CN113219116B - Nano composite material and application thereof in detecting esters in wine - Google Patents

Abstract

The invention relates to the technical field of food detection, in particular to a nano composite material and application thereof in detecting ester substances in wine. The nano composite material is prepared by the following method: PAM @ GO and iron-containing element compound are chemically co-precipitated to obtain PAM @ GO @ Fe ₃ O ₄ . The nano composite material is further applied to detecting ester substances in wine, and is used as a magnetic adsorbent to adsorb the ester substances in a wine sample to be detected for qualitative and quantitative detection. The invention firstly constructs PAM @ GO @ Fe ₃ O ₄ The method realizes accurate qualitative and quantitative analysis of 9 key ester substances in the base liquor by MSPE of the adsorbent and combining GC-MS and GC-FID, and provides a new research strategy for the pretreatment method of flavor substances in the white liquor.

Description

Nano composite material and application thereof in detecting esters in wine

Technical Field

The invention relates to the technical field of food detection, in particular to a nano composite material and application thereof in detecting ester substances in wine.

Background

The white spirit is also called as distilled spirit, which is prepared by taking grains as raw materials and distiller's yeast as a saccharification leaven through the steps of boiling, saccharifying, fermenting, distilling, storing and blending the raw materials. The aroma of the white spirit is one of important indexes for evaluating the quality and acceptability of the white spirit, and volatile compounds play a key role in the flavor of the white spirit. The liquor contains 1870 multiple volatile substances, wherein the ester compounds are the most main flavor compounds in Luzhou-flavor liquor. In the strong aromatic Chinese spirits, the ester substances which play a main role in aroma generation mainly comprise ethyl caproate, ethyl lactate, ethyl acetate and the like, wherein the ethyl caproate is a main component which forms the main body aroma of the strong aromatic Chinese spirits, so that the strong aromatic Chinese spirits have the style characteristics of strong pit aroma, harmonious aroma and long aftertaste. The research on ester substances in the Luzhou-flavor liquor is earlier developed. In 1964, fenjiu and Maotai were tested by the original light industry, and the components such as esters in Chinese liquor were detected by paper layer chromatography. With the development and improvement of research methods, the research focus on the esters in the Luzhou-flavor liquor gradually changes from researching the types of the esters in the Luzhou-flavor liquor to determining key esters in the Luzhou-flavor liquor.

At present, the reported pretreatment methods of esters in white spirit mainly include Direct Injection (DI), liquid-liquid extraction (LLE), solid-phase microextraction (SPME), stir bar adsorption extraction (SBSE) and the like. Among them, the magnetic solid phase extraction Method (MSPE) is a new sample pretreatment method which is gradually developed in the field of separation and enrichment in recent years. The MSPE has the advantages of convenient operation, low organic solvent consumption, repeated recycling of the magnetic adsorbent, economy and environmental protection. The method is widely applied to the fields of detection of organic and inorganic environmental pollutants, detection of additives in food, pesticide and veterinary drug residues, detection of mycotoxins and heavy metals and the like, but few reports exist on application of the method in white spirit. Magnetic Fe ₃ O ₄ Nanoparticles are the most widely used nanoparticles in MSPE. However, it is easily agglomerated and oxidized, and has weak adsorption capacity and poor selectivity. Therefore, magnetic Fe is required ₃ O ₄ The nanoparticles are successfully applied to sample pretreatment, and need to be modified, so that the nanoparticles are more stable and have selectivity.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a nano composite material and application thereof in detecting ester substances in wine. The nano composite material can be used as a magnetic adsorbent to be applied to detecting esters in wine, and has high adsorption efficiency.

In a first aspect, the present invention provides a nanocomposite material, which is prepared by a method comprising:

PAM @ GO and iron-containing element compound are chemically co-precipitated to obtain PAM @ GO @ Fe ₃ O ₄ 。

Further, pam @ GO can be obtained by free radical polymerization of GO and acrylamide.

Further, the nanocomposite is prepared by a method comprising:

FeCl ₂ 、FeCl ₃ Dissolving in hydrochloric acid solution, adding PAM @ GO and ammonia water, and reacting at 90-100 deg.C for 4-5 hr.

