Method for high-precision detection of carbon stable isotope and content thereof in environmental sample

Abstract

The invention discloses a method for high-precision detection of carbon stable isotope and content thereof in an environmental sample. The method provided by the invention comprises the following steps: detecting environmental sample powder by using an elemental analysis-stable isotope mass spectrometer; the sampling amount of the environmental sample powder is greater than or equal to 0.4 mg; in the detection process, inert gas is introduced into an opening flow divider in a Conflo universal interface of the elemental analysis-stable isotope mass spectrometer, and the inert gas is mixed with sample gas obtained by combustion in an elemental analyzer. According to the method provided by the invention, the situation that a sample signal is too high and exceeds a linear range is avoided, the representativeness of the sample is improved, the possibility of data abnormity caused by nonuniformity of the sample is reduced, and the aim of rapidly and accurately detecting the stable carbon isotope and the content of the stable carbon isotope at the same time is fulfilled.

Description

Technical Field

[0001] The present invention belongs to the technical field of stable isotope analysis, and in particular relates to a method for detecting carbon stable isotopes and their contents in environmental samples such as soil, plants, and animals. Background Art

[0002] Stable isotope technology, with its multiple functions of tracing, integration, and indication, as well as its rapid detection and accurate results, is increasingly showing broad application prospects in the natural sciences. Stable isotope technology plays a vital role in the development of ecology and has brought new opportunities for its development. Stable isotopes are used as tracers to study the circulation of biological elements in ecosystems and their relationship with the environment. The spatial and temporal integration capabilities of stable isotopes are used to study ecological processes and mechanisms at different temporal and spatial scales. Furthermore, the indicator function of stable isotopes can be used to reveal the changing patterns of ecosystem function.

[0003] In recent years, stable isotope technology has been widely applied in ecology, becoming a crucial tool for understanding ecosystem dynamics. Its applications span a wide range of ecological research areas, including plant physiological and ecological adaptation mechanisms, plant-animal interactions, the effects of global change, the global carbon cycle, rational water resource utilization, food web structure and trophic relationships, and paleovegetation and paleoclimate reconstruction. This has given rise to the field of stable isotope ecology. Stable isotope technology can be used to track the geochemical cycles of biogenic elements (carbon and nitrogen), study the responses of plants and animals to environmental stresses, estimate optimal crop fertilization recipes and timing, understand the composition, sources, and potential for adulteration of agricultural and forestry products, and track the sources and fate of pollutants. This technology plays a crucial role in supporting a number of major national research projects.

[0004] Currently, the most common method for analyzing solid carbon stable isotopes is continuous flow analysis, which combines an elemental analyzer with a stable isotope mass spectrometer. This allows for simultaneous measurement of both stable carbon isotopes and carbon percentage in a single test. In actual testing, environmental samples often contain high carbon contents, typically exceeding 40%, while conventional sampling volumes are typically small, at only 40-50µg. This places extremely high demands on sample homogeneity. Inadequate pulverization or inhomogeneous mixing can result in suboptimal test results, large relative errors in stable carbon isotopes, and even errors in percentage content exceeding the allowable range.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to provide a method for detecting carbon stable isotopes and their contents in environmental samples such as soil, plants, and animals. By increasing the amount of sample tested on the machine by 10 to 20 times and simultaneously using He to dilute and divert the sample gas, the method avoids the sample signal being too high and exceeding the linear range, improves the sample representativeness, and reduces the possibility of data anomalies caused by sample heterogeneity, thereby achieving the purpose of rapid and accurate detection of carbon stable isotopes and their contents.

[0007] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for detecting carbon stable isotopes and their contents in environmental samples, comprising the following steps: detecting environmental sample powder using an elemental analysis-stable isotope mass spectrometry instrument; The sampling amount of the environmental sample powder is ≥0.4 mg; During the detection process, an inert gas is introduced into the open splitter in the Conflo universal interface of the elemental analysis-stable isotope mass spectrometry instrument, and the inert gas is mixed with the sample gas obtained by combustion in the elemental analyzer.

[0008] Normally, the open splitter in the Conflo universal interface used to connect the elemental analyzer and the stable isotope mass spectrometer is only opened before the sample peak appears and after the sample peak integration is completed to allow gas to enter the instrument to prevent air from entering the instrument and further reduce the background. It remains closed during the sample peak process.

