CN107478740B - Method for measuring polychlorinated biphenyl in aquatic vegetables - Google Patents
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Abstract
The invention discloses a method for measuring 21 PCBs in aquatic vegetables, which comprises the following steps: (1) sample pretreatment: uniformly mixing an aquatic vegetable sample to be tested, sodium chloride and an organic solvent, distilling and extracting to obtain distillate, oscillating and extracting by using the organic solvent to obtain an organic solvent layer, dehydrating and concentrating the solvent to dryness, dissolving again, purifying, and centrifuging to obtain a test sample; (2) gas chromatography-high resolution mass spectrometer analysis. The method has the advantages of multiple PCBs detection types, high accuracy, low detection limit, capability of eliminating interference of other compounds in the extraction process, small organic solvent consumption, high extraction efficiency, easiness in operation, suitability for qualitative and quantitative analysis of polychlorinated biphenyl compounds in aquatic vegetables and good application prospect.
Description
Technical Field
The invention belongs to the technical field of food safety detection, and relates to a method for measuring polychlorinated biphenyl in aquatic vegetables.
Background
Polychlorinated biphenyl (PCBs for short) is also called chlorinated biphenyl, is a synthetic product of biphenyl substituted by chlorine atoms to different degrees, is a widely-existing environmental pollutant, and has 209 isomers discovered so far; PCBs have carcinogenic, teratogenic and mutagenic 'three-cause' effects, are proposed to be strictly prohibited in the 'Stockholm convention', and are still widely present in the atmosphere, water, soil, animals and plants and other media until now due to the factors of stable chemical properties, difficult degradation, global migration and the like. The exposure of the meal is a main channel for PCBs to enter human bodies, and due to the lipophilicity of PCBs, the residual quantity of PCBs in plant-derived foods such as vegetables is far lower than that of meat, but the bioavailability of the vegetables is far higher than that of the meat (the bioavailability of the vegetables is 25%, and the bioavailability of the meat is only 3%). Therefore, sufficient attention should be paid to the detection of PCBs remaining in aquatic plants such as aquatic vegetables.
In the current detection methods for polychlorinated biphenyl in food, the pretreatment extraction method mainly focuses on a Soxhlet extraction method, an oscillation extraction method, an accelerated solvent extraction method, a microwave-assisted extraction method, an ultrasonic-assisted extraction method and the like; common purification methods include solid phase extraction, gel permeation chromatography combined solid phase extraction, matrix solid phase extraction, acid treatment and the like; the pretreatment methods have the defects of high equipment requirement, poor selectivity, complex pretreatment operation steps, large consumption of organic solvents and the like; meanwhile, the detection of polychlorinated biphenyl pollutants still takes methods such as a gas chromatography-electron capture detector (GC-ECD), a gas chromatography-mass spectrum (GC-MS) or a gas chromatography-tandem mass spectrum (GC-MS-MS) as mainstream technologies, and the methods are easy to introduce interference so as to bring false positive results and influence the accuracy of measurement results.
Polychlorinated biphenyl in food is mainly concentrated in meat products, and related literature reports on a polychlorinated biphenyl detection method in aquatic vegetables are few at present. The determination method of polychlorinated biphenyl in Jixian branch and food researches the university of agriculture and forestry science and technology in northwest in 2013 research institute paper and discloses a microwave-assisted extraction-solid phase extraction purification-gas chromatography-mass spectrometry combined technology for determining PCBs in fish meat, the method adopts a microwave-assisted extraction method to pre-treat samples, the equipment requirement is high, the operation is complex, the variety of organic solvents is required, and the consumption is high; in addition, the detection method has low sensitivity, detects few types of PCBs, and can only detect 4 types of PCBs.
Disclosure of Invention
In order to solve the problems, the invention provides a method for measuring 21 polychlorinated biphenyls in aquatic vegetables.
The invention relates to a method for measuring 21 polychlorinated biphenyls in aquatic vegetables, which adopts a measuring method of distillation extraction-gas chromatography-high resolution mass spectrometry, and comprises the following steps:
(1) sample pretreatment: uniformly mixing an aquatic vegetable sample to be detected, sodium chloride and an organic solvent, and distilling and extracting to obtain distillate; oscillating and extracting distillate with an organic solvent to obtain an organic solvent layer, and dehydrating and concentrating the solvent to dryness; re-dissolving, purifying, and centrifuging to obtain test sample;
(2) and (3) analyzing by a gas chromatography-high resolution mass spectrometer: gas chromatography conditions: TR-PESTICIDE chromatographic column, column temperature programming: 100 ℃ and 310 ℃, helium flow rate: 1.3 mL/min; high resolution mass spectrometry conditions: ion source temperature: bombardment source (EI) at 280 ℃: 70eV, quadrupole temperature: 150 ℃, analytical mode: a SIM mode; and (5) performing qualitative and quantitative analysis.
