A method for preparing a stable isotope standard substance with adjustable ratio

Abstract

The present invention relates to the field of measurement test standard value transfer technology and laboratory internal quality control, and in particular to a stable isotope (δ) with adjustable ratio in a laboratory widely used in research and monitoring work in the food, environment, agriculture and geology sectors. 13 C.δ 15 N, δ 2 H and δ 18 O) A method for preparing a standard substance, comprising the following steps: selecting two or more existing stable isotope standard substances according to the δ value of the analyzed sample; mixing the selected two or more stable isotope standard substances in proportion to obtain a series of samples; performing stable isotope analysis on the mixed series of samples to obtain the measured values ​​of the series of samples; performing correlation analysis on the standard values ​​and measured values ​​of the series of samples; after determining the δ value of the required standard substance, inferring the ratio of two or more existing standard substances according to the regression equation for preparation; performing uniformity test, parallel test, stability investigation, and laboratory joint determination on the prepared samples, the prepared samples can be used as stable isotope standard substances. The present invention innovates on the basis of existing standard substances, adopts a method of optimizing the proportion of mixing two or more standard substances to obtain a standard substance with an actual required δ value, thereby better realizing the internal quality control of the laboratory, and provides new ideas and methods for the field of research and development of existing stable isotope standard substances in my country.

Description

Technical Field

[0001] The present invention relates to the field of measurement test standard value transfer technology and laboratory internal quality control, and in particular to a stable isotope (δ) with adjustable ratio in a laboratory widely used in research and monitoring work in the food, environment, agriculture and geology sectors. 13 C.δ 15 N, δ 2 H and δ 18 O) Preparation method of standard substances. Background Art

[0002] Stable isotope reference materials are standard materials for unified isotope measurement and are an important basis for ensuring the comparability of global isotope data. Stable isotope reference materials are used to calibrate mass spectrometers, evaluate the accuracy of measurement methods and the detection capabilities of detection laboratories, and provide guarantees for the transfer and traceability of measurement values. In addition, reference materials can also be used for quality control to achieve quality control of the system at different time periods during the analysis process. Existing stable isotope reference materials From the 1950s to the 1960s, stable isotope technology developed rapidly, and isotope reference materials for hydrogen, oxygen, carbon and nitrogen were established.

[0003] The selection of stable isotope reference materials should select reference materials with the same or similar chemical composition as the sample to be analyzed to improve the analysis accuracy and reduce the analysis error. In addition, the "same treatment principle" of samples and reference materials should be followed in stable isotope analysis, with the aim of making the samples and reference materials experience the same reaction path and reaction conditions to prevent the occurrence of potential isotope fractionation. At present, the calibration methods of stable isotope reference materials are mainly divided into single-point calibration method and two-point and multi-point calibration methods based on linear regression. When using the single-point calibration method, reference materials with similar δ values ​​to the sample δ value should be selected and analyzed to reduce the error. The two-point and multi-point calibration methods based on linear regression require the use of two or more reference materials to construct a regression equation between the measured value of the reference material and the given value (the linear fitting coefficient should be >0.995), and the linear range of the δ value of the reference material should include the δ value of the analyzed sample. At present, international stable isotope reference materials are mainly produced by the International Atomic Energy Agency (IAEA), the United States Geological Survey (USGS) and the British Elemental Analysis Company. Among them, the most common bio-organic isotope standard materials are USGS42, USGS43, B2155, B2157 and B2159. China's isotope standard materials are mainly developed by the China Institute of Metrology, China Petroleum Exploration and Development Research Institute and China Hydrogeological Research Institute. Among them, the main bio-organic isotope standard materials are GBW04416, GBW04417, GBW04407, GBW04408, GBW04458, GBW04459, GBW04460 and GBW04461. These standard materials, especially carbon isotope standard materials, are used to determine geological and mineral isotopes that cannot meet the requirements of stable isotope analysis of biological products. Some are even out of stock. However, these existing standard materials are far from meeting actual needs. First of all, there are few types of standard materials, and the types of actual samples vary greatly. For example, animal samples include muscle tissue samples, feather samples, shell samples, hair samples, bone tissue samples, etc., plant samples include roots, stems, leaves, etc., and there are other sample types such as microorganisms, minerals, and water. In addition, the δ values ​​of different types of samples are also very different, and the δ values ​​of existing standard substances cannot cover all natural abundances observed in nature. Therefore, it is extremely necessary to innovate on the basis of existing standard substances and adopt the method of mixing two or more standard substances in an optimized ratio to obtain standard substances with the actual required δ values, so as to better realize the internal quality control of the laboratory.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art, to innovate on the basis of existing standard substances, to obtain standard substances with the actual required δ values ​​by mixing two or more standard substances in an optimized ratio, so as to better realize the internal quality control of the laboratory, and to provide new ideas and methods for the field of research and development of existing stable isotope standard substances in my country.

