Raman spectrum rapid detection method of ammonia nitrogen in water body

Abstract

The application discloses a Raman spectrum rapid detection method of ammonia nitrogen in water, utilizes a derivatization technology to convert ammonia nitrogen into hexamethyl tetramine, the hexamethyl tetramine has obvious Raman characteristic peak values, and there is a quantitative relationship between the characteristic peak values and the concentration of ammonium ions, so that the Raman spectrum rapid determination of ammonia nitrogen is realized, and the nano gold sol is utilized to realize the determination of low-concentration ammonia nitrogen by using the enhancement effect of the nano gold sol on the Raman spectrum, and the detection limit is as low as 5 mg / L, and the detection steps are simple, rapid and sensitive.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water quality detection, and more particularly relates to a method for rapidly detecting ammonia nitrogen in water bodies by using Raman spectroscopy. BACKGROUND

[0002] Ammonia nitrogen (NH3-N) is an important reagent in industrial and agricultural production processes, and widely exists in natural water bodies in the form of free ammonia (NH3) and ammonium ion (NH4 + ), and the composition ratio of the two mainly depends on the pH value of the solution. The ammonia nitrogen content in water bodies to some extent reflects the pollution situation of nitrogen-containing organic matter, and plays an extremely important role in human production and health and the stability of the ecological system. In the Comprehensive Discharge Standard of Sewage (GB8078-1996) and the Environmental Quality Standard for Surface Water (GB3838-2002), ammonia nitrogen is an important monitoring index.

[0003] At present, the national standard determination method of ammonia nitrogen in water bodies includes the Nash reagent method, the indigo phenol blue method and the hypobromite oxidation method. The Nash reagent method generates a light red brown complex with ammonia nitrogen in an alkaline solution of mercuric iodide and potassium iodide, and then the determination is carried out by using the photometric method; therefore, there are problems of insufficient high sensitivity, many interference factors and mercury pollution. The indigo phenol blue method reacts ammonium, phenol and hypochlorite to obtain indigo phenol blue under the action of a catalyst, and then the determination of ammonium is realized by using the photometric method; although it has high sensitivity, the operation is relatively complicated, the reagent is not stable enough, and the reproducibility is poor. The hypobromite oxidation method oxidizes ammonia nitrogen into nitrite nitrogen by hypobromite in an alkaline medium, the excess hypobromite is destroyed by acid sulfonamide, and the excess alkali is neutralized at the same time, and then the total amount of nitrite nitrogen is determined by using the diazo azo spectrophotometric method in an acid medium, and the ammonia nitrogen concentration is obtained by deducting the original nitrite nitrogen concentration; similarly, there are problems of complicated operation steps, high blank value and unsuitability for water bodies containing much organic matter. In summary, when the traditional photometric analysis method is used to determine ammonia nitrogen, there are problems of complicated operation, time-consuming and low analysis efficiency, and it is difficult to meet the demand for high-frequency detection of ammonia nitrogen in the process of water quality monitoring and wastewater treatment. Therefore, how to provide a rapid, simple and sensitive ammonia nitrogen detection method is a problem to be researched and solved in the technical field.

[0004] Raman spectroscopy has the characteristics of fast detection speed, no need for complex sample pretreatment and easy realization of online continuous analysis, and is particularly suitable for the determination of various components in water samples. Therefore, it is an ideal way to realize the rapid detection of ammonia nitrogen in water bodies by using Raman spectroscopy. However, the Raman signals of free ammonia (NH3) and ammonium ion (NH4 + ) in water bodies are very weak, and it is difficult to realize the rapid detection thereof by directly using the traditional Raman spectroscopy method. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application aims to provide a method for rapidly detecting ammonia nitrogen in water, to solve the problem that the Raman signals of free ammonia (NH3) and ammonium ions (NH4 + ) in water are very weak, and it is difficult to realize rapid detection thereof by using traditional Raman spectroscopy.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] A method for rapidly detecting ammonia nitrogen in water by Raman spectroscopy, which utilizes derivatization technology to convert ammonia nitrogen in water into hexamethyltetramine, and utilizes the fact that hexamethyltetramine has a clear Raman characteristic peak and there is a quantitative relationship between the characteristic peak and the concentration of ammonium ions, to realize indirect determination of the Raman spectrum of ammonia nitrogen in water, with a detection limit of 50 mg / L.