The 21 polychlorinated biphenyl compounds are PCB1, PCB3, PCB10, PCB14, PCB15, PCB18, PCB28, PCB30, PCB33, PCB37, PCB44, PCB52, PCB54, PCB70, PCB77, PCB101, PCB104, PCB105, PCB108, PCB118 and PCB 126.
Wherein, in the step (1),
the aquatic vegetables include rhizoma Nelumbinis, corm Eleocharitis, rhizoma Sagittariae Sagittifoliae, herba seu radix Dolichoris, caulis Zizaniae Caduciflorae, herba Oenanthes Javanicae, and semen euryales;
and/or the organic solvent is isooctane, normal hexane or dichloromethane;
and/or the impurity removing agent in the purification treatment is C18.
Wherein in the step (1), the sample is treated, the homogenized aquatic vegetable to be detected, sodium chloride and isooctane are distilled and extracted according to the ratio of 2:1:1(g: g: ml), the distillate and the isooctane are oscillated and extracted for 15-25min according to the ratio of 20:1(v/v), the mixture is kept stand and layered, the water layer is extracted once again, the used isooctane accounts for 3/5 for the first time, the isooctane layers are combined, anhydrous magnesium sulfate is dehydrated, and the mixture is concentrated to be nearly dry at 40 ℃ to obtain a concentrate; dissolving the concentrate in isooctane, mixing isooctane solution, C18 and anhydrous magnesium sulfate at a ratio of 1:50:250(ml: mg: mg), vortexing for 2min, centrifuging at 12000r/min at 4-5 deg.C for 5min, and collecting supernatant to obtain the sample.
Wherein, in the step (2), the length of the TR-PESTICIDE chromatographic column multiplied by the inner diameter multiplied by the film thickness is 30m multiplied by 0.25mm multiplied by 0.25 μm.
In the step (2), the chromatographic column adopts programmed temperature rise, and the conditions are as follows: the initial temperature is 100 deg.C, maintained for 2min, raised to 200 deg.C at 30 deg.C/min, raised to 270 deg.C at 2.5 deg.C/min, and raised to 310 deg.C at 20 deg.C/min.
Wherein, in the step (2), the gas chromatography conditions further comprise: the sampling mode is non-shunting sampling, shunting flow: 60mL/min, no-split time: 1min, injection port temperature: 280 ℃, sample introduction: 1 mu L of the solution;
and/or, the high resolution mass spectrometry conditions further comprise: mass spectrometry transmission line temperature: 280 ℃, solvent delay time: and 5 min.
Wherein, in the step (2), the qualitative and quantitative analysis method comprises the following steps: the qualitative determination is carried out by quantitative ions (M/z) M and qualitative ions N1, N2; quantification was done by peak area external standard method.
Wherein, the ions of the standard are as follows: the characteristic quantitative ion M of PCB1 was 188.0397, and the characteristic qualitative ions N1 and N2 were 190.0360 and 152.0621; PCB3 has M188.0380, N1 and N2 190.0351 and 152.0612; PCB10 has M221.9998, N1 and N2 223.9969 and 152.0620; PCB14 has M221.9995, N1 and N2 223.9965 and 152.0618; PCB15 has M221.9990, N1 and N2 223.9962 and 152.0614; PCB18 has M255.9583, N1 and N2 257.9554 and 186.0213; PCB28 has M255.9590, N1 and N2 257.9560 and 186.0217; PCB30 has M255.9593, N1 and N2 257.9565 and 186.0221; PCB33 has M255.9603, N1 and N2 257.9574 and 186.0227; PCB37 has M255.9608, N1 and N2 257.9580 and 186.0232; PCB44 has M291.9171, N1 and N2 289.9199 and 219.9827; PCB52 has M291.9183, N1 and N2 289.9212 and 219.9837; PCB54 has M291.9177, N1 and N2 289.9206 and 219.9832; PCB70 has M291.9172, N1 and N2 289.9200 and 219.9827; PCB77 has M291.9185, N1 and N2 289.9214 and 219.9837; PCB101 has M325.8779, N1 and N2 327.8749 and 253.9435; the PCB104 has M325.8799, N1 and N2 327.8770 and 253.9450; PCB105 has M325.8803, N1 and N2 327.8773 and 253.9452; the PCB108 has M325.8828, N1 and N2 327.8799 and 255.9444; PCB118 has M of 325.8802, N1 and N2 of 327.8772 and 253.9453; the PCB126 has M325.8800, N1 and N2 327.8770 and 253.9451.
