System and method for detecting near dryness of concentrated sample by nitrogen blowing concentrator

Abstract

The invention discloses a system and a method for detecting near dryness of a concentrated sample by a nitrogen blowing instrument, and belongs to the technical field of evaporation concentration chemical analysis, the system comprises a nitrogen blowing needle and a sampling needle which are mounted on a motion module, and further comprises a nitrogen blowing gas path communicated with the nitrogen blowing needle and a gas detection gas path communicated with the sampling needle, the inlet end of the nitrogen blowing gas path is connected with a nitrogen gas source, and a nitrogen input total amount control valve and a nitrogen blowing independent valve are further sequentially installed on the nitrogen blowing gas path. A VOC (volatile organic compound) sensor and a vacuum pump are sequentially mounted on the gas detection gas path. The VOC sensor is adopted to detect the volatilization amount of the organic solvent in the centrifugal tube in real time, and then the evaporation condition of the solvent in the sample is evaluated, so that the height of the liquid level in the centrifugal tube is calculated, and accurate volume determination is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of evaporation and concentration for chemical analysis. Specifically, it relates to a system and method for detecting and concentrating samples to near dryness using a nitrogen blowing instrument. Background Art

[0002] The nitrogen blowing instrument evaporates the organic solvent in a large-volume, low-concentration sample to near dryness by means of heating, blowing nitrogen, etc., and then redissolves it by adding a certain volume (much smaller than the original sample volume) to concentrate the low-concentration sample, so as to improve the signal intensity of subsequent liquid phase, gas phase, and mass spectrometry detections and enhance the accuracy of detections. However, when a testing institution needs to test a large number of samples in a short time, dozens of low-concentration samples need to be concentrated by nitrogen blowing simultaneously. During this process, some samples may be prematurely dried and some samples may take a long time to dry due to various reasons. In this case, if it is impossible to accurately detect whether each sample has been blown to near dryness and turn off the nitrogen supply to the corresponding sample, then the prematurely dried samples will be over-blown for a long time, resulting in a decrease in the amount of the test target redissolved in the small-volume redissolution solution due to caking, volatilization, etc. This not only affects the redissolution rate of the next step but also affects the subsequent test results.

[0003] To overcome the above problems, most nitrogen blowing products on the market currently have the function of sample concentration and volume determination. The method of sample concentration and volume determination is to use a specially made volumetric cup supporting the instrument to hold the sample, and a pair of photoelectric sensors are installed at the lower part of the volumetric cup. When the liquid level reaches below the photoelectric sensors due to sample evaporation, the photoelectric sensors will send out signals to stop the equipment from supplying gas. However, this method of sample concentration and volume determination has the following problems: 1. This technical means is generally applicable to the concentration of large-volume samples and cannot accurately control the concentration ratio of samples with only a few milliliters. 2. When the sample to be volumetrically determined absorbs the light wave emitted by the photoelectric sensor, this monitoring means will completely fail. 3. Since this technical means is generally applicable to the concentration of large-volume samples, the diameter of the concentration cup is generally very large. Then, in the unit projected area, the number of samples concentrated by the nitrogen blowing instrument using this means is unlikely to be very large. 4. Since the evaporation rate of the solvent in each concentration cup cannot be evaluated during the concentration process, when a large number of large-volume samples need to be concentrated and volumetrically determined, there will be a problem of a large difference in concentration rates. In order to prevent the solvent of the samples that have completed volume determination from evaporating abnormally due to long waiting and thus affecting the accuracy of volume determination, it is necessary to observe manually during the solvent concentration process to take out the samples that have completed volume determination in advance, reducing the automation degree of the equipment.

[0004] Therefore, there is an urgent need to provide a system and method that can accurately identify the evaporation of samples to near dryness. Summary of the Invention

[0005] The object of the present invention is to provide a system and method for detecting the near-dry state of a concentrated sample by a nitrogen blower. By using a VOC sensor to detect the evaporation amount of the organic solvent in the centrifuge tube in real time, the evaporation situation of the solvent in the sample is evaluated, and then the height of the liquid level in the centrifuge tube is calculated to achieve precise volume determination.