Further, the FeCl ₂ The FeCl ₃ And the mass ratio of PAM @ GO is (3-5): (8-12): (3-5).

In a second aspect, the invention provides a magnetic solid-phase extraction method, wherein the magnetic solid-phase extraction method takes the nano composite material as a magnetic adsorbent.

In a third aspect, the present invention provides a method for detecting esters in wine, comprising: and extracting the ester substances to be detected by adopting the nano composite material or the magnetic solid-phase extraction method.

Further, comprising:

adjusting the pH value of the wine sample to be measured to 6-7;

adding the nano composite material into the wine sample to be detected, fully adsorbing ester substances, and then discarding the supernatant;

and dissolving the ester substances adsorbed by the nano composite material by using an organic solvent.

Further, the dosage of the nano composite material is 2-10 g/L; the full adsorption is adsorption for 1-15 min; the organic solvent is one or more of acetone, ethyl acetate, dichloromethane, carbon tetrachloride or n-hexane, and dichloromethane is preferred.

Further, before the nano composite material is added, the alcoholic strength of the wine sample to be detected is adjusted to 15% -20%.

Further, still include:

performing qualitative determination on the extracted ester substances to be detected by GC-MS;

further, in the qualitative determination, the detection conditions of GC-MS were:

GC-MS chromatographic conditions: DB-WAX capillary column (60 m × 0.25mm × 0.25 μm); carrier gas: he (99.999%); constant current: the column flow rate was 1.0mL/min; the split ratio is 10: 1, and the sample injection amount is as follows: 1.0 μ L, injection port temperature: 250 ℃; temperature rising procedure: the initial temperature is 45 ℃, the temperature is increased to 80 ℃ at the speed of 10 ℃/min, and the temperature is kept for 5min; the temperature is raised to 245 ℃ at a speed of 10 ℃/min and kept for 2min.

GC-MS mass spectrum conditions: an Electron Impact (EI) source; electron energy 70e V; an ion source and a transmission line 300 ℃; the solvent delay time is 4min; full scanning in a scanning mode; the scanning mass range is 45-450 m/z, and the scanning time is 0.2s.

And quantitatively determining the extracted ester substances to be detected by GC-MS and GC-FID.

Further, in the quantitative detection:

GC-MS and GC-FID chromatographic conditions: DB-WAX capillary column (60 m × 0.25mm × 0.25 μm); carrier gas: he (99.999%); constant current: the column flow rate was 1.0mL/min; the split ratio is 10: 1, and the sample injection amount is as follows: 1.0 μ L, injection port temperature: 250 ℃; temperature rising procedure: the initial temperature is 45 ℃, the temperature is increased to 80 ℃ at the speed of 10 ℃/min, and the temperature is kept for 5min; the temperature is raised to 245 ℃ at a speed of 10 ℃/min and kept for 2min.

GC-MS mass spectrum conditions: an Electron Impact (EI) source; electron energy 70eV; an ion source and a transmission line 300 ℃; the solvent delay time is 4min; the scanning mode selects ion scanning, and the characteristic ion fragments of 9 ester substances and 4 isotope internal standard substances are shown in table 1; the scan time was 0.2s.

The invention further provides application of the nano composite material in detecting ester substances in wine.

The invention has the following beneficial effects:

the true bookTest design of magnetic properties of synthetic polyacrylamide graphene oxide (PAM @ GO @ Fe) ₃ O ₄ Or PAM/MGO) nano material, and is applied to the pretreatment of white spirit flavor substances to form an efficient, accurate and easily popularized operation flow, thereby having important theoretical and practical guiding significance for enriching the analysis method of white spirit flavor research and the daily quality control of enterprises.

Drawings

FIG. 1 is a drawing showing PAM @ GO @ Fe provided in example 1 of the present invention ₃ O ₄ Scheme of synthesis.

FIG. 2 shows GO, GO @ PAM and PAM @ GO @ Fe provided in embodiment 1 of the present invention ₃ O ₄ SEM and TEM images of (a); wherein A-C are GO, GO @ PAM and PAM @ GO @ Fe in sequence ₃ O ₄ SEM picture, D-F are GO, GO @ PAM and PAM @ GO @ Fe in turn ₃ O ₄ A TEM image of (a).

