Method for analyzing dissolved organic matters in soil based on pyrolysis gas chromatography-mass spectrometry

Abstract

The invention provides a method for analyzing soil soluble organic matters based on pyrolysis gas chromatography-mass spectrometry, and belongs to the technical field of soil analysis. The method provided by the invention comprises the following steps: mixing a soil sample with water, and carrying out water extraction to obtain soluble organic matters; carrying out thermal cracking on the soluble organic matter to obtain volatile gas; introducing the volatile gas into a gas chromatograph-mass spectrometer for testing and analysis; the temperature of the thermal cracking is 550 to 750 DEG C; the stationary phase of a gas chromatographic column in the gas chromatograph-mass spectrometer is polysiloxane; the scanning range of the mass spectrum in the gas chromatograph-mass spectrometer is 30 to 700 m / z. According to the method, a pyrolysis gas chromatography-mass spectrometry technology is utilized, proper detection conditions are selected, and the dissolved organic matter DOM in the soil is accurately identified and quantified; a water extraction method is used for extracting a soil sample, so that the use of an organic solvent is reduced, and the method is environment-friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of soil analysis, and in particular relates to a method for analyzing soil dissolved organic matter based on pyrolysis-gas chromatography-mass spectrometry. Background Art

[0002] Dissolved organic matter (DOM) refers to organic matter that can dissolve in water and pass through a 0.45μm filter membrane. It is a key component of soil organic matter (SOM). It plays an important role in improving soil fertility, promoting plant growth, enhancing nutrient cycling and protecting the environment. It is an important part of the global carbon cycle. Organic carbon in the soil is decomposed, transformed and moved in the form of DOM, affecting the carbon storage and flow in the soil and water. At the same time, DOM is also the main energy and carbon source for soil microorganisms, driving the metabolic activities and ecological functions of microorganisms. By promoting microbial activity, DOM plays an important role in the degradation, mineralization and nutrient release of organic matter.

[0003] DOM contains a variety of complex organic substances, such as sugars, fatty acids, phenols, aromatics and polycyclic aromatic hydrocarbons, etc., which are complex and traditional methods cannot fully detect the organic matter components in soil DOM. For example, wet chemical methods often use acid-base digestion or liquid phase extraction, which are cumbersome and may cause the loss or degradation of the target; spectral analysis uses ultraviolet-visible, fluorescence or infrared spectroscopy for preliminary qualitative analysis, but the recognition of specific compounds is insufficient; liquid chromatography can quantify some compounds, but the resolution is limited and cannot fully cover the complex components of DOM. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for analyzing soil dissolved organic matter based on pyrolysis gas chromatography-mass spectrometry. The method provided by the present invention is efficient, rapid, highly sensitive, and environmentally friendly, and can perform qualitative and quantitative analysis on soil.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] The present invention provides a method for analyzing soil dissolved organic matter based on pyrolysis-gas chromatography-mass spectrometry, comprising the following steps:

[0007] Soil samples were mixed with water for water extraction to obtain dissolved organic matter;

[0008] thermally cracking the dissolved organic matter to obtain volatile gas;

[0009] Introducing the volatile gas into a gas chromatograph-mass spectrometer for testing and analysis;

[0010] The temperature of the thermal cracking is 550-750°C;

[0011] The stationary phase of the gas chromatographic column in the gas chromatography-mass spectrometry instrument is polysiloxane;

[0012] The scanning range of the mass spectrometer in the gas chromatography-mass spectrometry instrument is 30-700 m / z.

[0013] Preferably, the thermal cracking is carried out under a protective gas atmosphere;

[0014] The thermal cracking time is 10 to 25 seconds.

[0015] Preferably, the chromatographic column of the gas chromatograph in the gas spectrometer is VF-5MS; the injection port temperature is 250-350°C; the detector temperature is 260-330°C; the injector temperature is 260-330°C; the delivery pipeline temperature is 220-260°C; and protective gas is used as the carrier gas.

[0016] Preferably, the column oven in the gas chromatograph uses staged temperature increase to separate the volatile gases.

[0017] Preferably, the stepwise heating includes maintaining the temperature at 38-43°C for 1-3 min, heating to 260-330°C at a rate of 6-10°C / min and maintaining the temperature for 8-15 min.

