A method for detecting the boron content in an alloy

Abstract

The present invention provides a method for detecting the boron content in an alloy. The sample is dissolved with a mixed acid, the test solution is taken and dried, in a sulfuric acid - glacial acetic acid medium, boron reacts with curcumin to form a stable red complex, coexisting metal ions are complexed with oxalic acid, acidified with an ammonium acetate solution containing ethanol, diluted and fixed volume with a (1 + 1) ethanol solution, and the absorbance is measured at a wavelength of 543 nm on a spectrophotometer, and then the mass fraction of boron is calculated therefrom. The method for detecting the boron content in the alloy provided by this application can quickly, accurately and precisely determine the boron content in the alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis in steel and alloys, and particularly to a method for detecting the boron content in alloys. Background Art

[0002] The content of boron also has a great influence on the properties of steel. Therefore, the detection of boron content is extremely important.

[0003] In the prior art, the boron content in steel is generally detected directly by the curcumin spectrophotometry according to the national standard. However, in this method, the phosphoric acid content in the color-developing solution is low during color development, titanium and vanadium have serious interference, and after color development, it is neutralized with ammonium acetate solution, the solution has a short stable time, is easy to become turbid, and the accuracy and precision of the detection result are poor.

[0004] Therefore, it is necessary to provide an analytical method for determining the boron content in steel with high speed, good stability, high accuracy and precision. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a detection method for determining the boron content in alloys with high speed, high accuracy and precision.

[0006] In view of this, the present application provides a method for detecting the boron content in alloys, including the following steps:

[0007] A) Mix the alloy sample with hydrochloric acid and nitric acid, decompose it, and then add phosphoric acid, sulfuric acid and perchloric acid, and react;

[0008] B) Mix the mixed solution obtained in step A) with sulfurous acid, react, and dry to obtain a test solution;

[0009] C) Mix the test solution with sodium phosphite solution, heat it up and then cool it, and then add a sulfuric acid - glacial acetic acid mixed solution to obtain a color-developing solution;

[0010] D) Add a curcumin solution to the color-developing solution for color development, then add an oxalic acid solution and an ammonium acetate solution to the obtained test solution, and then dilute it with ethanol, and measure the absorbance with a reference solution as a reference;

[0011] E) Weigh a number of standard sample specimens, measure the absorbance values, and linearly regress to obtain the working curve function;

[0012] F) Calculate according to the working curve function and the absorbance in step D) according to formula (I) to obtain the boron content in the alloy;

[0013] (I);

[0014] In the formula: m1 - the boron amount obtained from the working curve function, g;

[0015] m — mass of the test sample taken, g.

[0016] Preferably, during the calculation process, when the chromogenic solution and the reference solution contain 1.5 mL of phosphoric acid, the interference correction coefficient of vanadium: 1.00% vanadium is equivalent to 0.00106% boron; when the chromogenic solution and the reference solution contain 2.0 mL of phosphoric acid, the interference correction coefficient of vanadium: 1.00% vanadium is equivalent to 0.0008% boron.

[0017] Preferably, the reference solution includes an ammonium fluoride solution with a concentration of 35 - 45 g / L.

[0018] Preferably, in step A), if the total content of tungsten, molybdenum, and niobium in the alloy is less than 5 wt%, the volume ratio of hydrochloric acid to nitric acid is 1:3 - 1:5; if the total content of tungsten, molybdenum, and niobium in the alloy is 5 wt% - 10 wt%, the volume ratio of hydrochloric acid to nitric acid is 1:5 - 1:10; if the total content of tungsten, molybdenum, and niobium in the alloy is greater than 10 wt%, the volume ratio of hydrochloric acid to nitric acid is 1:12 - 1:14; if the alloy is low alloy steel or high speed steel, the volume ratio of hydrochloric acid to nitric acid is 1:1.

[0019] Preferably, in step C), before the test solution is mixed with the sodium hypophosphite solution, it also includes:

[0020] When the vanadium content in the test sample taken is ≤ 5.0 mg, no phosphoric acid is added to the test solution, and the test solution contains 1.5 mL of phosphoric acid; when the vanadium content in the test sample taken is 5.0 - 10.0 mg, 0.50 mL of phosphoric acid is added, and the test solution contains 2.0 mL of phosphoric acid.

