Pretreatment method for measuring < 14 > C content of microgram-level carbon content sample by accelerator mass spectrometer

Abstract

The invention provides a pretreatment method for determining the content of < 14 > C in a microgram-level carbon sample by an accelerator mass spectrometer. Comprising the following steps: (1) configuring the amount of a diluted sample according to the carbon content of a trace CO2 gas sample and preparing a diluted CO2 gas sample; (2) mixing the diluted CO2 gas and the trace CO2 gas; and (3) reducing the mixed CO2 gas into a graphite sample by a zinc-iron method, determining the 14C content of the mixed sample by using an accelerator mass spectrometer, and correcting the determination result by a formula to obtain the 14C content of the trace sample. The method solves the problems that graphite is difficult to synthesize and < 14 > C analysis is difficult due to low carbon content of microgram-grade carbon samples, and develops a simple, efficient and reliable pretreatment method suitable for determining microgram-grade carbon samples with different < 14 > C contents by an accelerator mass spectrometer; the method has certain significance in promoting the application of the micro sample 14C analysis in a plurality of research fields such as geoscience, environmental science and archaeology.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring technology; in particular, it relates to an accelerator mass spectrometer for determining microgram-level carbon content in samples. 14 Pretreatment method for C content. Background Technology

[0002] With the radioactive carbon isotopes ( 14 C) Measurement techniques are constantly developing. 14 Carbon (C) has important applications in many research fields, including Earth sciences, environmental sciences, archaeology, and biological sciences. However, many samples in these studies, such as bubbles in Antarctic ice cores, rock paintings, DNA in biological sciences, and atmospheric CH4 and CO, often yield only trace amounts of carbon, less than tens of micrograms. High-precision carbon analysis is crucial in these studies. 14 C accelerator mass spectrometry typically requires more than 100 micrograms of carbon for determination.

[0003] Currently measuring trace samples 14 There are two main methods for graphitization: one is to directly measure carbon dioxide gas samples using an accelerator mass spectrometer (AMS), which requires significant improvements to existing solid targets and ion sources. The other method is to prepare trace graphite samples and measure them using an accelerator mass spectrometer. However, the graphitization of trace samples still faces the following technical challenges. First, because the carbon content of trace samples is very low (≤100 μg), the requirements for the synthesis system are high. Modifications such as halving the volume of the reduction tube and replacing the existing sensor with a more accurate and sensitive pressure sensor are needed to meet the synthesis requirements. Second, because the mass and size of trace graphite samples are much smaller than those of conventional samples, the samples are difficult to load, and the results obtained by measuring them using an accelerator mass spectrometer have a large error.

[0004] These difficulties affect the high precision of micro-samples. 14 C-analysis has applications in archaeology, tracing environmental pollutants and greenhouse gases, and biomedicine. Therefore, developing a simple, efficient, stable, and applicable pretreatment method for various types of trace samples has become crucial for accelerator mass spectrometers. 14 The key challenges that urgently need to be overcome in the field of C analysis. Summary of the Invention

[0005] The purpose of this invention is to provide an accelerator mass spectrometer for determining microgram-level carbon samples. 14 Pretreatment method for C content.

[0006] This invention is achieved through the following technical solution:

[0007] This invention relates to an accelerator mass spectrometer for determining microgram-level carbon content in samples. 14 The pretreatment method for C content includes the following steps:

[0008] Step 1, according to the carbon content of the trace CO2 gas sample, configure the amount of dilution sample, and prepare the diluted CO2 gas sample;

[0009] Step 2, mix the diluted CO2 gas and the trace CO2 gas to obtain a mixed sample;

[0010] Step 3, reduce the mixed CO2 gas into a graphite sample by zinc-iron method, and use an accelerator mass spectrometer to determine the mixed sample 14 C content, after the determination result is corrected by a formula, the carbon content of the trace sample 14 C content.

[0011] Preferably, in step 1, the preparation of the diluted CO2 gas sample is specifically:

[0012] (1.1) After the trace sample with insufficient carbon content is treated into a pure CO2 gas sample in a high vacuum system, according to the carbon content of the trace CO2 gas sample, configure the amount of dilution sample;

[0013] (1.2) Connect the dilution sample to the high vacuum system and vacuumize it to ≤3×10 -6 torr, collect CO2 and H2O by a liquid nitrogen cold trap (-196℃);

[0014] (1.3) After heating the liquid nitrogen cold trap to release CO2 and H2O, collect H2O by an ethanol-liquid nitrogen cold trap (-90℃);

[0015] (1.4) Collect the CO2 gas for dilution in a gas collection tube.

