Device and method for automatically detecting ammonium salt in soy sauce
The soy sauce samples were processed through automatic detection devices and ionic strength regulators, and the potential value was measured using ammonia gas sensitive electrodes, and a standard curve was drawn to calculate the ammonium salt content in soy sauce, which solved the problem of time and energy consumption of existing detection methods, and achieved rapid and accurate ammonium salt detection in soy sauce, which was suitable for large batches of samples.
Patent Information
- Application Number
- CN202510579900.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-07
- Publication Date
- 2025-07-18
AI Technical Summary
The existing ammonium salt detection methods in soy sauce are cumbersome, time-consuming, energy-consuming and have large errors. They are not suitable for rapid detection of large batches of samples, affecting the quality and food safety of soy sauce.
The automatic detection device was used to pretreat the soy sauce sample with disodium ethylenediaminetetraacetate (EDTA-2Na) as an ionic strength regulator, combined with potassium hydroxide solution, and the potential value was measured by an ammonia gas sensitive electrode, and a standard curve was drawn to calculate the ammonium salt content in soy sauce.
It realizes rapid and accurate detection of ammonium salt in soy sauce, simplifies operational processes, reduces energy consumption, is suitable for large batches of samples, improves detection efficiency and precision, and complies with food safety standards.
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Figure CN120334331A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of food detection, and particularly relates to an automatic detection device and detection method for ammonium salts in soy sauce. Background Art
[0002] The statements in this part merely provide background technical information related to the present invention and do not necessarily constitute prior art.
[0003] Ammonium salts are non-nutritional components present in soy sauce. Excessive ammonium salt content not only affects the flavor of soy sauce but may also have a negative impact on human health. Excessive ammonium salts in soy sauce, on the one hand, may reflect that the raw materials are contaminated by miscellaneous bacteria, and inorganic ammonium is produced due to excessive decomposition of soybean protein during the fermentation process; on the other hand, it may be introduced by adding additives such as caramel color during the production process; in addition, production and operation enterprises may illegally add ammonium salt components to increase the total nitrogen and amino acid nitrogen content of soy sauce. Therefore, detecting the ammonium salt content is not only a necessary measure to ensure the quality of soy sauce, guarantee food safety and human health, but also a necessary means to prevent illegal acts and ensure the authenticity of soy sauce.
[0004] GB 5009.234-2016 "National Food Safety Standard - Determination of Ammonium Salts in Foods" stipulates the determination method of ammonium salts in soy sauce. The determination of this method requires the conversion of ammonium salts into ammonia in a free form through distillation under alkaline conditions. This operation method is cumbersome, time-consuming, energy-consuming and has a large error, and is not suitable for the rapid detection of a large number of samples. Therefore, establishing a rapid, accurate and low-energy-consuming detection method for ammonium salts in soy sauce plays a crucial role in meeting the regulatory requirements of soy sauce products and ensuring the high-quality development of soy sauce products. Summary of the Invention
[0005] To overcome the deficiencies of the above-mentioned prior art, the present invention provides an automatic detection device and detection method for ammonium salts in soy sauce.
[0006] To achieve the above object, one or more embodiments of the present invention provide the following technical solutions: In the first aspect of the present invention, a rapid detection method for the ammonium salt content in soy sauce is provided, which is based on an automatic detection device to measure a sample to be tested; The method includes adding an ionic strength regulator to the sample to be tested for pretreatment; The ionic strength regulator is a potassium hydroxide solution containing disodium ethylenediaminetetraacetate (EDTA-2Na); The potassium hydroxide solution is 4-6 mol / L, and disodium ethylenediaminetetraacetate is 0.3-0.8 mol / L.
[0007] In a specific embodiment of the present invention, the potassium hydroxide solution is 5 mol / L, and disodium ethylene diamine tetraacetate is 0.5 mol / L.
[0008] In a specific embodiment of the present invention, the ammonium salt (calculated as nitrogen) in soy sauce is calculated according to the following formula: (mg / 100 mL) = × 100 (1) C is the content of ammonium salt (calculated as nitrogen) in soy sauce (mg / 100 mL); X is the logarithm of the molar concentration of ammonium chloride calculated according to the measured potential value in soy sauce (mol / L); 14 is the molar mass of nitrogen, 14 g / mol, 1 is the actual sampling volume in mL; 50 is the sample constant volume (mL).
