Quantitative analysis method for mixed solution of hexavalent chromium and trivalent chromium and application of quantitative analysis method

Abstract

The invention provides a quantitative analysis method for a mixed solution of hexavalent chromium and trivalent chromium and application of the quantitative analysis method. The specific method comprises the following steps: removing impurities from a mixed solution to form a to-be-detected sample, establishing a mixed solution concentration standard curve through a standard solution, testing the to-be-detected sample through a high performance liquid chromatograph, and determining the content of hexavalent chromium and trivalent chromium in the mixed solution by using an external standard method. According to the method, the to-be-detected sample is subjected to impurity removal by dropwise adding the alkali liquor, the influence of other metal ions is eliminated, interference signals are reduced, and the accuracy is improved; a degree elution mode is adopted, ammonia water and ethyl alcohol are used as mobile phases, proper elution time is set according to components of the mobile phases, and compared with a single elution mode, peak positions of hexavalent chromium ions and trivalent chromium ions can be better distinguished. The method provided by the invention is convenient, efficient, economical and convenient, and the application range of the method in the field of electroplating wastewater detection is widened.

Description

Technical Field

[0001] The present invention belongs to the field of analytical technologies, and relates to an analytical method for quantifying a mixed solution of hexavalent chromium and trivalent chromium and its application. Background Art

[0002] Chromium exists in water bodies polluted by industrial wastewaters such as electroplating, smelting, leather-making, textile, and pharmaceutical industries. Chromium in nature often exists in elemental or trivalent states, and there are two valence states of chromium in water, namely trivalent chromium and hexavalent chromium. Both trivalent chromium and hexavalent chromium are harmful to human health. Generally, hexavalent chromium is more toxic, more easily absorbed by the human body and can accumulate in the body. Drinking water containing hexavalent chromium can cause damage to internal tissues; chromium accumulates in fish bodies and can also cause aquatic organisms to die, inhibiting the self-purification function of water bodies; irrigating crops with chromium-containing water, chromium can accumulate in fruits. Therefore, the detection and analysis of chromium in water bodies are of great importance.

[0003] The existing determination of chromium can adopt colorimetry, atomic absorption spectrophotometry and volumetry. When the content of hexavalent chromium in the water sample is relatively high, the ammonium ferrous sulfate volumetry can be used to determine its content. Hexavalent chromium in slightly polluted surface water can be directly determined by colorimetry; when using diphenylcarbazide colorimetry to determine chromium, hexavalent chromium can be directly determined by colorimetry. Only the content of hexavalent chromium can be directly determined by colorimetry or volumetry, while the content of trivalent chromium cannot be detected simultaneously. The content of trivalent chromium needs to be indirectly obtained by measuring the total chromium and hexavalent chromium. Moreover, in a complex solution system, in addition to trivalent chromium and hexavalent chromium, there will be the influence of other metal ions and organic substances. Quantifying by this method will have limitations. It is more suitable for the situation where the water body only contains trivalent chromium and hexavalent chromium and the content of other redox substances is relatively small. And in the prior art, when using an alkali solution to precipitate and remove other metal ions in industrial wastewater except trivalent chromium and hexavalent chromium, a saturated zinc hydroxide solution is commonly used, resulting in an increase in cost.

[0004] Therefore, how to develop an analytical method for simultaneously measuring hexavalent chromium and trivalent chromium in a mixed water sample, which is simple, fast, universal and efficient, and at the same time reduces costs, is an urgent problem to be solved by the present invention. Summary of the Invention

[0005] The purpose of the present invention is to provide an analytical method for quantifying a mixed solution of hexavalent chromium and trivalent chromium, and a new type of high-performance liquid chromatography analytical method is developed, which can simultaneously quantify trivalent chromium and hexavalent chromium in chromium-containing mixed solutions commonly used in electroplating, smelting and other aspects, and reduce costs. Specifically, it includes the following steps:

[0006] S1-1: Add an alkali solution to the mixed solution for impurity removal to obtain a test solution A;

[0007] S1-2: Mix standard trivalent chromium and hexavalent chromium solutions to establish a standard curve for the concentration of the mixed solution;

[0008] S1-3: Weigh the test solution A and add it to a beaker. Dilute and make up the volume with ammonia ethanol solution, and filter with an aqueous phase filter head to obtain the test solution B;

[0009] S1-4: Test the test solution B with a high performance liquid chromatograph. When using the high performance liquid chromatograph for testing, gradient elution is adopted. In the gradient elution, the mobile phase includes phase A and phase B. Phase A is ammonia water, and phase B is ammonia ethanol solution. The elution time sequence is: 0→8 - 10 min, 90% - 95% phase A; 8 - 10 min→20 min, 100% phase B;

[0010] S1-5: Use the standard curve of the concentration of the mixed solution prepared in S1-2 to quantitatively analyze the test solution B by the external standard method to obtain the contents of hexavalent chromium and trivalent chromium in the test solution B.

