A method for determining dithiocarbamates based on series microplasma-emission spectrum

Abstract

The present application relates to the technical field of pesticide detection, and provides a method for determining dithiocarbamate pesticides based on a tandem microplasma-emission spectrum, which comprises the following steps: using stannous chloride-hydrochloric acid (SnCl2-HCl) solution as a reducing agent, separating DTCs pesticides by liquid chromatography (LC), exciting the SnCl2-HCl system by a first-stage liquid electrode glow discharge (LEGD) microplasma to reduce the DTCs pesticides into carbon disulfide (CS2) in real time, exciting CS2 to emit a spectrum by a second-stage dielectric barrier discharge (DBD) microplasma, thereby forming a LEGD reduction-DBD determination tandem microplasma system, and achieving the detection of dithiocarbamate pesticides, wherein the method has the advantages of real-time, accuracy, rapidity, simplicity, and the ability to analyze each subclass of DTCs pesticides, and meets the requirement of rapidly determining dithiocarbamate pesticide residues in fruits and vegetables in a short period of time.

Description

Technical Field

[0001] This invention relates to the field of pesticide detection technology, and in particular to a method for determining mancozeb based on tandem microplasma-emission spectroscopy. Background Technology

[0002] Dithiocarbamates (DTCs), as important fungicides, are widely used in agriculture, accounting for 30% of the fungicides used in the agricultural industry (Kaul et al., 2021), with annual DTC consumption ranging from 25,000 to 35,000 metric tons. With the continuous increase in pesticide use, impacting human health and environmental safety, the issue of DTC pesticide residues has attracted serious attention.

[0003] Traditional DTC pesticide residue detection involves two parts: first, pretreatment to convert the pesticide residues into CS2, and second, determination of CS2 content using methods such as GC-ECD / MS. Commonly used pretreatment methods include solid-phase extraction, liquid-liquid extraction, and dispersion solid-phase extraction. However, these methods suffer from drawbacks such as long pretreatment times, poor repeatability due to CS2 loss, and large and expensive instruments. Over the past decade, several new technologies for DTC detection have been reported, such as surface-enhanced Raman spectroscopy, voltammetry, fluorescence probes, and infrared spectroscopy. However, due to selectivity limitations, these methods remain difficult to widely apply. Therefore, finding a new, short-time, efficient, and low-energy-consumption DTC pesticide determination technology is of great significance for the wider application of DTC pesticide subclass residue detection. Summary of the Invention

[0004] In view of this, the present invention proposes a method for determining DTC pesticides based on tandem microplasma-emission spectroscopy. The method uses a first-stage liquid electrode to electrolyze SnCl2-HCl solution using glow discharge to convert DTC pesticides into CS2. Then, residue analysis is performed using a second-stage dielectric barrier discharge microplasma (DBD). This method has the advantages of being real-time, accurate, rapid, simple, and capable of analyzing subclasses of each DTC pesticide, meeting the requirements for rapid determination of DTC pesticide residues in fruits and vegetables in a short period of time.

[0005] The technical solution of this invention is as follows:

[0006] A method for determining DTC pesticides based on tandem microplasma-emission spectroscopy is proposed. First, SnCl2-HCl solution is used as a reducing agent to separate each subclass of DTC pesticides by liquid chromatography. Then, the SnCl2-HCl system is excited by glow discharge of the first-stage liquid electrode to electrolyze and reduce the DTC pesticides to CS2 in real time. Finally, the emission spectrum of CS2 is excited by the second-stage dielectric barrier discharge microplasma. CS2 is used as a standard substance for DTC pesticides to determine the DTC pesticide content.

[0007] This invention mainly consists of a liquid electrode glow discharge electrolytic reduction system and a CS2 detection system. The first stage, the liquid electrode glow discharge electrolysis of stannous chloride-hydrochloric acid solution to CS2, is the reduction system; the second stage, the dielectric barrier discharge microplasma (DBD), is the CS2 detection system.