[0009] In a specific embodiment of the present invention, the method includes the following steps: S1. Prepare an ionic strength regulator, a standard stock solution of ammonium chloride, and a standard intermediate solution of ammonium chloride; S2. Prepare a standard working solution of ammonium chloride: Take the standard stock solution or the standard intermediate solution of ammonium chloride, dilute it with deionized water, add 2 mL of the ionic strength regulator, and make the volume constant to 50 mL, then transfer it to a potential measurement bottle for preparation of measurement; S3. Electrode calibration: Take ammonium chloride standard working solutions with a concentration difference of two orders of magnitude, and measure the potential values E1 and E2 respectively with an ammonia gas-sensitive electrode. The difference between E1 and E2 should be greater than 108 mV; S4. Plot the standard working curve: Take the prepared ammonium chloride standard working solutions, measure the potential values from low concentration to high concentration with an ammonia gas-sensitive electrode, and plot a standard curve with the electrode potential as the ordinate and the logarithm of the ammonium chloride molar concentration as the abscissa; S5. Prepare a sample solution of soy sauce to be measured: Take the sample to be measured, dilute it with deionized water, add 2 mL of the ionic strength regulator, make the volume constant to 50 mL, and transfer it to a potential measurement bottle for preparation of measurement; S6. Measurement of the soy sauce sample to be measured: Take the prepared soy sauce sample to be measured, measure the potential value with an ammonia gas-sensitive electrode, calculate the molar concentration of ammonium chloride in soy sauce according to the standard working curve, and then calculate the mass concentration of ammonium salt (calculated as nitrogen) in soy sauce.
[0010] In a specific embodiment of the present invention, the concentration of the standard stock solution of ammonium chloride is 0.1 mol / L; The concentration range of the standard intermediate solution of ammonium chloride is 10 -4 ~ 10 -2 mol / L, which is obtained by stepwise dilution of the standard stock solution; The concentration range of the ammonium chloride standard working solution is 10 -5 ~10 -2 mol / L, which is obtained by processing the standard stock solution or the standard intermediate solution through the steps of preparing the ammonium chloride standard working solution.
[0011] In a specific embodiment of the present invention, when preparing the ammonium chloride standard working solution or the sample solution to be measured, after accurately pipetting the standard stock solution (5 mL) or the standard intermediate solution (5 mL) or the sample to be measured (1 mL), deionized water is added for dilution (controlling the total volume of deionized water added for dilution to be 25 - 30 mL), and then an ionic strength regulator is added, and finally the volume is fixed to 50 mL.
[0012] In a specific embodiment of the present invention, for the calibration of the electrode, the ammonium chloride standard working solutions with a concentration difference of two orders of magnitude can be 10 -5 and 10 -3 、10 -4 and 10 -2 mol / L.
[0013] In a specific embodiment of the present invention, for the soy sauce sample to be measured, since the limit requirement for ammonium salt in GB / T 18186 - 2000 "Brewed Soy Sauce" is that the content of ammonium salt shall not exceed 30% of the content of amino acid nitrogen, and the content of amino acid nitrogen is the mass concentration (calculated as nitrogen), therefore, the molar concentration of ammonium chloride in soy sauce calculated according to the standard working curve needs to be converted into the mass concentration content of ammonium salt (calculated as nitrogen).
[0014] In the second aspect of the present invention, an automatic detection device for ammonium salt in soy sauce is provided, including: A sample tray assembly, which is provided with a plurality of holes for holding several groups of sample bottles, and realizes sequential sample injection into the volumetric flask through program control; A pretreatment assembly, including: A volumetric flask, which is connected with an oscillator below and is positioned for the volumetric flask through a fixing part, and a liquid level sensor for ensuring the accuracy of the solution volume in the volumetric flask is connected to the fixing part; An ionic strength regulator, which is transported into the volumetric flask through a pipeline according to a preset amount; Deionized water, which is transported into the volumetric flask through a pipeline according to a preset amount; A potential measurement assembly, including: A potential measurement bottle, through which the solution in the volumetric flask is transported into the potential measurement bottle, and a magnetic rotor is arranged inside the potential measurement bottle and is in transmission cooperation with the magnetic stirrer below; An ammonia gas sensitive electrode, which is fixed above the potential measurement bottle through a sealing cover, and the output end of the ammonia gas sensitive electrode is electrically connected to a pH meter; The waste liquid receiving bottle is connected to the solution in the potential measuring bottle through a pipeline to drain the solution into the waste liquid receiving bottle.
