WO2023215633A1

WO2023215633A1 - Extending the life of a system used for compound specific isotope analysis

Info

Publication number: WO2023215633A1
Application number: PCT/US2023/021322
Authority: WO
Inventors: Yongsong Huang; Rafael Tarozo; Ewerton SANTOS; Marcelo de Rosa ALEXANDRE
Original assignee: Brown University
Priority date: 2022-05-06
Filing date: 2023-05-08
Publication date: 2023-11-09

Abstract

Maintaining a constant flow rate of oxygen into a reactor of a gas chromatography and/or mass spectrometer system extends the lifetime of the reactor and the oxidant therein. A system can include a reactor including an oxidant and a gas chromatography oven including at least one column, which can be connected to the reactor. A sample and oxygen can be injected through the at least one column to the reactor. The system can also include a temperature sensor within the gas chromatography oven and an automatic pressure control system including a valve and a controller. The valve can connect a source of the oxygen to the at least one column and regulate the flow of oxygen therethrough. The controller can control the pressure through the valve based on at least the temperature in the gas chromatography oven to maintain the constant flow rate of the oxygen as the temperature changes.

Description

EXTENDING THE LIFE OF A SYSTEM USED FOR COMPOUND SPECIFIC ISOTOPE ANALYSIS

Cross-Reference to Related Application

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63/338,935, filed 6 May 2022, entitled “EXTENDING THE LIFE OF A SYSTEM USED FOR COMPOUND SPECIFIC CARBON ISOTOPIC ANALYSIS”. The entirety of this application is incorporated by reference for all purposes.

Technical Field

[0002] The present disclosure relates to systems for compound specific isotope analysis (CSIA), and, more specifically, to systems and methods for extending the life of a system used for CSIA by incorporating an automatic pressure control (APC) system to maintain the oxidative capacity of the system over prolonged use.

Background

[0003] Compound specific isotopic analysis (CSIA) is a common and powerful analytical technique used in areas such as earth science, environmental science, forensic science, and the like. CSIA can be performed with commercial gas chromatography and/or mass spectrometer systems. However, oxidation reactors of the commercial gas chromatography and/or mass spectrometer systems are costly and tend to have very short lifetimes (e.g., due to the reactor breaking, the oxidizable material fully oxidizing too quickly with repeated re-oxidation over short durations, or the like) and suffer from the need for frequent reoxidation and replacement. Such frequent needs for reoxidation and replacement also causes delays in analyses that can be large and can increase the potential for analytical errors.

Summary

[0004] It has been discovered that the life of an oxidation reactor and the oxidant therein used for compound specific isotopic analysis (CSIA) can be extended by incorporating an automatic pressure control (APC) system. The system and methods described herein provide for a comparatively long-lasting, reliable, and cost-efficient system for CSIA. The frequency of the need to replace at least the reactor of the system or the oxidizable material used by the reactor can be significantly reduced compared to the current cumbersome commercial systems and may increase productivity 10-fold or more while greatly improving data quality.

[0005] In one aspect, the present disclosure includes a system that can be used to extend the life of a reactor of a system used for CSIA and improving the precision and accuracy of the analysis. A reactor can be configured to convert an organic compound to carbon dioxide, which can be fed into a mass spectrometer, wherein an oxidizable material positioned within the reactor acts as an oxidant in a presence of oxygen. A gas chromatography oven can include at least one column connected to the reactor, wherein the organic compound in a carrier gas and oxygen in the carrier gas can be injected through the at least one column to the reactor. A temperature sensor within the gas chromatography oven can detect a temperature within the gas chromatography oven. An automatic pressure control (APC) system can include an ARC valve connecting a source of the oxygen in the carrier gas to the at least one column and regulating a flow rate of the oxygen in the carrier gas into the at least one column and an APC controller coupled to the temperature sensor and the APC valve. The APC controller can include a processor and can be configured to: receive the temperature of the gas chromatography oven as detected by the temperature sensor; and regulate the pressure of the oxygen in the carrier gas into the at least one column and then over the oxidizable material within the reactor by adjusting the pressure through the APC valve based on the temperature in the gas chromatography oven, an inner diameter of the at least one column, and a length of the at least one column connecting the valve to the reactor. The APC system can maintain a constant flow rate of the oxygen in the carrier gas through the reactor as the temperature in the gas chromatography oven changes and thereby extend the usable life of the reactor and the oxidizable material and improve the precision and accuracy of analytical results.

[0006] In another aspect, the present disclosure includes a method for extending the life of a reactor of a system used for CSIA and improving the precision and accuracy of the analysis. The method includes receiving, by an automatic pressure controller comprising a processor, a temperature of a gas chromatography oven of a system configured to convert an organic compound to carbon dioxide from a temperature sensor in the gas chromatography oven. The system can further include a reactor having an oxidizable material positioned within the reactor that acts as an oxidant in a presence of oxygen and at least one column positioned in the gas chromatography oven and connected to the reactor. The organic compound in a carrier gas and oxygen in the carrier gas can be injected through the at least one column to the reactor. The method also includes maintaining, by the automatic pressure controller, a constant flow rate of the oxygen in the carrier gas into the at least one column and then over the oxidizable material in the reactor as the temperature in the gas chromatography oven varies by altering an amount of pressure in an automatic pressure control (APC) valve to change the pressure of the oxygen in the carrier gas in response to a change in the temperature in the gas chromatography oven. The APC valve can be in communication with the automatic pressure controller and can connect a source of the oxygen in the carrier gas to the at least one column. By maintaining the flow rate of the oxygen in the carrier gas constant, the usable life of the reactor and the oxidizable material can be significantly extended and the precision and accuracy of analytical results can be improved.

