A liquor harmful substance synchronous identification method based on gas phase diffusion pretreatment

Abstract

The present application belongs to the technical field of food safety rapid detection, and discloses a liquor harmful substance synchronous identification method based on gas phase diffusion pretreatment. The present application utilizes the physical characteristics that the volatility of methanol and formaldehyde is significantly higher than that of ethanol and esters, carries out gas phase diffusion pretreatment under the condition that a closed container is at 40 DEG C to 60 DEG C, makes methanol and formaldehyde preferentially volatilize and be captured by two independent absorption chromogenic liquids respectively, makes ethanol and esters mainly remain in the liquor sample liquid, and the ethanol concentration in the absorption liquid is relatively reduced. Thus, the chromogenic reaction is carried out in the absorption liquid system in which the ethanol concentration is significantly reduced, and it is not necessary to dilute the liquor sample to low alcohol degree in a large amount, so that the technical problem that the traditional colorimetric method is seriously interfered by high alcohol degree ethanol and ester matrix is fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of rapid food safety detection technology, specifically to a method for simultaneous identification of harmful substances in baijiu (Chinese liquor) based on gas phase diffusion pretreatment. Background Technology

[0002] The production of baijiu (Chinese liquor) may introduce or generate various harmful substances, among which methanol, formaldehyde, and heavy metals (such as lead) are the main risk factors endangering human health. Methanol and formaldehyde mainly originate from the decomposition of pectin in raw materials during fermentation and distillation, while heavy metals are mainly related to brewing raw materials, production water, and distillation equipment. Therefore, establishing an efficient and reliable method for identifying harmful substances in baijiu is of great significance for ensuring the safety of baijiu consumption and strengthening the supervision of production sources.

[0003] In existing technologies, the detection methods for harmful substances in baijiu (Chinese liquor) are mainly divided into two categories: one is laboratory precision detection methods, such as gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), atomic absorption spectrometry (AAS), and inductively coupled plasma mass spectrometry (ICP-MS). These methods have the advantages of high sensitivity and accuracy, but they generally suffer from problems such as expensive equipment, complex operation, long detection cycle, and high requirements for experimental environment and operators, making it difficult to meet the rapid screening needs of production sites and distribution links. The other category is on-site rapid detection methods, such as colorimetric detection methods based on chromotropic acid or acetylacetone methods. These methods are relatively simple to operate and have low cost, but they suffer from significant matrix interference problems when applied to baijiu detection: the ethanol concentration in baijiu is usually as high as 50%~60% vol, and it contains a large amount of flavor substances such as esters and aldehydes. High concentrations of ethanol will inhibit the sensitivity of the colorimetric reaction, and esters will produce yellow background interference, leading to false positives or colorimetric failure. Taking the chromotropic acid method in the national standard rapid detection method as an example, the sample usually needs to be diluted to an ethanol concentration below 6% vol to effectively eliminate interference. This not only increases the number of operational steps but also significantly reduces the detection sensitivity. Furthermore, existing rapid detection methods typically only detect a single indicator at a time. To simultaneously identify methanol, formaldehyde, and heavy metals, separate sampling and multiple independent operations are required, resulting in a cumbersome and inefficient process. For heavy metal screening, organic acids and high concentrations of ethanol in liquor easily form complexes with heavy metal ions, leading to decreased test strip sensitivity and even false negatives.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The present invention aims to solve at least any of the above technical problems, and provides a method for simultaneous identification of harmful substances in liquor based on gas phase diffusion pretreatment.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for simultaneous identification of harmful substances in baijiu (Chinese liquor) based on gas-phase diffusion pretreatment includes the following steps: The liquor sample and two independent absorption and color-developing solutions were placed in the sample chamber and color-developing absorption chamber of the same sealed container, respectively. The sealed container was equipped with a gas-permeable and liquid-barrier membrane, so that the gas phase components volatilized from the liquor sample came into contact with the two independent absorption and color-developing solutions, while the liquid phases were isolated from each other. An insoluble solid acidic material was pre-placed in the sample chamber as a formaldehyde release promoter. The temperature of the sealed container is controlled at 40℃~60℃ and maintained for 10min~20min to allow methanol and / or formaldehyde that may be present in the liquor sample to volatilize and be absorbed by the two independent absorption and color development solutions. Take out the two independent absorption color-developing solutions after absorption, and keep them at 70℃~100℃ for 5min~15min to allow the color development reaction to be fully completed. Then, based on the color changes of the two independent absorption color-developing solutions, determine the presence of methanol and / or formaldehyde in the liquor sample and the semi-quantitative results. Heavy metal screening was performed using the residual liquid from the liquor sample retained in the sample chamber.

[0007] Preferably, the two independent absorption and color-developing solutions are a first absorption solution and a second absorption solution. The first absorption solution is an acetylacetone color-developing agent loaded on a porous solid support, used to react and generate a yellow compound in the presence of formaldehyde. The second absorption solution includes an oxidation absorption solution and a color-developing solution. The oxidation absorption solution is a phosphoric acid solution containing an oxidant, which oxidizes methanol to formaldehyde in the presence of methanol. After the gas phase diffusion is completed, a chromotropic acid-sulfuric acid solution is added to the oxidation absorption solution and heated to allow formaldehyde to react with the chromotropic acid to generate a blue-purple compound.

[0008] Preferably, the determination of the presence of methanol and / or formaldehyde and the semi-quantitative results include: The presence of formaldehyde is determined based on the color development of the first absorbent liquid. If it is present, a semi-quantitative result of formaldehyde is obtained by comparing it with a standard color card. The total amount of methanol and formaldehyde is determined based on the color development of the second absorbent. If they are detectable, a semi-quantitative result of the total amount is obtained by comparing with the standard color card. If both formaldehyde and methanol are detected, and the total semi-quantitative result is higher than the formaldehyde semi-quantitative result, then the relative semi-quantitative result of methanol is obtained by the difference between the total semi-quantitative result and the formaldehyde semi-quantitative result.

