Device for detecting concentration of oil in water based on fluorescence lifetime difference

Abstract

The invention provides a fluorescence lifetime difference-based oil concentration detection device in water, and relates to the technical field of analysis and detection equipment, the device comprises a shell, the shell is provided with an accommodating cavity, and the accommodating cavity is internally provided with a moving mechanism; the test light path is located on one side of the moving mechanism, and the test light path comprises an excitation light path assembly and an emission light path assembly which are perpendicular to each other; the cuvette comprises a measuring cell for accommodating the measuring cuvette and a reference cell for accommodating the reference cuvette; the cuvette is connected with the moving mechanism and can move along a preset track under the driving of the moving mechanism, so that the test light path acts on the measurement cuvette or the reference cuvette; and the moving mechanism and the test light path are both in communication connection with the control system. According to the invention, the interference of the natural water CDOM on the measurement of the oil fluorescence signal in water is effectively eliminated, the natural water polluted by crude oil can be detected, and the measurement accuracy of the oil concentration in water is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of analytical and detection equipment, and in particular to an oil concentration detection device in water based on fluorescence lifetime difference. Background Art

[0002] Marine oil spill pollution is one of the important challenges faced by the marine ecological environment. With the increasing intensity of offshore oil and gas development in China, frequent mining activities have led to an increasing probability of oil spill accidents in underwater production facilities, making the detection of oil concentration in water more urgent.

[0003] Most of the oils entering the water body contain strong carcinogens such as polycyclic aromatic hydrocarbons, which will cause great harm to human health through the enrichment effect of the biological chain. Petroleum substances can enter the human body through breathing, skin contact, eating contaminated food, etc., thus affecting the normal functions of various organs of the human body and causing various diseases. According to investigations, children who are frequently exposed to petroleum pollution have a risk of acute leukemia that is 4 times higher than the average level, and the probability of suffering from acute non-lymphocytic leukemia is 7 times that of ordinary children. It can be seen that the problem of water quality oil pollution cannot be ignored.

[0004] The ultraviolet fluorescence method is widely used in the detection of oil concentration in water. Oil substances usually emit specific fluorescence signals under ultraviolet light irradiation. By detecting these fluorescence signals, the ultraviolet fluorescence method can accurately detect oil substances at low concentrations, has high sensitivity, and does not require complex sample pretreatment, making it suitable for detecting trace oil pollution in water bodies.

[0005] The applicant of the present invention has found that the prior art has at least the following technical problems:

[0006] The spectra of crude oil spills and CDOM are very close, and the spectral crosstalk between them will affect the accuracy of qualitative and quantitative analysis of oil in water. The prior art cannot exclude the interference of fluorescent substances such as CDOM in water on the fluorescence signal of oil in water, resulting in low measurement accuracy of the oil concentration in water.

[0007] Therefore, there is an urgent need for an oil concentration detection device in water based on fluorescence lifetime difference to solve the above technical problems. Summary of the Invention

[0008] The purpose of the present invention is to provide an oil concentration detection device in water based on fluorescence lifetime difference to solve the technical problems existing in the prior art, that is, the spectra of crude oil spills and CDOM are very close, and the spectral crosstalk between them will affect the accuracy of qualitative and quantitative analysis of oil in water. The prior art cannot exclude the interference of fluorescent substances such as CDOM in water on the fluorescence signal of oil in water, resulting in low measurement accuracy of the oil concentration in water. The many technical effects that can be produced by the preferred technical solutions among the many technical solutions provided by the present invention will be elaborated below.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] An oil concentration detection device in water based on fluorescence lifetime difference provided by the present invention includes a housing, the housing is provided with an accommodation cavity, and the following are arranged in the accommodation cavity:

[0011] A moving mechanism;

[0012] A test optical path, located on one side of the moving mechanism, the test optical path includes an excitation optical path component and an emission optical path component arranged perpendicular to each other;

[0013] A colorimetric cell, including a measurement cell for accommodating a measurement cuvette and a reference cell for accommodating a reference cuvette; the colorimetric cell is connected to the moving mechanism and can move along a predetermined track under the drive of the moving mechanism, so that the test optical path acts on the measurement cuvette or the reference cuvette;

[0014] A control system, the moving mechanism and the test optical path are both communicatively connected to the control system.