[0018] Preferably, the mass spectrometer in the gas chromatography-mass spectrometry instrument adopts an EI ion source; the ionization energy is 60 to 80 eV; and a scan is performed once per second.

[0019] Preferably, the mass volume ratio of the soil sample to water is 1 g:6-10 mL.

[0020] Preferably, after the water extraction, the method further comprises: performing solid-liquid separation on the obtained water-extracted sample, performing membrane filtration on the separated liquid, and freeze-drying the filtrate.

[0021] Preferably, the pore size of the filter membrane used for the membrane filtration is 0.4-0.5 μm.

[0022] Preferably, the dissolved organic matter analyzed in the test includes one or more of nitrogen compounds, aliphatic hydrocarbons, aromatic hydrocarbons, lignin, phenolic compounds, polysaccharides and sulfur-containing compounds.

[0023] The present invention provides a method for analyzing soil dissolved organic matter based on pyrolysis gas chromatography-mass spectrometry, comprising the following steps: mixing a soil sample with water for water extraction to obtain dissolved organic matter; thermally cracking the dissolved organic matter to obtain volatile gas; introducing the volatile gas into a gas chromatography-mass spectrometer for testing and analysis; the temperature of the thermal cracking is 550-750°C; the stationary phase of the gas chromatographic column in the gas chromatography-mass spectrometer is polysiloxane; the scanning range of the mass spectrum in the gas chromatography-mass spectrometer is 30-700m / z. The present invention utilizes pyrolysis gas chromatography-mass spectrometry technology, selects appropriate detection conditions, accurately identifies and quantifies dissolved organic matter DOM in soil; utilizes water extraction to extract soil samples, reduces the use of organic solvents, and is environmentally friendly.

[0024] The beneficial effects of the present invention are as follows: (1) the pyrolysis process can rapidly decompose the sample and directly convert the complex organic matter into volatile compounds. The entire analysis process is faster than traditional chemical analysis. The use of a gas chromatography-mass spectrometry (GC-MS) instrument to identify the organic matter components of soil DOM reduces the cumbersome sample processing steps and improves the analysis efficiency. (2) The use of gas chromatography-mass spectrometry technology can be used to perform comprehensive qualitative and quantitative analysis of complex organic matter in DOM, including a variety of sugars, phenols, fatty acids, aromatic compounds, etc.; (3) by selecting appropriate gas chromatography-mass spectrometry analysis conditions, compounds with extremely low contents in the sample can be detected, with high detection sensitivity and selectivity. For DOM analysis of complex samples, trace organic pollutants can be effectively identified; (4) by comparing with a database and using a variety of data analysis methods, rich DOM chemical composition and structural information can be extracted from Py-GC-MS data. The data has strong repeatability and comparability, providing reliable data support for soil research. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 GC-MS spectra obtained in Example 1(a) and Example 2(b);

[0027] Figure 2 GC-MS spectra obtained in Example 3 and Comparative Example 1;

[0028] Figure 3 GC-MS spectra obtained in Comparative Examples 2 to 3;

[0029] Figure 4This is the GC-MS spectrogram obtained in Example 4;

[0030] Figure 5 This is the GC-MS spectrogram obtained in Example 5;

[0031] Figure 6 This is the GC-MS spectrum obtained in Example 6;

[0032] Figure 7 This is the GC-MS spectrum obtained in Example 7;

[0033] Figure 8 This is the GC-MS spectrum obtained in Example 8. DETAILED DESCRIPTION

[0034] The present invention provides a method for analyzing soil dissolved organic matter based on pyrolysis-gas chromatography-mass spectrometry, comprising the following steps:

[0035] Soil samples were mixed with water for water extraction to obtain dissolved organic matter;

[0036] thermally cracking the dissolved organic matter to obtain volatile gas;

[0037] Introducing the volatile gas into a gas chromatograph-mass spectrometer for testing and analysis;

[0038] The temperature of the thermal cracking is 550-750°C;

[0039] The stationary phase of the gas chromatographic column in the gas chromatography-mass spectrometry instrument is polysiloxane;

[0040] The scanning range of the mass spectrometer in the gas chromatography-mass spectrometry instrument is 30-700 m / z.

[0041] In the present invention, unless otherwise specified, the raw materials and equipment used are commercially available products well known in the art.