[0015] In a specific embodiment of the present invention, the sample disk assembly includes a driving base, on which a sample disk is drivably connected and driven to rotate; a lifting positioning rod is connected to the side of the driving base, and the lifting positioning rod is used to guide the pipeline to insert into the corresponding sample bottle for sampling.
[0016] In a specific embodiment of the present invention, peristaltic pumps are connected in all pipelines for transporting solutions to achieve unidirectional quantitative transportation of solutions.
[0017] In a third aspect of the present invention, a kit for detecting the ammonium salt content in soy sauce is provided, and the kit includes a 0.1 mol / L ammonium chloride standard stock solution and an ionic strength regulator; Preferably, the ionic strength regulator includes a 5 mol / L potassium hydroxide solution and a 0.5 mol / L disodium ethylenediaminetetraacetate.
[0018] The above one or more technical solutions have the following beneficial effects: 1. The automatic detection device for ammonium salts in soy sauce provided by the present invention successfully realizes the automatic detection of ammonium salts in soy sauce, which is simple, fast, has high accuracy, and the device is simple, easy to assemble, and conducive to industrial production.
[0019] 2. The detection method for the ammonium salt content in soy sauce provided by the present invention does not require heating, can also avoid using dangerous chemical drugs such as concentrated sulfuric acid, is green and low-carbon, has a short experimental period, few operation steps, and at the same time has the characteristics of low energy consumption, high efficiency, and high precision, and can be applied to the rapid detection of ammonium salts in a large number of soy sauce samples, saving manpower and material resources.
[0020] 3. In the determination method of the present invention, the soy sauce ammonium salt content (calculated as nitrogen) is spiked at the levels of 70 mg / 100 mL and 140 mg / 100 mL, and the recovery rate is between 101.56% - 104.94%, and the precision is between 0.82% - 1.25%. Compared with the national standard method GB 5009.234 - 2016, there is no significant difference between the two determination methods.
[0021] 4. The device for holding the test solution provided by the present invention has the function of being airtight and preventing gas from escaping for the determination of soy sauces of different varieties and different ammonium salt contents, and can further improve the accuracy of the determination results during batch operation.
[0022] 5. The advantages of the additional aspects of the present invention will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the present invention. Description of the Drawings
[0023] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.
[0024] Figure 1 This is a schematic structural diagram of an automatic detection device for ammonium salt in soy sauce in Example 1 of the present invention; Figure 2 For the present invention Figure 1 Schematic diagram of the structure of the medium-capacity bottle and the internal pipeline for lifting and suction.
[0025] Figures and tables: 1. Volumetric flask; 2. Oscillating device; 3. Sample tray; 4. Sample bottle; 5. Fixing parts; 6. Ionic strength regulator; 7. Deionized water; 8. Liquid level sensing device; 9. Potentiometric bottle; 91. Sealing cover; 10. Ammonia sensitive electrode; 11. pH meter; 12. Magnetic stirrer; 13. Magnetic rotor; 14. Waste liquid receiving bottle; 15. Peristaltic pump; 16. Lifting and positioning rod. DETAILED DESCRIPTION
[0026] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.
[0027] Embodiment 1 The present invention also provides an automatic detection device for ammonium salt in soy sauce, which comprises a sample tray assembly, wherein the sample tray assembly is provided with a plurality of holes for holding a plurality of groups of sample bottles 4, and sequentially injecting samples into a volumetric flask 1 is achieved through program control.
[0028] A pretreatment component includes a volumetric flask 1, an oscillator is connected to the bottom of the volumetric flask 1, and the volumetric flask 1 is positioned by a fixing member 5, and a liquid level sensor is connected to the fixing member 5 to ensure the accuracy of the volume of the solution in the volumetric flask 1; it also includes an ion strength regulator 6 and deionized water 7, which are both delivered to the volumetric flask 1 through a pipeline according to a preset amount.