[0008] Further, the method comprises the following steps:

[0009] S1: using ammonium sulfate as a simulated ammonia nitrogen component, and utilizing Raman spectroscopy to determine a calibration curve y=2.0353x+135.9; wherein y is the intensity of the 1047 cm -1 peak, and x is the concentration of ammonia nitrogen in water, in mg / L;

[0010] S2: taking 1 mL of a water sample after precipitation and filtration, adding 0.1 mL of a 37% formaldehyde solution to obtain a mixed solution, adding the same volume of a nano-gold sol, and uniformly mixing, and then performing Raman spectrum determination to obtain the intensity of the 1047 cm -1 peak;

[0011] S3: bringing the intensity of the 1047 cm -1 peak obtained in step S2 into the standard curve in step S1 to perform calculation, so as to obtain the average concentration of ammonia nitrogen in water.

[0012] Further, the nano-gold sol is prepared by the following method: heating and boiling 100 mL of a 0.01% chloroauric acid solution, dropwise adding 3 mL of a 1% trisodium citrate solution, continuously stirring until the solution turns into wine red, and then storing in a 4℃ refrigerator for standby.

[0013] The pH value of the water sample is 6-8.

[0014] The light source of the Raman spectrometer is 578 nm, and the power is 100 mW.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] 1. The Raman spectrum of ammonia nitrogen is very weak, making it difficult to analyze and determine directly. Therefore, this invention utilizes derivatization technology to convert ammonia nitrogen into hexamethylenetetramine. Hexamethylenetetramine has obvious Raman characteristic peaks, and there is a quantitative relationship between its characteristic peaks and the concentration of ammonium ions, thereby realizing the rapid Raman spectral determination of ammonia nitrogen.

[0017] 2. This invention utilizes the enhancement effect of nano-gold sol on Raman spectroscopy to improve the sensitivity of ammonia nitrogen detection, enabling the determination of low concentrations of ammonia nitrogen with a detection limit as low as 5 mg / L.

[0018] 3. The detection method of this invention is simple to operate and fast, completing the detection within one minute, which can meet the needs of high-frequency detection of ammonia nitrogen in water quality monitoring and wastewater treatment. Furthermore, this invention uses derivatization technology to avoid interference from other components, resulting in more accurate ammonia nitrogen content detection and avoiding environmental pollution problems. Attached Figure Description

[0019] Figure 1 Raman spectra of ammonium chloride, ammonium sulfate, and formaldehyde;

[0020] Figure 2 The Raman spectrum of the product after formaldehyde derivatization;

[0021] Figure 3 Raman spectra of formaldehyde before and after enhancement with gold nanoparticles;

[0022] Figure 4 Raman spectra of the derivatized products before and after the addition of gold sol;

[0023] Figure 5 Raman spectra of ammonium sulfate derivatized at different concentrations;

[0024] Figure 6 Example 1: Ammonia nitrogen content (mg / L) compared to 1047 cm⁻¹ -1 Calibration curve of peak intensity. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in further detail below with reference to specific examples.

[0026] The numerical ranges in this invention should be understood to also specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise indicated, all technical and scientific terms have the same meaning as those one of ordinary skill in the art of the application described herein would understand. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict between the content of the specification and that of any document incorporated herein by reference, the content of the specification controls. As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to permit but not limit the inclusion of elements or the number of elements, and that do not exclude additional elements or the number of elements.

[0028] The experimental methods used in the present application are conventional methods unless otherwise specified.

[0029] The materials, reagents and the like used in the present application can be purchased or synthesized by known methods unless otherwise specified.

[0030] The quantitative test in the present application is set up with three repeated experiments, and the average value is taken.

[0031] The present application is directed to the problem that the Raman spectrum of ammonia nitrogen is weak and difficult to be directly analyzed and determined, and the traditional detection method is difficult to realize rapid detection of ammonia nitrogen. The present application utilizes the reaction of formaldehyde and ammonium ion to generate hexamethyl tetramine with obvious Raman characteristic peak value, and there is a quantitative relationship between the characteristic peak value and the concentration of ammonia nitrogen, which realizes the rapid detection of ammonia nitrogen and greatly improves the selectivity of the detection method. At the same time, in order to improve the sensitivity of the detection method, the Raman enhancement effect of gold nanosol is utilized to realize the rapid detection of low concentration ammonia nitrogen, which provides technical support for the rapid detection of ammonia nitrogen in wastewater.