The method has the advantages of multiple PCBs detection types, high accuracy, low detection limit, capability of eliminating interference of other compounds in the extraction process, small organic solvent consumption, high extraction efficiency, easiness in operation, suitability for qualitative and quantitative analysis of polychlorinated biphenyl compounds in aquatic vegetables and good application prospect.
Obviously, many modifications, substitutions, and variations are possible in light of the above teachings of the invention, without departing from the basic technical spirit of the invention, as defined by the following claims.
The present invention will be described in further detail with reference to the following examples. This should not be understood as limiting the scope of the above-described subject matter of the present invention to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention.
Drawings
FIG. 1 is a chromatogram of standard Total Ion Current (TIC) for detecting 21 polychlorinated biphenyls by gas chromatography-high resolution mass spectrometry;
FIG. 2 is a sample labeling chromatogram using solid phase extraction as a pretreatment method;
FIG. 3 is a sample labeling chromatogram for a pretreatment method using steam distillation;
FIG. 4 is a sample labeling chromatogram using steam distillation-C18 purification as a pretreatment method.
Detailed Description
Example 1 detection method of the invention
1. Detection method
(1) Sample pretreatment
And (3) extracting a sample: weighing 20g of homogenized aquatic vegetable sample into a 250mL digestion tube, adding 10g of sodium chloride and 10mL of isooctane, uniformly mixing for 1min in a vortex manner, placing the mixture into an automatic distiller for steam distillation, and introducing distillate into a 500mL volumetric flask and distilling to a scale; transferring the distillate into a 1000mL separating funnel, adding 25mL of isooctane, performing oscillation extraction for 20 minutes, standing for layering, transferring an isooctane layer into a 50mL centrifuge tube, repeatedly extracting a water layer once by using 15mL of isooctane, combining the isooctane layers, performing dehydration treatment by using anhydrous magnesium sulfate, and performing reduced pressure concentration by using a parallel quantitative concentrator at 40 ℃ until the mixture is nearly dry;
sample purification: dissolving the concentrated solution with isooctane, diluting to 2mL, adding 500mg anhydrous magnesium sulfate and 100mg C18, vortexing for 2min, centrifuging at 12000r/min and 5 deg.C for 5min, and collecting the supernatant for gas chromatography-high resolution mass spectrometer analysis;
(2) and (3) analyzing by a gas chromatography-high resolution mass spectrometer: gas chromatography conditions, column: TR-PESTICIDE (30 m.times.0.25 mm.times.0.25 μm); and (3) sample introduction mode: SSL, no split sample injection, split flow: 60mL/min, no-split time: 1 min; carrier gas: he, 99.999%; sample inlet temperature: 280 ℃; the chromatographic column adopts programmed temperature rise: the initial temperature is 100 ℃, the temperature is kept for 2min, the temperature is increased to 200 ℃ at 30 ℃/min, the temperature is increased to 270 ℃ at 2.5 ℃/min, and the temperature is increased to 310 ℃ at 20 ℃/min; the column flow rate is 1.3 mL/min; sample introduction amount: 1 mu L of the solution; high resolution mass spectrometry conditions, ion source temperature: 280 ℃; electron impact ion source (EI): 70 eV; mass spectrometry transmission line temperature: 280 ℃; quadrupole temperature: 150 ℃; solvent delay time: 5 min; analysis mode: a SIM mode; the qualitative and quantitative analysis method comprises the following steps: the qualitative determination is carried out by quantitative ions (M/z) M and qualitative ions N1, N2; quantification was done by peak area external standard method.
