A method for preparing and determining the value of volatile organic compound standard substances in soil

Abstract

The present invention relates to VOC gas detection and belongs to the field of chemical analysis and detection. A method for preparing and determining the value of volatile organic compound standard substances in soil uses clay as a VOC carrier and soil as a base material. This method can simulate the soil environment to be tested to the greatest extent, eliminate experimental errors caused by differences in the composition of different standard substances, improve the accuracy of experimental results, and effectively avoid the catalytic decomposition of VOC gases by soil components. Under sealed storage of potassium chloride crystals, the stability of the standard substance under long-term storage is ensured to ensure that the VOC loss does not exceed 0.37% under storage for up to 13 months. In addition, the present invention adopts a method combining concentration curve and maximum value interval to accurately detect the VOC content in the sample. Taking toluene as an example, the standard deviation of the detection in the embodiment is 0.34.

Description

Technical Field

[0001] The present invention relates to detection technology, and in particular to a method for preparing a standard substance for volatile organic compounds in soil and determining its value. Background Art

[0002] VOCs are organic (carbon-based) gases, also known as hydrocarbons, emitted by many different products. The main components of VOCs are hydrocarbons, halogenated hydrocarbons, oxygenated hydrocarbons, and nitrogenated hydrocarbons. They include benzene series, organic chlorides, freon series, organic ketones, amines, alcohols, ethers, esters, acids, and petroleum hydrocarbon compounds. VOCs are the abbreviation for volatile organic compounds. These VOCs are commonly referred to as harmful chemicals (excluding heavy metals) in wall paint. These VOCs include formaldehyde, ammonia, ethylene glycol, esters, and other substances. When VOC concentrations in a room reach a certain level, they can cause symptoms such as headaches, nausea, vomiting, and fatigue. In severe cases, they can even cause convulsions, coma, damage the liver, kidneys, brain, and nervous system, and lead to serious consequences such as memory loss.

[0003] Existing VOC detection methods primarily include oven drying and internal standard methods. Specific conditions and procedures vary depending on the testing standard. VOC testing requires determining which standard to apply. For example, wood coatings are subject to GB 18581, industrial protective coatings to GB 30981, adhesives to GB 33372, cleaning agents to GB 38508, and inks to GB 38507. However, due to the high volatility of VOCs, their standard materials are unstable and difficult to prepare.

[0004] Volatile organic compounds (VOCs) in soil are a key indicator of environmental monitoring. Soil-based reference materials, as physical standards for testing, play a crucial role in ensuring accurate and reliable test results. Currently, there is no specific technology for accurately measuring VOC content in soil, primarily due to a shortage of soil-based reference materials. Given the complexity of soil composition, these reference materials can be unstable and uneven, resulting in poor precision and accuracy in test results.

[0005] Therefore, the rational design of soil matrix reference materials can ensure the stability and accuracy of the test results of soil VOC detection technology, and control the error of the test results within the accuracy requirement range, which is the key to ensuring the credibility of soil VOC test results. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing and determining the value of a standard substance for volatile organic compounds in soil, which can accurately detect the VOC content in soil with the help of the standard substance for volatile organic compounds in soil.

[0007] Technical Solution

[0008] A method for preparing a standard substance of volatile organic compounds in soil, comprising the following steps:

[0009] a. Prepare soil matrix;

[0010] b. Preparation of volatile organic compound adsorbents from clay components;

[0011] c. Mixing a soil matrix with a volatile organic compound adsorbent, determining the VOC content of a volatile organic compound standard substance in the soil, encapsulating the mixture in potassium chloride crystals, and then encapsulating the mixture.

[0012] Furthermore, the step of preparing the soil matrix includes:

[0013] a1. Ordinary soil vacuum drying oven drying;

[0014] a2. Dry the soil, grind it, and sieve it. Continue drying until no volatile organic compounds are detected after grinding.

[0015] Furthermore, the step a of preparing the soil matrix comprises:

[0016] a1. Dry ordinary soil in a vacuum drying oven for 5 to 24 hours;

[0017] a2. Dry the soil, grind it, and sieve it through an 80-250 mesh sieve. Continue drying until no volatile organic compounds are detected after grinding.