[0032] The materials involved include: 37% formaldehyde as a derivatization reagent, ammonium chloride and ammonium sulfate as simulated ammonia nitrogen components, chloroauric acid and trisodium citrate as materials for preparing gold nanosol.

[0033] The instruments involved: Raman spectrometer (578nm, 100mW) such as: IPS, product of Ocean Optics, USA.

[0034] I. Determination of the characteristic peak of formaldehyde derivatization ammonia nitrogen

[0035] 1. The Raman spectra of 100mg / L ammonium chloride, 10mg / L ammonium sulfate solution and 37% formaldehyde solution were determined by using Raman spectrometer to confirm the respective Raman characteristic peaks, and the results are shown in Figure 1

[0036] From Figure 1 ( including the Raman spectra of ammonium chloride, ammonium sulfate and formaldehyde), it can be seen that 100mg / L of ammonium chloride has no obvious Raman characteristic peak, 10mg / L of ammonium sulfate has a Raman characteristic peak at 980cm​-1 The characteristic peak is SO4 2- The Raman characteristic peaks indicate that traditional Raman spectroscopy cannot directly obtain NH4 in solution. + The Raman characteristic peaks of formaldehyde are observed at 540, 910, 1047, 1319, and 1494 cm⁻¹. -1 It has obvious characteristic peaks.

[0037] 2. Take 1 mL each of 50 mg / L and 150 mg / L (NH4)2SO4 solutions, add 0.1 mL of 37% formaldehyde solution to each, mix thoroughly at room temperature to allow the ammonium ions to undergo a derivatization reaction with formaldehyde, and measure the Raman spectra of the derivatized products. Figure 2 As shown.

[0038] Depend on Figure 2 It can be seen that after formaldehyde derivatizes ammonium ions, the concentrations at 501, 711, 916, and 1047 cm⁻¹ are... -1 The study demonstrated distinct characteristic peaks with a quantitative relationship to ammonium ion concentration, enabling rapid Raman spectroscopy determination of ammonia nitrogen. The peaks at 501, 711, and 916 cm⁻¹ were also observed. -1 This represents a new Raman characteristic peak generated after derivatization, and its peak value increases with increasing ammonium ion concentration. The peak value is 1047 cm⁻¹. -1 Although it overlaps with the characteristic Raman peak of formaldehyde, under the same formaldehyde derivatization conditions, its peak value increases with increasing ammonium ion concentration, and the increasing trend is more obvious. Therefore, the peak value of 1047 cm⁻¹ can be confirmed. -1 The peak value is also a characteristic peak of the derivatized product.

[0039] II. Research has found that nano-gold solutions have an enhancing effect on the Raman spectra of ammonia nitrogen derivatization products.

[0040] 1. To confirm whether the gold nanoparticle sol affects the Raman spectrum of the derivatization reagent formaldehyde, a 37% formaldehyde solution was mixed with the gold nanoparticle sol at a volume ratio of 1:1, and its Raman spectrum was measured. (See attached image.) Figure 3 .

[0041] Depend on Figure 3 It can be seen that no enhancement of the formaldehyde Raman spectrum was observed after the addition of gold sol. On the contrary, due to the dilution of the solution after the addition of gold sol, the corresponding Raman peak showed a weakening trend. Therefore, it can be confirmed that the nano gold sol has no Raman enhancement effect on formaldehyde.

[0042] The preparation method of the nano gold sol is as follows: take 100 mL of 0.01% chloroauric acid solution, heat and boil it, add 3 mL of 1% trisodium citrate solution, stir continuously until the solution turns wine red, which is the nano gold sol. After cooling, store it in a refrigerator at 4℃ for later use.

[0043] 2, take 10mg / L ammonium sulfate 1ml, add 0.1ml 37% formaldehyde solution mixed, and mixed with nano gold sol in volume ratio 1:1, measure the Raman signal of the product before and after adding gold sol, as shown in Figure 4 .

