Method for rapidly detecting high-concentration transition metal ions

Abstract

The invention discloses a method for rapidly detecting high-concentration transition metal ions. The method comprises the following steps: S1, preparing a series of ion solutions with different concentration gradients as standard samples; s2, respectively carrying out first-order derivation on the absorption spectrum of the ion solution at a characteristic peak to obtain a characteristic peak wavelength; s3, carrying out linear fitting on data of absorbance and molar concentration at the wavelength of the characteristic peak, and drawing a standard curve; and S4, determining the absorbance value of the metal ions of the sample to be detected under the characteristic peak wavelength, and then obtaining the concentrations of the four transition metal ions in the sample to be detected through the standard curve in the step S3 according to the absorbance value. According to the method, the concentration of the metal ions can be directly obtained through the absorbance of the to-be-detected ions, complicated pretreatment is not needed, the concentration of the transition metal ions in the solution can be rapidly determined, the detection concentration range is large, the accuracy is high, and the practicability is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral quantitative detection of solution ion concentration, and specifically relates to a method for rapidly detecting high-concentration transition metal ions Cr without a color developer. 3+ 、Co 2+ 、Ni 2+ 、Cu 2+ method. Background Art

[0002] Transition elements are chemical elements located in the d-block of the periodic table. Because they are all metallic, they are also called transition metals. Generally speaking, transition elements encompass ten groups, from Groups 3 to 12, and sometimes also include inner transition elements in the f-block. Among these, metallic elements such as chromium, cobalt, nickel, and copper, belonging to the first transition series, possess a range of unique properties, including high melting points, ductility, electrical conductivity, and transitional or variable oxidation states, making them suitable for a variety of applications. Industrial sectors such as metallurgy, batteries, and wire and cable generate wastewater containing these transition metal ions. With the acceleration of industrialization, the production and consumption of these transition metals continues to grow. Metal ions enter the environment in the form of wastewater, leading to a significant increase in their accumulation and persistent pollution. Therefore, water quality testing for transition metal ions is crucial. Common methods for metal ion detection include atomic absorption spectroscopy, liquid chromatography, inductively coupled plasma mass spectrometry, and ultraviolet-visible spectrophotometry.

[0003] Currently, the main method for detecting transition metal ion concentration is ultraviolet-visible spectrophotometry. The principle of traditional ultraviolet-visible spectrophotometry for ion concentration detection is to select a suitable organic reagent as a color developer, combine it with the organic reagent to prepare a color development system, develop the color of the metal ion to be tested under certain conditions, and determine its concentration using a standard curve method. However, after the metal ion and organic matter form a complex, its charge factor is easily affected by the environment, including temperature, pH and the phase system of the solution. At the same time, the OH in the solution - 、Cl - Isopolar anions also tend to affect light absorption at characteristic wavelengths. Therefore, colorimetric systems often require the addition of buffers and stabilizers, making them complex and only suitable for low-concentration ion determinations (<10 μM). When the detection concentration range is wide, the absorbance values at the characteristic wavelengths are inaccurate, presenting certain limitations. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for rapidly detecting high concentration transition metal ions without a color developer, so as to overcome the technical problems of the above-mentioned traditional ultraviolet-visible spectrophotometry method, such as cumbersome operation, small detection concentration range and certain limitations.

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions: A method for rapidly detecting high-concentration transition metal ions comprises the following steps: S1: preparing a series of transition metal ion solutions with different concentration gradients as standard samples; the transition metal ion solutions are solutions containing chromium ions, cobalt ions, nickel ions or copper ions; S2: collecting absorption spectra of the transition metal ion solutions with different concentration gradients in step S1 respectively, performing first-order derivatives at characteristic peaks, and obtaining characteristic peak wavelengths of the four transition metal ions respectively; S3: performing linear fitting on data of absorbance and ion concentration at the characteristic peak wavelengths, and drawing standard curves of the concentrations of the four transition metal ions respectively with known ion molar concentrations as the abscissa and corresponding absorbances as the ordinate; and S4: taking a sample to be tested containing the transition metal ions, measuring its absorbance value at the characteristic peak wavelength, and then, based on the absorbance value, obtaining the concentrations of the four transition metal ions in the sample to be tested using the standard curve in step S3.

