Method for detecting hexavalent chromium ions

Abstract

The invention belongs to the technical field of analysis and detection, and discloses a method for detecting hexavalent chromium ions. The method for detecting the hexavalent chromium ions comprises the following steps: (1) adding disodium ethylene diamine tetraacetate, acid, hydrogen peroxide and 3, 3 ', 5, 5'-tetramethyl benzidine into the hexavalent chromium ions with multiple concentrations, uniformly mixing and reacting, measuring the absorbance of a system, drawing a standard curve and calculating to obtain a linear equation; the final concentration of the disodium ethylene diamine tetraacetate is 10 [mu] mol / L to 500 [mu] mol / L; and (2) measuring the absorbance of a sample to be measured by using the method in the step (1), substituting the absorbance into the linear equation, and calculating to obtain the content of hexavalent chromium ions in the sample to be measured. The detection method is high in accuracy, good in stability, green and environment-friendly while detection can be completed within a short time, few wastes are generated, post-treatment is simple and easy to operate, the method is environment-friendly, and the method has wide application prospects in the fields of environment monitoring, water quality detection and the like.

Description

Technical Field

[0001] The invention relates to the technical field of analysis and detection, and in particular to a method for detecting hexavalent chromium ions. Background Art

[0002] Hexavalent chromium (Cr(VI)) is a strong oxidant that can react chemically with a variety of substances, and has a significant impact on human health and the ecological environment. It mainly comes from industrial activities such as electroplating, leather manufacturing, stainless steel welding, and fuel production. In the electroplating process, chromium is often used for passivation treatment of metal surfaces to improve the wear resistance and corrosion resistance of the workpiece and increase the service life of the workpiece; however, electroplating wastewater usually contains high concentrations of Cr(VI). If it is directly discharged without proper treatment, it will cause serious pollution to the environment. In the leather industry, in order to enhance the water resistance and wear resistance of leather and increase the aesthetics and comfort of the product, alkaline chromium sulfate is widely used as a raw material for leather tanning agents; however, in the leather manufacturing process, Cr(VI) may remain in the leather, posing a potential threat to human health.

[0003] According to the classification of the International Agency for Research on Cancer (IARC), Cr(VI) is classified as a Class I carcinogen, which means it has a significant impact on human health. Cr(VI) enters the human body mainly through inhalation. It can penetrate respiratory cells and accumulate inside the cells, thereby triggering inflammatory responses and cell damage, and ultimately leading to cell cancer. At the same time, inhaling Cr(VI) dust or smoke can also cause serious respiratory problems such as rhinitis, nasal ulcers, asthma and pulmonary fibrosis, and these symptoms will increase with the increase of exposure time.

[0004] Due to its toxicity, the emission and presence of Cr(VI) are strictly regulated around the world, and a variety of detection methods have been developed. However, the existing methods for detecting Cr(VI) generally have the following disadvantages: a. Complex operation: Traditional Cr(VI) detection methods usually require cumbersome sample pretreatment, such as collection, extraction, concentration, washing, etc., and then test on the machine. The operation is relatively complicated, the pretreatment is cumbersome and time-consuming, and professional operators are required to operate, which increases the difficulty and cost of detection and limits the popularization and application of detection methods. b. High cost: Traditional Cr(VI) detection methods rely on expensive instruments and equipment. c. Environmental pollution: Traditional Cr(VI) detection methods require the use of harmful reagents such as perchloric acid and generate harmful waste during the detection process, which causes a certain degree of environmental pollution.

[0005] Therefore, it is urgent to develop a more efficient, accurate, reliable, green, environmentally friendly and easy-to-operate hexavalent chromium ion detection method. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for detecting hexavalent chromium ions.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for detecting hexavalent chromium ions, comprising the following steps:

[0009] (1) adding disodium ethylenediaminetetraacetate, acid, hydrogen peroxide and 3,3',5,5'-tetramethylbenzidine to a series of hexavalent chromium ions of multiple concentrations, mixing and reacting, measuring the absorbance of the system, drawing a standard curve and calculating a linear equation; the final concentration of disodium ethylenediaminetetraacetate is 10 μmol / L-500 μmol / L;

[0010] (2) Using the method of step (1) to measure the absorbance of the sample to be tested, substituting it into the linear equation, and calculating the content of hexavalent chromium ions in the sample to be tested.

