INERT NON-ADSORBING CRIMPABLE CAPILLARIES AND DEVICES FOR ADJUSTING GAS FLOW IN ISOTOPE RATIO ANALYSIS

Abstract

A gas transfer system for transferring gas into an analytical instrument for isotope ratio analysis comprises a capillary for delivering sample and/or reference gas from a gas source, a first connector for connecting the capillary to the gas source, a second connector for connecting the capillary to the analytical instrument, a crimping device, wherein the internal surface of the capillary comprises a coating material to prevent or minimize adsorption of water to the surface. Also provided is a device for regulating gas flow in a gas inlet system of an analytical instrument, comprising a body member having an internal gas flow channel, and a clamping member for attachment to the body member such that when the clamping member is tightened onto the body member, the internal gas flow channel is adjustably and reversibly crimped, to adjust gas flow therethrough.

Claims

1. A gas transfer system, for transferring gas from at least one gas source into a mass spectrometer for isotope ratio analysis that comprises scrambling-free measurement of clumped isotopes, comprising: at least one crimpable capillary, for delivering sample and/or reference gas from the at least one gas source into the mass spectrometer; at least one first connector for connecting the at least one crimpable capillary to the at least one gas source; at least one second connector, for connecting the at least one capillary to the mass spectrometer, at least one crimping device, adapted to receive the at least one crimpable capillary and adjust gas flow into the mass spectrometer by crimping the at least one capillary, wherein the internal surface of the crimpable capillary comprises a coating material to prevent or minimize adsorption of water to the surface and which is sufficiently free of other contaminants that could cause isotope scrambling of clumped isotopes.

2. The gas transfer system of claim 1, wherein the crimpable capillary is a stainless steel, metal or alloy capillary coated on its internal surface with said coating.

3. The gas transfer system of claim 1, wherein the capillary coating comprises at least one silicon-based coating.

4. The gas transfer system of claim 1, wherein the coating is deposited on the internal surface by chemical vapor deposition (CVD).

5. The gas transfer system of claim 1, wherein said at least one gas source is a gas source with adjustable volume.

6. The gas transfer system of claim 1, further comprising two crimpable capillaries, for delivering respectively sample gas and reference gas from respective two gas sources into the mass spectrometer.

7. The gas transfer system of claim 1, wherein said crimping device comprises: i. a first body member having at least one groove for seating at least one capillary; ii. a second body member removably attachable to said first body member, the second body member holding a crimping member that is disposed so that when the second body member is attached to the first body member, the crimping member is adjustably forced onto a capillary in the groove so as to crimp the capillary and thereby reducing gas flow therethrough.

8. A method of isotope ratio analysis of a gas from a sample that comprises clumped isotopes, comprising: transmitting the sample gas from at least one gas source through a first capillary into a mass spectrometer and performing a first isotopic measurement, providing at least one reference gas from another reservoir, transmitting the at least one reference gas through a second capillary into the mass spectrometer and performing a second isotopic measurement, wherein gas flow into the isotope analytical instrument is adjusted by crimping the capillary, or an extension thereof, for the first and second isotopic measurements to obtain substantially equal gas flow during measurements of reference gas and sample gas.

9. The method of claim 8, wherein the capillary is a crimpable stainless steel, metal or alloy capillary coated on its internal surface with a coating material to prevent or minimize adsorption of water to the surface.

10. The method of claim 8, wherein the capillary is a non-crimpable glass, silica or ceramic capillary.

11. The method of claim 8, wherein a gas flow rate into the analytical instrument is achieved by means of a device as set forth in claim 8.

12. The method of claim 8, wherein said at least one gas source is a gas source with an adjustable volume.

13. The method of claim 8, wherein said reference gas is selected from carbon monoxide, carbon dioxide, hydrogen, nitrogen, nitrogen oxides, and sulfur dioxide.

14. The method of claim 8, wherein said at least one gas source is selected from a microvolume tube, an adjustable gas bellows system, a syringe and a gas bottle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] 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.