[0018] Production

[0019] Furthermore, the step b of preparing the volatile organic compound adsorbent comprises:

[0020] b1. The clay is dried, ground and sieved;

[0021] b2. Soaking the clay in a volatile organic compound solution to fully adsorb the volatile organic compounds until the clay is saturated;

[0022] b3. Repeat the ultrasonic-pause operation of the mixed solution, filter out the clay, and blow dry the surface solution as a volatile organic compound adsorbent.

[0023] Furthermore, the steps of encapsulating the mixture in potassium chloride crystals include: mixing the mixture with anhydrous potassium chloride powder and then pressing the mixture into blocks, placing the mixture in an environment with a high relative humidity greater than 95% to cause the potassium chloride powder to absorb moisture and form blocks, and encapsulating the mixture inside the potassium chloride crystals.

[0024] Furthermore, the particle size of the potassium chloride powder is no larger than 150 meshes; and the mass ratio of the potassium chloride to the mixture is 3 to 10:1.

[0025] Furthermore, the steps in step c include:

[0026] c1. Mix the volatile organic compound adsorbent and soil matrix thoroughly in a closed VOCs gas box;

[0027] c2. Take mixed soil samples of varying weights (e.g., 1g, 2g, 3g, 5g, 10g, etc.), measure the VOC concentrations, and plot a curve. Determine the minimum sampling volume that ensures a stable VOC concentration. Based on the minimum sampling volume, take 11 small samples for a one-way ANOVA homogeneity test. If the uniformity test fails, increase the sampling volume until the uniformity passes. This is then considered the minimum packaging volume (m3) of the reference material.

[0028] c3. In a sealed VOCs gas box, divide the standard substance into n portions and weigh them accurately. The mass of each portion is m3×5. Finally, encapsulate the standard substance with potassium chloride crystals and place it in polyethylene capsules.

[0029] A method for determining the value of volatile organic compound standard substances in soil, comprising the following steps:

[0030] I. Randomly sample capsules of the above standard substances and use F test to verify their consistency to ensure F <F 0.05(9,20) .

[0031] II. Stability test, test the content of volatile organic compounds within 1 to 13 months to ensure F <F 0.05(4,25) .

[0032] III. Using a benzene solution standard substance as a standard curve, preparing low- and high-concentration internal standard soil samples, and preparing low- and high-concentration calibration samples, the content of the test compound in the sample can be calculated using the following formula:

[0033] ;

[0034] --The amount of the compound being tested in the sample;

[0035] --The response ratio of the test compound and the marker in the sample;

[0036] --The response ratio of the test compound and the marker in the low concentration calibration sample;

[0037] --The response ratio of the test compound and the marker in the high concentration calibration sample;

[0038] --The mass ratio of the test compound and the marker in the high-concentration calibration sample;

[0039] --The mass ratio of the test compound and the marker in the low-concentration calibration sample;

[0040] --The mass of the marker in the sample;

[0041] --Sample quality.

[0042] Furthermore, the steps of using a benzene solution standard substance to make a standard curve, preparing low-concentration and high-concentration internal standard soil samples, and preparing low-concentration and high-concentration calibration samples include:

[0043] a) Using a benzene solution standard substance as a standard curve, determine the benzene content in the standard substance capsule and obtain its concentration as x1;

[0044] b) Prepare soil samples with low internal standard concentration: weigh the internal standard ( 13 C-labeled benzene) m n Add to the blank soil matrix and mix thoroughly to make the content of the internal standard in the soil sample 0.95*x1;

[0045] C) Prepare low-concentration calibration samples: Weigh the internal standard soil sample and the soil sample to be determined separately, making the mass ratio of the two 1:1, and mix thoroughly.

[0046] d) Prepare soil samples with high internal standard concentration: weigh the internal standard ( 13 C-labeled benzene) m n Add to the blank soil matrix and mix thoroughly so that the content of the internal standard in the soil sample is 1.05*x1;

[0047] e) Prepare high-concentration calibration samples: Weigh the internal standard soil sample and the soil sample to be determined separately, making the mass ratio of the two 1:1, and mix thoroughly.

