Method for detecting total iron and trivalent iron in baijiu

Abstract

The application discloses a detection method of total iron and trivalent iron in liquor, and belongs to the technical field of liquor detection. The method comprises the following steps: adding excessive maltol into a liquor sample to make the trivalent iron in the liquor sample completely complex and derive, determining the absorbance difference of the sample at 520nm before and after the derivation, and eliminating the interference of the background color of the liquor body; combining a trivalent iron standard curve, so that the specific and accurate quantitative detection of the trivalent iron content in the liquor can be realized. On this basis, the divalent iron in the liquor sample is completely oxidized into trivalent iron by an oxidizing agent, and the total iron content in the sample can be determined. The method only needs an ordinary ultraviolet-visible spectrophotometer to complete the detection, does not need large and precise instruments, has low reagent cost, and is simple in operation steps.

Description

Technical Field

[0001] This invention relates to a method for detecting total iron and ferric iron in baijiu (Chinese liquor), belonging to the field of baijiu testing technology. Background Technology

[0002] Iron is an essential trace element for the human body, and adequate iron intake is beneficial to health. Iron is also an important trace element that gradually accumulates during the aging process of baijiu (Chinese white liquor). The content and valence state distribution of iron in baijiu have a significant impact on the formation and regulation of trace flavor components during aging. Research on the iron content and valence state changes in baijiu plays a crucial role in regulating the color, aroma, and taste of aging baijiu; therefore, accurately determining the iron ion concentration in baijiu is of significant guiding importance for production process optimization and quality control.

[0003] The iron in baijiu exists in different valence states, mainly including divalent iron (Fe2+). 2+ ) and trivalent iron (Fe) 3+ Both (Fe and Fe) work synergistically to contribute unique color and aroma to the wine. 2+ with Fe 3+ Maintaining a dynamic balance within the liquor is a key factor in the formation of the slightly yellow hue of high-quality aged baijiu, giving it a mellow and elegant visual appeal. The valence transformation of iron gently catalyzes the association and transformation of flavor compounds such as esters and alcohols in the liquor, promoting the generation of complex aromas like aged and cellar notes, and enhancing the liquor's complexity and harmony. Furthermore, iron, as an essential trace element for the human body, exists in baijiu in a suitable form, and adequate intake helps supplement the iron intake from daily diets. Therefore, accurately measuring the iron content in baijiu not only helps in scientifically controlling the aging process and optimizing blending techniques, but also provides crucial technical support for improving baijiu quality and flavor control, driving the baijiu industry towards refinement and high quality.

[0004] Currently, there are various methods for detecting iron in the food industry. The main methods used for detecting iron in liquor include atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), spectrophotometry, and electrochemical methods. However, these methods have certain limitations in practical applications and cannot meet the needs for accurate and efficient detection of all-valent iron in liquor.