[0009] Preferably, the oxidant in the oxidation absorption liquid is a potassium permanganate-phosphoric acid solution.

[0010] Preferably, the colorimetric absorption chamber is divided into two interconnected sub-chambers by a partition, with the first absorbent and the second absorbent placed in the two sub-chambers respectively, and both sub-chambers connected to the sample chamber via the same gas phase space.

[0011] Preferably, the gas-permeable and liquid-blocking membrane is a polytetrafluoroethylene microporous membrane with a pore size of 0.1μm to 0.45μm.

[0012] Preferably, the volume of the liquor sample is 0.5 mL to 1.0 mL, and the volume of the second absorbent is 0.3 mL to 1.0 mL; the first absorbent exists in the form of a porous solid support, and the amount of the porous solid support is 1 cm². 2 ~4cm 2 .

[0013] Preferably, the temperature of the sealed container is controlled by placing it in a water bath at 40°C to 60°C.

[0014] Preferably, the heavy metal screening includes adding the residual liquid from the liquor sample to heavy metal colorimetric test paper and determining the presence of heavy metals based on the color change of the test paper.

[0015] Preferably, the target of the heavy metal screening is lead.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the physical property that methanol and formaldehyde are significantly more volatile than ethanol and esters. By controlling the gas-phase diffusion pretreatment in a sealed container at 40℃~60℃, methanol and formaldehyde preferentially evaporate and are captured by two independent absorption and colorimetric solutions, while ethanol and esters are mainly retained in the liquor sample solution, resulting in a relatively lower ethanol concentration in the absorption solution. Therefore, the colorimetric reaction takes place in an absorption solution system with a significantly reduced ethanol concentration, eliminating the need for extensive dilution of the liquor sample to a low alcohol content. This fundamentally solves the technical problem of traditional colorimetric methods being severely interfered with by high-alcohol-content ethanol and ester matrices.

[0017] This invention enables differential identification of formaldehyde and methanol by independently setting acetylacetone and chromotropic acid-sulfuric acid oxidation colorimetric reagents in the same sealed colorimetric absorption chamber. Simultaneously, the residual liquid retained in the sample chamber after gas-phase diffusion allows for direct screening of heavy metals. A single sampling and one-step operation enables simultaneous identification of methanol, formaldehyde, and heavy metals, significantly improving detection efficiency and simplifying the operational process.

[0018] This invention achieves gas-phase diffusion separation using only a simple sealed container and room-temperature water bath heating. The subsequent determination can be completed by observing the color development with the naked eye or comparing it with a standard color card. It does not require large and precision instruments such as gas chromatographs, mass spectrometers, or atomic absorption spectrometers. It is simple to operate, low in cost, and suitable for rapid screening scenarios in production sites and grassroots supervision. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other. Those skilled in the art should understand that the following descriptions are merely exemplary means of implementing this invention and not limiting conditions; any technical means employed to achieve the same or similar technical effects as this invention should fall within the protection scope of this invention.

[0020] The core of the method for simultaneous identification of multiple harmful substances in baijiu (Chinese liquor) described in this invention lies in utilizing gas-phase diffusion pretreatment to physically separate methanol and / or formaldehyde, which may be present in the baijiu sample, from ethanol and esters. Then, the absorbent liquid and residual liquid are identified separately, thereby achieving the goal of simultaneously identifying multiple harmful substances with a single sampling. The main steps are described in detail below.

[0021] This invention provides a method for simultaneous identification of harmful substances in baijiu (Chinese liquor) based on gas-phase diffusion pretreatment, including: S101, the liquor sample and two independent absorption and color-developing solutions are placed in the sample chamber and color-developing absorption chamber of the same sealed container, respectively. The sealed container is equipped with a gas-permeable and liquid-blocking membrane, so that the gas phase components volatilized from the liquor sample come into contact with the two independent absorption and color-developing liquid phases, while the liquid phases are isolated from each other; the sample chamber is pre-filled with an insoluble solid acidic material as a formaldehyde release promoter.

[0022] This step is a basic preparation step, the purpose of which is to create a closed environment for gas-phase diffusion, so that the liquor sample and the absorption color development solution are completely isolated in the liquid phase (to prevent high concentrations of ethanol and esters from directly mixing into the color development system), while being interconnected in the gas phase (to allow volatile harmful substances to migrate); at the same time, by pre-installing a formaldehyde release promoter, the problem that formaldehyde in liquor mainly exists in the form of hydrate (methylene glycol) and is difficult to volatilize directly is solved.

[0023] The sealed container is equipped with a gas-permeable and liquid-barrier membrane, which divides the sealed container into a sample chamber and a colorimetric absorption chamber, so that the gas phase components volatilized from the liquor sample come into contact with the gas phase of the two independent absorption and colorimetric liquids while being isolated in the liquid phase.

[0024] A gas-permeable and liquid-barrier diaphragm is a key structure for achieving gas-phase diffusion pretreatment. Its function is to allow methanol and / or formaldehyde molecules in the gas phase to pass freely based on partial pressure differences, while preventing liquid ethanol, water, esters, and non-volatile heavy metal ions from leaking from the sample chamber to the colorimetric absorption chamber or migrating in large quantities. Those skilled in the art will understand that any diaphragm material and structure capable of achieving the "gas-permeable and liquid-barrier" function can be used in this invention. For example, commonly used gas-permeable and liquid-barrier diaphragm materials include, but are not limited to, polytetrafluoroethylene microporous membranes, polypropylene microporous membranes, and polyethersulfone microporous membranes; their support structures can be conventional membrane fixation methods in the art, such as thermo-press sealing, ultrasonic welding, or clamping fixation.

