A method for determining the content of L-lysine hydrochloride and its application

Abstract

The present invention discloses a method for determining the content of L-lysine hydrochloride and its application, which belongs to the chemical composition detection technology. The method comprises the following steps: sample group: mixing a solution of L-lysine hydrochloride to be tested with a quantitative and excess amount of silver nitrate solution, and Fe 3+ as an indicator, and titrate excess silver nitrate with a standard thiocyanate titration solution until a light reddish brown color appears and remains unfaded for 30 seconds as the titration endpoint; blank group: except for not adding the L-lysine hydrochloride to be tested, the rest of the operations are the same as the sample group; the content of L-lysine hydrochloride in the L-lysine hydrochloride to be tested is calculated according to the following formula: This method is simple and fast, has good repeatability, is economical and affordable, has a wide range of applications, and the analysis results are accurate and reliable. It can reduce the use of toxic reagents, reduce reagent management costs and laboratory safety risks, and can be used to detect the content of L-lysine hydrochloride in feed, improve feed quality and feeding effects.

Description

Technical Field

[0001] The invention relates to the technical field of chemical component detection, and in particular to a method for determining the content of L-lysine hydrochloride and an application thereof. Background Art

[0002] Lysine is one of the essential amino acids for animals. It can promote animal development, enhance immune function, and improve the function of central nervous system tissue. In particular, lysine is the first limiting amino acid for pigs and is indispensable in pig feed. Since the lysine content in cereal foods is very low and is easily destroyed and lacking during processing, adding additional lysine additives to feed is one of the effective means to improve feed quality and enhance breeding benefits. Therefore, the quality of lysine directly affects the quality of feed and the effect of breeding. At present, most of the lysine single preparations sold on the market are L-lysine hydrochloride.

[0003] L-Lysine hydrochloride is white or light brown powder and granules, tasteless or with a slight special smell, easily soluble in water, difficult to dissolve in ethanol or ether, and has a molecular formula of C6H 14 N2O2·HCl, molecular weight is 182.65.

[0004] At present, the conventional detection standard method of lysine is the expensive non-aqueous titration method. This non-aqueous titration method is based on the non-aqueous titration theory, with glacial acetic acid and formic acid as the medium, mercuric acetate as the catalyst, α-naphthol phenyl methanol as the indicator, and perchloric acid as the standard titrant. The two amino groups on a lysine molecule react with two molecules of perchloric acid, and the solution changes from orange-yellow to yellow-green, which is the titration end point.

[0005] The above method has at least the following problems:

[0006] (1) The color change at the reaction endpoint is not obvious, which affects the observation and endpoint determination, thus affecting the test results;

[0007] (2) The reagent safety risk is high. This method uses highly toxic mercuric acetate as a catalyst. The perchloric acid used in this method is one of the six major inorganic strong acids, which can support combustion, decompose at room temperature, and explode when heated. It is highly corrosive and irritating and can cause burns to the human body. Acetic anhydride used to prepare the standard perchloric acid titration solution is a precursor reagent that is flammable and corrosive. The medium used in this method (glacial acetic acid, formic acid) is volatile and produces harmful gases, which have adverse effects on the operator and the environment.

[0008] (3) The reaction has high requirements on the environment, especially temperature. The operating environment temperature must be controlled at 20-30°C and kept constant.

[0009] (4) The detection process is complicated and time-consuming.

[0010] In addition, there are high-performance liquid chromatography and optical rotation methods for detecting the content of L-lysine hydrochloride. However, the two methods require high-cost instruments and equipment (high-performance liquid chromatography, polarimeter), and the detection procedures are complicated. They require high skills of the detection personnel and the detection is time-consuming, making them difficult to popularize in ordinary laboratories.

[0011] Therefore, a new method for detection that is both affordable, safe and accurate is urgently needed.

[0012] In view of this, the present invention is proposed. Summary of the invention

[0013] One of the objects of the present invention is to provide a method for determining the content of L-lysine hydrochloride to solve at least one of the technical problems.

[0014] A second object of the present invention is to provide an application of the above-mentioned determination method.