[0005] For example, atomic absorption spectrometry is a commonly used and classic method for detecting iron in baijiu (Chinese liquor). It achieves quantitative analysis by measuring the absorption of light at specific wavelengths by iron atoms, and has the advantages of high detection accuracy and strong selectivity. However, this method can only determine the total iron content and cannot distinguish between Fe2+ and Fe3+. 2+ and Fe 3+The specific content of the sample needs to be determined, and the sample pretreatment requires wet digestion, microwave digestion, and other methods. The operation steps are complicated and time-consuming. A large amount of strong acid reagents are used in the digestion process, which not only easily introduces impurities that interfere with the test results, but also poses reagent contamination and operational safety hazards. At the same time, the cost of the instruments and equipment is high, making it difficult to apply to the routine testing of small and medium-sized liquor enterprises. Inductively coupled plasma mass spectrometry (ICP-MS) has the advantages of extremely high sensitivity and simultaneous detection of multiple elements, enabling the detection of trace iron. Some improved methods can even determine iron in its full valence state. However, this method involves expensive equipment and high maintenance costs, requires highly skilled personnel, and still requires complex digestion and separation steps in sample pretreatment, resulting in low detection efficiency. It cannot meet the rapid detection needs of large batches of liquor samples and is difficult to widely apply to routine quality control in the liquor industry. Spectrophotometry is a method of quantitative analysis based on the formation of colored complexes between iron ions and specific chromogenic agents, and the measurement of absorbance. The o-phenanthroline method is a commonly used method specified in national standards; it is simple to operate and low in cost. It can be achieved by adding a reducing agent to react the iron ions with the phenanthroline complex. 3+ Reduced to Fe 2+ Total iron detection is achieved through direct colorimetric analysis. 2+ Detection, and then calculation of Fe 3+ However, this method has significant drawbacks in the detection of baijiu samples: baijiu contains a large amount of ethanol, esters, organic acids, and other components, which can interfere with the stability of the colorimetric reaction, leading to incomplete color development and poor stability of the complex, thus affecting the detection accuracy; at the same time, the detection limit of this method is relatively high, making it difficult to meet the detection requirements of trace amounts of fully valent iron in low-alcohol and high-end baijiu, and the detection process requires multiple adjustments to the pH value of the system and the addition of various reagents, making the operation process cumbersome and prone to human error; Electrochemical methods offer advantages such as speed and convenience, making them suitable for rapid on-site screening. However, these methods suffer from poor selectivity, as the complex matrix in liquor can easily interfere with the detection signal, leading to significant deviations in test results. Furthermore, they cannot achieve Fe... 2+ and Fe 3+ The precise differentiation and simultaneous determination can only be used for qualitative or semi-quantitative detection of iron, which is insufficient to meet the requirements of precise quality control in the liquor industry.

[0006] In summary, current methods for detecting total iron and ferric iron in baijiu (Chinese liquor) suffer from numerous shortcomings, including insufficient detection accuracy, inability to simultaneously distinguish valence states, complex sample pretreatment, low detection efficiency, high instrument costs, and weak anti-interference capabilities. These limitations make it difficult to meet the practical needs of quality control, process optimization, and food safety supervision in the baijiu industry. Therefore, developing a method that is simple to operate, accurate, efficient, rapid, highly resistant to interference, and low in cost, capable of simultaneously determining total iron and ferric iron in baijiu, and addressing the deficiencies of existing technologies, is of significant practical importance and application value for promoting high-quality development in the baijiu industry and protecting consumer health. Summary of the Invention

[0007] [Technical Issues] The methods for detecting total iron and ferric iron in baijiu (Chinese liquor) have many drawbacks, including insufficient detection accuracy, inability to simultaneously distinguish valence states, complex sample pretreatment, low detection efficiency, high instrument costs, and weak anti-interference capabilities.

[0008] [Technical Solution] To address the aforementioned problems, this invention provides a method for detecting total iron and ferric iron (Fe3+) in baijiu (Chinese liquor). Specifically, this invention involves adding excess maltol to a baijiu sample to completely complex and derivatize the ferric iron, then measuring the difference in absorbance at 520 nm before and after derivatization to eliminate interference from the base color of the liquor. Combined with a ferric iron standard curve, this allows for specific and precise quantitative detection of the ferric iron content in baijiu. Furthermore, by completely oxidizing the ferrous iron (Fe2+) in the baijiu sample to ferric iron using an oxidizing agent, the total iron content in the sample can be determined.

[0009] The first objective of this invention is to provide a method for detecting total iron and ferric iron in baijiu (Chinese liquor), comprising the following steps: (1) Add hydrochloric acid-sodium acetate buffer solution to the sample of liquor to be tested, and make up to volume with an ethanol-water solution that matches the alcohol content of the sample to be tested, and shake well; use the simulated liquor as a reference, measure the absorbance at a wavelength of 520nm and record it as A0; (2) Add hydrochloric acid-sodium acetate buffer solution and maltol derivatizing agent solution to the same batch of liquor samples to be tested, and dilute to the mark with an ethanol aqueous solution that matches the alcohol content of the sample to be tested, and shake well; react in the dark at 25-35℃ for 3-15 min; use simulated liquor as a reference, measure the absorbance at a wavelength of 520nm, and record it as A1; (3) Calculate the absorbance difference A=A1-A0 before and after derivatization of the sample to eliminate the interference of the base color of the wine; (4) Substitute the absorbance difference A into the standard curve for the detection of ferric iron to obtain the theoretical mass concentration ρ (mg / L) of ferric iron in the liquor sample to be tested. (5) The actual mass concentration of trivalent iron in the liquor sample to be tested is calculated according to the formula X=ρ×V0 / V1; Where X: the content of ferric iron in the liquor sample, in mg / L; ρ: the concentration of ferric iron in the sample test solution obtained from the standard curve, in mg / L; V1: the final volume of the sample test solution, in mL; V0: the sampling volume, in mL.

