1. A method for detecting iron ions in a hydrolysate by adopting an indirect iodometry method is characterized in that the hydrolysate is pretreated before detection, and the pretreatment steps are as follows: adding iodo compound containing acetyl into the hydrolysate, and shaking up to obtain pretreatment solution;

the hydrolysate is prepared from raw materials containing cornu Bubali powder.

2. The method of claim 1, wherein the acetyl group-containing iodo compound is iodoacetamide and/or iodoacetic acid.

3. The method of any one of claims 1 to 2, wherein the method is applied to detection of iron ions in qingkailing hydrolysate.

4. A method for rapidly judging whether the content of iron ions in qingkailing hydrolysate exceeds the limit is characterized by comprising the following steps:

s1, pretreatment: adding iodo compound containing acetyl into the hydrolysate, and shaking up to obtain pretreatment solution;

s2, judging a result:

s2-1, adding an acid solution into the pretreatment solution, and shaking up;

s2-2, adding a starch indicating solution, and shaking up to make the solution system blue;

s2-3, adding a sodium thiosulfate standard solution, shaking up, converting the dosage of the sodium thiosulfate standard solution according to the iron ion content standard and the stoichiometric theory, and obtaining the formula as follows:

in the formula: v₁The volume of the standard solution of sodium thiosulfate is mL;

C₁the concentration is the concentration of a sodium thiosulfate standard solution, mol/L;

C₂the content of iron ions in the hydrolysate is g/mL;

V₂the volume of the hydrolysate is mL;

s2-4, judging whether the content of iron ions exceeds the limit:

when the blue color of the solution system is faded, the content of iron ions is judged to be qualified;

when the blue color of the solution system is not faded, the content of the iron ions is judged to be out of limit.

5. The method according to claim 1 or 4, wherein in step S1, the mass-to-volume ratio of the iodo compound containing acetyl group to the hydrolysate is 0.2-1 g:1 mL.

6. The method according to claim 5, wherein in step S1, the content of amino acids in the hydrolysate is 0.01-0.1 g/mL.

7. The method according to claim 4, wherein in step S2-1, the volume ratio of the acidic solution to the pretreatment solution is 0.1 to 1: 1.

8. The method according to claim 4 or 7, wherein in step S2-1, the concentration of the acidic solution is 0.01-6.0 mol/L.

9. The method according to claim 4 or 7, wherein in step S2-1, the acidic solution is sulfuric acid, hydrochloric acid, nitric acid, acetic acid, potassium dihydrogen phosphate and/or sodium dihydrogen phosphate.

10. The method according to claim 4, wherein in step S2-3, the concentration of the standard solution of sodium thiosulfate is 0.001-0.01 mol/L.

Background

The buffalo horn powder is an important variety in the traditional Chinese medicine clinical and traditional Chinese medicine pharmaceutical industry, and has the effects of clearing heat and calming. The aqueous cornu bubali powder is generally prepared from hydrolysate, and iron ions are inevitably introduced due to the influence of raw and auxiliary materials, reaction equipment and the like in the process of preparing the hydrolysate from the cornu bubali powder. Iron ions are one of the essential trace elements of human body, and participate in the synthesis of hemoglobin, cellular respiration, electron transfer and DNA synthesis, and also participate in enzymatic activity reaction. However, it has been shown that excessive intake of iron ions can cause many diseases in the body, such as heart and liver diseases, senile dementia, Parkinson's disease, tumor, etc. Therefore, it is necessary to detect the iron ion content in the hydrolysate.