[0008] To further explain, a method for determining mancozeb pesticides based on tandem microplasma-emission spectroscopy includes the following steps:

[0009] Step 1: Dissolve the dithiocarbamate pesticide sample in disodium EDTA solution and set aside;

[0010] Step 2: Take SnCl2-HCl solution and pump it into the reduction tube simultaneously with the pesticide sample dissolved in Step 1. Separate each subclass of DTC pesticides through a liquid chromatography column to obtain a liquid chromatography separated mixture.

[0011] Step 3: The SnCl2-HCl system is excited by glow discharge of the first-stage liquid electrode with a voltage of 1.5-2.1kV to reduce the mixture separated by liquid chromatography to CS2 in real time. The argon flow rate is controlled at 280-320mL / min, the carrier liquid flow rate is 18-22mL / min, and the electrode distance is 2.8-3.2mm.

[0012] Step 4: CS2 is fed into the second-stage dielectric barrier discharge microplasma to excite CS2 emission spectra. CS2 is then used as a DTCs standard for quantitative analysis to determine the DTCs pesticide content. This invention uses a first-stage liquid electrode glow discharge (LEGD) coupled with dielectric barrier discharge (DBD) microplasma-molecular emission spectroscopy as a detector, and stannous chloride-hydrochloric acid (SnCl2-HCl) solution as the mobile phase to perform short-time, high-efficiency, and low-energy-consumption determination of mancozeb (DTCs) in fruits and vegetables.

[0013] More preferably, in step 2, the SnCl2-HCl solution has a SnCl2 mass concentration of 20 g / L and an HCl mass concentration of 3 mol / L.

[0014] More preferably, in step 3, the voltage of the glow discharge of the first-stage liquid electrode is 1.8kV, the argon flow rate is 200mL / min, the carrier liquid flow rate is 20mL / min, and the electrode distance is 3mm.

[0015] More preferably, the second-stage dielectric barrier discharge voltage is 0.75-0.85kV.

[0016] More preferably, the second-stage dielectric barrier discharge voltage is 0.8kV.

[0017] More preferably, the detection limit for the DTC pesticide content is 0.10 mg / kg. -1 .

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] (1) This invention uses SnCl2-HCl solution as a reducing agent. Based on the separation of DTC pesticides by liquid chromatography (LC), the dithiocarbamate pesticides are rapidly electrolytically reduced to CS2 by the first-stage liquid electrode glow discharge to excite stannous chloride solution. The electrolytic reduction method is more stable and efficient, and can ensure that the reaction occurs in a very short time, effectively shortening the pretreatment time and realizing efficient detection and analysis of pesticide residues.

[0020] (2) Compared with the traditional microwave-assisted stannous chloride acid hydrolysis method for DTCs, the stability and precision of the method of the present invention are significantly improved. It can determine dithiocarbamate pesticides in a short time without relying on large and expensive instruments, and can clearly distinguish and analyze each DTC pesticide subclass. It has the characteristics of high selectivity, short time and high efficiency.

[0021] (3) The present invention is not only simple in equipment, easy to move and detect anytime and anywhere, but also has lower detection cost and extremely high detection efficiency, which is conducive to the wider promotion and application of rapid detection of DTC pesticide subclass residues. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the liquid electrode glow discharge electrolytic reduction-dielectric barrier discharge microplasma method for determining dithiocarbamate pesticide residues according to the present invention.

[0023] Figure 2 This is a schematic diagram showing the identification results of molecular emission of different gases at 257.94 nm according to the present invention; where a is argon gas; b is CS2 gas; the horizontal axis in the figure is wavelength in nm, and the vertical axis is signal intensity;

[0024] Figure 3 This is a schematic diagram comparing the response of the DTCs pesticide of the present invention with other types of pesticides to the molecular emission of CS2 at 257.94 nm; the horizontal axis in the figure is wavelength in nm, and the vertical axis is signal intensity.

