Method for measuring oxygen isotope ratio of water in high-alcohol-content white spirit

Abstract

The invention provides a method for determining the oxygen isotope ratio of water in high-alcohol-content Baijiu, and relates to the field of stable isotope ratio mass spectrometry detection. The determination method comprises the following steps: diluting to-be-determined high-degree white spirit by using water with a known oxygen isotope ratio to obtain a diluted target spirit sample; performing equilibrium exchange reaction on 16O of water in the target wine sample and 18O of the carbon dioxide standard gas to obtain a reaction wine sample; measuring the oxygen isotope ratio of water in the reaction wine sample; and performing conversion to obtain the oxygen isotope ratio. According to the method, the high-degree white spirit is diluted with water with the known oxygen isotope ratio, the ethanol concentration is reduced to avoid interference of isotopic, and the original value is inversely calculated by combining the mass conservation principle. According to the method, tedious off-line physical separation is not needed, automatic analysis can be carried out by directly utilizing the on-line mass spectrometer, the operation process is greatly simplified, and the detection efficiency is remarkably improved while it is guaranteed that the result is accurate and reliable.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of stable isotope ratio mass spectrometry, and particularly relates to a method for determining the oxygen isotope ratio of water in high-alcohol liquor. BACKGROUND

[0002] As an advanced physicochemical detection method, stable isotope analysis has played an increasingly important role in the fields of food safety, provenance tracing, and product authenticity identification in recent years. The water sources formed under different geographical and climatic conditions have unique hydrogen and oxygen isotope fingerprint characteristics, which makes the determination of the oxygen isotope ratio (δ 18 O) of water in liquor products an important basis for identifying the production area of liquor, judging the fermentation process (such as the difference between solid-state fermentation and liquid-state fermentation), and identifying the year of production. In particular, in the quality control and market supervision of high-end liquor, the establishment of a rapid and accurate isotope detection method has significant scientific value and application prospects for combating counterfeit and inferior products and maintaining market order.

[0003] At present, the general method for determining the oxygen isotope ratio of water in a liquid sample in a laboratory is based on the principle of "CO2-H2O isotope exchange", and is usually realized by means of an online gas preparation-stable isotope mass spectrometer (Gasbench-IRMS). The basic process of this method is to introduce carbon dioxide standard gas (CO2) into a sample bottle to promote oxygen isotope equilibrium exchange between CO2 in the gas phase and H2O in the liquid phase. The abundance of 18 O in CO2 after equilibrium can represent the abundance of 18 O in water. Subsequently, the instrument extracts the equilibrium gas in the headspace portion through a sampling needle into a mass spectrometer for detection, thereby indirectly obtaining the oxygen isotope ratio of water. For pure water or low-alcohol samples, this technology has become the mainstream detection method in the industry due to its high degree of automation, small sample size, and good reproducibility.

[0004] However, when the above general method is directly applied to the detection of high-alcohol liquor with an ethanol content greater than 40%, it faces a serious physical interference problem. High-alcohol liquor contains high concentrations of ethanol, and since ethanol has strong volatility, a large amount of ethanol vapor will enter the mass spectrometer along with CO2 during the gas equilibrium and headspace sampling process. When the isotope mass spectrometer measures the oxygen isotope composition of CO2, the main monitored mass numbers are 44, 45, and 46 (isotope molecules such as 12 C 16 O2、 13 C 16 O2, etc.), and the mass number of the ethanol molecule (C2H6O) is also 46. This overlap of mass numbers will directly interfere with the determination of the δ 18The determination of O makes the instrument detection data greatly deviate and cannot accurately reflect the real isotope characteristics of water in liquor.

[0005] In addition, in addition to the cumbersome operation, the offline physical separation method (such as atmospheric distillation or vacuum extraction) also has a defect that is difficult to overcome in theory. Since water and ethanol both have intermolecular forces, during the phase change of distillation or extraction, isotopic fractionation effect inevitably occurs, resulting in that the separated water cannot truly represent the isotope composition in the original liquor sample. In addition, for azeotrope system, it is difficult to completely extract water by physical separation, and the residual water is often enriched in heavy or light isotopes, thereby introducing systematic deviation. Therefore, the determination value of the traditional offline separation is often used as the 'true value' to evaluate the isotope characteristics of the alcohol-containing system, which often lacks accuracy.

