CN108918736B

CN108918736B - Method for detecting pesticide residues on fruits and vegetables by using magnetic solid-phase extraction technology

Info

Publication number: CN108918736B
Application number: CN201810895967.9A
Authority: CN
Inventors: 纪玢琪; 郑锦彪; 周新光; 宋国新; 袁敏; 赵炳醨; 王思
Original assignee: Shanghai Envitek Environment Technology Co ltd
Current assignee: Shanghai Envitek Environment Technology Co ltd
Priority date: 2018-08-08
Filing date: 2018-08-08
Publication date: 2021-06-04
Anticipated expiration: 2038-08-08
Also published as: CN108918736A

Abstract

The invention discloses a method for detecting pesticide residues on fruits and vegetables by using a magnetic solid-phase extraction technology, which comprises the following steps: (1) homogenizing; (2) shaking and extracting; (3) adsorption separation; (4) eluting, concentrating by nitrogen blowing, and filtering; (5) and (5) analyzing and detecting. The invention adopts the magnetic solid phase extraction technology for pretreatment, finishes two steps of extraction and purification by one-time operation, and has the advantages of simple operation, trouble and labor saving and low cost. The invention adopts the nonpolar chromatographic column as a one-dimensional column and the polar chromatographic column as a two-dimensional column, and separates various substances to be measured according to the molecular size when passing through the one-dimensional nonpolar column and separates again according to the polarity when passing through the two-dimensional polar chromatographic column, thereby achieving the separation effect of GC x GC and efficiently separating complex matrixes.

Description

Method for detecting pesticide residues on fruits and vegetables by using magnetic solid-phase extraction technology

Technical Field

The invention belongs to the field of analysis and test, relates to a method for detecting pesticide residues in fruits and vegetables by using a magnetic solid-phase extraction technology, and particularly relates to a method for analyzing pesticide residues in fruits and vegetables by using a magnetic solid-phase extraction and solid-state thermal modulation comprehensive two-dimensional gas chromatography-mass spectrometry combined technology.

Background

The problem of pesticide residue in agricultural products and environmental fields is always concerned by people, at present, pesticide residue detection of domestic agricultural products generally refers to GB/T5009.218-2008 for determining pesticide residue in fruits and vegetables or GB 23200.8-2016 for determining the residue of 500 pesticides and related chemicals in fruits and vegetables which are national standard for agricultural product safety and gas chromatography-mass spectrometry GB 23200.8-2016 for determining the residue of 51 pesticides in vegetables and fruits, and NY mass spectrometry/T1380-2007, and pretreatment processes of the reference standards generally have more steps and have two obvious defects: one disadvantage is that the extraction process requires the use of large amounts of highly pure organic reagents, which are expensive and pose different levels of harm to the health of laboratory personnel; another disadvantage is that the purification process requires the use of expensive solid phase adsorption cartridges, which must be properly disposed of after use, which is generally time consuming, labor intensive, and costly. If the method can realize quick, simple, effective and low-cost pretreatment and one-time sample introduction to quickly and accurately screen and confirm the pesticide components in agricultural products, the method is a target of researchers in various countries for many years. On the other hand, with the increasing variety of pesticides and the difference of different agricultural product matrixes, the existing commonly used pesticide residue analysis methods including gas chromatography, liquid chromatography, gas chromatography-mass spectrometry combined method, liquid chromatography-mass spectrometry combined method and the like have the phenomenon of co-outflow of components in different degrees, namely, the components of the pesticide to be detected and the matrixes cannot be effectively separated, so that the accuracy and reliability of results are interfered. For the separation of complex samples, the full two-dimensional gas chromatography has obvious advantages. The method adopts two chromatographic columns with different properties, all components flowing out of a first chromatographic column are concentrated and enriched in a modulator and then are re-fed into a second chromatographic column, and because the two chromatographic columns have different separation polarities, no separated compound can be separated in the first chromatographic column in the second chromatographic column, so that the effect of orthogonal separation is realized, the peak capacity is greatly improved, the interference is reduced, and the sensitivity can be obviously improved. The comprehensive two-dimensional gas chromatography and mass spectrometry combined technology can meet the requirements of rapid analysis and accurate qualitative and quantitative determination of multiple pesticide residues in common fruits and vegetables to a great extent.

Some researches have been carried out to analyze pesticide residues by using a full two-dimensional gas chromatography technology, but a jet refrigerant modulation technology is generally adopted. The technology needs to use liquid nitrogen or a large amount of refrigerating gas generated by a refrigerator for modulation, and has large daily consumption and inconvenient use. Under normal use frequency, a common liquid nitrogen tank (250L) can only be maintained for about 1 week. This also presents a significant challenge to the provision of refrigerants such as liquid nitrogen. In addition, this jet refrigerant modulation technique requires a period of time to prime both on and off equipment, which affects operating efficiency. Therefore, the technology is difficult to popularize and apply in common laboratories at present due to the limitation of the current conditions. The solid state thermal modulation technology disclosed by the invention adopts semiconductor refrigeration, completely discards the use of a refrigerant, is simple to operate, basically does not need maintenance, greatly saves daily maintenance time and cost, can run uninterruptedly for a long time, obviously improves the working efficiency, and is suitable for being used in a conventional analysis laboratory.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to design and provide a simple, quick, accurate and reliable full-flow analysis method for pesticide residue in common fruits and vegetables, which is easy to popularize and use in common laboratories.

In order to solve the technical problems, the technical scheme provided by the invention is as follows: a method for analyzing and detecting pesticide multi-residue components in common fruits and vegetables by utilizing a solid state thermal modulation full-two-dimensional gas chromatography-mass spectrometry combined technology is used.

A method for detecting pesticide residues on fruits and vegetables by using a magnetic solid-phase extraction technology comprises the following steps:

(1) homogenizing agricultural products by a homogenizer, and adding water and acetonitrile for dispersing;

(2) adding magnetic nano materials for continuous oscillation extraction;

(3) separating the magnetic nano material for extracting and adsorbing the pesticide from the solution of the agricultural products by using a magnet;

(4) eluting the magnetic nano material adsorbed with the pesticide by using an organic reagent, carrying out nitrogen-blowing concentration, and filtering to obtain a solution to be detected;

(5) and analyzing and detecting the liquid to be detected by utilizing a solid state thermal modulation full-two-dimensional gas chromatography-mass spectrometer.

Specifically, the method for detecting pesticide residues on fruits and vegetables by using a magnetic solid-phase extraction technology comprises the following steps:

(1) homogenizing 100-150 g of agricultural products by using a homogenizer to obtain slurry; taking 5-15 g of slurry into a 20-80 mL centrifuge tube with a plug, then adding 15-40 mL of water and 1-3 mL of acetonitrile, and shaking for 2-6 minutes;

(2) adding 50-150 mg of magnetic nano material into the centrifuge tube with the plug in the step (1), and continuing to vibrate for 3-9 minutes;

(3) placing a magnet on the side wall of a centrifuge tube, fully adsorbing the pesticide in the agricultural product by the magnetic nano material, adsorbing the magnetic nano material with magnetism on the side wall close to the magnet, discarding a mixed solution of the agricultural product, acetonitrile and water, washing the magnetic nano material with water for 2-3 times, and discarding a cleaning solution;

(4) ultrasonically eluting the magnetic nano material in the centrifuge tube with the plug for 3-9 minutes by using 2-5 mL of organic solvent, and eluting the pesticide adsorbed by the magnetic nano particles into the organic solvent to obtain eluent; then, concentrating the eluent to 0.8-1.2 mL by using a nitrogen blowing instrument, and filtering to obtain a liquid to be detected;

(5) and (3) analyzing the liquid to be detected by using a solid state thermal modulation full-two-dimensional gas chromatography-mass spectrometer on the computer, adding an internal standard working solution before sample introduction, and performing qualitative and quantitative determination by using an internal standard working curve method to obtain an analysis result of the multiple pesticide residues in the agricultural products.

