Method for detecting water hardness by surface-enhanced raman and application thereof

Abstract

This invention belongs to the field of water quality monitoring technology, specifically relating to a method for detecting water hardness using surface-enhanced Raman spectroscopy and its application. The method for detecting water hardness using surface-enhanced Raman spectroscopy includes the following steps: 1) Adding 4,4-bipyridine solution and SERS silver nanocube sol to the water sample to be tested, and then measuring the Raman spectrum of the solution from 600 to 1800 cm⁻¹. ‑1 Peak height I of the absorption peak c , and / or the Raman spectrum of the test solution from 600 to 1800 cm⁻¹ ‑1 Peak height I of the absorption peak m ;2) According to Ca 2+ Standard working curve linear equation and I c The calculation yields Ca 2+ The concentration of Mg; based on 2+ Standard working curve linear equation and I m Calculations yielded Mg 2+ The concentration of Ca in water. The surface-enhanced Raman spectroscopy (SERS) technology provided by the technical solution of this invention can directly detect the concentration of Ca in water. 2+ Mg 2+ The concentration method is used to detect water hardness. This method is fast, accurate, allows for quantitative detection, and is unaffected by sodium content. + K + The interference from the water directly determines the hardness of the water.

Description

Technical Field

[0001] This invention belongs to the field of water quality monitoring technology, specifically relating to a method for detecting water hardness using surface-enhanced Raman spectroscopy and its application. Background Technology

[0002] In daily life, it's common to see limescale buildup on the inner walls of kettles after prolonged use. This is because the water used contains many inorganic salts, such as calcium and magnesium salts. These salts are invisible to the naked eye at room temperature, but once the water is heated and boiled, many calcium and magnesium salts, as well as carbonates, precipitate out and adhere to the kettle wall, forming limescale. The calcium and magnesium ion content in water is usually expressed using the indicator of hardness. Excessive calcium and magnesium ions can affect the serum alkaline phosphatase levels in people exposed to fluoride. However, calcium and magnesium ions are essential nutrients for the human body every day, and limescale is a calcium and magnesium compound. Drinking water can supplement a certain amount of calcium and magnesium ions. However, long-term consumption of water with excessively high calcium and magnesium ion content may lead to certain diseases. Scientific research shows that in areas with higher water hardness, the incidence of cardiovascular disease is lower, but the incidence of kidney stones increases with increasing water hardness. Southern my country mostly has soft water, while northern China mostly has hard water. my country's drinking water standard stipulates that the hardness should not exceed 25 degrees, with the most suitable drinking water hardness being 8-18 degrees, which is considered slightly to moderately hard water. Household water and drinking water are constantly related to our health. Even a small amount of soluble impurities in drinking water can affect the overall quality of the water body.

[0003] Calcium and magnesium ions are important sources of hardness in water, and their levels directly affect water hardness and pH, thus influencing the growth and metabolism of aquatic microorganisms, plants, and animals. Furthermore, appropriate hardness and pH levels help maintain the buffering capacity of water bodies, keep dissolved oxygen and carbon dioxide levels balanced, and facilitate the self-regulation of ecosystems in aquaculture. Water hardness primarily refers to the presence of soluble calcium and magnesium salts in the water. Total hardness is usually expressed as milligrams of calcium carbonate per liter of water, i.e., mg / L.

[0004] The current national standard method for testing water quality is the EDTA titration method. This method is complex to operate and is suitable for laboratory testing but not for rapid on-site testing. It requires a large number of expensive laboratory instruments, so this method is not suitable for large-scale testing needs.

[0005] Raman spectroscopy offers advantages such as rapid analysis speed and direct qualitative identification via fingerprint spectroscopy for constant-volume substances, making it suitable for rapid on-site detection. However, it requires samples at constant-volume levels, and for samples with complex compositions, the concentrations of active or atopic components are often far below the sensitivity limit for direct detection. Surface-enhanced Raman spectroscopy (SERS), using specialized reinforcing nanomaterials, can achieve extremely high Raman spectral signal enhancement. SERS is an ultrasensitive vibrational spectroscopy technique capable of detecting molecules adsorbed or near the surface of noble metal nanoparticles. It offers advantages such as rich spectral information, high sensitivity, and rapid detection speed. Furthermore, with the recent rapid development of portable Raman spectrometers, SERS offers advantages such as high sensitivity, no sample pretreatment required, and immunity to water interference. Currently, SERS is considered a potentially excellent on-site analytical technique. This invention proposes a method for directly detecting water hardness using SERS, which can rapidly, accurately, and quantitatively determine whether the hardness in water exceeds the standard.

