QCM sensor detection system

Abstract

The utility model discloses a QCM sensor detection system which comprises a machine body, a dynamic gas distribution enrichment module, a QCM sensor detection module, a control module and a power supply module, and the dynamic gas distribution enrichment module, the QCM sensor detection module, the control module and the power supply module are all installed on the machine body; the dynamic gas distribution enrichment module is connected with the QCM sensor detection module through a gas circuit; and the power supply module and the control module are connected with the dynamic gas distribution enrichment module and the QCM sensor detection module through wires and are used for power supply and control.

Description

Technical Field

[0001] The utility model relates to the technical field of detection, in particular to a QCM sensor detection system. Background Art

[0002] Gas, as a kind of marker, can be used in various detection scenarios. With the development of science and technology, there are higher requirements for gas detection technology in the fields of environmental monitoring, food safety, medical detection, etc. At present, gas detection technology mainly relies on laboratory instrument analysis methods, such as gas chromatography-mass spectrometry, ion mobility spectrometry, etc. Although these detection technologies have extremely high detection accuracy and selectivity, they have problems such as high equipment price, complex operation steps, time-consuming and laborious, and cannot perform gas detection in real time and quickly. The electronic nose device based on the metal oxide semiconductor (MOS) sensor array can realize sample detection quickly and efficiently, but the MOS sensor has the problems of requiring a high-temperature working environment and poor selectivity. The QCM sensor detection system based on the quartz crystal microbalance (QCM) sensor can realize rapid detection of samples at room temperature and has extremely high detection accuracy.

[0003] The QCM sensor has a mass-sensitive characteristic, which converts the micro mass change generated by odor molecules adsorbed on the electrode surface into a frequency change to reflect sample information, and the detection accuracy can reach the nanogram level. The Sauerbrey equation explains the basic principle of the QCM sensor. There is a corresponding linear relationship between the frequency change of the quartz crystal and the mass change adsorbed on its surface:

[0004]

[0005] Where Δf is the change amount of the resonant frequency of the quartz crystal, and the negative sign represents a negative correlation. f 0 is the inherent oscillation frequency of the quartz crystal, A is the effective working area of the quartz crystal resonance, μ q is the shear modulus of the quartz crystal, ρ q is the density of the quartz crystal, m is the mass of the quartz crystal, and Δm is the change amount of the mass on the surface of the quartz crystal electrode. When Δm / m << 1, the above formula is the Sauerbrey equation.

[0006] The QCM sensor needs to be modified by preparing sensitive materials to have characteristics such as high selectivity and high sensitivity. In addition, in order to improve the detection performance of the QCM detection system, it is also necessary to design modules such as the gas distribution system, temperature, and humidity control. Summary of the Utility Model

[0007] To this end, the present utility model proposes a QCM sensor detection system, which can achieve rapid detection of the volatile odor of a sample to be measured under room temperature conditions, and has the advantages of high sensitivity, good selectivity, and small temperature and humidity interference.

[0008] To achieve the purpose of the present utility model, the following technical solutions are adopted:

[0009] A QCM sensor detection system includes a body, a dynamic gas distribution and enrichment module, a QCM sensor detection module, a control module, and a power supply module, where: the dynamic gas distribution and enrichment module, the QCM sensor detection module, the control module, and the power supply module are all installed on the body; the dynamic gas distribution and enrichment module is connected to the QCM sensor detection module through a gas path; the power supply module and the control module are connected to the dynamic gas distribution and enrichment module and the QCM sensor detection module through wires for power supply and control.

[0010] The QCM sensor detection system described above, where: the dynamic gas distribution and enrichment module includes a gas source balance gas path, a sample volatile odor enrichment gas path, a low-flow baseline acquisition gas path, a humidity control gas mixing and detection gas path, and a high-flow cleaning gas path.

[0011] The QCM sensor detection system described above, where: the gas flow path of the gas source balance gas path includes: nitrogen gas flows out from the main valve of the nitrogen gas cylinder, and successively passes through the input port and output port of the pressure reducing valve, the second port and the third port of the first two-way three-way solenoid valve, the second port and the third port of the second two-way three-way solenoid valve, the filter, and then is discharged into the air.

[0012] The QCM sensor detection system described above, where: the gas flow path of the sample volatile odor enrichment gas path includes: nitrogen gas flows out from the main valve of the nitrogen gas cylinder, and successively passes through the input port and output port of the pressure reducing valve, the second port and the first port of the first two-way three-way solenoid valve, the input port and output port of the first mass flow controller, the second port and the third port of the fourth two-way three-way solenoid valve, the input port and output port of the sample chamber, the third port and the second port of the fifth two-way three-way solenoid valve, and the input port of the aluminum foil gas sampling bag.

