CN109212071B - Gas chromatography for determining trace ethephon in pears - Google Patents

Gas chromatography for determining trace ethephon in pears Download PDF

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CN109212071B
CN109212071B CN201811117961.5A CN201811117961A CN109212071B CN 109212071 B CN109212071 B CN 109212071B CN 201811117961 A CN201811117961 A CN 201811117961A CN 109212071 B CN109212071 B CN 109212071B
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ethephon
gas chromatography
derivatization
adsorbent
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CN109212071A (en
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丁立平
张睿
蔡春平
郑麟毅
姜晖
郑铃
郑香平
黄菁菁
陈志涛
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Integrated Technical Service Center Fuqing Enty-Exit Inspection & Quarantine Bureau
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Abstract

The invention relates to a method for analyzing and detecting trace harmful substances, in particular to a gas chromatography for determining trace ethephon in pears. The method comprises the steps of crushing a sample, extracting with deionized water, enriching a target compound in an extracting solution by using a novel adsorbent nitrate-magnesium-aluminum type hydrotalcite, dissolving the adsorbent by using an acid to realize complete elution of the target compound, extracting the compound with a small amount of organic solvent at high efficiency, and performing rapid analysis and determination by using a gas chromatography after derivatization. The novel adsorbent adopted by the method realizes the rapid and efficient adsorption of the target object by adopting a dispersed solid phase extraction mode; the complete desorption of the target can be realized by using the acid to dissolve the adsorbent; the deionized water is used for extraction and dissolution, and only a small amount of organic solvent is used for extraction, so that the method has the advantages of safety, environmental protection and economic advantage.

Description

Gas chromatography for determining trace ethephon in pears
Technical Field
The invention relates to a method for analyzing and detecting harmful trace substances, in particular to a gas chromatography for determining trace ethephon in pears.
Background
Ethephon is a low-toxicity fruit ripener, but a high concentration of ethephon and a long-lasting intake also have certain influence on the reproductive system of animals. On 29.9.2017, regulation No. 2017/1777 issued by the European Commission (EU) specifies the maximum residual limit of ethephon in various fruits, wherein the maximum residual limit of ethephon in pears is 0.05mg/kg, and the requirement is strict.
At present, the main method for detecting trace amount of ethephon in fruits is gas chromatography, wherein the main principle of the headspace gas chromatography detection method for ethephon in food is that after alkali liquor is added into a sample, the sample is heated at constant temperature, ethephon is rapidly decomposed into ethylene gas in an alkaline medium, the upper layer gas in a headspace bottle is sucked, and a GC-FID detector is used for detection. The method has two problems in detection, namely, the target substance is decomposed into ethylene by using alkali, the ethylene is detected, and the compound which is decomposed into the ethylene by the alkali is probably not ethephon, so that a false positive result is caused; secondly, the gas chromatograph is used for analysis, and the gas chromatograph equipped with headspace sampling has low popularity, thereby objectively limiting the application of the method.
Layered Double Hydroxide (LDHs) is a typical Layered material with a supramolecular intercalation structure, and is mainly composed of positively charged laminates formed by combining Hydroxides of divalent and trivalent metals and negatively charged anions intercalated between the laminates. Two notable features of this material are: space adjustability between the laminate layers and replaceability of the intercalated anions. Based on the method, people can modify the LDHs material according to the difficulty of replaceability of intercalation anions of the LDHs material and the adjustability of the distance between the layers, and then select different types of intercalation anions according to the requirements of practical application to modify the material to obtain a functional material with novel application.
In the field of LDHs materials used as adsorbents, different intercalation anions can be selected to synthesize different types of modified LDHs materials according to various factors such as molecular size, structure, polarity, functional groups and the like of adsorbed targets. The modified LDHs materials have different interlayer spacing, so that the modified LDHs materials have the adsorption selection effect of limiting the molecules of a specific target substance to enter the interlayer; meanwhile, the modified material intercalation anions have different replacement difficulty degrees, so that the modified material intercalation anions show different adsorption selectivity on different targets. Therefore, in practical application, the adsorption effect of different LDHs materials on a specific kind of target needs to be selected, verified and optimized through adsorption experiments.
The inventor carries out adsorption experiments on ethephon in water by using various modified magnesium-aluminum type hydrotalcite adsorbents in previous researches, and the results show that the nitrate-magnesium-aluminum type hydrotalcite adsorbents have good adsorption effects on target objects. On the basis, the inventor further optimizes the performance and application method of the developed adsorbent for enriching the target compound, and establishes the gas chromatography for detecting trace ethephon in pears by taking nitrate-magnesium-aluminum type hydrotalcite as the adsorbent.