The prior art methods for detecting the content of iron ions mainly comprise a potassium thiocyanate colorimetric method, a potassium ferricyanide titration method, an o-diazaphenanthrene spectrophotometry method, a cerium sulfate titration method, a portable iron ion detector, an indirect iodometry method and the like. However, these methods are not adequate for use with hydrolysates. For example, the colorimetric method of potassium thiocyanate and the titration method of potassium ferricyanide judge the content of iron ions in solution through the color change after the color reagent reacts with the iron ions, the reaction is very sensitive, and the reaction can be carried out with KSCN or K only by trace amount of iron ions₃Fe(CN)₆A darker color reaction is generated, but most of hydrolysate has certain background color (such as brownish red, brown or earthy yellow), erroneous judgment that the content of iron ions exceeds the limit easily occurs, and the error of the colorimetric result of the method is larger; the indirect iodometry has a large measurement range and is simple and convenient to operate, but in actual operation, when the conventional indirect iodometry is adopted to detect the hydrolysate, the phenomenon of repeated color reversion of the endpoint often occurs, so that the endpoint judgment is inaccurate, the background color of the hydrolysate can influence the endpoint color judgment during detection, and the accuracy of determination is reduced(ii) a Similarly, the o-phenanthroline spectrophotometry is only suitable for analyzing colorless samples to be detected and is not suitable for detecting hydrolysate with the background color; although the cerium sulfate titration method can accurately detect the content of iron ions, the determination needs to be carried out under the condition that the sample is cooled to room temperature, and for field analysis, the method is relatively complicated in operation, poor in timeliness and capable of reducing the production efficiency; a portable iron ion detector belongs to a precise instrument, cannot be placed in a workshop production field, has low measurement limit, requires that the iron ion concentration of a sample to be detected is below 10mg/L, has medium and strong acidity of the pH of hydrolysate, and is easy to corrode a probe of the portable iron ion detector, so the portable iron ion detector has the characteristics of low limit, incapability of being placed in the workshop production field, small coverage, unsuitability for production and use, and the like, and cannot meet the requirement of field rapid monitoring.

A series of QINGKAILING products, such as QINGKAILING oral liquid, QINGKAILING injection, QINGKAILING granule, QINGKAILING Capsule, etc., are prepared by hydrolyzing intermediate hydrolysate of cornu Bubali powder and Concha Margaritifera powder with concentrated sulfuric acid, precipitating, and filtering. One of the quality requirements of the intermediate product hydrolysate relates to the limit control of iron ions. In the actual production, excessive iron ions can affect the stability, color and taste of qingkailing series products, even cause the precipitation of two liquid preparations of qingkailing injection and oral liquid, and cause quality accidents. From the process route analysis, the iron ions in the hydrolysate can be derived from two sources: firstly, feeding and carrying in auxiliary materials in the preparation process of hydrolysate; secondly, the reaction kettle and the production pipeline are introduced in the production process. In terms of the first source, because the production process is deterministic and stable, and each batch of raw and auxiliary materials has a relevant ion detection report, the iron ions brought into the hydrolysate by the fed materials and the raw and auxiliary materials are known numbers; while the second source, which is less controlled by the introduction of iron ions from the production line and may vary from batch to batch, is unknown as to whether or not iron ions are introduced or the amount of iron ions introduced. In the actual production process, iron ions are inevitably brought into the hydrolysate, excessive iron ions influence the quality of the qingkailing series products, and according to the experience of an applicant, the limit of the iron ions needs to be controlled within 0.0448mg/mL, so that in the preparation process of the qingkailing series products, whether the iron ion content of the intermediate product hydrolysate exceeds the limit needs to be detected and monitored, and a judgment can be quickly and efficiently made on a workshop production field, so that the method is a release basis for the subsequent process steps. Meanwhile, whether the iron ion content in the hydrolysate exceeds the limit or not is quickly judged, and whether the production pipeline is abnormal or not can be measured, so that greater production resource waste is avoided.

Based on the defects in the prior art or the current situation that the detection method is not suitable for hydrolysate products prepared from buffalo horn powder, a method for quickly and accurately detecting iron ions in the hydrolysate prepared from the buffalo horn powder and a method for quickly judging whether the content of the iron ions in the qingkailing hydrolysate exceeds the limit are urgently needed to be used as a release basis of the subsequent process steps and improve the production efficiency.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings of the prior art and provide a method for detecting iron ions in hydrolysate.

The invention also aims to provide application of the method for detecting iron ions in hydrolysate in the aspect of detecting iron ions in qingkailing hydrolysate.

