A method and apparatus for detecting polycyclic aromatic hydrocarbons based on ultraviolet fluorescence and absorption spectroscopy

Abstract

This invention discloses a method for detecting polycyclic aromatic hydrocarbons (PAHs) based on ultraviolet fluorescence and absorption spectroscopy, comprising: Step 1, acquiring the ultraviolet absorption spectrum and the fluorescence emission spectrum of a water sample under ultraviolet light excitation; Step 2, analyzing the corresponding CDOM fluorescence spectrum using the ultraviolet absorption spectrum obtained in Step 1; Step 3, subtracting the CDOM fluorescence spectrum obtained in Step 2 from the fluorescence emission spectrum obtained in Step 1 to obtain a mixed fluorescence spectrum containing multiple PAHs; Step 4, performing multivariate fitting on the mixed fluorescence spectrum obtained in Step 3 to obtain the type and concentration of each PAH in the water sample. This invention also provides a PAH detection device. The method provided by this invention is simple to operate and can directly detect raw water samples, thereby obtaining more accurate PAH detection results.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring technology, and in particular relates to a method and device for monitoring polycyclic aromatic hydrocarbons based on ultraviolet fluorescence and absorption spectroscopy. Background Technology

[0002] Water is an indispensable resource for human survival. With the development and utilization of the environment by humans, the pollution of natural water bodies, including surface water, groundwater, and marine water, has become increasingly serious. Among them, polycyclic aromatic hydrocarbons (PAHs) are highly toxic, mutagenic, and carcinogenic organic pollutants that can remain stable in natural water bodies for a long time and are not easily degraded. They can harm human health through direct ingestion and food chain transmission, and are therefore a key priority pollutant for control.

[0003] Polycyclic aromatic hydrocarbons (PAHs) are hydrocarbons containing two or more benzene rings or heterocycles in their chemical structure. They are produced by the incomplete combustion of organic polymers such as coal and petroleum. Atmospheric deposition, oil spills, factory emissions, and domestic sewage discharge all contribute to the release of large amounts of PAHs into natural water bodies. Due to the widespread presence of PAHs in natural water bodies and their high degree of harm to humans, establishing in-situ, rapid, and high-precision PAH detection methods is crucial for the management of aquatic environments.

[0004] Currently, the main methods for detecting polycyclic aromatic hydrocarbons (PAHs) include gas chromatography, high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), infrared spectroscopy, fluorescence spectroscopy, and surface-enhanced Raman spectroscopy (SMR). While HPLC, GC-MS, and infrared spectroscopy offer advantages such as high precision and selectivity, they require cumbersome sample pretreatment and cannot be directly applied to natural water samples. Therefore, they are time-consuming, costly, and difficult to apply in situ. SMR technology is not yet mature enough. Therefore, existing PAH sensors on the market all use fluorescence spectroscopy for rapid detection of PAHs, employing single excitation / emission wavelength pairing. Furthermore, colored soluble organic matter (CDOM) in natural water bodies also exhibits fluorescence characteristics, and its wavelength largely overlaps with that of PAHs, causing interference and resulting in lower accuracy for fluorescence-based PAH determination.

[0005] Patent document CN104865237A discloses an apparatus and method for on-site detection of polycyclic aromatic hydrocarbons (PAHs) in water samples. This method adsorbs PAH molecules using an imprinting material, processes the adsorbed PAH molecules with a prepared washing solution, eluent, regeneration solution, and enhancement solution, and finally determines the presence of PAHs in the water sample by comparing the Raman spectrum and fingerprint spectrum. This method uses a self-made reagent solution to wash the water sample, thus eliminating the influence of impurities; however, interference from colored soluble organic matter still exists during the subsequent spectral comparison.

[0006] Patent document CN109060748A discloses a rapid method for determining the content of anthracene and pyrene in ice phase. This method includes using acetonitrile as a co-solvent to freeze samples containing anthracene and pyrene into ice; secondly, using synchronous fluorescence spectra, examining the synchronous fluorescence spectra of samples at 10 nm intervals within the wavelength range of Δλ = 0-180 nm, and performing constant-wavelength synchronous scanning with different wavelength differences to determine the optimal detection conditions for the synchronous fluorescence method of anthracene and pyrene; finally, using the optimized detection conditions for the synchronous fluorescence method of anthracene and pyrene, establishing a synchronous fluorescence standard curve for the determination of anthracene and pyrene. This method reduces the interference of other impurities on the detection of polycyclic aromatic hydrocarbons by freezing; however, this method requires freezing the water sample and is not suitable for practical in-situ detection. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for detecting polycyclic aromatic hydrocarbons (PAHs) based on ultraviolet fluorescence and absorption spectroscopy. This method is simple to operate and can directly detect raw water samples, thereby obtaining more accurate PAH detection results.