[0006] To achieve the above technical objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for preparing a stable isotope standard substance with adjustable ratio, comprising the following steps:

[0008] S1. Select two or more existing stable isotope standard materials according to the δ value of the analyzed sample;

[0009] S2. mixing the selected two or more stable isotope standard substances in different proportions to obtain a series of samples;

[0010] S3. performing stable isotope analysis on the mixed series of samples to obtain measurement values ​​of the series of samples;

[0011] S4. Conduct correlation analysis on the standard values ​​and measured values ​​of the series of samples;

[0012] S5. After determining the δ value of the required standard substance, the ratio of two or more existing standard substances is inferred according to the regression equation for preparation;

[0013] S6. After the prepared samples have been subjected to uniformity test, parallel test, stability test and laboratory joint determination, they can be used as internal laboratory standard substances.

[0014] The present invention has the following beneficial effects:

[0015] The present invention innovates on the basis of existing standard substances, and adopts a method of mixing two or more standard substances in an optimized ratio to obtain a standard substance with an actually required δ value, thereby better realizing the internal quality control of the laboratory, and providing new ideas and methods for the existing stable isotope standard substance research and development field in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0017] Figure 1The series of samples were mixed with standard materials IAEA-600 and USGS 62 in the ratio of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1. 13 Correlation analysis chart of C standard value and test value.

[0018] Figure 2 The series of samples were mixed with standard materials IAEA-600 and USGS 62 in the ratio of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1. 15 Correlation analysis chart of N standard value and test value.

[0019] Figure 3 The series of samples δ are obtained by mixing the standard substances CBS and KHS in the ratios of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1. 2 Correlation analysis chart of H standard value and test value.

[0020] Figure 4 The series of samples δ are obtained by mixing the standard substances CBS and KHS in the ratios of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1. 18 OCorrelation analysis chart between standard value and test value. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0022] Example 1

[0023] 1. Select international standard substances IAEA-600 (caffeine, δ 13 C=-27.771‰,δ 15 N = 1‰) and USGS 62 (caffeine, δ 13 C=-14.79‰,δ 15 N = 20.17‰).

[0024] 2. Mix the selected IAEA-600 and USGS 62 stable isotope reference materials in the ratios of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1. Make at least 3 parallel samples for each ratio to obtain a series of samples.

[0025] 3. After mixing, the series of samples were weighed and wrapped in a tin cup and then put into the elemental analysis and stable isotope mass spectrometry (IRMS) for stable isotope ratio analysis. The samples were fed into the elemental analyzer through an automatic sample injector. The cracking tube temperature of the elemental analyzer was 960°C. The C and N in the samples were reduced to CO2 and N2 by the glassy carbon in the cracking furnace. The whole process was carried out automatically online. CO2 and N2 were separated by gas phase, and the column temperature was 50°C. CO2 and N2 were respectively fed into the IRMS through the ConFlo IV device to determine the ratio of C and N isotopes. The flow rate of the carrier gas helium was 100mL / min. USGS43(δ 13 C=-21.28‰,δ 15 N=8.44‰), USGS62(δ 13 C=-14.79‰,δ 15 N=20.17‰) and IAEA-600(δ 13 C=-27.771‰,δ 15 N = 1‰) as the correction δ 13 C and δ 15 Standard sample of N.δ 13 C and δ 15 The analytical precision of N is 0.15‰. The obtained data are calibrated with standard substances to obtain the measured values ​​of the series of samples.

