Quantitative analysis method and quantitative analysis apparatus

Abstract

(Problem) Provided are a quantitative analysis method and a quantitative analysis device that speed up calibration in mass spectrometry using a mass spectrometer, and that are less likely to be affected by a device state (fluctuations in sensitivity). (Solution) This quantitative analysis method using a mass spectrometer for a measurement target comprises: a gas introduction step for introducing, into a mass spectrometer, a mixture of a gas of the measurement target and a carrier gas that is different from the gas of the measurement target and that has at least two natural isotopes; a mass spectrometry step for performing mass spectrometry on the gas of the measurement target and the at least two natural isotopes in the carrier gas, using the mass spectrometer; and a gas concentration calculation step for calculating the concentration of the gas of the measurement target, using, as a calibration reference, an analysis value of the at least two natural isotopes in the carrier gas obtained in the mass spectrometry step.

Description

[Technical Field]

[0001] The present invention relates to a quantitative analysis method, and more particularly to a quantitative analysis method and quantitative analysis apparatus for quantitatively analyzing a target using two or more natural isotopes contained in a carrier gas as standards. [Background technology]

[0002] Quantitative analysis is used in various forms in industrial, medical, and biomedical fields, as well as chemical analysis. One typical example of quantitative analysis is mass spectrometry. Mass spectrometry focuses on the mass of a target substance, identifies the substance based on its mass difference, and quantifies it based on the detection intensity. More specifically, a mass spectrometer consists of a sample introduction unit, an ionization unit (ion source), a mass separation unit (analyzer), a detection unit (detector), a vacuum pump, and a device control / data processing unit (data system). During measurement, the introduced sample is ionized by the ion source to become ions present in the gas phase. Since ions have different kinetic properties depending on their mass / charge ratio (m / z), they are separated by the analyzer using various principles and detected by the detector. The analyzer and detector are maintained at a vacuum level that ensures a sufficient mean free path to prevent ions from colliding with other particles and impairing separation and detection. Alternatively, the target of measurement may be segmented using chromatography before introducing the sample into the mass spectrometer. Compared to other methods, mass spectrometry has the advantage of identifying and quantifying numerous gaseous components with high sensitivity in a single analysis. Furthermore, mass spectrometry can also be used to measure the concentration of the target substance.

[0003] Vacuum level significantly affects the measurement and detection sensitivity in mass spectrometry. Specifically, the ionization efficiency of the target substance, the attenuation of ions due to inevitable collisions with other charges during flight, and even the sensitivity of the detector itself can be affected by the vacuum level. Therefore, maintaining a certain level of vacuum is crucial to ensuring the instrument's condition, detection sensitivity, and quantitative accuracy.

[0004] Each time the mass spectrometer is started up, or even while it is running, the degree of vacuum may vary slightly. Therefore, in order to perform quantitative analysis of a sample using a mass spectrometer, it is common practice to prepare a standard sample each time the instrument is started up and create a calibration curve using this sample.

[0005] However, preparing such a standard sample involves certain costs, as well as time loss in creating a calibration curve using the standard sample. Furthermore, depending on the degree of change in the sensitivity of the mass spectrometer, it may be necessary to recreate the calibration curve frequently, presenting challenges.

[0006] In the past, various efforts have been made to improve the accuracy and reproducibility of mass spectrometry and to enhance work efficiency. For example, Patent Document 1 relates to a measurement method capable of measuring in real time the amount of unburned fuel in exhaust gas discharged from an internal combustion engine or the like using a mass spectrometry method. Specifically, by excluding non-volatile components in the exhaust gas to be measured and introducing only volatile components in the exhaust gas into a mass analyzer for analysis, the amount of unburned fuel in the exhaust gas is calculated from the results of on-line analysis of the mass spectrometry and the results of preliminary analysis of a sample of the fuel that generates the exhaust gas to be measured in advance. It is described that this method simplifies the analytical instrument and enables measurement during driving in an internal combustion engine mounted on an automobile.

[0007] Patent Document 2 relates to a highly accurate quantitative method using a mass spectrometry method. Specifically, it includes a step of calculating a quantitative value of a test substance for each of a plurality of internal standard substances based on a calibration curve and averaging the quantitative values to calculate a first quantitative value, a step of calculating a correction coefficient, and a step of correcting the first quantitative value with the correction coefficient to calculate a second quantitative value. The measurement for creating the calibration curve is performed using a chromatograph mass spectrometer tuned with a standard sample for the first time, and the measurement of the test sample is performed using a chromatograph mass spectrometer tuned with a standard sample for the second time. In the process of calculating the correction coefficient, the correction coefficient is calculated based on the signal intensity ratio between the test substance and the internal standard substance calculated from the first mass spectrum of the first tuning, and the signal intensity ratio between the test substance and the internal standard substance calculated from the second mass spectrum of the second tuning. It is stated that this method can correct for variations in the detection sensitivity of the analyzer and obtain highly accurate quantitative values.

[0008] Patent Document 3 relates to a method for creating calibration curves in gas mass spectrometry. It simplifies the creation of calibration curves in a mass spectrometer by utilizing known natural isotope ratios. For example, carbon monoxide (CO) has four isotopes with mass numbers 28, 29, 30, and 31, each consisting of a combination of carbon (C) and oxygen (O) isotopes. The relative abundance (concentration) of these four CO isotopes is calculated based on the isotopic abundance of C and O. These CO isotopes are used as standard gases at four different concentrations. This method allows for the creation of calibration curves without the need to prepare numerous standard samples at varying concentrations.

[0009] Incidentally, quantitative analysis is used in a wide range of fields, and as mentioned above, it is used in various forms in industrial fields, medical and life science fields, chemical analysis, etc. In particular, quantitative analysis of the components in metals is essential when manufacturing metal materials such as iron and steel, and for some iron and steel products, the components in the iron and steel must be listed on the mill sheet.

[0010] For the quantitative determination of nitrogen in iron and steel, several methods are specified in JIS G 1228:2006 (Non-Patent Literature 1), and among them, the inert gas fusion-thermal conductivity method is widely used because it offers high accuracy and reproducibility, and allows for analysis in a short time. In this method, the target iron and steel samples are placed in a graphite crucible and rapidly heated using an impulse furnace in an inert gas stream, vaporizing the nitrogen from the iron and steel, and the gaseous N2 (nitrogen) is quantitatively measured. In this process, helium (He) is used as the inert gas and is used directly as a carrier to the detector, allowing for highly sensitive measurement using a thermal conductivity detector (TCD) by utilizing the large difference in thermal conductivity between He and N2.

[0011] He is extremely important in the method described above. Industrially, He is produced as a by-product of LNG production, and its main production is limited to specific regions and countries. Furthermore, the price of He continues to rise, and the future outlook is uncertain.

[0012] Therefore, there is a need to develop quantitative analysis methods for components in metals that do not use helium (He). Compared to Helium, argon (Ar) is a candidate as an inexpensive inert gas that can be expected to have a stable supply. However, in the method disclosed in Non-Patent Document 1 mentioned above, in which gas components generated by heating in an impulse furnace are detected with a thermal conductivity analyzer, it was difficult to detect and quantify N2 because the thermal conductivity of N2 and Ar are similar. Patent Document 4 proposes a method for quantifying nitrogen in steel by emission spectrometry under an Ar atmosphere, while avoiding the use of He. More specifically, the method for analyzing nitrogen in a metal sample according to Patent Document 4 comprises a melting step in which a metal sample containing nitrogen components is melted by impulse heating under an argon gas atmosphere to vaporize the nitrogen components, and an analysis step in which the nitrogen gas generated from the melting step and the argon gas are analyzed by gas discharge emission spectrometry to quantify the nitrogen in the metal sample.