[0025] In one specific embodiment of the present invention, the gas-permeable and liquid-blocking membrane is a polytetrafluoroethylene microporous membrane with a pore size of 0.1 μm to 0.45 μm. This pore size range is a preferred range verified by the present invention: if the pore size is too large, the liquid may leak under insufficient surface tension or vibration, resulting in a large amount of ethanol and esters entering the colorimetric absorption chamber; if the pore size is too small, the gas phase diffusion resistance increases significantly, prolonging the time required to reach diffusion equilibrium, and may even lead to insufficient diffusion of trace amounts of formaldehyde and methanol. Those skilled in the art can adjust the pore size within a reasonable range according to the hydrophilicity / hydrophobicity, thickness, and specific properties of the liquor sample, which is a conventional choice in the art.

[0026] The material and shape of the sealed container are not particularly limited; it can be made of glass, plastic, or metal, as long as it can withstand temperatures of 40℃ to 60℃ and remain sealed. The connection between the upper and lower parts of the sealed container can be achieved using conventional sealing methods in the art, such as threaded tightening, rubber stopper sealing, snap-fit ​​connection, or thermoforming. In one specific embodiment of the invention, the sealed container is a plastic tube composed of two interlocking parts: the upper part is a colorimetric absorption chamber, and the lower part is a sample chamber, separated by a thermoforming seal using a polytetrafluoroethylene microporous membrane. This structure is easy to process and for single use, but those skilled in the art can also use other conventional structures according to actual needs.

[0027] The colorimetric absorption chamber is divided into two interconnected sub-chambers by a partition. Two independent absorption and colorimetric solutions (i.e., the first absorbent and the second absorbent) are each independently housed in one of the two sub-chambers. Both sub-chambers are connected to the sample chamber via the same gas phase space. "Independently housed" means that the first and second absorbents do not come into contact with or mix with each other in physical space.

[0028] The design aims to ensure that methanol and / or formaldehyde in the gas phase can simultaneously reach both sub-chambers under the same gas phase partial pressure and be absorbed by two independent absorption and color-developing solutions. Simultaneously, a partition isolates the two sub-chambers in the liquid phase space, preventing direct contact and chemical reaction between the first and second absorbent solutions. The partition can be a conventional liquid phase separation structure in the art, such as a plastic rib integrally formed with the sealed container, a plug-in partition, or an adhesive strip. A connecting gas phase channel is provided above the two sub-chambers to ensure the symmetry and synchronicity of gas phase diffusion.

[0029] The first absorbent is acetylacetone as a colorimetric agent, used to react and generate a yellow compound in the presence of formaldehyde. The first absorbent is loaded onto a porous solid support, which increases the contact area with the gas phase and concentrates the colorimetric product. In one specific embodiment of the invention, the porous solid support can be a porous material such as a silica gel plate, glass fiber paper, or a sponge block, with a specific surface area significantly higher than the droplet plane. After the porous solid support is pre-impregnated with the acetylacetone colorimetric agent, it is dried at low temperature until there are no obvious free droplets on the surface, but the support as a whole remains soft and moist (water content approximately 30%~60%, based on 30%~50% of the support's saturated water absorption capacity), and then placed in the first sub-chamber of the colorimetric absorption chamber. This moist state can be determined by the following: no reflective liquid film on the support surface, no liquid dripping when squeezed, but noticeably moist to the touch, and uniform color without dry white spots. Because acetylacetone has a high boiling point (approximately 140°C) and ammonium acetate in the colorimetric agent is a non-volatile salt, the above-mentioned low-temperature drying treatment does not lead to significant loss of key components.

[0030] The second absorbent comprises an oxidation absorbent and a colorimetric solution. The oxidation absorbent is a phosphoric acid solution containing an oxidant, which oxidizes methanol to formaldehyde in the presence of methanol. After gas-phase diffusion, a chromotropic acid-sulfuric acid solution is added to the oxidation absorbent and heated, causing the formaldehyde to react with the chromotropic acid to form a blue-violet compound. In one specific embodiment of the invention, the oxidant is a potassium permanganate-phosphoric acid solution, prepared using conventional techniques in the art. The oxidation absorbent begins oxidizing methanol during the gas-phase diffusion stage at 40°C to 60°C. After diffusion, the methanol is oxidized to formaldehyde and retained in the liquid phase.

[0031] Although the two sub-chambers are connected above the same gas phase space, the liquid phase is completely isolated by the partition during the gas phase diffusion process, and the partial pressure of acid mist in the gas phase is extremely low, which is insufficient to affect the weakly acidic environment of the acetylacetone colorimetric reagent in the first sub-chamber.

[0032] After gas-phase diffusion, the oxidizing absorbent is removed from the colorimetric absorption chamber and transferred to a heat-resistant container. A chromotropic acid-sulfuric acid solution is added as the colorimetric solution, mixed thoroughly, and then heated in a boiling water bath for 5-15 minutes. At this time, the formaldehyde already generated in the oxidizing absorbent reacts with the chromotropic acid under concentrated sulfuric acid conditions to form a blue-violet compound. Because the oxidant and the chromotropic acid colorimetric solution are separated in time and space, oxidation damage and color interference in the premixed state are avoided.