[0051] FIG. 1 shows a schematic diagram illustrating a dual inlet IRMS.

[0052] FIG. 2 shows a gas inlet system suitable for an isotope ratio instrument.

[0053] FIG. 3A shows the side view of an upper part of a crimping device for crimping a capillary, as further described herein; FIG. 3B shows the end-on side view.

[0054] FIG. 4 shows the top view of a lower part of a crimping device for crimping a capillary, as further described herein.

[0055] FIG. 5A shows a cross-sectional view along the longitudinal axis of a device for regulating gas flow comprising a body member with an internal gas flow channel, and a crimping member; FIG. 5B shows the top view of the device.

[0056] FIG. 6 shows a cross-sectional three-dimensional view of the device in FIG. 5.

[0057] FIG.7 shows drawings of the device, top view of the body member (left), and bottom view of crimping member.

[0058] FIG. 8 shows a view of the assembled device.

DETAILED DESCRIPTION OF THE INVENTION

[0059] 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.

[0060] 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.

[0061] It should be appreciated that the invention is applicable for elemental and isotope analysis of liquid or gaseous samples in general by mass spectrometry techniques. In general, therefore, the sample that is being analysed in the system will be variable.

[0062] The present invention provides a gas inlet system for delivery of gas into a mass spectrometer for isotope ratio measurements. In particular, the invention provides a solution to the practical problem of gas flow regulation into isotope ratio mass spectrometers, and at the same time avoid or reduce introduction of artefacts that can influence the determination of isotope ratio, for example due to isotope scrambling.

[0063] Thus, the invention finds particular use during measurement of clumped isotopes, for example rare isotopologues within a single molecular species, such as .sup.13C.sup.18O.sup.16.

[0064] In dual inlet isotope ratio mass spectrometry (dual inlet IRMS), the gas flow into the mass spectrometer is alternated between a sample gas and a reference (or standard) gas, so that a comparison of measurements for the two gases can be made. The reference gas can be analysed either before or following the sample gas, or both before and following the sample gas (so-called bracketed measurements).

[0065] In FIG. 1 there is shown a schematic diagram illustrating a dual inlet IRMS. Sample gas and reference gas can be provided by gas reservoirs or bellows 12,13. Gas flows through capillaries 2,2′ from the sample bellows and into the ion source 11 of the mass spectrometer.

[0066] Alternatively, or additionally, sample gas can be provided by means of a sample preparation system 9. In such a system, sample gas is generated or prepared in situ for subsequent analysis in the mass spectrometer. The sample gas is transferred from the sample preparation system 9 to into the ion source 11 via capillary 2″. An exemplary sample preparation system is provided by the Kiel IV Carbonate Device from Thermo Fisher Scientific™. In this device, calcium carbonate is digested using phosphoric acid, resulting in the release of carbon dioxide (CO.sub.2) gas. Water and other interfering species are removed using cryotraps before transferring the carbon dioxide gas into the mass spectrometer via capillary 2″. As such preparation devices are commonly used together with small sample amounts, the resulting sample gas volume may be so small an adjustment of the gas flow by adjusting a bellows is not an option. Therefore, the gas flow through the respective capillary has to be adjusted by crimping.

[0067] Referring to FIG. 2, there is shown a gas inlet system for use with a mass spectrometer for isotope ratio measurement and which may, in some embodiments, form a part of a dual inlet system, for example of the type shown in FIG. 1. The gas inlet system is at one end connected to a gas source 14, which can for example be provided by gas tanks or gas bellows as sources of sample or reference gas, or other source of sample gas, such as a Kiel IV sample preparation system. At the other end, the gas inlet system is connected to the inlet 15 of a mass spectrometer for isotope ratio measurements, for example the inlet of a mass spectrometer ion source. Sample and/or reference gas flows through an internally coated crimpable capillary 2, which has an internal surface that is coated with a chemically inert or deactivated coating to prevent or reduce isotope scrambling due to water or other species present on the capillary wall that could introduce such scrambling.