[0010] In one embodiment of the present invention, the liquor sample to be tested in step (1) is one of the following: sauce-flavored liquor, light-flavored liquor, or strong-flavored liquor.

[0011] In one embodiment of the present invention, the alcohol content of the liquor sample to be tested in step (1) is 46%-53%. If the alcohol content of the liquor sample to be tested is too high, it needs to be diluted to 46%-53% before testing.

[0012] In one embodiment of the present invention, the volume ratio of the liquor sample to be tested, the hydrochloric acid-sodium acetate buffer solution, and the volume adjustment in step (1) is 10:5-10:25; the pH of the hydrochloric acid-sodium acetate buffer solution is 3-4.

[0013] In one embodiment of the present invention, in step (2), the volume ratio of the same batch of liquor sample to be tested, hydrochloric acid-sodium acetate buffer solution, maltol derivatizing agent solution, and volume adjustment is 10:5:0.1-1.25:25; the pH of the hydrochloric acid-sodium acetate buffer solution is 3-4; the maltol derivatizing agent solution is obtained by dissolving maltol in a 50% volume fraction ethanol aqueous solution, with a concentration of 1-10 g / L.

[0014] In one embodiment of the present invention, the batch of liquor samples to be tested in step (2) has the same mass as the liquor samples to be tested in step (1).

[0015] In one embodiment of the present invention, the method for preparing the simulated wine in steps (1) and (2) is as follows: Acetic acid, lactic acid, ethyl acetate, ethyl lactate, and a 50% (v / v) aqueous solution of ethanol were mixed thoroughly to obtain a simulated wine. The concentrations of acetic acid, lactic acid, ethyl acetate, and ethyl lactate in the 50% ethanol aqueous solution are 1 g / L, 0.8 g / L, 200 ppb, and 200 ppb, respectively.

[0016] In one embodiment of the present invention, the hydrochloric acid-sodium acetate buffer solution in steps (1) and (2) is prepared using an ethanol aqueous solution with a volume fraction of 50%.

[0017] In one embodiment of the present invention, the method for preparing the standard curve for the detection of ferric iron in step (4) is as follows: Accurately weigh 0.8634 g of ferric acetate standard reagent, dissolve it in 0.5% nitric acid ultrapure water and dilute to 1 L to obtain a ferric standard stock solution with a concentration of 100 mg / L. The ferric iron standard stock solution was serially diluted with a 50% (v / v) ethanol aqueous solution to prepare standard working solutions with concentrations of 0.1 mg / L, 0.2 mg / L, 0.5 mg / L, 1.0 mg / L, 2.0 mg / L, 5.0 mg / L, and 10.0 mg / L. Take 10 mL of standard working solution into a 25 mL colorimetric tube, add 5 mL of pH 4.5 hydrochloric acid-sodium acetate buffer solution and 1.25 mL of 10 g / L maltol derivatizing agent solution in sequence, and make up to 25 mL with 50% ethanol aqueous solution by volume, and shake well; place in a 30℃ constant temperature water bath and react in the dark for 10 min; Using a blank reagent (without ferric standard solution, and the amounts of other reagents added were exactly the same as in the operation) as a reference, the absorbance of each standard solution was measured at a wavelength of 520 nm using a 1 cm quartz cuvette. A standard curve was plotted with the concentration of the ferric iron standard working solution on the x-axis and the corresponding absorbance on the y-axis, and a linear regression equation was obtained by fitting the curve.