[0026] 4. Calculate the standard value of the series of samples based on the standard value of the reference material and the corresponding ratio. For example, IAEA-600(δ 13 C=-27.771‰) and USGS 62(δ 13 C=-14.790‰) The standard value of the sample after mixing at 0.1:0.9 is δ 13 C = -27.771‰ × 0.1 + (-14.790‰ × 0.9) = -16.088‰. Then, the correlation analysis was performed on the standard value and the measured value of the series of samples. Figure 1 It can be seen that δ 13 C 标准值 =0.9743×δ 13 C 测试值 -0.1652, R 2 =0.9673. Figure 2 It can be seen that δ 15 N 标准值 =1.079×δ 15 N 测试值 +2.4897, R 2 =0.9197.

[0027] 5. After determining the δ value of the required standard substance, prepare it by inferring the ratio of two or more existing standard substances according to the regression equation.

[0028] Example: Preparation of δ 13 C 标准值 The standard substance is about -20.000‰;

[0029] δ 13 C 标准值 =0.9743×δ 13 C 测试值 -0.1652, then δ 13 C 测试值 =-20.358‰;

[0030] Let IAEA-600:USGS 62 = X:(1-X);

[0031] Then δ 13 C 测试值 =-27.771‰×X-14.790‰×(1-X)=-20.358‰, then X=0.429;

[0032] Then IAEA-600(δ 13 C=-27.771‰) and USGS 62(δ 13 C=-14.79‰) and mixed in a ratio of 0.429:0.571 to obtain δ 13 C 标准值 It is a standard substance of -20.359‰.

[0033] 6. After the prepared samples have been subjected to uniformity test, parallel test, stability test and laboratory joint determination, they can be used as internal laboratory standard substances.

[0034] Example 2

[0035] 1. Select international standard material CBS (reindeer hoof, δ 2 H=-157.0‰,δ 18 O=3.8‰) and KHS (antelope horn, δ 2 H=-35.3‰,δ 18 O = 20.3‰).

[0036] 2. Mix the selected CBS and KHS stable isotope standard substances in the ratios of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1. Make at least 3 parallel samples for each ratio to obtain a series of samples.

[0037] 3. After mixing, the series of samples were weighed and wrapped in a tin cup and then put into the elemental analysis and stable isotope mass spectrometer for stable isotope ratio analysis. After drying and defatting, the samples were weighed and wrapped in a silver cup and then put into the elemental analysis and stable isotope mass spectrometer (IRMS) for isotope ratio analysis. The samples entered the elemental analyzer through an automatic sample injector. The cracking tube temperature of the elemental analyzer was 1420°C. The H and O in the samples were reduced to H2 and CO by the glassy carbon in the cracking furnace. The whole process was carried out automatically online. H2 and CO were separated by gas phase. The chromatographic column temperature was 80°C. H2 and CO entered the IRMS through the ConFlo IV device respectively to determine the ratio of H and O isotopes. The flow rate of the carrier gas helium was 100mL / min. B2205 (δ 2 H=-87.8‰,δ 18 O=26.9‰), CBS(δ 2 H=-157.0‰,δ 18 O=3.8‰) and KHS (δ 2 H=-35.3‰,δ 18 O = 20.3‰). As the correction δ 2 H and δ 18 Standard sample of O.δ 2 The analytical accuracy of H is 3‰. 18 The analytical accuracy of O is 0.4‰. The obtained data are calibrated with standard substances to obtain the measured values ​​of the series of samples.