[0011] As a further improvement, the working conditions of the high performance liquid chromatograph in S1-4 are as follows:

[0012] Chromatographic column: Ailgent Eclipse Plus C18, particle size 5 μm, inner diameter 4.6 mm, length 250 mm; Injection volume: 1 - 10 μL; Flow rate: 0.2 - 1 mL / min; Column temperature: 25 - 35 °C.

[0013] As a further improvement, in the mobile phase in S1-4, phase A is 0.2% - 0.5% ammonia water, and phase B is ammonia ethanol solution. The ammonia ethanol solution is a mixture of 25% - 28% ammonia water and 90% - 95% ethanol.

[0014] As a further improvement, the volume ratio of 25% - 28% ammonia water to 90% - 95% ethanol in the ammonia ethanol solution is (5 - 3):1.

[0015] As a further improvement, the gradient elution time sequence in S1-4 is: 0→8 min, 90% - 95% phase A; 8→20 min, 100% phase B.

[0016] As a further improvement, the preparation method of the test solution A in step S1-1 includes the following steps:

[0017] S6-1: Add an alkali solution to the mixed solution, stir for 10 - 20 min, let it stand for 30 - 40 min, and filter to obtain solution C and a precipitate intermediate;

[0018] S6-2: Add a saturated calcium hydroxide solution to the precipitate intermediate obtained in S6-1, ultrasonically stir for 10 - 20 min, let it stand for 30 - 40 min, and filter to obtain solution D;

[0019] S6-3: Mix the solution C obtained in S6-1 and the solution D obtained in step S5-2 to form the test solution A.

[0020] As a further improvement, in S1-2, the standard trivalent chromium and hexavalent chromium solutions are a trivalent chromium single-element standard solution and a hexavalent chromium single-element standard solution.

[0021] As a further improvement, in S1-1, the alkaline solution includes one or more of a saturated calcium hydroxide solution and a saturated zinc hydroxide solution.

[0022] As a further improvement, in S1-5, the method of external standard quantification is to establish a standard curve with the peak areas of the response peaks of trivalent chromium ions and hexavalent chromium ions as the ordinate and the concentrations of trivalent chromium ions and hexavalent chromium ions as the abscissa.

[0023] An analytical method for quantifying a mixed solution of hexavalent chromium and trivalent chromium provided by the present invention is used for the analysis and treatment of electroplating sewage.

[0024] The beneficial effects of the present invention are:

[0025] The analytical method for a mixed solution of trivalent chromium and hexavalent chromium provided by the present invention can simultaneously perform quantitative analysis on trivalent chromium and hexavalent chromium by using a high-performance liquid chromatograph. This type of method is fast, convenient, and universal. This method removes impurities from the test sample by dropping an alkaline solution to exclude the influence of other metal ions. It adopts a gradient elution method with ammonia water and ethanol as the mobile phase, and then sets an appropriate elution time according to the composition of the mobile phase. Compared with a single elution method, it can better distinguish the peak positions of hexavalent chromium ions and trivalent chromium ions, making the quantification more accurate, the overall analytical method more efficient, and when removing impurities from the mixed solution (i.e., industrial wastewater), a saturated calcium hydroxide solution can be used to reduce the economic cost of the analytical method. Specific Embodiments

[0026] The following will illustrate the present invention in conjunction with specific implementation schemes. It should be noted that the following examples are examples of the present invention and are only used to illustrate the present invention, rather than to limit the present invention. Other combinations and various improvements within the concept of the present invention can be made without departing from the main idea or scope of the present invention.

[0027] In the following examples, the compound monomers and related reagents used can be purchased from the market. Among them, the mixed solution (i.e., the test sample) is taken from the chromium-containing electroplating wastewater of a certain electroplating factory, and the trivalent chromium single-element standard solution and the hexavalent chromium single-element standard solution are purchased from the National Standard Substance Resource Sharing Platform.

[0028] The following Examples 1-3 and Comparative Examples 1-2 all include steps S1-1 and S1-2, specifically as follows:

[0029] S1-1: Preparation method of test solution A-1, comprising the following steps:

[0030] S6-1: Add 0.5 g of saturated calcium hydroxide solution to 5 g of mixed solution (i.e., test sample), stir for 15 min, let stand for 30 min, and filter to obtain solution C and precipitate intermediate;

[0031] S6-2: Add saturated calcium hydroxide solution to the precipitate intermediate obtained in step S6-1 until the precipitate dissolves to obtain solution D;

[0032] S6-3: Mix solution C obtained in step S6-1 and solution D obtained in step S6-2 to form test solution A-1.