[0015] This application can be implemented as follows:

[0016] In a first aspect, the present application provides a method for determining the content of L-lysine hydrochloride, comprising the following steps:

[0017] Sample group: Mix the solution of L-lysine hydrochloride to be tested with a quantitative and excess amount of silver nitrate solution to form Fe 3+ As an indicator, excess silver nitrate is titrated with thiocyanate standard titration solution until a light reddish brown color appears and remains unchanged for 30 seconds, which is the titration endpoint;

[0018] Blank group: except that no L-lysine hydrochloride was added, the rest of the operations were the same as those of the sample group;

[0019] The content of L-lysine hydrochloride in the L-lysine hydrochloride to be tested is calculated according to the following formula:

[0020]

[0021] Wherein, X is the mass fraction of L-lysine hydrochloride, in %; m is the mass of L-lysine hydrochloride to be tested, in g; V0 is the volume of thiocyanate standard titration solution consumed by the blank group, in mL; V is the volume of thiocyanate standard titration solution consumed by the sample group, in mL; c is the concentration of thiocyanate standard titration solution, in mol / L; ω is the mass of water contained in 100g of L-lysine hydrochloride to be tested, in g; 100 is the mass of L-lysine hydrochloride to be tested converted to 100g of dry sample, in g; 0.18265 is the mass of L-lysine hydrochloride in grams equivalent to 1.00mL of thiocyanate standard titration solution with a concentration of 1.000mol / L.

[0022] In an alternative embodiment, the solution of L-lysine hydrochloride to be tested is acidified with a nitric acid solution before being mixed with a quantitative and excess amount of silver nitrate solution.

[0023] In an optional embodiment, the mass of L-lysine hydrochloride to be measured is 0.15-0.25 g.

[0024] In an alternative embodiment, Fe 3+ The indicator includes any one of an ammonium ferric sulfate solution, a ferric nitrate solution, and a ferric sulfate solution.

[0025] In a preferred embodiment, Fe 3+ The indicator is a saturated solution of ammonium ferric sulfate.

[0026] In an optional embodiment, the thiocyanate standard titration solution is selected from a potassium thiocyanate standard titration solution, a sodium thiocyanate standard titration solution or an ammonium thiocyanate standard titration solution.

[0027] In an optional embodiment, for each determination of 0.15-0.25 g of L-lysine hydrochloride sample solution, 10 mL of nitric acid solution, 2 mL of saturated ammonium ferric sulfate solution, and 10 mL of silver nitrate solution are used;

[0028] The nitric acid solution is a mixture of concentrated nitric acid with a mass fraction of 65-68% and water in a volume ratio of 1:1;

[0029] The concentration of the silver nitrate solution is 25 g / L.

[0030] In an optional embodiment, the concentration of the thiocyanate standard titration solution is 0.05 mol / L.

[0031] In an optional embodiment, before adding the silver nitrate solution, the method further includes adding a precipitation protective agent to the solution of L-lysine hydrochloride to be tested for titration; the precipitation protective agent is selected from nitrobenzene, 1,2-dichloroethane, dibutyl phthalate or glycerol.

[0032] In an optional embodiment, 5 mL of precipitation protective agent is used for each measurement of 0.15-0.25 g of L-lysine hydrochloride sample solution.

[0033] In an alternative embodiment, the measuring temperature is 20-25°C.

[0034] In a second aspect, the present application provides an application of the determination method according to any one of the aforementioned embodiments, for example, the method can be used to determine the content of L-lysine hydrochloride in feed additives.

[0035] The beneficial effects of this application include:

[0036] (1) The color change at the titration endpoint of this method is clear and obvious, the titration error between different people is small, the accuracy is higher, and the repeatability is better.

[0037] (2) The experimental reagents in this method have low safety risks and low costs.

[0038] (3) The reaction in this method has low environmental requirements and does not require special control of experimental temperature and humidity. It can be achieved in ordinary laboratory experimental environmental conditions, and the specific experimental temperature can be room temperature.

[0039] (4) This method has a simple experimental process, takes little time, and can detect a large number of samples in a short period of time, meeting the requirements of enterprises for high efficiency and speed.