[0068] Preferred inert or deactivated surface coatings include: silicon or silicon based coatings (specific examples include SilcoNert ®1000 or Silcosteel coated capillaries and SilcoNert ® 2000 or SulfiNert® or SilTek® coated capillaries); coatings that are deposited by chemical vapor deposition (CVD), including such coatings as the SilcoNert ® or SulfiNert® coatings mentioned and coatings applied by thermal decomposition and fuctionalization of silanes (described in U.S. Pat. No. 6,444,326, incorporated herein). Preferably, the inert or deactivated surface coating does not allow water to adsorb on its surface, or other species that induce scrambling. Capillaries that are made of metal, e.g., steel or nickel, and have an inert or deactivated inner coating are preferred. Such capillaries are crimpable but inert on their inner surface.

[0069] Gas flow into the mass spectrometer can be adjusted using a crimping device 20, which is positioned on the capillary near the spectrometer end of the capillary. The crimping device 20 has a first body member in the form of lower part 3 and a second body member in the form of upper part 4, and which can be used to crimp the capillary 2 to adjust gas flow through the capillary. Crimping of the capillary is adjusted by means of screws 10 that adjust the force applied by the crimping device 20 onto the capillary. The capillary 2 sits between the upper and lower parts, and is held in place by metal plate 5, which has screws for holding the capillary in place on the crimping device 20.

[0070] A metal piece 6 can be soldered around the capillary and serves as an electrical contact. The capillary may be heated after installation by an electrical current through the metal piece, capillary, and the (grounded) mass spectrometer. This ensures complete removal of water traces residing in the capillary despite the coating. The capillary is furthermore enclosed by a silicone tubing 7, which serves to provide protection to the capillary 2.

[0071] A metal cylinder 1, is soldered to the capillary 2 and used to connect the capillary at one end to the mass spectrometer source and at the other end to the sample source (e.g., dual inlet and/or Kiel IV device, not shown), using connector 8, for example Swagelok™ fitting.

[0072] Application of force to the capillary 2 at a localised portion thereof by the crimping device 20 adjusts the gas flow through the capillary by partial closing of the capillary. The torque applied by the crimping device determines the degree to which the capillary is closed at the crimped portion, thereby restricting gas flow through the capillary.

[0073] In FIG. 3, a side view of the upper part 4 (second body member) of the crimping device 20 is shown in (a). The upper part 4 comprises a metal (e.g. steel) block 21, on which a crimping member in the form of a cylinder 22 is attached, and which provides the force that compresses the capillary. The cylinder 22 in some embodiments may be formed integrally as part of the block 21 in the form of a cylindrical surface part thereof. The cylinder 22 is long enough to provide uniform force across the capillary when force is applied to the capillary. The cylinder 22 can typically be provided with a length that is about ⅓ to about ½ of the width of the metal block.

[0074] The upper part 4 furthermore has two holes (indicated by dashed lines in FIG. 3) for introducing therethrough the clamping screws 10 (not shown in FIG. 2), flanking the cylinder 22.

[0075] In FIG. 3(b), an end-on side view is shown, showing how the cylinder 22 is provided in a shallow depression or groove in the metal block 21, providing structural support to the cylinder as force is applied to compress the capillary.

[0076] A top view of the lower part 3 of the crimping device is shown in FIG. 4. The lower part 3 has two larger threaded holes 23, for receiving clamping screws 10. Also shown are smaller threaded holes 24, that receive screws (not shown) securing the plate 5 that holds the capillary 2 in place. Along the lower part 3, there is also a groove 25, for holding the capillary 2 in place.

[0077] The upper part 4 clamps onto the lower part 3, so that the cylinder 22 extends perpendicular to the groove 25, within which capillary 2 sits. As force is applied to the cylinder 22 by means of the clamping screws 10, the capillary is crimped by the cylinder 22, thereby restricting gas flow through the capillary. Thereby, gas flow adjustment is possible, using the chemically inert capillary 2.