[0011] The present invention utilizes the principle of Fenton's reaction to rapidly react Cr(VI), catalyzes hydrogen peroxide (H2O2) under weak acidic conditions to generate hydroxyl radicals (·OH) with strong oxidizing ability, and further oxidizes the colorless color substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the solution to form blue TMB. + , which is converted into yellow TMB under acidic conditions. 2+ (Reaction principle and flow chart are shown in Figure 1 ), and then complete the quantitative detection and analysis of Cr(VI) in a short time; at the same time, disodium ethylenediaminetetraacetic acid in the system is used as a masking agent to eliminate the influence of interfering ions on the detection method. The detection method has high accuracy and good stability. It can complete the detection in a short time and is green and environmentally friendly, with less waste generated, simple and easy post-processing, and is environmentally friendly. It has broad application prospects in environmental monitoring, water quality testing and other fields.

[0012] As a preferred embodiment of the method for detecting hexavalent chromium ions of the present invention, the final concentration of disodium ethylenediaminetetraacetate is 100 μmol / L-250 μmol / L.

[0013] Preferably, the final concentration of disodium edetate is 150 μmol / L.

[0014] As a preferred embodiment of the method for detecting hexavalent chromium ions of the present invention, the acid is at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

[0015] Preferably, the acid is sulfuric acid; the final concentration of the sulfuric acid is 4.9 mg / L-98 mg / L.

[0016] Further preferably, the final concentration of the sulfuric acid is 29.4 mg / L-98 mg / L.

[0017] Most preferably, the final concentration of sulfuric acid is 49 mg / L.

[0018] As a preferred embodiment of the method for detecting hexavalent chromium ions of the present invention, in step (1), the reaction temperature is 5°C-60°C and the reaction time is 5 min-60 min.

[0019] Preferably, the reaction temperature is 20°C-50°C, and the reaction time is 20min-50min.

[0020] More preferably, the reaction temperature is 40° C. and the reaction time is 30 min.

[0021] As a preferred embodiment of the method for detecting hexavalent chromium ions of the present invention, the final concentration of the hydrogen peroxide is 1 g / L-50 g / L; the final concentration of the 3,3',5,5'-tetramethylbenzidine is 100 μmol / L-2000 μmol / L.

[0022] Preferably, the final concentration of the hydrogen peroxide is 5 g / L-20 g / L; the final concentration of the 3,3',5,5'-tetramethylbenzidine is 1000 μmol / L-2000 μmol / L.

[0023] More preferably, the final concentration of the hydrogen peroxide is 10 g / L; and the final concentration of the 3,3',5,5'-tetramethylbenzidine is 2000 μmol / L.

[0024] As a preferred embodiment of the method for detecting hexavalent chromium ions of the present invention, the detection range of the hexavalent chromium ions is 0.1 μmol / L-10 μmol / L.

[0025] Preferably, the detection range of hexavalent chromium ions is 0.1 μmol / L-5 μmol / L.

[0026] As a preferred embodiment of the method for detecting hexavalent chromium ions of the present invention, the linear correlation coefficient r of the standard curve is 2 ≥0.999.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: first, the method for detecting hexavalent chromium ions of the present invention realizes the quantitative determination of hexavalent chromium ions by adding specific chemical reagents, and the detection method has good linearity (linear correlation coefficient 0.9993) in the range of (0.1-5.0) μmol / L (i.e., 5.2 μg / L-260 μg / L); this means that the method of the present invention can accurately determine the content of hexavalent chromium ions in a wide concentration range, and can be applied to the detection of water samples with different pollution degrees. At the same time, the method of the present invention has good stability, and the detection limit is 0.053 μmol / L (2.76 μg / L); this means that the method of the present invention can detect very low concentrations of hexavalent chromium ions, and is also highly sensitive to trace hexavalent chromium pollution in the environment. In addition, the method of the present invention can reduce interference during the detection process and improve the accuracy and reliability of the detection. This is crucial to ensure the accuracy and reliability of the detection results. Therefore, the method for detecting hexavalent chromium ions of the present invention is an efficient, accurate and reliable hexavalent chromium ion detection method, which has broad application prospects in the fields of water quality monitoring, environmental protection, food safety, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The principle and process diagram of the method for detecting hexavalent chromium ions of the present invention;

[0029] Figure 2 This is a wavelength scanning spectrum of the positioning peak after the hexavalent chromium ion reaction in Example 1 of the present invention;

