CN109212108B - Gas chromatography-mass spectrometry combined method for simultaneously determining three trace quinoline herbicides in rice and soybean - Google Patents
Gas chromatography-mass spectrometry combined method for simultaneously determining three trace quinoline herbicides in rice and soybean Download PDFInfo
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Abstract
The invention relates to a method for analyzing and detecting trace harmful substances, in particular to a gas chromatography-mass spectrometry combined method for simultaneously determining trace chloromethylquinolinic acid, dichloroquinolinic acid and imidazoquinolinic acid in rice and soybean. The method comprises the steps of ultrasonically extracting a target object in a sample by using an alkaline 10% acetonitrile aqueous solution, enriching the target compound in an extracting solution by using a novel adsorbent 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite roasted product, dissolving the adsorbent by using a hydrochloric acid solution to realize complete elution of the target object, efficiently extracting the compound by using a small amount of organic solvent, and rapidly analyzing and determining by using a gas chromatography after derivation. The novel adsorbent adopted by the method realizes rapid and efficient adsorption of the target object by adopting a dispersed solid phase extraction mode, and can save a large amount of adsorption time compared with gel permeation chromatography and a solid phase extraction method; the complete desorption of the target can be realized by using the acid to dissolve the adsorbent; the method is only suitable for extracting a small amount of organic solvent, and has the advantages of safety, environmental protection and economic advantage.
Description
Technical Field
The invention relates to a method for analyzing and detecting harmful trace substances, in particular to a gas chromatography-mass spectrometry combined method for simultaneously determining trace amounts of cloquintocet, quinclorac and quinclorac in rice and soybean.
Background
The quinoline acid herbicide is an important one in the current herbicides, and the types sold and used in the market comprise chloroquinate, quinclorac, imidazoquinate and ester compounds thereof, all belong to low-toxicity herbicides, and have certain toxicity to human bodies, animals and aquatic products. At present, the Maximum Residual Limit (MRL) of the quinclorac in the brown rice is set to be 1.0mg/kg in China, and the Maximum Residual Limit (MRL) of the quinclorac in the soybean is set to be 0.05mg/kg, so that the requirements are strict.
Quinclorac is a specific medicine for killing cockspur grass which is a malignant weed in rice field, and clomazone and imidazoquinolinic are commonly used for broad-leaved weeds such as polygonum, chenopodium, amaranthus retroflexus, sticktight, xanthium, abutilon and the like in soybean and rice fields, and also have certain control effect on gramineous weeds such as brachiaria, digitaria, broomcorn millet, setaria and the like.
The current standard method for detecting the residual quantity of the substances in the food is mainly 'detection method gas chromatography-mass spectrometry' of the residual quantity of 31 acidic herbicides in SN/T2228-2008 import and export food, wherein a detection method of quinclorac is specified, and the detection of other two herbicides is not involved. Most impurities can be removed by applying gel permeation chromatography for pretreatment in the standard, a good pretreatment effect is achieved, but the pretreatment process has the defects of time consumption, low efficiency, consumption of a large amount of organic solvents and the like, is not suitable for rapid screening and detection of a large-flux sample, and a new pretreatment method is urgently needed to solve the problem of rapid and efficient detection and screening. The detection of quinoline acid herbicides in food is mainly related to high performance liquid chromatography, the pretreatment mainly focuses on extraction by organic solvent and purification by solid phase extraction, but the solid phase extraction method is used as a purification means, so that the defects of high labor consumption, low efficiency and limited types of selectable solid phase extraction materials are overcome.
Since 2011, the inventor research team has conducted extensive research on Layered Double hydroxide metal oxides (LDHs) and modified materials thereof, prepared LDHs and LDO materials modified by different intercalation anions, and utilized the synthetic materials to develop application research aiming at screening, investigating and optimizing adsorption enrichment performance of different target compounds. In the previous research, the inventor uses the 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent to perform adsorption research on various quinoline acid herbicides and intermediates thereof in water, and obtains good selective adsorption effect. On the basis, the inventor further optimizes the performance and application method of the developed adsorbent for enriching three target compounds, and establishes a gas chromatography-mass spectrometry combined method for detecting the residual quantity of trace chloromethylquinolinic acid, dichloroquinolinic acid and imidazoquinolinic acid in rice and soybean by using the benzene sulfonate-magnesium aluminum type hydrotalcite as the adsorbent.
