Pretreatment method of dry-method cationic starch substitution degree detection sample

Abstract

The invention belongs to the technical field of cationic starch detection methods, and particularly relates to a pretreatment method of a dry-process cationic starch substitution degree detection sample, which comprises the following steps: S1, weighing 25g of sample, adding 200ml of ice water (below 4 DEG C), stirring, pouring into a dehydrator with 400-mesh filter cloth, and spin-drying at a high speed for 30 seconds; s2, putting the filter cloth into 200ml of ice water to wash out the sample, then putting the filter cloth into the dehydrator, pouring the sample, and spin-drying at a high speed for 4 minutes; s3, 1 g of the spin-dried sample is weighed, the substitution degree of the spin-dried sample is detected through a Kjeldahl method, the moisture of the sample is detected synchronously so that the substitution degree can be calculated, and through the steps of the method, the process steps are simplified, and pollution to the environment is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of cationic starch detection methods, and in particular relates to a pretreatment method for dry-process cationic starch substitution degree detection samples. Background Art

[0002] Currently, there are three major methods for preparing modified starch in the industry, namely physical, chemical and enzymatic treatment. Among them, when using chemical methods, starch can be modified by cationization to produce modified starch. Starch reacts with a cationizing agent to generate a starch derivative containing amino groups. Since the nitrogen atom carries a positive charge, it is called cationic starch.

[0003] Currently, there are three main methods for producing cationic starch: A. wet process B. dry process C. semi-dry process. The wet process involves chemically modifying cassava or corn starch before cationization. This process requires multiple steps, including chemical reactions such as esterification and etherification, and therefore poses significant environmental risks. The dry process involves directly cationizing the starch. This process is simple and less polluting. Summary of the Invention

[0004] The purpose of the present invention is to provide a dry method for pre-treating samples for detecting the degree of substitution of cationic starch, aiming to solve the technical problems of complicated steps and high pollution in the detection methods in the prior art.

[0005] To achieve the above object, the present invention provides a pre-treatment method for dry-process cationic starch substitution degree detection sample, comprising:

[0006] S1: Weigh 25g of sample, add 200ml of ice water (below 4℃), stir, pour into a dehydrator with 400 mesh filter cloth and spin dry at high speed for 30 seconds;

[0007] S2: Place the filter cloth in 200ml of ice water to wash out the sample, then place the filter cloth in a dehydrator, pour in the sample and spin dry at high speed for 4 minutes;

[0008] S3: Weigh 1 g of the dried sample and use the Kjeldahl method to determine its degree of substitution. Simultaneously, the moisture content of the sample is tested to facilitate the calculation of the degree of substitution.

[0009] Preferably, in step S1, the temperature of the ice water is below 4°C to prevent gelatinization of the high-degree-of-substitution starch during the washing process.

[0010] Preferably, in step S1, the drying speed of the dehydrator is high, the first drying time is 30 seconds, and the second drying time is 4 minutes, so as to ensure that the unreacted etherifying agent in the sample is fully removed.

[0011] Preferably, in the step S3, the operation steps of the Kjeldahl method include:

[0012] S3.1: Place 1 g of the pretreated sample in a Kjeldahl flask, add potassium sulfate, copper sulfate, and selenium powder as catalysts, and drip concentrated sulfuric acid along the flask wall.

[0013] S3.2: Heat the digestion on a hot plate until the solution turns clear green.

[0014] S3.3: Cool the digestate and transfer it to a distillation unit, add sodium hydroxide solution to alkalize it, and release ammonia by distillation;

[0015] S3.4: Absorb the distilled ammonia with boric acid solution and titrate to the endpoint with standard hydrochloric acid solution, recording the amount of hydrochloric acid consumed.

[0016] S3.5: Calculate the nitrogen content and degree of substitution of the sample based on the titration results.

[0017] Preferably, in step S3.1, the catalyst is composed of 0.3 g potassium sulfate, 0.3 g copper sulfate and 0.1 g selenium powder.

[0018] Preferably, in step S3.4, the concentration of the boric acid solution is 2%, and a methyl red-bromocresol green mixed indicator solution is added to determine the titration endpoint.

[0019] Preferably, in step S3, the calculation formula of the degree of substitution is

[0020]

[0021] Where V is the volume (mL) of 0.01 mol / L standard hydrochloric acid solution used in the solution, 0.01 is the concentration of the hydrochloric acid standard titrant in moles per liter (mol / L), 0.01401 is the mass of nitrogen equivalent to 1.0 mL of hydrochloric acid [c(HCl) = 1.000 mol / L] standard titrant in grams (g), and W is the absolute dry weight of the sample in g.