Brief Description of the Drawings

[0007] The foregoing and other features of the present disclosure will become apparent to those skilled in the art to which the present disclosure relates upon reading the following description with reference to the accompanying drawings, in which:

[0008] FIG. 1 shows a portion of a system for compound specific isotope analysis (CSIA) that extends the useful life of a reactor of the system;

[0009] FIG. 2 shows a schematic representation of an example of the system of FIG. 1 ;

[0010] FIG. 3 shows an example of a furnace interface including the reactor of the system of FIG. 2;

[0011] FIG. 4 shows a process flow diagram of a method for extending the life of a reactor of a system used for CSIA;

[0012] FIG. 5 shows a process flow diagram of a method for activating an oxidizable material used in the reactor; [0013] FIG. 6 shows a process flow diagram of a method for maintaining a constant flow rate of at least one gas into the reactor;

[0014] FIG. 7 shows a graphical representation of detrending analytical results using a prior art commercial system and indication of oxidation events and changes to a new reactor; and

[0015] FIG. 8-12 show graphical representations of results obtained using the improved system of FIGS. 1-3 without the need for frequent re-oxidations.

Detailed Description

I. Definitions

[0016] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure pertains.

[0017] As used herein, the singular forms “a,” “an,” and “the” can also include the plural forms, unless the context clearly indicates otherwise.

[0018] As used herein, the terms “comprises” and/or “comprising,” can specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups.

[0019] As used herein, the term “and/or” can include any and all combinations of one or more of the associated listed items.

[0020] As used herein, the terms “first,” “second,” etc. should not limit the elements being described by these terms. These terms are only used to distinguish one element from another. Thus, a “first” element discussed below could also be termed a “second” element without departing from the teachings of the present disclosure. The sequence of operations (or acts/steps) is not limited to the order presented in the claims or figures unless specifically indicated otherwise.

[0021] As used herein, the term “compound specific carbon isotope analysis”, and equivalently referred to as ^compound specific isotope analysis” (also referred to as CSIA), refers to an analytical method that measures the ratios of naturally occurring carbon stable isotopes in environmental organic compounds, as well as artificially carbon-13 labelled organic compounds. Although CSIA is often used to measure the ratios of carbon isotopes, it should be understood that CSIA may refer to any type of organic compound or contaminant to the organic compound.

[0022] As used herein, the term “reactor” refers to a container or apparatus in which substances are made to react chemically. For example, the reactor can be a catalytic reactor that is a part of a combustion system of a gas chromatograph and/or a mass spectrometer and can convert carbon atoms of organic compounds in gas chromatography effluents into carbon dioxide, or the like.

[0023] As used herein, the term “oxidizable material” or refers to any material that can undergo a chemical reaction in the presence of oxygen. Non-limiting examples of oxidizable materials are materials including nickel, platinum, and copper that can be oxidized to an become an oxidant such as nickel oxide, platinum oxide, and copper oxide, respectively.

[0024] As used herein, the term “activated” when used to describe a material refers to a material that has been previously exposed to pure oxygen and acts as an oxidant. For example, a nickel material can be oxidized into nickel oxide, and the nickel oxide can provide instant oxidation of organic compounds into carbon dioxide, or another gas including carbon and oxygen.

[0025] As used herein, the term “gas chromatography oven” (also referred to as “GC oven”) refers to a device that includes at least one column and provides a suitable thermal environment for separating and analyzing compounds that can be vaporized without decomposition.

[0026] As used herein, the term “column” refers to a gas chromatography column, which is often a narrow tube though which a vaporized sample can pass when carried along by a flow of a carrier gas. Components of a sample can pass through a column at different rates, depending on the components chemical and physical properties and the resulting interactions with the column lining or filling. A column can be, for example, a packed column or a capillary column. A packed column can be, for example, a stainless steel or glass tube filled with particulate packing material (e.g., an adsorbent material, or a support material coated or impregnated with a solid phase). A capillary column can be, for example, a thin, fused silica glass tube or metal tube lined with a liquid phase or absorbent material or having a chemical bonding layer. [0027] As used herein, the term “carrier gas” refers to an inert gas used to carry samples. Non-limiting examples of carrier gases include helium, nitrogen, hydrogen, and argon.

II. Overview

[0028] Compound specific isotopic analysis (CSIA) is a common and powerful analytical technique used in earth science, environmental science, forensic science, pharmaceutical development, and the like. Commercial systems for compound specific isotopic analysis, such as the Delta V or Delta V advantage system available from Thermo Fisher, are cumbersome and expensive. Additionally, reactors for these systems traditionally have a short usable lifetime and require frequent reoxidation of the oxidizable material used therein or full replacement. Such frequent re-oxidation and replacement of the reactor and/or oxidizable material is costly, can cause delays in analysis, and can significantly increase analytical errors (which may be due to instrument instability or drifts resulting from gas flow manipulations).

[0029] Traditional commercial systems for CSIA use a pressure gauge to apply a constant pressure of oxygen (often 1 % of oxygen in a carrier gas such as helium) through a gas chromatography oven (GC oven) to an oxidant in the reactor.

However, flow rate fluctuates depending on temperature. Modern GC separation generally employs oven temperature program for separation of organic compounds with different molecular weights and boiling points. The oven temperature program typically increases from about 40 -C to 300 -C at a rate of 3 to 8 ^QC per minute over the course of a sample analysis run. Based on the ideal gas law, PV=nRT, and temperature increase from 40 ^eC (313 K) to 300 ^eC (573 K) would lead to a gas volume expansion of 1 .83 times at the constant pressure. Therefore, when a constant pressure is used, the mass of oxygen delivered to the reactor will decrease as oven temperature increases. This is detrimental to both reactor and to analytical accuracy, as higher boiling point compounds elute chromatographically at higher oven temperatures and they contain more carbon atoms and require more oxygen for quantitative oxidation. The diminished oxygen flow to the reactor at higher oven temperatures can lead to incomplete oxidation. The fluctuating gas flow through the reactor over the course of a sample analysis can also lead to increased analytical errors. Commercial systems also typically use a copper oxidant because copper fully oxidizes to copper oxide. Copper oxide is brittle and easily degrades over the course of sample analysis and requires replacement during use (e.g., approximately every 3 days or 25 samples). As the copper, or other oxidizable material, is replaced and/or re-oxidized error can creep into the system decreasing the accuracy and/or precision of results. Other less brittle or degradable materials are not used effectively or are used only in conjunction with copper for various reasons, including the inability to maintain oxidative capacity in a reactor when not receiving a constant flow rate of oxygen. There is a significant need in the scientific community for prolonging usable reactor lifetime and reducing maintenance while simultaneously improving analytical precision for longer continuous analysis of samples.