Disclosure of Invention
In order to overcome the defects that the gel permeation chromatography is time-consuming and inefficient, a large amount of organic solvent is consumed, the method is not suitable for screening a large-flux sample, and the solid-phase extraction column is time-consuming and inefficient, the types of the solid-phase extraction column are limited and the like in the conventional standard method, the invention aims to solve the technical problem of providing a gas chromatography-mass spectrometry combined method which is based on novel adsorbent dispersed solid-phase extraction and is suitable for simultaneously detecting the residual amounts of trace chloroquinolinic acid, quinclorac and imazaquin in rice and soybean.
The invention achieves the above object by the following technical means.
A gas chromatography-mass spectrometry combination method for simultaneously determining three trace quinoline herbicides in rice and soybean is characterized by comprising the following steps:
step 1 extraction and adsorption of the compound: crushing rice and soybean samples, sieving the crushed rice and soybean samples with a 60-mesh sieve, sealing and storing the crushed rice and soybean samples, weighing 5.00g of the samples in a plastic centrifuge tube with a plug when in use, adding 20mL of alkaline 10% aqueous solution into the centrifuge tube, sealing and whirling the centrifuge tube, performing ultrasonic extraction, centrifuging, transferring supernatant into another plastic centrifuge tube with a plug, re-extracting once, and combining the extracted solution; adding 10mL of n-hexane into a centrifugal tube, oscillating, centrifuging, removing supernatant, adding 0.50g of 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent into the centrifugal tube, sealing, swirling, oscillating for a certain time to enable the adsorbent to adsorb a target compound in the extracting solution;
step 3, extraction and derivatization of compounds: adding a certain amount of anhydrous sodium sulfate and an organic solvent into the centrifuge tube for extraction, performing vortex and centrifugation, separating supernatant into a derivative bottle, adding 0.40mL of methanol and 0.2mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L, performing water bath at 30-50 ℃, and performing derivatization for 30 min;
analytical testing of the compound of step 4: adding a stop solution into a derivatization bottle to remove redundant derivatization agents, adding a proper amount of solid sodium bicarbonate and anhydrous sodium sulfate, carrying out vortex, absorbing an upper layer organic solution, filtering, and then carrying out analysis and test by using a gas chromatography-mass spectrometry method according to the following conditions:
a) a chromatographic column: DB-5MS capillary column, 30m × 0.25mm, 0.25 μm thick; column flow rate: 1.50 mL/min.
b) Sample inlet temperature: 260 ℃; and (3) sample introduction mode: no shunt sampling; sample introduction amount: 2 μ L.
c) Temperature rising procedure: 40 deg.C (1 min hold), 20 deg.C/min to 260 deg.C (4 min hold), 10 deg.C/min to 280 deg.C (8 min hold).
d) EI bombardment source: 70 ev; temperature of a chromatography-mass spectrometry connection port: 280 ℃; temperature of the quadrupole rods: 230 ℃; ion source temperature: at 150 ℃.
e) Carrier gas: high-purity helium (the purity is more than or equal to 99.999%).
f) Mass spectrum data acquisition mode: selected ion scan mode (SIM), solvent delay time: and 8 min.
g) The quantitative and qualitative ion of the compounds are given in the following table:
wherein the content of the first and second substances,
the three herbicides in the step 1 are chloromethylquinolinic acid, dichloroquinolinic acid and imidazoquinolinic acid, the pH of the alkaline 10% aqueous solution is adjusted to 9.0 by using 0.01mol/L sodium hydroxide solution, the ultrasonic extraction time is 15min, and the adsorption oscillation time is 15 min.
The hydrochloric acid solution in the step 2 is prepared from concentrated hydrochloric acid and water according to the volume ratio of 1:1, and the dosage is 3.00 mL.
The amount of anhydrous sodium sulfate added in step 3 was 2.0g, and the organic extraction solvent was 5.00mL of ethyl acetate and all was used for derivatization.
The stop solution in the step 4 is the hydrochloric acid solution in the step 2, the addition amount is 0.05mL, the addition amount of solid sodium bicarbonate is 0.10g, the addition amount of anhydrous sodium sulfate is 1.0g, the filter membrane is an organic phase filter membrane, and the pore diameter is 0.22 μm.