[0006] To achieve the object of the present invention, the technical solution adopted is: a system for detecting the near-dry state of a concentrated sample by a nitrogen blower, including a nitrogen blowing needle and a sampling needle installed on a motion module, and further including a nitrogen blowing gas path communicated with the nitrogen blowing needle and a gas detection gas path communicated with the sampling needle. The inlet end of the nitrogen blowing gas path is connected to a nitrogen gas source, and a total nitrogen input control valve and a nitrogen blowing independent valve are sequentially installed on the nitrogen blowing gas path; a VOC sensor and a vacuum pump are sequentially installed on the gas detection gas path.

[0007] Further, it further includes a sensor recovery gas path. The inlet end of the sensor recovery gas path is connected in parallel between the nitrogen gas source and the total nitrogen input control valve. An air path switching valve is also installed between the VOC sensor and the vacuum pump, and the outlet end of the sensor recovery gas path is connected to the air path switching valve; a flow valve is also installed on the sensor recovery gas path.

[0008] Further, the sampling needle is located on one side of the nitrogen blowing needle, or the sampling needle and the nitrogen blowing needle are arranged coaxially and radially spaced apart.

[0009] Further, there are multiple nitrogen blowing needles, sampling needles, VOC sensors and nitrogen blowing independent valves. The multiple nitrogen blowing independent valves are connected to the multiple nitrogen blowing needles one by one, and the inlet ends of the multiple nitrogen blowing independent valves are commonly connected in parallel to the outlet end of the total nitrogen input control valve; the inlet end of the gas detection gas path is connected in parallel with multiple branch pipelines. The inlet ends of the multiple branch pipelines are connected to the multiple sampling needles one by one, and multiple VOC sensors are installed on the multiple branch pipelines one by one.

[0010] A method for detecting the near-dry state of a concentrated sample by a nitrogen blower includes the following steps: S1. Open the nitrogen blowing independent valve: Open the nitrogen blowing independent valve corresponding to the sample to be blown to near dryness. S2. Adjust the input nitrogen gas volume: According to the number of samples to be concentrated selected, set the average flow rate of nitrogen gas blown into the centrifuge tube, and calculate and set the magnitude of the total nitrogen blowing flow rate. S3. Concentrate the sample: Set the running speed of the motion module to make the nitrogen blowing needle and the sampling needle track the sample liquid level, so that the distance between the nitrogen blowing needle, the sampling needle and the solvent liquid level is kept within a fixed height range. S4. Detect the near-dry state of the sample: The VOC sensor detects in real time the content of volatile organic compounds in the evaporated mixed gas during the concentration process of the corresponding sample, and calculates the liquid level height and the concentration degree of the sample in the centrifuge tube according to the content of volatile organic compounds in the evaporated mixed gas detected by the VOC sensor, and determines whether the sample in the centrifuge tube is nearly dry; S5. Close the nitrogen blowing independent valve: When it is calculated that the liquid level of the sample is nearly dry, close the nitrogen blowing independent valve corresponding to the nearly dry sample.

[0011] Further, before step S3, reset the VOC sensor: control the gas path switching valve to connect the VOC sensor to the nitrogen gas source adjusted by the flow valve for rapid reset of the VOC sensor; after the VOC sensor is reset, control the gas path switching valve to connect the sampling needle to the vacuum pump, control the movement module to move, and the movement module drives the nitrogen blowing needle and the sampling needle to move above the liquid level of the sample, and the vacuum pump is started.

[0012] The beneficial effects of the present invention are: 1. In the present invention, while blowing nitrogen, the evaporated mixed gas generated during the concentration process of the sample is collected, and the evaporation rate of the VOC gas in the solvent is determined by the content of volatile organic compounds in the evaporated mixed gas. Not only can the height of the sample liquid level be obtained, but also the concentration state of the sample can be detected, so that it is possible to quickly and accurately identify that the sample has been blown to nearly dry.

[0013] 2. Since there is no need to use a constant volume cup or a photoelectric sensor in the present invention, most commercially available centrifuge tubes can be directly used as the containers for holding the samples in the present invention, so there is no need to use special containers; 3. Since the concentration state and liquid level height of the sample are obtained by detecting the evaporated mixed gas during the concentration process of the sample in the present invention, therefore, during the concentration process of the sample, there is no restriction on the light transmission of the sample to be concentrated, and more sample concentration can be applied. Description of the Drawings

[0014] The drawings illustrate exemplary embodiments of the present invention and are used together with the description to explain the principles of the present invention. These drawings are included to provide a further understanding of the present invention, and the drawings are included in this specification and form a part of this specification.