In the process of research and development of the method, the inventor researches and optimizes the consumption of the adsorbent, the selection and the proportion of the extraction solvent, the selection and the optimization of a target substance derivatization method, the selection and the optimization of chromatographic separation conditions and other factors according to the characteristics of the adsorption target substance, and provides a relatively excellent detection method on the basis. 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.
Disclosure of Invention
In order to overcome the defects of false positive results possibly occurring in the detection of ethephon in food by the existing headspace gas chromatography and low equipment popularity, the invention aims to solve the technical problem of providing the gas chromatography which is based on the novel adsorbent, dispersed solid phase extraction and rapid adsorption and is suitable for detecting trace ethephon in pears.
Since ethephon contains phosphorus (P) element, a Flame Photometric Detector (FPD) -gas chromatograph equipped with a phosphorus filter having specific intensity can be selected for analysis.
The invention achieves the above object by the following technical means.
A gas chromatography method for measuring trace ethephon in pears is characterized by comprising the following steps:
adsorption of the compound of step 1: taking an edible part of pear, stirring the edible part into a paste, weighing a proper amount of sample in a 50mL plastic centrifuge tube with a plug, taking deionized water as an extracting solution, homogenizing and extracting at a high speed, centrifuging, taking supernate to another 50mL plastic centrifuge tube with a plug, adding 0.40g of nitrate-magnesium-aluminum type hydrotalcite adsorbent into the supernate, and oscillating for a certain time to enable the adsorbent to adsorb a target compound in water;
step 2 desorption of compound: centrifuging the centrifuge tube with the plug to separate the solid adsorbent from the water solution and discard the supernatant, adding a certain amount of hydrochloric acid solution to dissolve the solid adsorbent, and finishing desorption of the adsorbed compound;
step 3, extraction and derivatization of compounds: adding a certain amount of anhydrous sodium sulfate and an organic solvent into the centrifugal tube for extraction, performing vortex and centrifugation, taking supernatant liquid to a derivatization bottle, adding a derivatization reagent into the supernatant liquid, sealing, uniformly mixing, and putting the mixture in a constant-temperature water bath to finish the derivatization process;
analytical testing of the compound of step 4: adding a stop solution into the derivatization bottle to remove redundant derivatization reagent, adding a proper amount of solid sodium bicarbonate and anhydrous sodium sulfate, vortexing, sucking the upper organic solution, filtering, and then carrying out analytical test by using a gas chromatography.
Wherein the content of the first and second substances,
the sample weighing amount of the pears in the step 1 is 5.00g, the amount of deionized water added for extraction is 30mL, the speed of high-speed homogenizing is 15000rpm, the time is 1.0min, and the time of shaking adsorption is 10 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 1.00 mL.
In the step 3, 2.0g of anhydrous sodium sulfate, 5mL of ethyl acetate as an organic extraction solvent, 0.2mL of methanol as a derivatization reagent and 0.1mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L are added, the water bath temperature is 50 ℃, and the derivatization time is 30 min.
The stop solution in the step 4 is the hydrochloric acid solution in the claim 3, the addition amount is 0.05mL, the addition amount of solid sodium bicarbonate is 0.1g, the addition amount of anhydrous sodium sulfate is 0.5g, 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 analytical test conditions for gas chromatography used for the determination were:
a) a chromatographic column: DB1701 thin tube column, 30m multiplied by 0.32mm, 0.25 μm film thickness; constant flow mode, column flow rate: 2.50 mL/min.
b) Sample inlet temperature: 220 ℃; and (3) sample introduction mode: no shunt sampling; sample introduction amount: 2 μ L.
c) Temperature rising procedure: 70 deg.C (1 min hold), heating to 160 deg.C at a rate of 10 deg.C/min (1 min hold), and heating to 250 deg.C at a rate of 25 deg.C/min (1 min hold).
d) A detector: flame Photometric Detector (FPD), temperature: at 250 ℃ to obtain a mixture.
e) Detector gas and flow rate: high-purity hydrogen (the purity is more than or equal to 99.999 percent) and 75 mL/min; high-purity air (the purity is more than or equal to 99.999 percent) and 100 mL/min; gas carrying and tail blowing: high-purity nitrogen (purity is more than or equal to 99.999%), tail gas blowing flow: 60 mL/min.