[0022]

[0023] 1400 is the mass of nitrogen atoms (14*100), 152 is the molecular mass of the substituent, and 162 is the molecular mass of the glucose residue in starch.

[0024] Preferably, in step S1, it is applicable to dry-process cationic starch samples with a degree of substitution greater than 0.041, which can effectively avoid the influence of sample gelatinization on the test results.

[0025] Preferably, in step S2, ice water washing and high-speed drying are performed to remove unreacted etherifying agent, thereby reducing detection errors, and simultaneously detecting the moisture content of the sample to improve the accuracy of substitution degree calculation.

[0026] The above one or more technical solutions in the dry-process cationic starch substitution degree detection sample pretreatment method provided by the embodiment of the present invention have at least one of the following technical effects:

[0027] In a dry-process cationic starch substitution degree detection sample pretreatment method of the present invention, the following instruments are prepared: a 500ml Kjeldahl flask, a 500ml Erlenmeyer flask, and a constant nitrogen determination distillation apparatus; reagents include: 40% sodium hydroxide solution, 0.01mol / L hydrochloric acid standard solution, 2% boric acid solution, concentrated sulfuric acid, a catalyst (potassium sulfate, copper sulfate, selenium powder), and a mixed indicator solution (20ml of 0.1% methyl red ethanol solution, 30ml of 0.2% bromocresol green ethanol solution, and shaking well).

[0028] Use an electronic balance to weigh 1.0g of powder sample (accurate to 0.001g) and test its moisture content. Place it in a dry 250ml Kjeldahl test tube, add 0.3g of potassium sulfate, 0.3g of copper sulfate, and 0.1g of selenium powder, and then drop 5.0ml of concentrated sulfuric acid along the wall of the flask. Place a small funnel at the mouth of the Kjeldahl test tube. Preheat and shake the flask on an electric stove, then tilt the flask at 45° on the stove. After heating for 3 hours, when the solution turns clear green, remove the Kjeldahl flask, cool it to room temperature, and then distill it.

[0029] Distillation: Take 10 ml of 2% boric acid solution and place it in a 250 ml Erlenmeyer flask. Add 5 drops of methyl red-bromocresol green mixed indicator solution and insert the lower end of the condenser tube below the liquid surface. Then transfer the contents of the Kjeldahl flask to the distilling flask of the Kjeldahl nitrogen determination apparatus. Rinse the Kjeldahl flask and funnel with a small amount of water several times. Add 25 ml of 40% sodium hydroxide solution and rinse the funnel several times with a small amount of water. Close the funnel inlet and seal it with water. Allow steam to distill until the boric acid solution begins to change from wine red to green. Distill and collect about 75 ml of the contents of the Erlenmeyer flask. Lift the lower end of the cooling tube above the liquid surface and continue steam flushing for about 1 minute. After rinsing with water, stop distillation and titrate with 0.01 mol / L standard hydrochloric acid solution until the distillate turns gray. Record the hydrochloric acid consumption and perform a blank test at the same time. By following these steps, the accuracy of the results is improved and the steps are simplified. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is a flow chart of a sample pretreatment method for dry-process cationic starch substitution degree detection provided by an embodiment of the present invention.

[0032] Figure 2 A diagram of a constant nitrogen determination distillation apparatus for dry-process cationic starch substitution degree detection samples provided in an embodiment of the present invention.

[0033] Among them, the reference numerals in the figures are:

[0034] A—Electric furnace B—Round bottom flask C—Funnel

[0035] D—Nitrogen determination ball E—Kjeldahl flask F—Condenser

[0036] G—Erlenmeyer flask. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention in detail. Figures 1-2 , wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the embodiments of the present invention, but should not be understood as limiting the present invention.

[0038] In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0040] In the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to the specific circumstances.

[0041] In one embodiment of the present invention, Figure 1 As shown, a dry method for pre-treatment of cationic starch substitution degree detection samples is provided. Pre-treatment: the sample is mixed

[0042] 1. Principle

[0043] Under the action of catalyst, starch and its derivatives are digested with sulfuric acid, the reactants are alkalized with sodium hydroxide, and distilled to release ammonia. At the same time, it is absorbed with boric acid solution and titrated with a calibrated sulfuric acid standard solution.

[0044] 2. Instruments

[0045] 2.1 Kjeldahl flask: The capacity is between 500mL and 800mL, and a small funnel can be placed at the neck of the bottle.

[0046] 2.2 Digestion stand: It enables the Kjeldahl flask to be heated in an inclined position and only the flask wall below the liquid level is heated.

