to a bore diameter of a bore of the ion injector.

18. The method according to claim 15, wherein the capillary cap exit opening is radially offset relative to a central longitudinal axis of a bore of the ion injector.

19. The method according to claim 15, wherein the capillary cap exit opening includes a cross slot shape.

20. The method according to claim 15, wherein the capillary cap includes a muzzle brake configuration including a circular capillary cap exit opening and elongated slots along a side wall of the capillary cap.

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