A method for determining the content of chloroxuron in solid waste by solid phase extraction-liquid chromatography tandem mass spectrometry with isotopic internal standard

Abstract

The application discloses a method for determining the content of chloroxuron in solid waste by solid phase extraction-liquid chromatography tandem mass spectrometry with isotopic internal standard without derivatization, and belongs to the technical field of environmental analysis and detection. The method extracts chloroxuron in solid waste by using an acid aqueous solution containing methanol and formic acid, removes impurities through dichloromethane, adjusts the pH to protonate the chloroxuron, and then purifies and enriches the chloroxuron through a PCX mixed cation exchange solid phase extraction column. The method adopts an HILIC hydrophilic interaction chromatographic column for separation, combines mass spectrometry detection in a positive ion source multi-reaction monitoring mode, introduces an isotopic internal standard of chloroxuron to correct the matrix suppression effect, and realizes qualitative and quantitative analysis. The method is simple to operate, the detection limit can reach 0.06 mu g / kg, the recovery rate is stable, is suitable for accurate detection of trace chloroxuron in various solid wastes, and can provide technical support for solid waste pollution identification.

Description

Technical Field

[0001] This invention belongs to the field of environmental analysis and testing technology, specifically relating to a method for determining the herbicidal content in solid waste using solid phase extraction-liquid chromatography-tandem mass spectrometry isotope internal standard method. Background Technology

[0002] Amitrole is a heterocyclic, non-selective, systemic foliar herbicide and an important intermediate in organic synthesis. It is widely used in the preparation of antibiotics, triazole azo dyes, photosensitive materials, metal corrosion inhibitors, systemic fungicides, and plant growth regulators. Amitrole is highly water-soluble at room temperature and easily migrates from soil or solid waste into surface and groundwater via rainwater and leachate, and bioaccumulates through the food chain.

[0003] Toxicological studies have confirmed that glyphosate can directly act on the thyroid gland, interfering with the synthesis and secretion of thyroid hormones. Epidemiological studies have shown that its exposure is highly correlated with the occurrence of thyroid tumors. The International Agency for Research on Cancer (IARC) has classified glyphosate as a Group 2B carcinogen, the European Union has included it in the controlled components for reproductive toxicity, and countries such as Norway and Finland have completely banned its use. The United States has also established strict control standards for the disposal of waste containing glyphosate.

[0004] Appendix I of my country's current GB 5085.6-2007 "Identification Standard for Hazardous Waste - Identification of Toxic Substance Content" includes a method for determining the herbicidal potency in solid waste; however, this method has significant technical limitations: First, the method is designed only for liquid samples and does not include the extraction step of solid matrix. It cannot be directly applied to solid wastes with complex composition such as waste salt, ash, and biochemical sludge. At present, the demand for detection of herbicides in solid matrix for solid waste pollution identification is becoming increasingly urgent. Secondly, the method requires derivatization of the target analyte using hexyl chloroformate, which involves a cumbersome procedure, difficult control of reaction conditions, and derivatization efficiency susceptible to matrix interference, resulting in high human-introduced errors and a long detection cycle. It is generally accepted in the field that herbicides have small molecular weights and extremely high polarity, leading to insufficient sensitivity in electrospray ionization sources. Therefore, existing standard methods all employ derivatization to improve their mass spectrometry response, which has become a standard technical understanding in this field. Third, the method uses APCI ion source and single ion selection monitoring mode, which only uses a single ion for quantification and cannot perform qualitative confirmation through multiple ion pairs. False positive results are prone to occur in complex matrices. Fourth, the method uses external standard quantification, which cannot correct for the strong ion inhibition effect of solid matrix co-extraction, resulting in poor quantitative accuracy and failing to meet the accuracy requirements for trace detection. Furthermore, existing cationic solid-phase extraction methods have not optimized the column bed microenvironment for the weakly alkaline characteristics of herbicides, making the target analyte prone to partial desorption due to local pH fluctuations during sample loading, leading to low recovery rates and poor parallelism.