[0033] It should be noted that the amount of oxidant in the second absorbent solution is optimized and controlled to just meet the methanol oxidation requirements, avoiding excessive oxidant from oxidizing and damaging the chromotropic acid and interfering with the color. In one specific embodiment of the present invention, the amount of potassium permanganate-phosphoric acid solution is 0.1 mL to 0.3 mL (based on a concentration of 35 g / L). This amount is trace relative to the chromotropic acid-sulfuric acid system, and its deep purple color can be identified by comparing the background of the standard color chart after the blue-purple color product is generated. If the amount of oxidant results in an excessively deep purple background, the concentration or amount of potassium permanganate can be appropriately reduced, or other oxidants (such as potassium dichromate-sulfuric acid solution) can be used within the conventional range in the art. This is a conventional adjustment made by those skilled in the art based on the actual color development effect.

[0034] A formaldehyde release promoter, an insoluble solid acidic material, is pre-placed in the sample chamber. This promoter is used to catalyze the dehydration of formaldehyde hydrate in the liquor sample into free formaldehyde through surface acidic catalysis. The insoluble solid acidic material includes, but is not limited to, H-type zeolite molecular sieves, acidic alumina, or sulfonic acid-type cation exchange resin microspheres, and is used in amounts ranging from 2 mg to 10 mg. This insoluble solid acidic material is insoluble in the aqueous ethanol system and provides acidic catalytic sites solely through surface proton exchange, catalyzing the dehydration of methylene glycol to generate free formaldehyde. After gas-phase diffusion, the insoluble solid acidic material remains as solid particles at the bottom of the sample chamber. When collecting the residual liquid, the sample is taken from the upper clear liquid.

[0035] In one specific embodiment of the present invention, the volume of the liquor sample is 0.5 mL to 1.0 mL, and the volume of the second absorbent is 0.3 mL to 1.0 mL; the first absorbent exists in the form of being loaded on a porous solid support, and the amount of the porous solid support is 1 cm² in area. 2 ~4cm 2 The choice of this volume ratio ensures that gas-phase diffusion within the sealed container achieves a suitable mass transfer distance and equilibrium efficiency. If the sample volume is too large, the gas phase space is relatively reduced, leading to a lower diffusion rate; conversely, if the volume of the absorbent chromogenic solution is too large, the concentration of the chromogenic reagent is diluted, potentially affecting the chromogenic sensitivity. However, those skilled in the art can adjust the aforementioned volumes within a reasonable range based on the volume of the sealed container and the sensitivity of the chromogenic reagent; this is a standard optimization practice in the field.

[0036] S102, control the temperature of the sealed container to 40℃~60℃ and maintain it for 10min~20min, so that methanol and / or formaldehyde that may be contained in the liquor sample can volatilize and be absorbed by the two independent absorption and color development solutions.

[0037] The purpose of this step is to utilize the volatility differences between methanol (boiling point approximately 64.5℃) and formaldehyde (released in a free state after acid-catalyzed dehydration) and ethanol (boiling point approximately 78.4℃), as well as major esters in baijiu (such as ethyl acetate (boiling point approximately 77.1℃) and ethyl lactate (boiling point approximately 154℃), without using large precision instruments or undergoing complex chemical pretreatment. By controlling appropriate temperature, time, and a sealed environment, methanol and / or formaldehyde preferentially volatilize into the gas phase and pass through a gas-permeable, liquid-barrier membrane to be captured by two independent absorption and colorimetric solutions in the colorimetric absorption chamber. Meanwhile, high-concentration ethanol and most esters, due to their relatively low volatility or large molecular weight, are mainly retained in the liquid phase of the sample chamber. Thus, methanol and / or formaldehyde in the absorption and colorimetric solutions are relatively enriched, and the ethanol concentration is lower than that of the baijiu sample, thereby mitigating the interference of the high-alcohol baijiu matrix on the subsequent colorimetric reaction. Simultaneously, a residual solution containing heavy metal ions is retained for subsequent heavy metal screening.

[0038] It is important to note that this step utilizes the principle of physical gas-phase diffusion separation, rather than chemical extraction or adsorption separation. Methanol and / or formaldehyde evaporate from the liquid phase of the liquor sample into the headspace of the sealed container, and then, based on the partial pressure difference, pass through the gas-permeable liquid-barrier membrane into the colorimetric absorption chamber, where they are absorbed by the colorimetric solution. This process does not alter the chemical composition of the liquid phase in the sample chamber (except for the migration of methanol and formaldehyde, and the natural diffusion of trace amounts of ethanol). Therefore, the residual liquid in the sample chamber can be directly used for heavy metal screening in the future, without introducing new interference or complexation effects due to the introduction of chemical reagents.

[0039] The temperature of the sealed container is controlled within the range of 40℃ to 60℃, and the holding time is 10 min to 20 min. This temperature range is chosen based on the following physicochemical principles: methanol has a boiling point of 64.5℃. Under conditions of 40℃ to 60℃, methanol has sufficient vapor pressure to significantly volatilize from the baijiu sample and pass through the gas-permeable liquid-barrier membrane within 10 min to 20 min; free formaldehyde released by the catalysis of insoluble solid acidic materials also has a vapor pressure within this temperature range that allows for effective migration in the gas phase. Under conditions of 40℃ to 60℃, low-boiling-point esters such as ethyl acetate in baijiu have a certain vapor pressure. Although the saturated vapor pressure of ethyl acetate is relatively high, its molar fraction in the liquid phase of baijiu is much lower than that of ethanol (usually by 2 to 3 orders of magnitude), therefore its molar flux through the gas-permeable liquid-barrier membrane is usually lower than that of ethanol. However, if the ester content in the baijiu sample is extremely high (e.g., the total ester content of some strong-aroma baijiu > 3 g / L), trace amounts of esters may still migrate. Compared to adding the liquor sample directly to the colorimetric solution (where the ester concentration is at the level of the original liquor), the total amount of esters entering the absorption colorimetric solution after gas-phase diffusion is significantly reduced, and the strong acid environment in the absorption colorimetric solution can suppress the interference of the yellow background of esters to a certain extent.