[0006] Bipyridine is a class of products synthesized from pyridine through combined reactions. Common types include 2,2-bipyridine and 4,4-bipyridine, which are frequently used for the detection of ferrous iron, silver, cadmium, and molybdenum, and as redox indicators. Current detection reagents use 4,4-bipyridine, a pyridine derivative and a commonly used organic synthesis intermediate. It is primarily used for the synthesis and modification of pyridine ligands in organic chemical reactions, and can also serve as a ligand unit in supramolecular chemistry, assembling with metal complexes to form supramolecular compounds. Because its pyridine nitrogen atom also possesses a lone pair of electrons, it can be used as an organic ligand in metal-catalyzed reactions.

[0007] Silver nanocubes readily exhibit electromagnetic field enhancement effects when irradiated with lasers, due to the excitation of surface plasmon resonances on their surface by light waves. This results in strong localization and field enhancement properties. Silver nanocubes with sharp corners exhibit an even stronger field enhancement effect due to the "hot spot" effect. These nanoparticles possess unique optical, electrical, and thermal properties, leading to their application in numerous fields, including biological immunoassay, protein labeling, dark-field optical imaging, fluorescence enhancement, surface-enhanced Raman spectroscopy substrates, and drug delivery systems. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for detecting water hardness using surface-enhanced Raman spectroscopy (SERS) and its application. The surface-enhanced Raman spectroscopy (SERS) technology provided by this invention can directly detect Ca in water. 2+ Mg 2+The concentration method is used to detect water hardness. This method is fast, accurate, allows for quantitative detection, and is unaffected by sodium content. + K + The interference from the water directly determines the hardness of the water.

[0009] The technical solution provided by this invention is as follows:

[0010] A method for detecting water hardness using surface-enhanced Raman spectroscopy includes the following steps:

[0011] 1) Add 4,4-bipyridine solution and SERS silver nanocube sol to the test solution, and then measure the Raman spectrum of the test solution from 600 to 1800 cm⁻¹. -1 Peak height I of the absorption peak c , and / or the Raman spectrum of the test solution from 600 to 1800 cm⁻¹ -1 Peak height I of the absorption peak m ;

[0012] 2) According to Ca 2+ Standard working curve linear equation and I c The calculation yields Ca 2+ The concentration;

[0013] According to Mg 2+ Standard working curve linear equation and I m Calculations yielded Mg 2+ The concentration.

[0014] In the above technical solution:

[0015] Compared to existing detection reagents, the reaction products of 4,4-bipyridine solution and SERS silver nanocube sol exhibit specific peaks in Raman spectra acquired under the action of surface-enhanced SERS reagents, enabling accurate, rapid, and convenient detection of total water hardness values.

[0016] This method detects the Raman spectra of different metal ions, allowing identification of the corresponding metal ions through specific Raman peaks at different peak positions. A quantitative model is established based on the intensity of specific Raman peaks in the specific Raman spectra, within the range of 600–1800 cm⁻¹. -1 Within a range, for example, 769cm -1 1014cm -1 1064cm -1 1097cm -1 1293cm -1 etc. Below, 1014cm -1 Taking the Raman peak at that location as an example, by analyzing different Ca... 2+ The Raman spectral signal of the sample with ion concentration at 10¹⁴ cm⁻¹ was detected. -1The concentration-Raman peak intensity curve, obtained from concentration calibration, can be used to quantify analytes of unknown concentration, such as... Figure 2 As shown. Wherein Ca 2+ Ion concentration c1 and 10¹⁴ cm⁻¹ -1 Peak Intensity I c Satisfy the following relationship: I c =k c c1+b c In the formula, k c Let b be the slope of the linear fitting equation. c This is the y-intercept of the line. For Mg 2+ The situation is similar.

