A method for rapid detection of multiple types of organic matter in soil and sediment based on dynamic headspace-microextraction combination

Abstract

The application discloses a kind of based on dynamic headspace-micro extraction coupling fast detection method of multiple types of organic matters in soil and sediment, comprising the following steps: S1 takes homogeneous soil or sediment sample, in situ sealing sample, water is added to moisture content and is added deuterium substitution internal standard;S2 is blown by nitrogen at 40-80 DEG C, and VOCs is enriched in micro extraction tube;S3 continues to blow and enrich SVOCs by heating to 150-300 DEG C;S4 is rapidly heated to 220-320 DEG C thermal desorption;S5 desorption enters GC-MS detection;S6 is combined mass spectrum, and the concentration of VOCs and SVOCs is quantified using internal standard / external standard method.The method process is simple, efficient, green and environmentally friendly, and multiple types of organic matter can be detected simultaneously and quickly.The application couples dynamic headspace with micro extraction, which can simultaneously capture VOCs and SVOCs in a single pretreatment without separate processing, can shorten sample processing time, realize continuous detection of batch samples, and greatly improve efficiency compared with traditional methods, thereby reducing detection cost, and the detection limit can reach ppb-ppt level.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring and analysis technology, and specifically relates to a rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction. Background Technology

[0002] Soil and aquatic sediments serve as important carriers of environmental pollutants. Accurate detection of organic pollutants (including volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) such as benzene compounds, polycyclic aromatic hydrocarbons, organochlorine pesticides, and petroleum hydrocarbons) within them is a core technological support for environmental quality assessment, contaminated site remediation, ecological risk assessment, and emergency response to sudden environmental incidents. With increasingly stringent ecological and environmental protection requirements, higher standards are being set for the efficiency, accuracy, automation, and environmental friendliness of detection for various types of organic matter in soil and sediments. However, existing detection technologies have significant shortcomings and struggle to meet practical application needs.

[0003] Current conventional techniques for detecting organic matter in soil and sediments employ a separate pretreatment approach for VOCs and SVOCs, with the two techniques being completely separate and exhibiting extremely poor compatibility. VOCs detection often utilizes purge-and-trap or static headspace methods, relying on low-temperature purge and adsorption-and-trap to effectively extract VOCs, but cannot release higher-boiling-point SVOCs. SVOCs detection commonly employs solvent extraction methods such as Soxhlet extraction, pressurized fluid extraction, and ultrasonic extraction, consuming large amounts of organic solvents and only extracting heavy SVOCs, failing to simultaneously capture VOCs. This separate processing method requires at least two independent pretreatments and two instrument injections for a single sample to complete full-spectrum analysis of VOCs and SVOCs. The pretreatment process is cumbersome and time-consuming, with traditional methods typically taking 4-8 hours to process a single sample. This results in extremely low efficiency for batch sample detection and persistently high detection costs.

[0004] Meanwhile, existing technologies have serious shortcomings in terms of detection accuracy and sample representativeness. VOCs are highly volatile, and existing fractional processing requires multiple transfers and homogenizations of samples, which can easily lead to VOCs volatilization and loss, resulting in low detection results and poor data repeatability. The large amount of organic solvents used in solvent extraction methods not only introduces impurities and interference but also easily causes cross-contamination of samples. Furthermore, organic solvents themselves are toxic, posing health risks to laboratory personnel and secondary pollution of waste liquids, which is inconsistent with the development concept of green analytical chemistry.

[0005] Furthermore, existing detection technologies have extremely low levels of automation. The various pretreatment steps (sample loading, purging, extraction, enrichment, and injection) are separated, heavily reliant on manual operation. This results in numerous manual interventions and significant errors, making it difficult to achieve high-throughput, unattended continuous detection and unsuitable for the rapid screening needs of large batches of samples from contaminated sites. Therefore, there is an urgent need to develop a fully automated detection technology that integrates sample preparation, extraction, enrichment, and injection, simultaneously capturing VOCs and SVOCs, and possessing high efficiency, high accuracy, and environmental friendliness, to address the core pain points of existing technologies.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction, thereby overcoming the defects in the prior art.