[0006] In an optional embodiment, in step S1, chromium sulfate hydrate, cobalt chloride hexahydrate, nickel chloride hexahydrate or copper chloride hexahydrate is added to seawater using seawater as a solvent to prepare a transition metal ion solution.

[0007] In an optional embodiment, in step S1, the concentration range of the chromium ion solution is 10-1000 mM; the concentration range of the cobalt ion solution is 10-1000 mM; the concentration range of the nickel ion solution is 10-2000 mM; and the concentration range of the copper ion solution is 10-300 mM.

[0008] In an optional embodiment, the concentration gradient of the solution containing chromium ions is 50mM, 100mM, 200mM, 400mM, 600mM, and 800mM; the concentration gradient of the solution containing cobalt ions is 50mM, 100mM, 200mM, 400mM, 800mM, and 1000mM; the concentration gradient of the solution containing nickel ions is 50mM, 100mM, 200mM, 400mM, 800mM, 1000mM, and 1200mM; and the concentration gradient of the solution containing copper ions is 50mM, 100mM, 150mM, 200mM, and 250mM.

[0009] In an optional embodiment, in step S2, the characteristic peak wavelength of chromium ions is 410 nm, the characteristic peak wavelength of cobalt ions is 512 nm, the characteristic peak wavelength of nickel ions is 394 nm, and the characteristic peak wavelength of copper ions is 818 nm.

[0010] In an optional embodiment, in step S3, The fitting linear equation of the chromium ion standard curve is:

[0011] The correlation coefficient is 0.9999; The fitting linear equation of the cobalt ion standard curve is: The correlation coefficient is 0.99987; The fitting linear equation of the nickel ion standard curve is:

[0012] The correlation coefficient is 0.9996; The fitting linear equation of the copper ion standard curve is:

[0013] The correlation coefficient is 0.99801; Where A is absorbance and C is concentration.

[0014] In an optional embodiment, in step S4, in the sample to be tested, the concentration range of the chromium ion solution is 50-600 mM; the concentration range of the cobalt ion solution is 50-800 mM; the concentration range of the nickel ion solution is 50-1000 mM; and the concentration range of the copper ion solution is 50-200 mM.

[0015] In an optional embodiment, in step S4, the sample to be tested is seawater containing chromium ions, seawater containing cobalt ions, seawater containing nickel ions, or seawater containing copper ions.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention does not require the introduction of organic compounds into the metal ion liquid for complexation for detection. By establishing a linear relationship equation between absorbance and concentration as a detection standard for the four transition metal ions, the concentration of the metal ion can be directly calculated based on the absorbance of the ion to be tested. Without the need for complicated pretreatment, the concentration of the transition metal ion in the solution can be quickly determined, and the detection concentration range is wide, the accuracy is high, and the practicality is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Cr in Example 1 of the present invention 3+ 、Co 2+ 、Ni 2+ 、Cu 2+ The UV-visible absorption spectrum and the linear fitting relationship between the absorbance corresponding to the wavelength of the characteristic peak and the metal ion concentration; Figure 2 Fe of Comparative Example 2 of the present invention 3+UV-visible absorption spectrum of Figure 3 Mn is the Mn of Comparative Example 3 of the present invention 2+ UV-visible absorption spectrum. DETAILED DESCRIPTION

[0018] In order to help those skilled in the art better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0019] The detection method of the present invention is applied to the detection of metal ion concentrations in illegally discharged wastewater from sea areas, and the concentrations of the four transition metal ions in seawater are detected separately. Therefore, the following test samples are solutions prepared by simulating seawater containing the four transition metals at different concentrations. That is, four solutions containing different transition metal ions are prepared separately as test samples, rather than preparing solutions in which the four transition metal ions exist simultaneously. The seawater is uncontaminated seawater.