[0021] Preferably, when the phosphoric acid in the chromogenic solution is 1.5 mL, the chromogenic time ≥ 75 min; when the phosphoric acid in the chromogenic solution is 2.0 mL, the chromogenic time ≥ 120 min.

[0022] Preferably, when the boron content in the test sample is 0.0005 - 0.001%, the test sample is 1.0 g; when the boron content in the test sample is 0.001 - 0.004%, the test sample is 0.3 - 0.5 g; when the boron content in the test sample is 0.04 - 0.10%, the test sample is 0.2 g; when the boron content in the test sample is 0.10 - 0.20%, the test sample is 0.10 g.

[0023] Preferably, the vanadium content in the test sample is ≤ 10.0 mg.

[0024] Preferably, in step D), the wavelength for measuring the absorbance is 543 nm.

[0025] Preferably, the volume ratio of the test solution to the curcumin solution in step C) is 1:(4 - 10), the concentration of the curcumin solution is 4.00 g / L, and the solvent is glacial acetic acid; the volume ratio of the test solution to the sulfuric acid - glacial acetic acid mixture is 1:(5 - 10), and the volume ratio of sulfuric acid to anhydrous glacial acetic acid in the sulfuric acid - glacial acetic acid mixture is 1:9.

[0026] This application provides a method for detecting the boron content in an alloy. The test sample is dissolved with a mixed acid, the test solution is taken and dried. In a sulfuric acid - glacial acetic acid medium, boron reacts with curcumin to form a stable red complex. Coexisting metal ions are complexed with oxalic acid, acidified with an ammonium acetate solution containing ethanol, diluted and fixed volume with a (1 + 1) ethanol solution, and the absorbance is measured at a wavelength of 543 nm on a spectrophotometer, and then the mass fraction of boron is calculated. In this method, the content of phosphoric acid in the color - developing solution is high, titanium does not interfere, the interference of vanadium is small and linear, and the interference coefficient method is used for correction to solve the interference of vanadium and titanium; a large amount of curcumin and glacial acetic acid are added during color development. After color development, an oxalic acid solution and an ammonium acetate solution containing ethanol are added for neutralization; the linear range of boron in the color - developing solution is wide, from 0 to 11 micrograms, which is suitable for detecting boron in high - boron steel; the solution after color development is stable for a long time without turbidity, and the accuracy and precision of the detection results are high, and the probability of meeting the accuracy and precision tolerance requirements of the national standard methanol distillation - curcumin spectrophotometry > 99%. Detailed implementation manners

[0027] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0028] In view of the problems in the direct curcumin spectrophotometry for the boron content in an alloy in the prior art, where vanadium and titanium have serious interference, and when detecting nickel - cobalt - based superalloy samples, the stable time of the solution after color development is short, and the accuracy and precision of the detection results are poor, the embodiments of the present invention disclose a direct curcumin spectrophotometry for determining the boron content in steel grades, which has the advantages of rapidity, good stability, high accuracy and high precision. Specifically, this application provides a method for detecting the boron content in an alloy, including the following steps:

[0029] A) Mix the alloy sample with hydrochloric acid and nitric acid, decompose it, and then add phosphoric acid, sulfuric acid and perchloric acid for reaction;

[0030] B) Mix the mixture obtained in step A) with sulfurous acid, react, and dry to obtain a test solution;

[0031] C) Mix the test solution with a sodium phosphite solution, heat it up and then cool it, and then add a sulfuric acid - glacial acetic acid mixture to obtain a color - developing solution;

[0032] D) Add a curcumin solution to the color-developing solution for color development, then add an oxalic acid solution and an ammonium acetate solution to the resulting test solution, and then dilute with ethanol. Measure the absorbance using the reference solution as a reference;

[0033] E) Weigh several standard sample test specimens, measure the absorbance values, and perform linear regression to obtain the working curve function;

[0034] F) Calculate according to the working curve function and the absorbance described in step D) according to formula (Ⅰ) to obtain the boron content in the alloy;

[0035] (Ⅰ);

[0036] In the formula: m1 - the boron amount obtained from the working curve function, g;

[0037] m - the mass of the test sample weighed, g.