[0008] To achieve the above objectives, this invention provides a rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction, comprising the following steps: S1: In-situ sealed sample preparation. Take homogenized soil or water sediment samples, put the samples into sample bottles, add deionized water to adjust the water content, add deuterated isotope internal standard solution, and then seal the bottle. S2: Low-temperature dynamic headspace purge and VOCs microextraction enrichment. A purge needle and a gas outlet needle are inserted into the sample vial. Nitrogen gas is introduced as the purge carrier gas. The sample is purged at 40-80℃. The VOCs in the sample are introduced into the microextraction enrichment tube with the purge gas and are adsorbed and enriched. S3: High-temperature enhanced purging and deep enrichment of SVOCs. The sample vial is heated to 150-300℃ and purged continuously. The SVOCs in the sample are carried into the microextraction enrichment tube with the purging gas and are adsorbed and enriched. S4: Rapid thermal desorption. After step S3 is completed, the microextraction enrichment tube is rapidly heated to 220-320℃ to thermally desorb VOCs and SVOCs in the microextraction enrichment tube. S5: Gas chromatography-mass spectrometry analysis, sending thermally desorbed VOCs and SVOCs into a gas chromatography-mass spectrometry instrument for detection; S6: Qualitative and quantitative analysis, based on mass spectra, uses internal or external standard methods to quantitatively calculate VOCs and SVOCs to obtain concentration results.

[0009] Preferably, the nitrogen flow rate during step S2 purging is 20-80 mL / min, and the purging time is 5-20 min.

[0010] Preferably, the nitrogen flow rate during step S3 purging is 20-80 mL / min, and the purging time is 10-30 min.

[0011] Preferably, the microextraction enrichment tubes in steps S2 and S3 are filled with a composite adsorbent.

[0012] Preferably, the heating method in step S3 is linear heating or stepped heating.

[0013] Preferably, during the thermal desorption step S4, the heating rate is ≥80℃ / s, and the temperature is held constant for 1-5 minutes after reaching the target temperature.

[0014] Preferably, in step S5, gas chromatography uses a weakly polar capillary column, and mass spectrometry uses an electron impact ionization source.

[0015] Preferably, the VOCs include benzene, toluene, ethylbenzene, and xylene, and the SVOCs include naphthalene, phenanthrene, anthracene, organochlorine pesticides, and petroleum hydrocarbons.

[0016] Preferably, the method is applicable to contaminated site investigation, farmland soil monitoring, water sediment quality assessment, remediation process tracking, and emergency detection scenarios for sudden environmental accidents.

[0017] Compared with the prior art, one aspect of the present invention has the following beneficial effects: (1) This invention couples dynamic headspace with microextraction, and VOCs and SVOCs can be captured simultaneously in a single pretreatment without separate processing. This can shorten the sample processing time, realize continuous detection of batch samples, and significantly improve efficiency compared with traditional methods, thereby reducing detection costs. (2) The present invention adopts in-situ sealed sample loading throughout the process, without sample transfer and homogenization, which can effectively avoid VOCs volatilization loss, and the closed gas path reduces cross-contamination. Microextraction enrichment can improve sensitivity, and the detection limit can reach ppb-ppt level. (3) This invention requires no or only a trace amount of organic solvent, avoiding the large amount of reagent consumption of traditional solvent extraction, reducing the health hazards of toxic reagents to experimental personnel, reducing waste liquid treatment costs and secondary pollution risks, and meeting the development requirements of green analytical chemistry. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a rapid detection method for multiple types of organic matter in soil and water sediments based on dynamic headspace-microextraction. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0020] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0021] Example 1:

[0022] A rapid detection method for multiple types of organic matter in soil and aquatic sediments based on dynamic headspace-microextraction (HME) coupling includes the following steps: S1: In-situ sealed sample preparation: 2.0 g of homogeneous soil sample from a chemical contaminated site was directly placed into a 20 mL headspace sample vial with a polytetrafluoroethylene sealing septum; 0.5 mL of deionized water was added to adjust the sample moisture content and promote the release of volatile organic compounds; 100 μL of a mixed deuterated isotope internal standard solution containing deuterated benzene and deuterated naphthalene was added, and the vial was sealed. No sample transfer was performed throughout the process to avoid loss of volatile components. S2: Low-temperature dynamic headspace purge and VOCs microextraction enrichment. The sealed sample bottle is placed in the heated purge station, and the purge needle and gas path outlet needle are inserted into the bottle. High-purity nitrogen gas with a purity ≥99.999% is introduced as the purge carrier gas. The purge temperature is set to 60℃, the purge flow rate is 50mL / min, and the purge time is 12 min. Volatile organic compounds such as benzene, toluene, and xylene in the sample are continuously carried out with the purge gas and enter the microextraction enrichment tube filled with composite adsorbent (Tenax (poly(2,6-diphenyl-p-phenyl ether) and Carbopack (graphitized carbon black)) in the closed gas path, where they are selectively adsorbed and enriched. S3: High-temperature enhanced purging and deep enrichment of SVOCs. The purging gas path is kept closed and connected. The temperature of the sample vial is raised from 60 ℃ to 220 ℃ at a constant rate using a linear temperature program. The purging flow rate is kept constant at 50 mL / min and purging is continued for 18 min. Under high temperature conditions, high-boiling-point semi-volatile organic compounds such as naphthalene, phenanthrene, anthracene, organochlorine pesticides and petroleum hydrocarbons in the sample matrix are effectively released and enter the microextraction enrichment tube with the gas flow to complete deep adsorption and enrichment. S4: Rapid thermal desorption. After purging, the microextraction enrichment tube is subjected to rapid temperature-programmed thermal desorption. The heating rate is set to 120℃ / s, and the temperature is rapidly increased to 280℃ and held constant for 3 min. The volatile and semi-volatile organic compounds adsorbed in the enrichment tube are instantly thermally desorbed, forming a high-concentration organic component stream. S5: Gas chromatography-mass spectrometry (GC-MS) analysis. The desorbed organic components flow directly into the GC-MS instrument via a 200℃ constant-temperature heated transfer line. The GC uses a DB-5MS weakly polar capillary column with the following chromatographic conditions: initial column temperature 40℃, hold for 2 min, increase to 280℃ at a rate of 10℃ / min, and hold for 5 min. The mass spectrometry uses an electron impact ionization source with an ion source temperature of 230℃. Mass spectrometry data are acquired in full scan mode to achieve simultaneous separation and detection of multiple targets.