Preferably, the organic solvent in the step (4) is acetonitrile and methanol in a volume ratio of (3-4): 1, and a mixed solvent.

Preferably, the amount of water used for cleaning the magnetic nano material in the step (3) is 2-5 mL.

Preferably, the magnetic nano material in the step (2) is Fe₃O₄@SiO₂@PDA

Preferably, the magnetic nano material in the step (2) is Fe₃O₄@SiO₂@ mesoporous SiO₂@PDA。

Wherein PDA is polydopamine.

Said Fe₃O₄@SiO₂The specific synthetic process of @ PDA is as follows:

s1 FeCl₃·6H₂O and ethylene glycol in a solid-to-liquid ratio of 1: (50-60) (g/mL), stirring for 0.5-1 hour at 200-300 r/min under the action of magnetic stirring, and adding FeCl₃·6H₂Sodium acetate with the weight 2.5-3 times of that of O is continuously stirred for 0.5-1 hour at 200-300 revolutions per minute to obtain a mixed solution; transferring the mixed solution into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and heating and reacting for 10-13 hours at 180-200 ℃; separating and collecting the reaction product under the action of an external magnetic field, washing the reaction product by using absolute ethyl alcohol with the weight 40-60 times that of the reaction product, and drying the reaction product for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain black solid Fe₃O₄Nano-microspheres;

s2 mixing Fe₃O₄The nano-microsphere is prepared from the following components in a solid-liquid ratio (2-3): 1(mg/mL) is added into hydrochloric acid with the molar concentration of 1-2 mol/L, ultrasonic treatment is carried out for 5-10 minutes under the conditions of the ultrasonic power of 200-500W and the ultrasonic frequency of 25-35 kHz, and then Fe is used₃O₄Adding water with the weight of 80-200 times of that of the nano microspheres to Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding a mixed solution of 8-12 times of hydrochloric acid volume of ethanol/water with a volume ratio of 4/1 into the nano-microspheres, adding 28% by mass of concentrated ammonia water with 0.09-0.1 time of hydrochloric acid volume, and continuing to perform ultrasonic treatment at an ultrasonic power of 200-500WCarrying out ultrasonic treatment for 10-30 minutes under the condition of the acoustic frequency of 25-35 kHz to obtain a mixed solution; then, adding orthosilicate ester with the volume of 0.04-0.05 time of that of hydrochloric acid into the mixed solution, stirring and reacting for 5-7 hours at 25-30 ℃ at 200-300 r/min, and collecting reaction products; washing with absolute ethyl alcohol with the weight of 50-70 times of that of the reaction product, and drying for 6-10 hours at the temperature of 50-60 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain Fe₃O₄@SiO₂；

S3 weighing dopamine hydrochloride and Tris buffer solution with the molar concentration of 10mM, and mixing the solution in a solid-to-liquid ratio of 1: (0.8-1.2) (mg/mL); followed by addition of Fe₃O₄@SiO₂，Fe₃O₄@SiO₂And dopamine hydrochloride in a mass ratio of 1: (4-5), stirring and reacting for 16-20 hours at the temperature of 20-30 ℃ at 200-300 r/min; after the reaction is finished, centrifuging the reaction solution for 10-15 minutes at 2000-3000 r/min, and collecting the bottom solid; washing the bottom solid with absolute ethyl alcohol with the weight 50-70 times of that of the bottom solid and water with the weight 100-200 times of that of the bottom solid, and drying for 6-10 hours at the temperature of 50-60 ℃ and under the vacuum degree of 0.07-0.09 MPa to obtain the Fe₃O₄@SiO₂@PDA。

As an improved technical scheme of the invention, the Fe₃O₄@SiO₂The specific synthetic process of @ PDA is as follows:

s1 FeCl₃·6H₂O and ethylene glycol in a solid-to-liquid ratio of 1: (50-60) (g/mL), stirring for 0.5-1 hour at 200-300 r/min under the action of magnetic stirring, and adding FeCl₃·6H₂Sodium acetate with the weight 2.5-3 times of that of O is continuously stirred for 0.5-1 hour at 200-300 r/min; continued addition of FeCl₃·6H₂Stirring a surfactant with the weight of 1.6-2 times that of O at 200-300 rpm for 15-25 minutes to obtain a mixed solution; transferring the mixed solution into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and heating and reacting for 10-13 hours at 180-200 ℃; separating and collecting the reaction product under the action of an external magnetic field, washing the reaction product by using absolute ethyl alcohol with the weight 40-60 times of that of the reaction product, and drying the reaction product for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain a black solidFe₃O₄Nano-microspheres;

s2 mixing Fe₃O₄The nano-microsphere is prepared from the following components in a solid-liquid ratio (2-3): 1(mg/mL) is added into hydrochloric acid with the molar concentration of 1-2 mol/L, ultrasonic treatment is carried out for 5-10 minutes under the conditions of the ultrasonic power of 200-500W and the ultrasonic frequency of 25-35 kHz, and then Fe is used₃O₄Adding water with the weight of 80-200 times of that of the nano microspheres to Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding a mixed solution of ethanol and water with the volume ratio of 4/1, wherein the volume of the mixed solution is 8-12 times that of hydrochloric acid, adding 28% by mass of concentrated ammonia water, the volume of which is 0.09-0.1 times that of the hydrochloric acid, and continuously performing ultrasonic treatment for 10-30 minutes under the conditions of ultrasonic power of 200-500W and ultrasonic frequency of 25-35 kHz to obtain a mixed solution; then, adding orthosilicate ester with the volume of 0.04-0.05 time of that of hydrochloric acid into the mixed solution, stirring and reacting for 5-7 hours at 25-30 ℃ at 200-300 r/min, and collecting reaction products; washing with absolute ethyl alcohol with the weight of 50-70 times of that of the reaction product, and drying for 6-10 hours at the temperature of 50-60 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain Fe₃O₄@SiO₂；

Further preferably, the Fe₃O₄@SiO₂@ mesoporous SiO₂The specific synthetic process of @ PDA is as follows:

s1 FeCl₃·6H₂O and ethylene glycol in a solid-to-liquid ratio of 1: (50-60) (g/mL),stirring for 0.5-1 hour at 200-300 r/min under the action of magnetic stirring, and then adding FeCl₃·6H₂Sodium acetate with the weight 2.5-3 times of that of O is continuously stirred for 0.5-1 hour at 200-300 r/min; continued addition of FeCl₃·6H₂Stirring a surfactant with the weight of 1.6-2 times that of O at 200-300 rpm for 15-25 minutes to obtain a mixed solution; transferring the mixed solution into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and heating and reacting for 10-13 hours at 180-200 ℃; separating and collecting the reaction product under the action of an external magnetic field, washing the reaction product by using absolute ethyl alcohol with the weight 40-60 times that of the reaction product, and drying the reaction product for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain black solid Fe₃O₄Nano-microspheres;