[0013] The method described in Patent Document 4 aims to quantify nitrogen in a metal, and separate analysis is required for the quantification of other components. Furthermore, in order to quantify nitrogen, operations such as oxidation and removal of other components (e.g., CO, CO2, H2, etc.) generated during the melting of the sample are necessary, but the oxidation catalysts, deCO2 removal agents, and dehydration agents used require replacement due to deterioration, and these operations are complex. Moreover, analysis using standard samples is essential for the calibration that forms the basis for the quantification of nitrogen, and the management of standard samples is necessary.

[0014] As described above, various studies have been conducted to improve mass spectrometry. However, Patent Document 1 only simplifies the analytical process for specific applications. Patent Document 2 contributes to improving analytical accuracy, but the process is more complex and requires longer analysis times. Patent Document 3 proposes the creation of a simple calibration curve by using isotopes for calibration, but the creation of the calibration curve must be performed separately from the measurement, as in the past. Furthermore, none of these documents offer any instruction or suggestion on how to avoid repeating the creation of calibration curves. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Japanese Patent Publication No. 2017-215275 [Patent Document 2] Japanese Patent Publication No. 2014-235088 [Patent Document 3] Japanese Patent Publication No. 2000-065797 [Patent Document 4] Patent No. 5846344 [Non-patent literature]

[0016] [Non-Patent Document 1] JIS G 1228:2006 [Overview of the project] [Problems that the invention aims to solve]

[0017] Mass spectrometers are generally highly sensitive and widely used. However, sensitivity can easily fluctuate due to factors such as the vacuum level of the vacuum chamber, requiring frequent calibration curve creation to achieve sufficient accuracy and reproducibility.

[0018] The present invention has been made in view of the above, and its objective is to provide a quantitative analysis method that accelerates calibration and is less affected by the condition of the instrument (sensitivity fluctuations) in mass spectrometry using a mass spectrometer.

[0019] Furthermore, one aspect of the present invention provides a method and apparatus that enable quantitative analysis of a target substance in a sample without being limited to nitrogen and without using helium. [Means for solving the problem]

[0020] The inventors conceived of a process control analysis method that can be used at any time without being affected by sensitivity fluctuations of the mass spectrometer, by using the carrier gas itself, which flows through the vacuum chamber at a predetermined flow rate, as the basis for the quantitative value.

[0021] The inventors of this invention have identified the following key points of this idea. Carrier gases are usually at a higher concentration than the gas to be measured, thus exceeding the concentration range to be measured. However, by using the natural isotopes of the carrier gas contained in the carrier gas as the target of mass spectrometry and using those natural isotopes as the calibration standard, internal standard calibration is possible.

[0022] For example, if the gas to be measured is N2 and Ar gas is used as the carrier gas, then the majority of the Ar gas will be 40 Ar acts as the carrier gas, and isotopes 36 Ar, and 38 Ar can be used to create calibration curves. 36 Ar, and 38The concentrations (abundance ratios) of Ar are 3365 ppm and 652 ppm, respectively, which are constant concentrations. Therefore, during the continuous measurement of the gas to be measured using Ar gas as the carrier gas, 36 Ar, and 38 by analyzing Ar, calibration curves for them can be continuously obtained. Therefore, even if sensitivity fluctuations occur, N2 in the gas to be measured can be continuously mass-analyzed with high accuracy and reproducibility.

[0023] Note that since the ionization potentials of N2 and Ar are almost the same (N2: 15.56 eV and Ar: 15.76 eV), without adjustment by a correction factor, 36 Ar, and 38 the N2 concentration can be determined from the calibration curves of Ar. (When the ionization potential is different between the carrier gas and the gas to be measured, the gas concentration to be measured can be determined by experimentally obtaining a correction factor in advance.)

[0024] Furthermore, the inventors of the present invention came to apply the above idea to a sample containing a metal. An example thereof is a quantitative analysis method that replaces the conventional inert gas fusion - thermal conductivity method. Generally, the quantitative analysis method includes melting a sample in an inert atmosphere such as Ar without using He, extracting the gas to be measured from the sample, transporting the extracted gas to a mass spectrometer, and quantitatively analyzing the measurement target (for example, nitrogen, oxygen, hydrogen, etc.) in the sample with an analyzer.

[0025] The inert gas such as Ar for melting the aforementioned sample can also be used as the carrier gas flowing through the mass spectrometer, and isotopes of the carrier gas (argon, etc.) can be used as the reference for calibration. Thereby, a process management analysis method that is not easily affected by sensitivity fluctuations of the mass spectrometer and can be used at all times can be provided.

[0026] The present invention is based on the above findings, and the following aspects are provided. [1] A quantitative analysis method for a measurement target using a mass spectrometer, comprising: A gas introduction step involves mixing the gas to be measured with a carrier gas that is different from the gas to be measured and has two or more natural isotopes, and introducing the mixture into a mass spectrometer. The mass spectrometry step involves using the aforementioned mass spectrometer to perform mass spectrometry on the gas to be measured and two or more native isotopes in the carrier gas. A gas concentration calculation step, which calculates the concentration of the gas to be measured using the analytical values ​​of two or more natural isotopes of the carrier gas obtained by the mass spectrometry step as a calibration standard, A quantitative analysis method for large objects. [2] The quantitative analysis method according to [1], wherein the carrier gas comprises at least one of Ar, N2, O2, or a mixture thereof. [3] A quantitative analysis method according to [1] or [2], comprising an extraction step of heating and melting a sample containing the target to be measured in the atmosphere of the carrier gas, and extracting the gas of the target to be measured from the sample. [4] The aforementioned sample contains 80% by mass or more of metal [3]. Quantitative analysis method as described above. [5] A quantitative analysis method according to any one of [1] to [4], comprising a gas quantity calculation step of calculating the amount of the gas to be measured by multiplying the concentration of the gas to be measured by the flow rate of the carrier gas that flowed during the time when the concentration was detected. [6] The quantitative analysis method according to [5], wherein in the gas quantity calculation step, the time in which the concentration of the gas to be measured is detected is subdivided, the amount of the gas to be measured Ci (i=1,2,...n; n is the number of subdivided sections) is calculated for each subdivided section, and the sum of the Ci is calculated as the amount of the gas to be measured. [7] Two or more natural isotopes in the carrier gas are 36 Ar and 38 The quantitative analysis method described in any one of the following items [1] to [6], wherein the result is Ar. [8] The quantitative analysis method according to any one of [1] to [7], wherein the object to be measured is one or more of nitrogen, carbon, oxygen, and hydrogen. [9] The quantitative analysis method according to any one of the following [1] to [8], wherein the mass spectrometer has a resolution capable of separately detecting the mass number of nitrogen gas 28.006 and the mass number of carbon monoxide gas 27.995.

[10] A quantitative analysis method according to any one of [1] to [9], wherein a correction coefficient used to calculate the concentration of the gas to be measured is determined by pre-mass spectrometry of the gas to be measured and the carrier gas, whose concentrations are known, using the mass spectrometer.

[11] A gas introduction function unit that mixes the gas to be measured with a carrier gas that is different from the gas to be measured and has two or more natural isotopes, and introduces the mixture into a mass spectrometer. The mass spectrometer is equipped with a mass spectrometry function unit that performs mass spectrometry on the gas to be measured and two or more natural isotopes in the carrier gas, A gas concentration calculation function unit calculates the concentration of the target gas using the analytical values ​​of two or more natural isotopes of the carrier gas obtained by the mass spectrometry function unit as a calibration standard, A quantitative analyzer having the following features.

[12] A sample containing the object to be measured is heated and melted in the atmosphere of the carrier gas, and the object to be measured is converted into a gas from the sample in a vaporization function unit. A quantitative analyzer according to

[11] , having the following features.

[13] A gas concentration calculation function calculates the concentration of the target gas using the signal intensity of the target gas measured by the mass spectrometry function and the signal intensity of two or more natural isotopes in the carrier gas. A quantitative analyzer according to

[11] or

[12] , having the following:

[14] The aforementioned mass spectrometry unit is A quantitative analyzer according to any one of the following

[11] -

[13] , having a resolution capable of separately detecting nitrogen gas with a mass number of 28.006 and carbon monoxide gas with a mass number of 27.995.