[0013] The QCM sensor detection system described above, where: the gas flow path of the low-flow baseline acquisition gas path includes: nitrogen gas flows out from the main valve of the nitrogen gas cylinder, and successively passes through the input port and output port of the pressure reducing valve, the second port and the third port of the first two-way three-way solenoid valve, the second port and the first port of the second two-way three-way solenoid valve, the input port and output port of the second mass flow controller, the third port and the second port of the third two-way three-way solenoid valve, the input port and output port of the gas detection chamber, the filter, and then is discharged into the air.

[0014] The described QCM sensor detection system, wherein: The airflow path of the humidity control gas mixing detection gas circuit includes: Nitrogen gas flows out from the main valve of the nitrogen gas cylinder, and successively passes through the input port and output port of the pressure reducing valve, the second port and the first port of the first two-way three-way solenoid valve, the input port and output port of the first mass flow controller, the second port and the first port of the fourth two-way three-way solenoid valve, the input port and output port of the electrolyte cell, the first port and the second port of the fifth two-way three-way solenoid valve, the input port and output port of the aluminum foil gas collection bag, the first port and the second port of the third two-way three-way solenoid valve, the input port and output port of the gas detection chamber, and the filter, and then is discharged into the air.

[0015] The described QCM sensor detection system, wherein: The airflow path of the high-flow cleaning gas circuit includes: Nitrogen gas flows out from the main valve of the nitrogen gas cylinder, and successively passes through the input port and output port of the pressure reducing valve, the second port and the third port of the first two-way three-way solenoid valve, the second port and the first port of the second two-way three-way solenoid valve, the input port and output port of the second mass flow controller, the third port and the second port of the third two-way three-way solenoid valve, the input port and output port of the gas detection chamber, and the filter, and then is discharged into the air.

[0016] The described QCM sensor detection system, wherein: The QCM detection module includes a gas detection chamber, a constant temperature heating table, a QCM sensor, a crystal oscillator test box, and a quartz crystal microbalance. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the QCM sensor detection system;

[0018] Figure 2 It is a wiring diagram of the hardware circuit of the detection system;

[0019] Figure 3 It is a diagram of the composite material modification on the surface of the QCM sensor electrode;

[0020] Figure 4 It is an equivalent circuit model diagram of the AT-type quartz crystal resonator;

[0021] Figure 5 It is a software interface diagram of the control module;

[0022] Figure 6 It is a response curve diagram of the detection system for detecting the volatile odor of the sample.

[0023] Figure 7 It is an overall schematic diagram of the QCM sensor detection system. Detailed Implementation Modes

[0024] The following combines with the attached Figure 1-7, a detailed description of the specific embodiments of the present utility model will be given. The described embodiments are exemplary and are only used to explain the present utility model and should not be construed as a limitation to the present utility model. Obviously, the embodiments described in the present utility model are only a part of the embodiments of the present utility model, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in the present utility model without creative efforts belong to the scope of protection of the present utility model.

[0025] As described in this specification, "an embodiment" or "some embodiments" etc. mean that in one or more embodiments of the present utility model, specific features, structures or characteristics described in combination with this embodiment are included. Thus, in this specification, the terms "include", "comprise", "have" and their variants all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0026] As Figure 1 shown, the QCM sensor detection system includes a body (not shown in the figure), a dynamic gas distribution and enrichment module, a QCM sensor detection module, a control module and a power supply module. Among them: the dynamic gas distribution and enrichment module, the QCM sensor detection module, the control module and the power supply module are all installed on the body; the gas source of this system is high-purity nitrogen, which is compressed and stored in a steel cylinder, and the dynamic gas distribution and enrichment module and the QCM sensor detection module are connected together through a silica gel gas pipe; the power supply module and the control module are connected to the dynamic gas distribution and enrichment module and the QCM sensor detection module through wires, playing the functions of power supply and control. As Figure 7 shown, the gas path part and the circuit part of the detection system are designed independently of each other and are located in the upper layer and the lower layer of the device respectively. Separating the gas path part and the circuit part can avoid mutual influence and reduce the failure rate of the detection system. When the system operates to perform sample detection, volatile gases to be detected in the gas path and factors such as moisture in the humidity control scheme may cause faults in the circuit, resulting in a short circuit of the detection system or even damage to components; due to the existence of the power supply module, the heat dissipation of the circuit part is relatively large. Separating it from the gas path part can prevent the interference of additional temperature field factors on sample detection. The open design of the system is also considered for this reason; in addition, separating the gas path and the circuit is beneficial to the maintenance and repair of the detection system, and the circuit wiring is more standardized, neat, beautiful and practical.

[0027] The described dynamic gas distribution and enrichment module includes a gas source balance gas path, a sample volatile odor enrichment gas path, a low-flow baseline acquisition gas path, a humidity control mixed gas detection gas path and a high-flow cleaning gas path.

