Method for analyzing and detecting methanol in soil

Abstract

The invention relates to the technical field of detection, in particular to a method for analyzing and detecting methanol in soil. Comprising the following steps: S1, collecting a sample: adding water into a headspace bottle, and collecting a soil sample into the headspace bottle by using a soil VOC non-disturbance sampler; s2, carrying out headspace sampling on the sample, and carrying out gas chromatographic analysis; s3, preparing a methanol standard series solution by using a methanol standard substance, carrying out gas chromatographic analysis, and establishing a standard working curve by taking the mass concentration of methanol as an abscissa and the peak area as an ordinate; and S4, calculating the content of methanol in the soil through the standard working curve. The detection method provided by the invention can improve precision and correctness.

Description

Technical Field

[0001] The present invention relates to the field of detection technology. Specifically, it relates to a method for analyzing and detecting methanol in soil. Background Art

[0002] The detection of methanol in soil is an important part of environmental monitoring and pollution control. As an industrial solvent and fuel additive, methanol may enter the soil environment due to leakage or improper disposal. Although its toxicity is relatively low, long-term accumulation can still pose a potential threat to the ecosystem and groundwater. Existing methanol detection technologies in soil have problems such as insufficient sensitivity, complex pretreatment steps, significant soil matrix interference, and limitations of standard methods.

[0003] Chinese invention patent CN114200049B discloses a method for detecting n-hexane and cyclohexanone in soil from retired plots. The detection limits of this method for n-hexane and cyclohexanone in soil are 1.2 μg / kg and 13.0 μg / kg respectively. The recovery ranges of actual sample spiking are 75.7% - 96.8% and 81.5% - 123% respectively, and the relative standard deviations are 5.8% - 7.6% and 3.8% - 4.7% respectively; S5. Under the experimental conditions of steps S1 - S4, the whole process of the soil sample from the retired plot is determined in parallel 6 times, and the relative standard deviations of the repeated determination results are all less than 10%. However, the detection limit and relative standard deviation of this invention need to be further improved. Summary of the Invention

[0004] The present invention provides a method for analyzing and detecting methanol in soil, including the following steps:

[0005] S1, Sample collection: Add water to a headspace vial, and use a non-intrusive soil VOC sampler to collect soil samples into the headspace vial;

[0006] S2, Perform headspace injection on the sample and conduct gas chromatography analysis;

[0007] S3, Prepare a methanol standard series solution with a methanol standard product, conduct gas chromatography analysis, use the mass concentration of methanol as the abscissa and the peak area as the ordinate to establish a standard working curve;

[0008] S4, Calculate the content of methanol in the soil through the standard working curve;

[0009] The parameters of the headspace injection include: heating equilibrium temperature is 60 - 80 °C; heating equilibrium time is 10 - 30 min; sampling needle temperature is 100 - 120 °C; transfer line temperature is 120 - 140 °C.

[0010] Optionally, the parameters of the headspace injection include: heating equilibrium temperature of 60 - 70 °C; heating equilibrium time of 10 - 20 min; sampling needle temperature of 110 - 120 °C; transfer line temperature of 130 - 140 °C.

[0011] The parameters of the headspace injection include: heating equilibrium temperature of 60 - 80 °C; heating equilibrium time of 10 - 30 min; sampling needle temperature of 100 - 120 °C; transfer line temperature of 120 - 140 °C, which can improve the efficiency and accuracy of methanol detection and meet the analysis requirements of trace methanol in soil. The equilibrium temperature directly affects the distribution coefficient of methanol between the gas and liquid phases. An increase in temperature will reduce the distribution coefficient, causing more methanol to volatilize from the liquid phase to the gas phase, thereby improving the detection accuracy. Coordinating with the equilibrium time to control the volatilization efficiency and increase the speed of reaching dynamic equilibrium, and then through the temperature control of the sampling needle and transfer line, the accuracy of headspace injection is improved.

[0012] The mass - to - volume ratio of the soil sample to water is 1 g : (3 - 7) mL.