FIG. 3 is PAM @ GO @ Fe provided by embodiment 1 of the present invention ₃ O ₄ An infrared spectrogram, a Zeta potential diagram, a thermogravimetric analysis diagram, an X-ray photoelectron spectrogram and a hysteresis loop diagram; wherein G is an infrared spectrogram, H is a Zeta potential diagram, I is a thermogravimetric analysis diagram, J is an X-ray photoelectron energy spectrogram, and K is a magnetic hysteresis loop diagram.

Fig. 4 is a SIM diagram of 9 esters provided in embodiment 1 of the present invention.

FIG. 5 is a graph showing the effect of the type of extraction solvent on the extraction efficiency in Experimental example 1 of the present invention.

FIG. 6 is a graph showing the effect of the extraction method of the present invention in Experimental example 1.

FIG. 7 is a graph showing the comparison of the recovery rates of wine samples with different alcohol contents according to the present invention in Experimental example 1.

Fig. 8 is a graph comparing the effect of pH on extraction of sorghum samples according to experimental example 1 of the present invention.

FIG. 9 is a graph showing the comparison of the recovery rates of different NaCl according to the present invention in Experimental example 1.

FIG. 10 is a graph comparing the recovery rates for different vortex times provided in Experimental example 1 of the present invention.

Detailed Description

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Example 1 PAM @ GO @ Fe ₃ O ₄ GC/MS combined determination of 9 ester substances in Luzhou aged wine base liquor sample

1、PAM@GO@Fe ₃ O ₄ Preparation and characterization of magnetic nano material:

(1) GO and acrylamide and the like through free radical polymerization reaction to generate PAM @ GO, and then PAM @ GO and FeCl ₂ 、FeCl ₃ By the chemical coprecipitation reaction to generate PAM @ GO @ Fe ₃ O ₄ . The specific reaction process is shown in figure 1.

The detailed steps in this example are as follows:

first 0.1988g ferrous chloride (FeCl) ₂ ·4H ₂ O) and 0.5406g ferric chloride (FeCl) ₃ ·6H ₂ O) was dissolved in 20mL of HCl solution (0.4 mol/L), 0.21g of synthesized PAM @ GO powder was dissolved in 20mL of ultrapure water, added dropwise to the above solution and stirred for 1 hour. Then, 160mL of an aqueous ammonia solution (1.25 mol/L) was added to the solution, and the reaction was carried out at 90 ℃ for 4 hours to produce PAM @ GO @ Fe ₃ O ₄ And then putting the product obtained by the reaction into a centrifuge, centrifuging for 20min at 8000r/min, removing the supernatant after the centrifugation is finished, adding ultrapure water, and repeating for several times until the pH is close to neutral. Drying the finally obtained product in a 50 ℃ drying oven, and grinding after drying to obtain PAM @ GO @ Fe ₃ O ₄ And (3) powder.

(2) Adopting transmission electron microscope, scanning electron microscope, fourier transform infrared spectrometer, X-ray photoelectron spectrometer, thermogravimetric analyzer, zeta potential analyzer and vibration sample magnetometer to PAM @ GO @ Fe ₃ O ₄ The nanocomposite is characterized, and FIG. 2 shows the results of the characterization that PAM @ GO @ Fe ₃ O ₄ Compared with GO and PAM @ GO, the structure of the catalyst has obvious change. By G, H, J characterization results analysis in FIG. 3, at PAM @ GO @ Fe ₃ O ₄ In the presence of PAM and Fe ₃ O ₄ The characteristic functional group of (1), indicates PAM @ GO @ Fe ₃ O ₄ The material synthesis is successful. The I characterization result in FIG. 3 shows PAM @ GO @ Fe ₃ O ₄ Has good thermal stability, and K represents a junction in figure 3Fruit indicates PAM @ GO @ Fe ₃ O ₄ Has good magnetic performance and can be used as a magnetic solid phase extraction adsorbent. Under the external magnetic field, the material and the solution can be separated conveniently and quickly, and conditions are provided for recycling the material.