[0028] The air source balance gas path is to prevent device damage caused by airflow impact due to the system being in a negative pressure state. Nitrogen gas flows out from the main valve of nitrogen gas cylinder 1, and successively passes through the input port and output port of pressure reducing valve 2, the second port and third port of the first two-way three-way solenoid valve 3, the second port and third port of the second two-way three-way solenoid valve 12, and filter 11, and then is discharged into the air.

[0029] The sample volatilization odor enrichment gas path is for preparing the detection sample. According to the volatility of the detection sample, the present utility model selects an aluminum foil gas sampling bag 9 with an appropriate capacity and sets the flow rate of the first mass flow controller 4, so as to determine the time for enriching and preparing the detection sample. First, the sample is placed into the sample chamber 7, the input valve of the aluminum foil gas sampling bag 9 is opened by rotating counterclockwise by 180°, and it is confirmed that the output valve of the gas sampling bag 9 is in the closed state. Nitrogen gas flows out from the main valve of nitrogen gas cylinder 1, and successively passes through the input port and output port of pressure reducing valve 2, the second port and first port of the first two-way three-way solenoid valve 3, the input port and output port of the first mass flow controller 4, the second port and third port of the fourth two-way three-way solenoid valve 5, the input port and output port of the sample chamber 7, the third port and second port of the fifth two-way three-way solenoid valve 8, and the input port of the aluminum foil gas sampling bag 9, so as to enrich the sample odor in the gas sampling bag 9.

[0030] Before sample detection, baseline acquisition is required to eliminate the interference of system factors such as airflow disturbance. For this purpose, the present utility model sets up a low-flow baseline acquisition gas path. In addition, to ensure the consistency of detection conditions, the second mass flow controller 13 is set to the low-flow mode (flow rate ≤ 1000 ml / min), which is consistent with the flow rate range of the first mass flow controller 4. Nitrogen gas flows out from the main valve of nitrogen gas cylinder 1, and successively passes through the input port and output port of pressure reducing valve 2, the second port and third port of the first two-way three-way solenoid valve 3, the second port and first port of the second two-way three-way solenoid valve 12, the input port and output port of the second mass flow controller 13, the third port and second port of the third two-way three-way solenoid valve 14, the input port and output port of the gas detection chamber 16, and filter 19, and then is discharged into the air.

[0031] Humidity control and mixed gas detection gas path. In the present utility model, an electrolyte cell (the humidity corresponding to the headspace vapor of different saturated salt solutions is different, see Table 1) is introduced into the sample detection gas path for humidity control to verify the performance of the system against humidity interference. Rotate the output valve of the aluminum foil gas sampling bag 9 counterclockwise by 180°. The nitrogen gas flow is released from the main valve of the nitrogen gas cylinder 1 and successively passes through the input port and output port of the pressure reducing valve 2, the second port and the first port of the first two-way three-way solenoid valve 3, the input port and output port of the first mass flow controller 4, the second port and the first port of the fourth two-way three-way solenoid valve 5, the input port and output port of the electrolyte cell 6, the first port and the second port of the fifth two-way three-way solenoid valve 8, the input port and output port of the aluminum foil gas sampling bag 9, the first port and the second port of the third two-way three-way solenoid valve 14, the input port and output port of the gas detection chamber 16, and the filter 19, and then is discharged into the air.

[0032] After the sample detection is completed, in order to desorb the odor molecules from the sensor more quickly, a high-flow cleaning gas path is set. Set the second mass flow controller 13 to the high-flow mode (flow rate ≤ 3000 ml / min). The nitrogen gas flow is released from the main valve of the nitrogen gas cylinder 1 and successively passes through the input port and output port of the pressure reducing valve 2, the second port and the third port of the first two-way three-way solenoid valve 3, the second port and the first port of the second two-way three-way solenoid valve 12, the input port and output port of the second mass flow controller 13, the third port and the second port of the third two-way three-way solenoid valve 14, the input port and output port of the gas detection chamber 16, and the filter 19, and then is discharged into the air.

[0033] The QCM detection module includes a gas detection chamber 16, a constant temperature heating table 17, a QCM sensor 18, a crystal oscillator test box 15, and a quartz crystal microbalance 20. The QCM sensor 18 is installed inside the gas detection chamber 16. The gas detection chamber 16 is placed on the constant temperature heating table 17. The constant temperature heating table 17 is used for detecting temperature control. The QCM sensor 18, the crystal oscillator test box 15, and the quartz crystal microbalance 20 are electrically connected in sequence. The crystal oscillator test box 15 is used to drive the QCM sensor 18 to generate an oscillation signal. Combining with the frequency measuring instrument of the quartz crystal microbalance 20, the frequency change of the QCM sensor 18 can be detected in real time, so as to reflect the information of the sample to be measured.

