Determination method for isotope atom ratio in sample and determination method for isotope molar ratio in sample

Abstract

To provide a determination method for the isotope atom ratio in a sample and a determination method for the isotope molar ratio in a sample that can determine the isotope atom ratio or the isotope molar ratio without using a high-resolution mass spectrometer such as a double convergence type mass analyzer or multiple circuiting flight time mass analyzer.SOLUTION: A determination method for the isotope atom ratio in a sample includes a reaction step S11 of carrying out recombination of isotope atoms among isotope molecules in a sample at random. a measurement step S12 of obtaining each isotope peak of the sample the isotope atoms of which have been recombined by the reaction step S11 using an analyzer that can obtain signals for each mass-to-charge ratio, and an atom ratio calculation step S13 of theoretically determining the isotope atom ratio in the sample by using the signals obtained in the measurement step S12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for determining an isotopic atomic ratio in a sample and a method for determining an isotopic molecular ratio in a sample. [Background technology]

[0002] Isotopes are used in the natural sciences and in industry as tracers in the semiconductor manufacturing process and in medicine. For industrial use, it is necessary to concentrate the isotope components in order to maximize the effect of the isotope. 13 Taking C) as an example, a method of concentrating by a distillation cascade process is known as one of the enrichment methods (Patent Document 1). In addition, in order to enrich to a high concentration of 99 atom% or more, a technique that combines an atomic recombination reaction with the distillation cascade process is used (Non-Patent Document 1). Here, the atomic recombination reaction is an isotope exchange reaction that randomly rearranges the atoms that make up a compound. In this technology, first, concentrated ethanol is extracted through a distillation cascade process. 12 C 18 A portion of the O gas is transformed into 13 C 18 Convert to O( 13 C 16 O+ 12 C 18 O → 12 C 16 O+ 13 C 18 O) 13 C 18 This gas is then returned to the distillation column and separated in a distillation cascade process. 13 C 16 O and 13 C 18 Concentrate O 13 C concentration is 99% or more. Not only for CO, but for any isotopic product produced by distillation, it is necessary to quantify the isotopic atomic composition to clarify the product specifications, and it is also desirable to grasp the isotope molecular (isotopologue) composition to accurately evaluate the enrichment process. The above content is not limited to CO isotope ratio analysis, but also applies to other compounds in which multiple components have the same mass number. An example is nitric oxide. It is known that oxygen isotopes can be concentrated simultaneously with nitrogen isotopes by distillation of nitric oxide, and Non-Patent Document 2 describes a method for co-producing 95 atom% or more oxygen and nitrogen isotopes by nitric oxide distillation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-164884 A [Non-patent literature]

[0004] [Non-Patent Document 1] McInteer, B.B., “Isotope Separation by Distillation: Design of a Carbon-13 Plant”, Separation Science and Technology, 1980, Vol. 15, No. 3, pp. 491-508 [Non-Patent Document 2] Shohei Isomura et al., "Separation of Nitrogen and Oxygen Isotopes by Low-Temperature Distillation of Nitric Oxide", RADIOISOTOPES, 1987, Vol. 36, No. 2, pp. 57-63 Summary of the Invention [Problem to be solved by the invention]

[0005] Mass spectrometry is a method commonly used to quantify isotopic atomic composition or isotopic molecular composition. Taking CO as an example, there are multiple molecular species with almost the same mass number in CO isotope molecules. Specifically, 12 C 17 O and 13 C 16 O, mass number 30 12 C 18 O and 13 C17 O, and the mass difference between them is at the millimass level, so the resolution is insufficient to separate and measure them with commonly used quadrupole mass spectrometers. Therefore, in order to directly quantify the isotopic atomic composition or isotopic molecular composition, separation analysis using a high-resolution mass spectrometer is necessary, and analyzers that can do this include double-focusing mass spectrometers and multi-orbit mass spectrometers. However, these are expensive and complex analyzers, and require advanced adjustment techniques for measurement, so engineers with specialized knowledge and dedicated equipment are required. As a result, it has been difficult to grasp product specifications in a timely manner or evaluate the enrichment process through on-site analysis.