[0025] Figure 4 The glow discharge voltage of the liquid electrode of this invention is relative to the standard solution of mancozeb (10 μg / mL). -1 The graph shows the influence of the response; in the graph, the horizontal axis represents the glow discharge voltage of the liquid electrode in kV, and the vertical axis represents the relative peak area in %.

[0026] Figure 5 The dielectric barrier discharge micro-plasma discharge voltage of the present invention is related to the manganese zinc standard solution (10 μg mL). -1 The graph shows the impact of the response; in the graph, the horizontal axis represents the dielectric barrier discharge voltage in kV, and the vertical axis represents the relative peak area in %.

[0027] Figure 6 The argon flow rate of this invention affects the standard solution of mancozeb (10 μg / mL). -1 The effect analysis curve of the response; in the figure, the horizontal axis is the argon flow rate, and the unit is mL min. -1 The vertical axis represents the relative peak area, in percentage.

[0028] Figure 7 The effect of the carrier fluid flow rate on the mancozeb standard solution (10 μg / mL) of this invention -1 The effect analysis curve of the response; in the figure, the horizontal axis is the carrier fluid flow rate, and the unit is mL min. -1 The vertical axis represents the relative peak area, in percentage.

[0029] Figure 8 The hydrochloric acid concentration of the present invention is relative to the standard solution of mancozeb (10 μg / mL). -1 The effect of the response is analyzed in the curve; in the figure, the horizontal axis represents the concentration of hydrochloric acid, and the unit is mol / L. -1 The vertical axis represents the relative peak area, in percentage.

[0030] Figure 9 The stannous chloride concentration of this invention is relative to the standard solution of mancozeb (10 μg / mL). -1 The effect of the response is analyzed in the curve; in the figure, the horizontal axis represents the concentration of stannous chloride, and the unit is g / L. -1 The vertical axis represents the relative peak area, in percentage.

[0031] Figure 10 The electrode distance of this invention is relative to the standard solution of mancozeb (10 μg / mL). -1 The graph shows the effect of the response; in the graph, the horizontal axis represents the electrode distance in mm, and the vertical axis represents the relative peak area in %.

[0032] Figure 11 The figure illustrates the interference of different concentrations of mancozeb in the sample matrix (a) and pesticide matrix (b) on the method of this invention. In the figure, the horizontal axis represents the fruit / vegetable and pesticide matrix, and the vertical axis represents the recovery rate (%).

[0033] Figure 12 This is a chromatogram of four DTCs detected by LC detector under optimal experimental conditions according to the present invention; in the figure, the horizontal axis is the integration time and the vertical axis is the signal intensity. Detailed Implementation

[0034] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0035] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0036] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0037] Example 1

[0038] A method for determining DTC pesticides based on tandem microplasma-emission spectroscopy is proposed. Using SnCl2-HCl solution as a reducing agent, each subclass of DTC pesticides is separated by liquid chromatography. A first-stage liquid electrode glow discharge excites the SnCl2-HCl system, electrolyzing and reducing the DTC pesticides to CS2 in real time. Then, a second-stage dielectric barrier discharge microplasma excites the CS2 emission spectrum. Using CS2 as a DTC standard, the DTC pesticide content is determined.

[0039] Example 2

[0040] A method for determining dithiocarbamate pesticides based on tandem microplasma-emission spectroscopy involves using a first-stage liquid electrode to electrolyze a stannous chloride-hydrochloric acid solution via glow discharge, reducing the dithiocarbamate pesticide to carbon disulfide (CS2), and then using a second-stage dielectric barrier discharge microplasma (DBD) for quantitative analysis and detection. The method includes the following steps (1) to (4):

[0041] (1) Dissolve the dithiocarbamate pesticide sample in a 50mL tube with EDTA disodium solution for later use;

[0042] (2) Take 20 mL of SnCl2-HCl solution and pump it into the reduction tube at the same time as 10 mL of pesticide sample dissolved in step 1. Separate each subclass of DTC pesticides by liquid chromatography column to obtain a liquid chromatography separated mixture; wherein, in the SnCl2-HCl solution, the mass concentration of SnCl2 is 20 g / L and the mass concentration of HCl is 3 mol / L.