[15] A quantitative analyzer according to any one of

[11] to

[14] or

[12] , further comprising a chromatographic function unit capable of separating the gas to be measured from other gases. [Effects of the Invention]

[0027] According to one embodiment of the present invention, a mass spectrometry method is provided that allows for rapid calibration and is less susceptible to the effects of instrument conditions (sensitivity fluctuations) in mass spectrometry using a mass spectrometer, particularly in continuous process control. Specifically, it is possible to omit the creation of calibration curves using standard gases, thereby reducing the costs required for analysis, especially the time loss. In addition, since it is less susceptible to sensitivity fluctuations due to changes in vacuum levels, analytical results with high accuracy and reproducibility can be obtained. Furthermore, this mass spectrometry method can also be applied to continuous process control, and naturally, analytical results with high accuracy and reproducibility can be obtained in that case as well. Furthermore, the accuracy and reproducibility in the analysis can be appropriately selected according to the desired degree and the constraints of the analytical instrument used. With respect to embodiments of the present invention, high accuracy may be within several tens of percent, typically within ±30%, ±25%, ±20%, ±19%, ±18%, ±17%, ±16%, ±15%, ±14%, ±10%, ±5%, ±3%, ±2%, or ±1% relative to the assumed quantitative value (theoretical calculation value) or reference quantitative value. Alternatively, when the concentration is low, for example, around several tens of ppm or less, it may be within several tens of ppm, typically within ±90 ppm, ±80 ppm, ±70 ppm, ±60 ppm, ±40 ppm, ±30 ppm, ±20 ppm, or ±10 ppm relative to the assumed quantitative value (theoretical calculation value) or reference quantitative value. Furthermore, with respect to embodiments of the present invention, high reproducibility may refer to a parallel tolerance equivalent to that of the inert gas fusion-thermal conductivity method specified in Non-Patent Literature 1, particularly Annex 5. The parallel tolerance is the difference in quantitative values ​​when one analyst performs experiments in the shortest possible time using the same equipment, the same conditions, and the same calibration curve. Typically, for standard concentrations of standard substances (samples) of 8 ppm to 5000 ppm, the parallel tolerance is approximately 2 ppm to 550 ppm (see Non-Patent Literature 1, particularly Annex 5). Alternatively, high reproducibility may refer to a relative standard deviation of several tens of percent, typically within ±20%, ±15%, ±12%, ±10%, ±8%, ±6%, ±5%, ±4%, ±3%, ±2%, or ±1%. Furthermore, according to one embodiment of the present invention, a method and apparatus are provided that enable quantitative analysis of a target to be measured in a sample that does not use helium and whose quantitative target component is not limited to nitrogen, and which may also contain metals or the like. In other words, while conventional inert gas fusion-thermal conduction methods use expensive helium (He), one embodiment of the present invention can use inert gases such as argon (Ar), which are cheaper and more stably supplied than helium. This is because this embodiment uses mass spectrometry, and a common type of inert gas can be used as the carrier gas. Furthermore, such an inert carrier gas does not fundamentally affect the sensitivity fluctuations of the mass spectrometry. Furthermore, the carrier gas supplied to the mass spectrometer can also be used as an inert gas to melt the sample. Furthermore, in one embodiment of the present invention, high-resolution mass spectrometry can be used, making it possible to analyze multiple measurement targets independently without pre-treating the gas vaporized from the sample. This eliminates the need to prepare and replace various pre-treatment components, chemicals, etc., resulting in lower costs, simplicity, and avoidance of a decrease in measurement accuracy due to the deterioration of these components. Furthermore, in one embodiment of the present invention, the carrier gas is Ar. The ionization rate of Ar is extremely stable. Therefore, by referring to and using as a standard value the measured value of the argon gas isotope, which is the carrier, it is possible to determine the concentration of the target component to be quantified in the sample gas. This eliminates the need for calibration using standard samples. In particular, when the target of measurement also has a stable ionization rate, mass spectrometry can be suitably performed, which is preferable. In other words, N2 and the like, which have a stable ionization rate, are preferred targets of measurement. Also, since CO and H2O, which are classified as inorganic gases, have stable ionization rates, they can be similarly quantitatively analyzed by correcting for differences in ionization energy. In addition, in one embodiment of the present invention, when performing quantitative analysis, the time for measuring the target substance is subdivided, the amount of the target substance Ci is calculated for each subdivided measurement interval, and the sum of each Ci is calculated as the total amount of the target substance. This makes it possible to perform quantitative analysis with even greater reproducibility (in other words, with less variability in measurement results). [Brief explanation of the drawing]

[0028] [Figure 1] This diagram schematically represents quantitative analysis using a conventional calibration curve. [Figure 2]This figure shows the results of mass spectrometry analysis of the gas being measured, performed according to an embodiment of the present invention. [Figure 3] This figure schematically represents the quantitative analysis performed over time according to an embodiment of the present invention. [Figure 4] A chart showing the comparison results between the conventional technology and the present invention is provided. [Figure 5] Figure 5 is a schematic diagram showing the general layout of the analytical apparatus. [Figure 6] Figure 6 shows an example of a high-resolution mass spectrometry spectrum in which the CO and N2 peaks have been separated. [Figure 7] Figure 7 shows an example of N2, 36Ar, and 38Ar measurements obtained using a high-resolution mass spectrometer. [Figure 8] Figure 8 shows the nitrogen analysis results according to an example of the present invention. [Figure 9] Figure 9 shows an example of a mass spectrum. [Figure 10] Figure 10 shows an example of a mass spectrometry spectrum obtained using chromatography. [Figure 11] Figure 11 shows a schematic configuration of a quantitative analyzer according to one embodiment of the present invention. [Modes for carrying out the invention]

[0029] The following describes in detail a mass spectrometry method according to one embodiment of the present invention. One embodiment of the present invention is a mass spectrometry method, which is a quantitative analysis method of a target to be measured using a mass spectrometer.

[0030] A mass spectrometer is a device that focuses on the mass of a gas to be measured, identifies the gas based on its mass difference, and quantifies it based on its detection intensity. Generally, a mass spectrometer consists of an introduction section for the gas to be measured, an ionization section (ion source), a mass separation section (analyzer), a detection section (detector), a vacuum pump, and a device control / data processing section (data system). During measurement, the introduced gas to be measured is ionized by the ion source to become ions present in the gas phase. Since ions have different kinetic properties depending on their mass / charge ratio (m / z), they are separated by the analyzer using various principles and detected by the detector. The analyzer and detector are maintained at a vacuum level that ensures a sufficient mean free path so that ions do not collide with other particles and impair the separation and detection.

[0031] In mass spectrometry, calibration curves are generally used. Specifically, a calibration curve is created in advance using standard samples of known concentrations, and the target substance in an unknown sample is quantified. Figure 1 schematically represents quantification using a conventional calibration curve. The calibration curves differ across three measurement days (Day X, Y, Z), even though the same standard samples are used. This is thought to be because the vacuum level of the instrument fluctuates depending on the measurement day, affecting the instrument's sensitivity. Therefore, it is necessary to create a calibration curve using standard samples (at point ○) each time a measurement is performed, and to quantify the measured value of the unknown sample (◇). Furthermore, even if there are fluctuations in the vacuum level of the mass spectrometer and the resulting fluctuations in instrument sensitivity after the calibration curve has been created, these fluctuations cannot be compensated for, and the accuracy and reproducibility of the quantification may not be sufficient.

[0032] A mass spectrometry method according to one embodiment of the present invention is a quantitative analysis method for a target to be measured using a mass spectrometer, A gas introduction step involves mixing the gas to be measured with a carrier gas that is different from the gas to be measured and has two or more natural isotopes, and introducing the mixture into a mass spectrometer. The mass spectrometry step involves using the aforementioned mass spectrometer to perform mass spectrometry on the gas to be measured and two or more native isotopes in the carrier gas. A gas concentration calculation step, in which the concentration of the gas to be measured is calculated using the analytical values ​​of two or more natural isotopes of the carrier gas obtained by the mass spectrometry step as a calibration standard, It has.