[0020] Example 1 1. Preparation of standard sample solution (1) Weigh 3.9 g of hydrated chromium sulfate into a beaker, dissolve it in 5 ml of seawater (sampled from Yazhou Bay (Sanya, Hainan, China)), and transfer it to a 10 ml volumetric flask to make up the volume. The concentration of chromium ions in the 10 ml solution is 1000 mM. Take out the ion solution of this concentration and dilute it to prepare ion solutions with a concentration gradient of 50 mM, 100 mM, 200 mM, 400 mM, 600 mM, and 800 mM. This will give a series of standard sample solutions of chromium ions.

[0021] (2) Weigh 2.4 g of hydrated cobalt chloride and add it to a beaker. Dissolve it in 5 ml of seawater and transfer it to a 10 ml volumetric flask to make up the volume. The concentration of cobalt ions in the 10 ml solution is 1000 mM. Take out the ion solution of this concentration and dilute it to prepare ion solutions with a concentration gradient of 50 mM, 100 mM, 200 mM, 400 mM, and 800 mM. You can get a series of standard sample solutions of cobalt ions.

[0022] (3) Weigh 4.8 g of hydrated nickel chloride and add it to a beaker. Dissolve it in 5 ml of seawater and transfer it to a 10 ml volumetric flask to make up the volume. The concentration of nickel ions in the 10 ml solution is 2000 mM. Take out the ion solution of this concentration and dilute it to prepare ion solutions with a concentration gradient of 50 mM, 100 mM, 200 mM, 400 mM, 800 mM, 1000 mM, and 1200 mM. You can get a series of standard sample solutions of nickel ions.

[0023] (4) Weigh 0.5 g of hydrated copper chloride into a beaker, dissolve it in 5 ml of seawater, and transfer it to a 10 ml volumetric flask to make up the volume. The concentration of copper ions in the 10 ml solution is 300 mM. Take out the ion solution of this concentration and dilute it to prepare ion solutions with a concentration gradient of 50 mM, 100 mM, 150 mM, 200 mM, and 250 mM. You can get a series of standard sample solutions of copper ions.

[0024] 2. Drawing of the standard curve The absorption spectra of the above four series of transition metal ion solutions were collected one by one using a UV-2600i ultraviolet-visible spectrophotometer. All measurements and data processing were performed on a PC equipped with LabSolutions UV-Vis (version: 1.15) software. The collected spectral data were fitted using Origin software, and the first-order derivative was calculated at the peak of the characteristic band to obtain the absorption peak wavelength at the peak. The absorbance at the characteristic peak wavelength was linearly fitted with the molar concentration data. Then, with the molar concentration of the ion as the horizontal coordinate and the absorbance as the vertical coordinate, the standard curves of the relationship between the concentration and absorbance of the four transition metal ions were prepared, and the correlation coefficients were determined. The absorption spectrum curves and standard curves of the four transition metal ion solutions with different concentrations in the characteristic band are shown as follows: Figure 1 As shown in Figures A, B, C, and D, Figure 1 In the left figure, Cr(III) represents Cr 3+ 、Co(II) represents Co 2+ , Ni (II) represents Ni 2+ 、Cu(II) represents Cu 2+ , the horizontal axis is wavelength and the vertical axis represents absorbance.