[0006] An object of the present invention is to provide a method for determining an isotope atomic ratio in a sample and a method for determining an isotope molecular ratio in a sample, which can determine an isotope atomic ratio or an isotope molecular ratio without using a high-resolution mass spectrometer such as a double-focusing mass spectrometer or a multi-orbit mass spectrometer. [Means for solving the problem]

[0007] The aspects of the present invention are as follows. [1] A reaction process that randomly recombines isotopic atoms between isotopic molecules in a sample. A measuring step of acquiring each isotope peak of the sample in which the isotope atoms have been recombined by the reaction step, using an analyzer capable of obtaining a signal for each mass-to-charge ratio; an atomic ratio calculation step of theoretically determining the isotope atomic ratio in the sample using the signal obtained in the measurement step; A method for determining an isotope atomic ratio in a sample, comprising: [2] a pre-reaction measurement step of acquiring each isotope peak of a sample before recombination of isotope atoms between isotope molecules using an analytical device capable of obtaining a signal for each mass-to-charge ratio; A reaction step of randomly recombining isotope atoms between isotope molecules in the sample; A post-reaction measurement step of acquiring each isotope peak of the sample in which the isotope atoms have been recombined by the reaction step using an analyzer capable of obtaining a signal for each mass-to-charge ratio; and A molecular ratio calculation step of theoretically determining the isotope molecular ratio in the sample before recombination of isotope atoms between the isotope molecules using the signals obtained in the pre-reaction measurement step and the post-reaction measurement step. A method for determining an isotopic molecular ratio in a sample, comprising: [3] The method for determining an isotope atomic ratio in a sample according to [1], wherein the analytical device is a mass spectrometer. [4] The method for determining an isotopic ratio of a sample according to [2], wherein the analytical device is a mass spectrometer. [5] The method for determining an isotope atomic ratio in a sample according to [3], wherein the mass spectrometer is a quadrupole mass spectrometer. [6] The method for determining an isotopic ratio of a sample according to [4], wherein the mass spectrometer is a quadrupole mass spectrometer. Effect of the Invention

[0008] According to the present invention, it is possible to provide a method for determining an isotope atomic ratio in a sample and a method for determining an isotope molecular ratio in a sample, which can determine an isotope atomic ratio or an isotope molecular ratio without using a high-resolution mass spectrometer such as a double-focusing mass spectrometer or a multi-orbit mass spectrometer. [Brief description of the drawings]

[0009] [Figure 1] 1 is a flowchart illustrating a method for determining an isotope atomic ratio in a sample according to an embodiment of the present invention. [Diagram 2] 10 is a flowchart illustrating a method for determining an isotope molecular ratio in a sample according to another embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram illustrating a schematic configuration of an analysis device used in the experimental examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In this specification and claims, when a numerical range is expressed using "~", the numerical range is intended to include the numerical values ​​on both sides of "~".

[0011] Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the embodiment described below, and various modifications are possible without departing from the gist of the present invention.

[0012] [Method for determining the atomic isotope ratio in a sample] As shown in FIG. 1, a method for determining an isotope atomic ratio in a sample according to one embodiment of the present invention includes a reaction step S11, a measurement step S12, and an atomic ratio calculation step S13.

[0013] <Reaction step S11> The reaction step S11 is a step of randomly recombining isotope atoms between isotope molecules in the measurement sample.

[0014] The recombination method is not particularly limited as long as it is a method that randomly recombines isotope atoms based on the probability of their existence, and examples of the recombination method include a heating reaction, a discharge reaction, and other methods that utilize other reversible reactions. However, as a recombination method, a method that has the effect of causing a bias in the isotope composition in the product when recombining isotope atoms (isotope effect) is not preferable.