[0044] From Figure 4 we can see that the Raman signal of 10mg / L ammonium sulfate is weak after derivatization, but when gold sol is added, there are obvious Raman signals at 442, 711, 761, 916, 1047 and 1093cm -1 , among which 711, 916 and 1047cm -1 are consistent with the peak values of the product after derivatization of 50, 150mg / L (NH4)2SO4 in Figure 2 , and the peak value of 1047cm -1 is the strongest. This shows that nano gold sol has obvious enhancement effect on the Raman spectrum of the product after derivatization, which can greatly reduce the detection limit and improve the sensitivity of the detection method.

[0045] 3, take 5, 50, 100mg / L ammonium sulfate 1ml, respectively, add 0.1ml 37% formaldehyde solution mixed, and mixed with nano gold sol in volume ratio 1:1, measure the Raman signal, as shown in Figure 5 .

[0046] From Figure 5 we can see that the 1047cm -1 peak is the most obvious, and with the increase of the concentration of ammonium sulfate, the 1047cm -1 peak value also increases, that is, there is a quantitative relationship between the concentration of ammonium ion, and accordingly a rapid detection method of ammonia nitrogen in water body can be established.

[0047] III. Examples

[0048] Example 1

[0049] Accurately weigh 0.010g of ammonium sulfate, dissolve and dilute to 100ml in a 100ml volumetric flask to obtain 100mg / L ammonium sulfate standard stock solution. Take 0.5ml, 2.0ml, 5.0ml, 10.0ml, 15.0ml of the ammonium sulfate standard stock solution in a 10ml colorimetric tube, and dilute to obtain 5mg / L, 20mg / L, 50mg / L, 100mg / L, 150mg / L ammonium sulfate standard solution. Take 1ml of each ammonium sulfate standard solution, add 0.1ml of 37% formaldehyde solution mixed, mix with nano gold sol in volume ratio 1:1 before detection, measure the Raman signal, draw the calibration curve, as shown in Figure 6 , y=2.0353x+135.9, R2=0.9992. Wherein, y is 1047cm -1The peak intensity, x is the concentration of ammonia nitrogen in water, unit is mg / L. The detection limit is 5 mg / L.

[0050] The repetitive test is carried out according to the above operation. The result is shown in Table 1, and the relative standard deviation is equivalent to that of the national standard Nessler's reagent method.

[0051] Table 1: The result of repetitive test of the present application

[0052]

[0053] Example 2

[0054] 100 mL of school lake water sample is filtered through a 0.45 μm microporous filter, and the pH value is measured as 6.8. 1 mL of the filtered lake water is taken as an analysis sample, and 0.1 mL of 37% formaldehyde solution is added to mix, and then mixed with the nano gold sol according to the volume ratio of 1:1. The Raman signals of the three samples are measured, and the 1047 cm -1 The peak intensity, x is the concentration of ammonia nitrogen in water, unit is mg / L. The detection limit is 5 mg / L.

[0055] Example 3

[0056] 100 mL of school lake water sample is filtered through a 0.45 μm microporous filter, and the pH value is measured as 6.8. 1 mL of the filtered lake water is taken as an analysis sample, and 0.1 mL of 37% formaldehyde solution is added to mix, and then mixed with the nano gold sol according to the volume ratio of 1:1. The Raman signals of the three samples are measured, and the 1047 cm -1 The peak intensity, x is the concentration of ammonia nitrogen in water, unit is mg / L. The detection limit is 5 mg / L.

[0057] Example 4

[0058] The standard addition recovery rate of the water sample is measured by the method of the present application and the national standard Nessler's reagent method. The specific steps of the Nessler's reagent method are as follows: 10 mg / L, 20 mg / L, 50 mg / L, 100 mg / L and 150 mg / L of ammonium chloride standard solution are respectively taken 25 mL into a colorimetric tube, 0.5 mL of 500 g / L potassium sodium tartrate solution is added, and mixed uniformly; 0.5 mL of Nessler's reagent (HgI2-KI-KOH) is added, and is placed for 20 minutes. The water is used as a reference, and the absorbance value of the sample is measured at a wavelength of 420 nm, and the standard curve y=0.0253x+0.0062, R 2 =0.9993 is drawn. In which, y is the absorbance value; x is the concentration of ammonia nitrogen, unit is mg / L. The ammonia nitrogen concentration in the water sample is calculated according to the standard curve. This method takes about 30 minutes to detect.