[0029] A potentiometric component includes a potentiometric bottle 9, which transfers the contents of a volumetric flask 1 to the potentiometric bottle 9 through a pipeline, wherein the potentiometric bottle 9 is provided with a magnetic rotor 13 and cooperates with a magnetic stirrer 12 below the potentiometric bottle 9 for transmission; and further includes an ammonia sensitive electrode 10, which is fixed above the potentiometric bottle 9 through a sealing cover 91, and a pH meter 11 is electrically connected to the output end of the ammonia sensitive electrode 10 for obtaining data collected by the ammonia sensitive electrode 10.
[0030] The waste liquid receiving bottle 14 is used to drain the solution in the potential measurement bottle 9 into the waste liquid receiving bottle 14 through a pipeline.
[0031] Furthermore, the sample disk assembly includes a driving base, on which a sample disk 3 is drivingly connected and driven to rotate. A plurality of groups of the above-mentioned hole positions are provided on the outer ring of the sample disk 3. A lifting positioning rod 16 is connected to the side of the driving base. The lifting positioning rod 16 includes a lifting rod, and a stepped guide frame is connected to the top of the lifting rod. The lower part of the guide frame is used to position the pipeline for guiding the pipeline to be inserted into the corresponding sample bottle 4 for sampling.
[0032] In this design, the driving base drives the upper sample disk 3 to rotate, so that the corresponding sample bottle 4 rotates to a position corresponding to the lifting positioning rod 16. The pipeline is guided by the lifting positioning rod 16 and inserted into the corresponding sample bottle 4, and then the solution in the sample bottle 4 can be transported into the volumetric flask 1. By the above procedure, sampling into the volumetric flask 1 is achieved in sequence.
[0033] In this embodiment, a vortex oscillator is adopted, which can make the solution in the volumetric flask 1 blend more fully. During the oscillation process, it is necessary to position the upper part of the volumetric flask 1 to prevent it from falling off during the oscillation. Therefore, a fixing member 5 is used for positioning. The fixing member 5 includes an annular base, and inwardly converging support rods are fixed above the annular base. The support rods are commonly connected to an annular airbag. The positioning of the volumetric flask 1 is achieved through the annular airbag, positioning its upper part during the process without affecting the vibration of the volumetric flask 1, and realizing more stable and sufficient fusion of the internal solution. A plurality of groups of support rods are fixedly connected above the bracket, and the support rods extend obliquely upward. A positioning plate is connected between the support rods to position the pipelines for transporting and discharging the solution into and from the volumetric flask 1.
[0034] In some other embodiments, a photographic positioning technique can also be adopted. Taking the calibration line in the volumetric flask 1 as a reference object, the current liquid level height is captured by a camera. With the calibration line as a reference, if the solution in the volumetric flask 1 is less than 50 mL, the peristaltic pump 15 is controlled to start injecting deionized water 7 into the volumetric flask 1 until it reaches 50 mL.
[0035] It should be noted that to keep the potential measurement bottle 9 in a relatively sealed state, a middle hole is opened on its sealing cover 91 for placing the measurement electrode 10, and side holes are opened on both sides of the middle hole for communicating with the pipeline to realize the inlet and outlet of the solution in the potential measurement bottle 9.
[0036] To ensure that the solutions in the volumetric flask 1 and the potentiometric measurement flask 9 are completely drained, lifting guides are provided beside the volumetric flask 1 and the potentiometric measurement flask 9 respectively. The lifting guides are connected to the corresponding output pipelines and are used to control the suction end of the pipeline to be completely placed at the bottom of the flask, so as to drain the solution in the flask as completely as possible. Further, for the pipelines used to suck the volumetric flask 1 and the potentiometric measurement flask 9, suction needles are provided at their suction ends. The suction needles, in cooperation with the lifting guides, can further reach the bottom, corners and other places where the solution accumulates, maximizing the contact with the solution and reducing the residue.
[0037] In this embodiment, the above pipelines are all made of rubber flexible pipes. Peristaltic pumps 15 are connected in the pipelines for transporting the solution, and the one-way quantitative transportation of the solution is realized through the peristaltic pumps 15. At the same time, the peristaltic pumps 15 can also avoid direct contact with the solution in the pipeline, so as to enhance the accuracy of the detection data.