[0005] To date, no standard method for detecting herbicides in solid waste based on ESI electrospray ionization sources, without derivatization, and with isotope internal standard correction has been established domestically or internationally. Therefore, developing a method for detecting herbicides that does not require derivatization, is applicable to complex solid matrices, and is accurate in both qualitative and quantitative analysis is of significant practical importance for filling the gap in solid waste environmental monitoring technology and supporting the identification and environmental management of hazardous waste. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies and aims to solve the following technical problems: 1. Existing detection methods are only applicable to liquid samples and lack a dedicated pretreatment and detection system for herbicides in solid waste, which cannot meet the actual needs of solid waste pollution identification and environmental supervision. 2. There is a technical bias in this field that the detection of herbicidal strength must be carried out by derivatization. Existing standard methods all require derivatization reactions, which are complicated in operation, have long detection cycles, and the derivatization efficiency is greatly affected by the matrix, and the risk of human error is high. 3. Solid waste has a complex matrix composition and strong matrix effect in co-extractants. Existing external standard methods have large quantitative errors, and single-ion monitoring modes have insufficient qualitative capabilities, which easily produce false positive results and have poor detection reliability.

[0007] II. Technical Solution To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for determining the herbicidal content in solid waste using solid-phase extraction-liquid chromatography-tandem mass spectrometry isotope internal standard method includes the following steps: Sample extraction: Take solid waste samples and use an acidic aqueous solution containing 8%~12% methanol and 0.3%~0.8% formic acid by volume as the extraction solvent for ultrasonic extraction. Combine the extracts obtained from multiple extractions.

[0008] Sample purification: Dichloromethane was added to the extract to remove nonpolar impurities, the organic phase was discarded, and the pH of the aqueous phase was adjusted to 3.0-4.0 to protonate the herbicides. Solid-phase extraction purification was performed using a PCX mixed cation exchange solid-phase extraction column. After activation, sample loading, and rinsing, the target analyte was eluted with ammoniated methanol solution. The eluent was collected and concentrated to dryness. Herbicides isotope internal standard was added, and the solution was diluted to volume with methanol-water solution. After filtration, the test solution was obtained.

[0009] Liquid chromatography separation: The test solution was separated by chromatographic separation using a HILIC hydrophilic column. The mobile phase consisted of an aqueous phase containing ammonium formate and a methanol phase containing ammonium formate.

[0010] Mass spectrometry detection: The herbicides and isotopic internal standards in the test solution were detected by mass spectrometry using an electrospray ESI positive ion source in multiple reaction monitoring (MRM) mode.

[0011] Qualitative and quantitative analysis: The herbicidal strength was qualitatively confirmed by retention time and characteristic ion pairs, and the content of herbicidal strength in the solid waste sample was calculated by isotope internal standard method.

[0012] The method of this invention does not require derivatization of the herbicides throughout the entire process, and the sample can be directly injected for analysis after extraction and purification.

[0013] Further, in step 1, the extraction solvent is preferably an aqueous solution containing 10% methanol and 0.5% formic acid by volume. The reason for choosing this acidic methanol-water solution as the extraction solvent is that: glyphosate is highly polar and readily soluble in water; adding an appropriate amount of methanol can improve the extraction efficiency of organically bound glyphosate in the solid matrix; formic acid provides an acidic environment, promoting the protonation of glyphosate, increasing its solubility in the aqueous solution, and simultaneously inhibiting its adsorption on the container wall. When the methanol volume fraction is below 8%, the extraction capacity for the organically bound target analyte is insufficient; when it is above 12%, more matrix impurities will be extracted simultaneously, increasing the burden on subsequent purification. When the formic acid volume fraction is below 0.3%, the protonation effect is insufficient; when it is above 0.8%, the system's acidity is too high, introducing too many impurity ions and affecting the subsequent solid-phase extraction effect. This extraction system is a combination of solid waste matrix and glyphosate physicochemical properties specifically optimized.

[0014] Furthermore, in step 1, 20 mL of extraction solvent is added to every 2.00 g of sample, and ultrasonic extraction is performed twice, with each extraction lasting 20 min. The preferred ultrasonic extraction conditions are a temperature of 25℃ and a power of 800 W. Two extractions ensure that the target analyte in the solid matrix is ​​fully extracted, and under these conditions, the extraction efficiency is stable and the operation is convenient.