[0030] Therefore, presented herein is a system and method that can extend the usable lifetime of a reactor and the oxidizable material needed therein, saving time and money and increasing the accuracy and/or precision of results. The system and method can provide and maintain a constant flow rate of oxygen to a reactor of a gas chromatography and/or mass spectrometry system using an APC system regardless of the fluctuations in temperature within the GC oven. The system can also include nickel as the oxidizable material, due to the improved control of the flow rate of the oxygen, which lasts longer than the traditional copper. The lifetime can be increased by days, months, or even years. For example, instead of replacing copper every approximately 25 samples in a traditional system, the improved system can use nickel and can analyze 3000 or more samples without the need for any change or maintenance. Accordingly, use of the system and method described herein can increase productivity (e.g., at least 10-fold, at least 100-fold, or the like) and can also increase data quality because less error can slip in due to interruptions in analysis.

III. System

[0031] Provided herein is a system that can extend the useful life of a reactor, and the oxidizable material used in the reactor, of a system for gas chromatography and/or mass spectrometry for compound specific isotope analysis (CSIA). The system can also improve the accuracy and/or precision of analytical results of the CSIA. The system can be a part of a gas chromatograph and/or a mass spectrometer.

[0032] FIG. 1 provides a box diagram schematic of the system 10 for extending the useful life of the reactor and the oxidizable material used therein. The system 10 can include a gas chromatography oven (GC oven) 12 for heating samples, as is known in the art. The GC oven 12 can include one or more columns (column(s) 16) connected to a reactor 18 and a temperature sensor 14. The column(s) 16 can be any type of appropriate column for gas chromatography and/or mass spectrometrybased analysis. The temperature sensor 14 can be positioned anywhere within the GC oven 12 to detect the temperature in the GC oven at any given time. While not shown, it should be understood that additional components such as, but not limited to, appropriate tubing and connectors, vents, heating elements, analytic elements, user interface elements, and the like can also be included in the GC oven 12. The system 10 can also include a reactor 18 that can be at least partially in fluid communication with at least one of the column(s) 16. The reactor 18 can be separate from the GC oven, partially attached to or in the GC oven (as shown), or fully attached to or in the GC oven. The reactor 18 can be configured to convert an organic compound (e.g., a gaseous organic compound that has eluted through the column(s) 16) to carbon dioxide or another oxygen containing gas. The carbon dioxide, or other gas, from the reactor can then be sent to a mass spectrometer and/or a detector for further analysis and/or processing. An oxidizable material 20 can be positioned within the reactor 18. The oxidizable material 20 can act as an oxidant in a presence of oxygen. It should be understood that oxidant can be used interchangeably with oxidizable material 20 when oxygen is present in the reactor and/or the oxidizable material is understood to have been activated. The oxidizable material 20 can be, for example, a nickel material.

[0033] The system 12 can include one or more valves (valve(s) 24) that can inject one or more gases into the column(s) 16 of the GC oven 12 and to the reactor 18. One or more of the valve(s) 24 can be at least partially within the GC oven 12 as shown, such that an inlet of each valve is outside the GC oven and an outlet of each valve is within the GC oven and connected to at least a tube and/or column (e.g., column(s) 16)) depending on the purpose of the valve. It should be understood, however, that one or more of the valve(s) 24 may be positioned entirely within the GC oven 12 or entirely outside the GC oven depending on structure of the base GC oven. The valve(s) 24 can connect an organic compound source 28 and a gas source 30 to the column(s) 16. The organic compound source 28 can be any container (e.g., gas tank) that can hold and supply an organic compound sample in a carrier gas into the column(s) 16 and to the reactor 18. The organic compound source 28 can in some examples include two components - one for the carrier gas and one of the organic compound sample. The gas source 30 can be any container (e.g., a gas tank) that can hold and supply oxygen in a carrier gas into the column(s) 16 and to the reactor 18. The gas source 20 can in some examples include two components - one for the oxygen and one for the carrier gas. The carrier gas may be stored in and supplied to both the organic compound source 28 and the gas source 30 from an additional source not shown.

[0034] The system 12 can also include the automatic pressure control (APC) system 22 integrated with or coupled to the GC oven 12. Simply, the APC system 22 can receive the temperature in the GC oven 12 and then automatically adjust the head pressure electronically. The APC system 12 can include at least one of the valve(s) 24 and a controller (APC controller 26). The APC valve (one of valve(s) 24) can connect a source of the oxygen in the carrier gas (the gas source 30) to the column(s) 16 and can regulate a flow rate of the oxygen in the carrier gas into the column(s) 16 and to the reactor 18. The APC valve can be, for example, a head pressure control valve. The APC controller 26 can be coupled (for wired and/or wireless communication) to the temperature sensor 14 and the APC valve (one of valve(s) 24). The APC controller 26 can include a processor and a non-transitory memory (not shown), additionally and/or alternatively, the APC controller can include one or more analog components for controlling the APC valve (one of valve(s) 24). The APC controller 26 can also include a user interface (not shown) or other means for storing the instructions and data in the non-transitory memory. The non-transitory memory can store at least executable instructions and data related to the length(s) and diameter(s) of the column(s) 16 in the GC oven 12, data comparing the effect of a given temperature on the flow rate of oxygen in a carrier gas in the column(s), or the like. For, example, for any given length and inner diameter of the column(s) 116, the pressure needs to be adjusted to certain level so that the outflow rate does not change.

[0035] The APC controller 26 can (via the processor) execute instructions to receive the temperature of the GC oven 12 as detected by the temperature sensor 14 and regulate the pressure of the oxygen in the carrier gas injected into the column(s) 16 and then over the oxidizable material 20 within the reactor 18 by adjusting the pressure through the APC valve (one of valve(s) 24) based on at least the temperature in the GC oven. The APC controller 26 can regulate the pressure through the APC valve (one of valve(s) 24) based on the temperature in the GC oven 12, an inner diameter of the column(s) 16, and a length of the column(s) connecting the APC valve to the reactor 18. Thus, the APC system 22 can maintain a constant flow rate of the oxygen in the carrier gas through the reactor 18 (and over the oxidizable material 20) as the temperature in the GC oven 12 changes.