[0033] S1-1: Preparation method of test solution A-2, comprising the following steps:

[0034] S6-1: Add 0.5 g of saturated zinc hydroxide solution to 5 g of mixed solution (i.e., test sample), stir for 15 min, let stand for 30 min, and filter to obtain solution C and precipitate intermediate;

[0035] S6-2: Add saturated zinc hydroxide solution to the precipitate intermediate obtained in step S6-1 until the precipitate dissolves to obtain solution D;

[0036] S6-3: Mix solution C obtained in step S6-1 and solution D obtained in step S6-2 to form test solution A-2.

[0037] S1-2: Prepare a standard curve for the concentration of the mixed solution:

[0038] Take a trivalent chromium single-element standard solution and an EDTA-2Na solution and place them in a centrifuge tube. React at 80 °C for 15 min and then cool to room temperature. Dilute to volume with ultrapure water to obtain a trivalent chromium-EDTA complex solution; Take the trivalent chromium-EDTA complex solution and a hexavalent chromium single-element standard solution and prepare a standard series of mixed working solutions with ultrapure water. The concentrations are trivalent chromium ions: 0, 20, 40, 80, 120, 160, 200 (unit: mg / L) and hexavalent chromium ions: 0, 20, 50, 100, 150 (unit: mg / L). Prepare and use immediately. Test the above-prepared mixed working solutions by high-performance liquid chromatography. Establish a standard curve for the concentration of the mixed solution with the peak areas of the response peaks of hexavalent chromium ions and trivalent chromium ions as the ordinate and the concentrations of each ion as the abscissa.

[0039] Example 1 provides an analytical method for quantifying a mixed solution of hexavalent chromium and trivalent chromium, further comprising the following steps,

[0040] S1-3: Weigh 2 mL of the test solution A-2 and add it to a 50 mL beaker. Dilute and make up the volume with the ammonia-ethanol solution, and filter it with a water-phase filter head to obtain the test solution B. Among them, the volume ratio of ammonia to ethanol in the ammonia-ethanol solution is 60:20, the ammonia is 25% ammonia water, and the ethanol is 95% ethanol;

[0041] S1-4: Test the test solution B with a high-performance liquid chromatograph. The working conditions of the high-performance liquid chromatograph are as follows: The chromatographic column uses Ailgent Eclipse Plus C18, with a particle size of 5 μm, an inner diameter of 4.6 mm, and a length of 250 mm; The injection volume is 2 μL; The mobile phase: Phase A is 0.5% ammonia water, and Phase B is the ammonia-ethanol solution. Among them, the volume ratio of ammonia to ethanol is 60:20; The flow rate is 0.5 mL / min; The program elution time sequence is 0-10 min, 95% Phase A; 10-20 min, 100% Phase B; The column temperature is 30 °C;

[0042] S1-5: Perform quantitative analysis on the test solution B according to the mixed solution concentration standard curve prepared in S1-2 to obtain the contents of hexavalent chromium and trivalent chromium in the test solution B.

[0043] Example 2 provides an analytical method for the quantification of a mixed solution of hexavalent chromium and trivalent chromium, which further includes the following steps:

[0044] S1-3: Weigh 2 mL of the test solution A-1 and add it to a 50 mL beaker. Dilute and make up the volume with the ammonia-ethanol solution, and filter it with a water-phase filter head to obtain the test solution B. Among them, the volume ratio of ammonia to ethanol in the ammonia-ethanol solution is 80:20, the ammonia is 28% ammonia water, and the ethanol is 92% ethanol;

[0045] S1-4: Test the test solution B with a high-performance liquid chromatograph. The working conditions of the high-performance liquid chromatograph are as follows: The chromatographic column uses Ailgent Eclipse Plus C18, with a particle size of 5 μm, an inner diameter of 4.6 mm, and a length of 250 mm; The injection volume is 5 μL; The mobile phase: Phase A is 0.2% ammonia water, and Phase B is the ammonia-ethanol solution. Among them, the volume ratio of ammonia to ethanol is 80:20; The flow rate is 0.2 mL / min; The program elution time sequence is 0-8 min, 90% Phase A; 8-20 min, 100% Phase B; The column temperature is 25 °C;

[0046] S1-5: Perform quantitative analysis on the test solution B according to the mixed solution concentration standard curve prepared in S1-2 to obtain the contents of hexavalent chromium and trivalent chromium in the test solution B.

