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

Abstract

The invention discloses a method for detecting pesticide residues in water samples by using a deep eutectic solvent-inorganic salt aqueous two-phase system, which comprises the following steps: an inorganic salt, a deep eutectic solvent and an internal standard compound are added into the water sample, stirred evenly, centrifuged and then layered, the upper-layer liquid is taken, the water is removed to obtain a test solution; the test solution is analyzed by a gas chromatography-mass spectrometry instrument; the deep eutectic solvent is a deep eutectic solvent mixed by triethylmethylammonium chloride and 1-aminoethanol. The solvent system of the invention has high polarity and a good hydrogen bond network, can effectively combine with the polar groups of pesticides, enhance the solubility of pesticides in the solvent, and thus significantly improve the extraction efficiency and detection sensitivity.

Description

Technical Field

[0001] The present invention relates to a method for detecting pesticide residues, and particularly to a method for detecting pesticide residues in water samples 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 of attention. Pesticides are widely used in agricultural production. Although crop yields have been increased, it has inevitably led to pesticide residues, especially the accumulation in water sources. Since the concentration of pesticides in water is usually low, and there are various interfering substances in water samples, the detection of pesticide residues has become extremely complex and difficult. Although existing detection methods can meet the requirements to a certain extent, due to the lack of efficient, environmentally friendly, and economical extraction technologies, 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 solvent consumption, low extraction efficiency, and long processing time. In addition, many solvents have strong toxicity, which will not only pollute the environment but also affect human health after use. Therefore, the development of green, low-toxic, and biodegradable alternative extraction solvents, as well as efficient and simple pretreatment technologies, has become an important topic in the 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 an unsatisfactory distribution with the water sample matrix and making it difficult to achieve effective separation. Although some studies have attempted to combine deep eutectic solvents with aqueous two-phase systems for water sample pretreatment, in the prior art, there are still problems such as difficult distribution of 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 to combine a deep eutectic solvent with an inorganic salt to form an aqueous two-phase system, and use liquid-liquid extraction combined with gas chromatography-mass spectrometry technology for pesticide residue detection. However, although this method has made certain progress in some aspects, there are still some problems. First, the deep eutectic solvents used, such as choline chloride combined with chlorophenol, phenol, and benzyl alcohol, etc., have not been fully optimized in terms of solvent polarity, extraction efficiency, etc. Especially when dealing with highly polar pesticides such as carbamates, their extraction efficiency is low and the extraction effect is not ideal. Therefore, the existing technology still has difficulty meeting the requirements of efficient, environmentally friendly, and simple pesticide residue detection. Summary of the Invention

[0006] In view of the above-mentioned defects existing 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 deep eutectic solvent-inorganic salt aqueous two-phase system.

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

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

[0009] An inorganic salt, a deep eutectic solvent, and an internal standard compound are added to the water sample, stirred evenly, centrifuged and then layered, the upper layer liquid is taken, and the water is removed to obtain a test solution;

[0010] The test solution is analyzed by a gas chromatography-mass spectrometry instrument;

[0011] The deep eutectic solvent is a deep eutectic solvent obtained by mixing triethylmethylammonium chloride with 1-aminoethanol.

[0012] Preferably, the deep eutectic solvent is a deep eutectic solvent obtained by mixing triethylmethylammonium chloride with 1-aminoethanol 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 dosages of the water sample, the inorganic salt, the internal standard compound, and the deep eutectic solvent are 4 mL:(0.02-0.18 g):(0.05-0.30 μg):(0.1-1.4 mL).

[0016] Preferably, the dosages of the water sample, the inorganic salt, the internal standard compound, and the deep eutectic solvent are 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 programmed to 150°C at 30°C / min, then to 300°C at 10°C / min, and held for 6 min;

[0021] Carrier gas: helium, purity ≥99.999%, flow rate: 1.0 mL / 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 deep eutectic solvent-inorganic salt aqueous two-phase system, wherein a high-polarity solvent system composed of triethylmethylammonium chloride and 1-aminoethanol is used as a deep eutectic solvent. Carbamate pesticides (such as carbofuran, methomyl and carbaryl) contain polar carbamate groups (-NH-COO-), which can undergo ion-dipole interactions with nitrogen atoms in triethylmethylammonium chloride and form stable bonds with amino and hydroxyl groups in 1-aminoethanol through hydrogen bonding. Because the solvent system has high polarity and a strong polar interaction network, it can effectively interact with the polar groups in the pesticide molecules, significantly improving the solubility of the pesticide in the solvent, thereby enhancing extraction efficiency and detection sensitivity. DETAILED DESCRIPTION

[0029] Embodiment 1:

[0030] 1. Preparation of a Deep Eutectic Solvent: Place triethylmethylammonium chloride and 1-aminoethanol in a round-bottom flask and stir continuously at 85°C for 2.5 hours to form a transparent, homogeneous liquid solvent, which is the deep 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 into a 15 mL centrifuge tube, add 0.3 g of the solid inorganic salt KCl and 10 μL of the internal standard compound 2-fluorobiphenyl (10 mg / L, methanol solution). After complete dissolution, add 2 mL of the deep eutectic solvent from step 1 above and vortex at 2500 rpm for 1 minute to mix thoroughly. Centrifuge at 5000 rpm for 3 minutes to separate the layers. Remove the upper organic layer using a gas chromatography injection needle and transfer it to a PCR tube containing anhydrous sodium sulfate for dehydration. Then, sample for gas chromatography-mass spectrometry analysis.