The invention also aims to provide a method for rapidly judging whether the content of iron ions in the qingkailing hydrolysate exceeds the limit.

The above purpose of the invention is realized by the following technical scheme:

a method for detecting iron ions in hydrolysate adopts indirect iodometry; wherein, the hydrolysate is pretreated before detection, and the pretreatment comprises the following steps: adding iodo compound containing acetyl into the hydrolysate, and shaking up to obtain pretreatment solution;

the hydrolysate is prepared from cornu Bubali powder.

Compared with other iron ion detection methods, the indirect iodometry method has the advantages of simplicity, convenience and quickness, but when the indirect iodometry method is applied to hydrolysate, the titration end point is subjected to repeated color reversion, and the iron ions cannot be accurately detected. Is divided intoThe hydrolysate prepared by hydrolyzing cornu Bubali powder contains sulfhydryl (-SH) compounds such as cysteine, wherein S atom of sulfhydryl (-SH) has strong electronic activity, and when iron ion (Fe) exists in the solution²⁺Or Fe³⁺) Mercapto (-SH) is easily reacted with iron ion (Fe)²⁺Or Fe³⁺) A coordination complex reaction occurs, which is a reversible reaction, followed by Fe³⁺Ions with I^-With Fe in redox reactions of ions³⁺The ions are consumed to sequentially release the coordination complex and release Fe³⁺Ions, resulting in sodium thiosulfate or Fe in the hydrolysate^{3 +}Ions can not react with iodine quickly and completely, and after oscillation, the blue color of the solution system appears between fading and returning to the blue color repeatedly, so that the final result judgment is unstable, and the problems of large error of test data, poor reproducibility and the like are caused. In addition, iron ions in the hydrolysate and mercapto (-SH) coordinate and complex to form a complex which is brownish red, brown or earthy yellow and the like, and becomes the background color of the hydrolysate, thereby influencing the color judgment during detection.

Based on the reasons, the inventor improves the conventional indirect iodometry, the hydrolysate to be detected is pretreated, an iodo compound containing acetyl is added, the iodo compound containing acetyl can rapidly react with mercapto (-SH) of compounds such as cysteine and the like, so that iron ions are changed back to a free state from a complex, the problem that accurate determination is difficult due to repeated color reversion of an end point in the detection process of the hydrolysate is solved, and meanwhile, after the coordination complex reaction is removed, the background color of the hydrolysate disappears to form a colorless solution, so that the interference of the background color of the hydrolysate is eliminated, and the reaction equation is as follows:

R-SH+ICH₂COR¹→R-S-CH₂COR¹+HI。

preferably, the acetyl group-containing iodo compound is iodoacetamide and/or iodoacetic acid.

The method can be well applied to the detection of iron ions in the qingkailing oral liquid hydrolysate, and comprises a qualitative method for quickly judging the content limit and a quantitative method for detecting the specific content.

The invention provides a method for rapidly judging whether the content of iron ions in qingkailing hydrolysate exceeds the limit, which comprises the following steps:

s1, pretreatment: adding iodo compound containing acetyl into the hydrolysate, and shaking up to obtain pretreatment solution;

s2, judging a result:

s2-1, adding an acid solution into the pretreatment solution, and shaking up;

s2-2, adding a starch indicating solution, and shaking up to make the solution system blue;

s2-3, adding a sodium thiosulfate standard solution, shaking up, converting the dosage of the sodium thiosulfate standard solution according to the iron ion content standard and the stoichiometric theory, and obtaining the formula as follows:

in the formula: v₁The volume of the standard solution of sodium thiosulfate is mL;

C₁the concentration is the concentration of a sodium thiosulfate standard solution, mol/L;

C₂the content of iron ions in the hydrolysate is g/mL;

V₂the volume of the hydrolysate is mL;

s2-4, judging whether the content of iron ions exceeds the limit:

when the blue color of the solution system is faded, the content of iron ions is judged to be qualified;

when the blue color of the solution system is not faded, the content of the iron ions is judged to be out of limit.