[0015] <Measurement process S12> The measurement step S12 is a step of obtaining signals using an analysis device capable of separating and analyzing each isotope peak of the measurement sample in which isotope atoms have been recombined in the reaction step S11.

[0016] The most important characteristic of isotopes is that they differ in mass, and a mass spectrometer is preferred as an analytical device that can easily obtain a signal for each isotope.

[0017] When a mass spectrometer is used as the analyzing device, it is preferable to use a peak height or a peak area value as the signal value.

[0018] As the mass spectrometer, a quadrupole mass spectrometer is more preferable from the viewpoints of ease of measurement and economy.

[0019] The quadrupole mass spectrometer applies DC and AC voltages to four electrode rods (quadrupoles) to form an electric field through which only ions with a certain mass-to-charge ratio (m / z value) can pass, allowing only ions with that certain m / z value to pass through the electrodes and reach the detector. By linearly varying the AC voltage while keeping the ratio of the DC and AC voltages constant, all ions can be allowed to pass.

[0020] The method for determining an isotope atomic ratio in a sample of the present embodiment is a method that does not necessarily require the use of a high-resolution mass spectrometer such as a double-focusing mass spectrometer or a multi-orbit mass spectrometer, and does not preclude the use of an analytical device other than a mass spectrometer or a high-resolution mass spectrometer other than a quadrupole mass spectrometer, such as a double-focusing mass spectrometer or a multi-orbit mass spectrometer, as the analytical device.

[0021] The method for ionizing the sample is not particularly limited, and any conventionally known ionization method can be used, such as electron ionization (EI), electrospray ionization (ESI), fast atom bombardment (FAB), matrix assisted laser desorption / ionization (MALDI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photo ionization (APPI), chemical ionization (CI), or field ionization (FI).

[0022] <Atomic ratio calculation step S13> The atomic ratio calculation step S13 is a step of theoretically determining the isotope atomic ratio in the measurement sample using the signal obtained in the measurement step S12.

[0023] In the atomic ratio calculation step S13, an isotope atomic ratio is calculated based on the probability of existence of each isotope atom from the signal values ​​of the isotope atomic fragment component and the isotope molecular component obtained in the measurement step S12. Specifically, it can be determined by the following method.

[0024] (CO case) Assume that the signals shown in Table 1 are obtained in the measurement step S12.

[0025] [Table 1]

[0026] The symbol I in parentheses in Table 1 indicates the signal value of each component. The signal value after the reaction is indicated by the subscript sc. sc It is written as follows.

[0027] The isotope atomic ratio is calculated based on the signals shown in Table 1 obtained in the measurement step S12. Since N2 is an interfering component in the analysis of the isotope composition of CO using a mass spectrometer, the reaction step S11 is carried out in a reaction field designed to be leak-tight so that nitrogen from the atmosphere does not mix with the CO during the reaction. Since it is difficult to reduce the detection of atmospheric components to zero using a general mass spectrometer, the isotope atomic ratio of nitrogen, which accounts for more than 99% of the natural abundance, is calculated. 14 N2 needs to be considered. On the other hand, 14 N 15 N and 15 The N2 component is so small that it can be ignored. For example, if we assume that several hundred ppm of air is mixed in, 14 N2 interferes with CO measurements at levels on the order of several hundred ppm. 14 N 15 N and 15 N2 is on the order of a few ppm, so it is quite small.

[0028] After the recombination reaction in reaction step S11, carbon atoms and oxygen atoms randomly bond without isotope selectivity to form carbon monoxide molecules, and the signal values ​​of each component are calculated using formulas (1) to (6). The ratio of each isotope can be calculated from the ratio of these signal values.

[0029]

number

[0030] I in the formula sc indicates the signal value of each component after the reaction.

[0031] (If NO) Assume that the signals shown in Table 2 are obtained in the measurement step S12.