The invention has the advantages that:
(1) the novel adsorbent nitrate radical-magnesium-aluminum type hydrotalcite adopted by the invention can quickly adsorb trace amount of ethephon in pear extracting solution by adopting a dispersed solid phase extraction mode, thereby realizing the purpose of high-efficiency and quick enrichment of target substances;
(2) according to the invention, by utilizing the characteristic that the nitrate radical-magnesium aluminum type hydrotalcite adsorbent can be dissolved in acid, the hydrochloric acid solution is used for dissolving the adsorbent after adsorbing the target object, so that the target object can be completely desorbed from the adsorbent;
(3) the invention takes deionized water as an extraction solvent and only uses a small amount of organic solvent as the extraction solvent of the target object, and has the advantages of safety, environmental protection and economic advantage.
Drawings
FIG. 1 is a chromatogram of a matrix standard solution of ethephon in a concentration of 200.0. mu.g/L, wherein 1 is ethephon, according to an embodiment.
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:
ethephon solid standard with purity of 98.0% or more, Shanghai Aladdin Biotechnology GmbH;
methanol, ethyl acetate, anhydrous sodium sulfate, 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.
(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 gas chromatograph equipped with a Flame Photometric Detector (FPD), Agilent technologies, Inc. of America.
(3) Analysis and test conditions of a gas chromatograph:
a) a chromatographic column: DB1701 thin tube column, 30m multiplied by 0.32mm, 0.25 μm film thickness; constant flow mode, column flow rate: 2.50 mL/min.
b) Sample inlet temperature: 220 ℃; and (3) sample introduction mode: no shunt sampling; sample introduction amount: 2 μ L.
c) Temperature rising procedure: 70 deg.C (1 min hold), heating to 160 deg.C at a rate of 10 deg.C/min (1 min hold), and heating to 250 deg.C at a rate of 25 deg.C/min (1 min hold).
d) A detector: flame photometric detector, temperature: at 250 ℃ to obtain a mixture.
e) Detector gas and flow rate: high-purity hydrogen (the purity is more than or equal to 99.999 percent) and 75 mL/min; high-purity air (the purity is more than or equal to 99.999 percent) and 100 mL/min; gas carrying and tail blowing: high-purity nitrogen (purity is more than or equal to 99.999%), tail gas blowing flow: 60 mL/min.
(4) Preparation of matrix calibration curve and determination of detection limit and quantitative limit
Accurately weighing the ethephon standard substance, dissolving with methanol to constant volume, and making into standard stock solution with concentration of 1000mg/L, and storing at-4 deg.C. 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.
Taking five 50mL centrifuge tubes with plugs, weighing 5.00g of mud samples of white pears respectively, adding 5.00mL of the standard use solution into the centrifuge tubes respectively, adding 30mL of deionized water, homogenizing at 15000rpm for 1min, centrifuging at 4500rpm for 3min, pouring the supernatant into another 50mL centrifuge tube with plugs, adding 0.40g of nitrate-magnesium-aluminum type hydrotalcite adsorbent into the centrifuge tube, and shaking for 10min to adsorb the adsorbent; centrifuging a 50mL centrifuge tube with a plug at 4500rpm for 3min to separate the solid adsorbent from the aqueous solution and discard the supernatant, adding 2.00mL of 1-time diluted hydrochloric acid solution, and realizing desorption of the adsorbed target after the solid adsorbent is dissolved; adding 2.0g of anhydrous sodium sulfate into the centrifuge tube, adding 5.0mL of ethyl acetate, whirling for 1min, centrifuging at the rotating speed of 4500rpm for 3min, separating the supernatant into a derivatization bottle, adding 0.2mL of methanol and 0.1mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L, sealing, uniformly mixing, standing in a water bath at 50 ℃ for derivatization for 30min, and finishing the derivatization process; adding 0.05mL of the above hydrochloric acid solution to the above derivatization bottle to remove excess trimethylsilylated diazomethane, then adding 0.1g of solid sodium bicarbonate and 0.5g of anhydrous sodium sulfate, vortexing to remove the remaining hydrochloric acid and water, and sucking the upper organic solution through an organic phase filter with a pore size of 0.22 μm, followed by analysis and testing by gas chromatography.
And (3) taking the concentration of ethephon in the sample solution as an X axis and the peak area of the chromatographic peak of ethephon on a gas chromatograph as a Y axis to draw a matrix standard curve and use the matrix standard curve for external standard method quantification.