[0034] As Figure 3As shown, the QCM sensor 18 is modified with a PVC / ZIF-8@MIPs composite sensitive material. ZIF-8 is a typical MOF 23 material with advantages such as good thermal stability, high porosity, and large specific surface area. MIPs 24 have high selectivity and affinity for the template molecule (target molecule), enabling selective adsorption of the target molecule. Polyvinyl chloride (PVC) 22 is an inert soluble polymer that can be used as an adhesive to fix ZIF-8@MIPs on the electrode surface. Therefore, the sensor simultaneously possesses the excellent characteristics of metal-organic framework (MOF) and molecularly imprinted polymer (MIPs). The novel composite material has ZIF-8 in the shape of a rhombic dodecahedron 23 as the core, providing more attachment sites for MIPs. MIPs coat ZIF-8 to form MIPs clusters, and the whole is firmly fixed on the electrode surface by the cobweb-like structure of PVC.

[0035] In the described composite sensitive modification material, ZIF-8 is a major representative of zeolitic imidazolate frameworks in the metal-organic framework (MOF) class, composed of Zn 2+ as nodes and imidazole as the connecting bridge, coordinatively assembled into a new type of inorganic-organic hybrid material. The three-dimensional porous structure endows it with an extremely large specific surface area. MIPs are prepared based on molecular imprinting technology (MIT). The preparation of molecularly imprinted polymer (MIPs) uses bulk polymerization. With the target molecule as the template molecule, a functional monomer is screened and pre-assembled with it to form a template molecule-functional monomer complex. Then, a cross-linking agent, initiator, and porogen are added for thermal-initiated polymerization reaction to fix the structure of the pre-assembled template molecule-functional monomer complex. The template molecule is removed from the above complex with an eluent, and thus the three-dimensional cavity polymer material (MIPs) with the target molecule is prepared. This three-dimensional cavity is completely complementary to the shape, size, and chemical bond energy of the target molecule, and the high affinity and strong selectivity of MIPs for the target molecule thus result. The introduction of polyvinyl chloride (PVC) increases the adhesion of the sensitive modification film on the QCM sensor electrode, but the amount of PVC added needs to be well controlled. Excessive PVC will cause a large number of cavities of MIPs to be buried and increase the relative mass of the sensitive modification film, greatly affecting the selectivity and sensitivity of the sensor.

[0036] In the described composite sensitive modification material, the mass ratio of ZIF-8, MIPs, and PVC materials during synthesis is 2:5:1, and the generation method is as follows: First, prepare a dichloromethane solution with PVC as the substrate, and the concentration of this solution is 1 mg / ml, that is, if the amount of PVC material is 1 mg, then the amount of dichloromethane solution is 1 ml; put the ZIF-8 and MIPs powders in the above ratio into the dichloromethane solution with PVC as the substrate (concentration of 1 mg / ml), then ultrasonically mix for 15 min to make it uniform, use a microinjector to extract this mixed solution and drop-coat it on the quartz crystal body of the QCM sensor. After the dichloromethane solution volatilizes, a QCM sensor modified with the composite sensitive modification material is formed.

[0037] In the present utility model, when the mass of the rigid adhesion layer formed by the sensitive film of the QCM sensor does not exceed 2% of the mass of the quartz crystal itself, the correctness of the Sauerbrey equation can be ensured. Otherwise, it is difficult for the QCM sensor to start oscillating or the quality factor Q will decrease. According to the mass of the quartz crystal body, the present utility model finally determines that the drop-coating amount of the composite sensitive modification material is 15 μL. The sensitivity of the prepared QCM sensor is 2 Hz / ppm, the detection limit (LOD) < 1 Hz / ppm, the response to the target gas molecules in the range of 1 - 200 ppm is much higher than that of non-target molecules, and the repeatability index Re ≥ 98%. This QCM sensor combines the properties of the metal-organic framework ZIF-8 with many pores and a large specific surface area and the high selectivity and affinity of the molecularly imprinted polymer, effectively realizing the rapid and real-time detection of samples at room temperature.

[0038] In the gas-phase detection of the described QCM sensor, an AT-type quartz crystal resonator is mostly used, and its equivalent circuit model ( Figure 4 ) can be simplified into a circuit composed of a resistor, a capacitor, and an inductor. According to the oscillation circuit theory, when the imaginary part and the phase of the total impedance Z of the equivalent circuit are both zero, the equivalent circuit generates resonance. At this time, the series resonance frequency f s , parallel resonance frequency f p , maximum impedance frequency f zmax and minimum impedance frequency f zmin are as follows:

[0039]

[0040] In the formula, C 0 is the static capacitance, C is the dynamic capacitance, L is the dynamic inductance, and Q is the quality factor. Because the resonance frequency f r and anti-resonance frequency f a of the QCM cannot be obtained by direct measurement, the usual practice is to use the series resonance frequency f s and the minimum impedance frequency f zmin to replace the resonance frequency fr Use the parallel resonance frequency f p and the maximum impedance frequency f zmax to replace the anti-resonance frequency f a .