[0016] Preferably, in step 2, the specific method of mixing the diluted CO2 gas and the trace CO2 gas is:

[0017] (2.1) Connect the gas collection tube containing the trace CO2 gas and the gas collection tube containing the diluted CO2 gas to the high vacuum system and vacuumize it to ≤3×10 -6 ;

[0018] (2.2) Close valve two, open the gas collection tube containing the trace sample and the gas collection tube containing the dilution sample, mix the diluted CO2 gas and the trace CO2 gas uniformly, then close valve one, and store the mixed CO2 gas in a section of pipeline containing a pressure sensor in a sealed manner;

[0019] (2.3) After the diluted CO2 gas and the trace CO2 gas are mixed uniformly, calculate the carbon content of the mixed sample by the pressure sensor;

[0020] The calculation formula is as follows:

[0021]

[0022] In formula (1), V is the volume of gas (mL), P is the pressure sensor reading (torr) of CO2 gas released to the pressure sensor at the pipe where the pressure sensor is located, P0 is the initial reading of the pressure sensor (torr), and C is the carbon content (mg).

[0023] (2.4) Collect the mixed CO2 gas in a gas collection tube;

[0024] (2.5) Calculate the dilution factor θ, which is the ratio of the carbon content of the diluted sample to the carbon content of the mixed sample, by the carbon content obtained by the pressure gauge.

[0025] Preferably, in step 3, the mixed CO2 gas is reduced to a graphite sample by the zinc-iron method, and the reducing agent is zinc particles and the catalyst is Fe powder; the reaction formula is as follows:

[0026]

[0027]

[0028] Preferably, in step 3, after the synthesis of graphite, the AMS measurement is performed, and the results after measurement are corrected by the following formula to obtain the 14 C content of the micro sample;

[0029]

[0030] In formula (2), Δ s ample is the Δ 14 C value of the micro sample, Δ m ix is the Δ 14 C value of the mixed sample, and θ is the dilution factor. d il is the Δ 14 C value of the diluted sample.

[0031] Preferably, in step 1, the diluted CO2 gas sample is generated from a anthracite standard sample or oxalic acid II standard sample.

[0032] Preferably, if the 14 C content of the micro CO2 gas sample is high, the diluted CO2 gas sample is recommended to be generated from an anthracite standard sample without 14 C.

[0033] Preferably, in step 2, the carbon content of the mixed sample of the diluted CO2 gas and the micro CO2 gas is ≥0.2 mg.

[0034] Preferably, in (2.5), the dilution factor obtained by the pressure gauge has no less than three decimal places, and the accuracy is less than 0.3%.

[0035] The present invention has the following advantages:

[0036] (1) This invention differs from traditional trace sample methods 14 Compared to the method for determining C, the procedure is simpler. This invention can utilize existing systems for synthesizing constant samples, eliminating the need to establish a dedicated system for synthesizing graphitic carbon from trace samples.

[0037] (2) This invention can provide a simple and reliable trace sample for samples where it is difficult to obtain sufficient carbon content. 14 Method for determining C.

[0038] (3) This invention is applicable to different 14 The determination of trace amounts of carbon content in samples; applicable not only to... 14 It is also suitable for trace samples with low C content. 14 Trace samples with high C content.

[0039] (4) This invention enables the precise determination of different types of trace samples using an accelerator mass spectrometer. 14 The C content expands its wide application in multiple research fields such as earth science, environmental science, archaeology, and biological science. Attached Figure Description

[0040] Figure 1 It is an accelerator mass spectrometer for measuring trace samples. 14 C flowchart;

[0041] The attached figures are labeled as follows: 1 is a liquid nitrogen cold trap, 2 is an ethanol-liquid nitrogen cold trap, 3 is a pressure sensor, 4 is a dilution sample gas collection tube, 5 is a micro sample gas collection tube, 6 is a mixed sample gas collection tube, 701 is the first reduction tube, and 702 is the second reduction tube. Detailed Implementation

[0042] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are merely further illustrations of the present invention, but the scope of protection of the present invention is not limited to the following embodiments.

[0043] Example

[0044] This embodiment relates to an accelerator mass spectrometer for determining microgram-level carbon samples. 14 For the pretreatment method of C content, see Figure 1 As shown, 1 is a liquid nitrogen cold trap, 2 is an ethanol-liquid nitrogen cold trap, 3 is a pressure sensor, 4 is a dilution sample gas collection tube, 5 is a micro-sample gas collection tube, 6 is a mixed sample gas collection tube, 701 is a first reduction tube, and 702 is a second reduction tube; the process includes the following steps:

[0045] Step 1: Prepare the amount of diluted sample based on the carbon content of the trace CO2 gas sample, and then prepare the diluted CO2 gas sample.