[0078] Turning to FIG. 5, there is shown in (a) a cross-sectional view of a device 30 for regulating gas flow. The device consists of a main body member 40 having a gas flow channel there through and a clamping member in the form of clamping body 39. A lower clamping piece (not shown in this view), containing threaded holes for receiving clamping screws, is attached to the main body 40, so that the clamping member can be attached and tightened on the main body. A capillary 31 is attached to the body 40 of crimping device 30 by means of a silver ferrule 33, which fits over the capillary and is received inside an open end of the gas flow channel, and a screw 32, which is screwed into an internally threaded end portion of the open end of the gas flow channel, so as to tighten the connection of the capillary 31 into the body 40. The use of the ferrules enables vacuum tight connection of virtually any capillary material to the spectrometer and the gas source. Within the device, there is a gas flow channel, having a narrow section 34 and a wider diameter main section 35. Gas flows through the attached capillary 31, into the gas flow channel of the device, exiting through its main section 35 after having passed through the narrow section 34.

[0079] The internal diameter of the gas flow channel in the wider section is preferably <2 mm and more preferably <1 mm (e.g. 500 μm to 1 mm). The gas flow channel can be manufactured e.g. by erosion of the metal of the body using a small, forward moving electrode. The narrow section 34 preferably has a diameter in the range of 200-500 μm such as about 300 μm, about 350 μm or about 400 μm.

[0080] A groove 41 is provided in the top of the main body 40. As a result of the groove 41, a wall 42 defining an upper portion of the narrow section 34 is formed. The thickness of the wall is relatively small, such as in the range of about 0.5 to 2 mm or the range 0.5 to 1.5 mm, or the range 0.75 mm to 1.25 mm, such as about 0.5 or about 1 mm and as a result the wall 42 is deformable by the application of external force to the wall by the clamping body 39. As a result, the narrow channel 34 is crimpable by the application of external force to the wall 42.

[0081] Force to the wall 42 is provided by the upper clamping body 39, which has a body provided as a steel block 36 which has two holes extending through, for insertion of clamping screws 37. In this cross-sectional view, only the screw head of screw 37 is shown. The clamping screws 37 screw into a threaded hole on the lower clamping body (not seen in this view). Extending from the lower surface of body 36 there is a cylinder 38, which rests on top of wall 42. Through application of force, provided by the tightening of clamping screws 37 perpendicular and downwardly onto channel 34, the channel 34 is narrowed and as a result, gas flow through the channel can be reduced.

[0082] Turning to FIG. 5 (b), there is shown a top view of the device 30. In this view, it can be seen how clamping screws 37 are arranged on the upper clamping body 39, the screws extending through the upper clamping body and screwing into a threaded hole in the lower clamping body (not seen in this view), flanking the main body 40.

[0083] A cross-sectional view of the FIG. 5 device is shown in FIG. 6. The crimping device 30 has upper 39 and lower 45 clamping bodies, the latter being attached onto the main body 40. The upper and lower bodies 39,45 are arranged such that when force is applied by tightening clamping screws 37 (not shown in FIG. 5) that extend through holes 46 on the upper clamping body 39 and screw into the lower clamping body 45, the channel 34 is narrowed by the torque applied to the wall 42 by a crimping portion in the form of a cylinder 38. Cylinder 38 is held in a groove or recess in the upper clamping body 39.

[0084] The device 30 is further illustrated in FIG. 7. The lower clamping body 45 is attached to the main body 40. If manufactured separately, the lower clamping body can be soldered to the main body, so as to generate a single main body 40 onto which the upper clamping body 39 can be fastened.

[0085] Alternatively, the lower clamping body can be designed and manufactured to be separate from the main body and retain its function when in use, for example if the main body 40 rests on the lower clamping body 45, so as to provide structural support when the upper clamping body 39 is connected to the lower clamping body and force is applied to the main body sitting between the two clamping bodies 39,45.