The qingkailing hydrolysate is prepared with buffalo horn powder and/or nacre powder and through hydrolysis in concentrated sulfuric acid, adding certain amount of Ca (OH)₂Precipitating and filtering to obtain the product. The compound containing sulfydryl (-SH) in the hydrolysate is mainly generated by hydrolyzing protein in the buffalo horn powder into amino acid and decomposing amino acid groups. Wherein the content of the first and second substances,the content of amino acid in the hydrolysate is less influenced by the using amount of the buffalo horn powder, and in the preparation process of the hydrolysate, the liquid amount of the extracting solution is correspondingly increased along with the increase of the buffalo horn powder, and finally the extracting solution is concentrated to a certain volume. Generally, the content of amino acid in the hydrolysate is in the range of 0.01-0.1 g/mL.

Preferably, the mass-volume ratio of the iodo compound containing acetyl to the hydrolysate is 0.2-1 g:1 mL.

Preferably, in the present invention, especially in step s1, the temperature of the hydrolysate is between room temperature and 70 ℃.

More preferably, in the step S1, the temperature of the hydrolysate is 50-70 ℃. In the production process, the temperature of the hydrolysate is usually 50-70 ℃, and the method can realize direct sampling detection in a production field without cooling treatment, simplifies the operation and ensures that the detection is quicker.

The method of the invention and the step S2-1, the acid solution is added, and Fe in the hydrolysate is added in the process of shaking up²⁺Ion dissolved oxygen in liquid and acid radical ion H of acid solution⁺Is oxidized into Fe³⁺Ion, the reaction equation is as follows:

4Fe²⁺+O₂+4H⁺＝4Fe³⁺+2H₂O

further, HI generated after the reaction of iodo compound having acetyl group in step S1, excess acid ion H in step S2-1⁺Can free reducing I^-Ions, possibly with Fe having a strong oxidizing property³⁺Ion oxidation-reduction reaction to generate I₂The reaction equation is as follows:

2Fe³⁺+2I^-＝2Fe²⁺+I₂

further, in step S2-2, starch indicator is added, and the hydrolysate is blue-colored.

Preferably, in the step S2-1, the volume ratio of the acidic solution to the pretreatment solution is 0.1 to 1: 1.

More preferably, in step S2-1, the volume ratio of the acidic solution to the pretreatment solution is 0.1-0.5: 1.

Preferably, in the step S2-1, the concentration of the acidic solution is 0.01-6.0 mol/L.

Preferably, in step S2-1, the acidic solution is sulfuric acid, hydrochloric acid, acetic acid, potassium dihydrogen phosphate and/or sodium dihydrogen phosphate.

Further, in step S2-3, a quantitative sodium thiosulfate standard solution is added, and the amount of the sodium thiosulfate standard solution is converted according to the stoichiometric theory according to the standard of the content of iron ions, and the formula is as follows:

in the formula: v₁The volume of the standard solution of sodium thiosulfate is mL;

C₁the concentration is the concentration of a sodium thiosulfate standard solution, mol/L;

C₂the content of iron ions in the hydrolysate is g/mL;

V₂the volume of the hydrolysate is mL;

preferably, in the step S2-3, the concentration of the sodium thiosulfate standard solution is 0.001-0.01 mol/L.

Preferably, in the step S2-3, the content of the iron ions is 0.0448 mg/mL.

Further, in step S2-4, it is determined whether the iron ion content exceeds the limit according to whether the blue color in the solution system is faded or not:

when the blue color of the solution system is faded, the content of iron ions is judged to be qualified;

when the blue color of the solution system is not faded, the content of the iron ions is judged to be out of limit.