[0038] Further, the pipelines are all made of rubber flexible pipes. Peristaltic pumps 15 are connected in the pipelines for transporting the solution, and the one-way quantitative transportation of the solution is realized through the peristaltic pumps 15. At the same time, the peristaltic pumps 15 can also avoid direct contact with the solution in the pipeline, so as to enhance the accuracy of the detection data.
[0039] The specific detection steps of this device are as follows: S1: Rotate the sample disk 3 according to the set program, rotate the specified sample bottle 4 under the lifting positioning rod 16, extend the pipeline into the sample bottle 4 through the lifting positioning rod 16, and then extract the solution in the sample bottle 4 into the volumetric flask 1 through the peristaltic pump 15; S2: Transport 25 - 30 milliliters of deionized water 7 into the volumetric flask 1 through the peristaltic pump 15 and the pipeline, then add a quantitative ion strength regulator 6 to avoid overly intense sample reactions. Obtain the content of the total solution in the volumetric flask 1 through the liquid level sensing device 8. If it does not reach 50 mL, continue to add deionized water 7 until the liquid content in the volumetric flask 1 reaches 50 mL; S3: Drive the oscillation device 2 to mix the liquid in the volumetric flask 1 through oscillation, and then transport all the liquid in the volumetric flask 1 into the potentiometric measurement flask 9 through the pipeline; S4: Start the magnetic stirrer 12 to drive the magnetic rotor 13 in the potentiometric measurement flask 9 to rotate and stir the solution inside. Then measure the potential of the solution through the measuring motor, and the measured data is obtained and displayed through the pH meter 11; S5: Drain all the solution in the potentiometric measurement flask 9 into the waste liquid receiving bottle 14 through the peristaltic pump 15 and the pipeline; S6: Cleaning and calibration. Transfer deionized water 7 into volumetric flask 1, and oscillate and clean the interior of volumetric flask 1 through oscillating device 2. Subsequently, transfer the deionized water 7 inside volumetric flask 1 into potential determination flask 9, start magnetic stirrer 12 to cooperate with magnetic rotor 13 to clean its interior again, and finally discharge the cleaned waste liquid into waste liquid receiving flask 14. Preferably, a program can be set to perform three - cycle cleaning using step S6 to make the electrode return to equilibrium, facilitating the determination of the next sample.
[0040] Example Two This example discloses a method for determining ammonium salts in soy sauce using an ammonia - sensitive electrode.
[0041] 1 Experimental Part 1.1 Instruments and Reagents 1.1.1 Instruments As Figure 1 shown, an automatic detection device for ammonium salts in soy sauce. Among them, the PNH3 - 1 - 01 type ammonia - sensitive electrode is purchased from Shanghai Yidian Scientific Instrument Co., Ltd.; the pH meter is purchased from Shanghai Yidian Scientific Instrument Co., Ltd.
[0042] 1.1.2 Reagents Potassium hydroxide (KOH).
[0043] Disodium ethylenediaminetetraacetate (C 10 H 14 N2Na2O8).
[0044] Ammonium chloride (NH4Cl) anhydrous.
[0045] 1.2 Preparation of Reagents Ionic strength regulator: 5 mol / L potassium hydroxide solution (containing 0.5 mol / L disodium ethylenediaminetetraacetate). Weigh 28.0 g of potassium hydroxide and 18.6120 g of disodium ethylenediaminetetraacetate, dissolve them in a small beaker, and then transfer them to a 100 mL volumetric flask and make up to the mark.
[0046] 1.3 Preparation of Standard Solution Ammonium chloride standard stock solution: Accurately weigh 2.6700 g of ammonium chloride anhydrous dried to constant weight at 100 ± 5 °C in a small beaker, dissolve it, and then transfer it to a 500 mL volumetric flask and make up to the mark. The concentration of this solution is 10 -1 mol / L.
[0047] Ammonium chloride standard intermediate solution: When in use, accurately pipette 10 mL of ammonium chloride standard stock solution (10 -1 mol / L) into a 100 mL volumetric flask and make up to the mark. At this time, the concentration of the ammonium chloride standard solution is 10 -2mol / L. And so on, to obtain 10 -3 、10 -4 mol / L standard intermediate solutions.