[0015] Preferably, the excitation optical path component includes a first convex lens, a band-pass excitation filter, a second convex lens and an excitation light source arranged in sequence, and the first convex lens is arranged close to the colorimetric cell;

[0016] The emission optical path component includes a third convex lens, a band-pass emission filter, a fourth convex lens and a photodetector arranged in sequence, and the third convex lens is arranged close to the colorimetric cell;

[0017] The excitation light source and the photodetector are both electrically connected to the control system.

[0018] Preferably, the distance between the photodetector and the fourth convex lens is less than the focal length of the third convex lens.

[0019] Preferably, the photodetector includes a SiPM or a PMT.

[0020] Preferably, the excitation light source includes an ultraviolet light-emitting diode and a semiconductor refrigeration device.

[0021] Preferably, the housing includes an upper housing and a lower housing that are snap-connected to each other. An inlet corresponding to the colorimetric cell is opened at the top of the upper housing, and a hatch is provided at the inlet.

[0022] Preferably, a surrounding shell protruding from the peripheral edge of the inlet is arranged around the inlet, and the hatch is arranged on the surrounding shell.

[0023] Preferably, the control system includes:

[0024] A circuit board, the circuit board including a wireless communication module;

[0025] A battery holder, connected to the circuit board and containing a battery therein.

[0026] Preferably, a display screen and control buttons are provided on the surface of the housing, and both the display screen and the control buttons are electrically connected to the control system.

[0027] Preferably, the moving mechanism includes a stepper motor and a ball screw system. The stepper motor is electrically connected to the control system and is used to drive the ball screw system to move; the cuvette is connected to the ball screw system.

[0028] The device for detecting the concentration of oil in water based on the fluorescence lifetime difference provided by the present invention sets the test optical path to include an excitation optical path component and an emission optical path component that are perpendicularly arranged to each other. The cuvette includes a measurement cell for accommodating a measurement cuvette and a reference cell for accommodating a reference cuvette; and the cuvette is connected to the moving mechanism and can move along a predetermined track under the drive of the moving mechanism, so that the test optical path acts on the measurement cuvette or the reference cuvette. By introducing the reference cell, the measurement interference of the natural water body CDOM on the fluorescence signal of the oil in water is effectively eliminated, the natural water body contaminated by crude oil can be detected, and the measurement accuracy of the concentration of oil in water is improved. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 is the schematic diagram of the fluorescence decay curves of normalized oil in water and CDOM;

[0031] Figure 2 is the structural schematic diagram of the device for detecting the concentration of oil in water based on the fluorescence lifetime difference of the present invention;

[0032] Figure 3 is Figure 2 the internal structural schematic diagram of;

[0033] Figure 4 is Figure 2 the exploded structural schematic diagram of

[0034] Figure 5 is the exploded structural schematic diagram of the optical path component in the device for detecting the concentration of oil in water based on the fluorescence lifetime difference of the present invention;

[0035] In the figure: 1. Housing; 11. Upper housing; 12. Lower housing; 13. Feed inlet; 14. Hatch cover; 15. Enclosure;

[0036] 2. Moving mechanism;

[0037] 3. Test optical path; 31. Excitation optical path component; 311. First convex lens; 312. Band-pass excitation filter; 313. Second convex lens; 314. Excitation light source; 32. Emission optical path component; 321. Third convex lens; 322. Band-pass emission filter; 323. Fourth convex lens; 324. Photoelectric detector;

[0038] 4. Colorimetric cell; 41. Measurement cell; 42. Reference cell;

[0039] 51. Measurement colorimetric cuvette; 52. Reference colorimetric cuvette;

[0040] 6. Control system; 61. Circuit board; 62. Battery holder;

[0041] 7. Battery; 8. Display screen; 9. Control button; 10. Wireless communication module. Detailed implementation manners

[0042] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other implementation manners obtained by those of ordinary skill in the art without making creative efforts based on the embodiments of the present invention fall within the scope protected by the present invention.