[0038] The detection method provided by this application uses a mixed acid to dissolve the alloy sample. In a sulfuric acid - glacial acetic acid medium, boron reacts with curcumin to form a stable red complex. Oxalic acid is used to complex coexisting metal ions, and the solution is acidified with an ammonium acetate solution containing ethanol, and then diluted and made up to volume with a (1 + 1) ethanol solution. Finally, the absorbance is measured on a spectrophotometer to calculate the mass fraction of boron.

[0039] The detection method provided by this application is applicable to various steels and alloys with a boron content mass fraction of 0.0005% - 0.200%.

[0040] In this application, first mix the alloy sample with hydrochloric acid and nitric acid. After decomposition, add phosphoric acid, sulfuric acid, and perchloric acid and react. In this process, the mixed acid of nitric acid and hydrochloric acid decomposes the sample. Add phosphoric acid, sulfuric acid, and perchloric acid and heat to fume off the perchloric acid until sulfuric - phosphoric acid fumes are emitted. The purpose is to remove nitrosyl hydrochloric acid and destroy all carbides so that all boron in the sample enters the solution. If the total content of tungsten, molybdenum, and niobium in the alloy is less than 5 wt%, such as superalloys, stainless steels, or precision alloys, the volume ratio of the hydrochloric acid to the nitric acid is 1:3 - 1:5; if the total content of tungsten, molybdenum, and niobium in the alloy is 5 wt% - 10 wt%, such as superalloys, the volume ratio of the hydrochloric acid to the nitric acid is 1:5 - 1:10; if the total content of tungsten, molybdenum, and niobium in the alloy is greater than 10 wt%, such as superalloys, the volume ratio of the hydrochloric acid to the nitric acid is 1:12 - 1:14; if the alloy is low - alloy steel or tool steel, the volume ratio of the hydrochloric acid to the nitric acid is 1:1.

[0041] Add water to the resulting reaction solution, add a sulfurous acid solution, heat and boil for 2 - 5 min, cool to room temperature, and dilute with water. The above process reduces high - valence manganese, vanadium, and chromium.

[0042] The above process is mainly the dissolution process of the test sample. Then, the obtained test sample in this application is divided into two parts, one part is used as the color-developing solution and the other part is used as the reference solution. Sodium phosphite solution is added to both test solutions, mixed evenly, then placed in an oven to heat up, taken out and cooled, and then a sulfuric acid - glacial acetic acid mixture is added. Ammonium fluoride solution is added to the reference solution, and ammonium fluoride solution is not added to the color-developing solution. In the above process, when the vanadium content in the weighed test sample is ≤5.0 mg, phosphoric acid is not added to the test solution, and the test solution contains 1.5 ml of phosphoric acid; when the vanadium content in the weighed test sample is 5.0 - 10.0 mg, 0.50 ml of phosphoric acid is added, and the test solution contains 2.0 ml of phosphoric acid. The volume ratio of the test solution to the curcumin solution is 1:(4 - 10), the concentration of the curcumin solution is 4.00 g / L, and the solvent is glacial acetic acid; the volume ratio of the test solution to the sulfuric acid - glacial acetic acid mixture is 1:(5 - 10), and the volume ratio of sulfuric acid to anhydrous glacial acetic acid in the sulfuric acid - glacial acetic acid mixture is 1:9.

[0043] Then, curcumin solution is added to both the obtained color-developing solution and reference solution in this application, and color development is carried out in a dry environment. When the phosphoric acid in the test solution is 1.5 ml, the color development time is ≥75 min; when the phosphoric acid in the color-developing solution is 2.0 ml, the color development time is ≥120 min. After color development is completed, oxalic acid solution and ammonium acetate solution are added, and then diluted with 1+1 ethanol. Using the reference solution as a reference, the absorbance of the color-developing solution is measured. The absorbance is measured using light with a wavelength of 543 nm.

[0044] According to the present invention, then several standard sample test specimens are weighed, and the absorbance values are measured according to the above method, and the working curve function is obtained by linear regression.