The detection limit and the quantification limit of each compound in the pear are calculated by taking the triple value of the signal-to-noise ratio S/N as the detection limit of the method (LOD, LOD is 3S/N), taking the ten times of the signal-to-noise ratio S/N as the quantification limit of the method (LOQ, LOQ is 10S/N) and 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 information relating to ethephon matrix standard curves, detection limits and quantitation limits
Figure BDA0001809319550000051
(5) Synthesis of nitrate-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 a nitrate-magnesium-aluminum type hydrotalcite adsorbent, which is a key substance 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:
sodium nitrate, analytically pure, group of national drugs;
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 a roasted product Mg6Al2O8(OH)2；
(b) Weighing: weighing 0.06mol of intercalation agent sodium nitrate and 0.02mol of roasting product Mg in a microwave digestion tank6Al2O8(OH)2。
(c) Microwave crystallization hydrothermal synthesis: boiling deionized water and keeping for 30min, adding 100mL into the microwave digestion tank filled with the intercalation agent and the roasting product, sealing, placing the microwave digestion tank into a microwave digestion instrument, and performing microwave heating at 150 ℃ for 30min 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, white pears were used as a sample matrix 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. adsorption of the compound:
taking 5.00g of a muddy sample, respectively taking 5.00mL of the standard use solution, adding 30mL of deionized water, homogenizing at 15000rpm for 1min, centrifuging at 4500rpm for 3min, pouring the supernatant into another 50mL centrifuge tube with a plug, adding 0.40g of nitrate-magnesium-aluminum type hydrotalcite adsorbent into the centrifuge tube, and shaking for 10min to adsorb the adsorbent;
2. desorption of the compound:
centrifuging a 50mL centrifuge tube with a plug at 4500rpm for 3min to separate the solid adsorbent from the aqueous solution and discard the supernatant, adding 2.00mL of 1-time diluted hydrochloric acid solution, and realizing desorption of the adsorbed target after the solid adsorbent is dissolved;
3. extraction and derivatization of compounds:
adding 2.0g of anhydrous sodium sulfate into the centrifuge tube, adding 5.00mL of ethyl acetate, whirling for 1min, centrifuging at the rotating speed of 4500rpm for 3min, taking the supernatant into a derivatization bottle, adding 0.2mL of methanol and 0.1mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L, sealing, uniformly mixing, standing in a water bath at 50 ℃ for derivatization for 30min, and finishing the derivatization process;
4. analysis and test:
to the above derivatization bottle was added 0.05mL of the above hydrochloric acid solution to remove excess trimethylsilylated diazomethane, followed by addition of 0.1g of solid sodium bicarbonate, 0.5g of anhydrous sodium sulfate, vortexing, and the upper organic solution was drawn up through an organic phase filter having a pore size of 0.22 μm and analyzed by gas chromatography.
The parameters relevant to the spiking recovery experiment of example 1 are shown in Table 2.
TABLE 2 Experimental data for the addition concentration and recovery rate of white pear samples (n ═ 6)
Figure BDA0001809319550000061
Example 2
In this example 2, a Huanghua pear sample matrix is used for a labeling recovery experiment to verify the feasibility of the method, and the method is processed according to the following steps:
1. adsorption of the compound:
taking 5.00g of a muddy sample, respectively taking 5.00mL of the standard use solution, adding 30mL of deionized water, homogenizing at 15000rpm for 1min, centrifuging at 4500rpm for 3min, pouring the supernatant into another 50mL centrifuge tube with a plug, adding 0.40g of nitrate-magnesium-aluminum type hydrotalcite adsorbent into the centrifuge tube, and shaking for 10min to adsorb the adsorbent;
2. desorption of the compound:
centrifuging a 50mL centrifuge tube with a plug at 4500rpm for 3min to separate the solid adsorbent from the aqueous solution and discard the supernatant, adding 2.00mL of 1-time diluted hydrochloric acid solution, and realizing desorption of the adsorbed target after the solid adsorbent is dissolved;
3. extraction and derivatization of compounds:
adding 2.0g of anhydrous sodium sulfate into the centrifuge tube, adding 5.00mL of ethyl acetate, whirling for 1min, centrifuging at the rotating speed of 4500rpm for 3min, taking the supernatant into a derivatization bottle, adding 0.2mL of methanol and 0.1mL of trimethylsilylated diazomethane n-hexane solution with the concentration of 2moL/L, sealing, uniformly mixing, standing in a water bath at 50 ℃ for derivatization for 30min, and finishing the derivatization process;
4. analysis and test:
to the above derivatization bottle was added 0.05mL of the above hydrochloric acid solution to remove excess trimethylsilylated diazomethane, followed by addition of 0.1g of solid sodium bicarbonate, 0.5g of anhydrous sodium sulfate, vortexing, and the upper organic solution was drawn up through an organic phase filter having a pore size of 0.22 μm and analyzed by gas chromatography.