[0040] That is, the method provided in this application is simple and fast, has a wide range of applications, and produces accurate and reliable analysis results. It can reduce the use of toxic reagents, reduce reagent management costs and laboratory safety risks, and is both economical and safe and accurate. It can be used to detect the L-lysine hydrochloride content in feed, and improve feed quality and feeding effects. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0042] The following is a detailed description of the method for determining the content of L-lysine hydrochloride provided in the present application and its application.

[0043] The present application proposes a method for determining the content of L-lysine hydrochloride, comprising the following steps:

[0044] Sample group: Mix the solution of L-lysine hydrochloride to be tested with a quantitative and excess amount of silver nitrate solution to form Fe 3+ As an indicator, excess silver nitrate is titrated with thiocyanate standard titration solution until a light reddish brown color appears and remains unchanged for 30 seconds, which is the titration endpoint;

[0045] Blank group: except that no L-lysine hydrochloride was added, the rest of the operations were the same as those of the sample group;

[0046] The content of L-lysine hydrochloride in the L-lysine hydrochloride to be tested is calculated according to the following formula:

[0047]

[0048] Wherein, X is the mass fraction of L-lysine hydrochloride, in %; m is the mass of L-lysine hydrochloride to be tested, in g; V0 is the volume of thiocyanate standard titration solution consumed by the blank group, in mL; V is the volume of thiocyanate standard titration solution consumed by the sample group, in mL; c is the concentration of thiocyanate standard titration solution, in mol / L; ω is the mass of water contained in 100g of L-lysine hydrochloride to be tested, in g; 100 is the mass of L-lysine hydrochloride to be tested converted to 100g of dry sample, in g; 0.18265 is the mass of L-lysine hydrochloride in grams equivalent to 1.00mL of thiocyanate standard titration solution with a concentration of 1.000mol / L.

[0049] In some preferred embodiments, the solution of L-lysine hydrochloride to be tested may be acidified with a nitric acid solution before being mixed with a quantitative and excess amount of silver nitrate solution.

[0050] By carrying out the above-mentioned acidification treatment, the reaction can be carried out under acidic conditions. On the one hand, the influence of interfering ions in the solution can be prevented, and the anions that react with silver nitrate are only Cl - (For example, interfering ions CO3 in the solution 2- PO4 3- and CrO4 2- The reaction with silver ions to form a water-insoluble precipitate will consume a certain amount of silver nitrate standard solution, but the above precipitate is soluble in nitric acid, so it will not affect the result); on the other hand, acidic conditions can prevent the hydrolysis of trivalent iron ions. Iron ions can form iron hydroxide precipitates in neutral or alkaline media. The hydrolysis process: Fe 3+ +3H2O=Fe(OH)3+3H + .

[0051] The acidification treatment in this application does not use other acidic reagents, such as HCl, which can avoid the introduction of Cl - affect the final experimental results.

[0052] For reference, in the present application, the mass of L-lysine hydrochloride to be measured is preferably set to 0.15-0.25 g, such as 0.15 g, 0.18 g, 0.20 g or 0.25 g, etc., and can also be any other value within the range of 0.15-0.25 g.

[0053] By measuring the L-lysine hydrochloride to be measured at the above mass, the accuracy of the measurement result can be improved.

[0054] Preferably, in this application, Fe 3+The indicator is a solution that can provide trivalent iron ions while the anions will not react with other ions in the solution, for example, it may include any one of ammonium ferric sulfate solution, ferric nitrate solution and ferric sulfate solution.

[0055] Preferably, Fe 3+ The indicator is a saturated solution of ammonium ferric sulfate. By using the saturated form, the Fe 3+ concentration and consume more SCN - , thereby reducing the SCN at the titration endpoint - concentration, reducing SCN - Replace Cl in AgCl - , thereby reducing errors.

[0056] The thiocyanate standard titration solution may be selected from a potassium thiocyanate standard titration solution, a sodium thiocyanate standard titration solution or an ammonium thiocyanate standard titration solution.

[0057] Taking potassium thiocyanate standard titration solution as an example, it can be prepared by the following method: weigh 4.9g potassium thiocyanate (KSCN) and dissolve it in water, transfer it to a 1000mL volumetric flask, dilute it to the scale with water, and shake well.