S3 mixing Fe₃O₄@SiO₂Anhydrous ethanol and water in a ratio of 1: (60-80): 80(g/mL/mL), and carrying out ultrasonic treatment for 15-20 minutes under the conditions of ultrasonic power of 200-500W and ultrasonic frequency of 25-35 kHz; then adding concentrated ammonia water with the mass fraction of 28% and Fe with the volume of 0.17-0.2 times of the water volume₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight 2-3 times of that of the raw materials is stirred for 30-40 minutes at 200-300 revolutions per minute; continuously adding orthosilicate ester with the volume 0.4-0.5 times of that of ammonia water and 3-aminopropyltriethoxysilane with the volume 0.06-0.07 times of that of the ammonia water, and stirring and reacting at the temperature of 20-30 ℃ at 200-300 r/min for 12-15 hours; after the reaction is finished, centrifuging the reaction solution for 10-15 minutes at 2000-3000 r/min, and collecting bottom sediment; washing the bottom sediment with absolute ethyl alcohol with the weight 50-70 times that of the bottom sediment, and drying for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂；

S4 weighing dopamine hydrochloride and Tris buffer solution with the molar concentration of 10mM, and mixing the solution in a solid-to-liquid ratio of 1: (0.8-1.2) (mg/mL); followed by addition of Fe₃O₄@SiO₂@ mesoporous SiO₂，Fe₃O₄@SiO₂@ mesoporous SiO₂And dopamine hydrochloride in a mass ratio of 1: (4-5), stirring and reacting for 16-20 hours at the temperature of 20-30 ℃ at 200-300 r/min; after the reaction is finished, centrifuging the reaction solution for 10-15 minutes at 2000-3000 r/min, and collecting the bottom solid; washing the bottom solid with absolute ethyl alcohol with the weight 50-70 times of that of the bottom solid and water with the weight 100-200 times of that of the bottom solid, and drying for 6-10 hours at the temperature of 50-60 ℃ and under the vacuum degree of 0.07-0.09 MPa to obtain the Fe₃O₄@SiO₂@ mesoporous SiO₂@PDA。

Even more preferably, said Fe₃O₄@SiO₂@ mesoporous SiO₂The specific synthetic process of @ PDA is as follows:

s1 FeCl₃·6H₂O and ethylene glycol in a solid-to-liquid ratio of 1: (50-60) (g/mL), stirring for 0.5-1 hour at 200-300 r/min under the action of magnetic stirring, and adding FeCl₃·6H₂Sodium acetate with the weight 2.5-3 times of that of O is continuously stirred for 0.5-1 hour at 200-300 r/min; continued addition of FeCl₃·6H₂Stirring a surfactant with the weight of 1.6-2 times that of O at 200-300 rpm for 15-25 minutes to obtain a mixed solution; transferring the mixed solution to a polytetrafluoroethylene-lined stainless steelHeating and reacting for 10-13 hours at 180-200 ℃ in a high-pressure reaction kettle; separating and collecting the reaction product under the action of an external magnetic field, washing the reaction product by using absolute ethyl alcohol with the weight 40-60 times that of the reaction product, and drying the reaction product for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain black solid Fe₃O₄Nano-microspheres;

s2 mixing Fe₃O₄The nano-microsphere is prepared from the following components in a solid-liquid ratio (2-3): 1(mg/mL) is added into hydrochloric acid with the molar concentration of 1-2 mol/L, ultrasonic treatment is carried out for 5-10 minutes under the conditions of the ultrasonic power of 200-500W and the ultrasonic frequency of 25-35 kHz, and then Fe is used₃O₄Adding water with the weight of 80-200 times of that of the nano microspheres to Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding a mixed solution of ethanol and water with the volume ratio of 4/1, wherein the volume of the mixed solution is 8-12 times that of hydrochloric acid, adding 28% by mass of concentrated ammonia water, the volume of which is 0.09-0.1 times that of the hydrochloric acid, and continuously performing ultrasonic treatment for 10-30 minutes under the conditions of ultrasonic power of 200-500W and ultrasonic frequency of 25-35 kHz to obtain a mixed solution; subsequently, adding orthosilicate ester with the volume 0.04-0.05 times of that of hydrochloric acid into the mixed solution, and adding graphene oxide into the mixed solution, wherein the mass ratio of the orthosilicate ester to the graphene oxide is 1: (0.05-0.15), stirring and reacting for 4-6 hours at 25-30 ℃ at 200-300 r/min, and then treating for 25-35min in a bipolar square wave high-voltage pulse electric field, wherein the strength of the pulse electric field treated in the bipolar square wave high-voltage pulse electric field is 7-13kV/cm, the electrode distance is 10-15mm, the frequency is 100-300Hz, and the pulse width is 40-60 mus; finally, carrying out ultrasonic treatment for 25-35min under the ultrasonic power of 350-500W and the ultrasonic frequency of 25-45kHz, and collecting reaction products; washing with absolute ethyl alcohol with the weight of 50-70 times of that of the reaction product, and drying for 6-10 hours at the temperature of 50-60 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain Fe₃O₄@SiO₂；

S3 mixing Fe₃O₄@SiO₂Anhydrous ethanol and water in a ratio of 1: (60-80): 80(g/mL/mL), and carrying out ultrasonic treatment for 15-20 minutes under the conditions of ultrasonic power of 200-500W and ultrasonic frequency of 25-35 kHz; then adding concentrated ammonia water with the mass fraction of 28% and the volume of 0.17-0.2 times of that of waterAnd Fe₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight 2-3 times of that of the raw materials is stirred for 30-40 minutes at 200-300 revolutions per minute; continuously adding orthosilicate ester with the volume 0.4-0.5 times of that of ammonia water and 3-aminopropyltriethoxysilane with the volume 0.06-0.07 times of that of the ammonia water, then adding anhydride with the weight of 10-30% of that of the 3-aminopropyltriethoxysilane, and stirring and reacting at 20-30 ℃ at 200-300 r/min for 12-15 hours; after the reaction is finished, centrifuging the reaction solution for 10-15 minutes at 2000-3000 r/min, and collecting bottom sediment; washing the bottom sediment with absolute ethyl alcohol with the weight 50-70 times that of the bottom sediment, and drying for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂；

The anhydride is at least one of butyl succinic anhydride and 2-methyl maleic anhydride. Further, the acid anhydride is prepared from butyl succinic anhydride and 2-methyl maleic anhydride in a mass ratio of 1: (0.2-0.3).

By adding Fe₃O₄@SiO₂The obtained magnetic nano material has the separation characteristic of the magnetic material and the large specific surface area characteristic of the mesoporous material, and meanwhile, the amino functionalization is carried out on the surface of the mesoporous silicon dioxide, so that the dispersion performance, the magnetic performance and the adsorption performance of the magnetic material are improved.

The surfactant is one or more of polyethylene glycol, sodium citrate and ethylenediamine.

In some technical schemes of the invention, no surfactant is added during preparation of the ferroferric oxide, and the obtained ferroferric oxide is similar to a sphere in shape, but the surface of the ferroferric oxide has a plurality of defects and incomplete spheres, which influence the magnetic property and the adsorption property of the magnetic material to a certain extent. The ferroferric oxide prepared by adopting polyvinyl alcohol and sodium citrate as surfactants has smooth surface, spherical shape and complete particle size distribution. Particularly, the ferroferric oxide prepared by taking sodium citrate as a surfactant has very uneven particle size distribution which is different from dozens of nanometers to hundreds of nanometers. The ferroferric oxide obtained by using ethylenediamine as a surfactant is approximately spherical, the surface is rough, the size is uniform, and the particle size distribution is very narrow.

The orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1, in a mixture of the components.

The agricultural products are rice, wheat, corn, apple, banana, grape, lemon, orange, blueberry, green vegetables and the like.