The relevant reaction formula is as follows:

2NaS₂O₃+I₂＝Na₂S₄O₆+2NaI

in step S2-4, if the blue color of the solution system fades, it shows that the Fe in the hydrolysate is completely consumed by the quantitatively added sodium thiosulfate standard solution³⁺I by oxidation of ions₂That is to say to explainIron ion content (Fe) in hydrolysate²⁺And/or Fe³⁺) Within the limits of preparation; on the contrary, if the blue color of the solution system is not faded, the iron ion content (Fe) in the hydrolysate is shown²⁺And/or Fe^{3 +}) The preparation limit is exceeded. Therefore, the method of the invention can visually and definitely observe whether the color in the hydrolysate is faded away or not, accurately determine the content of the iron ions in the hydrolysate, reduce human errors, have accurate detection results, can be applied to on-site rapid detection and greatly improve the production efficiency.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a method for detecting iron ions in hydrolysate prepared from buffalo horn powder and application of the method in qingkailing hydrolysate. The method is simple, feasible, scientific and accurate in route design improvement based on an indirect iodometry method, based on the characteristics of the hydrolysate, the hydrolysate to be detected is pretreated, and the iodo-compound containing acetyl is added, so that the problem that accurate determination is difficult due to the repeated color reversion of the endpoint of the hydrolysate when the hydrolysate is determined by the existing indirect iodometry method is solved, the interference of the background color of the hydrolysate is eliminated, the endpoint change can be judged by directly and clearly fading the color, and the accuracy and the stability of the detection result are effectively improved. The method is suitable for detecting the iron ions in the qingkailing hydrolysate, the hydrolysate at 50-70 ℃ can be taken as a sample on site in a production field for detection, whether the iron ion content of the hydrolysate exceeds the limit can be judged quickly and accurately, a release basis is provided for the subsequent process steps, and the basis of whether the production equipment pipelines such as iron pipelines have abnormity or not and whether the examination needs to be carried out or not can be measured by means of the color judgment result, so that the waste of greater production resources is avoided. Therefore, the detection method is accurate and stable, can be applied to on-site rapid detection, greatly improves the production efficiency and ensures the product quality.

Detailed Description

The present invention is further illustrated by the following specific examples, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Unless otherwise indicated, reagents and materials used in the following examples are commercially available.

The invention takes qingkailing hydrolysate as an example for experiment. Wherein iron ions (Fe) in QINGKAILING hydrolysate²⁺And/or Fe³⁺) The internal control standard is as follows: the upper threshold of iron ions was 0.0448 mg/mL. Through research and analysis, the hydrolysate is prepared by hydrolyzing cornu Bubali powder and Concha Margarit powder with concentrated sulfuric acid, and adding Ca (OH)₂Precipitating and filtering to obtain the product. The buffalo horn powder and the nacre powder which are used as raw materials for preparing the hydrolysate are subjected to factory inspection before feeding, metal ions contained in the buffalo horn powder and the nacre powder are determined, iron ions belong to trace levels, and the influence on the iron ion content in the hydrolysate and subsequent qingkailing finished products is negligible. And Ca (OH) as an auxiliary material for preparing the hydrolysate₂According to theoretical calculation and actual production statistics, iron ions with the mass not more than 0.2% of the mass of the iron ions are introduced, and therefore the upper limit threshold of the iron ions in the qingkailing hydrolysate is obtained through conversion.

Example 1 verification of stability and accuracy

Taking the determination of the iron ions of the qingkailing hydrolysate as an example, the following method is adopted to detect the iron ion content in the hydrolysate.

Preparation of starch indicator liquid: weighing 0.5g of soluble starch, adding 5mL of water, stirring uniformly, slowly adding into 100mL of boiling water, stirring, adding, boiling for 2min, cooling to room temperature, and collecting supernatant.

The method comprises the following steps:

indirect iodometry: taking 10mL of brownish red hydrolysate at the temperature of 50 +/-5 ℃ into a transparent tube, adding 1mL of hydrochloric acid at the concentration of 6mol/L, shaking up, adding 2g of potassium iodide powder, shaking up, adding 2mL of prepared starch indicating solution, enabling the hydrolysate to be blue, adding 0.001mol/L of sodium thiosulfate standard solution, and titrating until the blue color is faded to the end point.

The method 2 comprises the following steps:

pretreatment: 10mL of brownish red hydrolysate at 50 +/-5 ℃ is taken to be put into a transparent tube, 10g of iodoacetamide is added, and the mixture is fully shaken up to obtain the pretreatment liquid.