[0040] Those skilled in the art can achieve the above-mentioned temperature control using various conventional heating methods. For example, the sealed container can be placed in a constant-temperature water bath, with the water bath temperature controlled at 40℃~60℃, and the sealed container can be immersed or partially immersed in the water bath for 10min~20min; alternatively, conventional constant-temperature heating equipment in the art, such as a constant-temperature metal bath, a constant-temperature incubator, or a heating block, can be used. In one specific embodiment of the present invention, heating is performed in a constant-temperature water bath at 40℃~60℃ for 15min. It should be noted that the heating time can be adjusted appropriately according to the temperature: when the temperature is close to 60℃, the holding time can be shortened to about 10min; when the temperature is close to 40℃, the holding time can be extended to about 20min. Those skilled in the art can make conventional adjustments within the above range based on the volume of the sealed container, the permeability rate of the gas-permeable and liquid-resistant diaphragm, and the alcohol content of the liquor sample.

[0041] It should be noted that during the gas-phase diffusion process at 40℃~60℃, due to the fact that ethanol also has a certain vapor pressure, a small amount of ethanol will still pass through the gas-permeable liquid-barrier membrane and enter the absorption and color-developing solution. Therefore, the effectiveness of the method described in this invention does not depend on "complete retention of ethanol," but rather on the control of diffusion conditions to significantly reduce the ethanol concentration in the absorption and color-developing solution relative to the original wine, and to a level tolerable for the color-developing reaction. When implementing this invention, the ethanol concentration in the absorption and color-developing solution under different temperatures, times, and volume ratios should be determined through preliminary experiments, and the operating parameters should be optimized accordingly to ensure that the subsequent color-developing reaction is not significantly inhibited.

[0042] In this step, the formaldehyde release promoter in the sample chamber and the porous solid support in the colorimetric absorption chamber work synergistically. In the sample chamber, the insoluble solid acidic material catalyzes the dehydration of methanol, increasing the partial pressure of free formaldehyde in the gas phase. In the colorimetric absorption chamber, the porous solid support in the first sub-chamber efficiently captures formaldehyde in the gas phase by increasing the specific surface area and the micropore concentration effect. The two work synergistically to form a dual-enhancement mechanism of "release-capture," which significantly improves the sensitivity of simultaneous formaldehyde detection within a time range of 10 to 20 minutes, making simultaneous rapid screening of methanol feasible on-site.

[0043] S103, after absorption, the two independent absorption and color development solutions are taken out and heated at 70℃~100℃ for 5min~15min to allow the color development reaction to be fully completed. Then, based on the color changes of the two independent absorption and color development solutions, the presence of methanol and / or formaldehyde in the liquor sample and the semi-quantitative results are determined respectively.

[0044] The purpose of this step is to identify formaldehyde and methanol separately through specific colorimetric reactions by utilizing methanol and / or formaldehyde captured in the two sub-chambers of the colorimetric absorption chamber, and to make a semi-quantitative determination based on the intensity of the color. Because of the gas-phase diffusion pretreatment, methanol and / or formaldehyde in the absorption and colorimetric solution are relatively enriched, and the ethanol concentration is relatively reduced. This allows the colorimetric reaction to proceed under conditions close to standard methods, thus ensuring the reliability of the identification results.

[0045] The determination of presence and semi-quantitative results described in this invention refer to first determining the presence of the target substance by observing the color changes of two independent absorption color developing solutions (qualitative), and if present, obtaining an approximate content range by comparing it with a standard color chart (semi-quantitative).

[0046] It should be noted that the acetylacetone colorimetric reaction in the first absorbent and the chromotropic acid-sulfuric acid colorimetric reaction in the second absorbent typically require heating at 70℃~100℃ to achieve full color development. During the S102 gas-phase diffusion pretreatment stage (40℃~60℃), the two absorbents primarily perform gas-phase capture and initial reaction initiation, and color development may not be sufficient. Therefore, after the gas-phase diffusion pretreatment, the first absorbent (along with the porous solid support) and the second absorbent should be removed together, placed in separate heat-resistant containers, and then heated in a boiling water bath for 5min~15min to complete the color development reaction. This unified heating color development step is a standard post-treatment procedure in the field and can be performed simultaneously in the same boiling water bath, with a total color development time of 5min~15min.

[0047] When the first absorbent (acetylacetone colorimetric reagent supported on a porous solid support) is heated in a boiling water bath, if formaldehyde is present, a yellow 3,5-diacetyl-1,4-dihydropyridine derivative is formed. This reaction exhibits good selectivity for formaldehyde, and methanol does not interfere with the reaction.

[0048] Because the two sub-chambers of the colorimetric absorption chamber are connected to the sample chamber via the same gas phase space, methanol and / or formaldehyde in the gas phase can simultaneously enter both sub-chambers. The acetylacetone colorimetric reagent in the first absorption liquid reacts only with formaldehyde to form a yellow compound and does not react with methanol; the chromotropic acid-sulfuric acid system in the second absorption liquid reacts with both formaldehyde and formaldehyde generated from the oxidation of methanol to form a blue-violet compound. Therefore, the colorimetric result of the first absorption liquid reflects the amount of formaldehyde in the sample, while the colorimetric result of the second absorption liquid reflects the total amount of methanol and formaldehyde.

[0049] The presence of formaldehyde is determined based on the color development of the first absorbent: if the first absorbent (porous solid support) remains colorless or only very pale yellow, formaldehyde is determined to be undetectable or below the detection limit; if a distinct yellow color appears, formaldehyde is determined to be present. In the presence of formaldehyde, a semi-quantitative result is obtained by visually comparing it with a pre-prepared formaldehyde standard color chart. The standard color chart can be prepared by preparing a series of formaldehyde standard solutions of known concentrations and developing them under the same conditions; this is a conventional semi-quantitative colorimetric method in the art.