Compared with the prior art, the invention has the advantages that: the method has the advantages that the pesticide residues in the agricultural products are pretreated by the magnetic solid-phase extraction method, the treatment time and the cost can be greatly reduced, and the solid-state thermal modulation full-two-dimensional gas chromatography-mass spectrometer is adopted for measurement, so that the measurement is quicker and the qualitative determination is more accurate. Generally, the method of the invention is fast, economical, efficient and accurate, and reduces adverse effects on personnel and the environment.

Compared with the national standard method, the method for detecting pesticide residues in agricultural products has the advantages of convenient operation, short consumed time, less organic reagent consumption, low analysis cost, more accurate analysis result, lower detection limit and quantification limit and the like.

1. Sample introduction analysis by using solid state thermal modulation full-two-dimensional gas chromatography-mass spectrometry technology

Preparation of standard solution: respectively weighing pesticide standard substances, dissolving the pesticide standard substances with toluene and acetonitrile (1:1) to prepare 1mg/mL standard stock solution, and preparing pesticide standard working solutions with different concentrations according to the corresponding standard substances.

Preparing an internal standard working solution: weighing decafluorobiphenyl, dissolving with toluene and acetonitrile (1:1) to prepare a standard stock solution of 1 mg/mL. Preparing an internal standard using solution by using internal standard stock solution, preparing 0.01mg/mL internal standard using solution by using toluene and acetonitrile (1:1), and adding 10-200 mu L of the internal standard using solution into the standard solution or the solution to be detected before each sample injection.

And analyzing the pesticide standard solution and the sample solution by using a solid state thermal modulation comprehensive two-dimensional gas chromatography-mass spectrometry technology. Injecting a sample of 1 mu L into a solid-state thermal modulation full-two-dimensional gas chromatography-mass spectrometer by an automatic liquid injector, separating by a one-dimensional column, introducing the sample into a modulation column in a solid-state modulator, refrigerating by a semiconductor, rapidly moving the modulation column, moving a cooling substance into a hot zone for desorption, introducing the cooling substance into a two-dimensional column for re-separation, and detecting by a time-of-flight mass spectrometer or a quadrupole mass spectrometer.

2. Analysis of results

The full two-dimensional data is processed by full two-dimensional chromatographic data analysis software (snow science Canvas software is adopted in the invention). After reading the original mass spectrum data, automatically judging a modulation period by software, and drawing a two-dimensional spectrogram; then, carrying out peak detection, automatically identifying peaks according to a set signal-to-noise ratio threshold, automatically combining slice peaks of the same compound, and automatically calculating final peak information including peak height, peak width, peak area and the like; a peak list is obtained. And comparing the mass spectrum information of each peak with a NIST (NIST 17) standard spectrum library, and automatically identifying the substance when the similarity is greater than a set value to finish the qualitative determination. Quantification is accomplished by setting the quantity of ions, which are typically the most abundant fragment ions in the mass spectrum. And (3) drawing an internal standard working curve by measuring the ratio of the quantitative ion peak area of the standard working solution with different concentrations to the internal standard quantitative ion peak area. And (5) carrying out internal standard method on the sample by using a standard working curve to complete quantification. And finally, the final confirmation is carried out through one-dimensional two-dimensional retention time and 2-3 qualitative ions.

The pesticide standard in the step (4) is shown in table 1.

The conditions of the full two-dimensional gas chromatography in the step (4) are as follows:

one-dimensional column: HP-5ms,0.25mm,0.25 μm,30m

Two-dimensional column: DB-17ms,0.18mm,0.18 μm,1.2m

One-dimensional flow rate: 1.0 mL/min; two-dimensional flow: 1.0 mL/min; carrier gas: he (He)

A flow splitting mode: no shunt sampling; sample introduction amount: 1 mu L of the solution; sample inlet temperature: 250 ℃;

column oven temperature program:

100℃(2min)to 270℃(5min)/10℃/min

the mass spectrum conditions are as follows:

ion source temperature: 150 ℃; quadrupole temperature: 230 ℃; transmission line temperature: 280 deg.C

Scanning range: 50-400 amu; scanning speed 12500amu/z (-21 Hz)

The modulator conditions are:

preparing a column: DV series modulation column (suitable for C9-C40 +) 0.25mm

Modulator temperature:

a cold area: -51 ℃ C

Inlet hot zone: offset of column oven-100 deg.C (minimum 40 deg.C)

Outlet hot zone: offset of column oven-30 deg.C

Modulation period/release time: 4s/1 s.

The invention has the following advantages and positive effects:

the national standard method wastes time and labor for extracting pesticides in vegetables and fruits, has high cost and causes secondary pollution to the environment, adopts a magnetic solid phase extraction technology for pretreatment, finishes two steps of extraction and purification by one-time operation, and has the advantages of simple operation, trouble and labor saving and low cost. The qualitative property of the common gas chromatography or the liquid chromatography only depends on one retention time, and the full two-dimensional gas chromatography depends on two retention times, namely one-dimensional retention time and two-dimensional retention time, so that the qualitative accuracy is improved. The invention adopts the non-polar chromatographic column as the one-dimensional column and the polar chromatographic column as the two-dimensional column, a plurality of substances to be detected are firstly separated according to the molecular size when passing through the one-dimensional non-polar column and then separated again according to the polarity when passing through the two-dimensional polar chromatographic column, thereby achieving the separation effect of GC multiplied by GC and leading the complex matrix to be separated with high efficiency, and the method can simultaneously analyze a plurality of pesticide residues in the complex matrix by one-time sample injection.

The jet-propelled refrigerant modulation technology needs to consume a large amount of liquid nitrogen or refrigerating gas, has high maintenance requirement and is inconvenient to use. The solid state thermal modulation technology adopted by the invention does not need any refrigerant, greatly simplifies the operation and maintenance process, reduces the use cost, and simultaneously can carry out long-time uninterrupted work and improve the work efficiency. Is particularly suitable for daily application in common agricultural products and agricultural product analysis laboratories.

Time-of-flight mass spectrometers or quadrupole mass spectrometers can be used, depending on the particular conditions in the laboratory. The time-of-flight mass spectrometer has high scanning speed and more accurate qualitative and quantitative determination, and is particularly matched with the ultra-narrow peak width of the full two-dimensional gas chromatography.

Drawings

FIG. 1 is a full two-dimensional gas chromatography mass spectrum of all standards.

FIG. 2 is a full two-dimensional gas chromatography mass spectrum of an actual sample.

FIG. 3 is a comparison of measured mass spectrum of bifenthrin in standard solution and NIST.

FIG. 4 is the comparison between the measured mass spectrum and NIST of bifenthrin in the actual sample.

Detailed Description

The materials used were as follows:

dopamine hydrochloride, CAS number: 62-31-7, available from alfa aesar (china) chemical ltd. Tris buffer, 10mM in molar concentration, namely Tris (Tris hydroxymethyl aminomethane) buffer, 10mM in molar concentration, was purchased from Nantong, Youzu chemical Co. Polyethylene glycol, CAS No.: 25322-68-3, available from Shanghai Ringsu Biochemical technology, Inc., with a molecular weight of 8000. Sodium citrate, CAS No.: 6132-04-3 from Strobel chemical (Shanghai) Co., Ltd. Ethylenediamine, CAS No.: 107-15-3, available from Shanghai Allantin Biotechnology Ltd. Butylsuccinic anhydride, CAS No.: 2035-76-9. 2-methyl maleic anhydride, CAS No.: 616-02-4. Cetyl trimethylammonium bromide, CAS number: 57-09-0, available from Afahesar (China) chemical Co. 3-aminopropyltriethoxysilane, CAS No.: 919-30-2, available from Hangzhou geochemistry, Inc. Tetraethyl silicate, CAS No.: 78-10-4. N-butyl silicate, CAS No.: 4766-57-8. A refiner, model BILON, available from shanghai biran instruments manufacturing ltd. The vortex oscillator is made by Tan Shuihe Korea scientific experimenter, model XH-C. Graphene oxide is a thickness provided by the Islands science and technology Co., Ltd, Beijing Germany: 0.55-1.2nm, diameter: 0.5-3 μm, number of layers: 1-5 layers of graphene oxide.