[0006] In order to avoid the above interference, the prior art usually adopts an 'offline method' for pretreatment, that is, the water is manually separated from the liquor by manually building a special separation device, and then the water is determined. Although this method can remove the ethanol interference, it has obvious defects: first, the experimental personnel need to build the device by themselves, the operation process is very troublesome and time-consuming, and it is difficult to adapt to the rapid detection of batch samples; second, the cumbersome manual separation step not only increases the risk of introducing experimental errors, but also destroys the original online automation advantage of the Gasbench-IRMS system, making the detection process complex and having very limited applicability. Therefore, there is an urgent need in the field for a technical solution for accurately determining the oxygen isotope ratio of water in high-grade liquor without complex physical separation. SUMMARY

[0007] The purpose of the present application is to provide a method for determining the oxygen isotope ratio of water in high-grade liquor, which uses water with a known oxygen isotope ratio to dilute high-grade liquor to avoid ethanol interference, and combines the principle of mass conservation to recalculate, so as to realize efficient and accurate online automatic determination without physical separation.

[0008] In order to achieve the above purpose of the present application, the following technical solutions are adopted: In a first aspect, the present application provides a method for determining the oxygen isotope ratio of water in high-grade liquor, comprising: using water with a known oxygen isotope ratio to dilute the high-grade liquor to be tested to obtain a diluted target liquor sample; based on the principle of isotope exchange, promoting the oxygen isotope ratio of water in the target liquor sample to be equal to that of the water used for dilution; 16 O and the 18 O of the carbon dioxide standard gas to obtain a reaction liquor sample; using an online gas preparation-stable isotope mass spectrometer to determine the oxygen isotope ratio of water in the reaction liquor sample; The oxygen isotope ratio of water in the high-grade liquor to be tested is obtained by conversion through a mass conservation equation.

[0009] In an optional embodiment, the oxygen isotope ratio of the water with a known oxygen isotope ratio ranges from -20.0‰ to +20.0‰.

[0010] In an optional embodiment, the water with a known oxygen isotope ratio is prepared through evaporation and concentration treatment.

[0011] In an optional embodiment, after the high-grade liquor to be tested is diluted with the water with a known oxygen isotope ratio, the alcohol content of the target liquor sample ranges from 10%vol to 20%vol.

[0012] In an optional embodiment, the target liquor sample further includes standing for 8 hours to 10 hours before the equilibrium exchange reaction.

[0013] In an optional embodiment, the equilibrium exchange reaction lasts for 18 hours to 36 hours.

[0014] In an optional embodiment, when the oxygen isotope ratio of water in the reaction liquor sample is determined using an online gas preparation-stable isotope mass spectrometer, each target liquor sample is determined at least twice in parallel, and if the standard deviation SD between the data determined in parallel is less than 0.5‰, the data is determined to be reliable.

[0015] In an optional embodiment, the expression of the mass conservation equation is: ; wherein X 酒中水 represents the mass percentage of water in the high-grade liquor to be tested; X 添加水 represents the mass percentage of the water with a known oxygen isotope ratio during dilution, and X 酒中水 + X 添加水 = 100%; represents the oxygen isotope ratio of water in the reaction liquor sample determined; represents the oxygen isotope ratio of the water with a known oxygen isotope ratio; represents the oxygen isotope ratio of water in the high-grade liquor to be tested.

[0016] In an optional embodiment, the carbon dioxide standard gas is a mixture of carbon dioxide and helium; wherein the volume percentage of carbon dioxide is 0.2% to 1%.

[0017] In an optional embodiment, the temperature of the equilibrium exchange reaction is 25℃ to 30℃.

[0018] The application provides a method for determining the oxygen isotope ratio of water in high-grade liquor, which effectively reduces the ethanol concentration in the liquor sample by diluting the high-grade liquor to be measured with water with a known oxygen isotope ratio. Since the high-concentration ethanol in high-grade liquor has strong volatility, and the mass number of the ethanol molecule overlaps with the key mass number (such as mass number 46) in carbon dioxide isotope determination, direct determination will produce isobaric interference. The method significantly reduces the background interference of ethanol on mass spectrometric determination through dilution treatment, so that the sample can be directly analyzed automatically by an online gas preparation-stable isotope mass spectrometer. This processing method avoids the cumbersome physical pretreatment (such as offline distillation separation) that must be performed in the prior art to remove ethanol interference, does not require the construction of a special separation device, greatly simplifies the operation process, realizes the online detection process, significantly improves the detection efficiency, and saves time and effort.