[0033] Figure 2 shows an example of mass spectrometry results of a gas to be measured according to an embodiment of the present invention. More specifically, it shows the mass spectrometry results when N2, the gas to be measured, and Ar, a carrier gas having two or more natural isotopes different from the gas to be measured, are mixed and introduced into a mass spectrometer, and the N2, the gas to be measured, and the two or more natural isotopes of Ar in the carrier gas are quantified. The majority of the Ar in the carrier gas is 40 It is dominated by Ar and is an isotope. 36 Ar, and 38 It contains Ar. These isotopes can be used to create calibration curves. 36 Ar, and 38 The concentrations of Ar are constant, at 3365 ppm and 652 ppm, according to the isotopic abundance. A calibration curve is created by relating these known concentrations to the signal intensity (count) of the mass spectrum obtained by a mass spectrometer. Using this calibration curve, the concentration of the target gas, N2, is calculated from the intensity (count) of its mass spectrum. As a result, the concentration of N2 is quantified.

[0034] Furthermore, the carrier gas is continuously flowing during the measurement, making it possible to continuously obtain a calibration curve. Figure 3 schematically represents quantitative analysis performed over time according to an embodiment of the present invention. It schematically represents quantitative analysis performed on different days using the same sample. The detection sensitivity of the mass spectrometer may fluctuate over time. The signal intensity (count) of the mass spectrum of the natural isotopes in the carrier gas also fluctuates in accordance with the fluctuations in the detection sensitivity of the mass spectrometer. However, in the embodiment of the present invention, the natural isotopes in the carrier gas are continuously flowing, allowing for real-time updates of the calibration curve. Quantitative analysis can always be performed using the latest calibration curve. Therefore, highly reproducible quantitative analysis that is less affected by fluctuations in the sensitivity of the mass spectrometer is possible. Furthermore, according to the embodiment of the present invention, it is possible to omit the creation of a calibration curve using standard gases, which is performed in advance for each mass spectrometry analysis.

[0035] In one embodiment of the present invention, if the carrier gas is different from the gas to be measured and has two or more natural isotopes, then those two or more natural isotopes can be used as standard gases for mass spectrometry. However, since it is used as a carrier gas, it is preferable that it is readily available and low cost. In this respect, the carrier gas may be at least one of Ar, N2, and O2, or may contain a mixture thereof. This embodiment does not require the use of helium as a carrier gas, which is also a major advantage. Typically, two or more natural isotopes are 36 Ar and 38 Ar may be included. If more than two natural isotopes are present, three or more natural isotopes may be used as standard gases for mass spectrometry. This can improve the accuracy and reproducibility of the mass spectrometry. Here, the calibration curve can be obtained by appropriate fitting, such as a straight line obtained by the least squares method passing through the origin at 0% concentration. Such a process may be called the mass spectrometry process.

[0036] One embodiment of the present invention may include an extraction step in which a sample containing the object to be measured is heated and melted in an atmosphere of a carrier gas, and the gas of the object to be measured is extracted from the sample. In this embodiment, the carrier gas may be an inert gas. This is to avoid the object to be measured contained in the sample undergoing oxidation or other reactions when the sample is heated and melted. From this viewpoint, nitrogen, argon, etc. may be used as the inert carrier gas. With this embodiment, the extraction of the object to be measured from the sample and the analysis of the object to be measured using a mass spectrometer can be performed continuously. This is also applicable to continuous process control and is therefore preferable.

[0037] The sample containing the target substance is heated and melted under a carrier gas atmosphere, thereby vaporizing and extracting the target substance contained in the sample. For example, nitrogen, carbon, oxygen, and hydrogen in the sample vaporize as nitrogen gas, carbon monoxide gas, carbon dioxide gas, oxygen gas, and hydrogen gas, respectively. Generally, when a graphite crucible is used for heating, oxygen gas reacts with carbon to form carbon monoxide. In this specification, the generation of gas as a result of a reaction is also broadly defined as "vaporization."

[0038] An impulse furnace may be used as a means of heating and melting the sample. Typically, an impulse furnace is equipped with a crucible made of graphite or the like and electrodes for holding and heating the crucible. By placing the sample in the crucible and applying an electric current to the electrodes, the sample in the crucible is rapidly heated and melted, and the target substance to be measured contained in the sample can be vaporized. A carrier gas supply line may be provided to create a carrier gas atmosphere inside the impulse furnace, particularly around the sample.

[0039] The gas extracted from the sample is introduced into the mass spectrometer along with a carrier gas stream. This process may also be called the gas introduction process. The carrier gas stream introduced into the mass spectrometer may be the carrier gas used in the extraction process, supplied separately, or a mixture of both. A pressure regulator may be installed between the extraction process function unit or vaporization function unit (e.g., an impulse furnace) that performs the extraction process and the mass spectrometer to control the flow rates of the extracted target gas and the carrier gas stream by the pressure difference. A flow meter may also be installed to monitor the flow rate, and adjustment control may be performed by the pressure regulator according to the measured flow rate. Furthermore, a dust filter may be installed upstream of the pressure regulator or mass spectrometer. The dust filter can remove dust generated in the extraction process or vaporization process (e.g., an impulse furnace) and protect downstream equipment (pressure regulator or mass spectrometer, etc.). As the dust filter, a filter with good permeability, such as one made of silica fiber or polytetrafluoroethylene, can be used.

[0040] The sample is not particularly limited as long as it contains the substance to be measured and the substance to be measured can be extracted by heating and melting. The sample may contain metals. Typically, the sample may contain 80% or more by mass of metals. Note that metals refer to elements located to the lower left of the diagonal line connecting boron (B) and astatine (At) in the periodic table. In other words, metals are elemental symbols: B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, A. s, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Pm, S m, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, At, F It may include r, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, and Hs. In reality, the sample may contain various (non-metallic) components such as nitrogen, carbon, oxygen, and hydrogen, in addition to metallic components such as matrix metals and other alloying elements, and these may also be the targets of measurement. Typical examples of samples may include reduced iron, metal samples, steel samples, alloy samples, etc.

[0041] A quantitative analysis according to one embodiment of the present invention can calculate the concentration of the gas to be measured. Such a process may be called a gas concentration calculation process. Based on this, the amount of the gas to be measured transported by the carrier gas can also be calculated. That is, the amount of the gas to be measured can be calculated by multiplying the concentration of the gas to be measured by the flow rate of the carrier gas that flowed at the time the concentration was detected. This process may be called a gas quantity calculation process. The amount of the gas to be measured in the sample can also be calculated. The amount of gas may be converted to volume, or to mass, etc.

[0042] In the gas quantity calculation process, the time period during which the concentration of the gas to be measured is detected may be subdivided, and the amount of the gas to be measured, Ci (i=1,2,...n; n is the number of subdivided sections) may be calculated for each subdivided section, and the sum of Ci may be calculated as the amount of the gas to be measured.

[0043] The subdivided intervals may be determined according to the measurement frequency (measurement interval) of the mass spectrometer. This makes it possible to calculate the volume of the target gas from its concentration and measurement frequency (measurement interval). Typically, the volume of the target gas at each measurement interval (the interval from one measurement point to the next) is calculated by multiplying the concentration of the target gas measured at a certain measurement timing in the mass spectrometer by the carrier gas flow rate that flowed in the interval (in other words, the measurement interval) from that measurement timing (measurement point) to the next measurement timing (measurement point), and these are then accumulated. More specifically, the mass spectrometer may perform measurements (or acquire signal intensity) at a measurement frequency of about 10 to 1200 times / min., and for each measurement timing (measurement point), the calibration curve for natural isotopes may be updated using the signal intensity obtained at that measurement timing (measurement point), the concentration of the target gas may be calculated, and consequently, the amount of the target gas Ci at each measurement interval (the interval from one measurement point to the next) may be determined. The sum of the amounts of the target gas Ci measured at each measurement timing (measurement point) corresponds to the amount of the target gas in the sample.