[0013] Optionally, the mass - to - volume ratio of the soil sample to water is 1 g : (4 - 6) mL.

[0014] The mass - to - volume ratio of the soil sample to water being 1 g : (3 - 7) mL can improve the detection precision. It may affect the distribution state of water in the soil and the inter - phase distribution of ethanol. When the water content is too low, the adsorption of soil particles dominates and ethanol is not released sufficiently; when the water content is too high, the dilution effect is significant.

[0015] The stationary phase of the chromatographic column used in the gas chromatography is polyethylene glycol. The standard deviation can be lower than 0.05 mg / L, and the detection limit can reach 0.7 mg / Kg. This may be because polyethylene glycol belongs to a strongly polar stationary phase, which matches the polarity of methanol, can effectively separate methanol from other polar substances in the soil, reduce the influence of impurities on the accuracy, improve the peak symmetry and make the retention time stable. Further research found that the programmed temperature rise of the gas chromatography is defined as follows: maintaining at 40 - 60 °C for 0.5 - 1.5 min, rising to 55 - 75 °C at a rate of 3 - 7 °C / min, and then rising to 120 - 140 °C at a rate of 8 - 12 °C / min and maintaining for 0.5 - 1.5 min. This can further improve the detection precision and make the relative standard deviation lower than 4.5%. This may be because the polyethylene glycol column optimizes the separation of methanol, stably distributes the target substance, reduces baseline fluctuations and peak tailing, and improves the repeatability.

[0016] The concentration range of methanol in the methanol standard series solution is 5 - 150 mg / L.

[0017] Optionally, the concentration range of methanol in the methanol standard series solution is 10 - 100 mg / L.

[0018] The temperature programming of the gas chromatography includes: maintaining at 40 - 60°C for 0.5 - 1.5 min, rising to 55 - 75°C at a rate of 3 - 7°C / min, and then rising to 120 - 140°C at a rate of 8 - 12°C and maintaining for 0.5 - 1.5 min.

[0019] Optionally, the temperature programming of the gas chromatography includes: maintaining at 45 - 55°C for 0.5 - 1.5 min, rising to 60 - 70°C at a rate of 4 - 6°C / min, and then rising to 120 - 130°C at a rate of 8 - 12°C and maintaining for 0.5 - 1.5 min.

[0020] The inlet temperature of the gas chromatography is 170 - 200°C.

[0021] Optionally, the inlet temperature of the gas chromatography is 170 - 190°C.

[0022] The split ratio of the gas chromatography is (7 - 12):1.

[0023] Optionally, the split ratio of the gas chromatography is (8 - 11):1.

[0024] The detector temperature of the gas chromatography is 200 - 230°C.

[0025] Optionally, the detector temperature of the gas chromatography is 210 - 230°C.

[0026] The carrier gas of the gas chromatography is nitrogen, and the flow rate of nitrogen is 20 - 28 mL / min.

[0027] Optionally, the flow rate of nitrogen is 22 - 26 mL / min.

[0028] The fuel gas of the gas chromatography is hydrogen, and the flow rate of hydrogen is 25 - 35 mL / min.

[0029] Optionally, the flow rate of hydrogen is 28 - 35 mL / min.

[0030] Beneficial effects

[0031] 1. The parameters of headspace injection include: the heating equilibrium temperature is 60 - 80°C; the heating equilibrium time is 10 - 30 min;

[0032] the sampling needle temperature is 100 - 120°C; the transfer line temperature is 120 - 140°C, which can improve the efficiency and accuracy of methanol detection.

[0033] 2. The mass - volume ratio of the soil sample to water is 1 g:(3 - 7) mL, which can improve the detection precision.

[0034] 3. The stationary phase of the chromatographic column used in the gas chromatography is polyethylene glycol, with a standard deviation that can be lower than 0.05 mg / L and a detection limit that can reach 0.7 mg / Kg.