Example 1

The method for detecting the pesticide residues on the fruits and the vegetables by utilizing the magnetic solid-phase extraction technology comprises the following steps:

(1) homogenizing 100g of corn kernels with a homogenizer at 9500 rpm for 1 minute to obtain a slurry; taking 5g of slurry in a 50mL centrifuge tube with a plug, then adding 20mL of deionized water and 2mL of acetonitrile, and shaking at 1800 rpm for 2 minutes;

(2) adding 50mg of magnetic nano material into the centrifuge tube with the plug in the step (1), and continuing shaking at 1800 rpm for 4 minutes;

(3) placing a magnet on the side wall of a centrifuge tube, fully adsorbing the pesticide in the agricultural product by the magnetic nano material, adsorbing the magnetic nano material with magnetism on the side wall close to the magnet, discarding the mixed solution of the agricultural product, acetonitrile and water, cleaning the magnetic nano material for 3 times by 2mL of deionized water each time, and discarding the cleaning solution;

(4) ultrasonically eluting the magnetic nano material in the centrifuge tube with the plug by adopting 4mL of organic solvent under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz for 8 minutes, eluting the pesticide adsorbed by the magnetic nano particles into the organic solvent, then concentrating the eluent to 1mL on a nitrogen blowing instrument, and passing through a filter membrane with the aperture of 0.22 mu m to obtain a liquid to be detected; wherein the organic solvent is acetonitrile/methanol in a volume ratio of 3: 1;

(5) and (3) operating the machine to analyze the liquid to be detected by adopting a solid state thermal modulation full-two-dimensional gas chromatography-mass spectrometer, and adding 20 mu L of internal standard working solution before sample injection.

The magnetic nano material is Fe₃O₄@SiO₂@ mesoporous SiO₂@ PDA, said Fe₃O₄@SiO₂@ mesoporous SiO₂The specific synthetic process of @ PDA is as follows:

s1 mixing 1.35g FeCl₃·6H₂Mixing O and 75mL of glycol, stirring for 0.5 hour at 260 revolutions per minute under the action of a magnetic stirrer, then adding 3.6g of sodium acetate, and continuing to stir for 1 hour at 260 revolutions per minute; continuously adding 2.2g of ethylenediamine, and stirring for 15 minutes at 260 revolutions per minute to obtain a mixed solution; transferring the mixed solution into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle with the capacity of 200mL, and heating and reacting for 12 hours at 200 ℃; separating and collecting the reaction product under the action of an external magnetic field, cleaning the reaction product by using absolute ethyl alcohol with the weight 60 times that of the reaction product, and drying the reaction product for 8 hours in vacuum at 50 ℃ and the vacuum degree of 0.07MPa to obtain black solid Fe₃O₄Nano-microspheres;

s2 mixing 50mg Fe₃O₄Adding the nano-microspheres into 20mL hydrochloric acid with the molar concentration of 2mol/L, carrying out ultrasonic treatment for 5 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz, and then using Fe₃O₄Deionized water with the weight of 100 times of that of the nano microspheres is used for adding magnetic Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding 200mL of ethanol/water solution with the volume ratio of 4/1 into the nano microspheres, adding 2.0mL of 28% concentrated ammonia water by mass fraction, and continuing to perform ultrasonic treatment for 20 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz to obtain a mixed solution; then, adding 1.0mL of orthosilicate into the mixed solution, and adding graphene oxide into the mixed solution, wherein the mass ratio of the orthosilicate to the graphene oxide is 1: 0.06, stirring and reacting for 5 hours at the temperature of 28 ℃ at 300 revolutions per minute, and then treating for 30 minutes in a bipolar square wave high-voltage pulse electric field, wherein the strength of the pulse electric field treated in the bipolar square wave high-voltage pulse electric field is 10kV/cm, the electrode distance is 15mm, the frequency is 200Hz, and the pulse width is 50 mus; finally, carrying out ultrasonic treatment for 30min under the ultrasonic power of 400W and the ultrasonic frequency of 35kHz to complete hydrolysis and polycondensation of the orthosilicate ester, and collecting reaction products; will be reversedWashing the reaction product with 50 times of anhydrous ethanol, removing blank silicon dioxide particles, vacuum drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s3 mixing Fe₃O₄@SiO₂Absolute ethanol and deionized water at a ratio of 1: 70: 80(g/mL/mL), and carrying out ultrasonic treatment for 15 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25 kHz; then concentrated ammonia water with the mass fraction of 28 percent and Fe with the volume 0.17 time of the deionized water are added₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight being 3 times of that of the raw materials is stirred for 30 minutes at 260 revolutions per minute; and (2) continuously adding orthosilicate ester with the volume 0.5 time of that of the ammonia water and 3-aminopropyltriethoxysilane with the volume 0.07 time of that of the ammonia water, and then adding acid anhydride with the weight of 15% of that of the 3-aminopropyltriethoxysilane, wherein the acid anhydride is prepared from butyl succinic anhydride and 2-methyl maleic anhydride according to the mass ratio of 1: 0.25, and stirring and reacting at 25 ℃ at 300 revolutions per minute for 12 hours; after the reaction is finished, centrifuging the reaction solution at 2000 rpm for 10 minutes, and collecting bottom sediment; washing the bottom precipitate with 70 times of anhydrous ethanol, and drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s4 weighing 400mg dopamine hydrochloride and 400mL Tris buffer solution with the molar concentration of 10mM and mixing; then 100mg of Fe was added₃O₄@SiO₂@ mesoporous SiO₂Stirring and reacting at 25 ℃ at 300 revolutions per minute for 16 hours; after the reaction was completed, the reaction solution was centrifuged at 2600 rpm for 15 minutes, and the bottom solid was collected; washing the bottom solid with absolute ethyl alcohol with the weight 70 times of that of the bottom solid and deionized water with the weight 200 times of that of the bottom solid, and then carrying out vacuum drying for 10 hours at the temperature of 50 ℃ and the vacuum degree of 0.07MPa to obtain the Fe₃O₄@SiO₂@ mesoporous SiO₂@ PDA magnetic nanomaterial.

Configuration of the working curve:

taking standard stock solutions of pesticides, preparing the standard stock solutions into series of working solutions with the concentrations of 0.01mg/kg, 0.02mg/kg, 0.05mg/kg, 0.10mg/kg, 0.50mg/kg, 1.00mg/kg and 5.00mg/kg in samples respectively, taking 1.0mL of the standard stock solutions, adding 10 mu L of internal standard use solution into the solutions respectively, mixing the solutions uniformly, and carrying out sample injection analysis under the condition of identical product analysis.

And performing qualitative and quantitative determination on the result by adopting an internal standard working curve method to obtain an analysis result of the multiple pesticide residues in the agricultural product.