[0045] Finally, according to the working curve function and the absorbance obtained above, calculation is carried out according to formula (Ⅰ) to obtain the boron content in the alloy;

[0046] (Ⅰ);

[0047] In the formula: m1 - the boron amount obtained from the working curve function, g;

[0048] m - the mass of the weighed test sample, g.

[0049] In the above calculation process, when the color-developing solution and the reference solution contain 1.5 ml of phosphoric acid, the interference correction coefficient of vanadium: 1.00% vanadium is equivalent to 0.00106% boron; when the color-developing solution and the reference solution contain 2.0 ml of phosphoric acid, the interference correction coefficient of vanadium: 1.00% vanadium is equivalent to 0.0008% boron.

[0050] To further understand the present invention, the following is a detailed description of the method for detecting the boron content in the alloy provided by the present invention in combination with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0051] Example

[0052] 1 Reagents

[0053] Unless otherwise specified, only reagents confirmed to be of analytical purity and distilled water or deionized water or water of equivalent purity are used in the analysis; the following reagents are those used in the examples and their relevant parameters;

[0054] 1.1 Hydrochloric acid (ρ1.19 g / ml);

[0055] 1.2 Nitric acid (ρ1.42 g / ml);

[0056] 1.3 Phosphoric acid (ρ1.70 g / ml);

[0057] 1.4 Sulfuric acid (ρ1.84 g / ml);

[0058] 1.5 Perchloric acid (ρ1.75 g / ml);

[0059] 1.6 Glacial acetic acid (≥99.5%);

[0060] 1.7 Sodium hypophosphite solution (40 g / L);

[0061] 1.8 Sulfuric acid - glacial acetic acid mixture; 100.0 ml of sulfuric acid (1.84 g / ml) is mixed with 900.0 ml of anhydrous glacial acetic acid and cooled to room temperature;

[0062] 1.9 Ammonium fluoride solution (40 g / L);

[0063] 1.10 Curcumin solution (4.00 g / L), prepared with glacial acetic acid;

[0064] 1.11 Oxalic acid solution (100 g / L);

[0065] 1.12 Ammonium acetate solution (2.20 mol / L); In a 3000 mL wide-mouth beaker, add 1000 mL of water, add 339 g of ammonium acetate, stir to dissolve, add 500 mL of anhydrous ethanol, and mix well; Transfer to a 2000.0 mL volumetric flask and accurately dilute to 2000.0 mL with water, and mix well;

[0066] 1.13 (1 + 1) Ethanol; Anhydrous ethanol and water are mixed in equal volumes;

[0067] 1.14 Sulfurous acid solution (6%);

[0068] 2 Sample preparation

[0069] Sample preparation is carried out according to GB / T 20066 or an appropriate national standard.

[0070] 3 Analysis procedure

[0071] 3.1 Sample weighing amount

[0072] Weigh the test sample according to Table 1 (accurate to 0.0001 g) {control the vanadium content in the weighed test sample to be ≤ 10.0 mg};

[0073] Table 1 Relationship table between boron content and sample weighing amount

[0074] Boron content, % Sample weight, g 0.0005~0.001 1.0 0.001~0.04 0.3~0.5 0.04~0.10 0.2 0.10~0.20 0.10

[0075] 3.2 Dissolution of test sample

[0076] Place the test portion in a clean 300 mL quartz conical flask, add an appropriate amount of a mixed acid of hydrochloric acid (1.1) and nitric acid (1.2) in an appropriate ratio, heat it at low temperature until the test portion is completely decomposed, add 30.0 mL of phosphoric acid (1.3) and mix well; add 5.0 mL of sulfuric acid (1.4) and mix well; add 5 mL of perchloric acid (1.5) and mix well. Heat until sulfuric and phosphoric acid fumes rise from the bottom and suspend above the liquid surface, then cool to room temperature;

[0077] Add 50 mL of water and mix well; add 10.0 mL of sulfurous acid solution (6%) and mix well, {reduce high-valent manganese, vanadium and chromium}, heat to boiling for 2 minutes, cool to room temperature, and dilute to 100.0 mL with water and mix well;