[0059] Sample 1: Take 100 mL of water sample 1 (school lake water, ammonia nitrogen content 65.6 mg / L) twice, pretreat the water sample as in Example 2, add 1.0 mL of ammonia nitrogen standard solution with a concentration of 1000 mg / L, and determine the concentration of ammonia nitrogen in the solution after adding the standard under the same conditions by using the method of the application, n = 3.

[0060] Sample 2: Take 100 mL of self-made simulated water sample twice, the ammonia nitrogen content is 50.0 mg / L, add 1.0 mL of ammonia nitrogen standard solution with a concentration of 1000 mg / L, and determine the concentration of ammonia nitrogen in the solution after adding the standard under the same conditions by using the method of the application, n = 3.

[0061] Sample 3: Take 100 mL of water sample 2 (Huxi River water sample, ammonia nitrogen content 125.3 mg / L) twice, pretreat the water sample as in Example 3, add 1.0 mL of ammonia nitrogen standard solution with a concentration of 5000 mg / L, and determine the concentration of ammonia nitrogen in the solution after adding the standard under the same conditions by using the method of the application, n = 3.

[0062] Sample 4: Take 100 mL of simulated water sample twice, the ammonia nitrogen content is 120.0 mg / L, add 1.0 mL of ammonia nitrogen standard solution with a concentration of 5000 mg / L, and determine the concentration of ammonia nitrogen in the solution after adding the standard under the same conditions by using the method of the application, n = 3.

[0063] n = 3, all repeated 3 times.

[0064] The standard addition recovery rate results are shown in Table 2.

[0065] Table 2 Standard addition recovery test

[0066]

[0067] As can be seen from Table 2, the application can meet the needs of water quality ammonia nitrogen detection, the method is reliable, and the detection speed is fast, the error is small, while the Nessler's reagent method takes at least 20 minutes or more.

[0068] The above experiments use water without ammonia.

[0069] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the application and not to limit the technical solutions, and those of ordinary skill in the art should understand that those who modify or equivalently replace the technical solutions of the application without departing from the purpose and scope of the technical solutions should be covered in the scope of the claims of the application.

Claims

1. A rapid Raman spectroscopy method for detecting ammonia nitrogen in water, characterized in that, Using derivatization technology, ammonia nitrogen in water is converted into hexamethylenetetramine. Hexamethylenetetramine exhibits a distinct Raman characteristic peak, and... Its characteristic peak value has a quantitative relationship with the concentration of ammonium ions, enabling rapid indirect determination of ammonia nitrogen in water by Raman spectroscopy, with a detection limit of 5 mg / L; Includes the following steps: S1. Using ammonium sulfate as the simulated ammonia nitrogen component, a calibration curve was plotted as y = 2.0353x + 135.9; where y is 1047 cm⁻¹. -1 Peak intensity; x is the concentration of ammonia nitrogen in the water, in mg / L; S2. Take 1 mL of the water sample after sedimentation and filtration, add 0.1 mL of 37% formaldehyde solution to obtain a mixture, then add an equal volume of gold nanoparticle sol and mix thoroughly. Perform Raman spectroscopy to obtain a 1047 cm⁻¹ sample. -1 Peak intensity; S3, take the 1047 cm obtained in step S2 -1 The peak intensity is substituted into the calibration curve described in S1 for calculation, thus obtaining the average concentration of ammonia nitrogen in the water.

2. The rapid Raman spectroscopy detection method for ammonia nitrogen in water according to claim 1, characterized in that, The nano-gold sol was prepared by the following method: 100 mL of 0.01% chloroauric acid solution was heated to boiling, and 3 mL of 1% trisodium citrate solution was added dropwise while stirring continuously until the solution turned wine red. After cooling, it was stored in a refrigerator at 4°C for later use.

3. The rapid Raman spectroscopy detection method for ammonia nitrogen in water according to claim 1, characterized in that, The pH value of the water sample was 6-8.

4. The rapid Raman spectroscopy detection method for ammonia nitrogen in water according to claim 1, characterized in that, The Raman spectrometer has a light source of 578 nm and a power of 100 mW.

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