A gas phase determination method for dithiocyanomethane in aquatic products

Abstract

The present invention provides a gas phase determination method of dithiocyanomethane in aquatic products, and relates to the field of pesticide residue detection. The present invention aims to provide a gas chromatography (GC-PFPD) method for determining dithiocyanomethane in aquatic products, and to provide a simple, rapid and practical detection technology for monitoring dithiocyanomethane drug residues in aquatic products. The pretreatment method established in the present application is simple and easy to operate, and can enable stable and efficient recovery of MBT; the chromatographic conditions used in the present experiment make the peak shape of MBT sharp and symmetrical, without interference from impurity peaks. The method has high sensitivity, good repeatability and accuracy, and is suitable for residual analysis of dithiocyanomethane substances in aquatic products.

Description

Technical Field

[0001] The invention relates to the field of pesticide residue detection, in particular to a gas phase determination method of dithiocyanomethane in aquatic products. Background Art

[0002] Methylene Bisthiocyanate (MBT), a yellow-brown needle-shaped crystal with a molecular structure of CNS-CH2-SCN, is a volatile organic thiocyanate compound. Methylene Bisthiocyanate is an excellent non-oxidizing broad-spectrum bactericidal algaecide. It can kill and inhibit bacteria, fungi, algae, molds, and protozoa and metazoa in the leather industry, industrial circulating water, oil field water injection treatment and other industrial production. It can also be used as a preservative, mildew-proof and anti-fouling agent for drugs, food, hulls, cosmetics and crops. In aquaculture, methylene bisthiocyanate is used as a substitute for malachite green, mainly through full-pool spraying and immersion. In recent years, methylene bisthiocyanate has been proven in practical applications of aquaculture in reservoirs, ponds, etc. (Zhang Jiasong et al., 2006) to be effective against Pseudomonas fluorescens Pseudomonas fluorescence , Aeromonas punctata Aeromonas punctataf. furunalus , water type of Pseudomonas punctata Pseudomonas punctate f .ascitae , Myxococcus spp. Myxococcus pisciolas , Saprolegnia Sa-prolegnia and acidophilic dinoflagellate Oodinium acidophilum Studies have shown that dithiocyanomethane is non-systemic and easily decomposes into thiocyanate and formaldehyde in the environment. It has low residual toxicity, is non-toxic to birds, is moderately toxic to freshwater fish and aquatic invertebrates, and is poisonous to mammals.

[0003] In the prior art, the analysis methods of dithiocyanomethane reported more often are high performance liquid chromatography (HPLC) and gas chromatography analysis (GC-FID), but there is no report on the detection method of dithiocyanomethane in aquatic products. The present invention aims to provide a gas chromatography (GC-PFPD) method for determining dithiocyanomethane in aquatic products, providing a simple, rapid and practical detection technology for monitoring dithiocyanomethane drug residues in aquatic products. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a gas phase determination method of dithiocyanomethane in aquatic products.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A gas phase determination method for dithiocyanomethane in aquatic products comprises the following steps:

[0007] 1. Sample preparation: For fish, remove the scales and take the muscle along the spine (with skin); for shrimp, remove the head, shell and appendages and take the edible muscle part; for shellfish, remove the shell and take the edible part; for Chinese mitten crab and soft-shelled turtle, take the edible muscle part. Cut the samples into small pieces no larger than 0.5cm×0.5cm×0.5cm and mix them evenly. Mix them evenly with a high-speed blender, seal, label and store in a freezer below -18℃;

[0008] 2. Sample extraction: Weigh (1.00±0.01) g of sample, add 4 mL of 1:1 dichloromethane and n-hexane to a 10 mL stoppered glass centrifuge tube, vortex mix for 1 min, extract by ultrasonic oscillation at room temperature for 10 min, centrifuge at 5000 r / min for 5 min, transfer the supernatant to another 10 mL glass centrifuge tube with a glass rubber pipette, add 4 mL of 1:1 dichloromethane and n-hexane to the residue, repeat the extraction once, combine the two supernatants, mix well, blow nitrogen to about 0.5-1 mL at 40°C, and wait for purification;

[0009] 3. Purification and concentration: Take a neutral alumina solid phase extraction column, add 2g of anhydrous sodium sulfate and 2g of zinc acetate to the upper layer respectively, pass the liquid after nitrogen blowing through the column and collect it, wash the container with 2mL of 1:1 dichloromethane and n-hexane, pass through the column and collect it in the same test tube, then elute the column with 8mL of dichloromethane and collect it in the same test tube, blow the eluent to dryness with nitrogen at 40°C, and make it up to 1mL with 1:1 dichloromethane and n-hexane, vortex for 1min to completely dissolve it, and provide gas phase analysis;

[0010] 4. Gas chromatography analysis: Perform chromatographic analysis on the gas obtained in step 3 and compare it with the chromatographic curve of the standard sample to draw a conclusion on whether the aquatic product contains dithiocyanomethane.