[0086] The groove 41 in the main body 40 can be seen as a depression or trough into the otherwise generally cylindrical main body. The upper clamping body 39 is attached to the main body, with clamping screws 37 used to secure and fasten the upper clamping body 39 to the lower clamping body 45. Tightening the clamping screws results in the application of force perpendicular to the direction of the narrow channel within the main body, which in turn results in the cylinder 38 being forced onto the wall 42, which due to its relatively small thickness has elasticity that allows it to be forced into the channel 34, thereby crimping the channel 34 to restrict gas flow through the channel. Thus, the wall around the flow channel is so thin that it can be compressed to narrow the channel.

[0087] An assembled device is shown in FIG. 8, with the upper clamping body 39 sitting on the main body, secured by the clamping screws 37. Further, a nut (Swagelok nut) 47, used to secure a gastight connection to an analytical device (e.g., mass spectrometer) is shown on the assembly.

[0088] Before use of the capillaries for measurement, torque can be adjusted by tightening the clamping screws 37. By doing so, the crimpings of all capillaries present on an instrument are adjusted in such a way the resulting instrument signal (e.g. detector voltage) is approximately the same for a given gas pressure in the gas reservoir. Alternatively, the crimpings may be adjusted so that for the same or at a different gas pressure, the decay in the instrument signal over time is the same with all capillaries. The latter is essential if the gas bleeds from a finite reservoir into the ion source (e.g. from a microvolume). After adjustment, the crimpings usually will not be changed again and the capillaries can be used for measurement. Following the measurement of sample gas, which may require as long as 10 minutes, or more, of continued measurements, a reference gas can be measured.

[0089] One capillary and crimping device as illustrated in the Figures could be used for the sample and reference gas measurements. Alternatively, as in a dual inlet isotope ratio mass spectrometer, separate capillaries and associated crimping devices can be provided for each of the sample gas and reference gas respectively. Further alternatively, e.g. in another dual inlet isotope ratio mass spectrometer, separate capillaries can be provided for each of the sample gas and reference gas respectively but only one capillary, typically the reference gas capillary, is provided with a crimping device, thereby to allow the flow of reference gas through the capillary to match the measured sample gas flow.

[0090] In the embodiments shown in FIGS. 5 to 8, a crimp is not placed onto the capillary itself, but onto a small gas flow channel inside the body of a crimping device. Thus, such embodiments of crimping device can be regarded as a capillary crimping adapter, which enable the use of non-crimpable capillaries such as glass, silica, ceramic capillaries. Certain such non-crimpable capillaries, which preferably have chemically inert internal surfaces, can be advantageous to use, e.g. so as to avoid or reduce isotope scrambling effects. The invention enables such capillaries to be used whilst still enabling control of the gas flow through the capillary by a crimping mechanism.

[0091] The setup allows virtually all kinds of capillaries to be used, e.g. stainless steel capillaries with an internal inert coating, such as a SilcoNert® or a Sulfinert® coating, or deactivated fused silica capillaries. Variants accepting capillaries of different diameters can be produced.

[0092] In addition, the internal walls of the gas flow channel, constituting a relatively small section of the gas flow path inside the crimping device, may be deactivated by an inert coating.

[0093] In summary, the present invention provides numerous advantages, including: [0094] a. improved accuracy of isotope ratio measurements, especially of clumped isotopes, e.g., due to allowing scrambling-free measurement of clumped isotope abundance; [0095] b. use of deactivated capillaries for measurement of isotope ratios that can be affected by traces of water (e.g., .sup.18O/.sup.16O in CO.sub.2); [0096] c. use of a capillary crimping adapter to allow regulation of gas flows with capillaries that cannot be crimped due to material constrains (e.g., fused silica or capillaries with a larger or smaller outer diameter). [0097] d. sealing capillaries using ferrules (e.g. silver ferrules), which enables the application of capillaries which cannot be soldered to provide gas tight connections (e.g., deactivated fused silica).

[0098] As used herein, including in the clauses and 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.

[0099] 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.

[0100] 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).

[0101] 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”.

[0102] 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. 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.

[0103] 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.

[0104] 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.