[0018] In one embodiment of the present invention, the standard curve for the detection of ferric iron in step (4) is y = 0.0543x, where y is the mass concentration of ferric iron and x is the absorbance; R 2 =0.9986; the limit of detection is 0.005 mg / L, the limit of quantitation is 0.01 mg / L, and the detection range is 0.005-50 mg / L.

[0019] The second objective of this invention is to provide a method for detecting total iron in baijiu (Chinese liquor), comprising the following steps: Add dilute nitric acid solution and hydrogen peroxide solution to the liquor sample to be tested, shake well and vortex for 10-15 minutes to completely oxidize ferrous iron to ferric iron; cool, add methanol, mix well to obtain the oxidized sample to be tested. The oxidized sample was tested according to the method for detecting ferric iron in liquor as described in this invention to obtain the total iron content in the liquor sample.

[0020] In one embodiment of the present invention, the volume ratio of the liquor sample to be tested, dilute nitric acid solution, hydrogen peroxide solution, and methanol is 10:1:0.4:0.2.

[0021] In one embodiment of the present invention, the dilute nitric acid solution is a dilute nitric acid aqueous solution with a volume concentration of 0.5-10%.

[0022] In one embodiment of the present invention, the hydrogen peroxide solution is an aqueous solution of hydrogen peroxide with a mass fraction of 30%.

[0023] The third objective of this invention is to apply the method for detecting ferric iron or total iron in baijiu described herein to the field of baijiu testing.

[0024] [Beneficial Effects] (1) The present invention uses maltol to undergo a specific complexation color reaction with ferric iron, and does not react with ferrous iron. No masking agent or reducing agent is needed, and the specific detection of ferric iron in liquor can be achieved directly. This completely solves the technical pain points of traditional spectrophotometry, such as poor valence state differentiation ability and susceptibility to interference from ferrous iron.

[0025] (2) The background content of endogenous maltol in baijiu is less than 50 ppb, which is far lower than the amount of excess maltol added in the detection system, and has no significant interference with the complexation reaction. Moreover, the main flavor components such as alcohols, organic acids, and esters in baijiu have no characteristic absorption at 520 nm. By calculating the difference in absorbance before and after derivatization, the interference of the background color of the liquor can be completely eliminated. There is no need for complicated sample digestion, extraction, purification and other pretreatment steps, and baijiu samples can be directly detected.

[0026] (3) The maltol iron complex in this invention has a high thermal decomposition temperature and extremely strong chemical stability in the acidic detection environment of baijiu at room temperature. The absorbance after color development does not change significantly within 24 hours, which completely solves the defects of the traditional thiocyanate method, such as easy dissociation of complex, large fluctuation of detection results, and need for immediate detection after color development.

[0027] (4) The method of the present invention only requires a common UV-Vis spectrophotometer to complete the detection. No large precision instruments are required. The reagent cost is low, the operation steps are simple, dozens of samples can be processed in a single batch, and the detection cycle of a single sample can be controlled within 30 minutes. It is fully compatible with the routine quality testing needs of the entire process of raw material entry, production process control and finished product inspection of liquor production enterprises.

[0028] (5) The detection limit of this method can be as low as 0.005 mg / L, the quantitation limit is 0.01 mg / L, the spiked recovery rate is between 80% and 120%, and the accuracy of the detection results is not significantly different from that of conventional methods. It can be used as a conventional method for the detection of ferric iron in liquor. Attached Figure Description

[0029] Figure 1 This is the standard curve for the detection of ferric iron. Detailed Implementation

[0030] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0031] Test method: Inductively coupled plasma mass spectrometry (ICP-MS): Accurately pipette 5 mL of the liquor sample into a 15 mL test tube, place the test tube in a 75℃ oven and heat to evaporate the ethanol until the volume is reduced to 1.5 mL.

[0032] After the concentrated sample cooled to room temperature, 1 mL of concentrated nitric acid (68%) was added for digestion. The test tube was then placed in a 40 °C oven to remove excess nitric acid. The digested solution was transferred to a 25 mL volumetric flask and diluted to the mark with ultrapure water. The volume concentration of nitric acid in the diluted solution was 4%. Finally, the solution was filtered through a 0.22 μm filter membrane into a clean test tube to obtain the final sample.