[0047] Example 3 provides an analytical method for the quantification of a mixed solution of hexavalent chromium and trivalent chromium, which further includes the following steps:

[0048] S1-3: Add 2 mL of the test solution A-2 into a 50 mL beaker, dilute and make up the volume with an ammonia ethanol solution. After filtering with an aqueous phase filter head, it becomes the test solution B. Among them, the volume ratio of ammonia to ethanol in the ammonia ethanol solution is 100:20, the ammonia is 25% ammonia water, and the ethanol is 95% ethanol;

[0049] S1-4: Test the test solution B with a high performance liquid chromatograph. The working conditions of the high performance liquid chromatograph are as follows: The chromatographic column uses Ailgent Eclipse Plus C18, with a particle size of 5 μm, an inner diameter of 4.6 mm, and a length of 250 mm; The injection volume: 2 μL; The mobile phase: Phase A is 0.5% ammonia water, and Phase B is an ammonia ethanol solution with a concentration where the volume ratio of ammonia to ethanol is 100:20; The flow rate: 1 mL / min; The order of the programmed elution time is 0 - 8 min, 95% Phase A; 8 - 20 min, 100% Phase B; The column temperature: 30 °C;

[0050] S1-5: Conduct quantitative analysis on the test solution B according to the standard curve of the mixed solution concentration prepared in S1-2 to obtain the contents of hexavalent chromium and trivalent chromium in the test solution B.

[0051] Example 4 provides an analytical method for the quantification of a mixed solution of hexavalent chromium and trivalent chromium. The steps are basically the same as those in Example 3, except that in S1-4, the volume ratio of ammonia to ethanol in the ammonia ethanol solution is 60:40.

[0052] Comparative Example 1 provides an analytical method for the quantification of a mixed solution of hexavalent chromium and trivalent chromium. The steps are basically the same as those in Example 1, except that in S1-4, when testing with the high performance liquid chromatograph, programmed elution is used, and the order of the programmed elution time is 0 - 5 min, 95% Phase A, 5 - 20 min, 100% Phase B.

[0053] Comparative Example 2 provides an analytical method for the quantification of a mixed solution of hexavalent chromium and trivalent chromium. The steps are basically the same as those in Example 1, except that in S1-3, 2 mL of the test solution A-2 is replaced with 2 mL of the test solution A-1; In S1-4, when testing with the high performance liquid chromatograph, programmed elution is used, and the order of the programmed elution time is 0 - 5 min, 95% Phase A, 5 - 20 min, 100% Phase B.

[0054] Through the test methods provided in Examples 1-4 and Comparative Examples 1-2, the results of testing the concentrations of hexavalent chromium and trivalent chromium in the mixed solution are shown in Table 1:

[0055] Table 1

[0056] Trivalent chromium ion concentration / ppm Hexavalent chromium ion concentration / ppm Example 1 27 51 Example 2 28 50 Example 3 26 52 Example 4 20 48 Comparative Example 1 18 38 Comparative Example 2 10 43

[0057] The content of total chromium in the mixed solution (i.e., the sample to be measured) was determined by the potassium permanganate oxidation method - diphenylcarbazide spectrophotometry, and the content of hexavalent chromium ions in the mixed solution (i.e., the sample to be measured) was determined by inductively coupled plasma mass spectrometry. The two contents were subtracted to obtain the content of trivalent chromium ions in the electroplating sewage. The measurement results showed that the total chromium content in the mixed solution (i.e., the sample to be measured) was 80 ppm, the hexavalent chromium ion content was 53 ppm, and the trivalent chromium ion content was 27 ppm. The differences between the two measurement methods are shown in Table 3.

[0058]

[0059] As can be seen from Examples 1 - 3, for an analytical method for quantifying a mixed solution of hexavalent chromium and trivalent chromium provided by the present invention, when measuring an electroplating sewage sample, after removing impurities with an alkali solution, the working conditions of the high-performance liquid chromatograph provided by the present invention are set, and the programmed elution mode is adopted. Ammonia water is used as phase A, and an ammonia water - ethanol solution is used as phase B. At the same time, the elution time of phase A is set to 8 - 10 minutes, and the elution time of phase B is 12 - 10 minutes, so that the contents of hexavalent chromium and trivalent chromium can be measured quickly and accurately at the same time. Compared with the standard method, the difference is less than 3.