[0009] The present invention is a creative improvement based on the existing analysis and detection method - continuous flow analysis. By increasing the injection volume of the test sample on the machine by 10 to 20 times and introducing inert gas into the open splitter in the Conflo universal interface during the detection process, the sample gas is diluted. This not only reduces the stringent requirements of the data on sample uniformity, but also avoids the sample signal being too high beyond the detection range. At the same time, it also reduces the influence of background blank, improves data accuracy and precision, and reduces relative error, thereby achieving the purpose of rapid and accurate detection.

[0010] In the above method, the environmental sample is one or more of soil, plants and animals.

[0011] In the above method, the carbon content of the environmental sample ranges from 1.50% to 50.0%. If the environmental sample is soil, its carbon content ranges from 1.50% to 20.0%, and its sampling amount ranges from 1.0 to 20.0 mg, for example, 2 mg; if the environmental sample is plant or animal, its carbon content ranges from 35% to 45%, and its sampling amount ranges from 0.4 to 1.50 mg.

[0012] Typically, the sampling size of environmental samples is determined by their carbon percentage, with conventional sampling sizes of only 40-50µg for plant and animal samples. This present invention increases the sample size by 10-20 times. In practical applications, the sampling size can be adjusted based on the sample type and carbon content to achieve optimal signal strength. For example, the sampling size for plant or animal samples is approximately 0.4-1mg. For samples with higher carbon contents, a larger sampling size improves the accuracy and precision of carbon stable isotopes and percentages, reducing relative error.

[0013] In the above method, the inert gas is helium.

[0014] In the above method, the inert gas is introduced at a flow rate of 40-80 ml / min, preferably 60 ml / min. By controlling the gas flow rate, the sample gas is diluted, thereby resolving the problem of balancing sample uniformity, sample signal strength, and data accuracy and precision.

[0015] In the above method, the environmental sample is pretreated before being put on the machine; the pretreatment includes: drying the environmental sample and crushing it; the drying temperature is 55-65°C, preferably 60°C; and crushing the sample to a particle size of 80-100 mesh.

[0016] In the above method, the conditions of the elemental analyzer in the detection are: carrier gas flow rate of 95~105ml / min, preferably 100ml / min, helium backflush flow rate in the injector is 110ml / min, oxygen flow rate is 180ml / min, duration is 3s, oxidation furnace temperature is 1020℃, reduction furnace temperature is 680℃, and chromatographic column temperature is 40℃.

[0017] In the above method, the analysis conditions of the stable isotope mass spectrometer in the coupled instrument are: the ion source vacuum is 2.1x10 -6 mBar, and the ion source voltage was 3 kV.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The detection method provided by the present invention has the advantages of good repeatability, high accuracy, low requirement for sample homogeneity, small relative error, etc. The accuracy of carbon stable isotope analysis is RSD ≤ 0.15‰, and the accuracy of carbon percentage analysis is RSD ≤ 0.5%, which meets the needs of routine sample detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This paper analyzes the detection precision and accuracy of carbon content and stable isotopes of two standard substances under different injection volumes.

[0020] Figure 2 The carbon content and13 Determination of stability analysis of C. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific examples, but the present invention is not limited to the following examples.

[0022] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0023] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0024] The sources of reagents and materials used in the following examples are as follows: The plant sample was citrus leaf number GSB-11, which was purchased from the Institute of Geophysical and Geochemical Exploration.

[0025] The soil samples were random blind samples collected in the laboratory.

[0026] Standard chemical glutamic acid USGS40: product number-8573, purchased from Tianjin Oujie Technology Co., Ltd.

[0027] Example 1: Detection of Carbon Stable Isotopes and Their Contents in Plant Samples The specific steps are as follows: (1) Take plant leaf samples, dry them at 60°C, and grind them in a mixer grinder; (2) Wrap about 0.6 mg of the sample to be tested in a tin cup and use elemental analysis-stable isotope mass spectrometry to detect the sample to be tested; in: The operating conditions of the elemental analyzer were as follows: carrier gas flow rate of approximately 100 ml / min, injector He backflush flow rate of 110 ml / min, oxygen flow rate of 180 ml / min, duration of 3 s, oxidation furnace temperature of 1020 °C, reduction furnace temperature of 680 °C, and chromatographic column temperature of 40 °C.