[0042] The present invention mixes soil samples with water for water extraction to obtain soluble organic matter.

[0043] In the present invention, the soil sample preferably includes paddy field soil, pasture soil, wetland soil or cotton field soil.

[0044] In the present invention, the ratio of the mass of the soil sample to the volume of water is preferably 1g:6-10mL. In a specific embodiment, the ratio of the mass of the soil sample to the volume of water can be 1g:6mL, 1g:8mL, 1g:9mL or 1g:10mL.

[0045] In the present invention, the water extraction is preferably carried out in an oscillating manner, and the frequency of the oscillation is preferably 150 to 300 rpm, more preferably 200 rpm; the oscillation time is preferably 25 to 35 min, more preferably 30 min.

[0046] In the present invention, after the water extraction, the method preferably further comprises: performing solid-liquid separation on the obtained water-extracted sample, performing membrane filtration on the separated liquid, and freeze-drying the filtrate.

[0047] The present invention has no special requirements for the solid-liquid separation method, and the commonly used technical means in the art can be used. In a specific embodiment of the present invention, a centrifugal method is used to obtain a supernatant, and the rotation speed is preferably 3500 rpm and the centrifugal time is preferably 20 minutes. The supernatant contains soluble organic matter.

[0048] In the present invention, the separated liquid is subjected to membrane filtration, and the filtrate is freeze-dried. The pore size of the filter membrane used for the membrane filtration is preferably 0.4-0.5 μm. In a specific embodiment, the pore size of the filter membrane used for the membrane filtration can be 0.40 μm, 0.42 μm, 0.45 μm, 0.48 μm or 0.50 μm.

[0049] Specifically, the soil sample is mixed with water, shaken, centrifuged, the supernatant is filtered, and the filtrate is freeze-dried to obtain dissolved organic matter.

[0050] After obtaining the soluble organic matter, the present invention performs thermal cracking on the soluble organic matter to obtain volatile gas.

[0051] In the present invention, the temperature of the thermal cracking is 550-750°C. In a specific embodiment, the temperature of the thermal cracking can be 550°C, 600°C, 620°C, 650°C, 700°C or 750°C; the time of the thermal cracking is preferably 10-25s. In a specific embodiment, the time of the thermal cracking can be 10s, 15s, 20s or 25s. In the present invention, the thermal cracking is preferably carried out under a protective gas atmosphere, such as a nitrogen atmosphere. The present invention decomposes organic matter into small molecular gases by thermal cracking.

[0052] After obtaining the volatile gas, the present invention introduces the volatile gas into a gas chromatograph-mass spectrometer for testing and analysis.

[0053] In the present invention, the chromatographic column of the gas chromatograph in the gas chromatograph-gas spectrometer is preferably VF-5MS; the stationary phase of the gas chromatographic column is polysiloxane; the specification of the gas chromatographic column is preferably Varian factor FOUR VF-5MS30m×0.25mm×0.25μm. In the present invention, the injection port temperature of the gas chromatograph is preferably 250-350°C. In a specific embodiment, the injection port temperature of the gas chromatograph may be 250°C, 300°C or 350°C. In the present invention, the detector temperature of the gas chromatograph is preferably 260-330°C. In a specific embodiment, the detector temperature of the gas chromatograph may be 260°C, 300°C or 330°C. In the present invention, the temperature of the injector of the gas chromatograph is preferably 260-330°C. In a specific embodiment, the temperature of the injector of the gas chromatograph may be 260°C, 300°C or 330°C. In the present invention, the temperature of the delivery pipeline of the gas chromatograph is preferably 220-260° C. In a specific embodiment, the temperature of the delivery pipeline of the gas chromatograph can be 220° C., 240° C. or 260° C. In the present invention, the gas chromatograph preferably uses a protective gas as a carrier gas, such as helium.

[0054] In the present invention, the column oven in the gas chromatograph preferably uses segmented heating to separate volatile gases. The segmented heating preferably includes maintaining at 38-43°C for 1-3 minutes, heating to 260-330°C at a rate of 6-10°C / min and maintaining for 8-15 minutes; specifically, first adjusting the column oven temperature to 40°C and maintaining for 2 minutes, then increasing the temperature to 300°C at a heating rate of 8°C / min and maintaining for 10 minutes.

