Method for detecting content of melamine based on terahertz spectrum technology

Abstract

The invention discloses a melamine content detection method based on a terahertz spectrum technology. The melamine content detection method comprises the following steps: preparing a standard melamine sample in a predetermined gradient content range; the method comprises the following steps: collecting THz spectral data information of a standard melamine sample in a test range of 0.5-3 Thz, and carrying out de-noising treatment on a spectrogram signal to obtain an absorption peak spectrogram of the melamine sample; the method comprises the following steps: determining a content-related characteristic peak signal in a THz spectrogram of a melamine sample, and establishing a database model between the melamine content and the characteristic peak signal; and constructing a database calculation model, collecting THz characteristic absorption peaks of melamine with unknown content, and inputting the THz characteristic absorption peaks into the calculation model to obtain a corresponding melamine content detection result. According to the melamine content detection method based on the terahertz spectrum technology, rapid response can be achieved, the detection efficiency is greatly improved, a sample is analyzed in a non-contact mode, the integrity of the sample is kept, cross contamination and operation errors possibly introduced in the traditional chemical detection process are avoided, and the detection accuracy is improved. And nondestructive, rapid and efficient detection of the components and the content of the melamine is realized. And important application values are provided for melamine content detection and food safety additive detection in the environmental field.

Description

Technical Field

[0001] The present invention relates to the field of environmental and food safety analysis, and in particular to a method for detecting melamine content by utilizing terahertz spectroscopy technology. Background Art

[0002] Melamine, a nitrogen-containing heterocyclic organic compound of the triazine family, is a very important chemical raw material. In the food industry, the addition of melamine is illegal and must never be added to food as a food additive under any circumstances. Long-term consumption of foods containing melamine exceeding the permitted limits can seriously affect human health. Therefore, the determination of melamine content is a key area of food safety analysis, particularly the development of non-destructive, rapid, accurate, and efficient quantitative detection technologies for melamine additives in related products.

[0003] Currently, traditional melamine detection methods include potentiometric titration, reagent kit detection, ion chromatography, liquid chromatography, liquid chromatography-mass spectrometry (LC-MS / MS), gas chromatography-mass spectrometry (GC-MS), and molecular spectroscopy. However, these methods often face challenges such as expensive testing equipment, limited accuracy, long testing cycles, complex operations, strong dependence on test personnel, and high purity requirements for the relevant reagents. Furthermore, during the testing process, traditional methods generally require sample pretreatment, which often damages the sample. Compared to traditional detection technologies, terahertz (THz) spectroscopy has been widely used in food, medicine, and environmental testing in recent years. THz non-destructive testing technology offers unique characteristics such as high efficiency, speed, safety, transparency, and fingerprint spectroscopy, making it well suited to the needs of melamine content detection.

[0004] The frequency of the terahertz spectrum lies between millimeter waves and infrared waves, with its short-wavelength approaching the far-infrared spectrum. Its energy lies precisely in the transition region from electronics to photonics. The rotational energy levels within and between melamine molecules lie precisely within the THz band, generating a characteristic absorption spectrum within this frequency range. This characteristic absorption spectrum can be used to determine the composition and content of the melamine molecule. Therefore, developing an efficient melamine content detection method based on terahertz spectroscopy has significant theoretical research significance for food safety and enormous potential for industrial application. Summary of the Invention

[0005] The present invention aims to provide a method for detecting melamine content based on terahertz spectroscopy. This method enables non-destructive, rapid, and efficient detection of melamine composition and content. This method offers significant application value for melamine content detection in environmental fields and for food safety additive testing.

[0006] A method for detecting melamine content based on terahertz spectroscopy technology is carried out in the following steps: Step 1: preparing a standard melamine sample with a predetermined gradient content range; Step 2: Collect THz spectrum absorption coefficient data of a standard melamine sample, with the test range of 0.5-3 Thz. After denoising the spectrum signal, obtain the characteristic absorption peak of the melamine sample; Step 3: Complete the THz spectrum acquisition of melamine samples with different content gradients, determine the characteristic peak signals related to the content, extract key descriptive factors, and establish a database model between melamine content and characteristic peak signals.

[0007] Step 4: Build a database calculation model, collect the THz characteristic absorption peak of melamine of unknown content and input it into the calculation model to obtain the corresponding melamine content detection result.

[0008] The present invention provides a method for detecting melamine content based on terahertz spectroscopy, enabling non-destructive melamine content detection. The low terahertz wave spectrum energy matches the energy required for melamine molecule rotation, enabling bond rotation in the melamine molecular structure to produce an absorption spectrum. By analyzing the absorption wavelength and intensity of melamine's THz spectrum, the correspondence between characteristic absorption peaks of samples with different melamine contents and the THz spectrum is studied, and characteristic peak signals associated with content are determined. A database correlating melamine content and characteristic peak signals is generated. A reliable database recognition model is established, a spectral library matching algorithm is optimized, and a detection technique is developed to match characteristic absorption peaks of THz spectra of samples with unknown melamine content with signals associated with content. This method utilizes THz spectroscopy to achieve non-destructive, rapid screening and content detection of melamine.