[0030] Figure 3 This is a schematic diagram of a hexavalent chromium ion detection device according to Example 1 of the present invention;

[0031] Figure 4 The standard working curve of hexavalent chromium ions of different concentrations in Example 1 of the present invention is shown;

[0032] Figure 5 This is a schematic diagram showing the effect of different reaction temperatures and times on the absorbance of the Cr-Fenton system in Test Example 1 of the present invention;

[0033] Figure 6 This is a schematic diagram of the effect of different H2O2 dosages on the absorbance of the Cr-Fenton system in Test Example 2 of the present invention;

[0034] Figure 7 This is a schematic diagram of the effect of different types of acids on the absorbance of the Cr-Fenton system in Test Example 3 of the present invention;

[0035] Figure 8 Schematic diagram of the effect of chloride ions on the absorbance of the Cr-Fenton system in Test Example 3 of the present invention;

[0036] Fig. 9Schematic diagram of the effect of different H2SO4 dosages on the absorbance of the Cr-Fenton system in Test Example 4 of the present invention;

[0037] Fig.10 This is a schematic diagram showing the effect of different TMB dosages on the absorbance of the Cr-Fenton system in Test Example 5 of the present invention;

[0038] Fig.11 This is a schematic diagram of the effect of different EDTA-disodium dosages on the absorbance of the Cr-Fenton system at 1 mL TMB dosage in Test Example 6 of the present invention;

[0039] Fig.12 It is the Cr(VI)-Abs linear curve diagram in Test Example 6 of the present invention;

[0040] Fig.13 This is a schematic diagram of the effect of different EDTA-disodium dosages on the absorbance of the Cr-Fenton system at 2 mL TMB dosage in Test Example 7 of the present invention. DETAILED DESCRIPTION

[0041] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] The following is an elaboration in conjunction with specific embodiments to illustrate the practical effects of the solutions of the present invention.

[0043] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, equipment, etc. used, unless otherwise specified, can be obtained from commercial sources.

[0044] The instruments and reagents used in the examples and comparative examples of the present invention are as follows:

[0045] Instruments: UV-1800 ultraviolet-visible spectrophotometer (SHIMADZU), constant temperature bath (Ningbo Tianheng Instrument Factory), all measuring instruments involved in the present invention are calibrated and qualified.

[0046] Reagents: 3,3',5,5'-Tetramethylbenzidine (TMB) was prepared with anhydrous ethanol, and the other reagents were prepared with 18.2 MΩ·cm ultrapure water to prepare solutions for use.

[0047] Table 1: Manufacturers and concentrations of reagents used in the examples and comparative examples of the present invention

[0048]

[0049] Example 1: A method for detecting hexavalent chromium ions

[0050] (1) Qualitative confirmation - peak location: First, the maximum absorption peak wavelength of hexavalent chromium ions needs to be confirmed. The instrument required is a UV-visible spectrophotometer. The instrument setting parameters are: wavelength scanning range: 650nm-340nm, scanning speed (C): medium speed, sampling interval (I): 0.2nm, peak detection threshold (T): 0.001. By scanning the spectrum (such as Figure 2 The maximum absorption peak wavelength is 450.22 nm.

[0051] (2) To a 10 mL volumetric flask pre-added with 5 mL of pure water, add 150 μL of 0.01 mol / L EDTA-disodium, (10, 50, 100, 200, 500) μL of a series of K2Cr2O7 with a concentration of 100 μmol / L, and then add 0.5 mL of 0.01 mol / L H2SO4. After shaking well, add 1 mL of 10% (mass fraction) H2O2 and 2 mL of 0.01 mol / L TMB, shake to volume, react in a thermostatic bath at 40°C for 30 min, then immediately add 0.5 mL of 2% (mass fraction) H2SO2 and measure the absorbance at 450 nm.

[0052] (3) Draw a standard curve with hexavalent chromium ion concentration as the horizontal axis and absorbance as the vertical axis (e.g. Figure 4 As shown) and calculate to obtain the linear equation;

[0053] (4) Using the same method as step (2), the absorbance of the sample system containing hexavalent chromium ions is measured, and the content of hexavalent chromium ions in the sample is calculated by substituting into the linear equation.

[0054] like Figure 4 As shown, the method for detecting hexavalent chromium ions of the present invention has good linearity, and its linear correlation coefficient (r 2 ) up to 0.9993.