[0050] If the oxidant's purple color is too deep and affects visual judgment before heating the second absorbent in a boiling water bath, the second absorbent can be transferred to a glass test tube before heating in a boiling water bath to develop the color. During the heating process, excess potassium permanganate may partially decompose or fade in color. Furthermore, the blue-purple product and the purplish-red background are distinguishable in hue, and can be effectively compared using a pre-prepared standard color chart containing the background.

[0051] If methanol and / or formaldehyde are present in the second absorbent (chromotropic acid-sulfuric acid solution containing oxidant) after heating in a boiling water bath, the methanol in the absorbent will be oxidized to formaldehyde and react with chromotropic acid to form a blue-purple compound.

[0052] The total levels of methanol and formaldehyde are determined based on the color development of the second absorbent: if the second absorbent remains colorless, the total amount of methanol and formaldehyde is below the detection limit; if a blue-purple color appears, it is detectable. In the detectable case, a semi-quantitative result of the total amount of methanol and formaldehyde is obtained by visually comparing it with a methanol standard color chart (prepared by oxidation of methanol as a reference).

[0053] If both formaldehyde and methanol are detected, meaning both the first and second absorbent solutions show obvious color development, and the total semi-quantitative result is higher than the formaldehyde semi-quantitative result, the relative semi-quantitative result of methanol is obtained by calculating the difference between the total semi-quantitative result and the formaldehyde semi-quantitative result. This difference calculation can effectively eliminate the positive interference of the original formaldehyde in the sample on the methanol determination.

[0054] It should be noted that due to subjective errors in visual colorimetry, the total semi-quantitative result may be lower than or equal to the formaldehyde semi-quantitative result (e.g., the difference is zero or negative). This indicates that the methanol content in the liquor sample is extremely low, below the detection limit of this method or within the range of method error aggregation; or that the formaldehyde semi-quantitative result is overestimated due to visual error, leading to distorted difference calculation. In the above cases, difference calculation is not performed, and only the total semi-quantitative result is reported as an upper limit reference, and methanol is determined to be undetectable or at extremely low levels. Those skilled in the art will understand that in rapid screening scenarios, when the target analyte content is close to the detection limit, a negative difference is a normal phenomenon within the inherent error range of the method and does not affect the overall judgment of sample safety.

[0055] Since the two sub-chambers are connected to the sample chamber through the same gas phase space, formaldehyde in the gas phase can theoretically enter the two sub-chambers simultaneously. To ensure the effectiveness of the differential calculation, the distribution and absorption of gas phase formaldehyde in the two sub-chambers should be consistent. This invention achieves distribution balance in the following ways: (1) Structural symmetry design: The volume, liquid level, and gas phase opening area of ​​the two sub-chambers are kept consistent, so that the partial pressure and diffusion path of gas phase molecules above the two sub-chambers are basically symmetrical; (2) Synchronous calibration of standard color card: When preparing the standard color card, the same batch and the same specification of sealed containers and diaphragms are used, and the formaldehyde standard solution of known concentration is operated according to the method described in this invention, and the color development results of the first absorption liquid and the second absorption liquid (without oxidant, only containing chromotropic acid-sulfuric acid) are read respectively. If there is a systematic difference in the color development depth of the two subcompartments for the same concentration of formaldehyde, a correction coefficient k (k = formaldehyde standard color scale reading of the second subcompartment / formaldehyde standard color scale reading of the first subcompartment) is introduced into the difference calculation of subsequent sample detection. The semi-quantitative result of formaldehyde is multiplied by the correction coefficient k and then the difference is calculated with the total semi-quantitative result.

[0056] In one specific embodiment of the present invention, when a symmetrically designed dual-chamber structure is used and the two sub-chambers use the same volume of absorption and colorimetric solution, the correction coefficient k can be determined through a calibration experiment. If k deviates significantly from the calibration value due to process deviations, the sub-chamber structure or liquid level should be adjusted until k returns to a reasonable range. Those skilled in the art will understand that the semi-quantitative results of visual colorimetry have inherent subjective errors, typically within ±1 color level. In differential calculations, the errors of the two semi-quantitative results are superimposed and propagated to the final relative semi-quantitative result for methanol. Therefore, the relative semi-quantitative result for methanol is not a precise value, but rather an estimated range with error propagation. In practical applications, the following principles should be followed: (1) When the total semi-quantitative result differs from the formaldehyde semi-quantitative result by two color levels or more, the differential calculation result has screening significance, and methanol can be determined to be present and a relative semi-quantitative range can be given; (2) When the two differ by only one color level, the differential calculation result is in the error superposition critical zone, and "methanol may be detected, and further precise testing is recommended" should be reported; (3) When the two are the same or the total amount is lower than that of formaldehyde, differential calculation is not performed according to the aforementioned rules, and methanol is determined not to be detected. The above processing principles are in line with the technical positioning of rapid on-site screening: The purpose of this invention is to quickly identify whether there is significantly excessive methanol and formaldehyde in liquor samples, rather than to provide laboratory-level precise content data. For samples at the critical value, the actual regulatory needs can be met by a two-level mode of screening and retesting.