[0009] The method of the present invention utilizes a pre-established terahertz spectroscopy time-domain signal detection system. In step 1, a standard melamine sample with a predetermined gradient content range is prepared. This can be prepared by mixing and pressing melamine of varying masses with a fixed mass of polyethylene into a pellet. Polyethylene powder is chosen as the viscous mixing material because it has virtually no absorption characteristics in the THz test band.

[0010] Preferably, in step 1, the amount of polyethylene used is 50-200 mg, and the melamine content is 5%-50%.

[0011] As a further preference, the composition gradient interval of samples with different melamine contents is 0.5%.

[0012] Preferably, melamine and polyethylene are thoroughly ground in an agate mortar and pestle, and then the sample is pressed into pellets using a pressure of 2 to 15 tons.

[0013] Preferably, the melamine sample pellet is a circular uniform sheet with a diameter of 13.00 mm and a thickness of 0.2 to 5.0 mm.

[0014] For samples with different melamine contents, pressed tablets were placed in the signal collection area of the terahertz spectroscopy detection system to collect terahertz spectral signal information of the samples in the 0.5~3.0 THz band.

[0015] Preferably, the terahertz spectrum signal information collected in step 2 includes a time domain spectrum signal, a frequency domain spectrum signal after Fourier transformation of the time domain spectrum information, and absorption coefficient information.

[0016] De-noising is performed to remove the absorption effect of air on the terahertz spectrum, and to remove the effects of high-frequency random noise, baseline drift, sample inhomogeneity, light scattering, etc.

[0017] Preferably, in step 3, the absorption peaks of the sample at 2.0 THz and 2.28 THz bands are extracted as characteristic absorption peaks.

[0018] The characteristic absorption peak intensity of the melamine-containing sample is obtained according to the transmission spectrum, and the melamine content in the sample is quickly detected by utilizing the linear relationship between the absorption peak of the sample and the melamine concentration.

[0019] Furthermore, in order to more accurately describe the morphology and concentration dependence of the two characteristic absorption peaks of melamine, the Gaussian distribution function is introduced in step 4 to describe the shape of the absorption peak.

[0020] Preferably, the width, center position and relationship of the characteristic absorption peak of the sample in step 4 to the concentration are as follows: in: and are the intensities of the first and second characteristic absorption peaks, and are the center frequencies of the two characteristic absorption peaks, and are the standard deviations of the first and second absorption peaks, respectively.

[0021] Compared with the existing technology, the melamine content detection method based on terahertz spectroscopy technology of the present invention has the following beneficial effects: 1. Fast and efficient detection capability: The detection method based on terahertz spectroscopy can complete detection in a very short time, and the rapid response can greatly improve the detection efficiency.

[0022] 2. Non-destructive testing and non-contact analysis: Terahertz spectroscopy can analyze samples in a non-contact manner, maintaining the integrity of the samples and avoiding cross-contamination and operational errors that may be introduced during traditional chemical testing.

[0023] 3. High sensitivity and high selectivity: Terahertz spectroscopy has a very unique sensitivity to the molecular vibrations of specific substances such as melamine, which can avoid common interference factors and improve the accuracy of detection.

[0024] In summary, the melamine content detection method based on terahertz spectroscopy technology provides a new solution for the accurate detection of melamine with its advantages of rapidity, high efficiency, non-destructiveness, sensitivity and environmental protection. It has broad application prospects, especially in the fields of food safety and chemical testing, and has very important practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the frequency domain spectral signals of air samples and melamine samples.

[0026] Figure 2 This is the absorption coefficient spectrum of melamine sample. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical features and advantages of the embodiments of the present invention clearer and more specific, the specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. In the present invention, unless otherwise specified, the devices, reagents, methods, etc. used are conventional devices, reagents, methods in the art.

[0028] The present invention provides a method for detecting melamine content based on terahertz spectroscopy technology, comprising the following steps: (1) Sample preparation: Polyethylene powder was selected as the mixed viscous material. Different masses of melamine and a fixed mass of polyethylene were mixed and pressed into tablets. The composition gradient interval of the samples with different melamine contents was 0.5%. Melamine and polyethylene were thoroughly ground in an agate mortar and pressed into tablets.