[0044] This subdivision further improves the accuracy and reproducibility of quantitative analysis. For example, compared to using an isotope calibration curve obtained a few seconds before the target gas begins to be detected, the quantitative analysis results obtained through subdivision can be more accurate and reproducible. In other words, quantitative analysis results with less variability can be obtained.

[0045] The carrier gas flow rate and the measurement frequency (measurement interval) of the mass spectrometer are not particularly limited. Generally, the more measurements (measurement points) of isotopes and target components per unit time, in other words, the higher the measurement frequency and the shorter the measurement interval, the smaller the variability in the quantitative analysis results. Therefore, the number of measurements (measurement points) may be increased. In other words, the measurement frequency may be increased (the measurement interval may be shortened), and depending on the accuracy required for quantification, the typical measurement frequency within the range of 10 to 1200 times / min. may be selected. Furthermore, the carrier gas flow rate may be appropriately selected according to the operating conditions of the mass spectrometer, and is typically selected within the range of 10 to 10000 mL / min.

[0046] In one embodiment, the target of measurement may be one or more of nitrogen, carbon, oxygen, and hydrogen. Compared to other methods (e.g., inert gas fusion-thermal conductivity method), mass spectrometry has the advantage of identifying a large number of gas components in a single analysis (measurement) and quantifying them with high accuracy. Therefore, the target of measurement is not limited to nitrogen, but may be one or more of nitrogen, carbon, oxygen, and hydrogen. Typically, it is also possible to quantify nitrogen and other components, such as carbon monoxide, simultaneously.

[0047] In one embodiment, the mass spectrometer may have a resolution capable of separating and detecting the mass number of nitrogen gas (28.006) and carbon monoxide gas (27.995). The theoretically required resolution for CO and N2 is R = 27.995 / (28.006 - 27.995) = 2545, but a higher resolution is desirable in practice. On the other hand, sufficient accuracy can be obtained with a resolution of R = 25000 or less in relation to sensitivity, so typically, a resolution of R = 20000 is acceptable. This allows the mass spectrometer to separate nitrogen gas and carbon monoxide gas and obtain quantitative results with sufficient accuracy. In other words, separation of nitrogen gas and carbon monoxide gas is unnecessary in the pre-analysis step using the mass spectrometer, which simplifies the analysis procedure and enables analysis at a lower cost, making it preferable. Furthermore, if nitrogen gas and carbon monoxide gas are separated in the pre-processing step before quantitative analysis using a mass spectrometer, or if the oxygen content in the sample is low and there is no influence from carbon monoxide, i.e., if it does not affect the measurement of the signal intensity of nitrogen gas with a mass number of 28.006, a mass spectrometer without the above resolution may be used.

[0048] Regarding mass spectrometry, the following corrections may be made. In mass spectrometry, it is essential to ionize the introduced sample using an ion source to convert it into ions present in the gas phase. Here, the ionization potential differs depending on the substance. Therefore, if the ionization potentials of the gas to be measured and the standard gas (two or more natural isotopes) are equivalent, they can be efficiently ionized with a single ion source. In other words, there is no need to correct the quantitative value of the gas to be measured obtained from the calibration curve of the standard gas. However, if the ionization potentials of the gas to be measured and the standard gas (two or more natural isotopes) differ and affect the accuracy of the quantitative value, a correction factor to correct the quantitative value may be experimentally determined. By using this correction factor, the accuracy of the quantitative determination of the gas to be measured can be improved. Typically, the known concentrations of the gas to be measured and the carrier gas can be quantitatively analyzed in advance, and the ratio of the known concentration to the measured quantitative value can be used as the correction factor. Also, if the carrier gas is a mixed gas, it is preferable to use a gas with equivalent ionization potential and no correction factor as the standard gas. However, depending on the concentration of the gas being measured, a correction factor may be required for some gases, or multiple gases may be used as standard gases. Note that nitrogen has almost the same ionization potential as argon (N2: 15.56 eV and Ar: 15.76 eV), so no adjustment with a correction factor is necessary. 36 Ar, and 38 The N2 concentration can be determined from the Ar calibration curve. In other words, nitrogen and argon are examples of preferred combinations of analytes and carrier gases.

[0049] According to one embodiment of the present invention, a quantitative analyzer (110) is provided. The quantitative analyzer (110) is, An introduction function unit (111) mixes the gas to be measured with a carrier gas that is different from the gas to be measured and has two or more natural isotopes, and introduces the mixture into a mass spectrometer (112), The mass spectrometer (112) is equipped with a mass spectrometry function unit (112-1) that performs mass spectrometry on the gas to be measured and two or more native isotopes in the carrier gas, A gas concentration calculation function (113) calculates the concentration of the target gas using the analytical values ​​of two or more natural isotopes of the carrier gas obtained by the mass spectrometry function (112-1) as a calibration standard, It has. Figure 11 shows a schematic configuration of the quantitative analyzer (110) of this embodiment. The dashed blocks in Figure 11 indicate optional additional components.

[0050] According to this apparatus, the quantitative analysis method, which is one embodiment of the present invention as described above, can be appropriately carried out.

[0051] In one embodiment, the quantitative analyzer (110) may be equipped with a vaporization function unit (121) that heats and melts a sample containing the target to be measured in a carrier gas atmosphere, thereby converting the target to be measured into a gas from the sample. This embodiment allows for continuous operation from vaporization or extraction of the target to be measured by a mass spectrometer (112). This is also applicable to continuous process control and is therefore preferable.

[0052] In one embodiment, the quantitative analyzer (110) may be equipped with a gas concentration calculation function unit (113) that calculates the concentration of the target gas using the signal intensity of the target gas measured by the mass spectrometry function unit (112-1) and the signal intensity of two or more natural isotopes in the carrier gas. The gas concentration calculation function unit (113) may be composed of a computer that performs calculation processing. This embodiment illustrates a typical calculation procedure within the mass spectrometer (110). The mass spectrometry unit (112-1) measures the signal intensity of the target substance and the signal intensity of two or more natural isotopes in the carrier gas. The gas concentration calculation unit (113) uses the signal intensity measured by the mass spectrometry unit (112-1) to calculate the concentration of the target gas.

[0053] In one embodiment, the mass spectrometry unit (112-1) may have a resolution capable of separating and detecting nitrogen gas with a mass number of 28.006 and carbon monoxide gas with a mass number of 27.995. The theoretically required resolution for CO and N2 is R = 27.995 / (28.006 - 27.995) = 2545, but a higher resolution is desirable in practice. On the other hand, sufficient accuracy can be obtained with a resolution of R = 25000 or less in relation to sensitivity, so typically, a resolution of R = 20000 may be sufficient. This allows the mass spectrometry unit (112-1) to separate nitrogen gas and carbon monoxide gas and obtain quantitative results with sufficient accuracy. In other words, separation of nitrogen gas and carbon monoxide gas is unnecessary in the pre-analysis step by the mass spectrometry unit (112-1), which simplifies the analysis procedure and enables analysis at a lower cost, which is preferable. Furthermore, if nitrogen gas and carbon monoxide gas are separated in the pre-processing step before quantitative analysis by the mass spectrometry unit (112-1), or if the oxygen content in the sample is low and there is no influence from carbon monoxide, i.e., if it does not affect the measurement of the signal intensity of nitrogen gas with a mass number of 28.006, then a mass spectrometry unit (112-1) without the above resolution may be used.