[0008] A method for detecting polycyclic aromatic hydrocarbons based on ultraviolet fluorescence and absorption spectroscopy includes:

[0009] Step 1: Obtain the ultraviolet absorption spectrum of the water sample and the fluorescence emission spectrum of the water sample under ultraviolet light excitation;

[0010] Step 2: Using the ultraviolet absorption spectrum obtained in Step 1, analyze the corresponding CDOM fluorescence spectrum;

[0011] Step 3: Subtract the CDOM fluorescence spectrum obtained in Step 2 from the fluorescence emission spectrum obtained in Step 1 to obtain a mixed fluorescence spectrum containing multiple polycyclic aromatic hydrocarbons;

[0012] Step 4: Based on the mixed fluorescence spectrum obtained in Step 3, perform multivariate fitting on various polycyclic aromatic hydrocarbons to obtain the types and concentrations of each polycyclic aromatic hydrocarbon in the water sample.

[0013] This invention generates a corresponding CDOM fluorescence spectrum from the ultraviolet absorption spectrum of the raw water sample, processes the fluorescence emission spectrum of the raw water sample, thereby eliminating the influence of organic impurities in the raw water sample on the detection and obtaining an accurate concentration of polycyclic aromatic hydrocarbons.

[0014] Specifically, in step 2, the ultraviolet absorption spectrum is analyzed using the constructed multi-wavelength absorbance fitting model, and the corresponding CDOM concentration is output;

[0015] The three-dimensional fluorescence spectrum of CDOM concentration was obtained using a three-dimensional fluorescence spectroscopy scanner. A linear relationship was constructed based on the obtained CDOM concentration and the corresponding three-dimensional fluorescence spectrum, and the corresponding CDOM fluorescence spectrum was obtained by fitting.

[0016] Specifically, the multi-wavelength absorbance fitting model is constructed by measuring the absorbance of CDOM samples using an ultraviolet spectrophotometer based on CDOM samples configured with typical concentration gradients of natural water bodies.

[0017] Specifically, in step 4, the polycyclic aromatic hydrocarbons are compared with a pre-constructed standard spectral database based on the excitation and emission wavelengths of the mixed fluorescence spectrum, and classified according to the number of rings. The standard spectral database includes three-dimensional fluorescence spectra of various polycyclic aromatic hydrocarbon samples at different concentrations.

[0018] Specifically, in step 4, the concentration of the polycyclic aromatic hydrocarbon is calculated based on the fluorescence intensity and absorbance of the mixed fluorescence spectrum, using the following formula:

[0019]

[0020] In the formula, C PAH F represents the concentration of polycyclic aromatic hydrocarbons. total A represents the fluorescence intensity at the characteristic wavelength of polycyclic aromatic hydrocarbons. total denoted as absorbance at the characteristic wavelength of CDOM, b1 and k1 are constants representing the linear relationship between absorbance and CDOM concentration, b2 and k2 are constants representing the linear relationship between CDOM fluorescence contribution and CDOM concentration in the three-dimensional fluorescence spectrum, and b3 and k3 are constants representing the linear relationship between fluorescence intensity and concentration of polycyclic aromatic hydrocarbons at the characteristic wavelength.

[0021] This invention also provides a polycyclic aromatic hydrocarbon (PAH) detection device, which achieves detection using the aforementioned PAH detection method based on ultraviolet fluorescence and absorption spectroscopy. The device has a simple structure and is easy to operate, comprising:

[0022] A miniature fiber optic spectrometer for scanning and acquiring absorption and fluorescence spectra, a controller for controlling the scanning mode of the miniature fiber optic spectrometer, an excitation selector, and an excitation light source, wherein the excitation selector includes a rotating disk and a color filter fixed on the rotating disk, the color filter being located in the output optical path of the excitation light source.

[0023] Specifically, the excitation source is a pulsed xenon lamp to ensure high light intensity under low voltage and low power consumption conditions. The output end of the xenon lamp is connected to an optical fiber, and a collimating lens is integrated at the optical fiber outlet to ensure that the excitation light is parallel light.