[0011] Preferably, the chromatographic conditions of the chromatographic analysis described in step 4 above are: chromatographic column: HP-5MS quartz capillary column (30 m×0.32 mm, particle size 0.25 μm, Agilent, USA); injection mode: splitless injection; injection port temperature: 110°C; detector temperature: 250°C; carrier gas: nitrogen, purity ≥99.999%, flow rate 2mL / min; fuel gas: hydrogen, purity ≥99.999%, flow rate 13mL / min; auxiliary gas: air, purity ≥99.999%, flow rate 17mL / min. Gate delay is 6, gate opening width is 20, trigger point is 200; column flow rate is 1.0mL / min, column temperature: initial column temperature 50°C, hold for 1 min, heat to 180°C at 25°C / min, hold for 2min; injection volume: 1.0μL.

[0012] The present invention also includes a sample pretreatment device for gas phase determination of dithiocyanomethane in aquatic products, the device comprising a box body, a sample inlet arranged at the top of the box body, a short lower connection of the sample inlet to a spiral propulsion mechanism arranged at the upper part of the box body, the propulsion main shaft of the spiral propulsion mechanism adopts a hollow structure, the micro end of the spiral propulsion mechanism is connected to a crushing mechanism arranged on one side of the box body, a screen is arranged at the bottom of the crushing mechanism, a sample storage room is arranged on the other side of the box body, a cooling pipe is arranged in the sample storage room, the bottom of the sample storage room is connected to the lower part of the screen, and a sample removal outlet is also arranged on one side of the sample storage room.

[0013] The beneficial effects of the present invention are as follows: the pretreatment method established in the present application is simple and easy to operate, and can enable stable and efficient recovery of MBT; the chromatographic conditions used in the present experiment make the peak shape of MBT sharp and symmetrical, without interference from impurity peaks. The method has high sensitivity, good repeatability and accuracy, and is suitable for residual analysis of dithiocyanomethane substances in aquatic products. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 MBT standard curve.

[0015] Figure 2 Chromatogram of the standard solution.

[0016] Figure 3 Chromatogram of the spiked sample.

[0017] Figure 4 Chromatogram of blank sample.

[0018] Figure 5 Schematic diagram of the sample pretreatment box structure.

[0019] In the figure, 1 is the sample inlet, 2 is the spiral propulsion mechanism, 3 is the propulsion spindle, 4 is the crushing mechanism, 5 is the screen, 6 is the cooling pipe, 7 is the box, and 8 is the sample outlet. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings:

[0021] Combination Figure 5 The sample pretreatment box provided by the present invention puts the sample to be processed into the sample inlet, preliminarily premixes it through the spiral propulsion mechanism, and then enters the crushing mechanism. During this process, cooling water flows through the hollow structure of the propulsion main shaft in the propulsion mechanism to prevent the sample from heating up and deteriorating. After the sample is crushed, it is filtered through the screen at the bottom of the crushing mechanism and enters the sample storage room, and is stored in a low-temperature environment created by the cooling pipe arranged in the sample storage room. When it is needed, it can be used from the sample outlet.

[0022] Weigh 0.0050 g of dithiocyanomethane standard, dissolve it in acetonitrile as solvent, and dilute to volume in a brown volumetric flask. Dilute the mother liquor with 1:1 n-hexane and dichloromethane to MBT concentrations of 1.0 mg / L, 2.0 mg / L, 5.0 mg / L, 10.0 mg / L, and 20.0 mg / L.

[0023] The chromatographic analysis was performed under the following chromatographic conditions: chromatographic column: HP-5MS quartz capillary column (30 m×0.32 mm, particle size 0.25 μm, Agilent, USA); injection mode: splitless injection; injection port temperature: 110°C; detector temperature: 250°C; carrier gas: nitrogen, purity ≥99.999%, flow rate 2 mL / min; fuel gas: hydrogen, purity ≥99.999%, flow rate 13 mL / min; auxiliary gas: air, purity ≥99.999%, flow rate 17 mL / min. Gate delay was 6, gate opening width was 20, and trigger point was 200. Column flow rate was 1.0 mL / min, column temperature: initial column temperature 50°C, maintained for 1 min, heated to 180°C at 25°C / min, maintained for 2 min; injection volume: 1.0 μL.