[0054] In another embodiment, the mass spectrometer (110) may have a chromatographic function unit (131) capable of separating the gas to be measured from other gases. Before introducing the gas to be measured into the mass spectrometer (112), the gas to be measured may be segmented through chromatography. This can further improve the accuracy of quantitative analysis. The configuration of the chromatographic function unit (131) may be appropriately selected or adjusted depending on the gas to be separated. In a typical example, a chromatograph capable of separating carbon monoxide and nitrogen over time may be used. This allows nitrogen gas and carbon monoxide gas, which have similar mass numbers, to be separated before being introduced into the mass spectrometer (112). As a result, the two gases can be distinguished, and highly accurate quantitative results can be obtained for each. The quantitative analysis results according to this embodiment are in close agreement with the quantitative analysis results obtained by wet chemical analysis. On the other hand, the quantitative analysis results by the inert gas fusion-thermal conductivity method show some differences from the quantitative analysis results obtained by wet chemical analysis. In this respect, quantitative analysis using this embodiment can have higher accuracy than the inert gas fusion-thermal conductivity method. [Examples]

[0055] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the examples.

[0056] [Example I] (Example I-1) Carrier gas: Ar, Gas to be measured: N2 Quantitative analysis of Ar gas as the carrier gas and N2 gas as the target gas was performed using an MSI-TOKYO high-resolution mass spectrometer (HV-infiTOF). The following three methods were then compared. (1) Create a calibration curve each time (conventional technique) (2) Continue using the calibration curve created at the start of the test (conventional technology) (3) Quantitative determination based on the natural isotope ratio of the carrier gas (Ar gas) (Example of the present invention) To a carrier gas of Ar gas at a rate of 1000 ml / min, N2 gas was mixed to a concentration in the range of 600-700 ppm, and the N2 concentration was analyzed weekly. Figure 4 shows the results of a comparison between the conventional technique (Methods (1) and (2)) and the present invention (Method (3)). The calibration curves used in methods (1) and (2) were created by measuring mixed gases of Ar gas and N2 gas with different N2 concentrations (N2 concentrations: 100 ppm, 800 ppm, and 1500 ppm) using a high-resolution mass spectrometer, and combining the N2 concentrations with the analytical values ​​obtained from the mass spectrometer. In this study, the calibration curve creation process took approximately two hours. When the calibration curve was created each time a measurement was taken, the maximum and minimum errors (difference between the maximum and minimum values) were approximately 20 ppm (Method (1)). When the calibration curve created initially was used continuously, large discrepancies occurred in the measured values, and the maximum and minimum errors sometimes exceeded 100 ppm (Method (2)). In this example, the measurement was performed simultaneously with the measurement of N2 gas. 36 Ar and 38 Assuming that Ar has natural isotope ratios of 3365 ppm and 632 ppm, the N2 concentration was calculated using Equation 1 (Method (3)). N2 concentration (ppm) =N2 peak intensity ×(3365ppm-632ppm) / ( 36 Ar peak intensity - 38 Ar peak intensity) ... (Equation 1) In this invention, the maximum and minimum error was approximately 20 ppm, demonstrating quantitative accuracy equivalent to method (1). On the other hand, in this example, since no work of circulating a standard gas for calibration is required, no time loss occurred.

[0057] (Example I-2) Carrier gas: Ar, Gases to be measured: O2, CO, CO2 We investigated the analysis when the carrier gas was Ar gas and the target gases were O2, CO, and CO2 gases. For every 1000 ml / min of carrier gas, we mixed in an introduction gas containing O2, CO, and CO2 (a mixture of air (O2 concentration 20.9%) with CO at a concentration of 1000 ppm and CO2 at a concentration of 2000 ppm) at seven levels: 250, 200, 150, 100, 50, 30, and 15 ml / min for analysis. The natural isotopes of the carrier gas used for calibration were as follows: 36 Ar, 38 The Ar peak was used. From the natural isotope ratios... 36 Ar, 38 Ar concentrations were set to 3365 ppm and 632 ppm, and the concentrations of various gases were calculated using Equation 2. The results are shown in Table 1. It was confirmed that the analytical values ​​were obtained with high accuracy even when different gases were mixed in the gas being measured. Concentration of the gas being measured (ppm) = Peak intensity of the gas being measured ×(3365ppm-632ppm) / ( 36 Ar peak intensity - 38 Ar peak intensity) ... (Equation 2)

[0058] [Table 1]

[0059] (Example I-3) Carrier gas: O2, Gas to be measured: Ar We investigated the analysis when the carrier gas was O2 gas and the target gas was Ar gas. For every 1000 ml / min of carrier gas, an Ar-containing introduction gas (Ar: 1.0%, N2: 99.0%) was mixed at seven levels: 10.0, 8.0, 6.0, 4.0, 2.0, 1.0, and 0.5 ml / min, and analyzed. The natural isotopes in the carrier gas used for calibration showed appropriate peak intensities. 17 O 16 O, and 18 O 16 The O peak was used. From the natural isotope ratios... 17 O16 O, and 18 O 16 The concentrations of O were set to 380 ppm and 2046 ppm, and the concentration of Ar was determined using Equation 3. The results are shown in Table 2. It was confirmed that analytical values ​​were shown for the mixed concentrations with the same accuracy as in Examples I-1 and I-2. Ar concentration (ppm) = Gas peak intensity of the target to be measured ×(2046ppm-380ppm) / ( 18 O 16 O-peak intensity - 17 O 16 O-peak intensity) ... (Equation 3)

[0060] [Table 2]

[0061] (Example I-4) Carrier gas: N2, Gas to be measured: Ar We investigated the analysis when N2 was used as the carrier gas and Ar gas was used as the target gas. For every 1000 ml / min of carrier gas, an Ar-containing introduction gas (Ar: 1.0%, N2: 99.0%) was mixed at seven levels: 10.0, 8.0, 6.0, 4.0, 2.0, 1.0, and 0.5 ml / min, and analyzed. The natural isotopes in the carrier gas used for calibration showed appropriate peak intensities. 15 N 14 The peak of N was used. In this experiment, 15 N 14 Since there were no other natural isotopes besides N that had a good peak intensity, we assumed that a concentration of 0% would have a peak intensity of 0. 15 N 14 Calibration was performed using only N. From the natural isotope ratio 15 N 14 The concentration of N was set to 3629 ppm, and the concentration of Ar was determined using Equation 4. The results are shown in Table 3. It was confirmed that analytical values ​​were shown for the mixed concentration with the same accuracy as in Examples I-1, I-2, and I-3. Ar concentration (ppm) = Gas peak intensity of the target gas × (3692 ppm / 15 N 14 N-peak intensity) ... (Equation 4)

[0062] [Table 3]

[0063] (Example I-5) Carrier gas: Ar, Gas to be measured: N2, He We investigated the analysis when the carrier gas was Ar and the target gases were N2 and He. For every 1000 ml / min of carrier gas, an introduction gas containing N2 and He (He: 3000 ppm, N2: 3000 ppm, O2: 99.4%) was mixed at seven levels: 10.0, 9.0, 7.0, 5.0, 3.0, 2.0, and 1.0 ml / min, and analyzed. The natural isotopes of the carrier gas used for calibration were as follows: 36 Ar, 38 The Ar peak was used. From the natural isotope ratios... 36 Ar, 38 Ar concentrations were set to 3365 ppm and 632 ppm, and the concentrations of N2 and He were calculated using Equation 5. The results are shown in Table 4. The concentration of N2 was accurately analyzed, similar to Examples I-1 to I-4, but the concentration of He did not match the calculated concentration based on the flow rate. This is presumed to be due to the difference in ionization potential between He and Ar. The ionization potential of He is 24.587 eV, and the ionization potential of Ar is 15.76 eV, meaning that He requires more energy to ionize. It is thought that the measured value decreased because some He molecules did not ionize under the same electron bombardment conditions in mass spectrometry. Concentration of the gas being measured (ppm) = Peak intensity of the gas being measured ×(3365ppm-632ppm) / ( 36 Ar peak intensity - 38 Ar peak intensity) ... (Equation 5)

[0064] [Table 4]

[0065] For these results, we confirmed that the calculated concentration based on flow rate and the analytical value agreed well by multiplying the He concentration analysis result by 1.2.