[0019] Meanwhile, the method combines the principle of mass conservation, uses the known data of the added water and the measured mixed sample data, and can accurately calculate the oxygen isotope ratio of the water in the original high-grade liquor through mathematical conversion. This "dilution-determination-reverse calculation" strategy effectively avoids ethanol interference while ensuring the accuracy and reliability of the final results, solves the problems faced by the existing methods for analyzing the oxygen isotope of water in high-grade liquor, and provides strong technical support for detection and research in related fields. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope of protection of the present application. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0021] Figure 1 The calibration curve of the oxygen isotope ratio in Example 1 of the present application; Figure 2 The verification result graph of the oxygen isotope ratio of water in the alcohol solution with different water addition ratios in Example 2 of the present application; Figure 3 The ion flow spectrum of the oxygen isotope of water in high-grade liquor in Example 3 of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the present application will be described in detail below with reference to Examples, but those skilled in the art will understand that the following Examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions not specified in the Examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, but are conventional products that can be obtained commercially.

[0023] The present application provides a method for determining the oxygen isotope ratio of water in high-alcohol liquor, comprising: Step S1, using water with known oxygen isotope ratio to dilute the high-alcohol liquor to be measured to obtain a diluted target liquor sample.

[0024] The above step refers to selecting a water with a known oxygen isotope ratio (δ 18 O) value as a diluent, and adding it to high-alcohol liquor with high ethanol content (which can be greater than 40%) for mixing.

[0025] Through this physical mixing process, the alcohol content of the liquor sample is reduced, thereby preparing a mixed solution suitable for subsequent detection, i.e., a "target liquor sample", and ultimately obtaining a mixed solution with lower alcohol content (e.g., 5% to 20% vol) and composed of two parts of water, i.e., "water in the original liquor" and "additional known water".

[0026] It should be noted that the high concentration of ethanol (mass number 46) in high-alcohol liquor can seriously interfere with the determination of carbon dioxide (mass numbers 44, 45, and 46) by mass spectrometry. Through the dilution step, the ethanol concentration is effectively reduced, thereby reducing or avoiding the interference of ethanol evaporation on subsequent isotope determination, and online detection can be performed without complex physical separation (such as distillation).

[0027] Specifically, first, prepare known water, i.e., water with a specific oxygen isotope ratio (e.g., in the range of -20.0‰ to +20.0‰), and then mix the above water with a known oxygen isotope ratio with high-alcohol liquor at a certain ratio, so that the alcohol content of the mixture is within a specific concentration range, such as between 5 and 20% vol.

[0028] The present application has found that the alcohol content after dilution (the concentration of the target liquor sample) has a significant impact on the precision of the determination results, and there is an optimal balance interval.

[0029] On the one hand, if the dilution is excessive (e.g., the alcohol content is too low), although ethanol interference is completely eliminated, the excessive amount of known water added will result in a low mass percentage of the original wine sample in the system (water in wine X). According to the error propagation principle, the weighing error or instrument system error will be amplified in this case, leading to a larger deviation in the back-calculation results. On the other hand, if the dilution is insufficient (e.g., the alcohol content is too high), although more information about the original wine sample is retained, the residual ethanol concentration in the system may still be at the critical interference level, resulting in slightly higher background noise during mass spectrometry.

[0030] Therefore, this method can preferably control the alcohol content of the target wine sample between 12% vol and 18% vol, with the most preferably around 15% vol, in order to achieve the best balance between 'suppressing ethanol interference' and 'reducing error amplification'.

[0031] Step S2, based on the principle of isotope exchange, promotes the exchange of water in the target wine sample. 16 O and carbon dioxide standard gas 18 O undergoes an equilibrium exchange reaction, yielding a reacted wine sample.

[0032] This step is the core pretreatment step for gas isotope ratio mass spectrometry analysis.

[0033] Carbon dioxide standard gas is introduced into a container containing the target wine sample. Under constant temperature and sealed conditions, carbon dioxide (CO2) in the gas phase and water (H2O) in the liquid phase undergo oxygen atom exchange until the oxygen isotopes in the two phases (CO2 and H2O are converted to carbon dioxide and water) are in constant temperature and sealed conditions. 16 O and 18 O) reaches chemical equilibrium, thus obtaining the "reaction wine sample" (i.e., a gas-liquid mixture that has reached isotopic equilibrium). At this point, the carbon dioxide in the gas phase... 18 O abundance is sufficient to represent water in the liquid phase. 18 O abundance.

[0034] Using CO2 as a probe gas, oxygen isotope information that is difficult to measure directly in water can be "transferred" to CO2 molecules, making it easier for mass spectrometers to perform gas-phase detection.

[0035] Specifically, the process begins with gasification, which involves injecting a mixed gas (e.g., CO2:He = 0.2%~1%) into a glass tube containing the target wine sample. Then, equilibrium control is performed by placing the sample in a constant temperature environment (e.g., 28°C) for a certain period (e.g., 18 to 36 hours) to ensure the exchange reaction reaches full equilibrium.