[0043] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "lateral", "length", "width", "height", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "side", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0044] In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "mounted", "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] The spectrum of crude oil spills is very close to that of CDOM, and the spectral crosstalk between them will affect the accuracy of qualitative and quantitative analysis of oil in water. The existing technology cannot exclude the interference of fluorescent substances such as CDOM in water on the fluorescence signal of oil in water, which is also the biggest interference factor for accurate quantification of crude oil in actual sea areas at present. Figure 1 It is the schematic diagram of the fluorescence decay curves of normalized oil in water and CDOM. As Figure 1 shown, the fluorescence lifetime of CDOM in natural water excited by 280nm light and emitting fluorescence at 340nm is usually several nanoseconds, while the fluorescence lifetime of crude oil in water is more than 20 nanoseconds. The significant difference in the fluorescence lifetimes of oil in water and CDOM provides the possibility to exclude the fluorescence crosstalk of CDOM on oil in water. For this reason, a device for detecting the concentration of oil in water based on fluorescence lifetime difference with self-calibration deduction and time resolution ability is proposed.

[0046] Figure 2 It is the structural schematic diagram of this embodiment. Figure 3 It is Figure 2 the internal structural schematic diagram of Figure 2 and Figure 3 shown. This embodiment provides a device for detecting the concentration of oil in water based on fluorescence lifetime difference, which includes a housing 1. The housing 1 is provided with an accommodation cavity, and a moving mechanism 2, a test optical path 3, a cuvette 4, a colorimetric dish and a control system 6 are arranged in the accommodation cavity.

[0047] The housing 1 in this embodiment adopts a square structure, and rounded corners are arranged on the periphery of the square housing. While being simple and beautiful, the internal accommodation cavity has a larger space, and the peripheral rounded corners are convenient for use, with stronger practicability.

[0048] The moving mechanism 2 includes a stepping motor and a ball screw system. The moving mechanism 2 is communicatively connected with the control system 6. The test optical path 3 is arranged on one side of the moving mechanism 2 for convenient testing, and the test optical path 3 is communicatively connected with the control system 6. Specifically, the test optical path 3 includes an excitation optical path component 31 and an emission optical path component 32 arranged perpendicular to each other, and through the cooperation of the excitation optical path component 31 and the emission optical path component 32, it is used to detect the sample in the cuvette 4.

[0049] Figure 4 It is the exploded structural schematic diagram of this embodiment. As Figure 4 shown, the cuvette 4 includes a measurement cell 41 for accommodating the measurement colorimetric dish 51 and a reference cell 42 for accommodating the reference colorimetric dish 52.

[0050] The colorimetric cell 4 in this embodiment has an overall V-shaped structure. Square windows are opened on both the measurement cell 41 and the reference cell 42 to facilitate the passage of the test optical path 3. The colorimetric cell 4 is connected to the moving mechanism 2 and can move along a predetermined track under the drive of the moving mechanism 2, so that the test optical path 3 acts on the measurement cuvette 51 or the reference cuvette 52.

[0051] Specifically, the colorimetric cell 4 in this embodiment is connected to a ball screw system. The control system 6 controls the stepping motor to drive the ball screw system to move, driving the measurement cell 41 and the reference cell 42 to move parallel along a predetermined track, so that the fluorescence signal of the sample is continuously or alternately detected by the fluorescence detector.

[0052] The control system 6 in this embodiment includes a circuit board 61 and a battery holder 62. The circuit board 61 is used for signal acquisition, arithmetic processing, and communication. Specifically, the circuit board 61 includes a wireless communication module 10, a data acquisition module, and a data processing module. Among them, the wireless communication module 10, the data acquisition module, and the data processing module are all welded on the circuit board 61.

[0053] The wireless communication module 10 in this embodiment can be wirelessly connected to a mobile phone through Bluetooth, and information such as the oil concentration in water can be viewed on the mobile phone APP; the data acquisition module uses a TCSPC (Time-Correlated Single Photon Counting) module to collect the fluorescence decay curve and extract the fluorescence lifetime data through an exponential fitting method; the data processing module compares the fluorescence lifetime data with a known standard curve to calculate the oil concentration in water.

[0054] The battery holder 62 is connected to the circuit board 61. A battery 7 is provided inside the battery holder 62. The battery 7 in this embodiment includes a rechargeable lithium battery, specifically an 18650 lithium battery pack, which is used to supply power to the device.

[0055] As an optional implementation method, Figure 5 is an exploded structural schematic diagram of the optical path assembly in this embodiment. As Figure 5 shown, the excitation optical path assembly 31 includes a first convex lens 311, a band-pass excitation filter 312, a second convex lens 313, and an excitation light source 314 arranged in sequence. The first convex lens 311 is arranged close to the colorimetric cell 4, and the excitation light source 314 is electrically connected to the battery holder 62.