[0015] Further, in step 2, the pH value is adjusted using a 10% (v / v) formic acid solution or ammonia solution, with an optimal pH value of 3.5. Herbicides are basic heterocyclic compounds with a pKa of approximately 4.0. Under acidic conditions of pH 3.0–4.0, they can be fully protonated to acquire a positive charge, thus enabling them to be firmly retained on the PCX mixed cation exchange column via cation exchange. Neutral and acidic impurities cannot be retained, achieving efficient separation of the target analyte from matrix interferences. When the pH value is below 3.0, the excessive acidity of the solution introduces too many impurity ions, affecting the retention stability of the solid-phase extraction column. When the pH value is above 4.0, herbicides are not fully protonated, and the cation exchange retention efficiency decreases significantly. Therefore, pH 3.0–4.0 is the optimal range that balances target analyte retention efficiency with matrix purification effects.

[0016] Further, in step 2, the activation steps of the PCX mixed cation exchange solid-phase extraction column are as follows: activation is performed sequentially with 5 mL of methanol and 5 mL of 5% (v / v) formic acid aqueous solution; the rinsing steps are as follows: rinsing is performed sequentially with 5 mL of ultrapure water and 5 mL of methanol; the elution steps are as follows: elution is performed with 5 mL of 6% (v / v) ammoniated methanol solution. Using 5% (v / v) formic acid aqueous solution as a protective agent for glyphosate creates a stable acidic microenvironment for the cation exchange column during the activation stage. This allows the protonated cation state of glyphosate to be continuously locked during the loading process, preventing premature desorption and loss of the target analyte due to local pH fluctuations. This design is a purification optimization scheme customized for the weakly alkaline physicochemical properties of glyphosate, which can significantly improve the retention stability and method recovery rate of solid-phase extraction; the ammoniated methanol can change the column bed pH value, deprotonating the glyphosate and thus desorbing and eluting it from the cation exchange column.

[0017] Furthermore, in step 2, the herbicidal isotope internal standard is... 13 C2H4N 15 N2. The isotopic internal standard has highly consistent physicochemical properties with the target analyte, and its chromatographic behavior is synchronized with the ionization characteristics of mass spectrometry. It can accurately correct the matrix inhibition effect during mass spectrometry detection and significantly improve the quantitative accuracy under complex matrices.

[0018] Further, in step 2, the eluent is concentrated to dryness under nitrogen blowing in a 45°C water bath; the volume is adjusted to 1 mL using a 70% methanol aqueous solution; and filtration is performed using a 0.22 μm polytetrafluoroethylene (PTFE) filter membrane. The 70% methanol aqueous solution is highly compatible with the mobile phase system of the HILIC column, avoiding peak distortion caused by solvent effects.

[0019] Furthermore, in step 3, the HILIC hydrophilic interaction column is used because: Herbicides are extremely polar, exhibiting very weak retention on conventional reversed-phase C18 columns, resulting in poor peak shape and susceptibility to solvent interference. The HILIC column, through its hydrophilic interaction mechanism, retains highly polar compounds, providing excellent retention and symmetrical peak shapes for herbicides. Simultaneously, it exhibits excellent compatibility with ESI positive ion sources, enhancing mass spectrometry response sensitivity. This invention, through the synergistic optimization of the HILIC chromatographic retention mechanism and ESI source parameters, achieves superior detection sensitivity without the need for derivatization, breaking the technical bias that herbicides detection requires derivatization.

[0020] Preferably, the chromatographic column is a ZORBAX Hilic Plus column with dimensions of 50 mm × 2.1 mm and a diameter of 1.8 μm. The liquid chromatography conditions are: injection volume 5 μL, flow rate 0.2 mL / min, column temperature 30 °C; the mobile phase is isocratic elution, with a volume ratio of aqueous phase to methanol phase of 30:70, and the concentration of ammonium formate in both the aqueous and methanol phases is 5 mmol / L. Ammonium formate, as a mobile phase additive, can improve peak shape and promote the ionization of the target analyte, thereby enhancing detection sensitivity.