[0036] Step S3: Use an online gas preparation-stable isotope mass spectrometer to determine the oxygen isotope ratio of water in the reaction wine sample.

[0037] In this step, the gas balanced in the previous step is sampled and analyzed using a special analytical instrument: online gas preparation-stable isotope mass spectrometer (Gasbench-IRMS). The instrument detects the mass number change in the gas, thereby determining the oxygen isotope ratio of water in the mixed solution (i.e. the reaction wine sample), thereby obtaining the oxygen isotope ratio data of the "target wine sample" (the diluted mixed solution).

[0038] Compared with offline manual separation determination, the use of Gasbench-IRMS can realize automatic online detection, simple operation, time and labor saving, and high data stability.

[0039] Specifically, the instrument uses a Gasbench-IRMS combination instrument, and parallel samples can be set for each sample. According to the parallel samples, it is determined that the instrument is stable, and the data measured can be reliable and can be used for subsequent calculation.

[0040] Step S4, the oxygen isotope ratio of water in the high liquor to be measured is obtained by conversion through the mass conservation equation.

[0041] Since the value measured in step S3 is the value of the "diluted mixed solution", not the value of the "original wine", it is necessary to use mathematical tools to calculate. Based on the law of conservation of mass, the total amount of isotopes before and after mixing remains unchanged.

[0042] By constructing an equation set containing the relationship between "water in the original wine", "added water" and "water after mixing", the unknown original wine data is calculated, and the final analysis result: the oxygen isotope ratio of water in the high liquor to be measured is obtained.

[0043] Through this step, the isotopic characteristics of the original high liquor can be accurately restored from the diluted mixed sample data, which not only avoids the detection interference of high concentration ethanol, but also ensures the accuracy of the results.

[0044] In some embodiments, the oxygen isotope ratio of the water with a known oxygen isotope ratio ranges from -20.0‰ to +20.0‰. For example, it can be -20.0‰, -15.0‰, -10.0‰, -5.0‰, 0‰, +5.0‰, +10.0‰, +15.0‰, +20.0‰, etc. It should be noted that the above values can be positive or negative.

[0045] The above numerical range is an effective interval verified in the method. Selecting water in this range as added water provides an accurate and appropriately sized known quantity for the "mass conservation equation". Using this enriched positive water for dilution helps to form a clear isotopic difference with the test wine sample (usually negative) in the mathematical conversion, thereby facilitating the accurate back calculation of the oxygen isotope ratio of water in the high liquor to be measured through the equation.

[0046] In some embodiments, the water with known oxygen isotope ratio is prepared by evaporation concentration treatment.

[0047] In one embodiment of the present application, the water with known oxygen isotope ratio is prepared by evaporation concentration treatment. The specific evaporation concentration method is not particularly limited as long as it can volatilize light oxygen isotopes in water and thereby enrich heavy oxygen isotopes.

[0048] As a preferred embodiment, it can be achieved by electric heating plate heating, reduced pressure rotary evaporation or a combination of the two.

[0049] In some embodiments, after dilution of the to-be-tested high-grade liquor using water with known oxygen isotope ratio, the alcohol content of the target liquor sample ranges from 10% vol to 20% vol. For example, it can be 10% vol, 12% vol, 14% vol, 16% vol, 18% vol, 20% vol, etc.

[0050] The above limitation must control the mixing ratio of water with known oxygen isotope ratio and to-be-tested high-grade liquor when preparing the "target liquor sample", so that the volume percentage of ethanol (alcohol content) in the final mixed solution falls within the specific interval of 10% vol to 20% vol, thereby obtaining a to-be-tested sample solution with low alcohol content.

[0051] Compared with the original to-be-tested high-grade liquor with ethanol content usually greater than 40%, the ethanol concentration of the processed target liquor sample is significantly reduced and stably maintained between 5% vol and 20% vol. This specific concentration range is to solve the "ethanol interference" problem in mass spectrometry. Since high-grade liquor (> 40%) has strong volatility, ethanol molecules (mass number 46) are easy to enter the mass spectrometer, directly interfering with the determination of key isotope mass number 46 (C 12 C 16 O 18 O) in carbon dioxide gas. By diluting the alcohol content to a low concentration range of 10% vol to 20% vol, the volatilization of ethanol can be effectively inhibited, preventing it from entering the mass spectrometer in large quantities to cause isobaric interference, thereby ensuring the accuracy of oxygen isotope ratio (δ 18 O) determination.