[0017] The SERS-enhancing reagent of this invention employs silver nanocube sol. Silver nanocubes are metallic nanoparticles with specific shapes and sizes. They are composed of silver atoms and have a cubic structure. These nanoparticles support the LSP mode; they are localized and exhibit a strong field enhancement effect, especially those with sharp-cornered shapes, where the electric field is primarily localized at the corners.

[0018] Specifically, the concentration of 4,4-bipyridine in the solution is 10. -6 ~10 -1 mol / L. Excessively high concentrations can lead to competition between free 4,4-bipyridine and the binding of SERS silver nanocube sol, and between the free 4,4-bipyridine and the metallic Ca. 2+ When combined, the effective signal intensity decreases during Raman signal acquisition. Too low a concentration can lead to the SERS silver nanocube sol reacting with metallic Ca. 2+ It cannot be completely assembled on the pyridine ring in 4,4-bipyridine, and therefore cannot fully exhibit Ca 2+ The actual content.

[0019] Specifically, the concentration of silver nanocubes in the solution for SERS is 0.01–0.1 g / L. Too high a concentration will result in poor transmittance, high noise, and a weak signal during Raman spectroscopy. Too low a concentration is insufficient for the absorption of metallic Ca. 2+ Enhancement tests were performed on the complex assembled with 4,4-bipyridine.

[0020] SERS silver nanocube sol can be prepared using existing SERS silver nanocube materials through common sol preparation methods, for example, through the following specific steps:

[0021] 1) Prepare a 20 mg / ml PVP-EG solution; a 3 mM Na2S-EG solution; and a 48 mg / ml AgNO3-EG solution;

[0022] 2) Take 6 ml of ethylene glycol (EG) into a three-necked flask and heat it in an oil bath at 200-350 rpm for 1 hour;

[0023] 3) After heating the ethylene glycol solution in step 2) for 1 hour, add 0.07-0.1 ml of 3 mM Na2S-EG solution, keep the temperature constant, and continue heating for 8-9 minutes;

[0024] 4) Add 1.5 ml of 20 mg / ml PVP-EG solution and 0.5 ml of 48 mg / ml AgNO3-EG solution to step 3) above. Stop the reaction after about 10 min to 4 h. Cool the three-necked flask to room temperature.

[0025] 5) The silver cube sol obtained in step 4) should be washed by centrifugation 3-4 times with ethanol solvent, and then sonicated with distilled water for 10 min, followed by centrifugation and washing twice to obtain the silver nano cube sol required for the experiment.

[0026] Specifically, in step 1): after adding 4,4-bipyridine solution and SERS silver nanocube sol, 4,4-bipyridine and SERS silver nanocube material form a complex.

[0027] In the above technical solution, Ca 2+ Mg 2+ Using heavy metal ions as target molecules, the two electron-rich nitrogen atoms on the symmetrical pyridine ring of 4,4-Bpy bind to the metal ions through coordination bonds. The added SERS silver nanocube sol binds to the other nitrogen atom on the pyridine ring of 4,4-Bpy, enabling quantitative detection by Raman spectroscopy. The principle is as follows: Figure 1 As shown.

[0028] Specifically, Ca 2+ The standard working curve linear fitting equation is: I c =k c c1+b c c1 is Ca 2+ The concentration, k c The value range is 2000 to 20000, b c The value range is -800 to 800.

[0029] Preferably, in step 2), Ca 2+ The linear equation of the standard working curve is: I c =6140.6c1-307.83, where c1 is Ca 2+ The concentration.

[0030] Specifically, Mg 2+ The standard working curve linear fitting equation is: Im =k m c2+b m c2 is Mg 2+ The concentration, k m The value range is 500 to 20000, b m The value range is -500 to 800.

[0031] Preferably, in step 2), Mg 2+ The linear equation of the standard working curve is: I m =1373.2c² + 69.993, where c² is Mg 2+ The concentration.

[0032] Specifically, Ca 2+ The detection concentration is 0–5.0 μg / ml.

[0033] Specifically, Mg 2+ The detection concentration is 0–5.0 μg / ml.