[0028] The operating conditions of the stable isotope mass spectrometer are: the ion source vacuum is 2.1x10 -6 mBar, ion source voltage is 3KV; During the detection process, inert gas was introduced into the open splitter in the Conflo universal interface of the elemental analysis-stable isotope mass spectrometry instrument and mixed with the sample gas obtained by combustion in the elemental analyzer; the Conflo He dilution gas flow rate was 60 ml / min.

[0029] The carbon content of animal samples is similar to that of plant samples. The above method can also be used to detect the carbon stable isotopes and their contents in animal samples.

[0030] Example 2: Detection of Carbon Stable Isotopes and Their Contents in Soil Samples The specific steps are as follows: (1) Take a soil sample, dry it at 60℃, and grind it in a mixer grinder; (2) Wrap about 2 mg of the sample to be tested in a tin cup and use elemental analysis-stable isotope mass spectrometry to detect the sample to be tested; in: The operating conditions of the elemental analyzer were as follows: carrier gas flow rate of approximately 100 ml / min, injector He backflush flow rate of 110 ml / min, oxygen flow rate of 180 ml / min, duration of 3 s, oxidation furnace temperature of 1020 °C, reduction furnace temperature of 680 °C, and chromatographic column temperature of 40 °C.

[0031] The operating conditions of the stable isotope mass spectrometer are: the ion source vacuum is 2.1x10 -6 mBar, ion source voltage is 3KV; During the detection process, inert gas was introduced into the open splitter in the Conflo universal interface of the elemental analysis-stable isotope mass spectrometry instrument and mixed with the sample gas obtained by combustion in the elemental analyzer; the Conflo He dilution gas flow rate was 60 ml / min.

[0032] Example 3: Detection of Carbon Stable Isotopes and Their Contents in Standard Chemicals The specific steps are as follows: (1) Take the standard chemical glutamic acid, wrap about 0.6 mg of the sample to be tested in a tin cup, and use elemental analysis-stable isotope mass spectrometry to detect the sample to be tested; in: The operating conditions of the elemental analyzer were as follows: carrier gas flow rate of approximately 100 ml / min, injector He backflush flow rate of 110 ml / min, oxygen flow rate of 180 ml / min, duration of 3 s, oxidation furnace temperature of 1020 °C, reduction furnace temperature of 680 °C, and chromatographic column temperature of 40 °C.

[0033] The operating conditions of the stable isotope mass spectrometer are: the ion source vacuum is 2.1x10 -6 mBar, ion source voltage is 3KV; During the detection process, inert gas was introduced into the open splitter in the Conflo universal interface of the elemental analysis-stable isotope mass spectrometry instrument and mixed with the sample gas obtained by combustion in the elemental analyzer; the Conflo He dilution gas flow rate was 60 ml / min.

[0034] Test Case 1. Precision (1) Detection using different analytical methods In order to compare the detection accuracy of the improved method provided by the present invention with that of the conventional continuous flow analysis method, the present invention also uses the conventional continuous flow analysis method to detect the samples in Examples 1-3.

[0035] The specific detection steps of the improved continuous flow analysis method are as follows: Accurately weigh the sample to be tested using a 1 / 100000 balance, wrap and compact it with a tin cup, record the weight, and place it in the sample tray of the element analyzer automatic sampler in sequence. Use elemental analysis-stable isotope mass spectrometry to detect the sample to be tested; in: The operating conditions of the elemental analyzer were as follows: carrier gas flow rate of approximately 100 ml / min, injector He backflush flow rate of 110 ml / min, oxygen flow rate of 180 ml / min, duration of 3 s, oxidation furnace temperature of 1020 °C, reduction furnace temperature of 680 °C, and chromatographic column temperature of 40 °C.

[0036] The operating conditions of the stable isotope mass spectrometer are: the ion source vacuum is 2.1x10 -6 mBar, ion source voltage is 3KV; During the detection process, inert gas was introduced into the open splitter in the Conflo universal interface of the elemental analysis-stable isotope mass spectrometry instrument and mixed with the sample gas obtained by combustion in the elemental analyzer; the Conflo He dilution gas flow rate was 60 ml / min.