[0052] Specifically, the amount of water required for dilution can be calculated according to the initial degree of the original liquor.

[0053] In some embodiments, the target liquor sample further includes standing for 8 hours to 10 hours before performing the equilibrium exchange reaction. For example, it can be 8 hours, 8.2 hours, 8.5 hours, 8.8 hours, 9 hours, 9.2 hours, 9.5 hours, 9.8 hours, 10 hours, etc.

[0054] The above steps define that after the "dilution" step is completed to obtain the target liquor sample, but before the next step of "isotope equilibrium exchange reaction" (i.e. filling with carbon dioxide gas) is performed, a standing treatment step needs to be added. The specific operation is to place the prepared target liquor sample in a container and keep it in a static state without violent disturbance, and the duration is controlled between 8 hours and 10 hours, so as to obtain a target liquor sample with a more stable system and more uniform component mixture.

[0055] This standing step helps the added "known water" to fully fuse with the original components (water and ethanol, etc.) in the "to-be-tested high-grade liquor" at the microscopic level, eliminates the initial unevenness of the mixture, and ensures that the system reaches a thermodynamic and physical stable state. This provides a uniform liquid phase basis for the subsequent isotope exchange reaction, which helps to improve the precision and accuracy of the final determination results.

[0056] For example, the diluted liquor sample can be sealed in a container and placed at room temperature.

[0057] In some embodiments, the time of the equilibrium exchange reaction is 18 hours to 36 hours. For example, it can be 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, etc.

[0058] In the time limit of the "equilibrium exchange reaction" step, the time length required for the oxygen isotope exchange reaction between carbon dioxide in the gas phase and water in the liquid phase to reach dynamic equilibrium after the carbon dioxide standard gas is introduced into the target liquor sample is specified, so that within this time range, the reaction system reaches the chemical equilibrium state of oxygen isotope.

[0059] At this time, the 18 O abundance of the carbon dioxide in the gas phase can accurately and stably represent the 18 O abundance of the water in the liquid phase.

[0060] The lower limit (18 hours) is set to ensure that there is enough time for the isotope exchange reaction to proceed to the end, and to avoid deviation of the determination results from the true value due to insufficient reaction time. The upper limit (36 hours) is set to control the detection period while ensuring equilibrium, avoid unnecessary time waste, and improve detection efficiency. This time range has been verified and can ensure the accuracy and reproducibility of the final determination data.

[0061] Specifically, the sample bottle filled with mixed gas (CO2) is placed in a constant temperature (e.g. 28°C) device, and the state is maintained until the set time point is reached. For example, in a specific implementation, 24 hours can be selected as the equilibrium time.

[0062] In some embodiments, when determining the oxygen isotope ratio of water in the reaction wine sample using an online gas preparation-stable isotope mass spectrometer, each target wine sample is determined at least twice in parallel (for example, it can be determined three times in parallel), and if the standard deviation SD between the parallel determination data is less than 0.5 ‰, it is determined that the data is reliable.

[0063] This step provides a data quality control (QC) process in the instrument analysis stage.

[0064] Specifically, when detecting the sample using an online gas preparation-stable isotope mass spectrometer (Gasbench-IRMS), it cannot be relied on a single measurement result. The operator needs to perform at least two repeated determinations (parallel determinations) on the same sample (i.e., the wine sample obtained in the foregoing step). Subsequently, the standard deviation (Standard Deviation, SD) between the parallel determination data is calculated using a statistical method, thereby obtaining a set of oxygen isotope ratio data of parallel determination (for example, determination value 1 and determination value 2) and a calculated standard deviation value (SD). According to the comparison result of the SD value and the preset threshold value (0.5 ‰), a conclusion is drawn about whether the data is valid and the instrument state is stable.

[0065] By setting the standard of SD < 0.5 ‰, the running state of the mass spectrometer during the determination process can be effectively monitored. If the deviation is too large, it means that the instrument may have fluctuations or faults, so that the systematic error can be timely excluded; only the data meeting the parallel requirement is adopted, which excludes abnormal values caused by accidental errors or operation errors, and ensures that the basic data used for the quality conservation calculation is accurate and reliable.

[0066] Specifically, a sequence is set on the Gasbench-IRMS, and the gas in the same sample bottle is sampled and analyzed multiple times, or two identical parallel sample bottles are prepared for determination, and determination values y1, y2, … yn (where n≥2) are obtained. Then, SD is calculated, and the dispersion degree of the data is calculated using the standard deviation formula. For two parallel determinations (n=2), the calculation logic (formula 1) of SD is as follows: ; Wherein, is the average value.