[0021] Furthermore, in step 4, the mass spectrometry ion source parameters are: spray voltage 560V, evaporation temperature 350℃, sheath gas pressure 25Arb, auxiliary gas pressure 10Arb, capillary temperature 250℃, and collision gas pressure 0.9mTorr.

[0022] The monitoring ion pairs for glyphosate are m / z 85.0→43.1 and m / z 85.0→57.0, with corresponding collision energies of 25V and 15V, respectively; the monitoring ion pairs for the glyphosate isotope internal standard are m / z 89.0→44.2 and m / z 89.0→59.2, with corresponding collision energies of 32V and 16V, respectively. Using dual ion pairs, one as a quantitative ion and the other as a qualitative ion, can effectively reduce the probability of false positives and improve the reliability of qualitative results.

[0023] Furthermore, the solid waste includes, but is not limited to, environmental solid samples such as waste salt, ash residue, and biochemical sludge.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. Fills the gap in solid matrix detection and has wide applicability. This invention establishes for the first time a complete detection method from solid sample extraction and purification to detection. It can be directly applied to various complex solid wastes such as waste salt, ash, and biochemical sludge, and overcomes the technical limitation of existing national standards that only apply to liquid samples. It can meet the detection needs of various scenarios such as identification of hazardous characteristics of solid waste and investigation of contaminated sites.

[0025] 2. Overcoming technical bias, eliminating the need for derivatization, and offering simple and efficient operation. This invention breaks the technical bias that herbicidal efficacy detection requires derivatization. Through the synergistic optimization of the HILIC chromatographic retention mechanism and ESI source parameters, excellent detection sensitivity is achieved without derivatization. The method completely eliminates the derivatization reaction step; samples can be directly injected for analysis after extraction and purification, significantly shortening the detection cycle, reducing human error caused by fluctuations in derivatization reaction conditions and efficiency, and significantly improving the operability and throughput of the method.

[0026] 3. Multi-stage purification combined with isotope internal standard ensures accurate and reliable quantification. This invention employs a multi-stage purification system of "dichloromethane liquid-liquid impurity removal + pH-controlled protonation + PCX cation exchange solid-phase extraction," which effectively removes non-polar organic matter, neutral impurities, and acidic impurities from the solid matrix, significantly reducing matrix effects. Simultaneously, a strong herbicidal isotope internal standard is introduced. Utilizing the high consistency between the isotope internal standard and the target's physicochemical properties, the matrix inhibition effect during mass spectrometry detection is precisely corrected, resulting in quantification accuracy far superior to traditional external standard methods. Combined with the column protection mechanism of 5% formic acid aqueous solution, the cation form of the target analyte is maintained, further improving the stability of the solid-phase extraction recovery rate and reducing parallel sample bias under complex matrices.

[0027] 4. Dual-ion-pair MRM detection offers accurate qualitative analysis and high sensitivity. This invention employs an ESI positive ion source combined with multiple reaction monitoring (MRM) mode, using dual characteristic ion pairs for qualitative confirmation, effectively reducing the risk of false positives in complex matrices. The method has a detection limit as low as 0.06 μg / kg, meeting the requirements for trace detection. It exhibits good recovery and precision in various solid matrices, and the method performance meets the specifications for environmental monitoring and analysis. Attached Figure Description

[0028] Figure 1 The image shows the MRM mass spectrum of the herbicide standard, where peak 1 represents herbicide and peak 2 represents the herbicide isotope internal standard. Figure 2 The image shows the MRM mass spectrum of a blank sludge sample, where peak 2 is the herbicidal isotope internal standard. Figure 3 The image shows the MRM mass spectrum of the spiked sludge sample, where peak 1 represents glyphosate and peak 2 represents the glyphosate isotope internal standard. Figure 4 Linearity graph showing the relationship between different concentrations of herbicidal standard solutions. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example 1: Establishment of the detection method 1. Reagents and Materials Herbicides standard (purity ≥98%); Herbicides isotope internal standard ( 13 C2H4N 15 N2 (purity ≥98%) Methanol, formic acid, ammonia, dichloromethane, and ammonium formate were all of chromatographic purity; the water used in the experiment was ultrapure water (resistivity ≥ 18.2 MΩ). cm); PCX mixed cation exchange solid-phase extraction column (60 mg / 3 mL); 0.22 μm PTFE filter membrane.