[0048] Ammonium chloride standard working solution: When in use, accurately pipette 5 mL of the ammonium chloride standard stock solution or standard intermediate solution into sample bottle 4, transfer it through a pipeline to 50 mL volumetric flask 1, dilute it with deionized water 7, control the total volume after adding deionized water to be 25 - 30 mL, add 2 mL of ionic strength regulator 6, and make up to the mark. The concentration range of the ammonium chloride standard working solution is 10 -5 ~10 -2 mol / L.
[0049] 1.4 Preparation of the soy sauce sample solution to be measured Accurately pipette 1 mL of the sample to be measured into sample bottle 4, transfer it through a pipeline to 50 mL volumetric flask 1, dilute it with deionized water 7, control the total volume after adding deionized water to be 25 - 35 mL, add 2 mL of ionic strength regulator 6, and make up to the mark. Transfer it to the potentiometric determination bottle 9 for preparation of measurement.
[0050] 1.5 Cleaning of the electrode Note to place the electrode in deionized water, covering the sensitive membrane of the electrode, turn on the stirrer for stirring and cleaning, avoid stirring too fast so that bubbles adhere to the electrode, and keep the stirring rate constant. During the cleaning process, the deionized water can be changed 2 - 3 times, and the cleaning is completed when the potential reading is positive.
[0051] 1.6 Electrode calibration Before using the electrode, it is necessary to check the electrode performance, that is, the electrode slope. Take the prepared ammonium chloride standard working solutions with a concentration difference of two orders of magnitude, and record the electrode potential values E1 and E2 respectively. When the temperature of the solution to be measured is 20 - 25 °C, the absolute value of the difference between the potential values E1 and E2 is greater than 108 mV, the electrode meets the requirements, and the ammonium chloride standard working solutions can be 10 -5 and 10 -3 、10 -4 and 10 -2 mol / L.
[0052] 1.7 Plotting of the standard working curve Take the standard working solutions, from low concentration to high concentration, and measure the potential values respectively using the ammonia gas sensing electrode of the automatic detection device. Plot the standard curve with the electrode potential as the ordinate and the logarithm of the ammonium chloride molar concentration as the abscissa.
[0053] 1.8 Determination of the soy sauce sample to be measured Take the prepared soy sauce sample solution to be tested, and use the ammonia gas-sensitive electrode of the automatic detection device to measure the potential value of the soy sauce sample to be tested. Calculate the molar concentration of ammonium chloride in the soy sauce according to the standard working curve, and then convert it to the mass concentration (mg / 100 mL) of ammonium salt (calculated as nitrogen) in the soy sauce.
[0054] The result of calculating ammonium salt (calculated as nitrogen) in soy sauce is as follows: (mg / 100 mL) = × 100 (1) C is the content of ammonium salt (calculated as nitrogen) in soy sauce (mg / 100 mL); X is the logarithm (mol / L) of the molar concentration of ammonium chloride calculated based on the actual measured potential value in the soy sauce; 14 is the molar mass of nitrogen 14 g / mol, 1 is the actual sampling volume in mL; 50 is the sample constant volume (mL).
[0055] 1.9 Methodology evaluation Take 2 different types of soy sauce, and add standards at concentration levels of 70 mg / 100 mL and 140 mg / 100 mL of ammonium salt (calculated as nitrogen) respectively, and independently detect each concentration level 6 times. For the soy sauce samples before and after spiking, use the ammonia gas-sensitive electrode to measure the soy sauce samples to be tested. Calculate the molar concentration of ammonium chloride in the soy sauce according to the standard working curve, and then convert it to the mass concentration (mg / 100 mL) of ammonium salt (calculated as nitrogen) in the soy sauce before and after spiking, and then calculate the spiking recovery rate and precision.
[0056] 2 Results and discussion 2.1 Electrode calibration results and selection of calibration solution Based on the measured potential values, the absolute value of the potential difference of ammonium chloride solutions with a concentration difference of 2 orders of magnitude is greater than 108 mV. Therefore, the electrode slope meets the requirements, and the calibration solution concentration can be selected according to the actual situation. Usually, according to the estimated actual concentration of ammonium salt in soy sauce, it is recommended that the calibration solution concentrations be 10 -3 and 10 -5 mol / L.
[0057] 2.2 Linear range and standard working curve Take ammonium chloride standard working solutions with concentrations of 10 -5 、10 -4 、10 -3 、10 -2 mol / L respectively, measure the potential values, and draw the standard working curve.