[0046] Step 2, mixing the diluted CO2 gas and the trace CO2 gas to obtain a mixed sample;

[0047] Step 3, reducing the mixed CO2 gas into a graphite sample by zinc-iron method, and determining the mixed sample by using an accelerator mass spectrometer 14 C content, the determination result is corrected by a formula to obtain the trace sample 14 C content.

[0048] According to the method principle involved in the present embodiment:

[0049] Firstly, three groups of parallel samples A1, A2, B1, B2, C1 and C2 are treated as pure CO2 gas samples. A1 and A2 are a group of parallel samples, B1 and B2 are a group of parallel samples, and C1 and C2 are a group of parallel samples. A1, A2, B1 and B2 are atmospheric CO2 samples, and C1 and C2 are atmospheric CO samples. Among them, A1, B1 and C1 are constant samples without dilution, and A2, B2 and C2 are trace samples. According to the carbon content of the trace CO2 gas samples A2, B2 and C2, the amount of the required dilution sample is configured so that the carbon content of the mixed sample is ≥0.2 mg. The dilution sample for diluting A2 is selected from CO2 gas generated by oxalic acid II. The dilution sample for diluting B2 and C2 is selected from CO2 gas generated by anthracite. The dilution sample is connected to the vacuum system, and vacuumized to ≤3×10 -6 torr, and then the CO2 and H2O therein are collected by a liquid nitrogen cold trap 1 (-196°C). After heating the liquid nitrogen cold trap to release CO2 and H2O, H2O is captured by an ethanol-liquid nitrogen cold trap (-90°C), and the CO2 gas for dilution is collected in the dilution sample gas collection tube 4.

[0050] Then, the gas collection tube 5 containing the trace CO2 gas and the gas collection tube 4 containing the dilution CO2 gas are connected to the vacuum system, and vacuumized to ≤3×10 -6 torr. Valve two is closed, and the gas collection tube 5 containing the trace sample and the gas collection tube 4 containing the dilution sample are opened, so that the dilution CO2 gas and the trace CO2 gas are mixed uniformly. Then, valve one is closed, and the mixed CO2 gas is stored in a section of pipeline containing a pressure sensor. Then, the carbon content of the mixed sample is calculated by the pressure reading of the pressure sensor 3. The calculation formula is as follows:

[0051]

[0052] wherein V is the volume of gas (mL), P is the pressure sensor reading (torr) of the mixed CO2 gas released to the pressure sensor at the pipe where the pressure sensor is located, P0 is the initial reading of the pressure sensor (torr), and C is the carbon amount (mg). Finally, the mixed CO2 gas is collected in the mixed sample gas collecting pipe 6 by liquid nitrogen (-196℃). Then, the dilution factor θ, i.e. the ratio of the carbon amount of the diluted sample to the carbon amount of the mixed sample, is calculated by the carbon amount obtained by the pressure gauge.

[0053] Finally, the mixed CO2 gas sample and the undiluted sample are reduced into graphite samples by the zinc-iron method for accelerator mass spectrometer 14 C analysis, wherein an excess of zinc particles is added as the reducing agent in the first reduction pipe 701, and 1 mg of Fe powder is added as the catalyst in the second reduction pipe 702; the reaction formula is specifically as follows:

[0054]

[0055] The result after the determination is corrected by the following formula to obtain the carbon content of the micro sample: 14

[0056]

[0057] wherein Δ s C of the micro sample, Δ 14 C of the diluted sample, and θ is the dilution factor. The Δ m C of the mixed sample, Δ 14 C of the diluted sample, and θ is the dilution factor. The Δ d C of the mixed sample, Δ 14 C of the diluted sample, and θ is the dilution factor. The Δ 14 C of the constant samples A1, B1 and C1 without dilution are -41.6±2.0‰, -38.0±1.9‰ and -548.8±1.7‰, respectively. The specific conditions of the diluted samples are shown in Table 1.

[0058] Table 1

[0059] Sample name Dilution factor θ Mixed sample delta 14 C (‰) Sample Δ 14 C (‰) Constant CO2 sample A1 - - -41.6±2.0 trace CO2 sample A2 0.823 265.4±2.4 -40.3±1.4 Constant CO2 sample B1 - - -38.0±1.9 trace CO2 sample B2 0.663 -674.6±1.3 -38.7±3.5 Constant CO sample C1 - - -548.8±1.7 Micro-CO sample C2 0.760 -888.7±1.2 -545.9±4.0

[0060] Note: The dilution factor θ is the ratio of the carbon amount of the diluted sample to the carbon amount of the mixed sample.