[0031] Standard stock solution: Accurately weigh 10.0 mg of the herbicide standard, dissolve it in methanol and dilute to 10 mL to prepare a 1000 mg / L standard stock solution, and store it at -20±5℃ protected from light.

[0032] Internal standard stock solution: Accurately weigh 10.0 mg of herbicides isotope internal standard, dissolve it in methanol and dilute to 100 mL to prepare a 100 mg / L internal standard stock solution, and store it at -20±5℃ protected from light.

[0033] Series of standard working solutions: The standard stock solution is diluted stepwise to prepare a series of standard working solutions with concentrations of 0.5, 1, 5, 10, 50, 100, and 250 μg / L. An equal amount of internal standard is added to each working solution to keep the internal standard concentration consistent.

[0034] 2. Instruments and Equipment High-performance liquid chromatography-tandem mass spectrometry (with electrospray ionization source); CNC ultrasonic cleaner; nitrogen blower; precision pH meter; analytical balance (0.0001 g); high-speed centrifuge.

[0035] 3. Sample pretreatment (1) Extraction: Accurately weigh 2.00g of ground, sieved and mixed solid waste sample into a 100mL stoppered glass screw bottle, add 20mL of aqueous solution containing 10% (volume fraction) methanol + 0.5% (volume fraction) formic acid, vortex mix, place in an ultrasonic cleaner, and ultrasonically extract for 20min at 25℃ and 800W; after filtering the supernatant through qualitative filter paper, transfer it to a 250mL separatory funnel; add 20mL of extraction solvent to the residue and repeat ultrasonic extraction once, and combine the two extracts.

[0036] (2) Purification: Add 20 mL of dichloromethane to the combined extract, shake and extract for 2 min, let stand and separate into layers, discard the lower dichloromethane organic phase to remove non-polar interfering substances; adjust the pH of the upper aqueous phase to 3.5 with 10% formic acid solution or 10% ammonia water under pH meter monitoring to ensure that the herbicides are fully protonated.

[0037] The PCX solid-phase extraction column was activated sequentially with 5 mL of methanol and 5 mL of 5% (v / v) formic acid aqueous solution. This step established an acidic protective atmosphere for the column bed using formic acid aqueous solution, ensuring that the herbicide remained in a protonated state throughout the loading process, achieving stable retention. Activation was stopped just before the packing material was exposed to air. The pH-adjusted extract was then transferred entirely to the activated PCX column at a flow rate of approximately 1 mL / min. After the extract had completely eluted, it was rinsed sequentially with 5 mL of ultrapure water and 5 mL of methanol, and the eluent was discarded. Finally, the target analyte was eluted with 5 mL of 6% (v / v) ammoniated methanol solution, and the eluent was collected in a 15 mL nitrogen-blown concentration flask.

[0038] Place the eluent in a 45°C water bath, concentrate it to near dryness by nitrogen blowing, remove it, accurately add 10 μL of internal standard working solution, and make up to 1 mL with 70% (volume fraction) methanol aqueous solution. Vortex mix for 30 s, filter through a 0.22 μm PTFE membrane, and transfer the filtrate to a sample vial for testing.

[0039] 4. Chromatographic and Mass Spectrometric Conditions (1) Liquid chromatography conditions Column: ZORBAX Hilic Plus (50mm×2.1mm, 1.8μm); Injection volume: 5 μL; Flow rate: 0.2 mL / min; Column temperature: 30℃; Mobile phase: Phase A is an aqueous solution containing 5 mmol / L ammonium formate, and Phase B is a methanol solution containing 5 mmol / L ammonium formate; Elution program: isocratic elution, A:B=30:70 (V / V), run time 6 min.