In the above steps, the vortex is 1min to 2min, and the centrifugation is carried out for 3min at the rotating speed of 4500 rpm.
The method needs to be explained in the research and development process:
in the process of developing the method, three herbicides such as chloroquinolinic acid, quinclorac, imidazoquinolinic acid and the like have certain weak acidity and can be dissolved in alkaline aqueous solution. Therefore, the inventors selected an extraction solvent composed of water and acetonitrile which can be dissolved in water, based on the solubility characteristics of the target substance, in combination with the characteristics of the target substance which is soluble in an organic solvent and an aqueous alkaline solution. In the experiment, the optimum pH value range of the target substance adsorbed by the adsorbent is considered to be 4-9, so that the pH value of the extracting solution is adjusted to 9.0 by using 0.01mol/L sodium hydroxide solution, the extraction efficiency of the target substance by the extracting solvent is increased, and the co-extraction impurities are reduced.
Because different intercalation anions are used for modifying the LDHs material, the interlayer spacing of the material and the species of the intercalation ions are adjusted, so that when the LDHs material is used in the field of adsorbents, different modified LDHs are influenced by various factors such as the molecular size, the structure, the polarity and the functional groups of adsorbed targets to show different selective adsorption performances. In order to realize better adsorption effect on three targets, a plurality of developed LDHs and roasting product materials thereof are selected as adsorbents in experiments for carrying out adsorption performance screening; meanwhile, in order to enable the adsorbent to quickly and completely adsorb the target object, the using amount of the adsorbent is optimized according to the size of the sample amount in the experiment.
The inventors compared various derivatization methods such as methanol-sulfuric acid method, methanol-sodium hydroxide method, trimethylsilylated diazomethane method and the like in experiments, and found that the reaction conditions are mild by using the trimethylsilylated diazomethane method and the derivatization effect on three targets is best. But because the adsorbent of the invention achieves better purification effect, the invention does not carry out further solid phase extraction purification on the derivative product.
Meanwhile, in consideration of quantitative accuracy of the target object, the method quantifies the target object by adopting the matrix correction curve on the premise that the isotope of the target object cannot be obtained so as to quantify the target object by an isotope internal standard method, so that systematic errors are eliminated as much as possible, and the quantitative accuracy is improved.
The invention has the advantages that:
(1) the novel adsorbent 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adopted by the invention can rapidly adsorb trace amounts of residual chloromethylquinolinic acid, dichloroquinolinic acid and imidazoquinolinic acid in the extracting solution in a dispersed solid-phase extraction mode, and can save a large amount of adsorption time compared with a gel permeation chromatography and a solid-phase extraction mode of a standard method;
(2) according to the invention, by utilizing the characteristic that the 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent can be dissolved in acid, the adsorbent adsorbing the target object is dissolved by using a hydrochloric acid solution, so that the target object can be completely desorbed from the adsorbent;
(3) the method is only applicable to a small amount of organic solvent as the extraction solvent of the target object, and has obvious advantages of safety, environmental protection and economic advantages compared with the standard method and the literature report method which need to use a large amount of organic solvent.
Drawings
FIG. 1 is a chromatogram of a matrix standard solution of residual amounts of chloroquinolinic acid, quinclorac and imazaquin in one embodiment at a concentration of 500.0. mu.g/kg, wherein 1 is chloroquinolinic acid, 2 is quinclorac and 3 is imazaquin.
Detailed Description
For further disclosure, but not limitation, the present invention is described in further detail below with reference to examples.
(1) The reagent medicines involved in the embodiments of the present invention are as follows:
the solid standard products of the three compounds, namely chloroquinolinic acid, quinclorac and imidazoquinolinic acid, have the purity of more than or equal to 98.0 percent and are prepared by Dr.Ehrenstontorfer GmbH science and technology Co., Ltd, Germany;
methanol, ethyl acetate, acetonitrile, anhydrous sodium sulfate, sodium hydroxide, sodium bicarbonate, analytically pure, group of Chinese medicines;
hydrochloric acid, super pure, group of national medicine; the water is first-grade water meeting the GB/T6682 specification.
Trimethylsilyldiazomethane solution, 2.0M in hexane, Alfa Aesar.