[0058] In some embodiments, 0.15-0.25 g of L-lysine hydrochloride to be tested may be weighed for determination.

[0059] Specifically, 0.15-0.25 g of L-lysine hydrochloride sample was weighed into a 250 mL conical flask, accurate to 0.0001 g, 50 mL of deionized water was added, and the mixture was shaken to dissolve, and nitric acid, saturated ammonium ferric sulfate solution and silver nitrate solution were added.

[0060] In a preferred embodiment, for every 0.15-0.25 g of the sample solution of L-lysine hydrochloride to be measured, 10 mL of nitric acid solution, 2 mL of saturated ammonium ferric sulfate solution and 10 mL of silver nitrate solution are used. This ratio can make the measurement result more accurate.

[0061] The nitric acid solution is a mixture of concentrated nitric acid with a mass fraction of 65-68% and water in a volume ratio of 1:1. The concentration of the silver nitrate solution can be 25g / L, which can be prepared by the following method: weigh 25g of silver nitrate (AgNO3) and dissolve it in water, transfer it to a 1000mL volumetric flask, dilute it to the scale with water, shake it well, and transfer it to a brown reagent bottle for storage. The saturated ammonium ferric sulfate solution can be prepared by the following method: weigh 50g of ammonium ferric sulfate dodecahydrate (NH4Fe(SO4)2·12H2O) and dissolve it in 100mL of water.

[0062] The concentration of the thiocyanate standard titration solution used in the present application may be 0.05 mol / L.

[0063] In some preferred embodiments, before adding the silver nitrate solution, the method further comprises adding a precipitation protective agent to the solution of L-lysine hydrochloride to be tested for titration. The precipitation protective agent is exemplarily selected from nitrobenzene, 1,2-dichloroethane, dibutyl phthalate or glycerol.

[0064] Since the solubility product of AgCl is larger than that of AgSCN, when the stoichiometric point is reached, a slightly excess of SCN - The standard solution will displace Ag + , precipitation transfer occurs: AgCl (precipitation) + SCN - =AgSCN(precipitate)+Cl - Therefore, by adding the above-mentioned precipitation protective agent, the AgCl precipitation can be wrapped to avoid the transformation of the precipitation and ensure the accuracy of the titration result.

[0065] For reference, 5 mL of precipitation protective agent can be used for each measurement of 0.15-0.25 g of the sample solution of L-lysine hydrochloride to be measured.

[0066] The water used in this application preferably complies with the third-level water specification in GB / T 6682, and the reagents used are analytically pure unless otherwise specified.

[0067] Based on the above, the determination principle of this application is as follows:

[0068] After the L-lysine hydrochloride to be tested is dissolved in water and acidified with nitric acid, a quantitative and excessive amount of silver nitrate solution is added to Fe 3+ (such as saturated ammonium ferric sulfate solution) is used as an indicator, and excess silver nitrate is titrated with a standard thiocyanate titration solution. The chloride ion content in the L-lysine hydrochloride to be measured is determined according to the consumption of the standard thiocyanate titration solution, and then the lysine hydrochloride content in the L-lysine hydrochloride to be measured is calculated.

[0069] The chemical reactions involved in the above process are: Cl - +Ag + (excess) = AgCl↓, Ag + (Remaining)+SCN - =AgSCN↓, end point: SCN - +Fe 3+ =FeSCN 2+ (red).

[0070] This method has at least the following advantages:

[0071] (1) The color change at the titration endpoint of this method is clear and obvious, the titration error between different people is small, the accuracy is higher, and the repeatability is better. However, in the prior art perchloric acid non-aqueous titration method, the color change at the reaction endpoint is not obvious, which affects the observation and endpoint judgment. The error of the endpoint judgment between different people can reach 5 drops (0.20-0.25mL), thus affecting the accuracy and repeatability of the test results.

[0072] (2) The experimental reagents in this method have low safety risks and low costs.

[0073] (3) The reaction in this method has low environmental requirements, and does not require special control of experimental temperature and humidity. It can be achieved in ordinary laboratory experimental environmental conditions, and the specific experimental temperature can be room temperature. In the prior art, the non-aqueous titration method has high environmental requirements, especially temperature.