[0023] S6: Qualitative and quantitative analysis, qualitative identification is performed by comparing chromatographic retention time with standard mass spectrum library; calibration curve is established using internal standard method, and quantitative calculations are performed on target substances such as benzene, toluene, naphthalene, and phenanthrene in the sample to obtain the concentration results of each organic compound.

[0024] The detection results of this embodiment show that the detection limit for benzene is 0.1 ppb, the detection limit for toluene is 0.05 ppb, and the detection limit for total xylene is 0.08 ppb. The detection limits for naphthalene are 0.3 ppb, for phenanthrene 0.20 ppb, and for petroleum hydrocarbons 3.5 ppb. The total time from sample loading to result output for a single sample is approximately 29 minutes. Compared with traditional separate pretreatment methods, the detection efficiency is significantly improved. Furthermore, it requires no organic solvents, is environmentally friendly, and provides good data accuracy and repeatability.

[0025] Example 2:

[0026] A rapid detection method for multiple types of organic matter in soil and aquatic sediments based on dynamic headspace-microextraction (HME) coupling includes the following steps: S1: In-situ sealed sample loading: 3.0g of homogeneous sediment sample from the surface layer (0-10cm) of a freshwater lake was selected. After low-temperature and light-protected transportation, freeze-drying, and grinding through a 1mm sieve, it was directly loaded into a 20mL headspace sample vial with a polytetrafluoroethylene sealing septum. 0.8mL of deionized water was added to adjust the sample moisture content and optimize the release efficiency of volatile organic compounds. 100μL of a mixed deuterated isotope internal standard solution containing deuterated ethylbenzene and deuterated phenanthrene was added, and the vial was sealed. There was no sample transfer or open operation throughout the process to avoid loss of volatile components and external contamination. S2: Low-temperature dynamic headspace purge and VOCs microextraction enrichment. The sealed sample bottle is placed in the heated purge station, and a 1 / 16-inch stainless steel purge needle and gas path outlet needle are inserted into the bottle. High-purity nitrogen gas with a purity ≥99.999% and an oxygen content <2ppm is introduced as the purge carrier gas. The purge temperature is set to 50℃, the purge flow rate is 60mL / min, and the purge time is 15min. Volatile organic compounds such as ethylbenzene, o-xylene, m-xylene, and p-xylene in the sample are continuously carried out with the purge gas and enter the microextraction enrichment tube filled with composite adsorbent (Tenax (poly(2,6-diphenyl-p-phenyl ether) GR and Carbopack (graphitized carbon black) X) in the 80℃ constant temperature closed gas path, where they are selectively adsorbed and enriched. S3: High-temperature enhanced purging and deep enrichment of SVOCs. The purging gas path is kept closed and continuously flowing. A step-by-step temperature program is used to gradually increase the temperature of the sample vial from 50℃ to 250℃. The purging flow rate is kept constant at 60mL / min and purging is continued for 20min. Under high temperature conditions, high-boiling-point semi-volatile organic compounds such as phenanthrene, fluoranthene, DDT, and phthalates in the sample matrix are fully released and enter the microextraction enrichment tube with the gas flow to complete deep adsorption and enrichment. S4: Rapid thermal desorption. After purging, the microextraction enrichment tube is subjected to rapid programmed temperature rise thermal desorption. The heating rate is set to 100℃ / s, rapidly rising to 300℃ and holding at a constant temperature for 2 minutes. The volatile and semi-volatile organic compounds adsorbed in the enrichment tube are instantly thermally desorbed, forming a high-concentration organic component stream. After desorption, the enrichment tube is purified by high-temperature baking to eliminate residual memory effect. S5: Gas chromatography-mass spectrometry (GC-MS) analysis. The desorbed organic components flow directly into the GC-MS instrument via a 200℃ isothermal heated transfer line, using splitless injection mode with an injection port temperature of 270℃. GC employs a DB-5MS weakly polar capillary column with the following chromatographic conditions: initial column temperature 45℃, hold for 2 min, ramp to 180℃ at a rate of 12℃ / min, hold for 1 min, then ramp to 290℃ at a rate of 6℃ / min, hold for 6 min. Mass spectrometry uses an electron impact ionization source with an ion source temperature of 230℃ and a transfer line temperature of 280℃. Full scan mode (m / z 35-500) is used to acquire mass spectrometry data, enabling simultaneous separation and detection of multiple targets. S6: Qualitative and quantitative analysis. Qualitative identification is performed by comparing the chromatographic retention time (deviation < 0.1 min) with the NIST 2020 standard mass spectrometry library. A 5-point calibration curve is established using the internal standard method. Quantitative calculations are performed on target substances such as ethylbenzene, xylene, phenanthrene, and DDT in the sample to obtain the concentration results of each organic compound.