[0078] 3.3 Color development

[0079] Accurately pipette 5.00 mL of the test solution in two portions into two 100.0 mL quartz volumetric flasks respectively. {When the vanadium content in the weighed test sample is ≤ 5.0 mg in the same batch of operations, phosphoric acid (ρ 1.70 g / ml) is not added to this batch, and each solution contains 1.5 mL of phosphoric acid (ρ 1.70 g / ml); when there is vanadium with a content of 5.0 - 10.0 mg in the weighed test sample in the same batch of operations, 0.50 mL of phosphoric acid (ρ 1.70 g / ml) is added to this batch, and each solution contains 2.0 mL of phosphoric acid (ρ 1.70 g / ml);}, add 1.00 mL of sodium hypophosphite solution (1.6) and mix well; {when weighing 1.0 g of the iron-based test sample, add 2.00 mL of sodium hypophosphite solution (1.6)}, place it in a constant temperature drying oven, heat up to 145 ± 1 °C, keep drying for no less than 120 minutes, take it out, cool to room temperature, add 25.00 mL of sulfuric acid - glacial acetic acid mixed solution (1.8) and mix well;

[0080] Reference solution: Add 1.0 ml of ammonium fluoride solution (1.9) and mix well;

[0081] Color-developed solution: Do not add ammonium fluoride solution;

[0082] Add 20.00 mL of curcumin solution (1.10) to each, mix well; stopper the volumetric flask and place it in a constant temperature drying oven to develop color at (45.0 ± 0.5) °C. {When in the same batch of operations, when each solution contains 1.5 mL of phosphoric acid (ρ 1.70 g / ml), control the color development time ≥ 75 minutes; when in the same batch of operations, when each solution contains 2.0 mL of phosphoric acid (ρ 1.70 g / ml), control the color development time ≥ 120 minutes}, take out, add 10.0 mL of oxalic acid solution (1.11), add 35.0 mL of ammonium acetate solution (1.12), mix well; {The addition order of the oxalic acid solution and the ammonium acetate solution can be exchanged}, cool to room temperature, dilute to the mark with (1 + 1) ethanol, and mix well;

[0083] 3.4 Measurement of absorbance

[0084] On a visible spectrophotometer, select an appropriate size of cuvette, use the reference solution as a reference, and measure the absorbance of the corresponding developed color solution at a wavelength of 543 nm;

[0085] 3.5 Measurement of the working curve function

[0086] Weigh six portions of standard sample test materials, control the boron content in the test samples to be within the range of the boron content of the series of standard sample test materials, operate according to the analysis steps, measure the series of absorbance values, and perform linear regression to obtain the working curve function;

[0087] 3.6 Calculation

[0088] Calculate the boron content according to the following formula:

[0089]

[0090] Where: m1 - the boron amount obtained from the working curve function, g;

[0091] m - the mass of the test sample weighed, g;

[0092] When the developed color solution and the reference solution contain 1.5 mL of phosphoric acid (ρ 1.70 g / ml): Vanadium interference correction coefficient: 1.00% vanadium is equivalent to 0.00106% boron;

[0093] When the developed color solution and the reference solution contain 2.0 mL of phosphoric acid (ρ 1.70 g / ml): Vanadium interference correction coefficient: 1.00% vanadium is equivalent to 0.0008% boron.

[0094] Some standard samples were detected using the above method, and the results are shown in Table 3.

[0095] Table 3 Data table of the results of detecting standard samples using the direct curcumin spectrophotometry method of this application

[0096] Standard sample number Standard sample name Standard value of B% B% (detected value) Permissible critical difference of national standard methanol distillation - curcumin photometry BH85-5 Low alloy steel 0.0006 0.000630.00058 0.00018 BH85-4 Low alloy steel 0.0013 0.001350.00126 0.00025 BH85-2 Low alloy steel 0.008 0.00820.0079 0.0009 A43 H220 0.0195 0.01980.0194 0.002 YSBC11501-93 GH49 0.028 0.02830.0288 0.0028 A37 GH118 0.0174 0.01760.0169· 0.0018 YSBC11515-93 K3 0.034 0.03420.0346 0.0034 YSBC11516-93 K13 0.100 0.10230.1012 0.0097

[0097] In Table 3, the differences between the results of detecting the boron content in some standard samples by using a new direct curcumin photometric method for determining the boron content in steel and the corresponding standard values are less than the allowable critical difference of the national standard methanol distillation-curcumin photometric method, indicating that the results of detecting the boron content in steel by this method are accurate and reliable.