[0025] from Figure 1 As shown in Figure A (left), Cr (III) has a stable absorption in the visible light region of 350-450 nm and has a characteristic peak. Figure 1 As shown in Figure B (left), Co (II) has a stable absorption in the visible light region of 400-600 nm and has a characteristic peak. Figure 1As shown in Figure C (left), Ni (II) has a stable absorption in the visible light region of 300-500 nm and has a characteristic peak. Figure 1 As shown in Figure D (left figure), Cu (II) has stable absorption in the near-infrared region of 750-900 nm, and there is a characteristic peak. As the concentration of the four metal ions increases, the absorbance in the interval where the characteristic peak is located shows an upward trend, and the linear shape remains unchanged. The absorption capacity at the characteristic peak is the strongest, and the accuracy of quantitative analysis is high. The wavelength at the characteristic peak is obtained by taking the first-order derivative of the spectral curve to find the zero point. The characteristic peak of Cr (III) is 410 nm (the inset in the right figure of Figure A), the characteristic peak of Co (II) is 512 nm (the inset in the right figure of Figure B), the characteristic peak of Ni (II) is 394 nm (the inset in the right figure of Figure C), and the characteristic peak of Cu (II) is 818 nm (the inset in the right figure of Figure D). The absorbance at the characteristic peak wavelengths of the four transition metal ions corresponds to the molar concentration one by one. After fitting, a straight line is obtained, and the linearity of the straight line is good, as shown in FIG. Figure 1 As shown in the right figure of , the equation and fit are shown in Table 1 below. The results of linear fitting show that in the section where the characteristic peaks are located, the overall absorbance is proportional to the concentration of transition metal ions, which reflects that the absorption spectra at the characteristic peaks of these four transition metal ions are highly stable. Any wavelength within these intervals has the possibility of quantitative analysis of the four transition metal ions. When the metal ion concentration exceeds a certain value, the absorbance of some transition metal ions is no longer proportional to the concentration, and the closer the measured absorbance value is to the intercept of the standard curve equation, the less accurate the concentration result will be (such as Figure 1 (The highest concentration curve in Figures A, B, C, and D on the left shows fluctuations in absorption value or band shift at the absorption peak, and the highest concentration point in the right figure deviates from the fitted straight line.) It can be concluded that the concentration measurement ranges of these four transition metal ions are 50-600 mM for Cr(III), 50-800 mM for Co(II), 50-1000 mM for Ni(II), and 50-200 mM for Cu(II), respectively (Table 1, the theoretical LDR is shown in the last column of the table; the experimental measurement ranges are all within the LDR range).

[0026] Table 1 Parameters of the absorption peak and concentration relationship curves of four transition metal ion solutions

[0027] Example 2 In order to verify that the established standard curve is suitable for detecting high-concentration transition metal ions in seawater in the same area, seawater from the same area (the same as the seawater sampled in Example 1) was used as a solvent, and transition metal ion solutions of known concentrations were prepared as test solutions. These solutions simulated actual seawater containing these four transition metal ions, and their absorbance was measured at a specific wavelength (the wavelength corresponding to the wavelength of the absorption peak of the different ions in Example 1). The concentration value corresponding to the absorbance was obtained according to the standard curve drawn in Example 1. The specific steps are as follows: 1. Sample preparation Using seawater (sampled from Yazhou Bay (Sanya City, Hainan Province, China)) as the solvent, chromium ion solutions with concentrations of 60mM, 200mM, and 580mM; cobalt ion solutions with concentrations of 70mM, 400mM, and 750mM; nickel ion solutions with concentrations of 60mM, 500mM, and 950mM; and copper ion solutions with concentrations of 55mM, 125mM, and 190mM were prepared. The above solutions containing transition metal ions were used as test solutions (verification samples), and pure seawater (which does not contain any transition metal ions) was used as a blank control sample for each group of verification samples.

[0028] 2. Sample absorbance determination The absorbance of each verification sample at a specific wavelength was measured using the detection instrument and steps in Example 1. Specifically, the absorbance values of the different concentrations of the chromium ion solution were measured at a wavelength of 410 nm, the absorbance values of the different concentrations of the cobalt ion solution were measured at a wavelength of 512 nm, the absorbance values of the different concentrations of the nickel ion solution were measured at a wavelength of 394 nm, and the absorbance values of the different concentrations of the copper ion were measured at a wavelength of 818 nm. The absorbance of each concentration verification sample was measured in parallel three times, and the absorbance values of the corresponding ion solutions of the blank control samples were measured at the same wavelength.