[0035] 4. The programmed temperature rise of the gas chromatography is defined as follows: maintain at 40 - 60 °C for 0.5 - 1.5 min, and then rise to

[0036] 55 - 75 °C at a rate of 3 - 7 °C / min, and then rise to 120 - 140 °C at a rate of 8 - 12 °C / min and maintain for 0.5 - 1.5 min, which can further improve the detection precision and make the relative standard deviation lower than 4.5%.

[0037] 5. The inlet temperature of the gas chromatography is 170 - 200 °C and the split ratio is (7 - 12):1, which can meet the precision requirements for different spiked concentrations from high to low (60 mg / L - 2 mg / L). Specific implementation mode

[0038] Example 1

[0039] An analytical detection method for methanol in soil comprises the following steps:

[0040] S1. Collect samples: Before sampling, add 10 mL of water to a pre - washed and dried headspace vial, weigh it (accurate to 0.01 g) and record its mass m 1 . At the sampling site, collect about 2 g of samples into the headspace vial using a non - disturbed soil VOC sampler, quickly remove the samples adhering to the bottle mouth thread, tighten the bottle cap, remove the samples adhering to the outer surface of the headspace vial, and place it in a refrigerator for refrigerated and light - protected transportation;

[0041] S2. After restoring the sample obtained in step (1) to room temperature, weigh it (accurate to 0.01 g) and record its mass m 2 , shake it well, let it stand for sedimentation, and then detect it with a headspace / gas chromatograph;

[0042] S3. Prepare a methanol standard series solution with a methanol standard product, conduct gas chromatography analysis, use the mass concentration of methanol as the abscissa and the peak area as the ordinate to establish a standard working curve;

[0043] S4. Calculate the content of methanol in the soil through the standard working curve.

[0044] In step S1, the headspace vial is a 22 - mL screw - mouth headspace vial, and the sealing cap has a polytetrafluoroethylene gasket.

[0045] In step S1, collect parallel duplicate samples and a sample for determining the dry matter content of the soil.

[0046] In step S2, the model of the headspace sampler is THS - 45, and the model of the gas chromatograph is GC - 2030.

[0047] In step S2, the chromatographic column is HP-INNOWAX and the stationary phase is polyethylene glycol.

[0048] The headspace sampling reference conditions in step S2 are: heating equilibrium temperature: 70°C; heating equilibrium time: 20 min; sampling needle temperature: 110°C; transfer line temperature: 130°C; injection volume: 1.0 mL.

[0049] The gas chromatography reference analysis conditions in step S2 are:

[0050] The temperature programming of gas chromatography: the initial column temperature is maintained at 50°C for 1 min, then increased to 65°C at a rate of 5°C / min, and then increased to 130°C at a rate of 10°C / min and maintained for 1 min; injection port temperature: 180°C; split ratio: 10:1; carrier gas: nitrogen (purity ≥ 99.999%); flow rate: 24.0 mL / min; detector temperature: 220°C; fuel gas: hydrogen (purity ≥ 99.999%), flow rate 32 mL / min; combustion-supporting gas: air (oil-free compressed air, purified by molecular sieve), flow rate 200 mL / min.

[0051] The concentrations of methanol in the methanol standard series solutions in step S3 are 10 mg / L, 20 mg / L, 50 mg / L, 80 mg / L, and 100 mg / L respectively. Taking the mass concentration of methanol (mg / L) as the abscissa and the peak area as the ordinate, a working curve is established: f(C) = 575.513C, and the correlation coefficient (R) = 0.9997223.

[0052] In step S4, the spectral data is substituted into the calculation formula for calculation.

[0053] Calculation formula: C = C 0 ×V 0 ×K / M / W 2

[0054] In the formula:

[0055] C —— the concentration of methanol in the sample, mg / kg;

[0056] C 0 —— the injection concentration (spectral reading of the calibration curve loaded), mg / L;

[0057] V 0 —— the volume of constant volume, mL;

[0058] K —— the dilution factor of the sample;

[0059] M —— the sampling amount, g; M = m 2 -m 1 ;

[0060] W 2 —— Dry matter content of the sample, %.