[0098] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0099] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting the boron content in an alloy, comprising the following steps: A) Mix the alloy sample with hydrochloric acid and nitric acid, decompose it, and then add phosphoric acid, sulfuric acid and perchloric acid, and react; B) Mix the mixed solution obtained in step A) with sulfurous acid, react, and dry to obtain a test solution; C) Mix the test solution with sodium phosphite solution, heat it up and then cool it, and then add a sulfuric acid - glacial acetic acid mixed solution to obtain a color-developing solution; D) Add a curcumin solution to the color-developing solution for color development, then add an oxalic acid solution and an ammonium acetate solution to the obtained test solution, and then dilute it with ethanol. Using the reference solution as a reference, measure the absorbance; E) Weigh several standard sample specimens, measure the absorbance values, and perform linear regression to obtain the working curve function; F) According to the working curve function and the absorbance in step D), calculate according to formula (Ⅰ) to obtain the boron content in the alloy; During the calculation process, when the color-developing solution and the reference solution contain 1.5 ml of phosphoric acid, the interference correction coefficient of vanadium: 1.00% vanadium is equivalent to 0.00106% boron; when the color-developing solution and the reference solution contain 2.0 ml of phosphoric acid, the interference correction coefficient of vanadium: 1.00% vanadium is equivalent to 0.0008% boron; （Ⅰ）； In the formula: m1 - the boron content obtained from the working curve function, g; m - the mass of the test sample weighed, g.

2. The detection method according to claim 1, wherein, The reference solution includes an ammonium fluoride solution with a concentration of 35 - 45 g / L.

3. The detection method according to claim 1, characterized in that, In step A), if the total content of tungsten, molybdenum and niobium in the alloy is less than 5 wt%, the volume ratio of hydrochloric acid to nitric acid is 1:3 - 1:5; if the total content of tungsten, molybdenum and niobium in the alloy is 5 wt% - 10 wt%, the volume ratio of hydrochloric acid to nitric acid is 1:5 - 1:10; if the total content of tungsten, molybdenum and niobium in the alloy is greater than 10 wt%, the volume ratio of hydrochloric acid to nitric acid is 1:12 - 1:14; if the alloy is low alloy steel or tool steel, the volume ratio of hydrochloric acid to nitric acid is 1:

1.

4. The detection method according to claim 1, wherein Before mixing the test solution with the sodium phosphite solution in step C), it also includes: If the vanadium content in the weighed sample is ≤ 5.0 mg, no phosphoric acid is added to the test solution, and the test solution contains 1.5 ml of phosphoric acid; if the vanadium content in the weighed sample is 5.0 - 10.0 mg, add 0.50 ml of phosphoric acid, and the test solution contains 2.0 ml of phosphoric acid.

5. The detection method according to claim 1, wherein When the phosphoric acid in the color-developing solution is 1.5 ml, the color-developing time ≥ 75 min; when the phosphoric acid in the color-developing solution is 2.0 ml, the color-developing time ≥ 120 min.

6. The detection method according to claim 1, wherein When the boron content in the sample is 0.0005 - 0.001%, the sample is 1.0 g; when the boron content in the sample is 0.001 - 0.004%, the sample is 0.3 - 0.5 g; when the boron content in the sample is 0.04 - 0.10%, the sample is 0.2 g; when the boron content in the sample is 0.10 - 0.20%, the sample is 0.10 g.

7. The detection method according to claim 1, characterized in that, The vanadium content in the sample is ≤ 10.0 mg.

8. The detection method according to claim 1, characterized in that, In step D), the wavelength for measuring the absorbance is 543 nm.

9. The detection method according to claim 1, wherein The volume ratio of the test solution described in step C) to the curcumin solution is 1:(4-10), the concentration of the curcumin solution is 4.00 g / L, and the solvent is glacial acetic acid; the volume ratio of the test solution to the sulfuric acid-glacial acetic acid mixture is 1:(5-10), and the volume ratio of sulfuric acid to anhydrous glacial acetic acid in the sulfuric acid-glacial acetic acid mixture is 1:9.

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