[0043] (3) The SnCl2-HCl system was excited by glow discharge of the first-stage liquid electrode with a voltage of 1.5kV to reduce the mixture separated by liquid chromatography to CS2 in real time. The argon flow rate was controlled at 280mL / min, the carrier liquid flow rate was 18mL / min, and the electrode distance was 2.8mm.

[0044] (4) CS2 is sent into the second-stage dielectric barrier discharge microplasma to excite the emission spectrum of CS2. The second-stage dielectric barrier discharge voltage is 0.75kV. CS2 is used as a DTCs standard material for quantitative analysis to determine the DTCs pesticide content.

[0045] Example 3

[0046] A method for determining dithiocarbamate pesticides based on tandem microplasma-emission spectroscopy involves using a first-stage liquid electrode to electrolyze a stannous chloride-hydrochloric acid solution via glow discharge, reducing the dithiocarbamate pesticide to carbon disulfide (CS2), and then using a second-stage dielectric barrier discharge microplasma (DBD) for quantitative analysis and detection. The method includes the following steps (1) to (4):

[0047] (1) Dissolve the dithiocarbamate pesticide sample in a 50mL tube with EDTA disodium solution for later use;

[0048] (2) Take 20 mL of SnCl2-HCl solution and pump it into the reduction tube at the same time as 10 mL of pesticide sample dissolved in step 1. Separate each subclass of DTC pesticides by liquid chromatography column to obtain a liquid chromatography separated mixture.

[0049] (3) The SnCl2-HCl system was excited by glow discharge of the first-stage liquid electrode with a voltage of 2.1 kV, and the mixture separated by liquid chromatography was reduced to CS2 in real time. The argon flow rate was controlled at 320 mL / min, the carrier liquid flow rate was 22 mL / min, and the electrode distance was 3.2 mm. The SnCl2-HCl solution had a mass concentration of 20 g / L and a mass concentration of 3 mol / L.

[0050] (4) CS2 is sent into the second-stage dielectric barrier discharge microplasma to excite the emission spectrum of CS2. The second-stage dielectric barrier discharge voltage is 0.85kV. CS2 is used as a DTCs standard material for quantitative analysis to determine the DTCs pesticide content.

[0051] Example 4

[0052] A method for determining dithiocarbamate pesticides based on tandem microplasma-emission spectroscopy involves using a first-stage liquid electrode to electrolyze a stannous chloride-hydrochloric acid solution via glow discharge, reducing the dithiocarbamate pesticide to carbon disulfide (CS2), and then using a second-stage dielectric barrier discharge microplasma (DBD) for quantitative analysis and detection. The method includes the following steps (1) to (4):

[0053] (1) Dissolve the dithiocarbamate pesticide sample in a 50mL tube with EDTA disodium solution for later use;

[0054] (2) Take 20 mL of SnCl2-HCl solution and pump it into the reduction tube at the same time as 10 mL of pesticide sample dissolved in step 1. Separate each subclass of DTC pesticides by liquid chromatography column to obtain a liquid chromatography separated mixture.

[0055] (3) The SnCl2-HCl system was excited by glow discharge of the first-stage liquid electrode with a voltage of 1.8 kV, and the mixture separated by liquid chromatography was reduced to CS2 in real time. The argon flow rate was controlled at 300 mL / min, the carrier liquid flow rate was 20 mL / min, and the electrode distance was 3.0 mm. The SnCl2-HCl solution contained SnCl2 with a mass concentration of 20 g / L and HCl with a mass concentration of 3 mol / L.