[0055] By continuously recording the stability of the final product within 1 hour in steps of 5 seconds, its absorbance slowly decreased from A1=0.401 at t1=0s to A2=0.391 at t2=3600s. This slight change indicates that the final product maintains a high stability over a long period of time.

[0056] By measuring the sample blank eleven times, the detection limit of this method was calculated to be 0.053 μmol / L, as shown in Table 2. This method can detect very low concentrations of hexavalent chromium ions, thus having higher sensitivity and accuracy in practical applications.

[0057] Table 2: Blank sample measurement values ​​and detection limits

[0058]

[0059] Example 2: A method for detecting hexavalent chromium ions

[0060] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that the temperature of the thermostatic bath in step (2) is set to 5°C.

[0061] Example 3: A method for detecting hexavalent chromium ions

[0062] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that the temperature of the thermostatic bath in step (2) is set to 20°C.

[0063] Example 4: A method for detecting hexavalent chromium ions

[0064] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that the temperature of the thermostatic bath in step (2) is set to 50°C.

[0065] Example 5: A method for detecting hexavalent chromium ions

[0066] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that the temperature of the thermostatic bath in step (2) is set to 60°C.

[0067] Test Example 1:

[0068] In this test example, the absorbance at 450 nm of 200 μL of 100 μmol / L K2Cr2O7 solution added to the method for detecting hexavalent chromium ions in Examples 1-5 was measured, and the absorbance of the mixed solution containing 200 μL of 100 μmol / L K2Cr2O7 was recorded every 5 minutes after deducting the blank value of the mixed solution without K2Cr2O7 at the same time, to explore the influence of reaction temperature and reaction time on the method for detecting hexavalent chromium ions of the present invention.

[0069] like Figure 5 As shown in the experimental results, it can be seen that when the reaction temperature is lower than 20°C, the absorbance increases very slowly with the extension of the reaction time within 1h. This is because the decomposition of H2O2 in the Fenton reaction is slow at a lower reaction temperature, and the TMB produced by oxidation 2+It gradually accumulates over time, resulting in a slow rise in the absorbance of the system. Under the reaction condition of 40°C, the absorbance of the system increases rapidly with the increase of reaction time before 30 minutes, and the absorbance increase is small during 30 minutes to 50 minutes, until it reaches the maximum value at 55 minutes, and then the absorbance begins to decrease; when the reaction temperature rises to 50°C and 60°C, the maximum absorbance appears at the 15th minute and the 10th minute, respectively. The reason for this phenomenon is that the decomposition of hydrogen peroxide is affected by temperature. At higher temperatures, the self-decomposition rate of hydrogen peroxide is accelerated, and the absorbance of the blank control and the experimental group in the system both rise rapidly, resulting in a decrease in absorbance after deducting the blank. Therefore, the present invention is the best test condition at 40°C for a reaction time of 30 minutes.

[0070] Example 6: A method for detecting hexavalent chromium ions

[0071] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 0.1 mL of 10% H2O2 is added in step (2).

[0072] Example 7: A method for detecting hexavalent chromium ions

[0073] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 0.5 mL of 10% H2O2 is added in step (2).

[0074] Example 8: A method for detecting hexavalent chromium ions

[0075] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 2 mL of 10% H2O2 is added in step (2).

[0076] Example 9: A method for detecting hexavalent chromium ions

[0077] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 5 mL of 10% H2O2 is added in step (2).

[0078] Test Example 2:

[0079] This test example tests the effects of different amounts of hydrogen peroxide on the Cr-Fenton reaction system in the methods for detecting hexavalent chromium ions in Example 1 and Examples 6-9.

[0080] like Figure 6 As shown in the figure, when the amount of hydrogen peroxide is less than 2.0 mL, the absorbance of the system increases with the increase of the amount of hydrogen peroxide. This is because when the amount of hydrogen peroxide is small, the ·OH produced by decomposition is fully utilized to oxidize TMB to TMB +However, when the volume of hydrogen peroxide added is increased to 5.0mL, the absorbance of the system is obviously not as good as the absorbance when 2.0mL hydrogen peroxide is used. The reason for this phenomenon is that HO2·(E=1.7V) will be produced during the decomposition of excess hydrogen peroxide, and its oxidizing ability is much lower than ·OH(E=2.8V), resulting in the difference between the system and the blank control when the Cr(VI) content is high being less than expected. In addition, it was found in the experiment that the overall absorbance was higher after the color development reaction of different Cr(VI) contents was completed when the amount of hydrogen peroxide was high. This is because hydrogen peroxide self-decomposes and oxidizes TMB, which further leads to a decrease in the absorbance of the system after deducting the blank. At the same time, the absorbance difference between 1.0mL hydrogen peroxide and 2.0mL hydrogen peroxide is not much. Therefore, the present invention selects 1.0mL10% hydrogen peroxide as the optimal test condition.