[0056] The emission optical path assembly 32 includes a third convex lens 321, a band-pass emission filter 322, a fourth convex lens 323, and a photodetector 324 arranged in sequence. The third convex lens 321 is arranged close to the colorimetric cell 4; the photodetector 324 is electrically connected to the control system 6.

[0057] By arranging a first convex lens 311, a band-pass excitation filter 312, a second convex lens 313, and an excitation light source 314 in sequence from the colorimetric cuvette to the far end in the excitation optical path, and arranging a third convex lens 321, a band-pass emission filter 322, a fourth convex lens 323, and a photodetector 324 in sequence from the colorimetric cuvette to the far end in the emission optical path. The first convex lens 311 is used to converge the light passing through the band-pass excitation filter 312, so that a light spot of appropriate size can be formed in the colorimetric cuvette to excite the substance to be measured to emit fluorescence; the second convex lens 313 and the third convex lens 321 are used to convert the light into parallel light; the fourth convex lens 323 is used to converge the light passing through the second band-pass emission filter 322, so that a light spot of appropriate size can be formed on the photosensitive surface of the photodetector 324.

[0058] Specifically, the foci of the first convex lens 311 and the third convex lens 321 in this embodiment are both at the central position of the colorimetric cuvette. It can be understood that the colorimetric cuvette here can be the measurement colorimetric cuvette 51 or the reference colorimetric cuvette 52. The distance between the photodetector 324 and the fourth convex lens 323 is less than the focal length of the third convex lens 321, so that the light passing through the fourth convex lens 323 can form a light spot on the photodetector 324, and the area of the light spot matches the photosensitive area of the photodetector 324.

[0059] As an optional implementation manner, the photodetector 324 in this embodiment includes a SiPM or a PMT (photomultiplier tube). By setting the photodetector 324 as a SiPM or a PMT with time resolution ability, it is used to convert the optical signal into an electrical signal and transmit it to the circuit board 61.

[0060] In this embodiment, the gating circuit is mounted on the circuit board 61, and can regulate the working states of the light source and the photodetector with nanosecond-level response. By introducing the gating circuit, according to the different fluorescence lifetimes of oil in water and CDOM, the lighting time of the excitation light source and the fluorescence collection time are controlled from the time dimension. After the excitation light source emits a pulse, the gating circuit will control the photodetector 324 to start or stop collecting fluorescence signals within a specific time window. By selectively collecting the fluorescence signals within a certain time period and transmitting them to the signal acquisition and calculation circuit board 61, the circuit board 61 is used to calculate the oil concentration in water, and a concentration algorithm is carried to accurately calculate the oil concentration in water.

[0061] The circuit board 61 in this embodiment is fixed at the bottom of the accommodation cavity of the housing 1 and is connected to the end of the photodetector 324 away from the photosensitive surface.

[0062] For example: a pulsed light-emitting diode with a wavelength of 280 nm is used, and the pulse width is set to 2 ns. At 340 nm, a SiPM or a PMT is used to collect fluorescence signals, and the gating time of the SiPM or the PMT is set to 20 - 30 ns to ensure effective capture of the oil fluorescence signals in water and avoid the fluorescence signals of CDOM.

[0063] As an alternative embodiment, the excitation light source 314 includes an ultraviolet light-emitting diode and a semiconductor refrigeration device. Specifically, the excitation light source 314 includes a deep ultraviolet LED or a deep ultraviolet DPSS laser and a semiconductor refrigeration device.

[0064] As an alternative embodiment, the housing 1 includes an upper housing 11 and a lower housing 12 which are snap-connected to each other. A feeding port 13 corresponding to the colorimetric cell 4 is provided at the top of the upper housing 11, and a hatch cover 14 is provided at the feeding port 13 for light shielding. During use, the measurement cuvette 51 and the reference cuvette 52 are respectively inserted into the measurement cell 41 and the reference cell 42 through the feeding port 13.

[0065] Specifically, a surrounding shell 15 protruding from the peripheral edge of the feeding port 13 is provided around the feeding port 13 of the present embodiment, the hatch cover 14 is arranged on the surrounding shell 15, and the hatch cover 14 is detachably connected to the surrounding shell 15.

[0066] As an alternative embodiment, a display screen 8 and control buttons 9 are provided on the surface of the housing 1, and both the display screen 8 and the control buttons 9 are electrically connected to the control system 6.