[0027] The detection results of this embodiment show that the detection limit for ethylbenzene is 0.06 ppb, the detection limit for total xylene is 0.07 ppb, the detection limit for phenanthrene is 0.20 ppb, the detection limit for fluorescein is 0.25 ppb, and the detection limit for DDT is 0.15 ppb. The total time from sample loading to result output for a single sample is approximately 32 minutes. Compared with the traditional separate pretreatment method, the detection efficiency is significantly improved. The entire process requires no organic solvents, making it green and low-consumption. The data accuracy and repeatability are good in sediment matrices with high organic matter and high water content, making it suitable for rapid and accurate detection of trace organic matter of various types in aquatic sediments.

[0028] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction, characterized in that, Includes the following steps: S1: In-situ sealed sample preparation. Take homogenized soil or water sediment samples, put the samples into sample bottles, add deionized water to adjust the water content, add deuterated isotope internal standard solution, and then seal the bottle. S2: Low-temperature dynamic headspace purge and VOCs microextraction enrichment. A purge needle and a gas outlet needle are inserted into the sample vial. Nitrogen gas is introduced as the purge carrier gas. The sample is purged at 40-80℃. The VOCs in the sample are introduced into the microextraction enrichment tube with the purge gas and are adsorbed and enriched. S3: High-temperature enhanced purging and deep enrichment of SVOCs. The sample vial is heated to 150-300℃ and purged continuously. The SVOCs in the sample are carried into the microextraction enrichment tube with the purging gas and are adsorbed and enriched. S4: Rapid thermal desorption. After step S3 is completed, the microextraction enrichment tube is rapidly heated to 220-320℃ to thermally desorb VOCs and SVOCs in the microextraction enrichment tube. S5: Gas chromatography-mass spectrometry analysis, sending thermally desorbed VOCs and SVOCs into a gas chromatography-mass spectrometry instrument for detection; S6: Qualitative and quantitative analysis, based on mass spectra, uses internal or external standard methods to quantitatively calculate VOCs and SVOCs to obtain concentration results.

2. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, During the purging process in step S2, the nitrogen flow rate is 20-80 mL / min, and the purging time is 5-20 min.

3. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, During the purging process in step S3, the nitrogen flow rate is 20-80 mL / min, and the purging time is 10-30 min.

4. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, The microextraction enrichment tubes in steps S2 and S3 are filled with composite adsorbents.

5. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, The heating method in step S3 is either linear heating or stepped heating.

6. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, During the thermal desorption step S4, the heating rate is ≥80℃ / s, and the temperature is held constant for 1-5 minutes after reaching the target temperature.

7. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, In step S5, gas chromatography uses a weakly polar capillary column, and mass spectrometry uses an electron impact ionization source.

8. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, The VOCs include benzene, toluene, ethylbenzene, and xylene, while the SVOCs include naphthalene, phenanthrene, anthracene, organochlorine pesticides, and petroleum hydrocarbons.

9. The rapid detection method for multiple types of organic matter in soil and sediments based on dynamic headspace-microextraction as described in claim 1, characterized in that, The method is applicable to contaminated site investigation, farmland soil monitoring, water sediment quality assessment, remediation process tracking, and emergency detection scenarios for sudden environmental accidents.

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