The rice and soybean samples used in the experiment are purchased from Fuqing local supermarket, ground, sieved by a 60-mesh sieve, sealed, stored at 4 ℃, taken out before use and warmed to room temperature.
(2) The instruments involved in the examples of the present invention are as follows:
KH-75A type electric heating constant temperature air-blast drying oven, Kangheng instruments ltd, Guangzhou;
model 7890B-5977C gas chromatography-Mass Spectrometry spectrometer, Agilent technologies, Inc., USA.
(3) Analysis and test conditions of a gas chromatograph:
a) a chromatographic column: DB-5MS capillary column, 30m × 0.25mm, 0.25 μm thick; column flow rate: 1.50 mL/min.
b) Sample inlet temperature: 260 ℃; and (3) sample introduction mode: no shunt sampling; sample introduction amount: 2 μ L.
c) Temperature rising procedure: 40 deg.C (1 min hold), 20 deg.C/min to 260 deg.C (4 min hold), 10 deg.C/min to 280 deg.C (8 min hold).
d) EI bombardment source: 70 ev; temperature of a chromatography-mass spectrometry connection port: 280 ℃; temperature of the quadrupole rods: 230 ℃; ion source temperature: at 150 ℃.
e) Carrier gas: high-purity helium (the purity is more than or equal to 99.999%).
f) Mass spectrum data acquisition mode: selected ion scan mode (SIM), solvent delay time: and 8 min.
g) The quantitative and qualitative ion of the compounds are given in the following table:
| serial number | Name of Compound | Quantitative ion | Qualitative ion |
| 1 | Chloroquinolinic acid derivatives | 204.1 | 177.0，235.0 |
| 2 | Quinclorac derivatives | 224.0 | 226.0，197.0 |
| 3 | Imidazoquinolinic acid derivatives | 227.1 | 297.1，296.1 |
(4) Preparation of matrix calibration curve and determination of detection limit and quantitative limit
Accurately weighing the chloromethylquinolinic acid, the dichloroquinolinic acid and the imidazoquinolinic acid, dissolving the chloromethylquinolinic acid, the dichloroquinolinic acid and the imidazoquinolinic acid by using methanol to fix the volume, and preparing a standard stock solution with the concentration of 1000mg/L for storage at-4 ℃. When in use, the standard stock solution is gradually diluted by deionized water to prepare standard use solution with the concentration gradient of 10.0 mug/L, 20.0 mug/L, 40.0 mug/L, 100.0 mug/L and 200.0 mug/L.
Weighing 5.00g of a blank sample in five 50mL centrifuge tubes with plugs, adding 5.00mL of the standard use solution respectively to prepare a matrix calibration curve with a series of concentrations, adding 20mL of alkaline 10% acetonitrile aqueous solution with pH of 9 into the centrifuge tubes, sealing, vortexing, ultrasonically extracting for 15min, centrifuging, transferring the supernatant into another 50mL plastic centrifuge tube with a plug, re-extracting once, and combining the extracting solutions; adding 10mL of n-hexane into a centrifugal tube, oscillating, centrifuging, removing supernatant, adding 0.50g of 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent into the centrifugal tube, sealing, swirling, oscillating for a certain time to enable the adsorbent to adsorb a target compound in the extracting solution;
centrifuging the centrifuge tube with the plug, removing supernatant, adding 3.00mL of hydrochloric acid solution (prepared by concentrated hydrochloric acid and water according to the volume ratio of 1: 1) to dissolve the solid adsorbent, and finishing desorption of the adsorbed compound;
adding 2.0g of anhydrous sodium sulfate and 5.00mL of ethyl acetate into the centrifuge tube, extracting, swirling, centrifuging, separating supernatant into derivative bottles, adding 0.40mL of methanol and 0.2mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L, controlling the water bath temperature at 50 ℃ and the derivatization time at 30 min;
0.05mL of hydrochloric acid solution (concentrated hydrochloric acid and water at a volume ratio of 1: 1) was added to the derivatization flask to remove excess derivatization agent, 0.10g of solid sodium bicarbonate and 1.0g of anhydrous sodium sulfate were added, vortexed, and after standing, the upper organic solution was aspirated, filtered through a 0.22 μm organic phase filter and analyzed using gas chromatography-mass spectrometry.
