Method for detecting organochlorine pesticide in soil

[0030] Example 1

[0031] 1.1 Blank soil sample preparation

[0032] Collect a batch of soil near the drinking water source to remove impurities such as grass roots and gravel, put it on a sample pan, spread it to a thickness of about 20mm, freeze-dry, pass through a 60-mesh sieve and grind evenly to obtain a soil sample to be tested. The traditional method of rapid solvent extraction-solid phase extraction cartridge purification was used to test the 8 organochlorine pesticides in the samples, and the soil samples with the detection concentration lower than the detection limit of the method were selected as the blank soil samples to be tested.

[0033] 1.2 Preparation of the spiked soil for testing

[0034] Accurately weigh 50.0g of the blank soil to be tested, add 10mL of the standard solution of 8 kinds of organochlorine pesticides in n-hexane with a concentration of 1.0mg/L, then add 10mL of n-hexane solvent to immerse the soil, stir under a fume hood to make the mixture uniform, Then let the solvent evaporate to prepare the test spiked soil with a concentration of 200μg/kg.

[0035] 1.3 Matrix solid phase dispersion extraction steps

[0036] Accurately weigh 0.5000g of the test soil sample with a spiked concentration of 200μg/kg and 1.5000g of dispersant into a mortar, grind evenly with a pestle, transfer the sample to an empty solid-phase extraction column, and wash with 10mL solvent , Collect the eluent, concentrate it to 1.0 mL in a nitrogen blowing instrument, and detect it in a gas chromatograph.

[0037] Example 2

[0038] This application also tested the optimization of chromatographic conditions and the selection of internal standard substances of the above detection method, and the test results are as follows.

[0039] 2.1 Optimization of chromatographic conditions

[0040] The purpose of optimizing the chromatographic conditions is to make the separation and detection time the shortest and the best effect, while maximizing the detection sensitivity of the chromatogram. According to the principle of similar compatibility, since the organochlorine pesticides are all weakly polar substances, the HP-5 capillary column is selected. The gas chromatogram of 8 kinds of organochlorine pesticide standard mixed solutions is as follows figure 2 As shown, the experimental results show that under the chromatographic conditions, the target compound and the internal standard substance can be separated well, which can meet the experimental requirements.

[0041] 2.2 Selection of internal standard

[0042] Compared with the external standard method, the internal standard method can eliminate the error caused by the inaccurate injection volume and the matrix effect caused by the sample. Therefore, in order to improve the accuracy of the method and maintain good repeatability, it is possible to eliminate various factors as much as possible. For quantitative problems, the internal standard method is introduced for quantification. This experiment examines separately 13 C 12 -PCB-153 and 13 C 12 -The influence of PCB-194 two compounds on the determination results, the results show: 13 C 12 -PCB-194 and 13 C 12 -The retention time of PCB-153 is 13.524min and 18.220min, and both can be completely separated from the target component. Considering that the retention time of the target component should be as close as possible to the internal standard, 13 C 12- The peak time of PCB-153 is just between DDT and DDI, so this experiment uses 13 C 12 -PCB-153 is used as an internal standard.

[0043] Example 3

[0044] This application also tested the above detection methods. By examining the type of dispersant, eluent and elution volume, and the ratio of sample to dispersant, the recovery rate and standard deviation of organochlorine pesticides under different conditions were measured. The test results are as follows.

[0045] 3.1 Drawing of standard curve

[0046] Using n-hexane as the solvent, accurately pipette the stock solutions of 8 kinds of mixed organochlorine pesticides and prepare them into standard solutions with concentrations of 50, 100, 150, 200, 250 μg/L, and add 80 ppb 13 C 12 -PCB-153 is used as the internal standard, draw the standard curve with the concentration ratio as the abscissa and the peak area value as the ordinate. The calculated standard curve equation and correlation coefficient are shown in Table 1. From the data in Table 1, it can be seen that at 50 The linear correlation of 8 kinds of organochlorine pesticides in the mass concentration range of ~250μg/L is good, which meets the experimental requirements.

[0047] Table 1 Standard curves and linear correlation coefficients of eight organochlorine pesticides

[0048]

[0049] 3.2 Investigation of dispersant types

[0050] In the process of matrix solid-phase dispersion extraction, it plays a role of dispersion, adsorption, distribution, and purification. Therefore, the selection of solid-phase extraction fillers is particularly important. Different dispersants have different degrees of adsorption and binding to the target. Affect the extraction effect. Generally speaking, the adsorbents used in normal phase matrix solid phase dispersion are all polar, such as magnesium silicate adsorbent, Florisil, bonded silica gel, neutral alumina, etc., which are often used for the detection of pesticide residues. . In this experiment, the extraction effects of seven dispersants, including neutral alumina, diatomaceous earth, C18 filler, magnesium silicate, Florisil, magnesium trisilicate, and silica gel, on the extraction of organochlorine pesticides in the soil were investigated. 2 is the average recovery rate of each dispersant. The experimental results show that the extraction effect of Florisil on organochlorine is better. The average recovery rate of the eight substances is between 73% and 91%, followed by diatomite and The recovery rate of alumina, magnesium trisilicate and magnesium silicate is relatively low, between 47% and 70%, so Florisil is the best dispersant.

[0051] Table 2 The average recovery rate of seven different dispersants

[0052]

[0053] 3.3 Investigation of eluent and elution volume

[0054] In order to achieve a high extraction recovery rate, the desorption solvent should have a suitable elution capacity, which can desorb the adsorbed organochlorine pesticides without eluting impurities. Therefore, it is necessary to choose the most effective eluent, because the polarity of the solvent is too weak, some components will not be easily eluted, and the polarity of the eluent is too strong, and unnecessary components will be eluted together. This experiment examines the elution effects of four organic solvents such as n-hexane, acetone, n-hexane-acetone (1:1, v/v), and n-hexane-acetone (9:1, v/v). The experimental results show that the elution recovery rate of acetone is relatively ideal, but there are more interfering substances, and n-hexane is relatively poor. Therefore, n-hexane-acetone (1:1, v/v) was finally selected for elution. Regarding the volume of the eluent, the experimental results show that the recovery rate is higher when the eluent volume is 10mL. If you further increase the n-hexane- The volume of acetone (1:1, v/v) does not change significantly, so the final choice of n-hexane-acetone (1:1, v/v) volume is 10 mL.

[0055] 3.4 Investigation of the ratio of sample to dispersant

[0056] In order to increase the contact area between the sample and the adsorbent, this experiment investigated the extraction effect when the mass ratio of the tested soil sample to the dispersant was 1:1, 1:2, 1:3, and 1:4. The results show that when the ratio is 1:1, the extraction effect of the target is average. When the ratio is further increased, the recovery rate is significantly increased, but if the ratio exceeds 1:3, the recovery rate is almost unchanged. Therefore, in this experimental study, the mass ratio of the test soil sample to the dispersant is 1:3, which can achieve an ideal extraction effect with less samples and reagents.

[0057] 3.5 Standard addition recovery test

[0058] Select and prepare the test blank soil with no test substances and as few interfering substances as possible, accurately weigh and add 50, 100, and 200μg/kg mixed standard solutions at three levels of low, medium, and high respectively, and obtain the experimental results The recovery rate is shown in Table 3. The recovery rate of each pesticide component is between 60.3% and 94.3%, and the relative standard deviation is between 6.83% and 8.95%, indicating that the detection method meets the requirements of experimental analysis.

[0059] Table 3. Recovery rates and relative standard deviations of 8 kinds of organochlorine pesticides added to blank soil

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