[0033] The instrument parameter settings are shown in Table 1: Table 1. ICP-MS Instrument Parameters

[0034] After powering on the instrument, preheat it for 20 minutes. Set the instrument's operating conditions according to the table. Once all parameters meet the requirements, edit the measurement method, select the analyte, and measure the reagent blank, standard curve, sample blank, and sample solution respectively.

[0035] Raw materials used in the examples: Maltol: 98%, commercially available; Sample of liquor to be tested: finished liquor.

[0036] The method for preparing simulated wine is as follows: Acetic acid, lactic acid, ethyl acetate, ethyl lactate, and a 50% (v / v) aqueous ethanol solution were mixed evenly to obtain a simulated wine. The concentrations of acetic acid, lactic acid, ethyl acetate, and ethyl lactate in the 50% (v / v) aqueous ethanol solution were 1 g / L, 0.8 g / L, 200 ppb, and 200 ppb, respectively.

[0037] The hydrochloric acid-sodium acetate buffer solution was prepared using a 50% (v / v) aqueous ethanol solution.

[0038] Example 1 The method for preparing the standard curve for the detection of ferric iron includes the following steps: Accurately weigh 0.8634 g of ferric acetate standard reagent, dissolve it in 0.5% nitric acid ultrapure water and dilute to 1 L to obtain a ferric standard stock solution with a concentration of 100 mg / L. The ferric iron standard stock solution was serially diluted with a 50% (v / v) ethanol aqueous solution to prepare standard working solutions with concentrations of 22.4 mg / L, 11.2 mg / L, 5.6 mg / L, 2.24 mg / L, 1.12 mg / L, 0.56 mg / L, 0.224 mg / L, 0.224 mg / L, 0.112 mg / L, and 0.056 mg / L. Take 10 mL of standard working solution into a 25 mL colorimetric tube, add 5 mL of pH 4.5 hydrochloric acid-sodium acetate buffer solution and 1.25 mL of 10 g / L maltol derivatizing agent solution in sequence, and make up to 25 mL with 50% ethanol aqueous solution by volume, and shake well; place in a 30℃ constant temperature water bath and react in the dark for 10 min; Using a blank reagent (without ferric standard solution, and the amounts of other reagents added were exactly the same as in the operation) as a reference, the absorbance of each standard solution was measured at a wavelength of 520 nm using a 1 cm quartz cuvette. A standard curve was plotted with the concentration of the ferric iron standard working solution on the x-axis and the corresponding absorbance on the y-axis, and a linear regression equation was obtained by fitting the curve. Standard curve such as Figure 1 : The standard curve for the detection of ferric iron in step (4) is y = 0.0543x, where y is the mass concentration of ferric iron and x is the absorbance; R 2 =0.9986; the limit of detection is 0.005 mg / L, the limit of quantitation is 0.01 mg / L, and the detection range is 0.005-50 mg / L.

[0039] Example 2 A method for detecting ferric iron in baijiu (Chinese liquor) includes the following steps: (1) Add 5 mL of hydrochloric acid-sodium acetate buffer solution with pH 4.5 to 10 mL of the liquor sample to be tested (alcohol content of 53°, sauce aroma type, storage year of 8), and make up to 25 mL with ethanol aqueous solution matching the alcohol content of the sample to be tested, and shake well; use blank solvent (simulated liquor) as reference, measure absorbance at a wavelength of 520 nm, and record it as A0 (0.0019); (2) Add 5 mL of hydrochloric acid-sodium acetate buffer solution with pH 4.5 and 1.25 mL of 10 g / L maltol derivatizing agent solution (solvent is 50% ethanol aqueous solution by volume) to 10 mL of the same batch of baijiu sample to be tested. Make up to 25 mL with ethanol aqueous solution matching the alcohol content of the sample to be tested, and shake well. React at 30℃ in the dark for 10 min. Use blank solvent (simulated wine) as reference and measure absorbance at 520 nm wavelength, and record it as A1 (0.1460). (3) Calculate the absorbance difference A=A1-A0 before and after derivatization of the sample to eliminate the interference of the base color of the wine; (4) Substitute the absorbance difference A into the standard curve for the detection of ferric iron to obtain the theoretical mass concentration ρ (mg / L) of ferric iron in the liquor sample to be tested. (5) The actual mass concentration of trivalent iron in the liquor sample to be tested is calculated according to the formula X=ρ×V0 / V1; Where X: the content of ferric iron in the liquor sample, in mg / L; ρ: the concentration of ferric iron in the sample test solution obtained from the standard curve, in mg / L; V1: the final volume of the sample test solution, in mL; V0: the sampling volume, in mL.