[0041] The described control module is used to overall control the QCM sensor detection system, including a data acquisition card 10, a relay (not shown in the figure), and an industrial personal computer 21. The software of the control module of the QCM sensor detection system is written using Microsoft Visual Studio 2010 software. The written control software is embedded in the industrial personal computer 21 and all the environments for system operation are configured. The communication between the control module program and the data acquisition card 10 is established to call each function of the acquisition card. The operation functions intOpenUsbV12(void) and int CloseUsbV12(void) are called to realize the opening and closing of the acquisition card 10; the operation function int DASingleOutV12(int chan, int value) is called to realize the flow rate setting of the first mass flow controller 4 (0 - 1000 ml / min) and the second mass flow controller 13 (0 - 3000 ml / min); the operation function intADContinuV12(int ad_mod, int chan, int gain, int Num_Sample, int Rate_Sample, float*databuf) is called to realize the flow rate feedback of the first mass flow controller 4 (0 - 1000 ml / min) and the second mass flow controller 13 (0 - 3000 ml / min); the operation function int DoSetV12(unsigned char chan, unsignedchar state) is called to control the energization and de-energization of the relay (not shown in the figure), thereby controlling the gas path conversion of the two-way three-way solenoid valves 3, 5, 8, 12, 14 (when not energized: the first port of the solenoid valve is closed, and the second and third ports are connected; when energized: the third port of the solenoid valve is closed, and the first and second ports are connected).

[0042] The power supply module includes two groups of 24V power supplies and one group of 15V power supplies. After calculating the power of each load, the two groups of 24V power supplies respectively supply power to the two-way three-way solenoid valves 3, 5, 8, 12, 14, the industrial personal computer 21, and the constant temperature heating table 17, and the 15V power supply group supplies power to the mass flow controllers 4, 13.

[0043] As Figure 2As shown in the figure, for the hardware circuit layout of the QCM sensor detection system, the industrial control all-in-one computer 21 realizes control communication with the data acquisition card 10, the quartz crystal microbalance 20, and the constant temperature heating table 17 through USB; the OUT3 - OUT7 ports of the data acquisition card 10 control the on / off of five relays (not shown in the figure), thereby realizing the control of the working states of five two-position three-way solenoid valves 3, 5, 8, 12, and 14. The AD1 and AD2 ports of the data acquisition card 10 are connected to the SET ports of two mass flow controllers 4 and 13, and the flow value is set by inputting an analog voltage of 0 - 5V. The FB ports of the mass flow controllers 4 and 13 are connected to the DA1 and DA2 ports of the data acquisition card 10, and an analog voltage of 0 - 5V is output to feedback the real-time flow of the mass flowmeter. Two pins of the QCM sensor 18 are connected to the crystal oscillator box 15, and the crystal oscillator box 15 is connected to the COM port of the quartz crystal microbalance 20. This module converts the micro mass change generated by the odor molecules adsorbed on the surface of the QCM sensor into a frequency change and transmits it to the industrial control all-in-one computer.

[0044] As Figure 5 shown in the figure, the control software of the QCM sensor detection system includes the flow value setting and real-time flow feedback functions of two mass flow controllers 4 and 13, the functions of five two-position three-way solenoid valves 3, 5, 8, 12, and 14 to control different working processes of the QCM sensor detection system, and the start and stop functions of the QCM sensor detection system.

[0045] As Figure 6 shown in the figure, for the response curve graph of the detection system to detect the volatile odor of the sample, it starts with the baseline acquisition stage. The injection of the target gas to be measured causes the QCM sensor to generate a response signal (Δf and Δm are negatively correlated, so the curve goes down) until it stabilizes. The injection of N 2 starts the cleaning stage. The odor molecules are desorbed from the sensor surface, and the curve returns to the baseline state again. After saving the sample response data, the detection of this sample ends.

[0046] For the system described above, the working process of the QCM sensor detection system includes: the gas source balance debugging stage, the sample enrichment stage, the baseline acquisition stage, the mixed gas detection stage, the baseline recovery stage, and the data storage and processing stage.