[0060] Comparing Comparative Example 1 with Example 1, it can be seen that when the working conditions of the high-performance liquid chromatograph provided by the present invention are adopted and the programmed elution time sequence is: 0 → 8 - 10 min, 90% - 95% phase A; 8 - 10 min → 20 min, 100% phase B, it is more beneficial to improve the accuracy of measuring the contents of hexavalent chromium and trivalent chromium; comparing Comparative Example 2 with Comparative Example 1 and Example 1, it can be seen that when a saturated calcium hydroxide solution is used as the impurity removal agent and the elution time sequence provided by the present invention is used in combination, the accuracy of measuring the contents of hexavalent chromium and trivalent chromium is excellent.

[0061] Comparing Example 4 with Example 3, it can be known that when the ratio of ammonia water and ethanol in the mobile phase is within a certain range, the accuracy of measuring the contents of hexavalent chromium and trivalent chromium by the analytical method provided by the present invention is more excellent.

[0062] In summary, for an analytical method for quantifying a mixed solution of hexavalent chromium and trivalent chromium provided by the present invention, through a high-performance liquid chromatograph, by setting appropriate programmed elution time and mobile phase components, the contents of hexavalent chromium and trivalent chromium in the mixed solution can be determined simultaneously. This method is convenient, efficient, economical and convenient, which is conducive to its application in the analysis of electroplating sewage.

[0063] The above embodiments are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A quantitative analysis method for a mixed solution of hexavalent chromium and trivalent chromium, characterized in that: The analytical method comprises the following steps: S1-1: adding alkali solution to the mixed solution to remove impurities, to obtain a test solution A; S1-2: Mix standard trivalent chromium and hexavalent chromium solutions and establish a standard curve for the concentration of the mixed solution; S1-3: Weigh the test solution A and add it into a beaker, dilute it with an ammonia ethanol solution to make it constant, and filter it with an aqueous filter to obtain the test solution B; S1-4: Testing the test liquid B with a high performance liquid chromatograph, wherein the high performance liquid chromatograph is tested by program elution, wherein the mobile phase in the program elution comprises phase A and phase B, wherein phase A is ammonia water, and phase B is ammonia ethanol solution, and the elution time sequence is: 0→8-10 min, 90%-95% phase A; 8-10 min→20 min, 100% phase B; S1-5: Using the mixed solution concentration standard curve prepared in S1-2 to perform external standard method quantification on the test solution B, the contents of hexavalent chromium and trivalent chromium in the test solution B are obtained.

2. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 1, characterized in that: The working conditions of the high performance liquid chromatograph in step S1-4 are: Chromatographic column: Ailgent Eclipse Plus C18, particle size 5μm, inner diameter 4.6mm, length 250mm; injection volume: 1-10μL; flow rate: 0.2-1mL / min; column temperature: 25-35℃.

3. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 1, characterized in that: In the mobile phase of S1-4, phase A is 0.2%-0.5% ammonia water, and phase B is ammonia ethanol solution, which is a mixture of 25-28% ammonia water and 90-95% ethanol.

4. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 3, characterized in that: The volume ratio of 25-28% ammonia water and 90-95% ethanol in the ammonia ethanol solution is (5-3):

1.

5. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 1, characterized in that: The elution time sequence of the program in S1-4 is: 0→8min, 90%-95% phase A; 8→20min, 100% phase B.

6. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 1, characterized in that: The method for preparing the test liquid A in step S1-1 comprises the following steps: S6-1: Add alkali solution to the mixed solution, stir for 10-20 minutes, let stand for 30-40 minutes, and filter to obtain solution C and precipitated intermediate; S6-2: Add a saturated calcium hydroxide solution to the precipitated intermediate obtained in S6-1, stir with ultrasonic for 10-20 min, let stand for 30-40 min, and filter to obtain a solution D; S6-3: The solution C obtained in S6-1 and the solution D obtained in step S5-2 are mixed to form a test solution A.

7. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 1, characterized in that: The standard trivalent chromium and hexavalent chromium solutions in S1-2 are trivalent chromium single element standard solutions and hexavalent chromium single element standard solutions.

8. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 1, characterized in that: The alkaline solution in S1-1 includes one or more of a saturated solution of calcium hydroxide and a saturated solution of zinc hydroxide.

9. The quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to claim 1, characterized in that: The external standard quantitative method in S1-5 is to establish a standard curve with the peak area of ​​the trivalent chromium ion and hexavalent chromium ion response peak as the ordinate and the concentration of the trivalent chromium ion and hexavalent chromium ion as the abscissa.

10. Application of the quantitative analysis method of a mixed solution of hexavalent chromium and trivalent chromium according to any one of claims 1 to 9 in analysis and treatment of electroplating wastewater.

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