[0048] Furthermore, the content of the test compound in the sample in step III is tested by multiple groups of parallel samples, and the average value and standard deviation are determined.

[0049] Beneficial effects

[0050] The present invention uses natural soil as the standard material matrix to simulate the soil environment to the greatest extent possible, eliminating experimental errors caused by differences in the composition of different standard materials and improving the accuracy of experimental results;

[0051] This invention uses clay as a VOC gas carrier, effectively preventing the catalytic decomposition of VOC gases by soil components and ensuring the stability of the standard substance during long-term storage. Experimental data in the Examples section show that VOC loss does not exceed 0.37% after 13 months of storage.

[0052] The present invention uses clay as a VOC carrier and the similarity of soil components to achieve a high degree of uniform mixing. The experimental data of the embodiment show that F < F 0.05(9，20) ;

[0053] The standard substance prepared by the present invention is encapsulated in potassium chloride polycrystalline solid, which strictly isolates the VOC components from the external environment and ensures the stability of the standard substance during long-term storage.

[0054] The present invention adopts a method combining concentration curve and maximum interval to accurately detect the VOC content in the sample. Taking toluene as an example, the standard deviation of the detection in the embodiment can reach 0.34. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 4 is a line graph showing the sampling amount and the total toluene content measured in an embodiment of the present invention;

[0056] Figure 2 This is the spectrum of a soil sample with a sampling volume of 2g according to an embodiment of the present invention;

[0057] Figure 3 This is a schematic diagram of the traceability of the measurement value of the method of the present invention. DETAILED DESCRIPTION

[0058] The following is a detailed description of the embodiments and the appendix. Figures 1 to 3 , further illustrating the present invention.

[0059] 1. Preparation of standard substances:

[0060] (1) Preparation of soil matrix: Take ordinary soil (m1) and dry it in a vacuum drying oven for 12 hours. Then, dry it for 24 hours, grind it thoroughly, and pass it through a 100-mesh sieve to remove large particles to obtain a soil matrix. The soil matrix is sampled by gas chromatography headspace injection to determine whether it contains volatile organic compounds. If it still contains volatile organic compounds, it is further heated to volatilize it until the content of volatile organic compounds in the matrix is below the detection limit.

[0061] (2) Preparation of adsorbent: Dry, grind, and sieve the clay. Take m2 of clay and soak it in the volatile organic compound solution. Allow the clay to fully adsorb the volatile organic compounds until the clay is saturated. Ultrasonicate for 30 minutes, then stop for 30 minutes, then ultrasonicate for another 30 minutes. Repeat the above steps 20 times.

[0062] (3) Mix the saturated clay and soil matrix thoroughly in a sealed VOC gas box (check at any time to ensure the VOC gas concentration is constant).

[0063] Take 0.4g, 0.8g, 1.2g, 1.6g, 2.0g... mixed soil samples respectively, measure the concentration of VOCs, draw a curve, and determine the minimum sampling amount m that can ensure linearity 30 . Eleven small samples were taken from different locations of the mixed soil sample, and the sampling volume of each small sample was m 30 , the VOC concentration of 11 samples was determined by gas chromatography, and the uniformity was evaluated by single factor analysis. If qualified, the packaging volume was determined to be m 30 If it fails to meet the requirements, increase the sampling volume and repeat the above uniformity test until the sampling volume can ensure uniformity, and finally determine the packaging volume as m3.

[0064] from Figure 1 It can be seen that in the sampling range of 0.5g-1.5g, the sampling amount and the content are not linear, and from the range of 1.5g-2g, the sampling amount and the total amount measured are linearly related. Therefore, 1.5g is determined as the sampling amount of the small sample for the next step of uniformity test.