[0047] 2.3 Kjeldahl nitrogen determination apparatus: It has a 200 mL funnel and a splash-proof bulb, the latter of which can connect the Kjeldahl flask and the condenser.

[0048] 2.4 Burette: 25mL with 0.05mL scale or 10mL with 0.01mL scale.

[0049] 2.5 Analytical balance.

[0050] 3. Reagents

[0051] Analytical grade reagents and distilled water or water of equivalent purity should be used.

[0052] 3.1 Concentrated sulfuric acid: 96% (mass fraction), P20 = 1.84 g / mL.

[0053] 3.2 Sodium hydroxide solution: c = 30% (mass fraction), Pro = 1.33 g / mL.

[0054] NOTE: The solution concentration can be greater than 1.33 g / mL.

[0055] 3.3 Boric acid solution: c = 20 g / L.

[0056] 3.4 Mixed catalyst: It is a mixture of potassium sulfate and anhydrous copper sulfate in different proportions, such as 97g potassium sulfate and 3g anhydrous copper sulfate.

[0057] 3.5 Sulfuric acid standard solution: c = 0.01 mol / L or 0.05 mol / L.

[0058] 3.6 Indicator: Mix two parts of cold saturated neutral methyl red solution and one part of 0.25 g / L methylene blue solution, and store in a brown glass bottle. The cold saturated neutral methyl red solution and the 0.25 g / L methylene blue solution are both prepared with 50% (volume fraction) ethanol.

[0059] 4. Operation method

[0060] 4.1 Sample pretreatment

[0061] Mix the sample quickly and thoroughly.

[0062] 4.2 Sampling

[0063] Weigh up to 10 g of sample (4.1) according to the nitrogen content of the sample, accurate to 0.001 g, and then pour it into a dry Kjeldahl flask (6.1). Be careful not to let the sample stick to the inner wall of the bottleneck. For viscous or pasty samples, you can choose to weigh them on a glass container, aluminum sheet or plastic that does not generate nitrogen. You can also use a container with a known nitrogen content to weigh. If the container generates nitrogen, perform a blank measurement (7.6) and convert it.

[0064] 4.3 Digestion

[0065] Add 10 g of the catalyst (5.4) and an appropriate amount of concentrated sulfuric acid (5.1) using a graduated cylinder (amount added = 20 + 4 x sample mass, in ml). Allow the concentrated sulfuric acid to flow down the inner wall of the bottleneck. Gently swing the flask to mix the sample until all lumps disappear. Once the sample is completely soaked, add a boiling-proof material (e.g., glass beads) to prevent violent boiling. Place a small funnel at the bottleneck of the flask and place the flask on the digestion rack (6.2) to begin heating and digestion. Carefully heat the liquid to gradually boil. Once the liquid is clear, continue heating for 1 h. If gas is used to heat the digestion apparatus, ensure that the flame does not exceed the liquid portion of the flask to prevent nitrogen loss.

[0066] 4.4 Distillation and Titration: Cool the contents of the flask and quantitatively transfer them to a distillation flask. Rinse several times with water. Carefully add 50mL to 200mL of water (depending on the size of the distillation flask), mix the contents, and connect the flask to a distillation apparatus that has been pre-deaminated. Add 25mL to 50mL of boric acid solution (3.3) and 3 to 5 drops of indicator (3.6) to a 500mL Erlenmeyer flask. Adjust the lower end of the condenser of the nitrogen determination distillation apparatus so that it just touches the bottom of the 500mL Erlenmeyer flask. Then, add 150mL to 200mL of sodium hydroxide solution (3.2) through the funnel to alkalinize the digestate. Be careful not to drain the neck of the funnel to ensure a liquid seal. Remove the condensate from the condenser and begin distillation. The indicator in the flask will immediately turn alkaline. During this process, ensure that the amount of steam generated is constant. Stop heating, lower the conical flask, and move the condenser away from the liquid surface. Allow excess condensate to drip into the flask again. Rinse the end of the condenser with water, and water will also drip into the flask. The liquid in the flask will be green. Use a 10mL or 25mL burette (2.4) and a calibrated sulfuric acid standard solution (3.5) to titrate the liquid in the flask until the color changes to purple-red. Read the number of milliliters of sulfuric acid standard solution consumed.

[0067] 4.5 Number of measurements: Parallel experiments were performed.

[0068] 4.6 Blank determination Use the reagents for blank determination.

[0069] If the sample container contains nitrogen, the container should be subjected to a blank measurement.