[0056] (4) CS2 is sent into the second-stage dielectric barrier discharge microplasma to excite the emission spectrum of CS2. The second-stage dielectric barrier discharge voltage is 0.8kV. CS2 is used as a DTCs standard material for quantitative analysis to determine the DTCs pesticide content.

[0057] Example 5

[0058] The method of this invention was investigated for identifying molecular emission of different gases at 257.94 nm, and argon and CS2 gases were detected. Following the procedures in Example 4, the experimental conditions were set as follows: the first-stage liquid electrode glow discharge voltage was 1.8 kV, the second-stage dielectric barrier discharge voltage was 0.8 kV, and the argon flow rate was 300 mL / min. -1 The integration time for the CCD (charge-coupled device) was 100 ms. Experimental results are attached. Figure 2 This example demonstrates the ability of the present invention to detect dithiocarbamate pesticides by detecting these two gases.

[0059] Example 6

[0060] The response of DTC pesticides to the molecular emission of CS2 at 257.94 nm was investigated compared with that of other pesticides. Following the procedure in Example 5, 10 μg mL... -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the glow discharge voltage of the first-stage liquid electrode was 1.8 kV, the dielectric barrier discharge voltage of the second-stage electrode was 0.8 kV, and the argon flow rate was 300 mL / min. -1 The carrier fluid flow rate is 20 mL / min. -1 The SnCl2 concentration is 20 g / L. -1 The concentration of HCl is 3 mol / L. -1 The integration time for the CCD (charge-coupled spectrometer) is 100 ms. The experimental results for this embodiment are attached. Figure 3 .

[0061] Example 7

[0062] Investigating the effect of liquid electrode glow discharge voltage on mancozeb standard solution (10 μg mL) -1 The effect of the response. Referring to the operating procedure of Example 5, 10 μg mL -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: dielectric barrier discharge voltage of 0.8 kV and argon flow rate of 300 mL / min. -1 The carrier fluid flow rate is 20 mL / min. -1 The electrode distance is 3 mm, and the SnCl2 concentration is 20 g / L. -1 The concentration of HCl is 3 mol / L. -1 The test range for the glow discharge voltage of the liquid electrode is 1.0–2.6 kV. The experimental results of this embodiment are shown in the appendix. Figure 4 As shown in the figure, the relative peak area reaches its maximum when the glow discharge voltage of the liquid electrode is 1.8kV, thus determining that the optimal glow discharge voltage of the liquid electrode of the present invention is 1.8kV.

[0063] Example 8

[0064] Investigating the effect of dielectric barrier discharge microplasma discharge voltage on mancozeb standard solution (10 μg mL) -1 The effect of the response. Referring to the operating procedure of Example 5, 10 μg mL -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the glow discharge voltage of the liquid electrode was 1.8 kV, and the argon flow rate was 300 mL / min. -1 The carrier fluid flow rate is 20 mL / min. -1 The electrode distance is 3 mm, and the SnCl2 concentration is 20 g / L. -1 The concentration of HCl is 3 mol / L. -1 The dielectric barrier discharge microplasma discharge voltage test range is 0.4–1.0 kV. The experimental results of this embodiment are shown in the appendix. Figure 5 As shown in the figure, the relative peak area reaches its maximum when the voltage of the dielectric barrier discharge is 0.8kV. Therefore, the optimal voltage for the dielectric barrier discharge micro-plasma discharge of the present invention is determined to be 0.8kV.

[0065] Example 9

[0066] Investigating the effect of argon flow rate on mancozeb standard solution (10 μg / mL) -1 The effect of the response. Referring to the operating procedure of Example 5, 10 μg mL -1Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the glow discharge voltage of the liquid electrode was 1.8 kV, the dielectric barrier discharge voltage was 0.8 kV, and the carrier fluid flow rate was 20 mL / min. -1 The SnCl2 concentration is 20 g / L. -1 The electrode distance is 3 mm, and the HCl concentration is 3 mol / L. -1 The argon flow rate test range is 100–600 mL / min. -1 The experimental results of this embodiment are shown in the appendix. Figure 6 In the figure, when the argon flow rate is 300 mL / min -1 At this point, the relative peak area reaches its maximum, thus determining the optimal argon flow rate of this invention to be 300 mL / min. -1 .