[0067] If the calculated SD < 0.5 ‰, it is determined that the instrument is stable, and the data (y1, y2) is reliable, and the average value thereof can be used for subsequent calculation. If SD≥0.5 ‰, it is determined that the data is unreliable, and it may need to be re-determined or the instrument state is checked.

[0068] For example, assume that two parallel determinations were performed on a sample, and the results were -18.222‰ and -18.225‰, respectively. The difference between the two is calculated to be very small, and the standard deviation is obviously less than 0.5‰ (the specific deviation is only about 0.003‰), so the data set is determined to be reliable.

[0069] In some embodiments, the expression of the mass conservation equation (Formula 2) is: ; wherein X 酒中水 represents the mass percentage of water in the high-grade liquor to be tested; X 添加水 represents the mass percentage of water with a known oxygen isotope ratio during dilution, and X 酒中水 + X 添加水 = 100%; represents the oxygen isotope ratio of water in the reaction liquor sample determined; represents the oxygen isotope ratio of water with a known oxygen isotope ratio; represents the oxygen isotope ratio of water in the high-grade liquor to be tested.

[0070] The above steps provide the core mathematical model for final calculation. It is based on the law of conservation of mass in physical chemistry, that is, the total amount of oxygen isotopes in a mixed solution is equal to the sum of the amounts of oxygen isotopes in each component. The processing process is to substitute the "determination data" (isotope ratio of the diluted liquor sample) and "known data" (isotope ratio of the added water, mass ratio during dilution) obtained in the previous steps into the equation, and to deduct the effect of the added water through mathematical operation.

[0071] The expression provided in the examples can be based on the following logical model: (1) Total amount conservation premise: it is assumed that the mass of water in the diluted system is composed of two parts, namely "water in the original liquor" and "added water", and the sum of the mass percentages of the two is 100%. That is (Formula 3): X 酒中水 + X 添加水 = 100%; (2) Isotope mass balance: the total isotope characteristics after mixing is the weighted sum of the isotope characteristics of the two parts (Formula 4): ; (3) Final conversion algorithm (i.e., expression 2): by moving terms, the unknown original liquor isotope ratio is solved.

[0072] In the above expression, X 酒中水 represents the mass percentage of water in the high-grade liquor to be tested, which is a value determined according to the dilution ratio; X 添加水 represents the mass percentage of water with a known oxygen isotope ratio during dilution; represents the oxygen isotope ratio of the diluted mixed solution (reaction wine sample) actually measured by an online gas preparation-stable isotope mass spectrometer in the representative; represents the oxygen isotope ratio of water with a known oxygen isotope ratio, for example, 15 ‰; represents the oxygen isotope ratio of water in the to-be-tested high-grade liquor finally required.

[0073] The equation can accurately restore the "mixed value" to the "original value". Experimental data show that the value calculated by the mass conservation method is very close to the theoretical value (error of about 0.3 ‰), which meets the general requirements of stable isotope testing. Through mathematical inversion, the tester can first reduce the ethanol concentration by dilution to avoid the interference of mass spectrometric detection, and then obtain the true result by calculation, which ingeniously solves the contradiction between ethanol physical interference and data accuracy.

[0074] This step can be automatically completed by computer software (such as Excel or mass spectrometer matching data processing software). The operator only needs to input the weighing data (calculate X) during dilution and the known isotopic value of water, and combine the mixed sample isotopic value measured by the instrument to automatically output the final result according to the above formula.

[0075] In some embodiments, the carbon dioxide standard gas is a mixture of carbon dioxide and helium; wherein the volume percentage of carbon dioxide is 0.2% to 1%. For example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0076] When performing an isotopic exchange reaction, the gas injected into the reaction system is not pure carbon dioxide, but a mixture of carbon dioxide and helium. Helium is usually used as an inert carrier gas to carry the sample gas into the mass spectrometer, and also plays a role in dilution and transmission. The use of such a mixed gas can ensure that the mass spectrometer works at an appropriate pressure and flow rate, while providing a source of carbon dioxide required for isotopic exchange.

[0077] In some embodiments, the temperature of the equilibrium exchange reaction is 25°C to 30°C.

[0078] This concentration range is set in combination with the sensitivity and linear range of the instrument. Too high a concentration may cause the detector to saturate or have a nonlinear effect, and too low a concentration may result in insufficient signal strength. Controlling within 0.2% to 1% can obtain stable and moderate intensity mass spectrometric signals (such as ion currents of mass numbers 44, 45, and 46), thereby improving the signal-to-noise ratio and accuracy of δ 18 O determination.

