Method for detecting pesticide residues in water sample by deep eutectic solvent-inorganic salt aqueous two-phase system

Abstract

The invention discloses a method for detecting pesticide residues in a water sample by using a deep-eutectic solvent-inorganic salt aqueous two-phase system, which comprises the following steps: adding inorganic salt, a deep-eutectic solvent and an internal standard compound into the water sample, uniformly stirring, centrifuging, layering, taking supernatant liquid, and removing moisture to obtain liquid to be detected; analyzing the liquid to be detected by a gas chromatograph-mass spectrometer; the eutectic solvent is a mixture of triethyl methyl ammonium chloride and 1-aminoethanol. The solvent system disclosed by the invention has high polarity and a good hydrogen bond network, can be effectively combined with polar groups of the pesticide, and enhances the solubility of the pesticide in the solvent, so that the extraction efficiency and the detection sensitivity are remarkably improved.

Description

Technical Field

[0001] The invention relates to a method for detecting pesticide residues, and in particular to a method for detecting pesticide residues in a water sample using a deep eutectic solvent-inorganic salt aqueous two-phase system. Background Art

[0002] Environmental pollution, especially the problem of pesticide residues in water bodies, has become a global focus. Pesticides are widely used in agricultural production. Although they increase crop yields, they also inevitably lead to the accumulation of pesticide residues, especially in water sources. Since the concentration of pesticides in water is usually low and there are many interfering substances in water samples, the detection of pesticide residues becomes extremely complicated and difficult. Although the existing detection methods can meet the needs to a certain extent, due to the lack of efficient, environmentally friendly and economical extraction technology, many traditional methods still face problems such as high pollutant emissions, cumbersome operations and low extraction efficiency.

[0003] At present, liquid-liquid extraction (LLE) and solid phase extraction (SPE) are commonly used water sample pretreatment technologies. Although these methods can effectively extract pesticides, they generally have disadvantages such as large amount of solvent used, low extraction efficiency, and long processing time. In addition, many solvents are highly toxic, which will not only pollute the environment after use, but also affect human health. Therefore, the development of green, low-toxic, biodegradable alternative extraction solvents, as well as efficient and simple pretreatment technologies, has become an important topic in the current field of analytical chemistry.

[0004] In this regard, deep eutectic solvents (DES), as a new type of green solvent, have become a research hotspot due to their low toxicity, low vapor pressure, non-volatility and strong solubility. However, the application of deep eutectic solvents still faces some challenges. Especially in water sample analysis, deep eutectic solvents often have strong water solubility, resulting in unsatisfactory distribution with the water sample matrix and difficulty in achieving effective separation. Although some studies have attempted to combine deep eutectic solvents with two-phase aqueous systems for the pretreatment of water samples, the existing technology still has problems such as difficulty in distributing deep eutectic solvents in the sample matrix and poor extraction effect.

[0005] For example, the method for analyzing pesticide residues in water samples in Chinese invention patent CN109115898A proposes combining a deep eutectic solvent with an inorganic salt to form a two-phase aqueous system, and using liquid-liquid extraction combined with gas chromatography-mass spectrometry to detect pesticide residues. However, although this method has made some progress in some aspects, it still faces some problems. First, the deep eutectic solvents such as choline chloride and chlorophenol, phenol and benzyl alcohol used are not fully optimized in terms of solvent polarity, extraction efficiency, etc., especially when processing high-polarity pesticides such as carbamates, their extraction efficiency is low and their extraction effect is not ideal. Therefore, the prior art is still difficult to meet the needs of efficient, environmentally friendly and simple pesticide residue detection. Summary of the invention

[0006] In view of the above-mentioned defects in the prior art, the technical problem to be solved by the present invention is to provide a method for detecting pesticide residues in water samples using a low eutectic solvent-inorganic salt two-phase aqueous system.

[0007] Specifically, the technical solution of the present invention is:

[0008] A method for detecting pesticide residues in a water sample using a deep eutectic solvent-inorganic salt aqueous two-phase system, comprising the following steps:

[0009] Inorganic salts, low eutectic solvents and internal standard compounds are added to the water sample, stirred evenly, separated by centrifugation, and the upper layer of liquid is taken, and the water is removed to obtain the test solution;

[0010] Gas chromatography-mass spectrometry is used to analyze the liquid to be tested;

[0011] The low eutectic solvent is a mixture of triethylmethylammonium chloride and 1-aminoethanol.