2. Pretreatment method of strong aromatic base wine sample

(1) Preparation of base wine sample: taking 3-5mL of base wine sample in a 25mL centrifuge tube, adding ultrapure water to dilute the alcohol to 15 degrees, and adjusting the pH value to 6.5 by using 1-4mol/L hydrochloric acid solution;

(2) The adsorption process of the substance to be detected in the base wine sample comprises the following steps: PAM @ GO @ Fe prepared by adopting flow 1 ₃ O ₄ Adding 10mg of adsorbent into 5mL of the strong aromatic base wine sample prepared in the step (1), and vortexing for 15min to fully adsorb the adsorbent and the ester compounds in the base wine sample; then using magnet to adsorb PAM @ GO @ Fe outside wall ₃ O ₄ Adsorbent and supernatant discarded.

(3) Desorbing the substance to be detected in the base wine sample: PAM @ GO @ Fe in step (2) ₃ O ₄ Redisperse the adsorbent in 500. Mu.L of dichloromethane and desorb the adsorbent by ultrasound at 40 ℃ for 15min. Adsorbing PAM @ GO @ Fe with magnet ₃ O ₄ And obtaining supernatant and carrying out subsequent analysis process.

3. Using PAM @ GO @ Fe ₃ O ₄ The qualitative research of key ester substances in the Luzhou Laojiao base wine is carried out by combining the GC/MS method:

(1) Searching substances obtained after desorption of the desorption solvent by adopting an NIST 11.0 spectral library, and preliminarily determining an identification result;

(2) Comparing the Retention Index (RI) calculated on a polar (DB-WAX) and non-polar column (HP-5 MS) of the substance to be tested with RI in the literature;

(3) Further characterization is carried out by comparing the aroma compounds to be detected with the aroma characteristics reported in the literature;

(4) Using ester standard substances, respectively preparing mixed standard solutions of ethyl valerate, propyl caproate, ethyl heptanoate, butyl caproate, ethyl caprylate, hexyl caproate, ethyl phenylacetate and ethyl phenylpropionate with different concentration gradients by using absolute ethyl alcohol. And then adding four ester isotope internal standards (the final concentration is 20 mg/L), and comparing and analyzing the retention time of the substance to be detected and the standard substance and the mass spectrum cracking rule by GC-MS (gas chromatography-mass spectrometry), and finally determining the nature.

Wherein RI is calculated according to the modified Kovats method. The specific method comprises the following steps: adding normal alkane (C) into the wine sample to be tested ₈ -C ₃₀ ) Mixing standard solutions, and separating by applying the same GC-MS analysis conditions; by obtaining C ₈ -C ₃₀ The retention time of the unknown analyte is calculated to obtain the RI of the unknown analyte.

GC-MS chromatographic conditions: DB-WAX capillary column (60 m × 0.25mm × 0.25 μm); carrier gas: he (99.999%); constant current: the column flow rate was 1.0mL/min; the split ratio is 10: 1, and the sample injection amount is as follows: 1.0 μ L, injection port temperature: 250 ℃; temperature rising procedure: the initial temperature is 45 ℃, the temperature is increased to 80 ℃ at the speed of 10 ℃/min, and the temperature is kept for 5min; the temperature is raised to 245 ℃ at a speed of 10 ℃/min and kept for 2min.

GC-MS mass spectrum conditions: an Electron Impact (EI) source; electron energy 70e V; an ion source and a transmission line 300 ℃; the solvent delay time is 4min; full scanning in a scanning mode; the scanning mass range is 45-450 m/z, and the scanning time is 0.2s.

3. Using PAM @ GO @ Fe ₃ O ₄ The construction of the method for quantifying 9 esters in the Luzhou Laojiao base wine is realized by combining GC/MS:

and (3) quantifying 9 esters by adopting an isotope internal standard curve method, wherein the ethyl caproate with larger content is quantified by adopting GC-FID. Other esters were quantified using GC-MS, selective Scanning (SIM).

GC-MS and GC-FID chromatographic conditions: DB-WAX capillary column (60 m × 0.25mm × 0.25 μm); carrier gas: he (99.999%); constant current: the column flow rate was 1.0mL/min; the split ratio is 10: 1, and the sample injection amount is as follows: 1.0 μ L, injection port temperature: 250 ℃; temperature rising procedure: the initial temperature is 45 ℃, the temperature is increased to 80 ℃ at the speed of 10 ℃/min, and the temperature is kept for 5min; the temperature is raised to 245 ℃ at a speed of 10 ℃/min and kept for 2min.