An experimental instrument: gas chromatograph 7890B (agilent); 5977B single quadrupole mass spectrometer (agilent); solid state heat modulator SSM1800 (snow science and technology)

The full two-dimensional gas chromatography conditions are as follows:

one-dimensional column: HP-5ms,0.25mm,0.25 μm,30m

Two-dimensional column: DB-17ms,0.18mm,0.18 μm,1.2m

column oven temperature program:

100℃(2min)to 270℃(5min)/10℃/min

the mass spectrum conditions are as follows:

Scanning range: 50-400 amu; scanning speed 12500amu/z (-21 Hz)

The modulator conditions are:

preparing a column: DV series modulation column, 0.25mm

Modulator temperature:

a cold area: -51 ℃ C

Inlet hot zone: offset of column oven-100 deg.C (minimum 40 deg.C)

Outlet hot zone: offset of column oven-30 deg.C

Modulation period/release time: 4s/1s

The information of the qualitative and quantitative ions and the internal standard ions of the pesticide standard substance is shown in table 1, and the indexes of the linear range and the standard addition recovery rate of the method are shown in table 2. The detection result shows that 4 kinds of pesticides, namely simazine 0.23mg/kg, atrazine 0.08mg/kg, bifenthrin 0.78mg/kg and cypermethrin 0.55mg/kg, are detected in the agricultural products.

Table 1: pesticide standard substance full-two-dimensional chromatographic mass spectrum information

Table 2: example 1 Linear Range, quantitation Limit, spiked recovery results Table

Example 2

Essentially the same as in example 1, except that the Fe₃O₄@SiO₂@ mesoporous SiO₂The specific synthetic process of @ PDA is as follows:

s2 mixing 50mg Fe₃O₄Adding the nano-microspheres into 20mL hydrochloric acid with the molar concentration of 2mol/L, carrying out ultrasonic treatment for 5 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz, and then using Fe₃O₄Deionized water with the weight of 100 times of that of the nano microspheres is used for adding magnetic Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding 200mL of ethanol/water solution with the volume ratio of 4/1 into the nano microspheres, adding 2.0mL of 28% concentrated ammonia water by mass fraction, and continuing to perform ultrasonic treatment for 20 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz to obtain a mixed solution; then, adding 1.0mL of orthosilicate into the mixed solution, stirring and reacting for 5 hours at the temperature of 28 ℃ at the speed of 300 revolutions per minute, and then treating for 30 minutes in a bipolar square wave high-voltage pulse electric field, wherein the electric field intensity of pulses treated in the bipolar square wave high-voltage pulse electric field is 10kV/cm, the electrode distance is 15mm, the frequency is 200Hz, and the pulse width is 50 mus; finally, carrying out ultrasonic treatment for 30min under the ultrasonic power of 400W and the ultrasonic frequency of 35kHz to complete hydrolysis and polycondensation of the orthosilicate ester, and collecting reaction products; washing the reaction product with 50 times of anhydrous ethanol, removing blank silicon dioxide particles, vacuum drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s3 mixing Fe₃O₄@SiO₂Absolute ethanol and deionized water at a ratio of 1: 70: 80(g/mL/mL), and carrying out ultrasonic treatment for 15 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25 kHz; then concentrated ammonia water with the mass fraction of 28 percent and Fe with the volume 0.17 time of the deionized water are added₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight being 3 times of that of the raw materials is stirred for 30 minutes at 260 revolutions per minute; and (2) continuously adding orthosilicate ester with the volume 0.5 time of that of the ammonia water and 3-aminopropyltriethoxysilane with the volume 0.07 time of that of the ammonia water, and then adding acid anhydride with the weight of 15% of that of the 3-aminopropyltriethoxysilane, wherein the acid anhydride is prepared from butyl succinic anhydride and 2-methyl maleic anhydride according to the mass ratio of 1: 0.25, and stirring and reacting at 25 ℃ at 300 revolutions per minute for 12 hours; the reaction is finishedThen, the reaction solution was centrifuged at 2000 rpm for 10 minutes, and the bottom precipitate was collected; washing the bottom precipitate with 70 times of anhydrous ethanol, and drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

Table 3: example 2 Linear Range, quantitation Limit, spiked recovery results Table

Example 3

s1 mixing 1.35g FeCl₃·6H₂Mixing O and 75mL of glycol, stirring for 0.5 hour at 260 revolutions per minute under the action of a magnetic stirrer, then adding 3.6g of sodium acetate, and continuing to stir for 1 hour at 260 revolutions per minute; continuously adding 2.2g of ethylenediamine, and stirring for 15 minutes at 260 revolutions per minute to obtain a mixed solution; the mixture was transferred to a 200mL Teflon linerHeating and reacting for 12 hours at 200 ℃ in a stainless steel high-pressure reaction kettle; separating and collecting the reaction product under the action of an external magnetic field, cleaning the reaction product by using absolute ethyl alcohol with the weight 60 times that of the reaction product, and drying the reaction product for 8 hours in vacuum at 50 ℃ and the vacuum degree of 0.07MPa to obtain black solid Fe₃O₄Nano-microspheres;

s2 mixing 50mg Fe₃O₄Adding the nano-microspheres into 20mL hydrochloric acid with the molar concentration of 2mol/L, carrying out ultrasonic treatment for 5 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz, and then using Fe₃O₄Deionized water with the weight of 100 times of that of the nano microspheres is used for adding magnetic Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding 200mL of ethanol/water solution with the volume ratio of 4/1 into the nano microspheres, adding 2.0mL of 28% concentrated ammonia water by mass fraction, and continuing to perform ultrasonic treatment for 20 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz to obtain a mixed solution; then, adding 1.0mL of orthosilicate into the mixed solution, and adding graphene oxide into the mixed solution, wherein the mass ratio of the orthosilicate to the graphene oxide is 1: 0.06, stirring and reacting for 5 hours at the temperature of 28 ℃ at 300 revolutions per minute, then treating for 60 minutes in a bipolar square wave high-voltage pulse electric field, wherein the intensity of the pulse electric field treated in the bipolar square wave high-voltage pulse electric field is 10kV/cm, the electrode distance is 15mm, the frequency is 200Hz, and the pulse width is 50 microseconds, so that the hydrolysis and polycondensation of the orthosilicate are completed, and a reaction product is collected; washing the reaction product with 50 times of anhydrous ethanol, removing blank silicon dioxide particles, vacuum drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s3 mixing Fe₃O₄@SiO₂Absolute ethanol and deionized water at a ratio of 1: 70: 80(g/mL/mL), and carrying out ultrasonic treatment for 15 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25 kHz; then concentrated ammonia water with the mass fraction of 28 percent and Fe with the volume 0.17 time of the deionized water are added₃O₄@SiO₂Cetyl trimethyl ammonium bromide 3 times the weight of the solution, stirring at 260 rpm 30 minute; and (2) continuously adding orthosilicate ester with the volume 0.5 time of that of the ammonia water and 3-aminopropyltriethoxysilane with the volume 0.07 time of that of the ammonia water, and then adding acid anhydride with the weight of 15% of that of the 3-aminopropyltriethoxysilane, wherein the acid anhydride is prepared from butyl succinic anhydride and 2-methyl maleic anhydride according to the mass ratio of 1: 0.25, and stirring and reacting at 25 ℃ at 300 revolutions per minute for 12 hours; after the reaction is finished, centrifuging the reaction solution at 2000 rpm for 10 minutes, and collecting bottom sediment; washing the bottom precipitate with 70 times of anhydrous ethanol, and drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

Table 4: example 3 Linear Range, quantitation Limit, spiked recovery results Table