[0047] Among them, in the air source balance debugging stage, all two-way three-way solenoid valves are in the non-energized state (non-energized state: the second and third ports of the solenoid valve are connected; energized state: the first and second ports of the solenoid valve are connected, the same below). Open the main valve of the nitrogen cylinder 1 and adjust the pressure reducing valve 2 to output a nitrogen gas flow with appropriate flow rate. The nitrogen gas flow is discharged into the air through the second and third ports of the first two-way three-way solenoid valve 3, the second and third ports of the second two-way three-way solenoid valve 12, and the filter 11. In the sample enrichment stage, the first two-way three-way solenoid valve 3 is energized and in the energized state, and the rest of the two-way three-way solenoid valves are in the non-energized state. Put the sample into the sample chamber, open the input valve of the aluminum foil gas bag 9. The nitrogen gas flow enters the aluminum foil gas bag through the second and first ports of the first two-way three-way solenoid valve 3, the input port and output port of the first mass flow controller 4, the second and third ports of the fourth two-way three-way solenoid valve 5, the sample chamber 7, the third and second ports of the fifth two-way three-way solenoid valve 8, and the input valve of the aluminum foil gas collection bag 9. Set the flow rate of the first mass flow controller 4 and the enrichment stage time according to the volume of the gas bag. When the gas bag 9 is full, it will cause the real-time flow rate output of the first mass flow controller 4 to be abnormal (the flow rate setting of the first mass flow controller 4 requires an input voltage of 0 - 5V, corresponding to a flow rate of 0 - 1000 ml / min. The gas flow passing through the mass flow controller 4 will feedback a voltage of 0 - 5V, corresponding to a flow rate of 0 - 1000 ml / min. The input and feedback voltages of the mass flow controller 4 are set and received by a data acquisition card. When the gas bag is full, the air pressure at the output port position of the mass flow controller 4 will increase, and thus the real-time flow rate feedback by the mass flow controller 4 will be abnormal, which can be used as a sign that the gas bag is full, that is, the sample enrichment stage is completed). At this time, close the input valve of the aluminum foil gas bag 9, and the sample odor enrichment is completed.

[0048] In the baseline acquisition stage, the second two-way three-way solenoid valve 12 is in the energized state, and the rest of the two-way three-way solenoid valves are in the non-energized state. The nitrogen gas flow is discharged into the air through the second and third ports of the first two-way three-way solenoid valve 3, the second and first ports of the second two-way three-way solenoid valve 12, the input port and output port of the second mass flow controller 13, the third and second ports of the third two-way three-way solenoid valve 14, the input port and output port of the gas detection chamber 16, and the filter 19. In this stage, the nitrogen gas flow purges the gas detection chamber 16. When the frequency signal fluctuation of the QCM sensor 18 inside the detection chamber 16 is within ±1Hz, it is regarded as the completion of the baseline acquisition stage.

[0049] During the mixed gas detection stage, the first, third, fourth, and fifth two-way three-way solenoid valves 3, 14, 5, and 8 are all in the energized state, and the second two-way three-way solenoid valve 12 is in the non-energized state. Select the corresponding electrolyte solution according to the required humidity conditions and add it to the electrolyte cell 6 to control the humidity (humidity has a great influence on the QCM sensor signal. Therefore, this system needs to add a humidity control scheme to test the anti-humidity interference ability of the sensor. Different electrolyte solutions produce different volatile headspace humidities, which can provide different humidity control environments). Open the input valve and output valve of the aluminum foil gas sampling bag 9. Nitrogen gas flows through the second and first ports of the first two-way three-way solenoid valve 3, the input and output ports of the first mass flow controller 4, the second and first ports of the fourth two-way three-way solenoid valve 5, the electrolyte cell 6, the first and second ports of the fifth two-way three-way solenoid valve 8, the input and output ports of the aluminum foil gas bag 9, the first and second ports of the third two-way three-way solenoid valve 14, the input and output ports of the gas detection chamber 16, and the filter 19 and is discharged into the air. The high-purity nitrogen gas flow serves as the carrier gas, and the sample volatile odor with a certain humidity is sent into the gas detection chamber 16 for detection. The surface of the QCM sensor 18 (installed in the gas detection chamber) changes in mass due to the adsorption of odor molecules, thereby generating a frequency signal, and the mixed gas detection stage is completed.

[0050] During the baseline recovery stage, the second two-way three-way solenoid valve 12 is in the energized state, and the other two-way three-way solenoid valves are in the non-energized state. Set the second mass flow controller 13 to the high-flow mode (3000 ml / min). Nitrogen gas flows through the second and third ports of the first two-way three-way solenoid valve 3, the second and first ports of the second two-way three-way solenoid valve 12, the input and output ports of the second mass flow controller 13, the third and second ports of the third two-way three-way solenoid valve 14, the input and output ports of the gas detection chamber 16, and the filter 19 and is discharged into the air. The nitrogen gas flow purges the gas detection chamber 16. When the frequency signal of the QCM sensor 18 inside the detection chamber recovers to 95% of the baseline signal and the signal fluctuation is within ±1 Hz, it is considered that the baseline recovery stage is completed.

[0051] During the data storage and processing stage, the operating computer stores and processes the sample odor frequency signal to obtain the sample detection result.