Wherein, the invention detects 21 polychlorinated biphenyl compounds in aquatic vegetables: PCB1, PCB3, PCB10, PCB14, PCB15, PCB18, PCB28, PCB30, PCB33, PCB37, PCB44, PCB52, PCB54, PCB70, PCB77, PCB101, PCB104, PCB105, PCB108, PCB118, PCB 126.
The method adopts the conditions of gas chromatography-high resolution mass spectrometry, and obtains the specific response of a target compound by accurately measuring and monitoring the characteristic ions of the target compound through mass; the characteristic quantitative ion M of PCB1 was 188.0397, and the characteristic qualitative ions N1 and N2 were 190.0360 and 152.0621; PCB3 has M188.0380, N1 and N2 190.0351 and 152.0612; PCB10 has M221.9998, N1 and N2 223.9969 and 152.0620; PCB14 has M221.9995, N1 and N2 223.9965 and 152.0618; PCB15 has M221.9990, N1 and N2 223.9962 and 152.0614; PCB18 has M255.9583, N1 and N2 257.9554 and 186.0213; PCB28 has M255.9590, N1 and N2 257.9560 and 186.0217; PCB30 has M255.9593, N1 and N2 257.9565 and 186.0221; PCB33 has M255.9603, N1 and N2 257.9574 and 186.0227; PCB37 has M255.9608, N1 and N2 257.9580 and 186.0232; PCB44 has M291.9171, N1 and N2 289.9199 and 219.9827; PCB52 has M291.9183, N1 and N2 289.9212 and 219.9837; PCB54 has M291.9177, N1 and N2 289.9206 and 219.9832; PCB70 has M291.9172, N1 and N2 289.9200 and 219.9827; PCB77 has M291.9185, N1 and N2 289.9214 and 219.9837; PCB101 has M325.8779, N1 and N2 327.8749 and 253.9435; the PCB104 has M325.8799, N1 and N2 327.8770 and 253.9450; PCB105 has M325.8803, N1 and N2 327.8773 and 253.9452; the PCB108 has M325.8828, N1 and N2 327.8799 and 255.9444; PCB118 has M of 325.8802, N1 and N2 of 327.8772 and 253.9453; the PCB126 has M325.8800, N1 and N2 327.8770 and 253.9451.
Experimental example 1 study on detection of PCBs in aquatic vegetable sample to be detected according to the present invention
1. Experimental Material
(1) The instrument comprises the following steps: agilent 7890B gas chromatography high resolution mass spectrometer and workstation (Agilent); vapdest 200 automatic distiller (Gerhardt, germany); EYELA MMV-1000W oscillator (Tokyo, Japan); SIGMA 3-16K desk-top high speed centrifuge (sartoriussima, Germany); an IKA vortex mixer; bangqi R-24 type parallel quantitative concentrator (German Bangqi company)
(2) Reagent: isooctane (chromatographically pure), C18, anhydrous magnesium sulfate (CNW, germany); sodium chloride (analytical grade, Guangzhou chemical reagent works); the water is deionized water; 21 polychlorinated biphenyl standard products (Germany DR, purity is more than or equal to 95.0%)
(3) Sample preparation: watercress, lotus root and cane shoot come from domestic markets.
2. Experimental methods
(1) Preparing standard solution
PCB Standard stock solution: accurately weighing appropriate amount of each PCB standard substance, and preparing into standard stock solution of 200 μ g/mL with n-hexane. PCBs standard working solution: accurately measuring 1mL of each PCB standard stock solution, and preparing a mixed standard working solution of 2 mug/mL by using n-hexane. Mix standard working series solutions: accurately measuring 0.005 mL, 0.01 mL, 0.025 mL, 0.05 mL, 0.1 mL, 0.25 mL and 0.5mL of PCBs mixed standard working solution, diluting with n-hexane, and preparing into mixed standard series working solution.
(2) The detection method of example 1 was selected as the detection method
(3) And (2) accurately transferring the PCB mixed standard working solution for sensitivity verification, metering the volume by using normal hexane, preparing a standard working curve with the concentration of each component being respectively 10, 20, 50, 100, 200, 500 and 2000 mug/L, drawing the standard curve by taking the peak area Y of the quantitative ions as a vertical coordinate and the mass concentration X (mug/L) according to the step (2) of the detection method in the embodiment 1, and determining the detection limit of each target object by using a 3-time signal-to-noise ratio.