Example 4

s2 mixing 50mg Fe₃O₄Adding the nano-microspheres into 20mL hydrochloric acid with the molar concentration of 2mol/L, carrying out ultrasonic treatment for 5 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz, and then using Fe₃O₄Deionized water with the weight of 100 times of that of the nano microspheres is used for adding magnetic Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding 200mL of ethanol/water solution with the volume ratio of 4/1 into the nano microspheres, adding 2.0mL of 28% concentrated ammonia water by mass fraction, and continuing to perform ultrasonic treatment for 20 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz to obtain a mixed solution; then, adding 1.0mL of orthosilicate into the mixed solution, and adding graphene oxide into the mixed solution, wherein the mass ratio of the orthosilicate to the graphene oxide is 1: 0.06, stirring and reacting for 5 hours at the temperature of 28 ℃ at 300 r/min, then carrying out ultrasonic treatment for 60 minutes under the ultrasonic power of 400W and the ultrasonic frequency of 35kHz to complete hydrolysis and polycondensation of the orthosilicate ester, and collecting reaction products; washing the reaction product with 50 times of anhydrous ethanol, removing blank silicon dioxide particles, vacuum drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s3 mixing Fe₃O₄@SiO₂Absolute ethanol and deionized water at a ratio of 1: 70: 80(g/mL/mL), and ultrasonically treating the mixture under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz for 15The method comprises the following steps of (1) taking minutes; then concentrated ammonia water with the mass fraction of 28 percent and Fe with the volume 0.17 time of the deionized water are added₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight being 3 times of that of the raw materials is stirred for 30 minutes at 260 revolutions per minute; and (2) continuously adding orthosilicate ester with the volume 0.5 time of that of the ammonia water and 3-aminopropyltriethoxysilane with the volume 0.07 time of that of the ammonia water, and then adding acid anhydride with the weight of 15% of that of the 3-aminopropyltriethoxysilane, wherein the acid anhydride is prepared from butyl succinic anhydride and 2-methyl maleic anhydride according to the mass ratio of 1: 0.25, and stirring and reacting at 25 ℃ at 300 revolutions per minute for 12 hours; after the reaction is finished, centrifuging the reaction solution at 2000 rpm for 10 minutes, and collecting bottom sediment; washing the bottom precipitate with 70 times of anhydrous ethanol, and drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

Table 5: example 4 Linear Range, quantitation Limit, spiked recovery results Table

Example 5

s2 mixing 50mg Fe₃O₄Adding the nano-microspheres into 20mL hydrochloric acid with the molar concentration of 2mol/L, carrying out ultrasonic treatment for 5 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz, and then using Fe₃O₄Deionized water with the weight of 100 times of that of the nano microspheres is used for adding magnetic Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding 200mL of ethanol/water solution with the volume ratio of 4/1 into the nano microspheres, adding 2.0mL of 28% concentrated ammonia water by mass fraction, and continuing to perform ultrasonic treatment for 20 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz to obtain a mixed solution; then, adding 1.0mL of orthosilicate into the mixed solution, and adding graphene oxide into the mixed solution, wherein the mass ratio of the orthosilicate to the graphene oxide is 1: 0.06, stirring and reacting for 5 hours at the temperature of 28 ℃ at 300 revolutions per minute, and then treating for 30 minutes in a bipolar square wave high-voltage pulse electric field, wherein the strength of the pulse electric field treated in the bipolar square wave high-voltage pulse electric field is 10kV/cm, the electrode distance is 15mm, the frequency is 200Hz, and the pulse width is 50 mus; finally, carrying out ultrasonic treatment for 30min under the ultrasonic power of 400W and the ultrasonic frequency of 35kHz to complete hydrolysis and polycondensation of the orthosilicate ester, and collecting reaction products; washing the reaction product with 50 times of anhydrous alcohol, removing blank silicon dioxide particles, reacting at 50 deg.C,Vacuum drying for 8 hours under the vacuum degree of 0.07MPa to obtain Fe₃O₄@SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s3 mixing Fe₃O₄@SiO₂Absolute ethanol and deionized water at a ratio of 1: 70: 80(g/mL/mL), and carrying out ultrasonic treatment for 15 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25 kHz; then concentrated ammonia water with the mass fraction of 28 percent and Fe with the volume 0.17 time of the deionized water are added₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight being 3 times of that of the raw materials is stirred for 30 minutes at 260 revolutions per minute; continuously adding orthosilicate ester with the volume 0.5 time of that of the ammonia water and 3-aminopropyltriethoxysilane with the volume 0.07 time of that of the ammonia water, then adding anhydride with the weight 15% of that of the 3-aminopropyltriethoxysilane, wherein the anhydride is butyl succinic anhydride, and stirring and reacting at 25 ℃ at 300 revolutions per minute for 12 hours; after the reaction is finished, centrifuging the reaction solution at 2000 rpm for 10 minutes, and collecting bottom sediment; washing the bottom precipitate with 70 times of anhydrous ethanol, and drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

Table 6: EXAMPLE 5 Linear Range, quantitation Limit, spiked recovery results Table

Example 6

s2 mixing 50mg Fe₃O₄Adding the nano-microspheres into 20mL hydrochloric acid with the molar concentration of 2mol/L, carrying out ultrasonic treatment for 5 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz, and then using Fe₃O₄Deionized water with the weight of 100 times of that of the nano microspheres is used for adding magnetic Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding 200mL of ethanol/water solution with the volume ratio of 4/1 into the nano microspheres, adding 2.0mL of 28% concentrated ammonia water by mass fraction, and continuing to perform ultrasonic treatment for 20 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25kHz to obtain a mixed solution; then, adding 1.0mL of orthosilicate into the mixed solution, and adding graphene oxide into the mixed solution, wherein the mass ratio of the orthosilicate to the graphene oxide is 1: 0.06, stirring and reacting at 28 ℃ for 5 hours at 300 revolutions per minute, and then treating in a bipolar square wave high-voltage pulse electric field for 30 minutesThe pulse electric field intensity is 10kV/cm, the electrode distance is 15mm, the frequency is 200Hz, and the pulse width is 50 mus; finally, carrying out ultrasonic treatment for 30min under the ultrasonic power of 400W and the ultrasonic frequency of 35kHz to complete hydrolysis and polycondensation of the orthosilicate ester, and collecting reaction products; washing the reaction product with 50 times of anhydrous ethanol, removing blank silicon dioxide particles, vacuum drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s3 mixing Fe₃O₄@SiO₂Absolute ethanol and deionized water at a ratio of 1: 70: 80(g/mL/mL), and carrying out ultrasonic treatment for 15 minutes under the conditions of ultrasonic power of 300W and ultrasonic frequency of 25 kHz; then concentrated ammonia water with the mass fraction of 28 percent and Fe with the volume 0.17 time of the deionized water are added₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight being 3 times of that of the raw materials is stirred for 30 minutes at 260 revolutions per minute; continuously adding orthosilicate ester with the volume 0.5 time of that of the ammonia water and 3-aminopropyltriethoxysilane with the volume 0.07 time of that of the ammonia water, then adding anhydride with the weight 15% of that of the 3-aminopropyltriethoxysilane, wherein the anhydride is 2-methylmaleic anhydride, and stirring and reacting at 25 ℃ at 300 r/min for 12 hours; after the reaction is finished, centrifuging the reaction solution at 2000 rpm for 10 minutes, and collecting bottom sediment; washing the bottom precipitate with 70 times of anhydrous ethanol, and drying at 50 deg.C and 0.07MPa for 8 hr to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂(ii) a Wherein the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1;

s4 weighing 400mg dopamine hydrochloride and 400mL Tris buffer solution with the molar concentration of 10mM and mixing; then 100mg of Fe was added₃O₄@SiO₂@ mesoporous SiO₂Stirring and reacting at 25 ℃ at 300 revolutions per minute for 16 hours; after the reaction was completed, the reaction solution was centrifuged at 2600 rpm for 15 minutes, and the bottom solid was collected; washing the bottom solid with anhydrous ethanol 70 times the weight of the bottom solid and deionized water 200 times the weight of the bottom solid, and vacuum-washing at 50 deg.C and 0.07MPaDrying for 10 hours to obtain the Fe₃O₄@SiO₂@ mesoporous SiO₂@ PDA magnetic nanomaterial.