[0029] 3. Use the standard curve to obtain the corresponding concentration The absorbance values of each verification sample (and its parallel samples) (after deducting the absorbance value of the blank control sample) are respectively mapped to Figure 1 The linear fitting standard curve in the figure was used to obtain the corresponding concentration value at the absorbance. The average value of three parallel measurements at each concentration point was taken as the measured concentration value at that concentration point. The concentration value was compared with the actual concentration value. The results are shown in Table 2 below.

[0030] Table 2 Comparison of measured transition metal ion concentrations and actual concentrations in simulated seawater

[0031] As can be seen from Table 2, the actual concentrations of the four transition metal ions in the simulated seawater are not much different from the concentrations obtained by the linear standard curve, indicating that the linear curve obtained in the present invention is applicable to the detection of the concentrations of the four transition metal ions in seawater, and the detection concentration range is large, the detection is more convenient, and the practicability is strong.

[0032] It should be noted that when the concentration is directly derived using the standard curve between absorbance and concentration, the concentrations of samples measured in different parallels are not much different because the absorbances are not much different. After the concentration corresponding to one of the absorbances is determined, its concentration can be estimated based on the absorbance of the other parallel measured sample. The concentration difference of all parallel groups does not exceed 1. Since there will be a certain slight deviation when reading directly through the standard curve, this possible slight numerical deviation is regarded as normal. When the concentration value measured by the standard curve differs from the actual value by no more than ±5, it indicates that it is within the normal range.

[0033] Comparative Example 1 In order to verify whether traditional UV-visible spectrophotometry can be used to detect high-concentration ion solutions of these four transition metal ions contained in seawater in the same area, the transition metal ions prepared at different concentrations in Example 2 were used as detection solutions. Specifically, the concentrations of the chromium ion solutions were 60mM, 200mM, and 580mM; the concentrations of the cobalt ion solutions were 70mM, 400mM, and 750mM; the concentrations of the nickel ion solutions were 60mM, 500mM, and 950mM; and the concentrations of the copper ion solutions were 55mM, 125mM, and 190mM. Detection was performed using traditional UV-visible spectrophotometry. The specific detection steps are consistent with the prior art and are not discussed in this application. The results are shown in Table 3 below.

[0034] Table 3 Detection of different high-concentration ions in seawater using traditional UV-visible spectrophotometry

[0035] As can be seen from Table 3 above, when high concentrations of different transition metal ions were detected using the traditional method, none of them were detected, indicating that high concentrations of transition metal ions cannot be detected using the traditional UV-visible spectrophotometry method.

[0036] Comparative Example 2 Using seawater from the same area as the solvent, a series of ferric ion solutions with different concentration gradients were prepared, and the concentration gradients were: 10mM, 50mM, 100mM, 200mM, 400mM, 800mM, 1000mM; under the same conditions as in Example 1, the spectra of the ferric ion solutions with different concentrations were measured using a UV-visible spectrophotometer and plotted into a spectral curve graph. The obtained spectral curve graph is shown in FIG. Figure 2 As shown. Figure 2 As can be seen from the results, a linear relationship between absorbance and concentration cannot be formed using a standard gradient concentration, i.e., the ferric ions in the test solution cannot be detected. This indicates that the method of the present invention is not applicable to the detection of transition metal iron ion concentrations.

[0037] Comparative Example 3 Using seawater from the same area as the solvent, a series of divalent manganese ion solutions with different concentration gradients were prepared, and the concentration gradients were: 10mM, 50mM, 100mM, 200mM, 400mM, 800mM, 1000mM; under the same conditions as in Example 1, the spectra of the trivalent iron ion solutions with different concentrations were measured using a UV-visible spectrophotometer and plotted into a spectrum curve graph. The obtained spectrum curve graph is shown in FIG. Figure 3 As shown. Figure 3 As can be seen from the figure, a linear relationship between absorbance and concentration cannot be formed using a standard gradient concentration, i.e., it is impossible to detect divalent manganese ions in the test solution. This indicates that the method of the present invention is not applicable to the detection of high-concentration transition metal manganese ions.