[0032] [Table 2]

[0033] The symbol I in parentheses in Table 2 indicates the signal value of each component. The signal value after the reaction is indicated by the subscript sc. sc It is written as follows.

[0034] The isotope atomic ratio is calculated based on the signals shown in Table 2 obtained in the measurement step S12. Since O2 is an interfering component in the analysis of NO isotope composition using a mass spectrometer, the reaction step S11 is carried out in a reaction field designed to be leak-tight so that oxygen from the atmosphere does not mix with the NO during the reaction. Since it is difficult to reduce the detection of atmospheric components to zero using a general mass spectrometer, the isotope atomic ratio of oxygen, which accounts for more than 99% of the natural abundance, is calculated. 16 O2 needs to be considered. On the other hand, 16 O 17 The O component is so small that it can be ignored. For example, if we assume that several hundred ppm of air is mixed in, 16 O2 interferes with NO measurement at levels on the order of several hundred ppm. 16 O 17 O is in the sub-ppm range, so it is quite small.

[0035] After the recombination reaction in reaction step S11, nitrogen atoms and oxygen atoms are randomly bonded without isotope selectivity to form nitric oxide molecules, and the signal values ​​of each component are calculated using formulas (7) to (11). The ratio of each isotope can be calculated from the ratio of these signal values.

[0036]

number

[0037] I in the formula sc indicates the signal value of each component after the reaction.

[0038] [Method for determining the isotope ratio in a sample] A method for determining an isotope molecular ratio in a sample according to another embodiment of the present invention includes a pre-reaction measurement step S20, a reaction step S21, a post-reaction measurement step S22, and a molecular ratio calculation step S23, as shown in FIG.

[0039] <Pre-reaction measurement step S20> The pre-reaction measurement step S20 is a step of acquiring each isotope peak of the sample to be measured before recombination of isotopic atoms between isotopic molecules in the reaction step S21 described below, using an analytical device capable of acquiring a signal for each mass-to-charge ratio.

[0040] The pre-reaction measurement step S20 is similar to the measurement step S12 described above, except that the measurement target is a measurement target sample before recombination of isotope atoms between isotope molecules is carried out in a reaction step S21 described below.

[0041] <Reaction step S21> The reaction step S21 is a step of randomly recombining isotope atoms between isotope molecules in the measurement sample.

[0042] The reaction step S21 is similar to the reaction step S11 described above.

[0043] <Post-reaction measurement step S22> The post-reaction measurement step S22 is a step of acquiring each isotope peak of the measurement sample in which isotope atoms have been recombined in the reaction step S21, using an analyzer capable of acquiring a signal for each mass-to-charge ratio.

[0044] The post-reaction measuring step S22 is similar to the measuring step S12 described above, except that the measurement target is a measurement target sample after recombination of isotope atoms between isotope molecules has been carried out in the above-mentioned reaction step S21.

[0045] <Molecular ratio calculation step S23> The molecular ratio calculation step S23 is a step of theoretically determining the isotopic molecular ratio in the measurement sample before recombination of isotopic atoms between isotopic molecules, using the signals obtained in the pre-reaction measurement step S20 and the post-reaction measurement step S22.

[0046] In the molecular ratio calculation step S23, the isotopic molecular ratio can be calculated based on the probability of presence of each isotopic atom from the signal values ​​of the isotopic atomic fragment components and isotopic molecular components obtained in the pre-reaction measurement step S20 and the post-reaction measurement step S22. Specifically, it can be determined by the following method.

[0047] (CO case) The signal value obtained in the pre-reaction measurement step S20 is I, and the signal value obtained in the post-reaction measurement step S22 is I sc Let us assume that. The sum of the signal values ​​of each CO isotope molecule-derived component (mass numbers 28, 29, 30, 31) is normalized before and after the recombination reaction (Equation (12)). At this time, since the same individual mass spectrometer is used, the leak rate is considered to be the same. Therefore, the amount of nitrogen detected in the pre-reaction measurement step S20 and the post-reaction measurement step S22 can be considered to be the same.