[0067] For this device for detecting the oil concentration in water based on the fluorescence lifetime difference, firstly, a reference measurement cell is introduced to subtract the background signal value of the fluorescence interfering substances, improving the quantitative measurement ability of the oil concentration in water. Secondly, using a SiPM or a photomultiplier tube as the photodetector ensures the sensitivity to the detected substances. At the same time, a gating circuit is introduced in the circuit control to accurately control the lighting time of the light source and the fluorescence collection time from the time dimension. The gating circuit will control the photodetector to start or stop collecting fluorescence signals within a specific time window after the excitation light source emits a pulse. The fluorescence lifetime of CDOM in natural water excited at 280 nm and emitting fluorescence at 340 nm is usually several nanoseconds, and the fluorescence lifetime of crude oil in water is more than 20 nanoseconds. Utilizing the fluorescence lifetime difference between crude oil and CDOM, the fluorescence signals within a certain time period are selectively collected and transmitted to the signal acquisition and operation circuit board to calculate the oil concentration in water. By this method, the interference caused by the spectral overlap between crude oil and CDOM is further reduced, greatly improving the quantitative measurement ability of the oil concentration in water.

[0068] The following is a specific description through two embodiments:

[0069] Embodiment 1

[0070] In the oil concentration detection device in water based on fluorescence lifetime difference in this embodiment, a PMT is used as the photodetector, which is an end window with a double-alkali cathode, the cathode size is 8 mm, the LED wavelength is 280 nm, and the spectral half-width at half maximum is 12 nm. The excitation filter has a wavelength of 280 nm and a half-width at half maximum of 20 nm, and the emission filter has a central wavelength of 340 nm and a half-width at half maximum of 40 nm.

[0071] Fluorescent substances CDOM in natural water bodies, including protein-like and humic-like CDOM, generally have fluorescence lifetimes below 10 ns at 280 nm / 340 nm and 365 nm / 450 nm, while the fluorescence lifetime of crude oil is between 20 ns and 30 ns. A pulsed light-emitting diode with a wavelength of 280 nm is used, and the pulse width is set to 2 ns. A PMT is used to collect the fluorescence signal at 340 nm, and the gating time of the PMT is set to 20 - 30 ns to ensure effective capture of the oil fluorescence signal in water and avoid the fluorescence signal of CDOM. The data acquisition system uses a TCSPC (time-correlated single photon counting) module to collect the fluorescence decay curve and extracts the fluorescence lifetime data through an exponential fitting method. The data processing system compares the fluorescence lifetime data with a known standard curve to calculate the oil concentration in water.

[0072] For the detection of port seawater samples, the fluorescence spectrophotometry method in Part 4: Seawater Analysis of GB 17378.4 - 2007 "Marine Monitoring Specifications", SeaOWL UV-A, and Trios EnviroFlu-HC are respectively adopted. For the device of the present invention, port seawater and a natural water body sample not contaminated by crude oil are respectively placed in two square cuvettes, and then the cuvettes are successively placed in the measurement cell and the reference cell. The measurement chamber cover is covered, the power supply is turned on, and the device starts to measure.

[0073] Experimental results:

[0074] Using the national standard method to detect the oil concentration in port seawater is 2.35 mg / L, the oil concentration measured by Seaowl UV-A is 3.27 mg / L, and the oil concentration measured by Trios EnviroFlu-HC is 3.74 mg / L. The measurement results of the two commercial sensors deviate from the national standard method by 39.1% and 59.1% respectively. In contrast, the oil concentration measured by the device of the present invention is 2.29 mg / L, and the measurement result only differs from the national standard method by 2.55%. The results show that the device of the present invention can effectively avoid the interference of fluorescent substances such as CDOM in water and directly detect the oil concentration in water without pretreatment of the sample.

[0075] Example 2

[0076] The difference between this embodiment and Embodiment 1 lies in that: the PMT has a double-alkali photocathode window, and the effective cathode diameter is 25 mm. The wavelength of the LED is 275 nm, and the spectral half-width is 8 nm. The wavelength of the excitation filter is 280 nm, and the half-width is 20 nm. The center wavelength of the emission filter is 350 nm, and the half-width is 50 nm.