[0034] Specifically, for Ca 2+ The characteristic peak is located at 769 cm⁻¹ -1 1014cm -1 1064cm -1 1097cm -1 1293cm -1 etc.

[0035] For Mg 2+ The characteristic peak is located at 769 cm⁻¹ -1 1014cm -1 1064cm -1 1097cm -1 1293cm -1 etc.

[0036] Furthermore, when the test solution containing 4,4-bipyridine solution and SERS silver nanocube sol in step 1) contains sodium ions and / or potassium ions, no characteristic peaks of sodium ions and / or potassium ions are observed in the Raman spectrum.

[0037] Based on the above technical solution, the method for checking water hardness provided by the present invention is unresponsive to sodium ions and / or potassium ions, thereby avoiding interference from sodium ions and / or potassium ions.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] 1) 4,4-Bipyridine and Ca 2+ (or Mg) 2+The reaction process of metal ions such as Ca2+ ions was studied, including the reaction method and the ratio of added reagents. Simultaneously, SERS silver nanocube sol was used for detection, generating a detectable Raman-specific signal. This signal was then used to determine the reaction of Ca2+ ions with other metal ions. 2+ (or Mg) 2+ Detection of ions and other heavy metal ions to quantitatively calculate water hardness;

[0040] 2) This method is effective for Na + K + There was no response in the detection of ions, specifically Ca. 2+ (or Mg) 2+ The ions and other metal ions are highly sensitive to the response;

[0041] 3) 4,4-Bpy and this method can also measure other metal ions, which are consistent with the principle of this invention and are also within the scope of protection, such as lead, cadmium, mercury or copper;

[0042] 4) This detection method is fast, quantitative, easy to use, and has a long shelf life. It can directly detect the hardness of water and can be used for water quality index testing in daily life environments. Attached Figure Description

[0043] Figure 1 This is a schematic diagram illustrating the binding mechanism between 4,4-Bpy and SERS silver nanocube sol.

[0044] Figure 2 It is a different Ca 2+ The Raman spectral signal of the sample with ion concentration at 10¹⁴ cm⁻¹ was detected. -1 The peak height and concentration-Raman peak intensity curve at the concentration calibration.

[0045] Figure 3 It is Ca 2+ Mg 2+ Na + K + Raman spectrum of ion standard solution.

[0046] Figure 4 It is the standard concentration of Ca for detection 2+ Raman spectrum of ionic solution.

[0047] Figure 5 It is Ca 2+ Linear equation graph of the standard working curve of standard ions.

[0048] Figure 6 This is the Raman spectrum corresponding to the water sample to be tested.

[0049] Figure 7 It is the standard concentration of Mg for detection 2+ Raman spectrum of ionic solution.

[0050] Figure 8 It is Mg 2+ Linear equation graph of the standard working curve of standard ions.

[0051] Figure 9 This is the Raman spectrum corresponding to water sample 2.

[0052] Figure 10 These are the Raman spectra corresponding to the comparative model. Detailed Implementation

[0053] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0054] Example 1

[0055] The method for testing water hardness includes the following steps:

[0056] (1) Take 1.0 μg / ml of Ca 2+ Mg 2+ Na + K + 0.5 ml of the ion standard solution was added to 0.4 ml of 4,4-bipyridine solution, mixed thoroughly, and then 0.1 ml of SERS silver nanocube sol was added. Raman spectroscopy of the mixture was performed, and the spectral data measured under the same conditions are as follows. Figure 3 As shown. The Raman spectroscopy used a laser source with a wavelength of 785 nm and a spectral resolution of 6 cm⁻¹. -1 @25µm slit, spectral range 200–3200cm -1 Test conditions: laser power 350mW, integration time 5s, 5 acquisitions and average spectrum (subsequent steps are the same).

[0057] The Raman spectra of each ion show that this method is effective for Na. + K + No response signal was detected for Ca. 2+ Mg 2 + Detects specific signals that elicit a response.

[0058] (2) Take 0.5 ml of deionized water into a brown reagent bottle and add 0.4 ml of 0.02 mol / L 4,4-bipyridine solution (subsequent steps are the same), mix well, add 0.1 ml of 0.1 g / L SERS silver nanocube sol (subsequent steps are the same), collect Raman spectra of the mixture, and use the spectral data measured under the same conditions as blank control.