[0058] =-59.10 X -370.10 (2) The correlation coefficient R 2 is 0.9994, Y is the actually measured potential value (mV), X is the logarithm of the molar concentration of ammonium chloride (mol / L).
[0059] It can be seen from formula (2) that this method is linear in the range of 10 -5 ~10 -2 mol / L, with a correlation coefficient of 0.9994 and a slope of the regression equation of 59.10, meeting the requirement that the theoretical slope of the Nernst equation at 25°C is 59.16.
[0060] 2.3 Determination results of ammonium salts (calculated as nitrogen) in different varieties of soy sauce Table 1 Determination results of ammonium salts (calculated as nitrogen) in different varieties of soy sauce From the determination results, the content range of ammonium salts (calculated as nitrogen) in different soy sauce samples is between 66 mg / 100 mL and 196 mg / 100 mL. This method is applicable to the determination of ammonium salts in soy sauce with different varieties and different contents of ammonium salts (calculated as nitrogen).
[0061] 2.4 Determination of recovery rate and precision Table 2 Determination of spiked recovery rate and precision of ammonium salts (calculated as nitrogen) with different concentrations in different soy sauces It can be seen from Table 2 that according to GB / T 27417-2017 "Conformity assessment - Guidelines for the validation and verification of chemical analysis methods", at different spiked concentration levels, the recovery rate is between 101.56% and 104.94%, meeting the requirement of the method recovery rate range, and the precision is between 0.82% and 1.25%, meeting the precision requirement. This indicates that this method is feasible and applicable to the determination of ammonium salts in soy sauce.
[0062] Example 3: Comparison of the determination of ammonium salt content in soy sauce between the ammonia gas-sensing electrode method and the national standard method 1 Experimental part 1.1 The experimental steps of the ammonia gas-sensing electrode are the same as those in Example 2 1.2. The experimental steps of the national standard method are the same as those in the national standard method GB 5009.234-2016 2 Results and discussion 2.1 Comparison of determination results and precision Table 3 Comparison of the determination results of ammonium salts (calculated as nitrogen) between this method and the national standard method Data analysis was carried out by SPSS, and F-test and t-test were performed, indicating that there was no significant difference between the two measurement methods, and the confidence level of the conclusion was 95%. It can be seen from the measurement results that the measurement results of this method are generally higher than those of the national standard method. The reason may be that in the national standard method, ammonium salts need to be volatilized in the form of ammonia through heating and distillation, and then determined by titration method. There may be a situation where a small amount of ammonia solution is not distilled out; while this method directly measures ammonia in the solution, and the measurement method is more direct, so the measurement results are more accurate than those of the national standard method. In addition, this method has higher precision and better repeatability than the national standard method.
[0063] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative labor are still within the protection scope of the present invention.
Claims
1. A rapid detection method for the ammonium salt content in soy sauce, characterized in that, It measures the sample to be tested based on an automatic detection device; The method includes adding an ionic strength regulator to the sample to be tested for pretreatment; The ionic strength regulator is a potassium hydroxide solution containing disodium ethylenediaminetetraacetate (EDTA-2Na); The potassium hydroxide solution is 4 - 6 mol / L, and disodium ethylenediaminetetraacetate is 0.3 - 0.8 mol / L.
2. The rapid detection method for the ammonium salt content in soy sauce according to claim 1, characterized in that, The potassium hydroxide solution is 5 mol / L, and disodium ethylenediaminetetraacetate is 0.5 mol / L.
3. The rapid detection method for the ammonium salt content in soy sauce according to claim 1, characterized in that, The ammonium salt (calculated as nitrogen) in soy sauce is calculated according to the following formula: (mg / 100 mL) = ×100（1） C is the content of ammonium salts (calculated as nitrogen) in soy sauce (mg / 100 mL); X is the logarithm of the molar concentration of ammonium chloride (mol / L) calculated based on the actual measured potential value in soy sauce; 14 is the molar mass of nitrogen, 14 g / mol, 1 is the actual sampling volume in mL, and 50 is the sample volume after volume fixation (mL).