[0036] It should be noted that replacing a copper oxidizable material 20 with nickel can extend the useful life of the reactor 18 because nickel oxide (NiO) formed from the oxidation of nickel does not spontaneously degrade. As opposed to the inside out oxidation of copper oxide, nickel oxide is only formed on the surface of a nickel oxidizable material 20. While nickel oxide does have a lower loading of oxygen than copper oxide, the mechanical strength of nickel oxide is much higher than copper oxide. It is known that nickel oxide can lead to the formation of nickel- bound carbon phases, which can cause inaccurate isotopic results if a constant flow rate of oxygen over the nickel oxide is not maintained. Accordingly, the automatic pressure control (APC) system 22 ensures that oxygen flows over the nickel oxide (the oxidizable material 20/oxidant) at a constant flow rate, even with the varying temperature GC oven 12. With the constant flow of oxygen (e.g., 1 % oxygen in 99 % carrier gas, like helium, because 100 % oxygen gas is harmful to the system and may shorten the filament life), the nickel oxide (the oxidizable material 20/oxidant) is superior to copper. It is also noted that it is not necessary to use pure oxygen in the system (as little as 1 % is sufficient) to replenish the small amount of oxygen consumed by use of the system (in the form of nickel oxide). When the nickel oxide is consumed, the nickel oxide breaks apart into oxygen and nickel metal, but in the presence of a constant flow of oxygen (e.g., as little as 1 %), the nickel metal is instantly re-oxidized to nickel oxide, maintaining the oxidative capacity of the oxidizable material 20. Although nickel oxide has been used herein, it is possible that other oxides can be replenished in the same way.

[0037] FIG. 2, shows an example illustration of a system 100, which is a specific example of system 10 of FIG. 1 . It should be understood that this is merely one example for descriptive purposes. In system 100 the GC oven 112 includes two columns: a deactivated column 116a and an analytic column 116b, and two valves: APC valve 124a and a split/splitless injector valve 124b. The components of the GC oven 112 such as the columns and the valves can be connected by tubes 136, arrows show the direction of flow through the system 100 and dashed-line arrows show communication (wired and/or wireless) between APC system components. As noted, the APC system can receive the temperature in the GC oven 12 and then automatically adjust the head pressure electronically. Before operation for analyzing samples, the oxidizable material 120 in the lumen 138 of the reactor 118 can be activated. The oxidizable material 120 can be a nickel material. The nickel material can be activated by being oxidized with pure oxygen to be an activated nickel material at a time for a temperature (for example, for 30 minutes at 1100°C using countercurrent flows through a deactivated capillary tube connected to the top of the reactor). For example, The nickel material can be activated in pure oxygen to ensure sufficient surficial nickel oxide formation on the surface of the nickel material to sustain running samples in the presence of a given percentage (e.g., 1%, 2%, 5%, or the like) of oxygen in the presence of the carrier gas (e.g., helium, nitrogen, or the like). Optionally, another oxidizable material 120 can also be positioned in the reactor 118 with the activated nickel material. The other oxidizable material can include, for example, copper and/or platinum; and the ratio of materials can be two nickel to one other material such as the platinum.

[0038] Samples containing an organic compound in a carrier gas can be injected into the analytic column 116b from the organic compound source 128 via the split/splitless injector valve 124b and then towards the reactor 1 18. For example, the samples can be injected using a pulsed splitless mode at 320 °C to a 30 m x 0.32 mm x 0.25 pm analytic column 116b. The carrier gas used in system 100 can be helium. The flow rate of the sample organic compound in the helium carrier gas can be, for example, 1 mL/min. Oxygen in the carrier gas (e.g., helium) can be injected into the deactivated column 116a from the gas source 130 via the APC valve 124a and then towards the reactor 1 18. The APC valve 124(a) can be used in Split mode to provide oxygen in the carrier gas at a constant flow rate. The constant flow rate can be, for example, 0.1 mL/min column flow. The oxygen in the carrier gas can be 1% oxygen in helium. The deactivated column 116a can be (10 m x 0.32 mm). The output of the analytical column 116b and the output of the deactivated column 116a can be connected by a union connector 132 such that the sample organic compound in the carrier gas that has passed through (and been separated by) the analytical column can mix with the oxygen in the carrier gas. The union connector 132 can output to a backflush valve 134 (which can vent one or more portions of the combined gaseous mixture as the rest of the gaseous mixture (including the oxygen in the carrier gas and at least a portion of the organic compound in carrier gas) can travel into the reactor 118. The output of the reactor 118 (which can be one or more oxide gasses for isotopic composition measurements (e.g., CO2, NOx, or SO2)) can then be sent to a mass spectrometer and/or a detector.

[0039] The APC controller 126 can be in communication with the temperature sensor 114 positioned within the GC oven 112 and the APC valve 124. The temperature sensor 114 can sense the temperature in the GC oven 112 at any given time (e.g., can detect temperature at pre-determined intervals such as every 0.1 seconds, every second, every 10 seconds, every minute, every 5 minutes, or the like during use of the system). The APC controller 126 can receive the detected temperature and send a control signal to the APC valve 124a to change the pressure in/through the APC valve based on the sensed temperature to maintain the constant flow rate of the oxygen in the carrier gas that enters the reactor 118. The APC controller 126 can use, for example, one or more of proportional, integral, or derivative control laws to maintain the constant flow rate of the oxygen in the carrier gas as the temperature of the GC oven 112 varies. Maintaining the constant flow rate of the oxygen in the carrier gas can extend the useful life of the oxidizable material 120 in the reactor 118 because the constant flow rate can keep an oxidizable material (e.g., the nickel material) oxidized without causing degradation of the oxidizable material. Traditional systems maintain a constant pressure of oxygen in the carrier gas, however the flow rate changes based on the temperature if the pressure is maintained at constant, thus limiting the effective oxidizable material, and reactor, choices and life spans. The APC controller 126 and the APC valve 124a (the APC system) can increase the pressure of the oxygen in the carrier gas in the deactivated column (e.g., the at least one column of column(s) 16 of FIG. 1 ) and the reactor 118 as the temperature in the GC oven 112 increases to maintains the constant flow rate of the oxygen.