[0057] It should be noted that the semi-quantitative results of this invention are not precise numerical values, but rather concentration range estimates obtained through visual comparison with a standard color chart. The standard color chart should be prepared for the target liquor's alcohol content (e.g., 52% vol, 60% vol) and typical matrix to eliminate the influence of different alcohol contents on color depth. For samples at the color level boundary (e.g., color depth between 5 mg / L and 10 mg / L), it can be reported as a "5~10 mg / L" range, or the absorbance can be further measured using a portable spectrophotometer to improve the accuracy of the determination. Those skilled in the art will understand that the semi-quantitative determination has a visual error of ±1 color level. This error range is consistent with the technical positioning of rapid on-site screening and does not affect the qualitative determination of whether the sample exceeds the standard.

[0058] S104, using the residual liquid of the liquor sample retained in the sample chamber for heavy metal screening.

[0059] The purpose of this step is to fully utilize the residual liquid in the sample chamber after gas-phase diffusion pretreatment for rapid screening of heavy metals. During gas-phase diffusion, methanol and formaldehyde evaporate into the gas phase, while heavy metal ions (such as lead) are non-volatile and remain completely in the residual liquid in the sample chamber. The residual liquid in the sample chamber can be used directly for heavy metal screening without additional transfer or pretreatment steps.

[0060] The residual liquid refers to the liquid retained in the sample chamber of a sealed container after gas-phase diffusion pretreatment. The main components of this residual liquid are ethanol, water, esters, and non-volatile heavy metal ions. Undissolved, insoluble solid acidic material particles may remain at the bottom. Compared to the original liquor sample, the methanol and / or formaldehyde content in this residual liquid has decreased, but the ethanol concentration remains close to the original liquor level. Therefore, when used directly for heavy metal screening, heavy metal colorimetric test strips with a certain tolerance to high alcohol concentrations should be selected to avoid solvent interference and pigment diffusion problems caused by ethanol. When collecting the residual liquid, avoid the solid precipitate at the bottom to prevent particles from interfering with the color development of the test strip.

[0061] In one specific embodiment of the present invention, the heavy metal screening includes directly adding the residual liquid to a heavy metal colorimetric test strip, especially a heavy metal colorimetric test strip that exhibits colorimetric stability in an ethanol environment of 50% vol or higher, and determining the presence of heavy metals based on the color change of the test strip. This is a conventional method for rapid on-site screening of heavy metals in the art. The heavy metal colorimetric test strip can be a commercially available lead ion test strip, etc., and its colorimetric principle is generally based on the reaction of a specific colorimetric agent with heavy metal ions to produce a characteristic color change.

[0062] Those skilled in the art will understand that the selection and specific application methods of the heavy metal colorimetric test strips are conventional techniques in the field. For example, lead ion test strips are typically based on the principle that lead reacts with specific ligands to form red or purple complexes. The specific brand of the test strip, the colorimetric reagent formulation, and the operating method can all adopt conventional solutions known in the art. In this invention, the key lies in utilizing the residual liquid after gas-phase diffusion pretreatment for screening, rather than directly detecting the original liquor sample, thereby reducing, to some extent, the oxidation or reduction interference that methanol and formaldehyde may cause to the heavy metal test strips.

[0063] In one specific embodiment of the present invention, the target of the heavy metal screening is lead. Lead is the most common and most strictly regulated heavy metal contaminant in liquor, mainly originating from leaching from brewing equipment, pipes, and containers. The method of the present invention is particularly suitable for rapid on-site screening of this type of heavy metal. However, those skilled in the art will understand that, depending on actual regulatory needs and the availability of test strips, the method of the present invention can also be extended to screen for other heavy metal ions, such as cadmium and mercury, which is a conventional expansion of detection targets in the art.

[0064] The following examples illustrate in detail the method for simultaneous identification of harmful substances in baijiu based on gas phase diffusion pretreatment.

[0065] Example 1 Take 0.5 mL of 52% vol strong-aroma baijiu sample and place it in the lower sample chamber (inner diameter 15 mm, height 20 mm). Add 5 mg of H-type zeolite molecular sieve particles to the bottom of the sample chamber. Place a silica gel plate (10 mm × 10 mm, first absorption solution) impregnated with acetylacetone colorimetric reagent (15 g ammonium acetate, 0.3 mL glacial acetic acid, 0.2 mL acetylacetone, diluted to 100 mL with water) in the left sub-chamber of the colorimetric absorption chamber. Add 0.5 mL of the second absorption solution (0.5 g sodium chromotropic acid, 15 mL concentrated sulfuric acid, 0.2 mL potassium permanganate-phosphoric acid solution, freshly prepared before use) to the right sub-chamber. Seal the container with a polytetrafluoroethylene microporous membrane (pore size 0.22 μm, effective area 1.77 cm²). 2 Separate the silica gel plate and seal it, then place it in a 45°C constant temperature water bath for 15 minutes. After the gas phase diffusion is complete, transfer the silica gel plate and the second absorbent to glass test tubes respectively, and heat them together in a boiling water bath for 10 minutes.

[0066] Standard color chart comparison: The first absorbent (silica gel plate) did not turn yellow. Compared with the pre-prepared formaldehyde standard color chart (0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L), formaldehyde was determined to be undetectable or below the low concentration range. The second absorbent (after adding chromotropic acid-sulfuric acid) turned blue-purple. Compared with the pre-prepared methanol standard color chart (0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, color developed after oxidation), the color depth was between 5 mg / L and 10 mg / L, indicating that methanol was in the low concentration range (below 5 mg / L). 0.3 mL of residual liquid was taken from the top of the sample chamber and added to lead ion test paper; no color development was observed, indicating that lead was undetectable.

[0067] The method for preparing the formaldehyde standard color card is as follows: Prepare 52% vol ethanol aqueous solutions with formaldehyde concentrations of 0 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L. Perform gas-phase diffusion and color development reactions under the same conditions as in this embodiment, record the color development colors corresponding to each concentration, and prepare a visual standard color card. The method for preparing the methanol standard color card is as follows: Prepare 52% vol ethanol aqueous solutions with methanol concentrations of 0 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L. Perform gas-phase diffusion, oxidation, and color development reactions under the same conditions as in this embodiment, record the color development colors corresponding to each concentration, and prepare a visual standard color card.