[0066] From these results, it was found that when the target gas has a higher ionization potential than the carrier gas, the accuracy of the analytical value can be improved by applying a correction by multiplying the analytical value by a constant. In this experiment, the correction constant was 1.2, but this value is not limited as it can change depending on the intensity of the electron shock, etc.

[0067] (Example I-6) Carrier gas: Ar, Sample gas: N2 We investigated the analysis when the carrier gas was Ar and the target gas was N2. To a carrier gas flow rate of 400 mL / min, N2 gas was injected (mixed) at seven levels: 2.0, 5.0, 10.0, 15.0, 20.0, 25.0, and 30.0 μL. The injection volume was analyzed based on concentration and time. N2 concentration measurements were performed at a frequency of 300 times / min. Regarding the isotopes of the carrier gas used for calibration, 36 Ar, 38 Using the Ar peak, the concentrations were determined to be 3365 ppm and 632 ppm respectively based on the natural isotope ratio. The injection volume was calculated by summing the concentration measurements taken during the time from injection of N2 gas until the N2 gas was released from the mass spectrometer by the carrier gas, using Equation 6. The results are shown in Table 5. Even under conditions where the concentration changed, analytical results could be obtained with the same accuracy as in other examples, and the injection volume could be analyzed. N2 injection volume (μL) =Σ{N2 peak intensity} ×(3365ppm-632ppm) / ( 36 Ar peak intensity - 38 (Ar peak intensity) × (carrier gas flow rate (mL / min.) / concentration measurement frequency (times / min.)) × 1000 ... (Equation 6)

[0068] [Table 5]

[0069] [Example II] A function was incorporated into the mass spectrometer that allows for heating and melting the sample containing the target to be measured, and then vaporizing (extracting) the target from the sample, enabling quantitative analysis of the target.

[0070] (Device configuration) To conduct analytical experiments on the examples and comparative examples, a Horiba EMGA930 oxygen, nitrogen, and hydrogen analyzer was modified to use argon gas as the carrier gas, and a pressure regulator and flow meter were added immediately after the dust filter. A multi-turn high-resolution mass spectrometer infi-TOF-UHV manufactured by MSI.TOKYO was directly connected to this modified apparatus. A schematic diagram of the test apparatus is shown in Figure 5.

[0071] (Measurement sample) As measurement samples, we prepared three levels of steel standard samples from Seishin Shoji Co., Ltd., two levels of steel standard samples from JSS, a titanium standard sample from Seishin Shoji Co., Ltd., and six levels of reduced iron. In addition, measurements using only a crucible were used as a blank (sample). The following measurements, particularly the quantification of nitrogen contained in the samples, were performed on these samples. Table 6 shows the nitrogen content (certified values) of the steel standard samples. [Table 6]

[0072] (Preliminary analysis) The above steel standard samples were weighed, placed in a graphite crucible, and heated and vaporized in an impulse furnace of a modified device. The resulting gas was detected using a high-resolution mass spectrometer. Upon examining the mass spectrum of the measured gas, it was confirmed that only N2 was detected as nitrogen-based gas from the sample, and oxygen from the sample was detected only as CO, which was produced by the oxidation of the graphite crucible. Therefore, in the following examples and comparative examples, when quantifying nitrogen in steel standard samples through N2 quantification, it is necessary to separate the CO and N2 peaks. High-resolution mass spectrometry was performed to separate and measure their respective precise masses, 28.0062 and 27.9949. Figure 6 shows an example of a high-resolution mass spectrometry spectrum with separated CO and N2 peaks. While the present invention is not limited to the resolution required to obtain this spectrum, the instrument's resolution R = 20000 was approximately when this spectrum was obtained.

[0073] (Example II-1) The following analysis was performed using the test apparatus (Figure 5). Measurements were taken 10 times each for three levels of steel standard samples manufactured by Nishishin Shoji Co., Ltd., two levels of steel standard samples from JSS, and a blank sample. The following equation (Equation II-1) is used to quantify N2 based on the Ar isotope concentration in the carrier gas. The key point of equation (Equation II-1) is that the isotope is 36 Ar, and 38 The concentrations of Ar are constant, at 3365 ppm and 652 ppm, according to the isotopic abundance, and these known concentrations are correlated with the mass spectral measurements obtained by a mass spectrometer. Based on this correlation, the concentration of N2, the target gas, is quantified from the mass spectral measurements of N2. Furthermore, considering the measurement time, carrier gas flow rate, molecular weight of the target substance, sample mass, etc., the total nitrogen content N (ppm) in the metal sample can be determined.

[0074]

number

[0075] Here, we will explain each input value in (Equation II-1). "Measured value" refers to the detection intensity of the signal of the molecule being measured in a high-resolution mass spectrometer. "Sampling time" refers to the time interval (measurement interval) at which the signal is acquired at each measurement point. In other words, if the signal is acquired every second, the sampling time is 1 second. "Flow rate" refers to the gas flow rate of the carrier gas from the impulse reactor to the high-resolution mass spectrometer. In this example, N2 (measured value) was determined using the detection intensity for each signal acquisition. 36 Ar (measured value) and 38 Ar (measured value) was measured in the 5 seconds prior to the detection of a signal originating from N2. 36 Ar and 38 The average values ​​of each detected intensity of Ar were used. These were substituted into (Equation II-1). The Ni (ppm) calculated using (Equation II-1) for each signal acquisition was accumulated over the time period during which nitrogen-derived signals were detected, and the sum was obtained as the total nitrogen content N (ppm) in the steel sample.

[0076] This method demonstrated that, similar to the analysis results obtained by TCD using He gas, which was previously essential, it is possible to determine the nitrogen concentration in a sample using high-resolution mass spectrometry with Ar. The quantitative results for the JSS2 sample are shown in Table 7. Furthermore, since quantification was possible by measuring the isotope argon in the carrier without the calibration curve creation process that was previously required, it was confirmed that various costs related to standard gases required for quantification (materials, gas exchange process, overall measurement time, etc.) can be reduced.

[0077] [Table 7]

[0078] (Example II-2) The results when quantitative analysis was performed by applying (Formula II-1) to all measurement points are shown. The following analysis was performed using the same test apparatus as in Example II-1 (Figure 5). Measurements were taken 10 times each for three levels of steel standard samples manufactured by Nishishin Shoji Co., Ltd., two levels of steel standard samples from JSS, and a blank sample.

[0079] In this embodiment, at all measurement points over the time period during which a nitrogen-derived signal is detected, the measured N2 (measured value) 36 Ar (measured value) and 38Ni (ppm) was calculated using Ar (measured value) from (Equation II-1), and the sum was accumulated over all measurement points to obtain the total nitrogen content N (ppm) in the steel sample. The data acquired in this procedure starts at the moment the sample is placed in the impulse furnace. Subsequently, the sample is heated in the impulse furnace, and N2 detection begins. After the detection of N2 converges in about 30 seconds, the measurement ends when the furnace body has cooled for another minute or so. For 200 seconds from the start to the end of the measurement, measured data from a high-resolution mass spectrometer were recorded at 1 / 3 second sampling times, resulting in 600 data points. The sum of these 600 Ni (ppm) values ​​was obtained as the total nitrogen content N (ppm) in the steel sample quantified in this measurement. Figure 7 shows the N2 (measured value) obtained from the high-resolution mass spectrometer. 36 Ar (measured value) and 38 This figure shows an example of Ar (measured value). In Figure 7, the measurement starts at approximately 1.5 minutes on the horizontal axis (time) and ends at approximately 3.5 minutes.

[0080] Figure 8 shows the measurement results of the total nitrogen content N (ppm) in the steel sample obtained from the above procedure. The horizontal axis shows the standard value of the measurement sample, and the vertical axis shows the quantitative value. Within this measurement range, the chart of the measurement results showed high linearity, confirming that quantitative analysis with high accuracy and reproducibility is possible.