[0040] As an example, a 5 meter long, 0.15 mm inner diameter deactivated column can be used to connect the APC valve the reactor. The flow rate can be chosen (on the APC controller) to be a constant 0.1 mL/min of 1 % oxygen in helium. During the sample analysis, the GC oven temperature can be programmed and generally increases with time after sample injection. The APC controller can compute the head pressure needed to maintain a flow of 0.1 mL/min based on GC oven temperature at any given time, taking into consideration the length and inner diameter of the deactivated column (the smaller diameter, the longer the column, and the higher the temperature, the higher head pressure is needed).

[0041] Referring now to FIG. 3, a more descriptive illustration of the inside of a reactor 18 is shown, which could be reactor 118. As an example, the reactor 18 can include a reactor tube 46 at least partially surrounded by a furnace 40 and structural components 42. The reactor tube 46 can be in the form of a ceramic reactor tube having a lumen in which the oxidizable material(s) 20a and 20b can be positioned and the furnace 40 can surround the reactor tube. The furnace 40 can be change the temperature of and inside the reactor tube 46. The reactor tube 46 can be, for example a nonporous alumina ceramic tube (Length - 320 mm; I.D. - 0.55 mm; O.D. - 1 .5 mm). The reactor can include inlet and outlet metal unions 44 at each end of the reactor tube 26 for connecting with the GC oven (e.g., inlet) and a mass spectrometer and/or detector (e.g., outlet). Capillary tube 36 (e.g., from the GC oven) can flow the sample organic compound in a carrier gas and oxygen in the carrier gas into the lumen of the ceramic tube 46 and over the oxidizable material(s) 20a and 20b positioned within the lumen of the ceramic tube. The reactor 18 can convert the sample organic compound to carbon dioxide. In another example the reactor 18 can convert the sample organic compound to another oxide, such as NOx or SO2.

Reactor tube 46 may be centered along one or more axes of the furnace 40 to establish an appropriate heat distribution within the reactor tube. The exit of reactor tube 46 can be connected to an additional capillary 36 (not shown) via the output metal union 44 and ferrules or any suitable method of connection (not shown) to send output of the reactor 18 to the mass spectrometer and/or detector. Both ends of each metal union 44 (one at the entrance and the other at the exit of the reactor 18) may be placed far enough from furnace 40 to avoid damage from high temperatures and melt.

[0042] The oxidizable materials can be the activated nickel material 20a and another oxidizable (oxidized) material, such as platinum or copper, 20b. There can be at least two times as much of the activated nickel material as the other oxidizable material. In other examples, the oxidizable material can be only nickel material 20a. As an example, the nickel material 20a can be in the form of one or more wires including nickel that can be twisted with one or more wires including the other oxidizable material 20b (e.g., copper and/or platinum). For example, two nickel wires and a platinum wire can each have a diameter of about 0.005 inches of DIA and may be twisted together. An approximately 250-300 mm length of twisted metal wires can be inserted into a ceramic reactor tube and the combined ceramic reactor tube and nickel and platinum wires can be positioned in a region of a heated furnace. Advantageously, using nickel, as made effective by maintaining a constant flow rate of oxygen regardless of temperature fluctuations the system 10 can increase the lifetime if the nickel and the reactor 18, when used in a mass spectrometer and/or gas chromatograph compared to traditional reactor systems using copper as the oxidant, leading to an increase in productivity and data quality, with a reduced need for replacement of reactor and to longer periods of uninterrupted analysis.

IV. Method

[0043] Another aspect of the present disclosure can include methods (FIGS. 4- 6) that relate to extending the life of the oxidizable material in a reactor, and the reactor, used for compound specific isotope analysis (CSIA), for example a gas chromatograph and/or a mass spectrometer (as shown in FIGS. 1 -3). The method 50-70 are illustrated as process flow diagrams with flowchart illustrations. For purposes of simplicity, the methods 50-70 are shown and described as being executed serially; however, it is to be understood and appreciated that the present disclosure is not limited by the illustrated order as some steps could occur in different orders and/or concurrently with other steps shown and described herein. Moreover, not all illustrated aspects may be required to implement the methods 50-70.

[0044] FIG. 4 illustrates a method 50 for extending the lifetime of an oxidizable material (oxidant) in a reactor of a system used for CSIA. Traditional systems employ a constant pressure control of oxygen in carrier gas into the reactor and employ a mixture of copper, nickel, and/or platinum wires, using copper as the main oxidant. Traditionally, nickel cannot be used effectively as the oxidant because only the skin of the nickel can be oxidized and the inner core of the nickel cannot be oxidized. Thus, without a constant amount of oxygen to maintain the nickel as nickel oxide, the nickel loses oxidative capacity additionally a minimal temperature to use nickel oxide is 1000°C, otherwise oxidation can be incomplete and cause undesirable isotropic fractionation. Copper is usually used instead but has a short useful lifetime because once oxidized copper can become very brittle and spontaneously degrade, which limits the useful life of reactors that use copper oxide. [0045] Copper can be replaced with nickel because nickel oxide does not spontaneously degrade and a constant flow rate of oxygen over the nickel oxide can be maintained (to stop the formation of nickel-bound carbon phases, which can lead to inaccurate isotopic results) in order to extend the useful life of the reactor and to improve accuracy and precision of analytical results. Other oxidizable material can also have an extended usable lifetime when a constant flow rate of oxygen is maintained.

[0046] The method 50 can be implemented by the APC controller 26 of the APC system 22 of FIG. 1 . Simply, the APC system 22 can receive the temperature in the GC oven 12 and then automatically adjust the head pressure electronically. At 52, an automatic pressure controller including at least a processor can receive a temperature of a gas chromatography oven of a system configured to convert an organic compound to carbon dioxide (or another oxide gas) from a temperature sensor in the gas chromatography oven. The system (as described in more detail with respect to FIGS. 1 -3) can include a reactor having an oxidizable material (e.g., nickel) positioned within the reactor that acts as an oxidant in a presence of oxygen and at least one column positioned in the gas chromatography oven and connected to the reactor via. The organic compound in a carrier gas (e.g., helium) and oxygen in the carrier gas (e.g., 1% oxygen in helium) can be injected through the at least one column to the reactor. An APC valve can be in communication with the automatic pressure controller and connect a source of the oxygen in the carrier gas to the at least one column, through which it is connected to the reactor.