[0081] Example 10: A method for detecting hexavalent chromium ions

[0082] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 0.5 mL of 0.01 mol / L HCl is added in step (2).

[0083] Example 11: A method for detecting hexavalent chromium ions

[0084] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 1 is that 0.5 mL of HNO3 with a concentration of 0.01 mol / L is added in step (2).

[0085] Example 12: A method for detecting hexavalent chromium ions

[0086] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 1 is that 0.5 mL of H3PO4 with a concentration of 0.01 mol / L is added in step (2).

[0087] Test Example 3:

[0088] This test example tests the effects of different types of acids on the Cr-Fenton reaction system in the methods for detecting hexavalent chromium ions in Examples 1 and Examples 9-12.

[0089] like Figure 7 As shown, Figure 7-a reflects the relationship between Cr(VI) and absorbance when using different types of acids. From the figure, it can be seen that among the four acids, H3PO4 has the lowest absorbance, H2SO4 and HNO3 have similar absorbance, and HCl has the highest absorbance. The reason for this is that phosphoric acid is a ternary medium-strong acid, and the acidity of the solution is weaker than the other three at the same concentration, and the pH of the solution is one of the important factors affecting the Fenton reaction. In the experiment, it was found that when HNO3 was used to terminate the reaction, the product would quickly aggregate into a blue precipitate within a few minutes, and the absorbance of the solution would decrease rapidly. When acidified with HNO3, the product stability was significantly weaker than the other three.

[0090] At the same time, the experiment found that Cl - It has a significant catalytic effect, which is used to verify the Cl - The reaction system was indeed affected. 2 μmol / L Cr(VI) was selected and an additional (0.1-1.0) mL of 0.01 mol / L NaCl solution was added. The absorption spectrum of the mixed system at (350-600) nm was recorded (e.g. Figure 8 shown).

[0091] from Figure 8 -a and 8-c show that as the volume of NaCl increases, the absorption spectrum is significantly enhanced and the background noise becomes more obvious, especially in the HCl system. Figure 8 -b results show that when acidified with H2SO4, Cl - The influence on the color development reaction is not as strong as that of using HCl or H3PO4. Therefore, in order to avoid the influence of unknown concentration of chloride ions in the system on the color development reaction when quantitatively determining Cr(VI), the present invention selects sulfuric acid as the optimal test condition.

[0092] Example 13: A method for detecting hexavalent chromium ions

[0093] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Embodiment 1 is that 0.05 mL of H2SO4 with a concentration of 0.01 mol / L is added in step (2).

[0094] Example 14: A method for detecting hexavalent chromium ions

[0095] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Embodiment 1 is that 0.1 mL of H2SO4 with a concentration of 0.01 mol / L is added in step (2).

[0096] Example 15: A method for detecting hexavalent chromium ions

[0097] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Embodiment 1 is that 0.3 mL of H2SO4 with a concentration of 0.01 mol / L is added in step (2).

[0098] Example 16: A method for detecting hexavalent chromium ions

[0099] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Embodiment 1 is that 1 mL of H2SO4 with a concentration of 0.01 mol / L is added in step (2).

[0100] Test Example 4:

[0101] This test example tests the effects of different amounts of acid on the Cr-Fenton reaction system in the methods for detecting hexavalent chromium ions in Example 1 and Examples 13-16.

[0102] like Fig. 9 As shown in the figure, within the range of (0.05-1.0) mL of 0.01 mol / L sulfuric acid, the absorbance of the system shows an increasing trend as the amount of sulfuric acid increases. When 0.05 mL and 0.1 mL of 0.01 mol / L sulfuric acid are added, the acidity of the Cr-Fenton system is weak, and the decomposition of hydrogen peroxide in the Fenton reaction will consume H + When the amount of sulfuric acid is 0.5mL and 1.0mL, the gain of the system acidity on the absorbance of the mixed solution has weakened. Considering green cleaning and economy, the present invention selects 0.5mL of sulfuric acid with a concentration of 0.01mol / L as the optimal test condition.