[0081] Furthermore, in Example II-2, it was confirmed that the measurement accuracy was further improved compared to Example II-1, meaning that the standard deviation (variation) of the measured values ​​was reduced. Table 8 shows the measurement results for the JSS sample from both Example II-1 and Example II-2.

[0082] [Table 8]

[0083] In both Examples II-1 and II-2, the total nitrogen content N (ppm) in the steel sample was determined based on (Equation II-1). However, in Example II-2, by applying (Equation II-1) to all measurement points, it was confirmed that the measurement accuracy was further improved and the standard deviation (variation) of the measured values ​​was significantly reduced.

[0084] (Example II-3) For the quantitative determination of nitrogen in titanium, analysis was performed on a titanium standard sample Ti·Alloy-64-001 (certified value N: 42 ppm) manufactured by Nishishin Shoji Co., Ltd. The quantitative results obtained by the inert gas-fusion thermal conductivity method using helium gas as described in JIS H1612:1993 were compared with the results obtained by quantitative determination using the same procedure as in Example II-2 (Example II-3). For heating the titanium sample only, 1 g of platinum was used as the bath metal to assist in heating the titanium sample, as indicated in JIS H 1612:1993. Table 9 shows the respective N quantitative values ​​obtained from a 0.3 g sample using the method of the present invention according to Example II-2 and the inert gas-fusion thermal conductivity method using He (TCD reference example).

[0085] [Table 9]

[0086] From these results, it was confirmed that this method enables highly accurate analysis even when using titanium samples with relatively high melting points.

[0087] (Example II-4) For six reduced iron samples, the amount of nitrogen (N) in the samples was quantified using the following four methods. (Method 1: Thermal conductivity method) The amount of nitrogen in the sample was quantified using the inert gas fusion-thermal conductivity method with helium gas as specified in JIS G 1228. (Method 2: Mass spectrometry) The amount of nitrogen (N) in the samples was quantified using a modified system that directly connected a Horiba EMGA-930 mass spectrometer and a Kanomax Analytical multi-turn high-resolution mass spectrometer. Each reduced iron sample was melted in an argon gas atmosphere using an impulse furnace, and the generated gas was introduced into the mass spectrometer with argon as the carrier gas. The amount of nitrogen was then quantified based on the Ar isotope concentration in the same manner as in Example II-2. (Method 3: Development Method) Method 2 added a chromatography function to the above configuration. Specifically, the gas generated in the impulse furnace was passed through a Shincarbon-ST packed column (approximately 1 m) capable of separating CO and N2 at room temperature, and then introduced into a mass spectrometer to quantify nitrogen in reduced iron. (Method 4: Wet analysis) Nitrogen was quantified using the JIS G 1228 ammonia distillation separation amide sulfuric acid titration method and used as a reference value.

[0088] Figure 9 shows an example of a mass spectrum obtained by combining an impulse furnace and a mass spectrometer, using argon as the carrier gas. Even under conditions where CO and N2 are sufficiently separated for standard steel samples, it was found that when reduced iron containing a large amount of oxygen is used as the sample, the tail of the CO peak interferes with N2, affecting the quantitative value. The nitrogen content at each reduced iron sample was calculated by subtracting the CO tail as the background from the N2 peak. This is shown in Table 10 as the result of the mass spectrometry method (Method 2).

[0089] [Table 10]

[0090] The development method for Method 3 is described below. When the gas passed through the column was introduced into a mass spectrometer, it was confirmed that the appearance times of the CO and N2 mass peaks changed (chromatogram). Based on these results, a time period in which N could be reliably separated was selected. Figure 10 shows an example of the mass spectrometry spectrum during that time period, allowing confirmation of the N-only mass spectrometry spectrum. The quantitative value of nitrogen in each reduced iron was calculated by integrating the signal intensity of N2 during this time period. This is shown in Table 10 as the result of the mass spectrometry method of Method 3. (Development Method)

[0091] Table 10 also shows the quantitative results obtained by the thermal conductivity method of Method 1 and the wet analysis method of Method 4. From a comparison of these results, it was confirmed that the thermal conductivity method of Method 1 may overestimate nitrogen compared to the wet analysis method of Method 4, but the developed method of Method 3 yields results that are in close agreement with the wet analysis method of Method 4.

Claims

1. A quantitative analysis method for a target to be measured using a mass spectrometer, A gas introduction step involves mixing the gas to be measured with a carrier gas that is different from the gas to be measured and has two or more natural isotopes, and introducing the mixture into a mass spectrometer. The mass spectrometry step involves using the aforementioned mass spectrometer to perform mass spectrometry on the gas to be measured and two or more native isotopes in the carrier gas. A gas concentration calculation step, which calculates the concentration of the gas to be measured using the analytical values ​​of two or more natural isotopes of the carrier gas obtained by the mass spectrometry step as a calibration standard, A quantitative analysis method for large objects.

2. The carrier gas is Ar, N ２ , O ２ The quantitative analysis method according to claim 1, comprising at least one of the or a mixture thereof.

3. An extraction step in which a sample containing the object to be measured is heated and melted in the atmosphere of the carrier gas, and the gas of the object to be measured is extracted from the sample. A quantitative analysis method according to claim 1, comprising the characteristics of the method described in claim 1.

4. The quantitative analysis method according to claim 3, wherein the sample contains 80% by mass or more of metal.

5. The quantitative analysis method according to claim 1, further comprising a gas quantity calculation step of calculating the amount of the gas to be measured by multiplying the concentration of the gas to be measured by the flow rate of the carrier gas that flowed during the time in which the concentration was detected.

6. The quantitative analysis method according to claim 5, wherein in the gas quantity calculation step, the time in which the concentration of the gas to be measured is detected is subdivided, the amount of the gas to be measured Ci (i = 1, 2, ..., n; n is the number of subdivided sections) is calculated for each subdivided section, and the sum of the Ci is calculated as the amount of the gas to be measured.

7. Two or more natural isotopes in the carrier gas are ３６ Ar and ３８ The quantitative analysis method according to claim 1, wherein the material is Ar.

8. The quantitative analysis method according to claim 1, wherein the object to be measured is one or more of nitrogen, carbon, oxygen, and hydrogen.

9. The aforementioned mass spectrometer is The quantitative analysis method according to claim 1, having a resolution capable of separately detecting nitrogen gas with a mass number of 28.006 and carbon monoxide gas with a mass number of 27.

995.

10. The quantitative analysis method according to claim 1, wherein a correction coefficient used to calculate the concentration of the gas to be measured is determined by pre-mass spectrometry of the gas to be measured and the carrier gas, whose concentrations are known, using the mass spectrometer.

11. A gas introduction function unit that mixes the gas to be measured with a carrier gas that is different from the gas to be measured and has two or more natural isotopes, and introduces the mixture into a mass spectrometer. The mass spectrometer is equipped with a mass spectrometry function unit that performs mass spectrometry on the gas to be measured and two or more natural isotopes in the carrier gas, A gas concentration calculation function unit calculates the concentration of the target gas using the analytical values ​​of two or more natural isotopes of the carrier gas obtained by the mass spectrometry function unit as a calibration standard, A quantitative analyzer having the following features.

12. A sample containing the object to be measured is heated and melted in the atmosphere of the carrier gas, and the object to be measured is converted into a gas from the sample in a vaporization function unit. A quantitative analyzer according to claim 11, having the following features.

13. A gas concentration calculation function calculates the concentration of the target gas using the signal intensity of the target gas measured by the mass spectrometry function and the signal intensity of two or more natural isotopes in the carrier gas. A quantitative analyzer according to claim 11, having the following features.

14. The aforementioned mass spectrometry unit is The quantitative analyzer according to claim 11, having a resolution capable of separately detecting nitrogen gas with a mass number of 28.006 and carbon monoxide gas with a mass number of 27.

995.

15. The quantitative analyzer according to claim 11, further comprising a chromatography function unit capable of separating the gas to be measured from other gases.

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