[0047] At 54, the automatic pressure controller can maintain a constant flow rate of the oxygen in the carrier gas (e.g., 0.1 mL/min) into the at least one column and then over the oxidizable material in the reactor as the temperature in the gas chromatography oven varies by altering an amount of pressure in/through an automatic pressure control (APC) valve (e.g., a head pressure valve). Altering the amount of pressure in through the APC valve can change the pressure of the oxygen in the carrier gas as it flows towards the reactor in response to a change in the temperature in the gas chromatography oven. For example, the pressure of the oxygen in the carrier gas in the at least one column and the reactor can be increased (e.g., by changing the head pressure of the APC valve) as the temperature in the gas chromatography oven increases to maintain the constant flow rate of the oxygen. The APC controller can utilize at least one of proportional, integral, or derivative control to maintain the constant flow rate of the oxygen in the carrier gas as the temperature of the gas chromatography oven varies. Maintaining the constant flow rate of the oxygen in the carrier gas can extend the useful life of the oxidizable material in the reactor and increase the accuracy and/or precision of results found using the system as whole.

[0048] FIG. 5 illustrates a method 60 for activating an oxidizable material (e.g., nickel) positioned within a reactor before beginning CSIA. At 62, the oxidizable material (e.g., nickel material or nickel material and another material, such as, copper or platinum) can be installed within the reactor. For example as wires of nickel and/or wires of nickel and the other oxidizable material in at least a 2:1 ratio. At 64, the oxidizable material can be activated by oxidizing the nickel material in the reactor with 100% (pure) oxygen for a time at a temperature, (e.g., by exposing the nickel containing material to the 100 % oxygen for the time period at the temperature). For example, the pure oxygen can be flowed over the nickel material for 30 minutes at 1100°C. For example, the pure oxygen can be flowed over the nickel material in a direction opposite of a normal flow direction in the reactor (e.g., so the oxygen does not enter an ion source of the system used for CSIA. At 66, a plurality of samples (e.g., 10 fold, 100 fold, or more compared to a traditional system and method) can be continuously run with the reactor with the activated oxidizable material and the constant oxygen flow rate for CSIA, without need to re-oxidize the oxidizable material or replace the reactor. Thus, the usable life of the reactor and the oxidizable material can be significantly extended and the precision and accuracy of analytical results can be improved.

[0049] FIG. 6 illustrates an example method 70 for maintaining a constant flow rate of oxygen in a carrier gas to a reactor through at least one column in a gas chromatography oven. At 72, the automatic pressure controller can receive a temperature within the gas chromatography oven at a time from the temperature sensor as described previously. At 74, the automatic pressure controller can compare the received temperature at the time to a database. The database can be based on the specifications of the overall system (e.g., lengths and inner diameters of the one or more columns) and can include the corresponding pressure change of the APO valve required at any given temperature to maintain the flow rate of the oxygen in the carrier gas into the reactor constant (e.g., at 0.1 mL/min, or the like). The automatic pressure controller can, for example utilize at least one of proportional, integral, or derivative control. At 76, the automatic pressure controller can send a signal to the APC valve to adjust the pressure through the APC valve (e.g., the head pressure in a head pressure valve) based on the data in the database. At 78, the flow rate of the oxygen in the carrier gas to the reactor is maintained constant. The method can be looped to maintain the constant flow rate until the system is shut off.

V. Experimental

[0050] Compound-specific isotope analysis (CSIA) has been widely applied in many fields for various applications since its first development in 1990s (specifically carbon stable isotope analysis). However, the commercial reactors used for inline oxidation of organic compounds to carbon dioxide suffer from the need of frequent re-oxidation, short lifetime, in addition to their substantial cost. Users often resort to individualized solutions with variable performances. Developing a long-lasting, reliable and cost efficient reactor is thus of great importance.

[0051] Experiments were completed using two different gas chromatography isotope ratio mass spectrometry (GC-IRMS) systems to compare a commercial combustion reactor with the improved system described above.

[0052] The GC-IRMS system 1 (GIS-1 ) was performed using a ThermoFisher Trace 1310 GC coupled with a Thermo Delta V Advantage isotope ratio mass spectrometer (IRMS) with a Thermo GC Isolink II interface, connected via a Conflo IV interface. Samples and standard solutions were injected into the GC inlet with a Split/Splitless system using splitless mode at 320°C with the assistance of TriPlus RSH autosampler. Helium was used as carrier gas with a flow of 1 mL/min and the GC analytical column installed was ZB-1 ms (30 m x 0.32 mm x 0.25 pm;

Phenomenex, Torrance, CA, USA). The commercial Thermo Fisher Scientific reactor used in this research was composed of a ceramic tube containing a Nickel tube, nickel, and copper wires, operated at 1000 °C, and oxidized following Thermo Fisher Scientific designations using high purity oxygen flows at different temperature stages (600°C for 8 hours, followed by 900 °C for 4 hours, and followed by 1000 °C for 2 hours). Additionally, the approximately, 13 mm position of the combustion reactor soldering point and the heater was respected as indicated by the operational Thermo Fisher Scientific guidance. [0053] The GC-IRMS system 2 (GIS-2) (as shown in FIG. 2 above) was performed using an Agilent 6890N gas chromatography (GC) equipped with an autosampler GC Pal autosampler coupled to a Thermo Scientific DELTA V Plus isotope ratio mass spectrometer (IRMS-MS) via combustion (GC-III). All samples were injected in a split/splitless inlet using a pulsed splitless mode at 320 °C. Helium was used as carrier gas with a flow of 1 mL/min and the GC analytical column installed was ZB-1 ms (30 m x 0.32 mm x 0.25 pm; Phenomenex, Torrance, CA, USA). A nonporous alumina ceramic tube (Length - 320 mm; I.D. - 0.55 mm; O.D. - 1 .5 mm) was filled with 250 mm of Ni/Pt twisted wires (2:1 wires). An APC was used in Split mode to provide oxygen flow (1% 02 in helium, 0.1 mL/min column flow) to preserve the combustion reactor oxidized through a deactivated column (10 m x 0.32 mm). The analytical column, the deactivated column, and the backflush valve were connected to the ceramic reactor tube via a union connector (VICI Valeo Instruments Co. Inc., Houston, TX). Initially, the metal wires were heated at 1100 °C and oxidized in presence of high purity oxygen for 30 min using countercurrent flows through a deactivated capillary connected to the top of the reactor tube to produce nickel oxide. During operational combustion system uses, the metal wires were oxidized by the 1% oxygen in helium from the automatic pressure control (APC), which promotes the combustion of organic compounds as they pass through reactor metal wires.