[0070] 5. Calculation:

[0071]

[0072] V1-the number of milliliters of standard sulfuric acid solution used in the solution (mL);

[0073] V0- ml of standard sulfuric acid solution used in the solution (mL)

[0074] C-concentration of sulfuric acid standard titration solution, in moles per liter (mol / L);

[0075] W-dry weight of sample (g);

[0076]

[0077] 1400----Nitrogen atomic mass 14*100;

[0078] 152-----substituent molecular mass;

[0079] 162----Molecular mass of glucose residues in starch;

[0080] Since the purity of dry-process cationic starch is lower than that of wet-process cationic starch and there are more residual substances, which interferes with the detection of cationic substitution degree, this detection method is designed based on this problem.

[0081] Improvement plan:

[0082] Step 1: Weigh 25g of sample, add 200ml of room temperature distilled water, stir, pour into a dehydrator with a 400 mesh filter cloth and spin dry at high speed for 30 seconds;

[0083] Step 2: Place the filter cloth in 200ml of room temperature distilled water to wash out the sample, then place the filter cloth in a dehydrator, pour in the sample and spin dry at high speed for 4 minutes;

[0084] Step 3: Weigh 1 g of the dried sample and use the above method to detect its degree of substitution; and also detect the moisture content of the sample to facilitate the calculation of the degree of substitution;

[0085] Test results: When the degree of substitution is greater than 0.041, the starch gelatinization temperature becomes low and the powder gelatinization cannot be measured.

[0086] Pretreatment of samples for dry-process cationic starch substitution degree detection

[0087] 1. Pre-treatment:

[0088] 1.1: Weigh 25g of sample, add 200ml of ice water (below 4℃), stir, pour into a dehydrator with 400 mesh filter cloth and spin dry at high speed for 30 seconds;

[0089] 1.2: Place the filter cloth in 200ml of ice water to wash out the sample, then place the filter cloth in a dehydrator, pour in the sample and spin dry at high speed for 4 minutes;

[0090] 2. Instruments

[0091] a. Kjeldahl flask: 500 mL;

[0092] b. Erlenmeyer flask: 500mL.

[0093] Diagram of constant nitrogen distillation apparatus Figure 2 shown.

[0094] 3. Reagents

[0095] a. 40% sodium hydroxide solution;

[0096] b.0.01 mol / L hydrochloric acid standard solution

[0097] c. 2% boric acid solution;

[0098] d. concentrated sulfuric acid;

[0099] e. Catalyst: potassium sulfate, copper sulfate, selenium powder

[0100] f. Mixed indicator solution: add 20 mL of 0.1% methyl red ethanol solution to 30 mL of 0.2% bromocresol green ethanol solution and shake well.

[0101] 4. Test procedures

[0102] Weigh 1.0 g of powder (accurate to 0.001 g) of sample (1.2) using an electronic balance and test its moisture content. Place the sample in a dry 250 ml Kjeldahl test tube. Add 0.3 g of potassium sulfate, 0.3 g of copper sulfate, and 0.1 g of selenium powder. Add 5.0 ml of concentrated sulfuric acid dropwise along the wall of the tube. Place a small funnel at the mouth of the Kjeldahl test tube. Preheat and shake the mixture on an electric stove. Place the flask at an angle of 45 degrees on the stove. After heating for 3 hours, when the solution turns clear green, remove the Kjeldahl flask, cool it to room temperature, and then distill it.

[0103] Distillation: Place 10 ml of 2% boric acid solution in a 250 ml Erlenmeyer flask. Add 5 drops of a mixed indicator solution of methyl red and bromocresol green. Insert the lower end of the condenser tube below the liquid surface. Transfer the contents of the Kjeldahl flask to the distilling flask of a Kjeldahl nitrogen determination apparatus. Rinse the Kjeldahl flask and funnel several times with small amounts of water. Add 25 ml of 40% sodium hydroxide solution and rinse the funnel several times with small amounts of water. Close the funnel inlet and seal it with water. Allow steam to distill until the boric acid solution begins to change from wine red to green. Collect approximately 75 ml of the contents of the Erlenmeyer flask by distillation. Lift the lower end of the cooling tube above the liquid surface and allow steam to continue flushing for approximately 1 minute. Rinse with water, then stop distillation. Titrate with 0.01 mol / L standard hydrochloric acid solution until the distillate turns gray. Record the amount of hydrochloric acid consumed.