[0024] Specifically, the color filter includes three filters with different center wavelengths, namely 220nm, 250nm and 270nm.

[0025] Specifically, the absorption spectrum scanning range of the miniature fiber optic spectrometer is 200–400 nm.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The present invention eliminates the interference factors caused by CDOM by using absorption spectroscopy in combination, thereby improving the accuracy of detection.

[0028] (2) The device provided by the present invention uses a multi-band measurement method to replace the traditional single-band measurement, and at the same time realizes the scanning of both fluorescence spectrum and absorption spectrum through optical fiber and optical path switching, thereby achieving the purpose of in-situ detection. Attached Figure Description

[0029] Figure 1 A flowchart of the polycyclic aromatic hydrocarbon detection method based on ultraviolet fluorescence and absorption spectroscopy provided by the present invention;

[0030] Figure 2 This is a schematic diagram of the absorption spectrum of CDOM provided in this embodiment;

[0031] Figure 3 This is a schematic diagram of the three-dimensional fluorescence spectrum of CDOM provided in this embodiment;

[0032] Figure 4 This is a schematic diagram of the three-dimensional fluorescence spectrum of polycyclic aromatic hydrocarbons provided in this embodiment;

[0033] Figure 5 This is a schematic diagram of the polycyclic aromatic hydrocarbon detection device provided in this embodiment;

[0034] Figure 6 This is a schematic diagram of the excitation selector provided in this embodiment;

[0035] Figure 7 This is a verification graph showing the detection results of the polycyclic aromatic hydrocarbon (PAH) detection method. Detailed Implementation

[0036] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] like Figure 1 As shown, a method for detecting polycyclic aromatic hydrocarbons based on ultraviolet fluorescence and absorption spectroscopy includes:

[0038] Step 1: Obtain the ultraviolet absorption spectrum and the fluorescence emission spectrum of the water sample under ultraviolet light excitation. The polycyclic aromatic hydrocarbon pollutants targeted in this embodiment include: acenaphthene, naphthalene, phenanthrene, fluorene, anthracene, fluoranthene, and pyrene.

[0039] Step 2: Using the ultraviolet absorption spectrum obtained in Step 1, analyze the ultraviolet absorption spectrum using a pre-constructed multi-wavelength absorbance fitting model to output the corresponding CDOM concentration. Use a three-dimensional fluorescence spectrometer to scan and obtain the three-dimensional fluorescence spectrum of the CDOM concentration. Based on the obtained CDOM concentration and the corresponding three-dimensional fluorescence spectrum, construct a linear relationship and fit it to obtain the corresponding CDOM fluorescence spectrum. The multi-wavelength absorbance fitting model is constructed based on CDOM samples with typical concentration gradients in natural water bodies, and the absorbance of the CDOM samples is measured using an ultraviolet spectrophotometer.

[0040] Step 3: Subtract the CDOM fluorescence spectrum obtained in Step 2 from the fluorescence emission spectrum obtained in Step 1 to obtain a mixed fluorescence spectrum containing multiple polycyclic aromatic hydrocarbons;

[0041] Step 4: Based on the mixed fluorescence spectrum obtained in Step 3, the polycyclic aromatic hydrocarbons (PAHs) are compared with a pre-constructed standard spectral database based on the excitation and emission wavelengths of the mixed fluorescence spectrum, classified according to the number of rings, and the concentrations of various PAHs in the water sample are obtained. The standard spectral database includes three-dimensional fluorescence spectra of various PAH samples at different concentrations.

[0042] The concentration of cyclic aromatic hydrocarbons is calculated based on the fluorescence intensity and absorbance of the mixed fluorescence spectrum, using the following formula:

[0043]

[0044] In the formula, C PAH F represents the concentration of polycyclic aromatic hydrocarbons. total A represents the fluorescence intensity at the characteristic wavelength of polycyclic aromatic hydrocarbons. total denoted as absorbance at the characteristic wavelength of CDOM, b1 and k1 are constants representing the linear relationship between absorbance and CDOM concentration, b2 and k2 are constants representing the linear relationship between CDOM fluorescence contribution and CDOM concentration in the three-dimensional fluorescence spectrum, and b3 and k3 are constants representing the linear relationship between fluorescence intensity and concentration of polycyclic aromatic hydrocarbons at the characteristic wavelength.