(4) The recovery rate and precision are verified, and 3 samples of watercress, lotus root and cane shoot are taken for a standard-adding recovery test. Weighing 20g of blank sample, respectively adding two horizontal PCB standard mixed solutions of 0.01 and 0.02mg/kg, measuring according to the detection method of the embodiment 1, and calculating the recovery rate and the relative standard deviation of 21 kinds of PCBs by a peak area external standard method.
3. Results of the experiment
(1) Characteristic ion parameters of 21 PCBs
The results are shown in table 1:
table 1: characteristic ion parameters of 21 PCBs
The results are shown in table 1: the selective ion chromatographic peaks of the sample solution to be tested and the standard appeared at the same retention time (+ -0.5%), and the mass-to-charge ratio of the fragment ions corresponding to mass spectrum was consistent with that of the standard. Where target ions N1 and N2 are the exact mass numbers of two qualitative ions of the analyzed target, and target ion M is the exact mass number of a quantitative ion of the analyzed target.
Standard Total Ion Current (TIC) chromatograms of 21 polychlorinated biphenyls are shown in figure 1.
(2) Sensitivity of the probe
The results are shown in table 2:
TABLE 221 Linear Range, Linear equation, correlation coefficient, method detection Limit (LOD) of PCB
The results are shown in Table 2, and 21 kinds of PCB have good linear response, low detection limit and high sensitivity in the concentration range of 0.01 mg/L-2.00 mg/L, and can be used for detecting 21 kinds of PCB residues in the aquatic vegetables.
3. Recovery and precision
The results are shown in Table 3:
table 3 recovery and precision test results (n ═ 6)
The results are shown in table 3, the average recovery rate of 21 PCBs is 72.3% -95.6%, and the Relative Standard Deviation (RSD) is 1.8% -11.6%, and the two indexes show that the method provided by the invention has high accuracy and precision and good repeatability, and can be used for detecting 21 PCBs in the aquatic vegetables.
The experimental results show that: the method for detecting 21 polychlorinated biphenyls in the aquatic vegetables has the advantages of simplicity in operation, high sensitivity, good reproducibility, accurate qualitative and quantitative analysis and the like, and is suitable for qualitative and quantitative analysis of the mono-to pentachlorinated substituted biphenyls in the aquatic vegetables.
Experimental example 2 Condition-optimized screening test of the detection method of the present invention
1 method of experiment
(1) Selection of pretreatment method
The invention adopts the combination of steam distillation extraction and C18 purification as a sample pretreatment method, and compares the method with the conventional solid phase extraction method (the sample is extracted and concentrated by shaking with an organic solvent and then purified by a PSA small column).
(2) Influence of the number of chlorine atom substitutions on extraction efficiency
The invention adopts a steam distillation method, selects one to ten polychlorinated biphenyls substituted by decachloro, takes watercress as a sample, adds a standard concentration of 0.01mg/kg for recovery test, and inspects the influence of the substitution number of chlorine atoms on the extraction efficiency.
(3) Effect of collecting different distillate volumes on extraction efficiency
The invention adopts a steam distillation method, uses watercress as a sample, and carries out a recovery test with the standard concentration of 0.01mg/kg, and inspects the influence of different distillate volumes on the extraction efficiency.
(4) Screening test for extraction solvent
The invention adopts a steam distillation method, 3 organic solvents of n-hexane, dichloromethane and isooctane are respectively selected as extraction solvents for comparison, and watercress is taken as a sample and added with a standard concentration of 0.01mg/kg for recovery test.
(5) Screening test for purifying adsorbent dosage
The influence of the C18 dosage on the purification effect is examined, and the standard adding recovery test is respectively carried out on the watercress sample.
2 results of the experiment
(1) The purification effect is shown in fig. 2, fig. 3 and fig. 4. The result shows that the interference impurities of the extraction solution are obviously less than those of the conventional solid phase extraction method when the sample is extracted by adopting a steam distillation method; and C18 is added into the sample solution extracted by the steam distillation method for purification treatment, so that fat-soluble impurities in the extraction liquid can be effectively removed, and the interference impurities are further reduced. Therefore, the invention adopts water vapor distillation extraction combined with C18 purification as a sample pretreatment method.