And (3) taking the concentration of the quinolinic acid herbicide in the sample solution as an X axis, and taking the chromatographic peak area of the quinolinic acid herbicide derivative on a gas chromatograph as a Y axis to draw a matrix standard curve and use the matrix standard curve for quantification by an external standard method.
The triple value of the signal-to-noise ratio S/N is taken as the detection limit of the method (LOD, LOD is 3S/N), the ten times of the signal-to-noise ratio S/N is taken as the quantification limit of the method (LOQ, LOQ is 10S/N), and the detection limit and the quantification limit of each compound in water are calculated by combining the volume of the added matrix.
The relevant parameters of the matrix standard curve, LOD and LOQ are shown in Table 1.
TABLE 1 residual amount of trace chloroquinolinic acid, quinclorac and imazaquin
Information relating to standard curves, detection limits and quantification limits
(5) Synthesis of 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent
In order to enable those skilled in the art to repeatedly carry out the relevant experiments of the present invention, a method for synthesizing the key substance 2-naphthalenesulfonate-magnesium aluminum type hydrotalcite adsorbent used in the present invention is now provided, as follows:
the reagent and the drug related to the synthesis of the adsorbent are as follows:
2-sodium naphthalenesulfonate, analytically pure, shanghai shao reagent limited;
Mg6Al2(OH)16CO3·4H2o, analytical grade, Aldrich, usa.
② the apparatus related to the synthesis of the adsorbent is as follows:
an EXCEL type microwave digestion instrument, Shanghai Yao Instrument science and technology development Co., Ltd., digestion tank volume of 100 mL; microwave muffle furnace (sintering furnace), CEM corporation, usa; model VD53 vacuum drying cabinet, German Bindd technologies; HJ-5 multifunctional constant temperature stirrer, Kantai Ronghua Instrument manufacturing Co., Ltd; FS-12 type separatory funnel oscillator, New optical technology, Japan; 3K-15 type centrifuge, sigma technologies, germany; BF518945C-1 model box resistance furnace (muffle furnace), Saimer Feishell science, USA.
The concrete steps of synthesizing the adsorbent are as follows:
(a) roasting: mg of purchased Mg-Al type hydrotalcite6Al2(OH)16CO3·4H2Placing O in a muffle furnace, heating at a heating rate of 5 ℃/min to 500 ℃, and roasting for 6h to obtain Mg6Al2O8(OH)2；
(b) Weighing: 13.812g of intercalation agent 2-sodium naphthalenesulfonate and 7.236g of Mg are weighed in a microwave digestion tank6Al2O8(OH)2。
(c) Microwave crystallization hydrothermal synthesis: boiling deionized water and keeping for 30min, then adding 60mL into the microwave digestion tank filled with the intercalator, sealing, placing the microwave digestion tank into a microwave digestion instrument, and carrying out microwave heating for 30min at 130-150 ℃ to complete synthesis;
(d) washing and drying: pouring out all solids and liquid in the microwave tank, heating and stirring with deionized water boiled for more than 30min to remove carbon dioxide, shaking, washing, centrifuging, vacuum drying at 90 deg.C for 12h, grinding, and storing.