[0045] Among them, CDOM samples with typical concentration gradients (0.1 mg / L-5 mg / L) of natural water bodies were prepared, and their absorbance was measured using a UV spectrophotometer to establish an absorbance fitting model:

[0046] A FA =K1C FA +b1

[0047] In the formula, A FA C represents the absorbance of CDOM. FA The concentration of CDOM, according to Figure 2 The absorption spectrum curves shown determine b1 and k1;

[0048] The three-dimensional fluorescence spectrum of CDOM was scanned using a three-dimensional fluorescence spectrometer to obtain the fluorescence contribution of CDOM under the concentration gradient, and a linear relationship was established:

[0049] F FA =K2C FA +b2

[0050] In the formula, F FA Fluorescence contributed to CDOM, C FA The concentration of CDOM, according to Figure 3 The three-dimensional fluorescence spectra shown determine b2 and k2;

[0051] Common polycyclic aromatic hydrocarbon (PAH) samples were prepared at varying concentration gradients. Their three-dimensional fluorescence spectra were scanned using a three-dimensional fluorescence spectrometer to obtain the spectral characteristics of PAHs with different ring numbers. Based on these characteristics, typical excitation wavelengths and characteristic emission wavelengths were selected, and a linear relationship was established.

[0052] F Nap =K3C Nap +b3

[0053] In the formula, F Nap The fluorescence of polycyclic aromatic hydrocarbons, C Nap The concentration of polycyclic aromatic hydrocarbons, according to Figure 4 The three-dimensional fluorescence spectroscopy was used to determine b3 and k3.

[0054] A polycyclic aromatic hydrocarbon (PAH) detection device is provided, which achieves detection using the PAH detection method based on ultraviolet fluorescence and absorption spectroscopy proposed in the above embodiments. The device has a simple structure and is easy to operate.

[0055] like Figure 5 and Figure 6 The sensor's control system first sends a command to the excitation selector 4, causing the stepper motor 5 of the excitation selector 4 to rotate to a designated position, so that the color filter 6 is aligned with the straight mirror 3. Then, it sends a command to the optical path switcher 17 to switch the optical path, connecting the optical fiber 14 and the optical fiber 18, switching to the fluorescence measurement mode, and setting the scanning range of the miniature fiber optic spectrometer to 300-400nm. At this time, the pulsed xenon lamp 1 is activated, and the light emitted by the pulsed xenon lamp 1 is transmitted through the optical fiber 2 to the collimating mirror 3, becoming parallel light. After passing through the color filter 6, unwanted wavelengths are filtered out, and the light irradiates the sample flow cell through the incident window 10. The collimating mirror 13 and the SMA905 interface are installed in the measurement window 12 in the perpendicular incident direction. The fluorescence is transmitted through the optical fiber 14 to the optical path switcher 17, and then through the optical fiber 18 to the miniature fiber optic spectrometer 19, completing the 300-400nm ultraviolet fluorescence emission spectrum measurement at a 220nm excitation wavelength.

[0056] After the measurement is completed, the control system sends another command to the excitation selector 4. The stepper motor 5 of the excitation selector 4 rotates to another designated position so that the color filter 7 is aligned with the straight mirror 3. The other settings remain unchanged, and the 300-400nm ultraviolet fluorescence emission spectrum measurement at excitation wavelengths of 250nm and 270nm is completed in sequence.

[0057] After all fluorescence measurements are completed, the sensor's control system first sends a command to the excitation selector 4. The stepper motor 5 of the excitation selector 4 rotates to the designated position, so that the through hole 9 is aligned with the straight mirror 3. Then, it sends a command to the optical path switcher 17 to switch the optical path, connecting the optical fiber 16 and the optical fiber 18, switching to the absorbance measurement mode, and setting the scanning range of the miniature fiber optic spectrometer to 200-400nm. The pulsed xenon lamp 1 is started, and the light emitted by the pulsed xenon lamp 1 is transmitted through the optical fiber 2 to the collimating mirror 3, becoming parallel light. It passes through the through hole 9 and directly illuminates the sample flow cell through the incident window 10. The collimating mirror 15 and the SMA905 interface are installed in the measurement window 11 facing the incident direction. The transmitted light is transmitted through the optical fiber 16 to the optical path switcher 17, and then through the optical fiber 18 to the miniature fiber optic spectrometer 19 to complete the 200-400nm ultraviolet absorption spectroscopy measurement. Based on the data obtained from the scan, the types and concentrations of various aromatic rings in the water sample are analyzed and output.