[0067] Example 10

[0068] Investigating the effect of carrier fluid flow rate on mancozeb standard solution (10 μg mL) -1 The effect of the response. Referring to the operating procedure of Example 5, 10 μg mL -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the liquid electrode glow discharge voltage was 1.8 kV, the dielectric barrier discharge voltage was 0.8 kV, and the argon flow rate was 300 mL / min. -1 The electrode distance is 3 mm, and the SnCl2 concentration is 20 g / L. -1 The concentration of HCl is 3 mol / L. -1 The test range for the carrier fluid flow rate is 14–24 mL / min. -1 The experimental results of this embodiment are shown in the appendix. Figure 7 In the figure, when the carrier fluid flow rate is 20 mL / min -1 At this point, the relative peak area reaches its maximum, thus determining the optimal carrier fluid flow rate of this invention to be 20 mL / min. -1 .

[0069] Example 11

[0070] The effect of hydrochloric acid concentration on the effect of mancozeb standard solution (10 μg mL) was investigated. -1 The effect of the response. Referring to the operating procedure of Example 5, 10 μg mL -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the liquid electrode glow discharge voltage was 1.8 kV, the dielectric barrier discharge voltage was 0.8 kV, and the argon flow rate was 300 mL / min. -1 The carrier fluid flow rate is 20 mL / min. -1 The SnCl2 concentration is 20 g / L. -1The electrode distance was 3 mm, and the hydrochloric acid concentration was tested at a range of 1.5–4.0 mol / L. -1 The experimental results of this embodiment are shown in the appendix. Figure 8 In the figure, when the hydrochloric acid concentration is 3.0 mol L... -1 At this point, the relative peak area reaches its maximum, thus determining the optimal hydrochloric acid concentration of this invention to be 3.0 mol / L. -1 .

[0071] Example 12

[0072] Investigating the effect of stannous chloride concentration on mancozeb standard solution (10 μg mL) -1 The effect of the response. Referring to the operating procedure of Example 5, 10 μg mL -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the liquid electrode glow discharge voltage was 1.8 kV, the dielectric barrier discharge voltage was 0.8 kV, and the argon flow rate was 300 mL / min. -1 The carrier fluid flow rate is 20 mL / min. -1 The concentration of HCl is 3 mol / L. -1 The electrode distance was 3 mm, and the stannous chloride concentration test range was 5–30 g / L. -1 The experimental results of this embodiment are shown in the appendix. Figure 9 In the figure, when the concentration of stannous chloride is 20 g / L... -1 At this point, the relative peak area reaches its maximum, thus determining the optimal stannous chloride concentration of this invention to be 20 g / L. -1 .

[0073] Example 13

[0074] The effect of electrode distance on mancozeb standard solution (10 μg mL) was investigated. -1 The effect of the response. Referring to the operating procedure of Example 5, 10 μg mL -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the liquid electrode glow discharge voltage was 1.8 kV, the dielectric barrier discharge voltage was 0.8 kV, and the argon flow rate was 300 mL / min. -1 The carrier fluid flow rate is 20 mL / min. -1 The SnCl2 concentration is 20 g / L. -1 The concentration of HCl is 3 mol / L. -1 The electrode distance test range is 1–6 mm. The experimental results of this embodiment are shown in the appendix. Figure 10 In the figure, the relative peak area reaches its maximum when the electrode distance is 3 mm, thus determining that the optimal electrode distance of the present invention is 3 mm.