(2) Test result of chlorine atom substitution number on extraction efficiency
The results are shown in Table 4
TABLE 4 test results of the number of chlorine atom substitutions on extraction efficiency
The results are shown in Table 4, the recovery rates of the low-chlorine substituted biphenyl (1-3 chlorine) are more than 90%, and the recovery rates of the tetrachloro-and pentachloro-substituted biphenyl are lower than that of the mono-to trichloro-substituted biphenyl and are between 70% and 85%; along with the increase of the number of the chlorine atoms, the molecular weight of the polychlorinated biphenyl is correspondingly increased and is more and more difficult to be distilled by water vapor, and the standard recovery rate is lower and lower. Therefore, the method for determining the monochlorobiphenyl compounds substituted by 21 types of mono-pentachloride in the aquatic vegetables by using the steam distillation method has good extraction efficiency.
(3) Results of tests on extraction efficiency with different distillate volumes
The results are shown in Table 5
TABLE 5 test results of different distillate volumes on extraction efficiency
As shown in Table 5, the recovery rates of polychlorinated biphenyl were 75.3-95.2% when the distillate reached 500mL, and the distillate was bottled in 500mL capacity until the volume was fixed.
(4) Test results for spiked recovery of different extraction solvents
The results are shown in Table 6
TABLE 6 results of spiked recovery test of different extraction solvents
As can be seen from Table 6, the recovery rate of the standard addition recovery test is high by using normal hexane, dichloromethane and isooctane as extraction solvents; in particular, when isooctane was used as the extraction solvent, the effect of the recovery test by adding a standard was the best.
(5) Effect of C18 dosage on spiking recovery test
The results are shown in Table 7
TABLE 7 Effect of C18 amount on spiking recovery test
The results are shown in Table 7, the recovery rate of the spiked recovery test is influenced by the C18 dosage, when the addition amount of C18 is 0mg, 50mg and 100mg, the recovery rate of 5 polychlorinated biphenyls is not changed greatly, and the recovery rate is highest when the addition amount of C18 is 100mg, which indicates that the main effect of adding C18 is to remove some fat-soluble impurities; however, when the amount of C18 added was 200mg, the recovery of 5 polychlorinated biphenyls decreased inversely, indicating that the target compound was adsorbed by excess C18; thus, when 100mg of C18 was added for purification, the best purification effect was achieved while ensuring a high recovery rate.
The experimental results show that: through optimizing and screening the conditions of the detection method, the detection method has the advantages of simple operation, small organic solvent consumption, high extraction efficiency and capability of effectively eliminating the interference of other compounds in the extraction process, and is suitable for qualitative and quantitative analysis of polychlorinated biphenyl compounds in aquatic vegetables.
In conclusion, the method has the advantages of multiple PCBs detection types, high accuracy, low detection limit, capability of eliminating the interference of other compounds in the extraction process, small organic solvent consumption, high extraction efficiency, easiness in operation, suitability for qualitative and quantitative analysis of polychlorinated biphenyl compounds in aquatic vegetables and good application prospect.
Claims (8)
1. A method for measuring 21 polychlorinated biphenyls in aquatic vegetables is a measuring method adopting distillation extraction-gas chromatography-high resolution mass spectrometry, and comprises the following steps:
(1) sample pretreatment: uniformly mixing an aquatic vegetable sample to be detected, sodium chloride and isooctane, and distilling and extracting to obtain distillate; extracting the distillate by oscillating isooctane to obtain an isooctane layer, and dehydrating and concentrating the solvent to dryness; redissolving, purifying with C18, and centrifuging to obtain test sample;
(2) and (3) analyzing by a gas chromatography-high resolution mass spectrometer: gas chromatography conditions: TR-PESTICIDE chromatographic column, column temperature programming: 100 ℃ and 310 ℃, helium flow rate: 1.3 mL/min; high resolution mass spectrometry conditions: ion source temperature: electron impact ion source (EI) at 280 ℃: 70eV, quadrupole temperature: 150 ℃, analytical mode: a SIM mode; performing qualitative and quantitative analysis;
the 21 polychlorinated biphenyl compounds are PCB1, PCB3, PCB10, PCB14, PCB15, PCB18, PCB28, PCB30, PCB33, PCB37, PCB44, PCB52, PCB54, PCB70, PCB77, PCB101, PCB104, PCB105, PCB108, PCB118 and PCB 126.
2. The method of determining 21 polychlorinated biphenyls in aquatic vegetables as claimed in claim 1, wherein: in the step (1), the aquatic vegetables comprise lotus roots, water chestnuts, arrowheads, watercress, water bamboos, cress and gordon euryale seeds.