[0103] Example 17: A method for detecting hexavalent chromium ions

[0104] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 1 is that 0.1 mL of TMB with a concentration of 0.01 mol / L is added in step (2).

[0105] Example 18: A method for detecting hexavalent chromium ions

[0106] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 1 is that 0.5 mL of TMB with a concentration of 0.01 mol / L is added in step (2).

[0107] Example 19: A method for detecting hexavalent chromium ions

[0108] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 1 is that 1 mL of TMB with a concentration of 0.01 mol / L is added in step (2).

[0109] Test Example 5:

[0110] This test example tests the effects of different amounts of TMB on the Cr-Fenton reaction system in the method for detecting hexavalent chromium ions in Example 1 and Examples 17-19.

[0111] like Fig.10 As shown in the figure, the experimental results show that as the amount of TMB increases, the absorbance of the system tends to increase. Considering the economy and the absorbance of the system, 1mL of TMB with a concentration of 0.01mol / L is the best test condition.

[0112] Example 20: A method for detecting hexavalent chromium ions

[0113] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 10 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0114] Example 21: A method for detecting hexavalent chromium ions

[0115] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 25 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0116] Example 22: A method for detecting hexavalent chromium ions

[0117] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 50 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0118] Example 23: A method for detecting hexavalent chromium ions

[0119] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 100 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0120] Example 24: A method for detecting hexavalent chromium ions

[0121] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 250 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0122] Example 25: A method for detecting hexavalent chromium ions

[0123] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 500 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0124] Comparative Example 1: A method for detecting hexavalent chromium ions

[0125] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that EDTA-disodium is not added in step (2).

[0126] Comparative Example 2: A method for detecting hexavalent chromium ions

[0127] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 5 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0128] Comparative Example 3: A method for detecting hexavalent chromium ions

[0129] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in Example 19 is that 1000 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0130] Test Example 6:

[0131] This test example tests the effects of different amounts of EDTA-disodium on the Cr-Fenton reaction system in the method for detecting hexavalent chromium ions in Examples 19-25 and Comparative Examples 1-3 (1 mL of 0.01 mol / L TMB).

[0132] Fe 3+ and Cu 2+ It can also catalyze the Fenton reaction, thereby causing positive interference to the quantitative measurement of Cr(VI). To this end, 1 mL of simulated wastewater containing 2 ppm CuSO4-5 ppm FeCl3 was added under the conditions of the method for detecting hexavalent chromium ions of the present invention, and the absorbance at 450 nm was recorded after the reaction was completed.

[0133] like Fig.11 As shown, the experimental results show that Fe 3+ and Cu 2+ It will indeed have a great impact on the quantitative determination of Cr(VI), resulting in false positive results. As the volume of EDTA-disodium increases, Fe 3+ and Cu 2+ The effect was getting smaller and smaller. When the amount of EDTA-disodium added reached 25 μL, the absorption curve of the mixed system almost overlapped with that of the control group. Therefore, the working curve was drawn with 25 μL of 0.01 mol / L EDTA-disodium. Fig.12 As shown in the figure, as the concentration of Cr(VI) increases, the curve begins to bend and the linearity deteriorates. This is because the added EDTA-disodium is reactive to ·OH in the Fenton reaction, competing with TMB to cause a decrease in the content of oxidized TMB in the system.

[0134] Example 26: A method for detecting hexavalent chromium ions

[0135] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 10 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0136] Example 27: A method for detecting hexavalent chromium ions

[0137] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 25 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0138] Example 28: A method for detecting hexavalent chromium ions

[0139] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 50 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0140] Example 29: A method for detecting hexavalent chromium ions

[0141] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 100 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0142] Example 30: A method for detecting hexavalent chromium ions

[0143] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 200 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0144] Example 31: A method for detecting hexavalent chromium ions

[0145] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 250 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0146] Example 32: A method for detecting hexavalent chromium ions

[0147] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 500 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0148] Comparative Example 4: A method for detecting hexavalent chromium ions

[0149] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that EDTA-disodium is not added in step (2).

[0150] Comparative Example 5: A method for detecting hexavalent chromium ions

[0151] The only difference between the method for detecting hexavalent chromium ions in this embodiment and that in embodiment 1 is that 5 μL of 0.01 mol / L EDTA-disodium is added in step (2).