[0054] Two different types of external standard solutions were used for quality equipment control containing five homologs of fatty acid methyl ester (FAME) consisting of C16, C18, C22, C24, and C28; and seven n-alkanes homologs (AC20, AC22, AC24, AC26, AC29, AC31 , and AC32). For G IS- 1 , only fatty acids standard solutions were performed. Standards were injected once after every sixth injection during the IRMS operation or when it is needed. 013C values of sample compounds were referenced to gaseous carbon which had been calibrated against the known Indiana standard n-alkanes homologs solution (AC20, AC22, AC24, AC26, AC29, AC31 , and AC32). The isotope values were expressed per mille (%_o) relative to Vienna Pee Dee Belemnite (VPDB).

[0055] The following comparison of GIS-1 and GIS-2 for homologs fatty acids methyl ester and n-alkanes involved the following considerations, including (i) peak amplitude stability, peak width ratio (conversion efficiency), and (ii) precision of the isotope ratios.

[0056] Peak amplitude and width ratio for FAME analysis with GIS-1 [0057] In recent GIS-1 13C/12C isotope measurements there was observed a necessity of an often reoxidizing a reactor to obtain an acceptable sensitivity, peak shape, and isotope values. FIG. 7 shows the detrending amplitude/width ratio of homologs fatty acids methyl esters using GIS-1 . Solid vertical lines indicate the oxidation events. Dashed vertical lines demonstrate the change to a new reactor FIG. 7 represents the detrended ratio between peak amplitude and width, which reports 392 FAMEs (in-house standards) results obtained over 1293 unknown sample injections, the peak intensity is drastically changed and reactor conditionings with high purity oxygen were performed. The average peak amplitude and width ratio of each in-house standard was 62 mV (±36), 57 mV (±28), 53 (±23), 49 mV (±21 ), and 51 mV (±20), for C16, C18, C22, C24, and C28, respectively. On average, after 27 injections, reactor conditioning was performed, which promoted an improvement in peak height, but huge peak amplitude fluctuations were observed, indicating a low capacity of the designed reactor to preserve copper oxide (CuO) and nickel oxide (NiO) overanalyzes.

[0058] 13C/12C analysis of FAME with GIS-1

[0059] Determining the 13C/12C values of homologs fatty acid methyl esters using a GIS-1 showed isotope values and standard deviation of -29.5 ± 0.8 %o, -32.5 ± 0.8%o, -30.6 ± 0.67oo, -31 .4 ± 0.6%o, and -31 .7 ± 0.9%o, for C16, C18, 022, 024, and 028, respectively. As demonstrated previously, several oxidation steps were required to keep the amplitude of appropriate quality, which affected drastically the peak amplitudes. However, the oxidation steps did not affect the 5130 isotope ratio measurements (as shown in FIG. 8). FIG. 8 shows the 5130 measurements of homologs of fatty acids methyl ester using GIS-1 . Dashed vertical lines demonstrate the change to a new reactor. Peak amplitude and width ratio for FAME and n- alkanes analysis with GIS-2 These findings indicate a low isotope ratio deterioration represented by the isotope values precision, even reactor change, differently than observed previously, where the 515N values were less enriched after reoxidation phases and required a few injections until being established.

[0060] Peak amplitude and width ratio for FAME and n-alkanes analysis with GIS-2

[0061] Different from the results with commercial GIS-1 (FIG. 7), the system demonstrated here did not require reoxidation even though more than 1700 unknown samples, 153 FAME, and 189 n-alkanes in-house standards had been analyzed, which demonstrate a longer lifetime than the commercial reactor. FIG. 9 demonstrates the peak amplitude and width ratio for FAME in-house standard with 74 mV (±11 ), 148 mV (±33), 200 (±41 ), 149 mV (±29), and 163 mV (±49), for CI 6, C18, 022, C24, and C28, respectively. FIG. 9 shows the detrended amplitude/width ratio of homologs fatty acids methyl esters using GIS-2 reactor and oxidation system. There was no substantial difference between these results with results for GIS-1 , unless for compound C16, but it is important to mention that GIS-2 results were obtained using different FAME standard solutions, which contribute to the high fluctuation in this ratio, as demonstrated by standard deviation.

[0062] FIG. 10 demonstrates detrended peak amplitudes and peak width ratio for n-alkanes in-house standards. The amplitude and width ratio of average and standard deviation were 106 mV (±15), 102 mV (±14), 149 (±19), 149 mV (±18), 134 mV (±20), 201 mV (±40), and 236 mV (±31 ), for AC20, AC22, AC24, AC26, AC29, AC31, and AC32, respectively. In contrast to the GSI-1 system, no abrupt peak amplitude changes in the peak width are normally associated with the low reactor conversion capacity caused by reactor oxidation. ¹³C/¹²C analysis of FAME and n-alkanes with GIS-2. Determining the ¹³C/¹²C values of FAME using the GIS-2 exhibited excellent performance for isotope ratio precision (FIG. 1 1 ) with average and standard deviation for b¹³C of -31 .1 ± 0.3 %□, -30.7 ± 0.3%o, -29.9 ± 0.3%o, -31 .9 ± 0.3%o, and - 28.8 ± 0.3%o, for C16, C18, C22, C24, and C28, respectively. Analogous to the results with GIS-1 , the GIS-2 demonstrated here gave precise values for b¹³C isotope analysis of in-house FAME standard. FIG. 11 shows b¹³C measurements of homologs of fatty acids methyl ester using GSI-2 reactor design.