[0052] The performance evaluation of the described QCM sensor detection system includes the test sensitivity of the system, the lowest detection limit (LOD) of the system, and the test repeatability of the system. The evaluation process uses test gases with different concentration gradients prepared from chemically pure sample reagents (analytical grade ≥ 99%). The preparation process is as follows: First, calculate the saturated vapor concentration c of different substances (analytical pure) used for testing 饱和蒸气浓度 :

[0053]

[0054] Among them, P 蒸气压 — Vapor pressure of the substance, mmHg; t — Temperature, °C; A, B, and C are constants, which can be obtained from Table 2.

[0055]

[0056] Among them, D — Vapor density, mg / m 3 ; M — Molecular weight, g / mol; R — Gas constant, 8.314 Pa·m 3 / (K·mol); T — Absolute temperature, K.

[0057]

[0058] Among them, c 饱和蒸气浓度 — Saturated vapor concentration, ppm.

[0059] Taking the saturated vapor concentration value as the threshold, any concentration c' before the saturated vapor concentration is configured according to the following formula. At room temperature, inject a pure liquid sample substance into the container and let it stand and volatilize:

[0060]

[0061] Among them, c' — Concentration of the sample to be measured, ppm; ρ — Density of the liquid sample, g / mL; T — Temperature in the container (298 K at 25°C), K; V 注入 — Volume of the pure sample substance injected into the container, μL; M — Molecular weight of the substance, g / mol; V s — Volume of the container, L.

[0062] (1) The test sensitivity of the system is defined as the ratio of the change in frequency at equilibrium of the response to the corresponding concentration:

[0063]

[0064] Among them, S is the test sensitivity of the system, Δf is the change in frequency, and Δc is the corresponding concentration.

[0065] (2) The lowest detection limit (LOD) of the system is determined by three times the signal-to-noise ratio:

[0066]

[0067] Among them, S is the test sensitivity of the system.

[0068] (3) The test repeatability (Re) of the system is to evaluate the consistency of the system's response to the target gas at the same concentration:

[0069]

[0070] Among them, xi is the frequency value when the response reaches equilibrium, is the average value of the response frequency values obtained from multiple tests. When the test sample is at the same concentration gradient, k≥6) (Re is greater than or equal to 95%).

[0071] The QCM sensor detection system processes the collected sample odor information as follows:

[0072] (1) Perform data preprocessing on the collected sample odor frequency signal, and use the S-G five-point smoothing algorithm to process the original data;

[0073] (2) Extract the features of the frequency signal curve after smoothing processing, and extract the eigenvalue matrix of the frequency signal curve features;

[0074] (3) Input the eigenvalue matrix into the machine learning model for training and learning, and test and verify to obtain a reliable sample detection model.

[0075] The S-G smoothing algorithm for frequency data preprocessing in step (1) is as follows:

[0076]

[0077] where f is the sensor frequency response value, A = [a 0 、a 1 、a 2 、…、a k-1 is the coefficient matrix, is the improved value of the sensor frequency response. The filtering window width is n = 2m + 1, and each measurement point is f = (-m, -m + 1,..., -1, 0, 1,..., m - 1, m). The above k-1 degree polynomial is used to fit the data points within the window. n equations form a k-element linear equation system. n>k means the equation has a solution, and the fitting parameter A is determined by the least squares method.

[0078] In step (1), the S-G five-point cubic smoothing algorithm is adopted. The system uses n equally spaced points, takes two adjacent points before and after each current data point, and uses the cubic polynomial for approximation. The coefficients a 0 ,a 1 ,a 2 ,a 3 are determined by the least squares method. Finally, the five-point cubic smoothing formula is obtained as:

[0079]

[0080] where is the improved value of f i . The formula requires n≥5. Calculation of endpoints: For the 1st and 2nd points, use the formula At the (n - 1)th and nth points, use the formula For the remaining points, use the formula to perform smoothing processing.

[0081] In the step (2), extract the eigenvalue of the frequency signal curve: relative change value RCV, integral value INV, average differential value ADV.

[0082] RCV = maxf(t i ) - minf(t i )

[0083]

[0084] where f(t i ) is the frequency response of the sensor at the ith second, maxf(t i ) is the maximum value of the frequency response within n seconds during the sample injection detection, minf(t i ) is the minimum value of the frequency response within n seconds during the sample injection detection (the sampling frequency can be 1 Hz), is the overall time corresponding to when the frequency response curve reaches the peak.

[0085] In the step (3), the machine learning model is determined according to the sample detection requirements. The regression model and the classification model correspond to quantitative and qualitative analysis respectively.

[0086] Through the present utility model, it is possible to quickly achieve the targeted recognition of the characteristic volatile odor of the sample under room temperature conditions, and it has extremely high detection accuracy. Through the dynamic gas mixing and enrichment module, the electrolyte cell, the constant temperature heating table, etc., it is possible to flexibly simulate the test scenarios under conditions such as complex interfering gases, different humidity, and temperature. Therefore, this detection system has better reliability and applicability.