[0040] (2) Mass spectrometry conditions Ion source: Electrospray ionization (ESI) source, positive ion scanning mode; Detection mode: Multiple response monitoring (MRM); Ion source parameters: spray voltage 560V, evaporation temperature 350℃, sheath gas pressure 25Arb, auxiliary gas pressure 10Arb, capillary temperature 250℃, collision gas pressure 0.9mTorr; The monitoring ion pairs and corresponding parameters of herbicides and isotope internal standards are shown in Table 1.

[0041] Table 1. Mass spectrometry parameters of glyphosate and its isotopic internal standard

[0042] The herbicidal standard working solution was tested under the above conditions, and the resulting MRM mass spectrum is shown below. Figure 1 As shown, both the herbicides and the internal isotope standard exhibited symmetrical chromatographic peaks with no extraneous peaks, and the mass spectrometry response was good.

[0043] 5. Qualitative and Quantitative Methods Qualitative determination: If the retention time of the target chromatographic peak in the sample deviates from the retention time of the corresponding target analyte in the standard solution within ±2.5%, and the relative abundance ratio of qualitative ion pairs to quantitative ion pairs in the sample spectrum deviates from the relative abundance ratio of ion pairs in the standard solution of equivalent concentration within the allowable range, then the sample is determined to contain herbicides.

[0044] Quantitative calculation: A standard working curve was plotted with the ratio of the peak area of ​​the herbicidal strength to the peak area of ​​the internal standard in the series of standard working solutions as the ordinate and the corresponding herbicidal strength concentration as the abscissa. The peak area ratio of the herbicidal strength to the internal standard in the test solution was substituted into the standard curve to calculate the concentration of the test solution. Then, the herbicidal strength content in the solid waste sample was calculated based on the sample weight and dilution factor.

[0045] Example 2: Methodology Validation Experiment 1. Limit of detection and limit of quantification According to HJ 168, following all the steps of sample analysis, samples with concentration values ​​or contents that are 3 to 5 times the estimated method detection limit were subjected to (n≥7) parallel determinations. The standard deviation of n parallel determinations was calculated, and the method detection limit was calculated. The results are shown in Table 2.

[0046] Table 2. Results of method detection limit and quantitation limit

[0047] 2. Precision and accuracy The MRM mass spectrum of the blank sludge sample is shown below. Figure 2 As shown, there are no matrix interference peaks at the elution position of the target analyte, indicating that the method has good anti-interference ability. Four typical solid waste blank samples, namely sludge, waste salt, ash residue and biochemical sludge, were selected and spiked recovery experiments were carried out at three concentration levels: low, medium and high. Six samples were prepared in parallel for each spiked level and measured according to the method in Example 1. The average recovery rate and relative standard deviation (RSD) were calculated. The results are shown in Tables 3 and 4.

[0048] Table 3 Results of sludge substrate spiked recovery experiment

[0049] The MRM mass spectrum of the spiked sludge sample is as follows: Figure 3 As shown, the target analyte and the internal standard peaks are symmetrical and well separated, with no obvious interference from the matrix.

[0050] Table 4 Results of Spike Recovery Experiments on Different Solid Matrix

[0051] 3. Linear range A series of standard working solutions were determined according to the chromatographic and mass spectrometric conditions of Example 1. A standard curve was obtained by plotting the herbicidal concentration against the peak area ratio, as shown below. Figure 4 As shown, the linear relationship is good, meeting the requirements for trace quantitative detection. The herbicides showed good linearity in the concentration range of 0.5~250μg / L, with a correlation coefficient r>0.995, which meets the requirements for trace quantitative detection.

[0052] Experimental results show that this method has a low detection limit, good precision, and stable recovery rate. It can be applied to the qualitative and quantitative detection of herbicides in various complex solid waste matrices, and the method performance meets the technical requirements of environmental monitoring and analysis methods.