[0055] The present invention separates the small molecule gases in the volatile gas by means of a gas chromatograph, and then performs qualitative or quantitative analysis on the separated components by means of a mass spectrometer.

[0056] In the present invention, the scanning range of the mass spectrometer in the gas chromatography-mass spectrometry instrument is 30 to 700 m / z, preferably 45 to 600 m / z.

[0057] In the present invention, the mass spectrometer in the gas chromatography-mass spectrometer preferably adopts an EI ion source; the ionization energy is preferably 60 to 80 eV, more preferably 65 to 75 eV, and further preferably 70 eV; and preferably a scan is performed once per second.

[0058] In the present invention, the dissolved organic matter analyzed in the test preferably includes one or more of nitrogen compounds, aliphatic compounds, aromatic hydrocarbons, lignin, phenolic compounds, polysaccharides and sulfur-containing compounds. The present invention preferably compares the obtained spectrum with a database to identify and quantify each organic matter component in DOM and establish its chemical structure and content.

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described in conjunction with specific embodiments below. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Any modification, equivalent replacement, improvement, etc. made to the implementation methods of the present invention based on the technical essence and general principles of the present invention without creative work should be within the scope of protection of the present invention.

[0060] The gas chromatograph used a Varian factorFOUR VF-5MS capillary column coated with a polysiloxane stationary phase (30 m × 0.25 mm × 0.25 μm) to separate the volatile gases. The column oven temperature was first adjusted to 40 °C and maintained for 2 min, then increased to 300 °C at a heating rate of 8 °C / min and maintained for 10 min. Helium was used as the carrier gas, and the temperatures of the injector and delivery pipeline were maintained at 300 °C and 240 °C, respectively. The temperature of the GC interface and 1077 injector (split mode) was 300 °C.

[0061] The pyrolyzer used was a CDS 5000 pyroprobe platinum heating wire pyrolyzer (Chemical Data System Analytical, Oxford, PA).

[0062] The pyrolyzer was directly connected to a Varian 3900GC and coupled to a Varian Saturn 2100T ion trap mass spectrometer (MS).

[0063] Example 1

[0064] Paddy field soil samples of black soil were collected from Zhalong Wetland. 10 g of soil sample was mixed with 80 mL of deionized water and shaken at 200 rpm for 30 min to obtain a wet sample. The wet sample was centrifuged at 3500 rpm for 20 min, and the supernatant was retained to obtain dissolved organic matter. The supernatant was filtered using a 0.45 μm membrane filter, and the filtrate was freeze-dried to obtain a pure DOM sample.

[0065] The pure DOM sample was placed in a pyrolyzer and pyrolyzed and analyzed at 620°C for 20 seconds to obtain volatile gases. The volatile gases were introduced into a gas chromatograph (GC) for material separation to obtain separated compounds.

[0066] The separated compounds were directly put into the mass spectrometer (MS), and the mass spectrum was recorded once per second under the conditions of ionization energy of 70 eV and scanning range of 45-600 m / z. The organic matter components in the soil were determined by ionization and mass analysis. The analysis results were obtained. Figure 1In (a), N is a nitrogen compound, A is an aliphatic, Ar is an aromatic hydrocarbon, L is lignin, Ph is a phenolic compound, Ps is a polysaccharide, and S is a sulfur-containing compound.

[0067] Example 2

[0068] The soil sample was replaced with paddy soil from Kaiyuan, Yunnan. Other conditions were the same as in Example 1. The analysis results were Figure 1 Middle (b).

[0069] Example 3

[0070] The soil sample was replaced with pasture soil, placed in a pyrolyzer, and pyrolyzed and analyzed at 400°C for 20 seconds. Other conditions were the same as in Example 1. The analysis results were obtained. Figure 2 Middle 400℃ curve.

[0071] Comparative Example 1

[0072] The soil sample was replaced with pasture soil, placed in a pyrolyzer, and pyrolyzed and analyzed at 520°C for 20 seconds. Other conditions were the same as in Example 1. The analysis results were obtained. Figure 2 Middle 520℃ curve.

[0073] Comparative Example 2

[0074] The soil sample was replaced with pasture soil, placed in a pyrolyzer, and pyrolyzed and analyzed at 620°C for 20 seconds. Other conditions were the same as in Example 1. The analysis results were obtained. Figure 3 Middle 620℃ curve.