[0058] like Figure 7 As shown, this method can effectively compensate for the error caused by CDOM in the detection of polycyclic aromatic hydrocarbons, thus improving the accuracy of detection.

[0059] By adjusting the structure of the excitation selector, such as changing the center wavelength of the filter or adding new through-holes and filters, the measurement of new parameters can be achieved, thereby extending the sensor to the measurement of other organic pollutants and demonstrating good versatility.

Claims

1. A method for detecting polycyclic aromatic hydrocarbons based on ultraviolet fluorescence and absorption spectroscopy, characterized in that, include: Step 1: Obtain the ultraviolet absorption spectrum of the water sample and the fluorescence emission spectrum of the water sample under ultraviolet light excitation; Step 2: Using the ultraviolet absorption spectrum obtained in Step 1, analyze the corresponding CDOM fluorescence spectrum. The specific process is as follows: The ultraviolet absorption spectrum was analyzed using a pre-constructed multi-wavelength absorbance fitting model, and the corresponding CDOM concentration was output. The three-dimensional fluorescence spectrum of CDOM concentration was obtained using a three-dimensional fluorescence spectroscopy scanner. A linear relationship was constructed between the obtained CDOM concentration and the corresponding three-dimensional fluorescence spectrum, and the corresponding CDOM fluorescence spectrum was obtained by fitting. Step 3: Subtract the CDOM fluorescence spectrum obtained in Step 2 from the fluorescence emission spectrum obtained in Step 1 to obtain a mixed fluorescence spectrum containing multiple polycyclic aromatic hydrocarbons; Step 4: Based on the mixed fluorescence spectrum obtained in Step 3, perform multivariate fitting on various polycyclic aromatic hydrocarbons (PAHs) to obtain the types and concentrations of each PAH in the water sample. The concentrations of the PAHs are calculated based on the fluorescence intensity and absorbance of the mixed fluorescence spectrum, using the following formula: In the formula, This represents the concentration of polycyclic aromatic hydrocarbons. The fluorescence intensity at the characteristic wavelength of polycyclic aromatic hydrocarbons. The absorbance at the characteristic wavelength of CDOM. and A constant representing the linear relationship between absorbance and CDOM concentration. and Let be a constant representing the linear relationship between the fluorescence contribution of CDOM and the concentration of CDOM in a three-dimensional fluorescence spectrum. and This is a constant representing the linear relationship between fluorescence intensity and concentration of polycyclic aromatic hydrocarbons at a characteristic wavelength.

2. The method for detecting polycyclic aromatic hydrocarbons based on ultraviolet fluorescence and absorption spectroscopy according to claim 1, characterized in that, In step 4, the polycyclic aromatic hydrocarbons are compared with a pre-constructed standard spectral database based on the excitation and emission wavelengths of the mixed fluorescence spectrum, and classified according to the number of rings. The standard spectral database includes three-dimensional fluorescence spectra of various polycyclic aromatic hydrocarbon samples at different concentrations.

3. A polycyclic aromatic hydrocarbon (PAH) detection device, wherein detection is achieved by the PAH detection method based on ultraviolet fluorescence and absorption spectroscopy as described in any one of claims 1 to 2, characterized in that, The invention includes a miniature fiber optic spectrometer for scanning and acquiring absorption and fluorescence spectra, a controller for controlling the scanning mode of the miniature fiber optic spectrometer, an excitation selector, and an excitation light source. The excitation selector includes a rotating disk and a color filter fixed on the rotating disk, the color filter being located in the output optical path of the excitation light source.

4. The polycyclic aromatic hydrocarbon detection device according to claim 3, characterized in that, The color filter includes three filters with different center wavelengths, namely 220nm, 250nm and 270nm.

5. The polycyclic aromatic hydrocarbon detection device according to claim 3, characterized in that, The excitation source is a pulsed xenon lamp.

6. The polycyclic aromatic hydrocarbon detection device according to claim 3, characterized in that, The fluorescence spectral scanning range of the miniature fiber optic spectrometer is 300~400nm.

7. The polycyclic aromatic hydrocarbon detection device according to claim 3, characterized in that, The absorption spectral scanning range of the miniature fiber optic spectrometer is 200~400nm.

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