[0075] Example 14

[0076] The interference of different concentrations of mancozeb in the sample matrix (a) and pesticide matrix (b) on this method was investigated. Following the operating procedure of Example 5, 10 μg mL -1 Mancozeb was used as a representative analyte. The experimental conditions were set as follows: the liquid electrode glow discharge voltage was 1.8 kV, the dielectric barrier discharge voltage was 0.8 kV, and the argon flow rate was 300 mL / min. -1 The carrier fluid flow rate is 20 mL / min. -1 The SnCl2 concentration is 20 g / L. -1 The concentration of HCl is 3 mol / L. -1 The electrode distance was 3 mm. The sample matrix (a) consisted of banana, rice, cowpea, lychee, mango, and celery; the pesticide matrix (b) consisted of 6BA, pyraclostrobin, propamocarb, glufosinate, nereistoxin, and phoxim. The experimental results of this embodiment are attached. Figure 11 As shown in the figure, the recovery rates of mancozeb at different concentrations in sample matrix (a) are all above 60%, and the recovery rates of mancozeb at different concentrations in pesticide matrix (b) are all above 90%.

[0077] Example 15

[0078] Referring to the operating steps of Example 5, the chromatograms of the four DTC subclasses detected by the present invention under optimized experimental conditions were examined using an LC detector. The experimental results of this example are shown in the appendix. Figure 12 .

[0079] Example 16

[0080] To investigate the reduction efficiency of different types of DTCs pesticides in the reduction tube in the determination method of the present invention, 1 μg mL of each pesticide was prepared. -1 The electrolytic reduction of thiram, mancozeb, mancozeb, and propineb was determined using this system (liquid electrode glow discharge). The conversion rates of thiram, mancozeb, mancozeb, and propineb were calculated using CS2. Under the action of liquid electrode glow discharge electrolysis, DTC pesticides were reduced to CS2 by HCl-SnCl2 solution. The experimental results of this example are shown in Table 1.

[0081] Table 1. CS2 conversion rate of four DTC pesticides

[0082]

[0083] As can be seen from the table above, in the determination method of the present invention, mancozeb has the highest reduction efficiency in the reduction tube.

[0084] Example 17

[0085] The analytical characteristics of DTCs detected by the method of the present invention were examined under optimized experimental conditions. Following the operating steps of Example 5, the final result was obtained at a concentration of 1–25 mg / L. -1 The effects of concentrations of mancozeb, mancozeb, thiram, and propineb on CS2 emission intensity were studied within a certain concentration range. The experimental results of this embodiment are shown in Table 2.

[0086] Table 2 Recovery of DTCs pesticides at different concentrations in mango substrate

[0087]

[0088] Example 18

[0089] The detection limit of the method of the present invention was investigated. Using a 2 μL sample volume, the limit of detection (LOD) of CS2, defined as the concentration of zineb equivalent to 3S (standard deviation) of three repeated measurements of a blank solution, was 0.001 mg / L. -1 Repeat (n=3) 2 μL of 0.25 μg / mL solution. -1 The relative standard deviation (RSD) of the mancozeb standard solution is more than 1.0% accurate. The detection limit of the method of the present invention is better than that of traditional analytical methods. The experimental results of this embodiment are shown in Table 3.

[0090] Table 3 Comparison of this method with other detection methods

[0091]

[0092] Example 19

[0093] Because the microwave reaction is intense and requires a lot of power and consumes a lot of electricity during the online microwave-assisted acid hydrolysis of DTCs by stannous chloride, this invention improves the method of hydrolyzing DTCs by stimulating the DTCs standard solution and SnCl2-HCl mixture to convert it into CS2 gas through liquid electrode glow discharge (PDB).

[0094] To examine the advantages of the liquid electrode glow discharge electrolysis method of this invention compared with the traditional online microwave-assisted method, the precision and conversion-reduction efficiency of liquid electrode glow discharge and online microwave-assisted methods were analyzed. The method for determining DTCs by online microwave-assisted stannous chloride acid hydrolysis refers to the operation steps of patent 201810277183.X. The experimental results of this embodiment are shown in Tables 4 and 5.