[0038] Although the present invention has been described using the above preferred embodiments, they are not intended to limit the scope of protection of the present invention. Any person skilled in the art who makes various changes and modifications to the above embodiments without departing from the spirit and scope of the present invention still fall within the scope of protection of the present invention.

Claims

1. A method for rapid detection of high concentration transition metal ions, characterized in that: The steps include: S1: preparing a series of transition metal ion solutions with different concentration gradients as standard samples; the transition metal ion solutions are solutions containing chromium ions, cobalt ions, nickel ions or copper ions; S2: Collect the absorption spectra of the transition metal ion solutions with different concentration gradients in step S1, perform first-order derivatives at the characteristic peaks, and obtain the characteristic peak wavelengths of the four transition metal ions respectively; S3: Perform a linear fit on the absorbance and ion concentration data at the characteristic peak wavelength, and draw standard curves for the four transition metal ion concentrations, with the known ion molar concentration as the horizontal axis and the corresponding absorbance as the vertical axis; S4: Take the sample to be tested containing transition metal ions, measure its absorbance value at the characteristic peak wavelength, and then obtain the concentration of the four transition metal ions in the sample to be tested based on the absorbance value using the standard curve in step S3.

2. The method for rapid detection of high concentration transition metal ions according to claim 1, characterized in that: In step S1, chromium sulfate hydrate, cobalt chloride hexahydrate, nickel chloride hexahydrate or copper chloride hexahydrate is added to seawater as a solvent to prepare a transition metal ion solution.

3. The method for rapid detection of high concentration transition metal ions according to claim 1, characterized in that: In step S1, the concentration range of the chromium ion solution is 10-1000 mM; the concentration range of the cobalt ion solution is 10-1000 mM; the concentration range of the nickel ion solution is 10-2000 mM; and the concentration range of the copper ion solution is 10-300 mM.

4. The method for rapid detection of high-concentration transition metal ions according to claim 3, characterized in that: The concentration gradient of the solution containing chromium ions is 50mM, 100mM, 200mM, 400mM, 600mM, and 800mM; the concentration gradient of the solution containing cobalt ions is 50mM, 100mM, 200mM, 400mM, 800mM, and 1000mM; the concentration gradient of the solution containing nickel ions is 50mM, 100mM, 200mM, 400mM, 800mM, 1000mM, and 1200mM; the concentration gradient of the solution containing copper ions is 50mM, 100mM, 150mM, 200mM, and 250mM.

5. The method for rapid detection of high-concentration transition metal ions according to claim 1, wherein In step S2, the characteristic peak wavelength of chromium ions is 410 nm, the characteristic peak wavelength of cobalt ions is 512 nm, the characteristic peak wavelength of nickel ions is 394 nm, and the characteristic peak wavelength of copper ions is 818 nm.

6. The method for rapid detection of high-concentration transition metal ions according to claim 1, wherein In the step S3, The fitting linear equation of the chromium ion standard curve is: ; The correlation coefficient is 0.9999; The fitting linear equation of the cobalt ion standard curve is: ; The correlation coefficient is 0.99987; The fitting linear equation of the nickel ion standard curve is: ; The correlation coefficient is 0.9996; The fitting linear equation of the copper ion standard curve is: ;The correlation coefficient is 0.99801; Where A is absorbance and C is concentration.

7. The method for rapid detection of high-concentration transition metal ions according to any one of claims 1 to 6, characterized in that: In step S4, in the sample to be tested, the concentration range of the chromium ion solution is 50-600 mM; the concentration range of the cobalt ion solution is 50-800 mM; the concentration range of the nickel ion solution is 50-1000 mM; and the concentration range of the copper ion solution is 50-200 mM.

8. The method for rapid detection of high-concentration transition metal ions according to claim 1, wherein In step S4, the sample to be tested is seawater containing chromium ions, seawater containing cobalt ions, seawater containing nickel ions, or seawater containing copper ions.

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