[0012] Preferably, the low eutectic solvent is a low eutectic solvent in which triethylmethylammonium chloride and 1-aminoethanol are mixed in a molar ratio of 1:(1-3).

[0013] Preferably, the inorganic salt is KCl.

[0014] Preferably, the internal standard compound is 2-fluorobiphenyl.

[0015] Preferably, the amount of the water sample, inorganic salt, internal standard compound, and low eutectic solvent is 4 mL: (0.02-0.18 g): (0.05-0.30 μg): (0.1-1.4 mL).

[0016] Preferably, the amount of the water sample, inorganic salt, internal standard compound, and low eutectic solvent is 4 mL: (0.05-0.10 g): (0.08-0.16 μg): (0.2-0.8 mL).

[0017] Preferably, the pesticide is a carbamate pesticide, more preferably, the pesticide is at least one of carbofuran, methomyl and carbaryl, and even more preferably, the pesticide is carbofuran, methomyl and carbaryl.

[0018] Preferably, the chromatography-mass spectrometry conditions are as follows:

[0019] Chromatographic column: DB-5ms quartz capillary column (30m×0.25mm×0.25μm, Agilent);

[0020] Column temperature: 60°C for 2 min, then raised to 150°C at 30°C / min, then raised to 300°C at 10°C / min, and held for 6 min;

[0021] Carrier gas: helium, purity ≥99.999%, flow rate: 1.0mL / min;

[0022] Inlet temperature: 250°C;

[0023] Mass spectrometer detector: EI source, 70 eV;

[0024] Ion source temperature: 250°C;

[0025] Quadrupole temperature: 150°C;

[0026] Injection volume: 1.0 μL;

[0027] Injection method: splitless injection.

[0028] The present invention provides a method for detecting pesticide residues in water samples based on a low eutectic solvent-inorganic salt two-phase aqueous system, wherein a high polarity solvent system composed of triethylmethylammonium chloride and 1-aminoethanol is used as a low eutectic solvent. Carbamate pesticides (such as carbofuran, methomyl and carbaryl) contain polar carbamate groups (-NH-COO-), which can interact with nitrogen atoms in triethylmethylammonium chloride by ion-dipole interaction, and form a stable combination with amino and hydroxyl groups in 1-aminoethanol through hydrogen bonding. Since the solvent system has a high polarity and a strong polar interaction network, it can effectively interact with polar groups in pesticide molecules, significantly improve the solubility of pesticides in solvents, thereby enhancing extraction efficiency and detection sensitivity. DETAILED DESCRIPTION

[0029] Embodiment 1:

[0030] 1. Preparation of low eutectic solvent: Triethylmethylammonium chloride and 1-aminoethanol are placed in a round-bottom flask and stirred continuously at a constant temperature of 85°C for 2.5 hours to form a transparent and uniform liquid solvent, which is the low eutectic solvent. The molar ratio of triethylmethylammonium chloride to 1-aminoethanol is controlled to be 1:2.

[0031] 2. Sample determination: First, accurately measure 4 mL of the water sample to be tested in a 15 mL centrifuge tube, add 0.3 g of solid inorganic salt KCl and 10 μL of internal standard compound 2-fluorobiphenyl (10 mg / L, methanol solution), and after complete dissolution, add 2 mL of the low eutectic solvent in the above step 1, vortex at 2500 rpm for 1 minute on a vortex oscillator, and mix thoroughly. Centrifuge at 5000 r / min for 3 minutes to separate the layers, remove the upper organic layer with a gas chromatography injection needle, and transfer it to a PCR tube containing anhydrous sodium sulfate for dehydration. Then take a sample for gas chromatography-mass spectrometry analysis.

[0032] The analysis was performed using an Agilent 7890B / 5977 gas chromatograph-mass spectrometer. The chromatographic-mass spectrometric conditions were as follows:

[0033] Chromatographic column: DB-5ms quartz capillary column (30m×0.25mm×0.25μm, Agilent)

[0034] Column temperature: 60°C for 2 min, then raised to 150°C at 30°C / min, then raised to 300°C at 10°C / min, and held for 6 min;

[0035] Carrier gas: helium, purity ≥99.999%, flow rate: 1.0mL / min;

[0036] Inlet temperature: 250℃

[0037] Mass spectrometer detector: EI source, 70eV

[0038] Ion source temperature: 250°C

[0039] Quadrupole temperature: 150°C

[0040] Injection volume: 1.0 μL

[0041] Injection method: splitless injection.