4. The rapid detection method for the ammonium salt content in soy sauce according to claim 1, wherein The method includes the following steps: S1. Prepare an ionic strength regulator, a standard stock solution of ammonium chloride, and a standard intermediate solution of ammonium chloride; S2. Prepare a standard working solution of ammonium chloride: Take the standard stock solution or standard intermediate solution of ammonium chloride, add deionized water for dilution, then add 2 mL of the ionic strength regulator, and make the volume up to 50 mL and transfer it to a potentiometric determination bottle for preparation of determination; S3. Electrode calibration: Take ammonium chloride standard working solutions with a concentration difference of two orders of magnitude, and use an ammonia gas-sensitive electrode to measure the potential values E1 and E2 respectively. The difference between E1 and E2 should be greater than 108 mV; S4. Plot the standard working curve: Take the prepared ammonium chloride standard working solutions, measure the potential values with an ammonia gas-sensitive electrode from low concentration to high concentration, and plot a standard curve with the electrode potential as the ordinate and the logarithm of the ammonium chloride molar concentration as the abscissa; S5. Prepare a sample solution of soy sauce to be tested: Take the sample to be tested, add deionized water for dilution, then add 2 mL of the ionic strength regulator, make the volume up to 50 mL, and transfer it to a potentiometric determination bottle for preparation of determination; S6. Determine the soy sauce sample to be tested: Take the prepared soy sauce sample to be tested, use an ammonia gas-sensitive electrode to measure the potential value, calculate the molar concentration of ammonium chloride in the soy sauce according to the standard working curve, and then calculate the mass concentration of ammonium salt (calculated as nitrogen) in the soy sauce.
5. The rapid detection method for the ammonium salt content in soy sauce according to claim 4, wherein The concentration of the standard stock solution of ammonium chloride is 0.1 mol / L; The concentration range of the ammonium chloride standard intermediate solution is 10 -4 ~10 -2 mol / L, which is obtained by gradually diluting the standard stock solution; The concentration range of the ammonium chloride standard working solution is 10 -5 ~10 -2 mol / L, which is obtained by processing the standard stock solution or the standard intermediate solution through the steps for preparing the ammonium chloride standard working solution.
6. The rapid detection method for the ammonium salt content in soy sauce according to claim 1, wherein, The automatic detection device includes: A sample tray assembly, which is provided with a plurality of holes for holding several groups of sample bottles (4), and realizes sequential sampling into the volumetric flask (1) through program control; A pretreatment assembly, including: A volumetric flask (1), which is connected with an oscillator below, and is positioned for the volumetric flask (1) through a fixing member (5). A liquid level sensor for ensuring the accuracy of the solution volume in the volumetric flask (1) is connected to the fixing member (5); The ionic strength regulator (6), which is transported into the volumetric flask (1) according to a preset amount through a pipeline; Deionized water (7), which is transported into the volumetric flask (1) according to a preset amount through a pipeline; A potentiometric determination assembly, including: A potentiometric determination bottle (9), which transports the solution in the volumetric flask (1) into the potentiometric determination bottle (9) through a pipeline. The potentiometric determination bottle (9) is internally provided with a magnetic rotor (13) and is in cooperative transmission with the magnetic stirrer (12) below; An ammonia gas-sensitive electrode (10), which is fixed above the potentiometric determination bottle (9) through a sealing cover (91). The output end of the ammonia gas-sensitive electrode (10) is electrically connected to a pH meter (11); The waste liquid receiving bottle (14), and the solution in the potential measurement bottle (9) is discharged into the waste liquid receiving bottle (14) through a pipeline.
7. The rapid detection method for the ammonium salt content in soy sauce according to claim 6, wherein, The sample tray assembly includes a driving base, on which a sample tray (3) is drivingly connected and driven to rotate; a lifting positioning rod (16) is connected to the side of the driving base, and the lifting positioning rod (16) is used to guide the pipeline to be inserted into the corresponding sample bottle (4) for sampling.
8. The rapid detection method for the ammonium salt content in soy sauce according to claim 7, characterized in that, Peristaltic pumps (15) are connected in the pipelines for conveying the solution to achieve unidirectional quantitative conveyance of the solution.
9. A detection kit for the ammonium salt content in soy sauce, characterized in that, The kit includes a 0.1 mol / L ammonium chloride standard stock solution and an ionic strength regulator; The ionic strength regulator includes a 5 mol / L potassium hydroxide solution and a 0.5 mol / L disodium ethylenediaminetetraacetate.