[0079] The application will be further described below by means of specific examples, but it should be understood that these examples are only used for a more detailed description and should not be understood as limiting the application in any form.

[0080] Example 1 In this example, the oxygen isotope ratio of water in standard substance was determined. 18 O.

[0081] Experimental method: (1) 0.5 mL of three standard substances (GBW04458, δ 18 O = -0.15 ‰; GBW04459, δ 18 O = -8.61 ‰; GBW04460, δ 18 O = -19.13 ‰) were respectively taken into 12 mL glass tubes.

[0082] (2) Mixed gas (CO2:He=0.2%~1%) was injected into the glass tube, and the tube was equilibrated at 28℃ for 24 hours; (3) The δ 18 O value of water in the standard substance was determined by using Gasbench-IRMS, and the calibration curve table 1 was obtained, and the fitting equation was y=0.9842x-33.144, and the correlation coefficient R 2 =0.9999.

[0083] Table 1, oxygen isotope calibration curve of water

[0084] According to the linear fitting of the determination data in table 1 and the certificate value, the calibration curve as shown in Figure 1 The curve directly reflects the linear relationship between the instrument determination value and the standard value.

[0085] Example 2 In this example, the oxygen isotope ratio verification experiment of water in high-alcohol was carried out.

[0086] Experimental method: In order to verify the effectiveness of the method, anhydrous ethanol and water were used to prepare alcohol solution (22g anhydrous ethanol:24g distilled water), and the stable isotope ratio of the distilled water was-8.237±0.048‰, which was used to simulate 50° or so of liquor.

[0087] According to the ratio of 1:2 and 1:3 of alcohol solution and water, the normal dilution operation was simulated, and the alcohol degree was diluted to 10~15° interval, and the isotope ratio of the added water was-18.987±0.024‰.

[0088] The oxygen isotope ratio of water in the diluted alcohol solution is analyzed according to the above method, and the oxygen stable isotope ratio of water in the alcohol solution before dilution is calculated according to the principle of mass conservation, and compared with the water used for preparing the alcohol solution.

[0089] Results reference Figure 2 , Figure 2 It is shown that the oxygen isotope ratio of water calculated by the method combined with the principle of mass conservation is highly consistent with the actual added water at different dilution ratios (1:2 and 1:3).

[0090] The oxygen isotope ratio of water calculated by the mass conservation method after highly ethanol water dilution is very close to the test value before dilution. The test value of the sample with a dilution ratio of 1:2 is-8.35±0.28‰, and the test value of the sample with a dilution ratio of 1:3 is-8.59±0.35‰, which has an error of about 0.3‰ compared with the original added water-8.237±0.048‰, which meets the general requirements of stable isotope test. This shows that the method can accurately calculate the oxygen stable isotope ratio of water in highly liquor.

[0091] Example 3 In this embodiment, the determination of δ 18 O of water in highly liquor is carried out.

[0092] Experimental method: (1) Dilute a highly liquor with an alcohol content of 10, 15, and 20%vol with water having a known δ 18 O value (15.0‰) for 10 hours; (2) Take 0.5 mL into a 12 mL glass tube, inject mixed gas (CO2:He=0.2%-1%) into the glass tube, so that the δ 16 O of water in the liquor sample and the δ 18 O of carbon dioxide standard gas undergoes equilibrium exchange reaction, and the reaction temperature and time are 28℃ and 24 hours respectively; (3) Precise determination of highly liquor samples by online gas preparation-stable isotope mass spectrometer (Gasbench-IRMS). The typical ion flow spectrum obtained by the Gasbench-IRMS instrument during the determination is shown in Figure 3 , which shows the signal intensity change of mass numbers 44, 45 and 46.

[0093] The results are shown in Table 2: Table 2, determination of oxygen isotope ratio of water in highly liquor by Gasbench-IRMS

[0094] It should be noted that the samples in Table 2 are determined in parallel twice, and the standard deviation SD between the two data is less than 0.5 ‰, indicating that the instrument is stable and the data is reliable.

[0095] (4) The mass conservation conversion results are shown in Table 3: Table 3 Oxygen isotope results of water in high-grade liquor

[0096] Data analysis and determination of optimal conditions: Table 3 shows the back-calculation results at different dilutions. By comparing the three groups of data, it can be found that: When diluted to 15%vol, the back-calculation value is-11.28‰. At this concentration, the ethanol interference is effectively suppressed, and the dilution factor is moderate, the data is closest to the theoretical expectation, and is consistent with the verification trend of the simulation liquid in Example 2 (the error is only 0.3‰ under the optimal ratio in the simulation liquid). Therefore, it is determined that-11.28‰ is closest to the true value of the high-grade liquor.