[0029] (2) Data acquisition: The THz spectrum information of the standard melamine flake sample is collected. The test range is 0.5~3Thz. The frequency domain spectrum information after Fourier transformation is shown in Figure 1 After denoising, the data spectrum signal is processed to obtain the characteristic absorption peak of melamine sample. The absorption coefficient spectrum is shown in Figure 2 The pulse width is 1-2 ps, the time resolution is 0.025 ps, and the effective time window is 18.5 ps.

[0030] (3) Database model establishment: Data preprocessing: By measuring the transmission spectrum of a reference sample (such as air or a transparent substrate), the sample spectrum is calibrated to remove the influence of the system response and calibrate the raw data; the phase offset caused by the measurement system is corrected and the phase is corrected through Fourier transform or reference signal compensation; the time domain signal is fast Fourier transformed to convert it into frequency domain data; polynomial fitting is used to remove irregular baseline drift and correct the baseline; Savitzky-Golay filtering is used to reduce data noise while maintaining signal characteristics.

[0031] Sample feature extraction: The terahertz signal without a sample is measured as a reference signal. When a sample is placed, the terahertz sample signal is measured again. The time domain spectrum is fast Fourier transformed to obtain amplitude and phase information. The refractive index and absorption coefficient can be calculated by measuring the sample thickness d. The relevant formula is: (1) (2) in: is the angular frequency; is the sample thickness; is the speed of light in a vacuum; is the amplitude ratio of the sample signal to the reference signal; is the delay time of the sample signal relative to the reference signal.

[0032] According to the absorption spectrum data, melamine has characteristic absorption peaks in the 2.0 THz and 2.28 THz bands. Based on these two characteristic peaks, data of melamine samples with different concentrations were collected to establish a database.

[0033] (4) Building a database computing model: Using the sample data in the database, the corresponding Gaussian distribution model was established according to the relationship between the extracted melamine characteristic absorption peaks and the melamine content of the corresponding samples.

[0034] The Gaussian distribution function is as follows: in: is the absorption intensity at the frequency, is the intensity of the absorption peak, which depends on the concentration and can be expressed by a linear relationship: ; is the center frequency of the absorption peak, is the standard deviation of the absorption peak, which depends on the concentration ,Right now: ,in is the initial standard deviation, is the coefficient of variation related to concentration.

[0035] By summing the contributions of the two absorption peaks, we can get the total absorption spectrum expression: The total absorption spectrum is: in: and are the intensities of the first and second characteristic absorption peaks, and are the center frequencies of the two characteristic absorption peaks, and are the standard deviations of the first and second absorption peaks, respectively.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any modifications, changes and improvements made within the spirit and principles of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. The present invention relates to a method for detecting melamine content based on terahertz spectroscopy technology, characterized in that: include: Step 1: preparing a standard melamine sample with a predetermined gradient content range; Step 2: Collect THz spectrum data of a standard melamine sample within the 0.5-3 Thz test range. After denoising the spectrum signal, obtain the absorption peak spectrum of the melamine sample. Step 3: Determine the characteristic peak signal related to the content in the THz spectrum of the melamine sample, and establish a database model between the melamine content and the characteristic peak signal.

2. Step 4: Build a database calculation model, collect the THz characteristic absorption peak of melamine of unknown content and input it into the calculation model to obtain the corresponding melamine content detection results.

3. The method for detecting melamine content based on terahertz spectroscopy according to claim 1, characterized in that: In step 1, the amount of polyethylene used is 50-200 mg, and the melamine content is 5%-50%.

4. The method for detecting melamine content based on terahertz spectroscopy according to claim 1, wherein: The composition gradient interval of samples with different melamine contents is 0.5%.

5. The method for detecting melamine content based on terahertz spectroscopy according to claim 1, characterized in that: Melamine and polyethylene were thoroughly ground in an agate mortar and pestle, and then the samples were pressed into pellets using a pressure of 2 to 15 tons. The melamine sample pellets were round, uniform sheets with a diameter of 13.00 mm and a thickness of 0.2 to 5.0 mm.

6. The method for detecting melamine content based on terahertz spectroscopy according to claim 1, characterized in that: The terahertz spectrum signal information collected in step 2 includes a time domain spectrum signal, a frequency domain spectrum signal after Fourier transformation of the time domain spectrum information, and absorption coefficient information.

7. The method for detecting melamine content based on terahertz spectroscopy according to claim 1, characterized in that: In step 2, Savitzky-Golay filtering is used to reduce data noise and maintain signal characteristics.

8. The method for detecting melamine content based on terahertz spectroscopy according to claim 1, characterized in that: In step 3, the absorption peaks of the melamine sample at 2.0 THz and 2.28 THz bands are extracted as characteristic absorption peaks.

9. The method for detecting melamine content based on terahertz spectroscopy according to claim 1, characterized in that: In step 4, a corresponding Gaussian distribution model is established to accurately describe the dependence between the morphology of the two characteristic absorption peaks of melamine and the melamine concentration.

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