Claims

1. A method for determining the herbicidal content in solid waste using solid-phase extraction-liquid chromatography-tandem mass spectrometry isotope internal standard method, characterized in that, Includes the following steps: (1) Sample extraction: Take solid waste samples and use an acidic aqueous solution containing 8%~12% methanol and 0.3%~0.8% formic acid as the extraction solvent for ultrasonic extraction. Combine the extracts obtained from multiple extractions. (2) Sample purification: Dichloromethane was added to the extract to remove nonpolar impurities, the organic phase was discarded, and the pH of the aqueous phase was adjusted to 3.0~4.0 to protonate the herbicidal agent. Solid phase extraction purification was performed using a PCX mixed cation exchange solid phase extraction column. After activation, sample loading and rinsing, the target substance was eluted with ammoniated methanol solution. The eluent was collected and concentrated to dryness. Herbicidal isotope internal standard was added, and the volume was adjusted with methanol aqueous solution. After filtration, the test solution was obtained. (3) Liquid chromatography separation: The test solution was separated by chromatographic separation using a HILIC hydrophilic column. The mobile phase consisted of an aqueous phase containing ammonium formate and a methanol phase containing ammonium formate. (4) Mass spectrometry detection: The herbicidal strength and isotopic internal standard in the test solution were detected by mass spectrometry using an electrospray ESI positive ion source in multiple reaction monitoring (MRM) mode. (5) Qualitative and quantitative analysis: The herbicidal strength was qualitatively confirmed by retention time and characteristic ion pairs, and the content of herbicidal strength in solid waste samples was calculated by isotope internal standard method; The method does not require derivatization of the herbicides throughout the entire process.

2. The determination method according to claim 1, characterized in that, In step (1), the extraction solvent is an aqueous solution containing 10% methanol and 0.5% formic acid by volume; 20 mL of extraction solvent is added to each 2.00 g sample at a time, and ultrasonic extraction is performed twice, with each extraction lasting 20 min.

3. The determination method according to claim 2, characterized in that, In step (1), the conditions for ultrasonic extraction are: temperature 25℃ and power 800W.

4. The determination method according to claim 1, characterized in that, In step (2), the pH value is adjusted to 3.5 using a 10% (v / v) formic acid solution or ammonia solution; the herbicidal isotope internal standard is... 13 C2H4N 15 N2.

5. The determination method according to claim 1, characterized in that, In step (2), the activation steps of the PCX mixed cation exchange solid phase extraction column are as follows: activation is performed sequentially with methanol and 5% formic acid aqueous solution; the rinsing steps are as follows: rinsing is performed sequentially with ultrapure water and methanol; the elution steps are as follows: elution is performed with 6% ammoniated methanol solution.

6. The determination method according to claim 1, characterized in that, In step (2), the eluent is concentrated to dryness by nitrogen blowing under a water bath at 45°C; the volume is adjusted by a 70% methanol aqueous solution with a volume of 1 mL; and a 0.22 μm polytetrafluoroethylene filter membrane is used for filtration.

7. The determination method according to claim 1, characterized in that, In step (3), the chromatographic column is a ZORBAX Hilic Plus column with a size of 50 mm × 2.1 mm and a diameter of 1.8 μm. The liquid chromatography conditions are: injection volume 5 μL, flow rate 0.2 mL / min, column temperature 30 °C, mobile phase is isocratic elution, the volume ratio of aqueous phase to methanol phase is 30:70, and the concentration of ammonium formate in both aqueous and methanol phases is 5 mmol / L.

8. The determination method according to claim 1, characterized in that, In step (4), the mass spectrometry ion source parameters are: spray voltage 560V, evaporation temperature 350℃, sheath gas pressure 25Arb, auxiliary gas pressure 10Arb, capillary temperature 250℃, and collision gas pressure 0.9mTorr.

9. The determination method according to claim 1, characterized in that, In step (4), the monitoring ion pairs for chlorpyrifos are m / z 85.0→43.1 and m / z 85.0→57.0, with corresponding collision energies of 25V and 15V, respectively; the monitoring ion pairs for the chlorpyrifos isotope internal standard are m / z 89.0→44.2 and m / z 89.0→59.2, with corresponding collision energies of 32V and 16V, respectively.

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