GC-MS mass spectrum conditions: an Electron Impact (EI) source; electron energy 70eV; an ion source and a transmission line 300 ℃; the solvent delay time is 4min; the scanning mode selects ion scanning, and SIM graphs of 9 esters are shown in 4,9 esters and characteristic ion fragments of 4 isotope internal standard substances are shown in Table 1; the scan time was 0.2s.

TABLE 1 retention time and SIM parameters for the various esters

And taking the concentration ratio of the target esters to the isotope internal standard as a horizontal coordinate, and taking the peak area of the target esters and the peak area of the internal standard as a vertical coordinate. And (5) obtaining the concentration of the target esters in the wine sample through a standard curve. By linear correlation coefficient (R) ² ) Evaluating the linear relation of the standard curve, and measuring the signal-to-noise ratio (S/N) of chromatographic peak>The mass concentration at 3 is determined as the detection Limit (LOD), signal to noise ratio (S/N)<The mass concentration at 10 is determined as the limit of quantitation (LOQ) and the precision is assessed as the Relative Standard Deviation (RSD) of three parallel experiments.

The regression equation for the standard curve is shown in table 2. All analytes showed a good linear relationship, the correlation coefficient R ² Not less than 0.9932. Detection limit is less than or equal to 4.5 mug/L, quantification limit is less than or equal to 1.35 mug/L, and relative standard deviation RSD<7％。

The result shows that the method has good sensitivity and reproducibility and high precision. Valeric acid ethyl ester (C) ₇ H ₁₄ O ₂ ) Ethyl caproate (C) ₈ H ₁₆ O ₂ ) Propyl caproate (C) ₉ H ₁₈ O ₂ ) Ethyl heptanoate (C) ₉ H ₁₈ O ₂ ) Butyl caproate (C) ₁₀ H ₂₀ O ₂ ) Octanoic acid ethyl ester (C) ₁₀ H ₂₀ O ₂ ) Hexanoic acid hexyl ester (C) ₁₂ H ₂₄ O ₂ ) The concentration adding standard recovery rate is respectively as follows: 32%, 62%, 73%, 86%, 85%, 90%. From the results, it can be seen that the recovery rates of the esters having the same structure and molecular formula are similar. And the addition standard recovery rate of the ester substances shows a trend of rising along with the increase of the number of carbon atoms. Presumably, the reason is that the hydrophobic property of the ester substance is enhanced as the number of carbon atoms increases, which is advantageous for the ester substance and PAM @ GO @ Fe ₃ O ₄ Hydrophobic interaction between the two components, thereby being beneficial to the adsorption of ester substances。

The quantitative results are shown in tables 3 and 4. As can be seen from the quantitative results, the content of ethyl caproate is the highest, which accords with the description that ethyl caproate in the Luzhou-flavor liquor is the main component forming the main body flavor. The method is successfully applied to the quantitative analysis of 9 esters.

This experimental design has synthesized PAM @ GO @ Fe ₃ O ₄ The nano magnetic solid phase extraction material is applied to extraction of 9 key ester substances in Luzhou Laojiao base wine, and provides a new idea for extraction of flavor substances of white wine. Meanwhile, the experiment tries to introduce the isotope internal standard into the development of the GC-MS quantitative method, so that the accuracy of the quantitative method is improved.

TABLE 2 information about Standard curves

TABLE 3 quantitative analysis of esters

TABLE 4 quantitative results and OAV values for esters

Experimental example 1

1.1 evaluation of enrichment ratio

The effectiveness of the extraction efficiency was evaluated by the enrichment ratio (EFs) in this study.

EF(％)＝C _d /C ₀ ×100％

C _d : desorbing the concentration of a compound to be detected in the solution after MSPE extraction;

C ₀ : and (5) measuring the initial adding concentration of the compound to be detected in the simulated white spirit sample.