[0075] Comparative Example 3

[0076] The soil sample was replaced with pasture soil, placed in a pyrolyzer, and pyrolyzed and analyzed at 800°C for 20 seconds. Other conditions were the same as in Example 1. The analysis results were obtained. Figure 3 Middle 800℃ curve.

[0077] Figure 2 The GC-MS spectra obtained in Example 3 and Comparative Example 1 are shown. Figure 3 The GC-MS spectra obtained in Comparative Examples 2 to 3 are shown in FIG. Figures 2-3 The spectra of the samples were analyzed, from which it can be seen that under the same sample conditions, more dissolved organic matter in the soil can be detected by thermal cracking at 620℃. When the temperature is low, some dissolved organic matter cannot be cracked, resulting in the inability of GC-MS to detect it. When the temperature is too high, the corresponding optimal pyrolysis time may be shortened, resulting in more side reactions and a decrease in the yield of each product.

[0078] Example 4

[0079] The soil sample was replaced with soil from the coastal wetland of Minjiang River. Other conditions were the same as those in Example 1. The analysis results were Figure 4 curve.

[0080] Example 5

[0081] The soil sample was replaced with soil from Zoige peat wetland. Other conditions were the same as in Example 1. The analysis results were Figure 5 curve.

[0082] Example 6

[0083] The soil sample was replaced with cotton field soil. Other conditions were the same as in Example 1. The analysis results were obtained. Figure 6 curve.

[0084] Example 7

[0085] The soil sample was replaced with Kaiyuan soil. Other conditions were the same as in Example 1. The analysis results were Figure 7 curve.

[0086] Example 8

[0087] The soil sample was replaced with pasture soil. Other conditions were the same as in Example 1. The analysis results were Figure 8 curve.

[0088] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for analyzing soil dissolved organic matter based on pyrolysis-gas chromatography-mass spectrometry, characterized in that: The following steps are involved: Soil samples were mixed with water for water extraction to obtain dissolved organic matter; thermally cracking the dissolved organic matter to obtain volatile gas; Introducing the volatile gas into a gas chromatograph-mass spectrometer for testing and analysis; The temperature of the thermal cracking is 550-750°C; The stationary phase of the gas chromatographic column in the gas chromatography-mass spectrometry instrument is polysiloxane; The scanning range of the mass spectrometer in the gas chromatography-mass spectrometry instrument is 30-700 m / z.

2. The method according to claim 1, characterized in that The thermal cracking is carried out under a protective gas atmosphere; The thermal cracking time is 10 to 25 seconds.

3. The method according to claim 1, characterized in that The chromatographic column of the gas chromatograph in the gas chromatograph-gas spectrometer is VF-5MS; the injection port temperature is 250-350°C; the detector temperature is 260-330°C; the injector temperature is 260-330°C; the delivery pipeline temperature is 220-260°C; and protective gas is used as carrier gas.

4. The method according to claim 3, characterized in that The column oven in the gas chromatograph separates the volatile gas by heating in stages.

5. The method according to claim 4, characterized in that The stepwise heating includes maintaining the temperature at 38-43° C. for 1-3 min, heating to 260-330° C. at a rate of 6-10° C. / min and maintaining the temperature for 8-15 min.

6. The method according to claim 1, characterized in that The mass spectrometer in the gas chromatography-mass spectrometer adopts an EI ion source; the ionization energy is 60-80 eV; and a scan is performed once per second.

7. The method according to claim 1, characterized in that The mass volume ratio of the soil sample to water is 1 g:6-10 mL.

8. The method according to claim 1, characterized in that After the water extraction, the method further comprises: performing solid-liquid separation on the obtained water extraction sample, performing membrane filtration on the separated liquid, and freeze-drying the filtrate.

9. The method according to claim 8, characterized in that The pore size of the filter membrane used for the membrane filtration is 0.4-0.5 μm.

10. The method according to any one of claims 1 to 9, characterized in that: The volatile gases analyzed in the test include one or more of nitrogen compounds, aliphatic compounds, aromatic hydrocarbons, lignin, phenolic compounds, polysaccharides and sulfur-containing compounds.

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