[0077] The port seawater samples were collected and detected by fluorescence spectrophotometry, SeaOWL UV-A, and Trios EnviroFlu-HC in Part 4: Seawater Analysis of the GB 17378.4-2007 "Marine Monitoring Specifications". For the device of the present invention, the port seawater and the natural water sample not contaminated by crude oil were respectively placed in two square cuvettes, and then the cuvettes were successively placed in the measurement cell and the reference cell. The measurement chamber cover was covered, the power supply was turned on, and the device was started for measurement.

[0078] Experimental results:

[0079] The oil concentration in the port seawater detected by the national standard method is 1.93 mg / L. The oil concentration measured by the SeaOWL UV-A oil fluorescence sensor in water is 2.52 mg / L, and the oil concentration measured by the Trios EnviroFlu-HC is 2.61 mg / L. The deviations of the measurement results of the two commercial sensors compared with the national standard method are 30.1% and 35.2% respectively. In contrast, the oil concentration measured by the device of the present invention is 1.89 mg / L, and the measurement result only differs from the national standard method by 2.07%. The results show that the device of the present invention can effectively avoid the interference of fluorescent substances such as CDOM in water and directly detect the oil concentration in water without pretreatment of the sample.

[0080] As described above, the above are only the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An oil concentration detection device in water based on fluorescence lifetime difference, characterized in that, Comprising a housing, the housing is provided with a receiving cavity, and the receiving cavity is provided with: A moving mechanism; A test optical path, located on one side of the moving mechanism, the test optical path comprising an excitation optical path assembly and an emission optical path assembly arranged perpendicular to each other; A colorimetric cell, comprising a measurement cell for accommodating a measurement cuvette and a reference cell for accommodating a reference cuvette; the colorimetric cell is connected to the moving mechanism and can move along a predetermined track under the drive of the moving mechanism so that the test optical path acts on the measurement cuvette or the reference cuvette; A control system, the moving mechanism and the test optical path are both communicatively connected to the control system.

2. The device for detecting the concentration of oil in water based on fluorescence lifetime difference according to claim 1, characterized in that: The excitation optical path assembly comprises a first convex lens, a band-pass excitation filter, a second convex lens and an excitation light source arranged in sequence, and the first convex lens is arranged close to the colorimetric cell; The emission optical path assembly comprises a third convex lens, a band-pass emission filter, a fourth convex lens and a photodetector arranged in sequence, and the third convex lens is arranged close to the colorimetric cell; The excitation light source and the photodetector are both electrically connected to the control system.

3. The oil concentration detection device in water based on fluorescence lifetime difference according to claim 2, wherein, The distance between the photodetector and the fourth convex lens is less than the focal length of the third convex lens.

4. The oil concentration detection device in water based on fluorescence lifetime difference according to claim 2 or 3, characterized in that, The photodetector comprises a SiPM or a PMT.

5. The oil concentration detection device in water based on fluorescence lifetime difference according to claim 2 or 3, characterized in that, The excitation light source comprises an ultraviolet light-emitting diode and a semiconductor refrigeration device.

6. A device for detecting the oil concentration in water based on fluorescence lifetime difference according to any one of claims 1-3, characterized in that, The housing comprises an upper housing and a lower housing which are snap-connected to each other. An inlet corresponding to the colorimetric cell is opened at the top of the upper housing, and a hatch is arranged at the inlet.

7. The oil concentration detection device in water based on fluorescence lifetime difference according to claim 6, characterized in that, A surrounding shell protruding from the peripheral edge of the inlet is arranged around the inlet, and the hatch is arranged on the surrounding shell.

8. A device for detecting the oil concentration in water based on fluorescence lifetime difference according to any one of claims 1-3, characterized in that, The control system comprises: A circuit board, the circuit board comprising a wireless communication module; A battery holder, connected to the circuit board and internally provided with a battery.

9. A device for detecting the oil concentration in water based on fluorescence lifetime difference according to any one of claims 1 to 3, characterized in that, A display screen and control buttons are arranged on the surface of the housing, and the display screen and the control buttons are both electrically connected to the control system.

10. A device for detecting the oil concentration in water based on the difference in fluorescence lifetime according to any one of claims 1-3, characterized in that, The moving mechanism comprises a stepping motor and a ball screw system. The stepping motor is electrically connected to the control system and is used to drive the ball screw system to move; the colorimetric cell is connected to the ball screw system.

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