[0032] The analysis was performed using an Agilent 7890B / 5977 gas chromatograph-mass spectrometer. The chromatographic and 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 programmed to 150°C at 30°C / min, then to 300°C at 10°C / min, and held for 6 min;

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

[0036] Inlet temperature: 250°C

[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 used 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 three pesticides detected by this method

[0045]

[0046] III. Establishment of standard working curve:

[0047] Accurately weigh 100 mg of 2-fluorobiphenyl into a 100 mL beaker. After fully dissolving it with methanol, make up the volume to 100 mL in a volumetric flask to prepare an internal standard stock solution. Take 1 mL of the internal standard stock solution and make up the volume to 100 mL in a volumetric flask with methanol to prepare an internal standard working solution with a concentration of 10 mg / L. Accurately weigh 100 mg of each of the standard substances carbofuran, methomyl, and carbaryl into beakers respectively. Dissolve them with methanol and make up the volume to 100 mL in volumetric flasks to obtain a mixed standard stock solution. Take 2 mL of the mixed standard stock solution, dilute it with methanol and make up the volume to 100 mL in a 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 respectively, dilute them to 10 mL in volumetric flasks with methanol, and then add 10 μL of the internal standard working solution to each to prepare working curves with 7 concentrations of 5 μg / L, 10 μg / L, 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, and 500 μg / L relative to 4 mL of water sample. Then, perform gas chromatography-mass spectrometry analysis according to the conditions of sample analysis. Use 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 chromatogram of gas chromatography-mass spectrometry as the ordinate, and the concentration of the standard substance in the standard curve working solution as the abscissa to draw the standard working curve.

[0048] Parameters such as linear range, correlation coefficient, relative standard deviation, detection limit, and quantification limit were investigated. The results are listed in Table 2. The value of the detection limit was obtained when the signal-to-noise ratio (S / N) was 3. The spiked recovery rate was obtained by spiking 50 μg / L into blank water samples and repeating 5 times.

[0049] Table 2 Linear range, linear equation, correlation coefficient, detection limit, and spiked recovery rate indicators of three pesticides detected

[0050]

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

[0052] The qualitative analysis of pesticides in the water sample was carried out by comparing the retention time and mass spectrum of the total ion current chromatogram of the actual water sample and the total ion current chromatogram of the standard substance in gas chromatography-mass spectrometry. The ratio of the characteristic peak area value in the total ion current chromatogram of pesticides in the actual water sample to the characteristic peak area of the internal standard compound was obtained, and the standard working curve was used to carry out the quantitative analysis of the identified pesticides. The contents of 3 pesticides in the water sample were calculated and obtained as follows: carbofuran 12.92 μg / L, methomyl 13.85 μg / L, and carbaryl 15.97 μg / L.

[0053] Example 2:

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

[0055] Example 3:

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

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

[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 with 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 with 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 with 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 with a molar ratio of 1:2.

[0066] Table 3: Content test table of pesticides carbofuran, methomyl, and carbaryl in the water sample

[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 eutectic solvents described in Examples 1-3 are 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 combine with the nitrogen atom in triethylmethylammonium chloride through ion-dipole interactions and form stable bonds with the amino and hydroxyl groups in 1-aminoethanol through hydrogen bond interactions. Due to the high polarity of this solvent system and the strong ion-dipole interaction network, it can effectively interact with the polar groups in pesticide molecules, significantly increasing the solubility of pesticides in the solvent, thereby improving the extraction efficiency and detection sensitivity.

[0069] In contrast, the eutectic solvents of Comparative Examples 1-3 are composed of combinations of triethylmethylammonium chloride with chlorophenol, phenol, or benzyl alcohol, with lower polarity and stronger hydrophobicity of the aromatic ring, resulting in poor extraction effects on highly polar carbamate pesticides such as carbofuran, methomyl, and carbaryl. The carbamate groups of these pesticides need to bind to stronger hydrogen bond acceptors, but the hydrogen bond interactions of these solvent systems are weak, leading to their inability to effectively bind to pesticide molecules, thus affecting the extraction effect.

Claims

1. A method for detecting pesticide residues in water samples using a eutectic solvent-inorganic salt aqueous two-phase system, characterized in that, The steps include: Inorganic salts, deep eutectic solvents and internal standard compounds are added to the water sample, stirred evenly, centrifuged and separated into layers, the upper layer is collected, and the water is removed to obtain the test solution; Gas chromatography-mass spectrometry is used to analyze the liquid to be tested; The deep eutectic solvent is a mixture of triethylmethylammonium chloride and 1-aminoethanol; The inorganic salt is KCl; The amount of the water sample, inorganic salt, internal standard compound, and deep eutectic solvent used is 4 mL: (0.02-0.18 g): (0.05-0.30 μg): (0.1-1.4 mL); The pesticide is at least one of carbofuran, methomyl and carbaryl; 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 programmed to 150°C at 30°C / min, then to 300°C at 10°C / min, and held for 6 min; Carrier gas: helium, purity ≥99.999%, flow rate: 1.0 mL / 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.

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

3. The method for detecting pesticide residues in water samples by using a eutectic solvent-inorganic salt aqueous two-phase system as claimed in claim 1, wherein The internal standard compound is 2-fluorobiphenyl.

4. The method for detecting pesticide residues in water samples by using a eutectic solvent-inorganic salt aqueous two-phase system according to claim 1, characterized in that, The amount of the water sample, inorganic salt, internal standard compound, and deep eutectic solvent used is 4 mL: (0.05-0.10 g): (0.08-0.16 μg): (0.2-0.8 mL).

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