Example 1
In this example 1, a rice blank sample matrix was used to perform a spiking recovery experiment to verify the feasibility of the method of the present invention, and the processing was performed according to the following steps:
1. extraction and adsorption of the compound:
weighing 5.00g of a blank sample in a 50mL centrifuge tube with a plug, adding 5.00mL of three compound standard solutions with the concentrations of 10.0 mu g/L, 20.0 mu g/L and 200.0 mu g/L respectively to prepare a three-level six-parallel standard sample, adding 20mL of alkaline 10% acetonitrile aqueous solution with the pH of 9 into the centrifuge tube, sealing and vortexing, ultrasonically extracting for 15min, centrifuging, transferring the supernatant into another 50mL plastic centrifuge tube with a plug, re-extracting once, and combining the extracting solutions; adding 10mL of n-hexane into a centrifugal tube, oscillating, centrifuging, removing supernatant, adding 0.50g of 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent into the centrifugal tube, sealing, swirling, oscillating for a certain time to enable the adsorbent to adsorb a target compound in the extracting solution;
2. desorption of the compound:
centrifuging the centrifuge tube with the plug, removing supernatant, adding 3.00mL of hydrochloric acid solution (prepared by concentrated hydrochloric acid and water according to the volume ratio of 1: 1) to dissolve the solid adsorbent, and finishing desorption of the adsorbed compound;
3. extraction and derivatization of compounds:
adding 2.0g of anhydrous sodium sulfate and 5.00mL of ethyl acetate into the centrifuge tube, extracting, swirling, centrifuging, separating supernatant into derivative bottles, adding 0.40mL of methanol and 0.2mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L, controlling the water bath temperature at 50 ℃ and the derivatization time at 30 min;
4. analysis and test:
0.05mL of hydrochloric acid solution (concentrated hydrochloric acid and water at a volume ratio of 1: 1) was added to the derivatization flask to remove excess derivatization agent, 0.10g of solid sodium bicarbonate and 1.0g of anhydrous sodium sulfate were added, vortexed, and after standing, the upper organic solution was aspirated, filtered through a 0.22 μm organic phase filter and analyzed using gas chromatography-mass spectrometry.
The parameters relevant to the spiking recovery experiment of example 1 are shown in Table 2.
TABLE 2 Rice sample add-on concentration and recovery test data (n ═ 6)
Example 2
In this example 2, a blank sample matrix of soybean was used to perform a spiking recovery experiment to verify the feasibility of the method of the present invention, and the processing was performed according to the following steps:
1. extraction and adsorption of the compound:
weighing 5.00g of a blank sample in a 50mL centrifuge tube with a plug, adding 5.00mL of three compound standard solutions with the concentrations of 10.0 mu g/L, 20.0 mu g/L and 200.0 mu g/L respectively to prepare a three-level six-parallel standard sample, adding 20mL of alkaline 10% acetonitrile aqueous solution with the pH of 9 into the centrifuge tube, sealing and vortexing, ultrasonically extracting for 15min, centrifuging, transferring the supernatant into another 50mL plastic centrifuge tube with a plug, re-extracting once, and combining the extracting solutions; adding 10mL of n-hexane into a centrifugal tube, oscillating, centrifuging, removing supernatant, adding 0.50g of 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent into the centrifugal tube, sealing, swirling, oscillating for a certain time to enable the adsorbent to adsorb a target compound in the extracting solution;
2. desorption of the compound:
centrifuging the centrifuge tube with the plug, removing supernatant, adding 3.00mL of hydrochloric acid solution (prepared by concentrated hydrochloric acid and water according to the volume ratio of 1: 1) to dissolve the solid adsorbent, and finishing desorption of the adsorbed compound;
3. extraction and derivatization of compounds:
adding 2.0g of anhydrous sodium sulfate and 5.00mL of ethyl acetate into the centrifuge tube, extracting, swirling, centrifuging, separating supernatant into derivative bottles, adding 0.40mL of methanol and 0.2mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L, controlling the water bath temperature to be 30 ℃ and the derivatization time to be 30 min;
4. analysis and test:
0.05mL of hydrochloric acid solution (concentrated hydrochloric acid and water at a volume ratio of 1: 1) was added to the derivatization flask to remove excess derivatization agent, 0.10g of solid sodium bicarbonate and 1.0g of anhydrous sodium sulfate were added, vortexed, and after standing, the upper organic solution was aspirated, filtered through a 0.22 μm organic phase filter and analyzed using gas chromatography-mass spectrometry.
The parameters relevant to the spiking recovery experiment of example 2 are shown in Table 3.
TABLE 3 Rice sample add-on concentration and recovery Experimental data (n ═ 6)
The above-mentioned embodiments only express the embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the spirit of the invention, which falls within the scope of the invention, and therefore the scope of the patent of the invention shall be governed by the appended claims.