The parameters relevant to the spiking recovery experiment of example 2 are shown in Table 3.
TABLE 3 Experimental data on the addition concentration and recovery rate of white pear samples (n ═ 6)
Figure BDA0001809319550000071
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 method for measuring trace ethephon in pears is characterized by comprising the following steps:
(1) adsorption of the compound: taking an edible part of pear, stirring the edible part into a paste, weighing a proper amount of sample in a 50mL plastic centrifuge tube with a plug, homogenizing and extracting the paste at a high speed by taking deionized water as an extracting solution, centrifuging the paste, taking supernate to another 50mL plastic centrifuge tube with a plug, adding 0.40g of nitrate-magnesium-aluminum type hydrotalcite adsorbent into the supernate, and oscillating the mixture for a certain time to enable the adsorbent to adsorb a target compound in water;
(2) desorption of the compound: centrifuging the plastic centrifuge tube with the plug to separate the solid adsorbent from the aqueous solution and discard the supernatant, adding a certain amount of hydrochloric acid solution into the centrifugal tube 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 centrifugal tube for extraction, performing vortex and centrifugation, taking supernatant liquid to a derivatization bottle, adding a derivatization reagent into the supernatant liquid, sealing, uniformly mixing, and putting the mixture in a constant-temperature water bath to finish the derivatization process;
(4) analytical testing of compounds: adding a stop solution into a derivatization bottle to remove excessive derivatization agent, adding a proper amount of solid sodium bicarbonate and anhydrous sodium sulfate, vortexing, sucking an upper organic solution, filtering, and performing analytical test by using a gas chromatography according to the following conditions:
a) a chromatographic column: DB1701 thin tube column, 30m multiplied by 0.32mm, 0.25 μm film thickness; constant flow mode, column flow rate: 2.50 mL/min;
b) sample inlet temperature: 220 ℃; and (3) sample introduction mode: no shunt sampling; sample introduction amount: 2 mu L of the solution;
c) temperature rising procedure: maintaining at 70 deg.C for 1min, heating to 160 deg.C at a rate of 10 deg.C/min, maintaining for 1min, heating to 250 deg.C at a rate of 25 deg.C/min, and maintaining for 1 min;
d) a detector: flame photometric detector, temperature: 250 ℃;
e) detector gas and flow rate: high-purity hydrogen with the purity of more than or equal to 99.999 percent and 75 mL/min; high-purity air with the purity of more than or equal to 99.999 percent and 100 mL/min; gas carrying and tail blowing: high-purity nitrogen with the purity more than or equal to 99.999 percent, and the tail gas blowing flow: 60 mL/min.
2. The gas chromatography method for measuring the trace ethephon in the pears as claimed in claim 1, wherein the pear in step (1) is weighed to be 5.00g, the amount of deionized water added for extraction is 30mL, the speed of high-speed homogenization is 15000rpm, the time is 1.0min, and the time of shaking adsorption is 10 min.
3. The gas chromatography method for determining the trace ethephon in the pears as claimed in claim 1, wherein the hydrochloric acid solution in the step (2) is prepared by concentrated hydrochloric acid and water according to a volume ratio of 1:1, and the dosage is 2.0 mL.
4. The gas chromatography method for measuring trace ethephon in pears as claimed in claim 1, wherein the anhydrous sodium sulfate added in step (3) is 2.0g, the organic extraction solvent is 5.00mL ethyl acetate, the derivatization reagent is 0.2mL methanol and 0.1mL trimethylsilyl diazomethane n-hexane solution with concentration of 2moL/L, the water bath temperature is 50 ℃, and the derivatization time is 30 min.
5. The gas chromatography method for measuring the trace ethephon in the pear as claimed in claim 1, wherein the stop solution in the step (4) is hydrochloric acid solution, the addition amount is 0.05mL, the addition amount of solid sodium bicarbonate is 0.1g, the addition amount of anhydrous sodium sulfate is 0.5g, the filter membrane for filtration is an organic phase filter membrane, and the pore diameter is 0.22 μm.
6. The gas chromatography method for detecting the trace ethephon in the pears as claimed in claim 1, wherein the vortexing is performed for 1min to 2min, and the centrifugation is performed for 3min at 4500 rpm.
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