[0061] C 0 : 18.66 mg / L; V 0 : 10 mL; K: 1; M: 2.16 g; W 2 : 90.4%.

[0062] Performance test methods and data

[0063] 1. Method detection limit and determination lower limit

[0064] After pretreatment, the sample concentration is measured, and the standard deviation of the measurement results is calculated. According to the standard deviation, the method detection limit MDL = t (n-1,0.99) ×S (when n = 8, t = 2.998), and the detection limit MDL and the method quantification lower limit RQL are calculated by RQL = 4×MDL.

[0065] Prepare 7 laboratory blanks (water), add 50 μL of the standard stock solution (methanol aqueous solution of 1000 mg / L) respectively, shake well, let it stand for sedimentation, and then wait for measurement. The final spiked methanol concentration is 5 mg / L, and analyze by machine. The specific data are shown in Table 1.

[0066] 2. Precision and trueness

[0067] Prepare 18 blank samples (water), divided into 3 groups, with 6 samples in each group. The spiked concentrations are divided into three different levels: high, medium, and low. Add 20 μL of the standard stock solution to the low-concentration group, 200 μL of the standard stock solution to the medium-concentration group, and 600 μL of the standard stock solution to the high-concentration group. Shake well, let it stand for sedimentation, and then wait for measurement. The final spiked concentrations are low concentration (methanol concentration 2 mg / L), medium concentration (methanol concentration 20 mg / L), and high concentration (methanol concentration 60 mg / L) respectively, and analyze by machine. The specific data are shown in Tables 2 - 4, where Table 2 corresponds to the low concentration, Table 3 corresponds to the medium concentration, and Table 4 corresponds to the high concentration.

[0068] 3. Quality control results of spiked samples: Add 20 μL of methanol aqueous solution with a concentration of 10000 mg / L to the sample, shake well, and wait for measurement. As shown in Table 5.

[0069] Table 1 Table 2

[0070]

[0071] Table 3 Table 4 Table 5

[0072] Test Items Unit Test Results Spiked Amount Spike Recovery Rate % Control Range % Compliance Methanol mg / L 20.0 18.66 93.3 70-120 Compliant

Claims

1. A method for analyzing and detecting methanol in soil, characterized in that: The following steps are involved: S1, sample collection: add water to the headspace bottle and use the soil VOC non-disturbance sampler to collect soil samples into the headspace bottle; S2, injecting the sample into the headspace and performing gas chromatography analysis; S3, preparing a methanol standard series solution with methanol standard product, performing gas chromatography analysis, and establishing a standard working curve with the mass concentration of methanol as the abscissa and the peak area as the ordinate; S4, calculate the methanol content in the soil through the standard working curve; The parameters of the headspace injection include: heating equilibrium temperature of 60-80°C; heating equilibrium time of 10-30min; sampling needle temperature of 100-120°C; and transmission line temperature of 120-140°C.

2. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The mass volume ratio of the soil sample to water in step S1 is 1 g: (3-7) mL.

3. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The stationary phase of the chromatographic column used in the gas chromatography is polyethylene glycol.

4. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The concentration of methanol in the methanol standard series solution ranges from 5 to 150 mg / L.

5. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The programmed temperature rise of the gas chromatography includes: maintaining at 40-60°C for 0.5-1.5 min, increasing to 55-75°C at 3-7°C / min, and then increasing to 120-140°C at 8-12°C / min and maintaining for 0.5-1.5 min.

6. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The injection port temperature of the gas chromatograph is 170-200°C.

7. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The split ratio of the gas chromatograph is (7-12):

1.

8. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The detector temperature of the gas chromatograph is 200-230°C.

9. The method for analyzing and detecting methanol in soil according to claim 1, characterized in that: The carrier gas of the gas chromatography is nitrogen, and the flow rate of the nitrogen is 20-28 mL / min.

10. The method for analyzing and detecting methanol in soil according to claim 9, characterized in that: The fuel gas of the gas chromatograph is hydrogen, and the flow rate of the hydrogen is 25-35 mL / min.

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