[0095] Table 4 Precision Comparison

[0096]

[0097]

[0098] Table 5 Comparison of Conversion and Reduction Efficiency

[0099]

[0100] As can be seen from the table above, the stability and precision of the liquid electrode glow discharge electrolytic reduction of the present invention are significantly improved. Since the microwave heating of water to boiling is avoided, the acid hydrolysis of the target substance can be completed at room temperature, reducing the influence of water boiling and making the system more stable.

[0101] Furthermore, the liquid electrode glow discharge acidolysis reduction of this invention has a shorter time, completing the conversion within 5 seconds, while the original microwave method requires approximately 1 minute for acidolysis. The reduction efficiency of SnCl2-HCl solution excited by liquid electrode glow discharge is consistent with or higher than that of microwave, and the method exhibits good accuracy.

[0102] Compared to online microwave-assisted acid hydrolysis, this invention provides a more convenient method for the electrolytic reduction of DTCs using glow discharge of liquid electrodes. It does not require high-power voltage and is safer, simpler, and faster. This invention effectively replaces microwave-assisted acid hydrolysis, resulting in simpler testing equipment, lower testing costs, and convenient portability for testing anytime, anywhere.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining dithiocarbamates-based pesticides based on tandem microplasma-emission spectroscopy, characterized by: First, SnCl2-HCl solution is used as a reducing agent, each sub-class of DTCs pesticide is separated by liquid chromatography, then SnCl2-HCl system is excited by first-stage liquid electrode glow discharge, DTCs pesticide is electrolytic reduced into CS2 in real time, CS2 is excited by second-stage dielectric barrier discharge micro-plasma at 257.94 nm molecular emission spectrum, CS2 is used as DTCs standard substance to determine the content of DTCs pesticide; the second-stage dielectric barrier discharge voltage is 0.75-0.85 kV; CS2 comprises the following steps: Step 1: EDTA disodium solution is used to dissolve the sample of dithiocarbamate pesticide, for standby; Step 2: SnCl2-HCl solution is pumped into the reduction tube at the same time with the pesticide sample dissolved in step 1, each sub-class of DTCs pesticide is separated by liquid chromatography column, and mixed liquid separated by liquid chromatography is obtained; Step 3: the first-stage liquid electrode glow discharge with a voltage of 1.5-2.1 kV is used to excite SnCl2-HCl system, the mixed liquid separated by liquid chromatography is reduced and converted into CS2 in real time, the argon flow rate is controlled at 280-320 mL / min, the carrier liquid flow rate is controlled at 18-22 mL / min, and the electrode distance is controlled at 2.8-3.2 mm; Step 4: CS2 is sent into the second-stage dielectric barrier discharge micro-plasma to excite CS2 emission spectrum, CS2 is used as DTCs standard substance to perform quantitative analysis and determine the content of DTCs pesticide.

2. The method for determining dithiocarbamates pesticides based on tandem microplasma-optical emission spectroscopy according to claim 1, characterized in that: In step 2, the mass concentration of SnCl2 in the SnCl2-HCl solution is 20 g / L, and the mass concentration of HCl is 3 mol / L.

3. The method for determining dithiocarbamates pesticides based on tandem microplasma-optical emission spectroscopy according to claim 2, characterized in that: In step 3, the voltage of the first-stage liquid electrode glow discharge is 1.8 kV, the argon flow rate is 300 mL / min, the carrier liquid flow rate is 20 mL / min, and the electrode distance is 3 mm.

4. The method for determining dithiocarbamates pesticides based on tandem microplasma-optical emission spectroscopy according to claim 1, characterized in that: The second-stage dielectric barrier discharge voltage is 0.8 kV.

5. The method for determining dithiocarbamates pesticides based on tandem microplasma-optical emission spectroscopy according to claim 2, characterized in that: The detection limit of the content of DTCs pesticide is 0.10 mg kg-1.

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