[0040] The test results are as follows: The content of ferric iron in baijiu is 2.6538 mg / L; however, the actual content of ferric iron in baijiu is 2.6673 mg / L. It can be seen that the method of the present invention has high accuracy.

[0041] Example 3 Recovery rate of trivalent iron detection method Based on the o-phenanthroline spectrophotometric method (the classic method for the detection of iron in food according to national standard GB 5009.90-2016), the core logic is: o-phenanthroline reacts only with Fe... 2+ Specific complexation colorimetry was used to determine total iron by reduction method, and background Fe was subtracted. 2+ Fe 3+ Content; Fe throughout the process 2+ A calibration curve is plotted using standard solutions (i.e., the "ferrous iron method") to complete the quantification, and Fe is calculated based on this. 3+ Spike recovery rate.

[0042]

[0043] R:Fe 3+ The spiked recovery rate was %; C 3加标 Fe measured in spiked samples 3+ Concentration, μg / mL; C 3本底 Fe in unspiked samples 3+ Background concentration, μg / mL; V 定容 Final volume of sample, mL (50 mL in this protocol); m 加标 Add Fe 3+ Standard absolute mass, μg, (m 加标 = Fe 3+ (Standard solution concentration × volume added).

[0044] After testing: When the spiked concentration was 0.1 mg / L, the recovery rate was 86%. When the spiked concentration was 2 mg / L, the recovery rate was 88%. When the spiked concentration was 50 mg / L, the recovery rate was 109%.

[0045] That is, the recovery rate of the trivalent iron detection method is 80%-120%.

[0046] Example 4 Stability Test (1) Heating The sample shaken in steps (1) and (2) of Example 2 was heated at 50°C for 10 minutes, and then the absorbance was tested; the rest was the same as in Example 2.

[0047] The test results are as follows: The content of ferric iron in the liquor was 2.6426 mg / L, which is comparable to that in Example 2, indicating good heating stability.

[0048] (2) Light The sample shaken in steps (1) and (2) of Example 2 was irradiated under natural light for 1 hour, and then the absorbance was tested; the rest was the same as in Example 2.

[0049] The test results are as follows: The content of ferric iron in the liquor was 2.6452 mg / L, which is comparable to that in Example 2, indicating good light stability.

[0050] Example 5: Anti-interference capability test Prepare a simulated wine containing iron ions using acetic acid 1 g / L, lactic acid 0.8 g / L, ethyl acetate 200 ppb, ethyl lactate 200 ppb, ferric acetate (trivalent Fe ions) 2.6 mg / L, and 50% (v / v) ethanol aqueous solution as the solvent (prepare immediately before use). Mg, Al, Cu, Zn, and Ca were added to simulated wine as samples for testing of ferric iron. The results are as follows: Table 2

[0051] Note: The accuracy of ferric iron testing = the measured ferric iron concentration / the actual ferric iron concentration.

[0052] As can be seen from Table 2, the presence of metal ions such as Mg, Al, Cu, Zn, and Ca in the wine does not affect the test for ferric iron.

[0053] Example 6 Parameter Optimization Parameter 1: Absorbance wavelength Select a 0.2 mmol / L maltol-ferric aqueous solution; The absorbance wavelengths were selected as 450, 470, 490, 510, 520, 530, 550, 570, 590, 610, 630, and 650 nm for absorbance testing.

[0054] The test results are as follows: Table 3

[0055] As can be seen from Table 3, the absorbance is the highest and the display is the most obvious at 520nm, so 520nm was used in the later stages.