[0068] Example 2 Take 1.0 mL of 60% vol bulk baijiu sample and place it in the sample chamber (20 mm inner diameter, 25 mm height), add 2 mg of acidic alumina. Place glass fiber paper (15 mm × 15 mm) impregnated with acetylacetone colorimetric reagent in the left sub-chamber, and add 0.5 mL of the second absorption solution (0.8 g sodium chromotropic acid, 15 mL concentrated sulfuric acid, and 0.3 mL potassium permanganate-phosphoric acid solution, freshly prepared before use) to the right sub-chamber. Separate with a polytetrafluoroethylene microporous membrane (0.45 μm pore size) and incubate in a 50°C water bath for 10 min. After removal, heat in a boiling water bath for 5 min.

[0069] The first absorbent is yellow; compared to the formaldehyde standard color chart, its color depth is close to the 10 mg / L level, indicating that formaldehyde is in the medium concentration range (5~10 mg / L). The second absorbent is deep blue-purple; compared to the methanol standard color chart, its color depth exceeds the 20 mg / L level, indicating that the total methanol and formaldehyde content is in the high concentration range (greater than 10 mg / L). The total concentration result is higher than the formaldehyde result (two color levels higher), and the differential estimation indicates that methanol is in the medium concentration range. The residual liquid, when added to lead test paper, turns pale red; compared to the lead standard color chart, it indicates that lead is in the low concentration range.

[0070] Those skilled in the art should understand that the specific embodiments described above are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, or improvements made to the technical solutions of the present invention without departing from the technical principles thereof should fall within the scope of protection of the present invention.

Claims

1. A method for simultaneous identification of harmful substances in baijiu (Chinese liquor) based on gas-phase diffusion pretreatment, characterized in that, Includes the following steps: The liquor sample and two independent absorption and color-developing solutions were placed in the sample chamber and color-developing absorption chamber of the same sealed container, respectively. The sealed container was equipped with a gas-permeable and liquid-barrier membrane, so that the gas phase components volatilized from the liquor sample came into contact with the two independent absorption and color-developing solutions, while the liquid phases were isolated from each other. An insoluble solid acidic material was pre-placed in the sample chamber as a formaldehyde release promoter. The temperature of the sealed container is controlled at 40℃~60℃ and maintained for 10min~20min to allow methanol and / or formaldehyde that may be present in the liquor sample to volatilize and be absorbed by the two independent absorption and color development solutions. Take out the two independent absorption color-developing solutions after absorption, and keep them at 70℃~100℃ for 5min~15min to allow the color development reaction to be fully completed. Then, based on the color changes of the two independent absorption color-developing solutions, determine the presence of methanol and / or formaldehyde in the liquor sample and the semi-quantitative results. Heavy metal screening was performed using the residual liquid from the liquor sample retained in the sample chamber.

2. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 1, characterized in that, The two independent absorption and color-developing solutions are a first absorption solution and a second absorption solution. The first absorption solution is an acetylacetone color-developing agent loaded on a porous solid support, used to react and generate a yellow compound in the presence of formaldehyde. The second absorption solution includes an oxidation absorption solution and a color-developing solution. The oxidation absorption solution is a phosphoric acid solution containing an oxidant, which oxidizes methanol to formaldehyde in the presence of methanol. After the gas phase diffusion is completed, a chromotropic acid-sulfuric acid solution is added to the oxidation absorption solution and heated to allow formaldehyde to react with the chromotropic acid to generate a blue-purple compound.

3. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 2, characterized in that, The determination of the presence of methanol and / or formaldehyde and the semi-quantitative results include: The presence of formaldehyde is determined based on the color development of the first absorbent liquid. If it is present, a semi-quantitative result of formaldehyde is obtained by comparing it with a standard color card. The total amount of methanol and formaldehyde is determined based on the color development of the second absorbent. If they are detectable, a semi-quantitative result of the total amount is obtained by comparing with the standard color card. If both formaldehyde and methanol are detected, and the total semi-quantitative result is higher than the formaldehyde semi-quantitative result, then the relative semi-quantitative result of methanol is obtained by the difference between the total semi-quantitative result and the formaldehyde semi-quantitative result.

4. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 2, characterized in that, The oxidant in the oxidation absorption liquid is a potassium permanganate-phosphoric acid solution.

5. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 2, characterized in that, The colorimetric absorption chamber is divided into two interconnected sub-chambers by a partition. The first absorbent and the second absorbent are placed in the two sub-chambers respectively, and both sub-chambers are connected to the sample chamber through the same gas phase space.

6. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 1, characterized in that, The gas-permeable and liquid-blocking membrane is a polytetrafluoroethylene microporous membrane with a pore size of 0.1μm~0.45μm.

7. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 2, characterized in that, The volume of the liquor sample is 0.5 mL to 1.0 mL, and the volume of the second absorbent is 0.3 mL to 1.0 mL; the first absorbent exists in the form of a porous solid support, and the amount of the porous solid support is 1 cm². 2 ~4cm 2 .

8. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 1, characterized in that, The temperature of the sealed container is controlled by placing it in a water bath at 40℃~60℃.

9. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 1, characterized in that, The heavy metal screening involves adding the residual liquid from the liquor sample to heavy metal colorimetric test strips and determining the presence of heavy metals based on the color change of the test strips.

10. The method for simultaneous identification of harmful substances in baijiu based on gas-phase diffusion pretreatment as described in claim 1 or 9, characterized in that, The target of the heavy metal screening is lead.