[0048]

number

[0049] Since the normalized total signal values ​​of the O-containing components are the same, equations (13) to (15) hold true.

[0050]

number

[0051] After the recombination reaction, equations (16) to (18) hold for each mass number.

[0052]

number

[0053] The signal values ​​of each isotope molecule after the recombination reaction obtained in the post-reaction measurement step S22 are used to solve the simultaneous equations (12) to (18), thereby determining the signal values ​​of each component before the recombination reaction. The ratio of each isotope molecule before the recombination reaction can be determined from the ratio.

[0054] (If NO) The signal value obtained in the pre-reaction measurement step S20 is I, and the signal value obtained in the post-reaction measurement step S22 is I sc Let us assume that. The sum of the signal values ​​of the components derived from each NO isotope molecule (mass numbers 30, 31, 32, and 33) is normalized before and after the recombination reaction (Equation (19)). In this case, as in the case of CO described above, since the mass spectrometer of the same individual is used, the amount of oxygen detected in the pre-reaction measurement step S20 and the post-reaction measurement step S22 can be considered to be the same.

[0055]

number

[0056] Since the total signal value is the same for each O isotope component, equations (20) to (22) hold true.

[0057]

number

[0058] After the recombination reaction, the total signal value is the same for each mass number, so equations (23) and (24) hold true.

[0059]

number

[0060] The signal values ​​of each isotope molecule after the recombination reaction obtained in the post-reaction measurement step S22 are used to solve the simultaneous equations (19) to (24), thereby determining the signal values ​​of each component before the recombination reaction. The ratio of each isotope molecule before the recombination reaction can be determined from the ratio. EXAMPLES

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples described below.

[0062] [Experimental Example 1] The CO isotope product produced by distillation was used as the measurement sample. In CO isotope ratio analysis, nitrogen interferes as a component with the same mass number. In CO isotope products produced by distillation, the amount of N2 mixed in is generally very small, but there is a possibility of interference from the N2 component due to the inclusion of air during analysis. For this reason, we used the experimental apparatus 1, the configuration of which is shown in Figure 3.

[0063] In the experimental apparatus 1 shown in Fig. 3, a mass spectrometer 11, a discharge device 12, a vacuum pump 13, a purge gas supply source 14, and a measurement target sample supply source 15 are connected to a piping system (sample introduction line) for introducing a measurement target sample, and opening and closing valves V1, V2, V3, and V4 are arranged on the line. The sample introduction line has a leak-tight structure using metal piping and metal joints. The mass spectrometer 11 is a quadrupole mass spectrometer. The discharge device 12 can use discharge to recombine isotopic atoms between isotopic molecules in the measurement sample supplied from the measurement sample supply source 15. That is, the experimental apparatus 1 can perform mass analysis of the measurement sample before the recombination reaction by turning off the discharge of the discharge device 12, and can perform mass analysis of the measurement sample after the recombination reaction by turning on the discharge. The purge gas source 14 is an Ar( 40Ar is 99.600%) and Ne( 20 The source of purge gas is argon (Ne 90.48%).

[0064] As a preliminary preparation for conducting an experiment using the experimental apparatus 1, the sample introduction line was replaced with a purge gas to thoroughly purge atmospheric components, and then the vacuum pump 13 was operated to create an approximate vacuum in the sample introduction line.

[0065] (1) Pre-reaction measurement process S20 The measurement sample was supplied from the measurement sample supply source 15 to the discharge device 12 with the discharge turned off, and the signal value of each isotope component was obtained for the measurement sample before the recombination reaction was carried out in the mass spectrometer 11. The peak height was used as the signal value. Table 3 shows the signal values ​​before the recombination reaction.