[0152] Test Example 7:

[0153] This test example tests the effects of different amounts of EDTA-disodium on the Cr-Fenton reaction system in the method for detecting hexavalent chromium ions in Example 1, Examples 26-32 and Comparative Examples 4-5 (2 mL of 0.01 mol / L TMB).

[0154] Fe 3+ and Cu 2+ It can also catalyze the Fenton reaction, thereby causing positive interference to the quantitative measurement of Cr(VI). To this end, 1 mL of simulated wastewater containing 2 ppm CuSO4-5 ppm FeCl3 was added under the optimal conditions of the method for detecting hexavalent chromium ions of the present invention, and the absorbance at 450 nm was recorded after the reaction was completed.

[0155] like Fig.13 As shown in the experimental results, when the dosage of TMB is 2 mL and the dosage of EDTA-disodium reaches 150 μL, the UV absorption curve of the mixed system almost coincides with that of the control group. 3+ and Cu 2+ The effect on the quantitative determination of Cr(VI) is small. Therefore, the present invention selects 150 μL of 0.01 mol / L EDTA-disodium and 2 mL as the optimal test conditions.

[0156] From the above embodiments and test examples, it can be seen that in the method for detecting hexavalent chromium ions of the present invention, 150 μL of 0.01 mol / L EDTA-disodium is added to mask Fe 3+ and Cu 2+ , and in the presence of 1 mL 10% hydrogen peroxide, 2 mL of 0.01 mol / L TMB was used as a colorimetric agent to quantitatively determine Cr(VI) in aqueous solution. The detection method has good linearity (linear correlation coefficient 0.9993) in the range of (0.1-5.0) μmol / L (i.e., 5.2 μg / L-260 μg / L), good stability, and a detection limit of 0.053 μmol / L (2.76 μg / L).

[0157] The method for detecting hexavalent chromium ions of the present invention realizes the quantitative determination of hexavalent chromium ions by adding specific chemical reagents. The method has the advantages of wide linear range, low detection limit and good stability, and is an efficient, accurate and reliable hexavalent chromium ion detection method. Therefore, it has broad application prospects in the fields of water quality monitoring, environmental protection, food safety and the like.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for detecting hexavalent chromium ions, characterized in that: The following steps are involved: (1) adding disodium ethylenediaminetetraacetate, acid, hydrogen peroxide and 3,3',5,5'-tetramethylbenzidine to hexavalent chromium ions of various concentrations, mixing and reacting, measuring the absorbance of the system, drawing a standard curve and calculating a linear equation; the final concentration of disodium ethylenediaminetetraacetate is 10 μmol / L-500 μmol / L; (2) Using the method of step (1) to measure the absorbance of the sample to be tested, substituting it into the linear equation, and calculating the content of hexavalent chromium ions in the sample to be tested.

2. The method for detecting hexavalent chromium ions according to claim 1, characterized in that: The final concentration of disodium edetate is 100 μmol / L-250 μmol / L.

3. The method for detecting hexavalent chromium ions according to claim 1, characterized in that: The acid is at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

4. The method for detecting hexavalent chromium ions according to claim 3, characterized in that: The acid is sulfuric acid; the final concentration of the sulfuric acid is 4.9 mg / L-98 mg / L.

5. The method for detecting hexavalent chromium ions according to claim 1, characterized in that: In step (1), the reaction temperature is 5°C-60°C and the reaction time is 5 min-60 min.

6. The method for detecting hexavalent chromium ions according to claim 5, characterized in that: The reaction temperature is 20°C-50°C, and the reaction time is 20min-50min.

7. The method for detecting hexavalent chromium ions according to claim 1, characterized in that: The final concentration of the hydrogen peroxide is 1 g / L-50 g / L; the final concentration of the 3,3',5,5'-tetramethylbenzidine is 100 μmol / L-2000 μmol / L.

8. The method for detecting hexavalent chromium ions according to claim 7, characterized in that: The final concentration of the hydrogen peroxide is 5 g / L-20 g / L; the final concentration of the 3,3',5,5'-tetramethylbenzidine is 1000 μmol / L-2000 μmol / L.

9. The method for detecting hexavalent chromium ions according to claim 1, characterized in that: The detection range of the hexavalent chromium ion is 0.1 μmol / L-10 μmol / L.

10. The method for detecting hexavalent chromium ions according to claim 1, characterized in that: The linear correlation coefficient r of the standard curve 2 ≥0.999.

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