[0061] The Δ 14 C of the micro samples A2, B2 and C2 calculated after the formula correction is similar to the Δ 14 C of the undiluted samples A1, B1 and C1, and the results in Table 1 show that the pretreatment method involved in the present application is reliable. The method of the present application solves the problems that the microgram-level carbon amount sample has low carbon content, it is difficult to synthesize graphite, and some samples 14 have high carbon content and are difficult to perform 14 ​C Analysis of the problem, developed a simple and efficient, reliable, suitable for accelerator mass spectrometer determination of different 14 C content of microgram level carbon content sample pretreatment method, for promoting the application of micro sample analysis in the field of earth science, environmental science, archaeology and so on has certain significance. 14 C content of microgram level carbon content sample pretreatment method, for promoting the application of micro sample analysis in the field of earth science, environmental science, archaeology and so on has certain significance.

[0062] The specific embodiments of the application are described above. It should be understood that the application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or modifications within the scope of the claims, which does not affect the essence of the application.

Claims

1. An accelerator mass spectrometer for determining microgram-level carbon content in samples. 14 The pretreatment method for C content is characterized by... Includes the following steps: Step 1: Prepare the amount of diluted sample based on the carbon content of the trace CO2 gas sample, and then prepare the diluted CO2 gas sample. Step 2: Mix the diluted CO2 gas and trace amounts of CO2 gas to obtain a mixed sample; Step 3: The mixed CO2 gas is reduced to a graphite sample using the zinc-iron method, and the mixed sample is then analyzed using an accelerator mass spectrometer. 14 The C content, after being corrected by the formula, yields the trace sample. 14 C content.

2. The accelerator mass spectrometer described in claim 1 for determining microgram-level carbon samples. 14 The pretreatment method for C content is characterized by... In step 1, the preparation of the diluted CO2 gas sample specifically involves: (1.1) After processing the trace sample, which is difficult to obtain with sufficient carbon content, into a pure CO2 gas sample in a high vacuum system, the amount of diluted sample is prepared according to the carbon content of the trace CO2 gas sample. (1.2) Dilute the sample, connect it to the high vacuum system, and evacuate to ≤3×10⁻⁶. -6 torr collects CO2 and H2O through a liquid nitrogen cold trap (-196℃); (1.3) After reheating the liquid nitrogen cold trap to release CO2 and H2O, H2O is captured by the ethanol-liquid nitrogen cold trap (-90℃); (1.4) Collect the CO2 gas used for dilution in the gas collection tube.

3. The accelerator mass spectrometer described in claim 1 for determining microgram-level carbon samples. 14 The pretreatment method for C content is characterized by... In step 2, the specific method for mixing and diluting the CO2 gas and trace amounts of CO2 gas is as follows: (2.1) Connect the gas collecting tube containing a trace amount of CO2 gas and the gas collecting tube containing diluted CO2 gas to the high vacuum system and evacuate to ≤3×10. -6 ; (2.2) Close valve two, open the gas collecting tube containing the trace sample and the gas collecting tube containing the diluted sample, and after the diluted CO2 gas and the trace CO2 gas are mixed evenly, close valve one, so that the mixed CO2 gas is stored in a section of pipeline equipped with a pressure sensor. (2.3) After the CO2 gas and trace CO2 gas of the diluted sample are mixed evenly, the carbon content of the mixed sample is calculated by a pressure sensor; (2.4) Collect the mixed CO2 gas in the gas collecting tube; (2.5) Calculate the dilution factor θ, which is the ratio of the carbon content of the diluted sample to the carbon content of the mixed sample, based on the carbon content obtained from the pressure gauge reading.

4. The accelerator mass spectrometer described in claim 1 for determining microgram-level carbon samples. 14 The pretreatment method for C content is characterized by... In step 3, during the process of reducing mixed CO2 gas into graphite sample using the zinc-iron method, the reducing agent is zinc granules and the catalyst is Fe powder.

5. The accelerator mass spectrometer described in claim 1 for determining microgram-level carbon samples. 14 The pretreatment method for C content is characterized by... In step 1, the diluted CO2 gas sample is selected from a known standard generated from oxalic acid II standard or anthracite standard. 14 CO2 with C content; if a trace amount of CO2 gas sample 14 For samples with high C content, it is recommended to use anthracite standard samples to dilute CO2 gas samples. 14 C in CO2.

6. The accelerator mass spectrometer described in claim 1 for determining microgram-level carbon samples. 14 The pretreatment method for C content is characterized by... In step 2, the carbon content in the mixed sample made from diluted CO2 gas and trace amounts of CO2 gas is ≥0.2 mg.

7. The accelerator mass spectrometer described in claim 3 for determining microgram-level carbon samples. 14 The pretreatment method for C content is characterized by... In (2.5), the dilution factor obtained by the pressure gauge shall have no less than three decimal places and an accuracy of less than 0.3%.

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