[0104] Perform a blank experiment at the same time

[0105] 5. Calculation:

[0106]

[0107] V- the number of milliliters of 0.01 mol / L standard hydrochloric acid solution used in the solution (mL);

[0108] 0.01-concentration of hydrochloric acid standard titration solution, in moles per liter (mol / L);

[0109] W-dry weight of sample (g);

[0110] 0.01401 is the mass of nitrogen equivalent to 1.0 mL of hydrochloric acid [c(HCl) = 1.000 mol / L] standard titration solution, in grams (g);

[0111]

[0112] 1400----Nitrogen atomic mass 14*100;

[0113] 152-----substituent molecular mass;

[0114] 162----Molecular mass of glucose residues in starch;

[0115] Experimental data:

[0116]

[0117]

[0118] n 醚化剂 ---Amount of etherifying agent added / mol

[0119] n 淀粉 ---Amount of starch added / mol

[0120] Through the above method, the present invention has the following advantages:

[0121] 1. Compared with the national standard, the test results are the same while reducing the use of test reagents and saving costs.

[0122] 2. Comparison method: The current experimental results are too different from the theoretical results, which may easily cause quality accidents and bring losses.

[0123] 3. The test results after ice water pre-treatment have small errors, are convenient and easy to operate, and can prevent quality accidents and reduce losses.

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dry process cationic starch substitution degree detection sample pretreatment method, characterized by: include S1: Weigh 25g of sample, add 200ml of ice water (below 4℃), stir, pour into a dehydrator with 400 mesh filter cloth and spin dry at high speed for 30 seconds; S2: Place the filter cloth in 200ml of ice water to wash out the sample, then place the filter cloth in a dehydrator, pour in the sample and spin dry at high speed for 4 minutes; S3: Weigh 1 g of the dried sample and use the Kjeldahl method to determine its degree of substitution. Simultaneously, the moisture content of the sample is tested to facilitate the calculation of the degree of substitution.

2. The method for pre-treating a sample for detecting the degree of substitution of cationic starch by a dry process according to claim 1, wherein: In step S1, the temperature of the ice water is below 4° C., so as to prevent the high-degree-of-substitution starch from gelatinizing during the washing process.

3. The pre-treatment method for dry-process cationic starch substitution degree detection sample according to claim 1, characterized in that: In step S1, the dehydrator is operated at a high speed, the first drying time is 30 seconds, and the second drying time is 4 minutes, so as to ensure that the unreacted etherifying agent in the sample is fully removed.

4. The method for pre-treating a sample for detecting the degree of substitution of cationic starch by a dry process according to claim 1, wherein: In the step S3, the operating steps of the Kjeldahl method include: S3.1: Place 1 g of the pretreated sample in a Kjeldahl flask, add potassium sulfate, copper sulfate, and selenium powder as catalysts, and drip concentrated sulfuric acid along the flask wall. S3.2: Heat the digestion on a hot plate until the solution turns clear green. S3.3: Cool the digestate and transfer it to a distillation unit, add sodium hydroxide solution to alkalize it, and release ammonia by distillation; S3.4: Absorb the distilled ammonia with boric acid solution and titrate to the endpoint with standard hydrochloric acid solution, recording the amount of hydrochloric acid consumed. S3.5: Calculate the nitrogen content and degree of substitution of the sample based on the titration results.

5. The method for pre-treating a sample for detecting the degree of substitution of cationic starch by a dry process according to claim 4, wherein: In step S3.1, the catalyst is composed of 0.3 g of potassium sulfate, 0.3 g of copper sulfate and 0.1 g of selenium powder.

6. The method for pre-treating a sample for dry-process cationic starch substitution degree detection according to claim 4, wherein: In step S3.4, the concentration of the boric acid solution is 2%, and a methyl red-bromocresol green mixed indicator solution is added to determine the titration endpoint.

7. The method for pre-treating a sample for dry-process cationic starch substitution degree detection according to claim 1, wherein: In step S3, the calculation formula of the substitution degree is Where V is the volume (mL) of 0.01 mol / L standard hydrochloric acid solution used in the solution, 0.01 is the concentration of the hydrochloric acid standard titrant in moles per liter (mol / L), 0.01401 is the mass of nitrogen equivalent to 1.0 mL of hydrochloric acid [c(HCl) = 1.000 mol / L] standard titrant in grams (g), and W is the absolute dry weight of the sample in g. 1400 is the mass of nitrogen atom 14*100, 152 is the molecular mass of substituent, and 162 is the molecular mass of glucose residue in starch.

8. The method for pre-treating a sample for dry-process cationic starch substitution degree detection according to claim 1, wherein: In the step S1, it is applicable to dry-process cationic starch samples with a degree of substitution greater than 0.041, and can effectively avoid the influence of sample gelatinization on the test results.

9. The method for pre-treating a sample for dry-process cationic starch substitution degree detection according to claim 1, wherein: In step S2, ice water washing and high-speed drying are performed to remove unreacted etherifying agent, thereby reducing detection errors, and simultaneously detecting the moisture content of the sample to improve the accuracy of substitution degree calculation.

Images