3. The method of determining 21 polychlorinated biphenyls in aquatic vegetables as claimed in claim 1, wherein: in the step (1), the sample is treated, the homogenized to-be-detected aquatic vegetable, sodium chloride and isooctane are distilled and extracted according to the ratio of 2g to 1ml, the distillate and the isooctane are extracted for 15-25min by oscillation according to the ratio of 20:1 v/v, the distillate and the isooctane are kept stand and layered, the water layer is extracted once again, the amount of the used isooctane is 3/5 of the first time, the isooctane layer is combined, anhydrous magnesium sulfate is used for dehydration, and the mixture is concentrated to be nearly dry at 40 ℃ to obtain a concentrate; dissolving the concentrate in isooctane, mixing isooctane solution, C18 and anhydrous magnesium sulfate at a ratio of 1ml: 50mg:250mg, vortexing for 2min, centrifuging at 4-5 deg.C and 12000r/min for 5min, and collecting the supernatant to obtain the sample.
4. The method of determining 21 polychlorinated biphenyls in aquatic vegetables as claimed in claim 1, wherein: in the step (2), the length of the TR-PESTICIDE column multiplied by the inner diameter multiplied by the film thickness is 30m multiplied by 0.25mm multiplied by 0.25 μm.
5. The method of determining 21 polychlorinated biphenyls in aquatic vegetables as claimed in claim 1, wherein: in the step (2), the chromatographic column adopts programmed temperature rise, and the conditions are as follows: the initial temperature is 100 deg.C, maintained for 2min, raised to 200 deg.C at 30 deg.C/min, raised to 270 deg.C at 2.5 deg.C/min, and raised to 310 deg.C at 20 deg.C/min.
6. The method of determining 21 polychlorinated biphenyls in aquatic vegetables as claimed in claim 1, wherein: in the step (2), the gas chromatography conditions further include: the sampling mode is non-shunting sampling, shunting flow: 60mL/min, no-split time: 1min, injection port temperature: 280 ℃, sample introduction: 1 mu L of the solution;
and/or, the high resolution mass spectrometry conditions further comprise: mass spectrometry transmission line temperature: 280 ℃, solvent delay time: and 5 min.
7. The method of determining 21 polychlorinated biphenyls in aquatic vegetables as claimed in claim 1, wherein: in the step (2), the qualitative and quantitative analysis method comprises the following steps: the qualitative determination is carried out through quantitative ions m/z M and qualitative ions N1 and N2; quantification was done by peak area external standard method.
8. The method of determining 21 polychlorinated biphenyls in aquatic vegetables as claimed in claim 7, wherein: the PCB1 has characteristic quantitative ions M of 188.0397, and characteristic qualitative ions N1 and N2 of 190.0360 and 152.0621; PCB3 has M188.0380, N1 and N2 190.0351 and 152.0612; PCB10 has M221.9998, N1 and N2 223.9969 and 152.0620; PCB14 has M221.9995, N1 and N2 223.9965 and 152.0618; PCB15 has M221.9990, N1 and N2 223.9962 and 152.0614; PCB18 has M255.9583, N1 and N2 257.9554 and 186.0213; PCB28 has M255.9590, N1 and N2 257.9560 and 186.0217; PCB30 has M255.9593, N1 and N2 257.9565 and 186.0221; PCB33 has M255.9603, N1 and N2 257.9574 and 186.0227; PCB37 has M255.9608, N1 and N2 257.9580 and 186.0232; PCB44 has M291.9171, N1 and N2 289.9199 and 219.9827; PCB52 has M291.9183, N1 and N2 289.9212 and 219.9837; PCB54 has M291.9177, N1 and N2 289.9206 and 219.9832; PCB70 has M291.9172, N1 and N2 289.9200 and 219.9827; PCB77 has M291.9185, N1 and N2 289.9214 and 219.9837; PCB101 has M325.8779, N1 and N2 327.8749 and 253.9435; the PCB104 has M325.8799, N1 and N2 327.8770 and 253.9450; PCB105 has M325.8803, N1 and N2 327.8773 and 253.9452; the PCB108 has M325.8828, N1 and N2 327.8799 and 255.9444; PCB118 has M of 325.8802, N1 and N2 of 327.8772 and 253.9453; the PCB126 has M325.8800, N1 and N2 327.8770 and 253.9451.
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