Claims (6)
1. A gas chromatography-mass spectrometry combination method for simultaneously determining three trace quinoline herbicides in rice and soybean is characterized by comprising the following steps:
(1) extraction and adsorption of the compounds: crushing rice and soybean samples, sieving the crushed rice and soybean samples with a 60-mesh sieve, sealing and storing the crushed rice and soybean samples, weighing 5.00g of the samples in a plastic centrifuge tube with a plug when in use, adding 20mL of alkaline 10% acetonitrile aqueous solution into the centrifuge tube, sealing and whirling the centrifuge tube, performing ultrasonic extraction, centrifuging the centrifuge tube, transferring supernatant into another plastic centrifuge tube with a plug, re-extracting the supernatant once, and combining the extracted solution; adding 10mL of n-hexane into a centrifugal tube, oscillating, centrifuging, removing supernatant, adding 0.5g of 2-naphthalenesulfonate-magnesium-aluminum type hydrotalcite adsorbent into the centrifugal tube, sealing, vortexing, and oscillating for a certain time to make the adsorbent adsorb chloroquinolinic acid, dichloroquinolinic acid and imidazoquinolinic acid in the extracting solution;
(2) desorption of the compound: centrifuging the plastic centrifuge tube with the plug, discarding supernatant, adding a certain amount of hydrochloric acid solution to dissolve the solid adsorbent, and finishing desorption of the adsorbed compound;
(3) extraction and derivatization of compounds: adding a certain amount of anhydrous sodium sulfate and an organic solvent into the centrifuge tube for extraction, performing vortex and centrifugation, separating supernatant into a derivative bottle, adding 0.40mL of methanol and 0.20mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2mol/L, performing water bath at the temperature of 30-50 ℃, and performing derivatization for 30 min;
(4) analytical testing of compounds: adding a stop solution into a derivatization bottle to remove redundant derivatization agents, adding a proper amount of solid sodium bicarbonate and anhydrous sodium sulfate, vortexing, absorbing an upper organic solution, filtering, and performing analytical test by using a gas chromatography-mass spectrometry method according to the following conditions:
a) a chromatographic column: DB-5MS capillary column, 30m × 0.25mm, 0.25 μm thick; column flow rate: 1.50 mL/min;
b) sample inlet temperature: 260 ℃; and (3) sample introduction mode: no shunt sampling; sample introduction amount: 2 mu L of the solution;
c) temperature rising procedure: maintaining at 40 deg.C for 1min, heating to 260 deg.C at 20 deg.C/min, maintaining for 4min, heating to 280 deg.C at 10 deg.C/min, and maintaining for 8 min;
d) EI bombardment source: 70 ev; temperature of a chromatography-mass spectrometry connection port: 280 ℃; temperature of the quadrupole rods: 230 ℃; ion source temperature: 150 ℃;
e) carrier gas: high-purity helium with the purity more than or equal to 99.999 percent;
f) mass spectrum data acquisition mode: selection of ion scan mode, solvent delay time: 8 min;
g) the quantitative and qualitative ion of the compounds are given in the following table:
。
2. The gas chromatography-mass spectrometry combination for simultaneously determining three trace quinoline herbicides in rice and soybean as claimed in claim 1, wherein the alkaline 10% acetonitrile aqueous solution in step (1) is adjusted to pH 9.0 with 0.01mol/L sodium hydroxide solution, the ultrasonic extraction time is 15min, and the adsorption oscillation time is 15 min.
3. The gas chromatography-mass spectrometry combination for simultaneously determining three trace quinoline herbicides in rice and soybean as claimed in claim 1, wherein the hydrochloric acid solution in step (2) is prepared by concentrated hydrochloric acid and water according to a volume ratio of 1:1, and the dosage is 3.00 mL.
4. The gas chromatography-mass spectrometry combination for simultaneously determining three trace quinoline herbicides in rice and soybean as claimed in claim 1, wherein the anhydrous sodium sulfate added in step (3) is 2.0g, and the organic extraction solvent is 5.00mL of ethyl acetate.
5. The gas chromatography-mass spectrometry combination for simultaneously measuring three trace quinoline herbicides in rice and soybean as claimed in claim 1, wherein the stop solution in step (4) is hydrochloric acid solution, the addition amount is 0.05mL, the addition amount of solid sodium bicarbonate is 0.10g, the addition amount of anhydrous sodium sulfate is 1.0g, the filter membrane for filtration is an organic phase filter membrane, and the pore diameter is 0.22 μm.
6. The gas chromatography-mass spectrometry combination for simultaneously measuring three trace quinoline herbicides in rice and soybean as claimed in claim 1, wherein the vortex is 1min to 2min and the centrifugation is 3min at 4500 rpm.
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