[0024] The standard curve was drawn with the concentration of the analyte as the horizontal axis and the chromatographic peak area as the vertical axis. The MBT peak time was 6.18 min, and the MBT linear equation was Y = 4874.7X - 1823.3, with a correlation coefficient R 2 = 0.9971, e.g. Figure 1 shown.

[0025] The detection limit and quantification limit are determined by adding a certain concentration of the analyte (i.e., spiked sample) to a blank tissue without the analyte. According to the average baseline noise of 7 blank tissues, S / N = 3 is the detection limit, and S / N = 10 is the quantification limit. The detection limit of MBT is 0.1 mg / kg; the quantification limit is 0.5 mg / kg, respectively. This method meets the requirements of residue analysis. The chromatograms of the standard solution, spiked sample, and blank sample are shown in Figure 2-4 .

[0026] Depend on Figure 2-4 It can be seen that the gas phase determination method of dithiocyanato methane provided by the present application makes the peak shape of MBT sharp and symmetrical without interference from impurity peaks. The method has high sensitivity, good repeatability and accuracy, and is suitable for residual analysis of dithiocyanato methane substances in aquatic products.

Claims

1. A gas phase determination method for dithiocyanomethane in aquatic products, characterized in that: The following steps are involved: (1) Sample preparation: For fish, remove the scales and take the skin and muscle along the spine; for shrimp, remove the head, shell and appendages and take the edible muscle part; for shellfish, remove the shell and take the edible part; for Chinese mitten crab or soft-shelled turtle, take the edible muscle part. Cut the sample into small pieces no larger than 0.5 cm × 0.5 cm × 0.5 cm and mix them well. Mix them thoroughly with a high-speed blender, seal, label and store in a freezer below -18°C. (2) Sample extraction: Weigh (1.00±0.01) g of sample and add 4 mL of 1:1 dichloromethane and n-hexane into a 10 mL stoppered glass centrifuge tube. Vortex mix for 1 min. Extract under ultrasonic oscillation for 10 min at room temperature. Centrifuge at 5000 r / min for 5 min. Use a glass rubber-tipped pipette to transfer the supernatant into another 10 mL glass centrifuge tube. Add 4 mL of 1:1 dichloromethane and n-hexane to the residue. Repeat the extraction once. Combine the two supernatants, mix well, blow nitrogen at 40°C to 0.5-1 mL, and wait for purification. (3) Purification and concentration: Take a neutral alumina solid phase extraction column, add 2 g of anhydrous sodium sulfate and 2 g of zinc acetate to the upper layer, pass the liquid after nitrogen blowing through the column and collect it, wash the container with 2 mL of 1:1 dichloromethane and n-hexane, pass it through the column and collect it in the same test tube, then elute the column with 8 mL of dichloromethane and collect it in the same test tube, blow the eluent to dryness with nitrogen at 40°C, and make it up to 1 mL with 1:1 dichloromethane and n-hexane, vortex for 1 min to completely dissolve it, and provide it for gas phase analysis; (4) Gas chromatography analysis: The gas obtained in step (3) is subjected to chromatographic analysis and compared with the chromatographic curve of the standard sample to draw a conclusion on whether the aquatic product contains dithiocyanomethane.

2. The method for gas phase determination of dithiocyanomethane in aquatic products according to claim 1, characterized in that: The chromatographic conditions of the chromatographic analysis described in the above step (4) are as follows: chromatographic column: HP-5MS quartz capillary column, 30 m×0.32 mm, particle size 0.25 μm, Agilent, USA; injection mode: splitless injection; injection port temperature: 110°C; detector temperature: 250°C; Carrier gas: nitrogen, purity ≥99.999%, flow rate 2 mL / min; Fuel gas: hydrogen, purity ≥99.999%, flow rate 13 mL / min; auxiliary gas: air, purity ≥99.999%, flow rate 17 mL / min; gate delay is 6, gate opening width is 20, trigger point is 200; column flow rate is 1.0 mL / min, column temperature: initial column temperature 50°C, hold for 1 min, increase to 180°C at 25°C / min, hold for 2 min; injection volume: 1.0 μL.

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