[0074] In the non-aqueous titration method, firstly, the ambient temperature needs to be controlled at 20-30°C. The reason is that the expansion coefficient of glacial acetic acid is large, and the volume changes greatly with temperature. At the same time, too high a temperature will also increase the evaporation rate of glacial acetic acid, thereby causing changes in the concentration of perchloric acid. In addition, the freezing point of glacial acetic acid is 16.6°C. When the temperature is lower than the freezing point, glacial acetic acid will freeze, causing difficulties in operation. Secondly, the experimental temperature needs to be kept constant to ensure that the use temperature of the perchloric acid standard titration solution is consistent with the calibration temperature (temperature change <4°C). If the temperature changes, the volume of glacial acetic acid will change, which will lead to changes in the concentration of perchloric acid. If the use temperature differs from the calibration temperature by more than 10°C, or the perchloric acid standard solution is placed for more than one month, it needs to be recalibrated when used.

[0075] (4) This method has a simple experimental process and takes little time. It can detect a large number of samples in a short time, meeting the requirements of enterprises for high efficiency and speed. Specifically, this method can obtain effective test results within 15 minutes at the fastest, and each additional sample will increase the test time by about 5 minutes. The non-aqueous titration method requires the determination to be based on a constant weight after drying. The sample drying process takes more than 4 hours. Even if the perchloric acid calibration time is excluded, the total test time is as long as more than 5 hours.

[0076] That is, the method provided in this application is simple, fast, has a wide range of applications, and produces accurate and reliable analysis results. It can reduce the use of toxic reagents, reduce reagent management costs and laboratory safety risks, and is both economical and safe and accurate.

[0077] In addition, the present application also provides an application of the above-mentioned determination method, which is specifically used to determine the content of L-lysine hydrochloride, and is particularly suitable for determining the content of L-lysine hydrochloride in feed additives, and can achieve higher accuracy.

[0078] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0079] Example 1

[0080] 1. Preparation of Reagents

[0081] The water used in the laboratory complies with the third-level water specification in GB / T 6682, and all reagents used are of analytical grade unless otherwise specified.

[0082] 1.1 Saturated ammonium ferric sulfate solution: weigh 50 g of ammonium ferric sulfate dodecahydrate (NH4Fe(SO4)2·12H2O) and dissolve it in 100 mL of water;

[0083] 1.2 Potassium thiocyanate standard titration solution (0.05 mol / L): Weigh 4.9 g potassium thiocyanate (KSCN) and dissolve it in water. Transfer it to a 1000 mL volumetric flask, dilute it to the mark with water, and shake well.

[0084] 1.3 Silver nitrate solution (25 g / L): Weigh 25 g of silver nitrate (AgNO3) and dissolve it in water. Transfer it to a 1000 mL volumetric flask, dilute it to the mark with water, shake well, and transfer it to a brown reagent bottle for storage.

[0085] 1.4 Nitric acid solution (1+1): Measure 50 mL of concentrated nitric acid (HNO3, mass fraction 65-68%) and mix it evenly with 50 mL of distilled water.

[0086] 1.5 Nitrobenzene

[0087] 2. Sample determination

[0088] Weigh 0.20g of L-lysine hydrochloride sample in a 250mL conical flask, accurate to 0.0001g, add 50mL of deionized water, shake to dissolve, add 10mL of nitric acid solution, 2mL of saturated ammonium ferric sulfate solution and 5mL of nitrobenzene, shake well, accurately add 10mL of silver nitrate solution, shake vigorously to aggregate the precipitate, and titrate with 0.05mol / L potassium thiocyanate standard titration solution until a light reddish brown color appears and does not fade for 30s, which is the titration end point. At the same time, perform a blank experiment. Except for not adding a sample, the other operations of the blank experiment are the same as those of the sample.