[0066] (2) Reaction step S21 A sample to be measured was supplied from a sample to be measured supply source 15 to discharge device 12 with the discharge turned on, and a recombination reaction of the sample to be measured was carried out.

[0067] (3) Post-reaction measurement process S22 The signal value of each isotope component was obtained for the measurement sample after the recombination reaction was carried out in the mass spectrometer 11. The peak height was used as the signal value. Table 3 shows the signal values ​​after the recombination reaction.

[0068] [Table 3]

[0069] (4) Atomic ratio calculation step S13 Based on the signal values ​​after the recombination reaction shown in Table 3, the isotope atomic ratios were calculated in the atomic ratio calculation step S13, and the results are shown in Table 4 (column "quadrupole mass spectrometer"). Table 4 also shows the results of measurement using a double-focusing mass spectrometer, which is a high-resolution mass spectrometer (column "double-focusing mass spectrometer").

[0070] [Table 4]

[0071] When the calculated isotope atomic composition was compared with the double focusing measurement results, it was confirmed that the difference was within ±0.1 atom%.

[0072] (5) Molecular ratio calculation step S23 Table 5 shows the results of calculating the molecular ratio in the molecular ratio calculation step S23 based on the signal values ​​before and after the recombination reaction shown in Table 3 (column "quadrupole mass spectrometer"). Table 5 also shows the measurement results using a double-focusing mass spectrometer, which is a high-resolution mass spectrometer (column "double-focusing mass spectrometer").

[0073] [Table 5]

[0074] When the calculated isotopic molecular composition was compared with the double focusing measurement results, it was confirmed that the difference was within ±0.2%.

[0075] (6) Summary According to the method for determining the atomic ratio of isotopes in a sample and the method for determining the molecular ratio of isotopes in a sample of the present invention, it is possible to quantify the isotopic molecular composition and isotopic atomic composition of CO isotopes having the same mass number without using a high-resolution mass spectrometer such as a double-focusing mass spectrometer or a multi-orbit mass spectrometer. This method is also applicable to NO isotopes. [Explanation of symbols]

[0076] 1. Experimental equipment 11 Mass spectrometer 12 Discharge device 13 Vacuum Pump 14 Purge gas supply source 15 Source of sample to be measured V1, V2, V3, V4 opening and closing valves

Claims

1. A reaction step of randomly recombining isotopic atoms between isotopic molecules in a sample; A measuring step of acquiring each isotope peak of the sample in which the isotope atoms have been recombined by the reaction step, using an analyzer capable of obtaining a signal for each mass-to-charge ratio; an atomic ratio calculation step of theoretically determining the isotope atomic ratio in the sample using the signal obtained in the measurement step; A method for determining an isotope atomic ratio in a sample, comprising:

2. a pre-reaction measurement step of acquiring each isotope peak of the sample before recombination of isotope atoms between isotope molecules using an analyzer capable of obtaining a signal for each mass-to-charge ratio; A reaction step of randomly recombining isotope atoms between isotope molecules in the sample; A post-reaction measurement step of acquiring each isotope peak of the sample in which the isotope atoms have been recombined by the reaction step using an analyzer capable of obtaining a signal for each mass-to-charge ratio; and A molecular ratio calculation step of theoretically determining the isotope molecular ratio in the sample before recombination of isotope atoms between the isotope molecules using the signals obtained in the pre-reaction measurement step and the post-reaction measurement step. A method for determining an isotopic molecular ratio in a sample, comprising:

3. 2. The method of claim 1, wherein the analytical device is a mass spectrometer.

4. 3. The method of claim 2, wherein the analytical device is a mass spectrometer.

5. 4. The method for determining an isotope atomic ratio in a sample according to claim 3, wherein the mass spectrometer is a quadrupole mass spectrometer.

6. 5. The method for determining an isotope ratio of a sample according to claim 4, wherein the mass spectrometer is a quadrupole mass spectrometer.

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