[0042] Selected ion monitoring: One quantitative ion and two qualitative ions were selected for each target compound. 2-Fluorobiphenyl was selected as the internal standard, and the detection ions were 171 and 172.

[0043] The detected pesticides and chromatographic mass spectrometry information are shown in Table 1:

[0044] Table 1 Names, retention times, qualitative and quantitative ions of the three pesticides detected by this method

[0045]

[0046] 3. Establishment of standard working curve:

[0047] Accurately weigh 100 mg of 2-fluorobiphenyl in a 100 mL beaker, fully dissolve it in methanol and dilute it to a 100 mL volumetric flask to prepare an internal standard stock solution. Take 1 mL of the internal standard stock solution and dilute it to a 100 mL volumetric flask with methanol to prepare an internal standard working solution with a concentration of 10 mg / L. Accurately weigh 100 mg each of the standard substances carbofuran, methomyl, and carbaryl in a beaker, dissolve them in methanol and dilute them to a 100 mL volumetric flask to obtain a mixed standard stock solution. Take 2 mL of the mixed standard stock solution, dilute it with methanol and dilute it to a 100 mL volumetric flask to obtain a mixed standard working solution; take 10 μL, 20 μL, 40 μL, 100 μL, 200 μL, 400 μL and 1000 μL of the mixed standard working solution, dilute them with methanol to a 10 mL volumetric flask, and then add 10 μL of the internal standard working solution to each. μL, and a working curve with 7 concentrations of 5μg / L, 10μg / L, 20μg / L, 50μg / L, 100μg / L, 200μg / L and 500μg / L relative to 4mL of water sample was prepared. Then, gas chromatography-mass spectrometry analysis was performed according to the sample analysis conditions, and the standard working curve was drawn with the ratio of the characteristic peak area of ​​the standard substance to the characteristic peak area of ​​the internal standard substance in the total ion current diagram of the gas chromatography-mass spectrometry as the ordinate, and the concentration of the standard substance in the standard curve working solution as the abscissa.

[0048] The linear range, correlation coefficient, relative standard deviation, detection limit, quantification limit and other parameters were investigated. The results are listed in Table 2. The detection limit was obtained when the signal-to-noise ratio (S / N) was 3. The spike recovery was obtained by adding 50 μg / L to the blank water sample and repeating it for 5 times.

[0049] Table 2 Linear range, linear equation, correlation coefficient, detection limit and spike recovery index of the three pesticides tested

[0050]

[0051] 4. Qualitative and quantitative results of pesticide residues in actual water samples:

[0052] The pesticides in the water samples were qualitatively analyzed by comparing the retention time and mass spectrum of the gas chromatography-mass spectrometry total ion current in the actual water samples with that of the standard substances. The ratio of the characteristic peak area value in the gas chromatography-mass spectrometry total ion current of the pesticides in the actual water samples to the characteristic peak area of ​​the internal standard compounds was obtained, and the identified pesticides were quantitatively analyzed using the standard working curve. The contents of three pesticides in the water samples were calculated, and the results were as follows: 12.92μg / L for carbofuran, 13.85μg / L for methomyl, and 15.97μg / L for carbaryl.

[0053] Embodiment 2:

[0054] The difference from Example 1 is that the deep eutectic solvent is a mixture of triethylmethylammonium chloride and 1-aminoethanol in a molar ratio of 1:3.

[0055] Embodiment 3:

[0056] The difference from Example 1 is that the deep eutectic solvent is a mixture of triethylmethylammonium chloride and 1-aminoethanol in a molar ratio of 1:1.

[0057] The present invention uses triethylmethylammonium chloride as a hydrogen bond acceptor and 1-aminoethanol as a hydrogen bond donor. In the test of other pesticides in the prior art, choline chloride is also used as a hydrogen bond acceptor, and chlorophenol, benzyl alcohol and phenol are used as hydrogen bond donors. For comparison, they are tested together as follows.

[0058] Comparative Example 1:

[0059] The difference from Example 1 is that the deep eutectic solvent is a mixture of triethylmethylammonium chloride and p-chlorophenol in a molar ratio of 1:2.

[0060] Comparative Example 2:

[0061] The difference from Example 1 is that the deep eutectic solvent is a mixture of triethylmethylammonium chloride and benzyl alcohol in a molar ratio of 1:2.