[0059] (3) Detection standard concentration Ca 2+Raman spectroscopy of ionic solutions: Seven different concentration gradients of Ca (0 μg / ml, 0.5 μg / ml, 1.0 μg / ml, 2.0 μg / ml, 3.0 μg / ml, 4.0 μg / ml, and 5.0 μg / ml) were used. 2+ 0.5 ml of each standard solution was placed in a brown reagent bottle and mixed thoroughly with the added 4,4-Bpy solution. Then, SERS silver nanocube sol was added to each bottle and mixed thoroughly. Raman spectra of each standard sample were acquired under the same testing conditions, and the Raman spectra of the standards are shown below. Figure 4 As shown.

[0060] (4) According to the Ca 2+ 1014 cm⁻¹ in the Raman spectrum of the standard solution of the ion -1 Peak height I of the absorption peak c and Ca 2+ The concentrations of the ions corresponding to Ca 2+ Increased ion concentration, 10¹⁴ cm⁻¹ -1 Peak height I of the absorption peak c And it rose accordingly. (Based on Ca) 2+ Ion concentration is plotted on the x-axis, with a plot of 10¹⁴ cm⁻¹. -1 Plot a standard working curve with peak height as the ordinate, Ca 2+ Ion concentration C and 10¹⁴ cm⁻¹ -1 Peak Intensity I c Satisfy the following relationship: I c =k c c1+b c In the formula, k c Let b be the slope of the linear fitting equation. c This is the y-intercept of the line.

[0061] For example, for the detection of the above concentration standards, Ca was used at different concentration gradients of 0.5 μg / ml, 1.0 μg / ml, 2.0 μg / ml, 3.0 μg / ml, 4.0 μg / ml, and 5.0 μg / ml. 2+ Standard ion detection, with 10¹⁴ cm⁻¹ -1 Peak Intensity I c A linear fit between the two curves yields the linear equation of the standard working curve, as follows: Figure 5 As shown. The specific equation is: I c =6140.6x-307.83.

[0062] (5) Ca in actual water samples 2+Ion Detection: To verify the feasibility of the surface-enhanced Raman spectroscopy method for detecting water hardness proposed in this invention, Raman spectroscopy analysis of pure water was performed using the standard addition method under optimal conditions. This was achieved by adding Ca at a concentration of 0.35 ug / ml. 2+ The standard solution was used to test and recover the purified water sample. The water sample was processed according to the detection method in step (2), and surface-enhanced Raman spectroscopy was performed under the same conditions to obtain the Raman spectrum of the solution, as shown below. Figure 6 As shown.

[0063] (6) Comparison and Confirmation: The Raman spectral signal in step (5) is compared and confirmed with the standard Ca in step (3). 2+ In ion Raman spectroscopy, the Raman spectral signal of the test solution showed the presence of standard Ca. 2+ The presence of identical Raman characteristic peaks in the ion Raman spectrum indicates that the solution contains Ca. 2+ ion.

[0064] (7) Ca in the water sample to be tested 2+ Estimation of ion concentration: 10¹⁴ cm⁻¹ -1 absorption peak height I 样 =1700, and the linear equation of the standard working curve plotted in step (4) is used to obtain the concentration C of calcium ions in the water sample solution to be tested. 样 =0.33 μg / ml, the hardness in the water sample can be calculated to be 0.33 mg / L, with a recovery rate of 94.3%. Experimental results show that this invention, based on surface-enhanced Raman spectroscopy, can determine the Ca content in water. 2+ The ion method is indeed reliable and effective, and can be specifically applied to the analysis of Ca in actual water quality. 2+ For the detection of ions.

[0065] Example 2

[0066] For Mg 2+ Methods for testing water hardness.