[0087] Table 1 is the relative humidity table of the saturated vapor of different electrolyte salt solutions at 25°C room temperature

[0088] Saturated salt solution Relative humidity Lithium chloride 11.30％ Potassium acetate 22.51％ Magnesium chloride 32.78％ Potassium carbonate 43.16％ Magnesium nitrate 52.89％ Sodium chloride 75.29％ Potassium chloride 84.34％ Potassium sulfate 97.30％

[0089] Table 2

[0090] Table 2 Saturated vapor pressure parameters of some substances

[0091] Name Molecular formula Range (°C). A B C Ammonia NH3 -83～+60 7.55466 1002.711 247.885 Ethanol C2H6O \ 8.04494 1554.300 222.650 Acetonitrile C2H3N \ 7.11988 1314.400 230.000 Acetic acid C2H4O2 0～36 7.80307 1651.200 225.000 n-Octane C8H18 -20～+40 7.37200 1587.810 230.070 Methanol CH4O -20～+140 7.87863 1473.110 230.000 Phenol C6H6O \ 7.13617 1518.100 175.000 Trimethylamine C3H9N -60～+850 6.81628 937.490 235.350

[0092] The above is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in this application should be covered within the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claimed rights.

Claims

1. A QCM sensor detection system, comprising a body, a dynamic gas distribution enrichment module, a QCM sensor detection module, a control module and a power module, characterized in that: The dynamic gas distribution enrichment module, QCM sensor detection module, control module and power module are all installed on the machine body; the dynamic gas distribution enrichment module is connected to the QCM sensor detection module through the gas path; the power module and the control module are connected to the dynamic gas distribution enrichment module and the QCM sensor detection module through wires for power supply and control.

2. The QCM sensor detection system according to claim 1, characterized in that: The dynamic gas distribution and enrichment module includes a gas source balance gas circuit, a sample volatile odor enrichment gas circuit, a low-flow baseline collection gas circuit, a humidity-controlled mixed gas detection gas circuit and a high-flow cleaning gas circuit.

3. The QCM sensor detection system according to claim 2, characterized in that: The air flow route of the air source balancing gas circuit includes: the nitrogen flow is released from the main valve of the nitrogen cylinder, passes through the input port and output port of the pressure reducing valve, the second port and the third port of the first two-position three-way solenoid valve, the second port and the third port of the second two-position three-way solenoid valve, the filter, and then discharged into the air.

4. The QCM sensor detection system according to claim 2, characterized in that: The airflow route of the sample volatile odor enrichment gas path includes: the nitrogen flow is released from the main valve of the nitrogen bottle, and passes through the input port and output port of the pressure reducing valve, the second port and the first port of the first two-position three-way solenoid valve, the input port and the output port of the first mass flow controller, the second port and the third port of the fourth two-position three-way solenoid valve, the input port and the output port of the sample chamber, the third port and the second port of the fifth two-position three-way solenoid valve, and the input port of the aluminum foil gas collection bag.

5. The QCM sensor detection system according to claim 2, characterized in that: The air flow route of the low-flow baseline collection gas circuit includes: the nitrogen flow is released from the main valve of the nitrogen bottle, and passes through the input port and output port of the pressure reducing valve, the second port and the third port of the first two-position three-way solenoid valve, the second port and the first port of the second two-position three-way solenoid valve, the input port and the output port of the second mass flow controller, the third port and the second port of the third two-position three-way solenoid valve, the input port and the output port of the gas detection chamber, the filter, and then discharged into the air.

6. The QCM sensor detection system according to claim 2, characterized in that: The air flow route of the humidity-controlled mixed gas detection gas circuit includes: the nitrogen flow is released from the main valve of the nitrogen bottle, and passes through the input port and output port of the pressure reducing valve, the second port and the first port of the first two-position three-way solenoid valve, the input port and the output port of the first mass flow controller, the second port and the first port of the fourth two-position three-way solenoid valve, the input port and the output port of the electrolyte cell, the first port and the second port of the fifth two-position three-way solenoid valve, the input port and the output port of the aluminum foil gas collection bag, the first port and the second port of the third two-position three-way solenoid valve, the input and output ports of the gas detection chamber, the filter, and then discharged into the air.

7. The QCM sensor detection system according to claim 2, characterized in that: The air flow route of the high-flow cleaning gas circuit includes: the nitrogen flow is released from the main valve of the nitrogen bottle, and passes through the input port and output port of the pressure reducing valve, the second port and the third port of the first two-position three-way solenoid valve, the second port and the first port of the second two-position three-way solenoid valve, the input port and the output port of the second mass flow controller, the third port and the second port of the third two-position three-way solenoid valve, the input port and the output port of the gas detection chamber, the filter, and then discharged into the air.

8. The QCM sensor detection system according to claim 1, characterized in that: The QCM detection module includes a gas detection chamber, a constant temperature heating platform, a QCM sensor, a crystal oscillator test box, and a quartz crystal microbalance.

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