[0056] Parameter 2: Time for light-protected reaction Adjust the light-protected reaction time in step (2) of Example 2 to 0, 1, 2, 3, 4, 5, 6, 8, 10, and 15 min, while keeping the other steps the same as in Example 2, and test the absorbance.

[0057] The results are as follows: Table 4

[0058] Table 4 shows that the reaction was almost complete after 4 minutes; to further ensure the completeness of the reaction, 10 minutes was selected as the reaction time. Parameter 3: Dosage of maltol derivative solution The amount of maltol derivative solution in step (2) of Example 2 was adjusted to 0.025, 0.05, 0.125, 0.25, 0.5, and 1.25 mL, so that the final concentration of maltol in the whole shaken system was 10, 20, 50, 100, 200, and 500 ppm, while other parameters remained the same as in Example 2. The absorbance was then tested.

[0059] The results are as follows: Table 5

[0060] Table 5 shows that 50 ppm (2.6 mg) of maltol is sufficient for complete complexation; to ensure the complete binding of the subsequent approximately 20 mg of Fe, 500 ppm of maltol was selected as the complexing agent. Parameter 4: Storage Years The storage years of the liquor samples to be tested in Example 2 were adjusted to 5, 6, 8, 9, 10, 13, 15, 16, 17, 21, 24, and 25 years, while other aspects remained the same as in Example 2.

[0061] The results are as follows: Table 6

[0062] As can be seen from Table 6, the accuracy of the trivalent iron content detection is relatively stable.

[0063] Parameter 5: Optimization of the complexing agent In Example 2, maltol was replaced with thiocyanate, sulfosalicylic acid, and EDTA, while other components remained the same as in Example 2.

[0064] The results are as follows: Table 7

[0065] Table 7 shows that other complexing agents have the following disadvantages compared to maltol: they cannot directly detect Fe. 3+ The formulation is not fixed, the stability is poor, the quantitative reliability is low, the selectivity is poor, the anti-interference is weak, and it is impossible to achieve rapid and simple detection.

[0066] Parameter 6: Optimization of wine type The liquor type of the liquor sample to be tested in Example 2 (53° alcohol content, sauce aroma type, 8-year storage age) was adjusted to strong aroma type and light aroma type, while other aspects remained the same as in Example 2.

[0067] The test results are as follows: Table 8

[0068] As can be seen from Table 8, the method of the present invention is applicable to different types of wine, and the testing accuracy of different types of wine is not significantly different.

[0069] Parameter 7: Alcohol content optimization The alcohol content of the baijiu sample to be tested in Example 2 (53° alcohol content, sauce aroma type, 8-year storage age) was adjusted to 46° and 50°, while other aspects remained the same as in Example 2.

[0070] Table 9

[0071] As can be seen from Table 9, the method of the present invention is applicable to wines of 46-53° and has high detection accuracy; and the alcohol content does not affect the test results.

[0072] Example 7 A method for detecting total iron in baijiu (Chinese liquor) includes the following steps: Dilute nitric acid solution and hydrogen peroxide solution were added to the liquor sample to be tested. After shaking, the mixture was vortexed for 15 minutes to completely oxidize ferrous iron to ferric iron. After cooling, methanol was added and the mixture was stirred at 500 rpm for 5 minutes to obtain the oxidized sample to be tested. The oxidized sample was tested according to the method for detecting ferric iron in liquor as described in Example 2, and the total iron content in the liquor sample was obtained. The volume ratio of the tested liquor sample, dilute nitric acid solution, hydrogen peroxide solution, and methanol was 10:1:0.4:0.2. Dilute nitric acid solution is an aqueous solution of dilute nitric acid with a volume concentration of 5%. Hydrogen peroxide solution is an aqueous solution of hydrogen peroxide with a mass fraction of 30%.

[0073] The test results are as follows: The total iron content in baijiu is 4.2792 mg / L; however, the actual total iron content in baijiu is 4.5528 mg / L, and the ferrous iron content is 1.5122 mg / L. It can be seen that the method of the present invention has high accuracy.

[0074] Comparative Example 1 Methanol is omitted in Example 7, but everything else remains the same as in Example 7.