[0038] 4. Calculate the standard value of the series of samples based on the standard value of the reference material and the corresponding ratio. For example, CBS(δ 18 O=3.800‰) and KHS (δ 18 O=20.300‰) The standard value of the sample after mixing at 0.1:0.9 is δ 18 O = 3.800‰ × 0.1 + (20.300‰ × 0.9) = 18.650‰. Then, the correlation analysis is performed on the standard value and the measured value of the series of samples. Figure 3 It can be seen that δ 2 H 标准值 =0.8584×δ 2 H 测试值 -9.5341, R 2 =0.9422. Figure 4 It can be seen that δ 18 O 标准值 =0.9561×δ 18 O 测试值 +1.2984, R 2 =0.9598.

[0039] 5. After determining the δ value of the required standard substance, prepare it by inferring the ratio of two or more existing standard substances according to the regression equation.

[0040] Example: Preparation of δ 18 O 标准值 About 15.000‰ standard substance;

[0041] δ 18 O 标准值 =0.9561×δ 18 O 测试值 +1.2984, then δ 2 O 测试值 =14.331‰;

[0042] Let CBS:KHS = X:(1-X);

[0043] Then δ 18 O 测试值 =3.800‰×X+20.300‰×(1-X)=14.331‰, then X=0.362;

[0044] Then CBS(δ 18 O=3.800‰) and KHS (δ 18 O=20.300‰) and mixed in a ratio of 0.362:0.638 to obtain δ 18 O 标准值 It is a standard substance with a concentration of 14.311‰.

[0045] 6. After the prepared standard substances have been subjected to uniformity testing, parallel testing, stability testing, and laboratory joint determination, they can be used as internal standard substances in the laboratory.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a stable isotope standard substance with an adjustable ratio, comprising the following steps: S1. Select two or more existing stable isotope standard materials according to the δ value of the analyzed sample; S2. Mixing the selected two or more stable isotope standard substances in different proportions to obtain a series of samples; S3. performing stable isotope analysis on the mixed series of samples to obtain measured values ​​of the series of samples; S4. Conduct correlation analysis on the standard values ​​and measured values ​​of the series of samples; S5. After determining the δ value of the required standard substance, the ratio of two or more existing standard substances is inferred according to the regression equation for preparation; S6. The prepared samples can be used as standard materials after uniformity test, parallel test, stability test and laboratory joint determination.

2. The method according to claim 1, characterized in that In step S1, the two or more existing carbon and nitrogen stable isotope standard materials IAEA-600 (caffeine, δ 13 C=-27.771‰,δ 15 N = 1‰) and USGS 62 (caffeine, δ 13 C=-14.79‰,δ 15 N = 20.17‰).

3. The method according to claim 1, characterized in that In step S1, the two or more existing hydrogen and oxygen stable isotope standard materials CBS (reindeer hoof, δ 2 H=-157.0‰,δ 18 O=3.8‰) and KHS (antelope horn, δ 2 H=-35.3‰,δ 18 O = 20.3‰).

4. The method according to claim 1, characterized in that: In step S2, the selected IAEA-600 and USGS 62 stable isotope standard materials are mixed in proportions of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1, and at least three parallel samples of each proportion are prepared to obtain a series of samples.

5. The method according to claim 1, characterized in that In step S2, the selected CBS and KHS stable isotope standard substances are mixed in proportions of 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.7:0.2, and 0.9:0.1, and at least three parallel samples of each ratio are prepared to obtain a series of samples.

6. The method according to claim 1, characterized in that In step S3, the mixed series of samples are weighed and wrapped in a tin cup and then put into an elemental analysis and stable isotope mass spectrometer (IRMS) for stable isotope ratio analysis. The obtained data are calibrated with standard substances to obtain the measured values ​​of the series of samples.

7. The method according to claim 1, characterized in that In step S4, the standard values ​​of the series of samples are calculated according to the standard values ​​of the reference materials and the corresponding proportions, and then the correlation analysis is performed on the standard values ​​and the measured values ​​of the series of samples to obtain a linear equation.

8. The method according to claim 1, characterized in that After the δ value of the required standard substance is determined in step S5, the ratio of two or more existing standard substances is inferred according to the regression equation for preparation.

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