[0067] (1) Take 0.5 ml of deionized water and add 0.4 ml of 0.04 mol / L 4,4-bipyridine solution to a brown reagent bottle (subsequent steps are the same). Mix well, add 0.1 ml of 0.1 g / L LERS silver nanocube sol (subsequent steps are the same), and collect Raman spectra of the mixture. The spectral data measured under the same conditions are used as blank controls. The laser light source used for Raman spectroscopy has a wavelength of 785 nm and a spectral resolution of 6 cm⁻¹. -1 @25µm slit, spectral range 200–3200cm -1Test conditions: laser power 350mW, integration time 5s, 5 acquisitions and average spectrum (subsequent steps are the same).

[0068] (2) Detection standard concentration Mg 2+ Raman spectroscopy of ionic solutions: Seven different concentration gradients of Mg (0 μg / ml, 0.5 μg / ml, 1.0 μg / ml, 2.0 μg / ml, 3.0 μg / ml, 4.0 μg / ml, and 5.0 μg / ml) were used. 2+ 0.5 ml of each standard solution was placed in a brown reagent bottle, and 0.4 ml of 0.04 mol / L 4,4-Bpy solution was added to each bottle. The solutions were then mixed thoroughly, followed by 0.1 ml of 0.1 g / L LERS silver nanocube sol. The mixtures were then thoroughly mixed. Raman spectra of each standard sample were acquired under the same testing conditions, and the Raman spectra of the standards are shown below. Figure 7 As shown.

[0069] (3) According to the Mg 2+ 1097 cm⁻¹ in the Raman spectrum of the standard solution of the ion -1 Peak height I of the absorption peak m and Mg 2+ The concentrations of the ions corresponding to each ion, with respect to Mg 2+ Increased ion concentration, 1097 cm⁻¹ -1 Peak height I of the absorption peak m And it also rises accordingly. With Mg 2+ Ion concentration is plotted on the x-axis, with a plot of 1097 cm⁻¹ -1 Plot a standard working curve with peak height as the ordinate, Mg 2+ Ion concentration C and 1097 cm -1 Peak intensity I satisfies the following relationship: I m =k m c2+b m In the formula, k m Let b be the slope of the linear fitting equation. m This is the y-intercept of the line.

[0070] For example, for the detection of the above concentration standards, Mg was used at different concentration gradients of 0.5 μg / ml, 1.0 μg / ml, 2.0 μg / ml, 3.0 μg / ml, 4.0 μg / ml, and 5.0 μg / ml. 2+ Standard ion detection, with 1097 cm⁻¹ -1 Peak Intensity I m A linear fit between the two curves yields the linear equation of the standard working curve, as follows: Figure 8 As shown. The specific equation is: I m =1373.2x+69.993.

[0071] (5) Mg in actual water samples 2+ Ion Detection: To verify the feasibility of the surface-enhanced Raman spectroscopy method for detecting water hardness proposed in this invention, Raman spectroscopy analysis of pure water was performed using the standard addition method under optimal conditions. This was achieved by adding Mg at a concentration of 2 μg / ml. 2+ The standard solution was used to test and recover the pure water sample. The water sample was processed according to the detection method in step (2), and surface-enhanced Raman spectroscopy was performed under the same conditions to obtain the Raman spectrum of the solution, as shown below. Figure 9 As shown.

[0072] (6) Comparison and Confirmation: The Raman spectral signal in step (5) is compared and confirmed with the standard Mg in step (3). 2+ Ion Raman spectroscopy revealed the presence of standard Mg in the Raman spectral signal of the test solution. 2+ The presence of identical Raman characteristic peaks in the ion Raman spectrum indicates that the solution contains Mg. 2+ ion.

[0073] (7) Mg in the water sample to be tested 2+ Estimation of ion concentration: 1097 cm⁻¹ -1 absorption peak height I 样 =2700, and the linear equation of the standard working curve plotted in step (3) is used to obtain the concentration C of magnesium ions in the water sample solution to be tested. 样 =1.91 μg / ml, the hardness in the water sample can be calculated to be 1.91 mg / L, with a recovery rate of 95.5%. Experimental results show that this invention, based on surface-enhanced Raman spectroscopy, can determine the Mg content in water. 2+ The ion method is indeed reliable and effective, and can be specifically applied to the analysis of Mg in actual water quality. 2+ For the detection of ions.