[0089] 3. Calculation

[0090] The L-lysine hydrochloride content X is expressed as mass fraction and the value is expressed as %, and is calculated as follows:

[0091]

[0092] Where:

[0093] m is the mass of L-lysine hydrochloride to be measured, in g;

[0094] V0 is the volume of thiocyanate standard titration solution consumed by the blank group, in mL;

[0095] V is the volume of thiocyanate standard titration solution consumed by the sample group, in mL;

[0096] c is the concentration of the thiocyanate standard titration solution, in mol / L;

[0097] ω is the mass of water contained in 100 g of the L-lysine hydrochloride to be tested, in g;

[0098] 100 is the mass of the L-lysine hydrochloride to be tested converted to 100g of dry sample, in g;

[0099] 0.18265 is the mass of L-lysine hydrochloride expressed in grams equivalent to 1.00 mL of a 1.000 mol / L thiocyanate standard titration solution.

[0100] Example 2

[0101] The difference between this embodiment and embodiment 1 is that the L-lysine hydrochloride sample to be tested is 0.15 g.

[0102] Example 3

[0103] The difference between this embodiment and embodiment 1 is that the amount of the L-lysine hydrochloride sample to be tested is 0.18 g, and the precipitation protective agent is 1,2-dichloroethane.

[0104] Example 4

[0105] The difference between this embodiment and embodiment 1 is that the amount of the L-lysine hydrochloride sample to be tested is 0.25 g, and the precipitation protective agent is glycerol.

[0106] Example 5

[0107] The difference between this embodiment and embodiment 1 is that the amount of the L-lysine hydrochloride sample to be tested is 0.22 g, and the precipitation protective agent is dibutyl phthalate.

[0108] Example 6

[0109] The difference between this embodiment and embodiment 1 is that the thiocyanate standard titration solution is an ammonium thiocyanate standard titration solution.

[0110] Example 7

[0111] The difference between this embodiment and embodiment 1 is that the thiocyanate standard titration solution is a sodium thiocyanate standard titration solution.

[0112] Test example

[0113] The conclusions of this application are verified by the following experiments:

[0114] Among them, the main instruments, equipment and environmental requirements involved include the following:

[0115] 1. Instruments and Equipment

[0116] 1.1 Laboratory sample crusher.

[0117] 1.2 Analytical balance (Mettler ME204E): sensitivity 0.0001g.

[0118] 1.3 burette, 25mL.

[0119] 1.4 pipettes, 2mL, 5mL, 10mL.

[0120] 1.5 Erlenmeyer flask, 250mL.

[0121] 1.6 Graduated cylinder, 50mL.

[0122] 2. Environmental requirements

[0123] Room temperature.

[0124] 3. Experiment and Verification

[0125] The determination method provided in Example 1 of the present application is compared with "NY 39-1987 Feed Grade L-Lysine Hydrochloride" and "GB34466-2017 Feed Additive L-Lysine Hydrochloride" (collectively referred to as non-aqueous titration method). The implementation process listed below is carried out according to the steps and conditions required in Example 1 of the present application and "NY 39-1987 Feed Grade L-Lysine Hydrochloride" and "GB 34466-2017 Feed Additive L-Lysine Hydrochloride". The mass and other values ​​of the test sample are no longer repeated in this application, and only the calculation results are described. The determination results are shown below.

[0126] ① Method difference verification

[0127] In order to better compare the difference between this method and the perchloric acid non-aqueous titration method in determining the content of feed-grade L-lysine hydrochloride, the same product was measured 10 times using the method provided in Example 1 and the perchloric acid non-aqueous titration method, and the measurement results were tested using a paired sample t-test to test whether there was a difference in the average values ​​of the L-lysine hydrochloride content determined by the two methods. The measurement results are shown in Table 1.

[0128] Table 1 Statistical analysis of the results of the two methods

[0129]

[0130] As shown in the statistical results of Table 1, the paired sample t-test shows that there is no significant difference between the average values ​​of L-lysine hydrochloride content determined by the two methods (P=0.474>0.05), indicating that there is no significant difference in statistical significance between the results obtained by the determination method of the present application and the non-aqueous titration method.

[0131] Therefore, the technical solution of the present application can replace the perchloric acid non-aqueous titration method to determine the content of L-lysine hydrochloride.

[0132] ② Sample verification

[0133] The method provided in Example 1 of the present application and the perchloric acid non-aqueous titration method were used to determine the L-lysine hydrochloride standard (content 99.5%, Sigma Company), and 5 parallel experiments were performed in each group. The determination results are shown in Table 2.