[0063] FIG. 12 shows b¹³C measurements of homologs of n-alkanes using GSI- 2 reactor design. Similarly observed for in-house FAME standard results (FIG. 12), the GIS-2 reactor system also gave precise results, and true results also for the b¹³C isotope analysis of n-alkanes, which presented an average and standard deviation of -32.5 ± 0.2 %o, -33.1 ± 0.2 %_o, -33.6 ± 0.2 %□, -33.2 ± 0.3 %, -29.8 ± 0.3 %□, -29.9 ± 0.3 %o, and -29.9 ± 0.3 %o, for AC20, AC22, AC24, AC26, AC29, AC31 , and AC32, respectively. Additionally, the offset of each compound over more than 1400 injections, including unknown samples and n-alkanes standards, varied between 0.15 % (C20) and 0.47 %_o (C31).

[0064] From the above description, those skilled in the art will perceive improvements, changes, and modifications. Such improvements, changes and modifications are within the skill of one in the art and are intended to be covered by the appended claims. All patents, patent applications, and publications cited herein are incorporated by reference in their entirety.

Claims

What is claimed is:

1 . A system comprising: a reactor configured to convert an organic compound to carbon dioxide, wherein an oxidizable material positioned within the reactor acts as an oxidant in a presence of oxygen; a gas chromatography oven comprising at least one column connected to the reactor, wherein the organic compound in a carrier gas and oxygen in the carrier gas are injected through the at least one column to the reactor; a temperature sensor within the gas chromatography oven to detect a temperature within the gas chromatography oven; and an automatic pressure control (APC) system comprising: an APC valve connecting a source of the oxygen in the carrier gas to the at least one column and regulating a flow rate of the oxygen in the carrier gas into the at least one column; and an APC controller coupled to the temperature sensor and the APC valve, comprising a processor, wherein the APC controller is configured to: receive the temperature of the gas chromatography oven as detected by the temperature sensor; and regulate the pressure of the oxygen in the carrier gas into the at least one column and then over the oxidizable material within the reactor by adjusting the pressure through the APC valve based on the temperature in the gas chromatography oven, an inner diameter of the at least one column, and a length of the at least one column connecting the valve to the reactor, wherein the APC system maintains a constant flow rate of the oxygen in the carrier gas through the reactor as the temperature in the gas chromatography oven changes.

2. The system of claim 1 , wherein the oxidizable material is an activated nickel material that has been oxidized with pure oxygen.

3. The system of claim 2, wherein another oxidizable material is positioned in the reactor with the activated nickel material, wherein the other oxidizable material comprises copper and/or platinum.

4. The system of claim 3, wherein there is at least two times as much of the activated nickel material as the other oxidizable material.

5. The system of claim 2, wherein the activated nickel material has been oxidized in the reactor for a time at a temperature.

6. The system of claim 1 , wherein the system is part of a gas chromatograph and/or a mass spectrometer.

7. The system of claim 1 , wherein the reactor is in the form of a ceramic tube having a lumen, wherein the oxidizable material is positioned within the lumen of the ceramic tube and the organic compound in a carrier gas and oxygen in the carrier gas are flowed over the oxidizable material positioned within the lumen of the ceramic tube.

8. The system of claim 1 , wherein the oxygen in the carrier gas in the at least one column and the reactor is one percent oxygen in the carrier gas.

9. The system of claim 1 , wherein the carrier gas is helium.

10. The system of claim 1 , wherein the at least one column comprises an analytic column and a deactivated column and the organic compound in the carrier gas is injected through the analytic column to the reactor and the oxygen in the carrier gas is injected through the deactivated column to the reactor.

11 . The system of claim 1 , wherein the constant flow rate of the oxygen in the carrier gas extends the useful life of the oxidizable material in the reactor.

12. The system of claim 1 , wherein the APC system increases the pressure of the oxygen in the carrier gas in the at least one column and the reactor as the temperature in the gas chromatography oven increases to maintains the constant flow rate of the oxygen.

13. The system of claim 1 , wherein the constant flow rate of the oxygen in the carrier gas is maintained at 0.1 mL/min.

14. A method comprising: receiving, by an automatic pressure controller comprising a processor, a temperature of a gas chromatography oven of a system configured to convert an organic compound to carbon dioxide from a temperature sensor in the gas chromatography oven, wherein the system further comprises a reactor having an oxidizable material positioned within the reactor that acts as an oxidant in a presence of oxygen and at least one column positioned in the gas chromatography oven and connected to the reactor, wherein the organic compound in a carrier gas and oxygen in the carrier gas are injected through the at least one column to the reactor; and maintaining, by the automatic pressure controller, a constant flow rate of the oxygen in the carrier gas into the at least one column and then over the oxidizable material in the reactor as the temperature in the gas chromatography oven varies by altering an amount of pressure in an automatic pressure control (APC) valve to change the pressure of the oxygen in the carrier gas in response to a change in the temperature in the gas chromatography oven, wherein the APC valve is in communication with the automatic pressure controller and connecting a source of the oxygen in the carrier gas to the at least one column.

15. The method of claim 14, wherein the maintaining the constant flow rate of the oxygen in the carrier gas further comprises sending a signal, by the controller, to the APC valve to alter the amount of the pressure in the APC valve.

16. The method of claim 15, wherein the pressure of the oxygen in the carrier gas in the at least one column and the reactor is increased as the temperature in the gas chromatography oven increases to maintain the constant flow rate of the oxygen

17. The method of claim 14, wherein the oxygen in the carrier gas is one percent oxygen in helium.

18. The method of claim 14, wherein the constant flow rate of oxygen in the carrier gas is 0.1 mL/min.

19. The method of claim 14, wherein maintaining the constant flow rate of the oxygen in the carrier gas extends the useful life of the oxidizable material in the reactor.

20. The method of claim 14, wherein the automatic pressure controller utilizes at least one of proportional, integral, or derivative control to maintain the constant flow rate of the oxygen in the carrier gas as the temperature of the gas chromatography oven varies.