[0074] Comparative Example 1

[0075] SERS polycrystalline silver nanosol, synthesized from silver nitrate and sodium citrate, was used as a assay for detecting calcium in water. 2+ Mg 2 + A concentration-enhancing reagent is used to test water hardness.

[0076] (1) Take 1.0 μg / ml of Ca 2+ Mg 2+ Ion standard solutions were added to 4,4-bipyridine solution and mixed thoroughly. SERS polycrystalline silver nanoparticles were then added, and Raman spectroscopy was performed on the mixture. The spectral data measured under the same conditions are as follows. Figure 10As shown. The Raman spectroscopy used a laser source with a wavelength of 785 nm and a spectral resolution of 6 cm⁻¹. -1 @25µm slit, spectral range 200–3200cm -1 Test conditions: laser power 350mW, integration time 5s, 5 acquisitions and average spectrum (subsequent steps are the same).

[0077] (2) Under the same conditions as step (1) in Example 1, 1.0 μg / ml Ca 2+ Ion standard solutions at 10¹⁴ cm⁻¹ -1 Peak height I c In comparison, the reinforcing effect of SERS silver nanocube sol is superior to that of SERS polycrystalline silver nanosol; 1.0 μg / ml Mg 2+ Ion standard solutions at 1097 cm⁻¹ -1 Peak height I m In comparison, the reinforcing effect of SERS silver nanocube sol is superior to that of SERS polycrystalline silver nanosol. The comparison results are as follows: Figure 10 As shown.

[0078] This invention employs a bipyridine reagent to detect calcium and magnesium ions in water. Other reagents using the same detection principle as this patent should also be included within the scope of protection of this invention. The above description is merely a preferred embodiment of this invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for detecting water hardness using surface-enhanced Raman spectroscopy, characterized in that, Includes the following steps: 1) Add 4,4-bipyridine solution and SERS silver nanocube sol to the test solution, and then measure the 1014 cm⁻¹ Raman spectrum of the test solution. -1 Peak height I of the absorption peak c , and the Raman spectrum of the test solution at 1097 cm⁻¹ -1 Peak height I of the absorption peak m ; 2) According to Ca 2+ Standard working curve linear equation and I c The calculation yields Ca 2+ The concentration; According to Mg 2+ Standard working curve linear equation and I m Calculations yielded Mg 2+ The concentration.

2. The method for detecting water hardness using surface-enhanced Raman spectroscopy according to claim 1, characterized in that, In step 1): the concentration of 4,4-bipyridine in the solution is 10. -6 ~10 -1 mol / L.

3. The method for detecting water hardness using surface-enhanced Raman spectroscopy according to claim 1, characterized in that, In step 1), the concentration of SERS silver nanocubes in the solution is 0.01–0.1 g / L.

4. The method for detecting water hardness using surface-enhanced Raman spectroscopy according to claim 1, characterized in that, In step 1): After adding 4,4-bipyridine solution and SERS silver nanocube sol, 4,4-bipyridine and SERS silver nanocube material form a complex.

5. The method for detecting water hardness using surface-enhanced Raman spectroscopy according to claim 1, characterized in that: Ca 2+ The standard working curve linear fitting equation is: I c =6140.6c1-307.83, where c1 is Ca 2+ The concentration; Mg 2+ The standard working curve linear fitting equation is: I m =1373.2c² + 69.993, where c² is Mg 2+ The concentration.

6. The method for detecting water hardness using surface-enhanced Raman spectroscopy according to any one of claims 1 to 5, characterized in that: Ca 2+ The detection concentration is 0–5.0 μg / ml; and / or Mg 2+ The detection concentration is 0–5.0 μg / ml.

7. The method for detecting water hardness using surface-enhanced Raman spectroscopy according to any one of claims 1 to 5, characterized in that: When the test solution containing 4,4-bipyridine solution and SERS silver nanocube sol in step 1) contains sodium ions and / or potassium ions, no characteristic peaks of sodium ions and / or potassium ions are observed in the Raman spectrum.

8. An application of the method for detecting water hardness using surface-enhanced Raman spectroscopy according to any one of claims 1 to 7, characterized in that: Used for testing domestic water, river water, lake water, surface water, or groundwater to detect calcium. 2+ and / or Mg 2+ The concentration.

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