[0134] Table 2 Comparison of the results of the two methods

[0135]

[0136] It can be seen from Table 2 that the average value of the parallel samples measured by the method provided in this application is 99.57%, and its relative error is between -0.13% and 0.31%. The average value of the parallel samples measured by the non-aqueous titration method is 99.58%, and its relative error is between -0.35% and 0.48%.

[0137] It shows that the above two methods can obtain accurate measurement results.

[0138] ③ Recovery rate verification

[0139] Different masses of L-lysine hydrochloride standard (content 99.5%, Sigma) were added to 7 groups of L-lysine hydrochloride samples, and 2 parallel experiments were performed for each group of samples. The recovery rate was determined according to the technical scheme provided in Example 1 of the present application, and the results are shown in Table 3.

[0140] Table 3 Recovery rate verification

[0141]

[0142]

[0143] As can be seen from the above table, the method provided in the present application detects 7 groups of L-lysine hydrochloride samples, and the spiked recovery rate ranges from 98.08% to 102.55%, and the relative average deviation is small, which meets the national standard GB / T 27404 laboratory quality control specification for food physical and chemical testing requirements on recovery rate: the component of the tested substance is greater than 100 mg / kg, and the recovery rate ranges from 95% to 105%.

[0144] Therefore, the method provided in this application has high accuracy and precision.

[0145] ④Precision verification

[0146] The same batch of L-lysine hydrochloride samples and L-lysine hydrochloride standards (content 99.5%, Sigma) were determined using the technical solution provided in Example 1 of the present application and the perchloric acid non-aqueous titration method. Six parallel experiments were performed for each group of samples, and the repeatability is shown in Tables 4-1 and 4-2.

[0147] Table 4-1 Repeatability of L-lysine hydrochloride samples

[0148]

[0149]

[0150] Table 4-2 Repeatability of L-Lysine Hydrochloride Standard

[0151]

[0152] As can be seen from the above table, the same batch of L-lysine hydrochloride samples and L-lysine hydrochloride standards (content 99.5%, Sigma) were measured by the technical solution of the present application and the non-aqueous titration method, and the experimental results showed that both determination methods can obtain accurate test results, but the overall range and relative average deviation corresponding to the present method are slightly smaller than those of the non-aqueous titration method.

[0153] Therefore, the concentration method provided by the present application has better accuracy than the non-aqueous titration method.

[0154] As mentioned above, the technical solution provided in this application is more accurate and precise in determining the content of feed-grade L-lysine hydrochloride than the perchloric acid non-aqueous titration method in the national standard.

[0155] Comparative Example

[0156] ①The influence of different indicator concentrations on the test results

[0157] The technical scheme provided in Example 1 of the present application was adopted, and the content of L-lysine hydrochloride standard (content 99.5%, Sigma) was determined using indicators of different concentrations (taking ammonium ferric sulfate as an example). Five parallel samples were set for each concentration. Except for the different indicator concentrations, the other steps were carried out according to the technical scheme of Example 1 of the present application. The measurement results are shown in Table 5.

[0158] Table 5 Effect of different indicator concentrations on test results

[0159]

[0160] As can be seen from Table 5, the content of L-lysine hydrochloride standard (content 99.5%, Sigma Company) was measured with 5g / 100mL, 10g / 100mL, 20g / 100mL and saturated ammonium ferric sulfate solution, and the relative errors of the test results were -0.74%, -0.46%, -0.09% and 0.04% respectively, that is, when the indicator was a saturated solution, the test result had the highest accuracy. Therefore, the indicator should preferably be a saturated solution.

[0161] ② The influence of adding precipitation protective agent on the test results:

[0162] The technical scheme provided in Example 1 of the present application was adopted, and the content of L-lysine hydrochloride standard (content 99.5%, Sigma) was measured without adding a precipitation protective agent and with adding 5 mL of a precipitation protective agent (taking nitrobenzene as an example). Five parallel samples were set for each concentration. Except for whether or not to add a precipitation protective agent, the other steps were carried out according to the technical scheme provided in Example 1 of the present application. The measurement results are shown in Table 6.