Indirect iodometry: adding 1mL of 6mol/L hydrochloric acid into the pretreatment liquid, shaking up, adding 2g of potassium iodide powder, shaking up, adding 2mL of prepared starch indicating liquid, enabling the hydrolysis liquid to be blue, adding 0.001mol/L sodium thiosulfate standard solution, and titrating until the blue color is faded to the end point.

The method 1 and the method 2 are adopted for repeating the experiment for multiple times, the method 1 is used for detecting for 20 times and the method 2 is used for detecting for 20 times in each experiment, comparative analysis is carried out, the experiment results are recorded, and the overall experiment results are approximately the same. Table 1 illustrates the experimental procedure and comparative results in which one was randomly selected.

TABLE 1 stability and accuracy verification results

As can be seen from the results in Table 1, compared with the conventional indirect iodometry (method 1), the method 2 for pretreating the hydrolysate has the advantages of obvious titration endpoint change and good result reproducibility, so that the method obviously improves the accuracy and stability of detection.

Example 2 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: 10mL of brownish red hydrolysate at 50 +/-5 ℃ is taken to be put into a transparent tube, 10g of iodoacetamide is added, and the mixture is fully shaken up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, titrating with 0.001mol/L sodium thiosulfate standard solution, shaking and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 3 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 5g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.01 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 4 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 2g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 5 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 2g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 0.01mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 6 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 2g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 10mL of 0.01mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 7 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 2g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L sulfuric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 8 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 2g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of potassium dihydrogen phosphate of 6mol/L, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which represents that Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 9 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 2g of iodoacetic acid, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 10 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 1g of iodoacetic acid and 1g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 11 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 2g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.1 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 12 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: taking 10mL of brownish red hydrolysate at 50 +/-5 ℃ into a transparent tube, adding 1g of iodoacetic acid and 1g of iodoacetamide, and fully shaking up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.1 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 13 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: 10mL of brownish red hydrolysate at the temperature of 60 +/-5 ℃ is taken to be put into a transparent tube, 2g of iodoacetamide is added, and the mixture is fully shaken up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

Example 14 determination of whether the iron ion content of the hydrolysate is out of limits

S1, pretreatment: 10mL of brownish red hydrolysate at 70 +/-5 ℃ is taken to be put into a transparent tube, 2g of iodoacetamide is added, and the mixture is fully shaken up to obtain colorless pretreatment liquid. Wherein, the content of amino acid in the hydrolysate is 0.02 g/mL.

S2, judging a result:

s2-1, adding 1mL of 6mol/L hydrochloric acid, and shaking up;

s2-2, adding 2mL of prepared starch indicating liquid, wherein the hydrolysate is blue;

s2-3, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and shaking for 30 seconds;

s2-4, the blue color fades, the solution is shaken for 30 seconds again, and the solution is still colorless after being placed for 3-5 min, which indicates that the hydrolysate is Fe²⁺And/or Fe³⁺The ion concentration meets the preparation requirement of the hydrolysate.

The results of the examples 2 to 14 show that after the iodo-compound containing acetyl is added, the hydrolysate is changed from brownish red to colorless, the color of the end point does not return after the hydrolysate is placed for 3 to 5min, and the method is accurate and stable. In addition, examples 2, 13 and 14 show that the temperature does not affect the measurement results of the present invention.

Comparative example 1 conventional iodometry was used to determine whether the iron ion content of the hydrolysate exceeded the limit

Taking 10mL of 50 +/-5 ℃ brownish red hydrolysate of the same batch (the content of amino acid is 0.02g/mL), adding 1mL of 6mol/L hydrochloric acid into a transparent tube, shaking uniformly, adding 2g of potassium iodide powder, shaking uniformly, adding 2mL of prepared starch indicating solution, enabling the hydrolysate to show blue, adding 8mL of 0.001mol/L sodium thiosulfate standard solution, and repeatedly appearing the blue color of the solution system between fading and returning blue color in the shaking uniformly process, wherein the end point cannot be accurately judged.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.