Table 7: example 6 Table of Linear Range, quantitation Limit, and recovery with spiking

Claims

1. A method for detecting pesticide residues on fruits and vegetables by using a magnetic solid-phase extraction technology is characterized by comprising the following steps:

(5) on-machine analyzing the liquid to be measured by adopting a solid state thermal modulation full-two-dimensional gas chromatography-mass spectrometer, adding an internal standard working solution before sample injection, and performing qualitative and quantitative determination by adopting an internal standard working curve method to obtain an analysis result of multiple pesticide residues in agricultural products;

in the step (2), the magnetic nano material is Fe₃O₄@SiO₂@ mesoporous SiO₂@PDA；

Said Fe₃O₄@SiO₂@ mesoporous SiO₂The specific synthetic process of @ PDA is as follows:

s1 FeCl₃·6H₂O and ethylene glycol in a solid-to-liquid ratio of 1 g: (50-60) mL, stirring for 0.5-1 hour at 200-300 r/min under the action of magnetic stirring, and then adding FeCl₃·6H₂Sodium acetate with the weight 2.5-3 times of that of O is continuously stirred for 0.5-1 hour at 200-300 r/min; continued addition of FeCl₃·6H₂Stirring a surfactant with the weight of 1.6-2 times that of O at 200-300 rpm for 15-25 minutes to obtain a mixed solution; transferring the mixed solution into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and heating and reacting for 10-13 hours at 180-200 ℃; separating and collecting the reaction product under the action of an external magnetic field, washing the reaction product by using absolute ethyl alcohol with the weight 40-60 times that of the reaction product, and drying the reaction product for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain black solid Fe₃O₄Nano-microspheres;

s2 mixing Fe₃O₄The nano-microsphere is prepared from the following components in a solid-to-liquid ratio (2-3) mg: adding 1mL of the solution into hydrochloric acid with the molar concentration of 1-2 mol/L, carrying out ultrasonic treatment for 5-10 minutes under the conditions of the ultrasonic power of 200-500W and the ultrasonic frequency of 25-35 kHz, and then using Fe₃O₄Adding water with the weight of 80-200 times of that of the nano microspheres to Fe₃O₄Cleaning the nano microspheres; then washing the Fe₃O₄Adding a mixed solution of ethanol and water with the volume ratio of 4/1, wherein the volume of the mixed solution is 8-12 times that of hydrochloric acid, adding 28% by mass of concentrated ammonia water, the volume of which is 0.09-0.1 times that of the hydrochloric acid, and continuously performing ultrasonic treatment for 10-30 minutes under the conditions of ultrasonic power of 200-500W and ultrasonic frequency of 25-35 kHz to obtain a mixed solution; subsequently, adding orthosilicate ester with the volume 0.04-0.05 times of that of hydrochloric acid into the mixed solution, and adding graphene oxide into the mixed solution, wherein the mass ratio of the orthosilicate ester to the graphene oxide is 1: (0.05-0.15), stirring and reacting for 4-6 hours at 25-30 ℃ at 200-300 r/min, and then stirring and reacting at a bipolar square wave heightProcessing in a voltage pulse electric field for 25-35min, wherein the intensity of the pulse electric field processed in the bipolar square wave high-voltage pulse electric field is 7-13kV/cm, the electrode distance is 10-15mm, the frequency is 100-300Hz, and the pulse width is 40-60 mu s; finally, carrying out ultrasonic treatment for 25-35min under the ultrasonic power of 350-500W and the ultrasonic frequency of 25-45kHz, and collecting reaction products; washing with absolute ethyl alcohol with the weight of 50-70 times of that of the reaction product, and drying for 6-10 hours at the temperature of 50-60 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain Fe₃O₄@SiO₂；

S3 mixing Fe₃O₄@SiO₂Absolute ethanol and water at a ratio of 1 g: (60-80) mL: mixing 80mL of the mixture, and carrying out ultrasonic treatment for 15-20 minutes under the conditions of ultrasonic power of 200-500W and ultrasonic frequency of 25-35 kHz; then adding concentrated ammonia water with the mass fraction of 28% and Fe with the volume of 0.17-0.2 times of the water volume₃O₄@SiO₂Cetyl trimethyl ammonium bromide with the weight 2-3 times of that of the raw materials is stirred for 30-40 minutes at 200-300 revolutions per minute; continuously adding orthosilicate ester with the volume 0.4-0.5 times of that of ammonia water and 3-aminopropyltriethoxysilane with the volume 0.06-0.07 times of that of the ammonia water, then adding anhydride with the weight of 10-30% of that of the 3-aminopropyltriethoxysilane, and stirring and reacting at 20-30 ℃ at 200-300 r/min for 12-15 hours; after the reaction is finished, centrifuging the reaction solution for 10-15 minutes at 2000-3000 r/min, and collecting bottom sediment; washing the bottom sediment with absolute ethyl alcohol with the weight 50-70 times that of the bottom sediment, and drying for 6-10 hours at the temperature of 40-50 ℃ and the vacuum degree of 0.07-0.09 MPa to obtain Fe₃O₄@SiO₂@ mesoporous SiO₂(ii) a The acid anhydride is prepared from butyl succinic anhydride and 2-methyl maleic anhydride in a mass ratio of 1: (0.2-0.3);

s4 dopamine hydrochloride and Tris buffer solution with the molar concentration of 10mM are weighed, and the ratio of solid to liquid is 1 mg: (0.8-1.2) mL; followed by addition of Fe₃O₄@SiO₂@ mesoporous SiO₂，Fe₃O₄@SiO₂@ mesoporous SiO₂And dopamine hydrochloride in a mass ratio of 1: (4-5), stirring and reacting for 16-20 hours at the temperature of 20-30 ℃ at 200-300 r/min; after the reaction is finished, centrifuging the reaction solution for 10-15 minutes at 2000-3000 r/min, and collecting the bottom solidsA body; washing the bottom solid with absolute ethyl alcohol with the weight 50-70 times of that of the bottom solid and water with the weight 100-200 times of that of the bottom solid, and drying for 6-10 hours at the temperature of 50-60 ℃ and under the vacuum degree of 0.07-0.09 MPa to obtain the Fe₃O₄@SiO₂@ mesoporous SiO₂@PDA。

2. The method for detecting pesticide residues on fruits and vegetables by using the magnetic solid phase extraction technology as claimed in claim 1, wherein the organic solvent in the step (4) is acetonitrile and methanol in a volume ratio of (3-4): 1, and a mixed solvent.

3. The method for detecting pesticide residues on fruits and vegetables by using the magnetic solid-phase extraction technology as claimed in claim 1, wherein the amount of water used for washing the magnetic nano material in each time in the step (3) is 2-5 mL.

4. The method for detecting pesticide residues on fruits and vegetables by using the magnetic solid-phase extraction technology as claimed in claim 1, wherein the surfactant is one or more of polyethylene glycol, sodium citrate and ethylenediamine; the orthosilicate is tetraethyl silicate and butyl orthosilicate in a mass ratio of 4: 1, in a mixture of the components.