1.2PAM@GO@Fe ₃ O ₄ Optimization of dosage

The amounts of 5 different groups of adsorbents selected in the experiment were: 10mg, 20mg, 30mg, 40mg, 50mg. The ethanol solution was diluted to 15%, the pH was adjusted to 6.5, and NaCl was added to saturation. 5 groups of ethanol solutions are respectively taken to be 5mL, and 9 mixed standard solutions with ester concentration of 100 μ g/mL are respectively added to be 100 μ L. With different amounts of PAM @ GO @ Fe ₃ O ₄ Adding the nanometer material into the above solution respectively, performing vortex for 1min, and adsorbing PAM @ GO @ Fe with magnet ₃ O ₄ Pouring out supernatant to PAM @ GO @ Fe ₃ O ₄ Respectively adding 500 μ L of dichloromethane, and performing ultrasonic desorption at 40 deg.C for 15min. Adsorbing PAM @ GO @ Fe with magnet ₃ O ₄ And obtaining a supernatant. GC-MS analysis was performed. And (5) investigating the influence of different adsorbent dosages on the extraction effect.

The results are shown in FIG. 5, PAM @ GO @ Fe ₃ O ₄ The extraction effect is optimal when the dosage is 10mg, and the extraction effect is firstly reduced and then increased along with the increase of the dosage.

1.3 optimization of the volume of extraction solvent

The amount of adsorbent is a key factor affecting the extraction efficiency, and the use of an appropriate amount of adsorbent ensures efficient extraction of the target analyte. The choice of desorption solvent generally follows the principle of similar phase solubility. A desorption solvent is selected that has a similar polarity to the target analyte. The magnitude of the polarity can be characterized by a Roche polarity parameter (P'), with the polarity being stronger with larger values of the Roche polarity parameter. In the experiment, acetone (P ' = 5.4), ethyl acetate (P ' = 4.3), dichloromethane (P ' = 3.4), carbon tetrachloride (P ' = 1.6) and n-hexane (P ' = 0.06) were selected as desorption solvents, and the analyte in the adsorbent was desorbed. The experimental result shows that the recovery rate of the ester substances tends to increase firstly and then decrease along with the decrease of the polarity of the desorption solvent. Methylene chloride has a greater desorption capacity for analytes than other desorption solvents. Probably due to the similar polarity of the target ester species and the dichloromethane. As shown in fig. 6, when dichloromethane was used as the desorption solvent, the recovery rates of propyl hexanoate, ethyl heptanoate, butyl hexanoate, ethyl octanoate, and ethyl hexanoate were all higher than 60%. Methylene chloride was selected as the desorption solvent in consideration of the elution ability of the desorption solution.

1.4 alcohol content optimization of wine sample

This study examined recovery at three ethanol concentration levels of 15 °, 35 ° and 65 °. As can be seen from FIG. 7, the recovery of the ester compounds increased significantly as the ethanol concentration decreased. This may be because esters are generally poorly soluble in water and readily soluble in ethanol. When the alcoholic strength of the wine is reduced, the solubility of the esters is reduced and the esters are more easily adsorbed by the adsorbent. It is also possible that the adsorption of the esters is reduced by adsorbing more ethanol by the adsorbent when the alcohol content is high. The maximum recovery was obtained when the sample was diluted to 15 °, therefore 15 ° was chosen as the best alcohol for extraction.

1.5 optimization of pH of sorghum samples

PAEs belong to the class of esters that affect their partitioning between aqueous and solvent phases at different pH conditions. The influence of pH in the range of 2-12 on the adsorption of ester substances is experimentally researched by adding 1mol/L KOH or 0.1mol/L HCl with proper volume and adjusting the pH value of a wine sample. As shown in fig. 8, the recovery rate remained high at pH 4 to 6.5, and decreased at pH 6.5 to 7. The pH in solution affects the water chemistry and the surface binding sites of the adsorbent by dissociating functional groups, thereby promoting or inhibiting the adsorption of esters. According to the Zeta potential analysis result, pH =2.4 is PAM @ GO @ Fe ₃ O ₄ At pH =6.5, the material surface is negatively charged, and PAM @ GO @ Fe is presumed according to the experimental results ₃ O ₄ The negative charge of the surface moiety may facilitate adsorption of the ester species. The pH value of 6.5 was selected as the optimum pH level for the subsequent experiments based on the experimental results.