[0037] One injection can obtain two test results: carbon percentage and carbon stable isotope.

[0038] The test was repeated 6 times.

[0039] Table 1 Detection results of different analytical methods

[0040] It can be seen from the analysis results in Table 1 that for the determination of carbon content and carbon stable isotopes of the three samples, the precision of the detection method provided by the present invention is higher than that of the traditional continuous flow analysis method.

[0041] 2. Analysis of the precision and accuracy of carbon content and carbon stable isotopes under different injection volumes of two standard substances Small injection volume: The specific injection volume of the plant is about 40~50µg, of which the net carbon content is about 20µg; Large injection volume: The specific injection volume of plants is about 400~500µg, of which the net carbon content is about 200µg.

[0042] The test results are as follows Figure 1As shown, the small injection volume measurement corresponds to poor precision (large error bars), while the large injection volume measurement corresponds to better precision (relatively smaller error bars). At the same time, the small injection volume measurement corresponds to poor accuracy, that is, the measured value is far from the true value, while the large injection volume measurement corresponds to better accuracy, that is, the measured value is close to the true value.

[0043] 3. Carbon content and 13 Stability analysis of the determination of C The five blind samples are as follows: sample1, sample2, sample3, sample4, and sample5.

[0044] The test results are as follows Figure 2 As shown in the figure, for the error analysis of carbon content determination, the error corresponding to the small injection volume determination will increase with the increase of carbon content, while the measurement value corresponding to the large injection volume determination also has this rule, but the error is relatively much smaller. 13 C measurement error analysis shows that the measurement value corresponding to the small injection measurement has a larger error as the absolute value of the sample increases, while there is no such rule in the large injection measurement, and the error is very small.

[0045] In summary, the detection method provided by the present invention has the advantages of good repeatability, high accuracy, low requirement for sample homogeneity, and small relative error. The accuracy of carbon stable isotope analysis is RSD≤0.15‰, and the accuracy of carbon percentage analysis is RSD≤0.5%, which meets the needs of routine sample detection.

[0046] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for detecting carbon stable isotopes and their contents in environmental samples, comprising the following steps: detecting environmental sample powder using elemental analysis-stable isotope mass spectrometry; in: The sampling amount of the environmental sample powder is ≥0.4 mg; During the detection process, an inert gas is introduced into the open splitter in the Conflo universal interface of the elemental analysis-stable isotope mass spectrometry instrument, and the inert gas is mixed with the sample gas obtained by combustion in the elemental analyzer.

2. The method according to claim 1, characterized in that The environmental sample is one or more of soil, plants and animals.

3. The method according to claim 2, characterized in that The environmental sample is soil, the carbon content of which ranges from 1.50% to 20.0%, and the sampling amount of which ranges from 1.0 to 20.0 mg; The environmental sample is a plant or animal, has a carbon content in the range of 35-45%, and a sampling amount in the range of 0.4-1.50 mg.

4. The method according to any one of claims 1 to 3, characterized in that The inert gas is helium.

5. The method according to any one of claims 1 to 4, characterized in that The inert gas flow rate is 40-80 ml / min.

6. The method according to any one of claims 1 to 5, characterized in that The environmental samples are pre-treated before being put on the machine; The pretreatment includes: drying the environmental sample and crushing it; the drying temperature is 55-65° C., and the crushing is performed to a particle size of 80-100 mesh.

7. The method according to any one of claims 1 to 6, characterized in that The conditions of the elemental analyzer in the detection are as follows: carrier gas flow rate of 95-105 ml / min, helium backflush flow rate in the injector of 110 ml / min, oxygen flow rate of 180 ml / min, duration of 3 s, oxidation furnace temperature of 1020°C, reduction furnace temperature of 680°C, and chromatographic column temperature of 40°C.

8. The method according to any one of claims 1 to 7, characterized in that The analysis conditions of the stable isotope mass spectrometer in the combined instrument are: the ion source vacuum is 2.1x10 -6 mBar, and the ion source voltage was 3 kV.

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