[0075] The results showed that the measured total iron concentration was lower than the actual concentration, and the detection accuracy was less than 90%.

[0076] Example 8 Recovery rate of total iron detection method The recovery rate of Maotai-flavor liquor with different storage years was tested using the method in Example 2; the formula for calculating the recovery rate is as follows: Recovery rate = Total iron concentration measured by the method in Example 2 / Iron concentration measured by ICP-MS; The specific test results are as follows: Table 10

[0077] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for detecting ferric iron in baijiu (Chinese liquor), characterized in that, Includes the following steps: (1) Add hydrochloric acid-sodium acetate buffer solution to the sample of liquor to be tested, and make up to volume with an ethanol-water solution that matches the alcohol content of the sample to be tested, and shake well; use the simulated liquor as a reference, measure the absorbance at a wavelength of 520nm and record it as A0; (2) Add hydrochloric acid-sodium acetate buffer solution and maltol derivatizing agent solution to the same batch of liquor samples to be tested, and dilute to the mark with an ethanol aqueous solution that matches the alcohol content of the sample to be tested, and shake well; react in the dark at 25-35℃ for 3-15 min; use simulated liquor as a reference, measure the absorbance at a wavelength of 520nm, and record it as A1; (3) Calculate the absorbance difference A=A1-A0 before and after derivatization of the sample to eliminate the interference of the base color of the wine; (4) Substitute the absorbance difference A into the standard curve for the detection of ferric iron to obtain the theoretical mass concentration ρ (mg / L) of ferric iron in the liquor sample to be tested. (5) The actual mass concentration of trivalent iron in the liquor sample to be tested is calculated according to the formula X=ρ×V0 / V1; Where X: the content of ferric iron in the liquor sample, in mg / L; ρ: the concentration of ferric iron in the sample test solution obtained from the standard curve, in mg / L; V1: the final volume of the sample test solution, in mL; V0: the sampling volume, in mL.

2. The method according to claim 1, characterized in that, In step (1), the volume ratio of the liquor sample to be tested, the hydrochloric acid-sodium acetate buffer solution, and the volume adjustment is 10:5-10:25; the pH of the hydrochloric acid-sodium acetate buffer solution is 3-4.

3. The method according to claim 1, characterized in that, In step (2), the volume ratio of the same batch of liquor sample to be tested, hydrochloric acid-sodium acetate buffer solution, maltol derivatizing agent solution, and volume adjustment is 10:5:0.1-1.25:25; the pH of the hydrochloric acid-sodium acetate buffer solution is 3-4; the maltol derivatizing agent solution is obtained by dissolving maltol in a 50% ethanol aqueous solution with a concentration of 1-10 g / L.

4. The method according to claim 1, characterized in that, The standard curve for the detection of ferric iron in step (4) is y = 0.0543x, where y is the mass concentration of ferric iron and x is the absorbance; R 2 =0.9986.

5. The method according to claim 1, characterized in that, In step (1), the liquor sample to be tested is one of the following: sauce-flavored liquor, light-flavored liquor, or strong-flavored liquor.

6. The method according to claim 1, characterized in that, The alcohol content of the liquor sample to be tested in step (1) is 46%-53%.

7. The method according to claim 1, characterized in that, The quality of the liquor samples to be tested in the same batch in step (2) is the same as that of the liquor samples to be tested in step (1).

8. A method for detecting total iron in baijiu (Chinese liquor), characterized in that, Includes the following steps: Add dilute nitric acid solution and hydrogen peroxide solution to the liquor sample to be tested, shake well and vortex for 10-15 minutes to completely oxidize ferrous iron to ferric iron; cool, add methanol, mix well to obtain the oxidized sample to be tested. The oxidized sample was tested according to the method for detecting ferric iron in liquor as described in this invention to obtain the total iron content in the liquor sample.

9. The method according to claim 8, characterized in that, The volume ratio of the liquor sample to be tested, dilute nitric acid solution, hydrogen peroxide solution, and methanol was 10:1:0.4:0.

2.

10. The application of the method for detecting trivalent iron in liquor according to any one of claims 1-7 or the method for detecting total iron in liquor according to claim 8 in the field of liquor testing.

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