1.6 optimization of NaCl concentration of wine sample

In order to study the influence of ionic strength on ester adsorption, recovery rates of NaCl solutions with different concentrations (0-4 mol/L) on ester adsorption were experimentally examined, and as shown in FIG. 9, the recovery rates of most esters significantly increased with increasing NaCl concentration. Electrolytes (such as salts) in aqueous systems can influence the boundary properties of the phases and reduce the solubility of hydrophobic compounds by competing for water molecules, a process known as "salting out". The salting-out improves the adsorption capacity of the adsorbent. The salt concentration of 4mol/L was chosen as the optimum concentration for this study.

1.7 vortex time optimization of wine samples

The adsorption time is the minimum time required for the adsorbent to be able to maximally adsorb the target analyte, and the time required for the action sites on the adsorbent to be maximally occupied by the target analyte.

When adding PAM @ GO @ Fe into wine sample ₃ O ₄ Then, the esters in the liquor sample continuously move to PAM @ GO @ Fe ₃ O ₄ Surface migration, simultaneously, PAM @ GO @ Fe ₃ O ₄ The surface adsorbed ester substance is also continuously from PAM @ GO @ Fe ₃ O ₄ Is desorbed. When PAM @ GO @ Fe ₃ O ₄ When the action site on the surface is occupied by the ester substances to the maximum extent, the content of the ester substances in the wine sample is lower and lower, and the ester substances are migrated to PAM @ GO @ Fe from the wine sample ₃ O ₄ Rate of superficial ester species and from PAM @ GO @ Fe ₃ O ₄ When the rates of surface desorption of esters are equal, dynamic adsorption equilibrium is realized, and the time required by the process is called adsorption time. If the adsorption time is too short, PAM @ GO @ Fe ₃ O ₄ The adsorption sites on the surface can not sufficiently adsorb the ester substances; if the adsorption time is too long, PAM @ GO @ Fe ₃ O ₄ The esters enriched on the adsorption sites may be desorbed, thereby affecting the extraction efficiency and the cycle of the experiment. Therefore, selection of an appropriate adsorption time is an important factor affecting the experimental recovery and experimental cycle.

The extraction process of the esters in the experiment is carried out under the condition of vortex, and the experiment examines the change of the recovery rate of the vortex time from 0.5 to 15min. As shown in fig. 10, the recovery rate increases from the time period of 0.5-1 min by increasing the vortex time, but the recovery rate does not change significantly in the time range of 1-15 min, which indicates that the adsorption equilibrium of the ester substances can be reached rapidly. Therefore, in subsequent experiments, a vortex time of 1min was chosen.

Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims (6)

1. A method for detecting esters in wine is characterized by comprising the following steps:

extracting ester substances to be detected by a magnetic solid phase extraction method; the magnetic solid phase extraction method takes a nano composite material as a magnetic adsorbent;

the nano composite material is prepared by the following method:

PAM @ GO and iron-containing element compound are chemically co-precipitated to obtain PAM @ GO @ Fe ₃ O ₄ (ii) a The method specifically comprises the following steps: feCl is added ₂ 、FeCl ₃ Dissolving in hydrochloric acid solution, adding PAM @ GO and ammonia water, and reacting at 90 to 100 ℃ for 4~5 hours;

the FeCl ₂ The FeCl ₃ And the mass ratio of PAM @ GO is (3~5): (8 to 12): (3~5).

2. The method of claim 1, comprising:

adjusting the pH value of the wine sample to be detected to 6~7;

adding the nano composite material into the wine sample to be detected, fully adsorbing ester substances, and then discarding the supernatant;

and dissolving the ester substances adsorbed by the nano composite material by using an organic solvent.

3. The method according to claim 2, wherein the amount of the nanocomposite is 2 to 10g/L;

and/or the organic solvent is one or more of acetone, ethyl acetate, dichloromethane, carbon tetrachloride or n-hexane;

and/or the sufficient adsorption is adsorption for 1 to 15min.

4. The method as claimed in claim 2 or 3, further comprising adjusting the alcoholic strength of the wine sample to be tested to between 15% and 20% prior to adding the nanocomposite.

5. A method according to claim 2 or 3, characterized in that:

performing qualitative determination on the extracted ester substances to be detected by GC-MS;

and/or, carrying out quantitative determination on the extracted ester substances to be detected through GC-MS and GC-FID.

6. The method according to claim 1, wherein the wine is a bouquet based wine.

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