[0062] Comparative Example 3:

[0063] The difference from Example 1 is that the deep eutectic solvent is a mixture of triethylmethylammonium chloride and phenol in a molar ratio of 1:2.

[0064] Comparative Example 4:

[0065] The difference from Example 1 is that the deep eutectic solvent is a mixture of choline chloride and 1-aminoethanol in a molar ratio of 1:2.

[0066] Table 3: Test table of the content of pesticides carbofuran, methomyl and carbaryl in water samples

[0067] Carbofuran, μg / L Methomyl, μg / L Carbaryl, μg / L Example 1 12.92 13.85 15.97 Example 2 12.04 12.72 14.63 Example 3 11.29 12.15 13.92 Comparative Example 1 10.32 10.84 12.71 Comparative Example 2 9.40 10.03 11.73 Comparative Example 3 9.08 9.72 11.15 Comparative Example 4 8.43 9.19 10.66

[0068] The low eutectic solvent described in Examples 1-3 is composed of triethylmethylammonium chloride and 1-aminoethanol, forming a highly polar solvent system. Carbamate pesticides (such as carbofuran, methomyl and carbaryl) contain polar carbamate groups (-NH-COO-), which can bind to the nitrogen atoms in triethylmethylammonium chloride through ion-dipole interactions, and form a stable bond with the amino and hydroxyl groups in 1-aminoethanol through hydrogen bond interactions. Due to the high polarity and strong ion-dipole interaction network of the solvent system, it can effectively interact with the polar groups in the pesticide molecules, significantly improve the solubility of the pesticide in the solvent, thereby improving the extraction efficiency and detection sensitivity.

[0069] In contrast, the low eutectic solvents of Comparative Examples 1-3 are composed of a combination of triethylmethylammonium chloride and chlorophenol, phenol or benzyl alcohol, which have low polarity and strong hydrophobicity of the aromatic ring, making them less effective in extracting polar carbamate pesticides such as carbofuran, methomyl and carbaryl. The carbamate groups of these pesticides need to bind to strong hydrogen bond receptors, while the hydrogen bonding of these solvent systems is weak, which makes them unable to effectively bind to the pesticide molecules, thereby affecting the extraction effect.

Claims

1. A method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system, characterized in that: The steps include: Inorganic salts, low eutectic solvents and internal standard compounds are added to the water sample, stirred evenly, separated by centrifugation, and the upper liquid is taken to remove water to obtain the test solution; Gas chromatography-mass spectrometry is used to analyze the liquid to be tested; The low eutectic solvent is a mixture of triethylmethylammonium chloride and 1-aminoethanol.

2. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to claim 1, characterized in that: The low eutectic solvent is a low eutectic solvent in which triethylmethylammonium chloride and 1-aminoethanol are mixed in a molar ratio of 1:(1-3).

3. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to claim 1, characterized in that: The inorganic salt is KCl.

4. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to claim 1, characterized in that: The internal standard compound is 2-fluorobiphenyl.

5. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to any one of claims 1 to 4, characterized in that: The amount of the water sample, inorganic salt, internal standard compound, and low eutectic solvent used is 4 mL: (0.02-0.18 g): (0.05-0.30 μg): (0.1-1.4 mL).

6. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to claim 5, characterized in that: The amount of the water sample, inorganic salt, internal standard compound, and low eutectic solvent used is 4 mL: (0.05-0.10 g): (0.08-0.16 μg): (0.2-0.8 mL).

7. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to claim 5, characterized in that: The pesticide is at least one of carbofuran, methomyl and carbaryl.

8. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to claim 7, characterized in that: The pesticides are carbofuran, methomyl and ferric barbaryl.

9. The method for detecting pesticide residues in water samples using a deep eutectic solvent-inorganic salt aqueous two-phase system according to claim 5, characterized in that: When the gas chromatography-mass spectrometry is used to analyze the liquid to be tested, the chromatography-mass spectrometry conditions are as follows: Chromatographic column: DB-5ms quartz capillary column 30m×0.25mm×0.25μm, Agilent; Column temperature: 60°C for 2 min, then raised to 150°C at 30°C / min, then raised to 300°C at 10°C / min, and held for 6 min; Carrier gas: helium, purity ≥99.999%, flow rate: 1.0mL / min; Inlet temperature: 250°C; Mass spectrometer detector: EI source, 70 eV; Ion source temperature: 250°C; Quadrupole temperature: 150°C; Injection volume: 1.0 μL; Injection method: splitless injection.

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