[0097] When diluted to 10%vol, the back-calculation value is-12.15‰. Since the dilution factor is large (too much known water is added), the isotopic signal contribution rate of the original liquor sample in the mixed system is reduced, the error amplification factor during mathematical back-calculation is increased, and thus the result appears a certain degree of negative deviation.

[0098] When diluted to 20%vol, the back-calculation value is-10.92‰. At this time, it may be because the ethanol concentration is at the upper limit of the allowable range of the method, and the trace ethanol isobaric effect may not be completely eliminated, resulting in a slight positive deviation of the result.

[0099] Conclusion: The results of Example 3 show that the method can obtain referenceable isotopic data in the range of 10%vol to 20%vol (compared to the untreated direct injection which cannot be counted, which is a great progress), but in order to pursue high-precision detection results (error <0.5‰), it is recommended to strictly control the alcohol content after dilution to about 15%vol.

[0100] The results show that the method proposed by the present application, which dilutes the known oxygen isotope ratio of water and combines mass conservation conversion, can effectively obtain the oxygen isotope characteristic data of water in high-grade liquor, and realizes the quantitative analysis of high-grade liquor samples.

[0101] In order to further verify the reliability of the results, the present application has verified the accuracy of the method and the mass conservation model by'simulation liquid' (known true value) in Example 2.

[0102] In the determination of real high-alcohol liquor in Example 3, although the reference value is usually obtained by offline distillation, the research of the present application shows that the offline distillation method is easy to cause the deviation of oxygen isotope ratio due to phase separation effect in the heating or pressure reduction process when dealing with complex liquor matrix, and the determination value itself cannot be used as an absolute 'true value' standard. In contrast, the dilution method used in the present application is a physical mixing in liquid phase system, which does not involve phase separation, and avoids the error introduced by fractionation effect in principle.

[0103] In addition, as shown in Table 3, after diluting the same sample to different alcohol degrees (10%, 15%, 20% vol), the δ 18 Although the O value fluctuates slightly (affected by experimental operation error), it is overall in a reasonable range, and the results at different concentrations confirm each other, proving the internal consistency and stability of the method when dealing with complex matrix.

[0104] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent substitution for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining the oxygen isotope ratio of water in high-proof liquor, characterized in that, include: The high-proof liquor to be tested was diluted with water of known oxygen isotope ratio to obtain the diluted target liquor sample. Based on the principle of isotope exchange, the water in the target wine sample is promoted to... 16 O and carbon dioxide standard gas 18 O undergoes an equilibrium exchange reaction to yield the reacted wine sample; The oxygen isotope ratio of water in the reaction wine sample was determined using an online gas preparation-stable isotope mass spectrometer. The oxygen isotope ratio of water in the tested high-proof liquor was obtained by conversion using the mass conservation equation.

2. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, The known oxygen isotope ratio of water ranges from -20.0‰ to +20.0‰.

3. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, The water with the known oxygen isotope ratio was prepared through evaporation and concentration.

4. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, After diluting the high-proof liquor to be tested with water of known oxygen isotope ratio, the alcohol content of the target liquor sample ranges from 10% vol to 20% vol.

5. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, The target wine sample was allowed to stand for 8 to 10 hours before undergoing the equilibrium exchange reaction.

6. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, The equilibrium exchange reaction takes 18 to 36 hours.

7. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, When using an online gas preparation-stable isotope mass spectrometer to determine the oxygen isotope ratio of water in the reaction wine sample, each target wine sample should be measured in parallel at least twice. If the standard deviation (SD) between the parallel measurements is less than 0.5‰, the data is considered reliable.

8. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, The expression for the mass conservation equation is: ； Among them, X 酒中水 X represents the mass percentage of water in the tested high-proof liquor; 添加水 X represents the mass percentage of water with the known oxygen isotope ratio at the time of dilution, and X 酒中水 +X 添加水 =100%; The oxygen isotope ratio of water in the measured wine sample represents the oxygen isotope ratio of the water. The oxygen isotope ratio of water representing a known oxygen isotope ratio; This represents the oxygen isotope ratio of water in the high-proof liquor being tested.

9. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, The carbon dioxide standard gas is a mixture of carbon dioxide and helium; The volume percentage of carbon dioxide is 0.2% to 1%.

10. The method for determining the oxygen isotope ratio of water in high-proof liquor as described in claim 1, characterized in that, The temperature of the equilibrium exchange reaction is 25℃~30℃.

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