[0065] (5) In a sealed VOCs gas box, the standard substance is divided into n portions and accurately weighed, with the mass of each portion being m³×5. The weighed mixture is mixed with anhydrous potassium chloride powder and then pressed into blocks. The mixture is placed in an environment with a high relative humidity greater than 95% to cause the potassium chloride powder to absorb moisture and form agglomerates. The mixture is then encapsulated within potassium chloride crystals. The potassium chloride powder in this embodiment is sieved to a particle size of 180 mesh; the mass ratio of potassium chloride to the mixture is 6:1.

[0066] The standard substance is placed in a polyethylene capsule (before placing, the polyethylene capsule is checked to be free of VOC) to obtain a capsule-shaped standard substance.

[0067] 2. Reference Material Value Determination:

[0068] (1) Homogeneity test: Randomly take 10 capsules of standard substance, put them into a glass bottle, add 10ml of water, cut the capsules, and heat them to make the capsules release volatile organic compounds. Use gas chromatography to measure the volatile organic compounds released. F Check and verify its consistency. If it meets the requirements, proceed to the next step of setting the value.

[0069] Take toluene as an example

[0070]

[0071] (2) Stability test: Randomly sample the prepared soil standard material capsules at 1, 2, 4, 6, and 13 months, and use the same method to test their volatile organic compound content. Use the linear fitting method to verify its stability. If it meets the requirements, further determination is made.

[0072]

[0073] (3) Fixed value:

[0074] a) Use the benzene solution standard substance to make a standard curve and determine the benzene content in the standard substance capsule to obtain its concentration as x1.

[0075] b) Prepare soil samples with low internal standard concentration: weigh the internal standard ( 13 C-labeled benzene) m n Add it to the blank soil matrix and mix thoroughly so that the content of the internal standard in the soil sample is 0.95*x1.

[0076] C) Prepare low-concentration calibration samples: Weigh the internal standard soil sample and the soil sample to be determined separately, making the mass ratio of the two 1:1, and mix thoroughly.

[0077] d) Prepare soil samples with high internal standard concentration: weigh the internal standard ( 13 C-labeled benzene) m n Add it to the blank soil matrix and mix thoroughly so that the content of the internal standard in the soil sample is 1.05*x1.

[0078] e) Prepare high-concentration calibration samples: Weigh the internal standard soil sample and the soil sample to be determined separately, making the mass ratio of the two 1:1, and mix thoroughly.

[0079] Using headspace sampling, the peak area of the internal standard in the two calibration samples was determined by gas chromatography-mass spectrometry. The content of the standard substance to be determined was calculated according to the following formula: The content of the compound to be tested in the sample can be calculated by the following formula:

[0080] ;

[0081] --The amount of the compound being tested in the sample;

[0082] --The response ratio of the test compound and the marker in the sample;

[0083] --The response ratio of the test compound and the marker in the low concentration calibration sample;

[0084] --The response ratio of the test compound and the marker in the high concentration calibration sample;

[0085] --The mass ratio of the test compound and the marker in the high-concentration calibration sample;

[0086] --The mass ratio of the test compound and the marker in the low-concentration calibration sample;

[0087] --The mass of the marker in the sample;

[0088] --Sample quality.

[0089] f) Repeat the above steps to make 6 parallel samples. The results are shown in the following table:

[0090]

[0091] Discussion of the results of the examples:

[0092] 1. This technical solution achieves stable and uniform preparation of VOC reference materials in soil. Stability and uniformity are necessary conditions for determining the value of reference materials. However, due to the volatility of VOCs, the mass value of soil matrix reference materials will continuously decrease, resulting in inaccurate reference material mass values.

[0093] (1) This example adopts three measures to effectively ensure the stability of the standard substance:

[0094] One is to use clay to adsorb VOC gases. Due to the strong adsorption effect of clay, the volatilization of VOC into the environment is reduced, making the VOC content in the soil more stable.

[0095] Secondly, this embodiment encapsulates the soil standard substance in a saturated VOC gas atmosphere and uses small sealed capsules for packaging. Since the interior of the capsule is in VOC saturated vapor, the gas-solid two phases have reached dynamic equilibrium. Therefore, during long-term storage, the VOC in the soil will remain stable.

[0096] Third, potassium chloride crystal packaging is used to strictly isolate VOC gas from the external environment, ensuring the stability of standard substances during long-term storage.