[0163] Table 6 Effect of precipitation protective agent on test results

[0164]

[0165] As can be seen from Table 6, the relative errors of the test results of the L-lysine hydrochloride standard (content 99.5%, Sigma) without adding a precipitation protective agent and adding 5 mL of a precipitation protective agent were -0.14% and 0.04%, respectively, that is, when the precipitation protective agent was added, the test result was more accurate. Therefore, the corresponding precipitation protective agent should be added during the determination process.

[0166] In summary, the method for determining the content of L-lysine hydrochloride provided in the present application is simple, quick, has a wide range of applications, and the analysis results are accurate and reliable. It can reduce the use of toxic reagents, reduce reagent management costs and laboratory safety risks, and is economical, safe and accurate. It can be used to detect the content of L-lysine hydrochloride in feed and improve feed quality and feeding effects.

[0167] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining the content of L-lysine hydrochloride, characterized in that: The following steps are involved: Sample group: Mix the solution of L-lysine hydrochloride to be tested with a quantitative and excess amount of silver nitrate solution to form Fe 3+ As an indicator, excess silver nitrate is titrated with thiocyanate standard titration solution until a light reddish brown color appears and remains unchanged for 30 seconds, which is the titration endpoint; Blank group: except that no L-lysine hydrochloride was added, the rest of the operations were the same as those of the sample group; The content of L-lysine hydrochloride in the L-lysine hydrochloride to be tested is calculated according to the following formula: ； Wherein, X is the mass fraction of L-lysine hydrochloride, in units of %; m is the mass of L-lysine hydrochloride to be measured, in units of g; V0 is the volume of the thiocyanate standard titration solution consumed by the blank group, in units of mL; V is the volume of the thiocyanate standard titration solution consumed by the sample group, in units of mL; c is the concentration of the thiocyanate standard titration solution, in units of mol / L; ω is the mass of water contained in 100g of the L-lysine hydrochloride to be tested, in g; 100 is the mass of the L-lysine hydrochloride to be tested converted to 100g of dry sample, in g; 0.18265 is the mass of L-lysine hydrochloride in grams equivalent to 1.00 mL of 1.000mol / L thiocyanate standard titration solution; For each determination of 0.15-0.25 g of L-lysine hydrochloride sample solution, 10 mL of nitric acid solution, 2 mL of saturated ammonium ferric sulfate solution, and 10 mL of silver nitrate solution were used; The nitric acid solution is a mixture of concentrated nitric acid with a mass fraction of 65-68% and water in a volume ratio of 1:1; The concentration of silver nitrate solution is 25 g / L; Before adding the silver nitrate solution, the method further includes adding a precipitation protective agent to the solution of L-lysine hydrochloride to be tested for titration; the precipitation protective agent is selected from nitrobenzene, 1,2-dichloroethane, dibutyl phthalate or glycerol; Each time 0.15-0.25 g of L-lysine hydrochloride sample solution is measured, 5 mL of the precipitation protective agent is used.

2. The measuring method according to claim 1, characterized in that The solution of L-lysine hydrochloride to be tested is acidified with nitric acid solution before being mixed with a quantitative and excess amount of silver nitrate solution.

3. The measuring method according to claim 2, characterized in that The mass of the L-lysine hydrochloride to be measured is 0.15-0.25 g.

4. The measuring method according to claim 2, characterized in that Fe 3+ The indicator includes any one of an ammonium ferric sulfate solution, a ferric nitrate solution, and a ferric sulfate solution.

5. The measuring method according to claim 4, characterized in that Fe 3+ The indicator is a saturated solution of ammonium ferric sulfate.

6. The measuring method according to claim 4, characterized in that The thiocyanate standard titration solution is selected from a potassium thiocyanate standard titration solution, a sodium thiocyanate standard titration solution or an ammonium thiocyanate standard titration solution.

7. The measuring method according to claim 6, characterized in that The concentration of thiocyanate standard titration solution is 0.05 mol / L.

8. The measuring method according to claim 1, characterized in that The measuring temperature is 20-25°C.

9. The use of the assay method according to any one of claims 1 to 8, characterized in that The determination method is used to determine the content of L-lysine hydrochloride in feed additives.

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