[0097] (2) This embodiment adopts two measures to ensure the uniformity of the standard substance:

[0098] a. Utilize an infiltration-ultrasound method to fully adsorb volatile organic compounds onto the clay, maintaining a constant VOC concentration within a sealed gas chamber. This procedure ensures that the clay fully adsorbs VOCs and that the clay's adsorbed VOC content reaches a uniform saturation value. At this point, the VOC concentration in the prepared adsorbent is uniform.

[0099] b. In a closed gas VOC box, mix the adsorbent and soil thoroughly to ensure the uniformity of the VOC concentration of the soil standard substance.

[0100] c. Determine the packaging volume of the soil standard material through a sampling volume-VOC linearity test and a packaging volume-VOC uniformity assessment to ensure uniformity. (Solid samples cannot be fully uniform like liquid samples; they can only be uniform to a certain extent. Therefore, the sampling volume should be continuously increased to determine the maximum uniformity.)

[0101] 2. The use of isotope dilution ensures traceability and accuracy of the results. This example method eliminates losses caused by soil pretreatment by introducing an isotope internal standard. At the same time, the use of a benzene solution standard ensures that the results are traceable to national metrology standards.

Claims

1. A method for preparing a standard substance of volatile organic compounds in soil, characterized in that the steps include: a. Prepare soil matrix; b. Preparation of volatile organic compound adsorbents from clay components; c. mixing a soil matrix with a volatile organic compound adsorbent, encapsulating the mixture in potassium chloride crystals, and then encapsulating the mixture. After encapsulation, the VOC content of the volatile organic compound standard substance in the soil is measured; In step c, encapsulating the mixture in potassium chloride crystals comprises: mixing the mixture with anhydrous potassium chloride powder and then pressing the mixture into blocks, placing the mixture in an environment with a high relative humidity greater than 95% to cause the anhydrous potassium chloride powder to absorb moisture and form blocks, and encapsulating the mixture inside the potassium chloride crystals.

2. The method for preparing a standard substance of volatile organic compounds in soil according to claim 1, wherein: Step b includes: b1. The clay is dried, ground and sieved; b2. Soaking the clay in a volatile organic compound solution to fully adsorb the volatile organic compounds until the clay is saturated; b3. Repeat the ultrasonic-pause operation of the mixed solution, filter out the clay, and blow dry the surface solution as a volatile organic compound adsorbent.

3. The method for preparing a standard substance of volatile organic compounds in soil according to claim 1, wherein: The particle size of the anhydrous potassium chloride powder is no larger than 150 meshes; and the mass ratio of the anhydrous potassium chloride powder to the mixture is 3 to 10:

1.

4. The method for preparing a standard substance of volatile organic compounds in soil according to claim 1, characterized in that: Step c includes: c1. Mix the volatile organic compound adsorbent and soil matrix thoroughly in a sealed VOC gas box; c2. Take mixed soil samples of varying weights, measure the VOC concentrations, and plot a curve. The minimum sampling volume that ensures a stable VOC concentration is determined. Based on this minimum sampling volume, take 11 small samples and perform a one-way ANOVA homogeneity test. If the uniformity test fails, increase the sampling volume until the uniformity passes. This is then considered the minimum packaging volume (m3) of the reference material. c3. In a sealed VOCs gas box, divide the standard substance into n portions and weigh them accurately. The mass of each portion is m3×5. Finally, encapsulate the standard substance with potassium chloride crystals and place it in polyethylene capsules.

5. The method for preparing a standard substance of volatile organic compounds in soil according to claim 1, wherein: Step a includes: a1. Ordinary soil vacuum drying oven drying; a2. Dry the soil, grind it, and sieve it. Continue drying until no volatile organic compounds are detected after grinding.

6. The method for preparing a standard substance of volatile organic compounds in soil according to claim 1, wherein: Step a includes: a1. Dry ordinary soil in a vacuum drying oven for 5 to 24 hours; a2. Dry the soil, grind it, and sieve it through an 80-250 mesh sieve. Continue drying until no volatile organic compounds are detected after grinding.

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