[0015] Figure 1 It is a system diagram of the system for detecting that the concentrated sample is nearly dry by the nitrogen blowing instrument provided by the present invention.

[0016] Marks and corresponding component names in the drawings: 1. Nitrogen blowing gas path, 2. Sensor recovery gas path, 3. Gas detection gas path, 4. Movement module; 1-1. Nitrogen gas source, 1-2. Total nitrogen input control valve, 1-3. Independent nitrogen blowing valve, 1-4. Nitrogen blowing needle; 2-1. Flow valve; 3-1. Exhaust gas emission fan, 3-2. Vacuum pump, 3-3. Gas path switching valve, 3-4. VOC sensor, 3-5. Sampling needle. Detailed implementation manners

[0017] The present invention will be further described in detail below in conjunction with the accompanying drawings and implementation manners. It can be understood that the specific implementation manners described herein are only used to explain the relevant content and do not limit the present invention. In addition, it should be noted that for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings.

[0018] It should be noted that, without conflict, the implementation manners in the present invention and the features in the implementation manners can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the implementation manners.

[0019] As Figure 1 shown, a system for detecting that a concentrated sample is nearly dry by a nitrogen blowing instrument provided by the present invention includes a nitrogen blowing needle 1-4 and a sampling needle 3-5 installed on a motion module 4. The motion module 4 is the motion module 4 on an existing nitrogen blowing instrument, and its structure will not be described in detail here. The motion module 4 is used to drive the nitrogen blowing needle 1-4 and the sampling needle 3-5 to move up and down; the nitrogen blowing needle 1-4 is used to blow nitrogen gas into the sample in the centrifuge tube to evaporate and concentrate the sample in the centrifuge tube; the sampling needle 3-5 is used to suck the evaporation mixed gas generated during the sample concentration process, so as to collect the evaporation mixed gas generated during the sample concentration process for detection.

[0020] The system further includes a nitrogen blowing gas path 1 and a gas detection gas path 3; the nitrogen blowing gas path 1 is used to transport nitrogen gas to the nitrogen blowing needle 1-4 and discharge it through the nitrogen blowing needle 1-4. Therefore, the outlet end of the nitrogen blowing gas path 1 is connected to the nitrogen blowing needle 1-4; the gas detection gas path 3 is used to transport, detect, and discharge the evaporated mixed gas collected by the sampling needle 3-5. Therefore, the inlet end of the gas detection gas path 3 is connected to the sampling needle 3-5. The inlet end of the nitrogen blowing gas path 1 is connected to a nitrogen gas source 1-1, and the nitrogen gas source 1-1 provides the nitrogen gas required for nitrogen blowing. A total nitrogen input control valve 1-2 and a nitrogen blowing independent valve 1-3 are sequentially installed from the inlet end of the nitrogen blowing gas path 1 to the outlet end of the nitrogen blowing gas path 1. The total nitrogen input control valve 1-2 is used to adjust the flow rate of the nitrogen gas blown by the nitrogen blowing needle 1-4, and the nitrogen blowing independent valve 1-3 is used to control the opening and closing of the nitrogen blowing gas path 1, thereby controlling whether the nitrogen blowing needle 1-4 blows nitrogen gas. The inlet end of the gas detection gas path 3 is connected to the sampling needle 3-5, the outlet end of the gas detection gas path 3 is open, and a VOC sensor 3-4 and a vacuum pump 3-2 are also installed on the gas detection gas path 3. The vacuum pump 3-2 is used to create a negative pressure in the gas detection gas path 3, so that the evaporated mixed gas generated during the concentration of the sample in the centrifuge tube can enter the gas detection gas path 3 through the sampling needle 3-5 and be discharged through the outlet end of the gas detection gas path 3. When the evaporated mixed gas flows through the gas detection gas path 3, the VOC sensor 3-4 detects the evaporated mixed gas, thereby detecting the content of volatile organic compounds in the evaporated mixed gas.

[0021] In order to prevent the VOC sensor 3-4 from being interfered by the outside world during the detection of the mixed gas, the VOC sensor 3-4 is located on the gas detection gas path 3 close to the sampling needle 3-5, so that the evaporated mixed gas collected by the sampling needle 3-5 can be immediately detected by the VOC sensor 3-4; after the evaporated mixed gas is detected, in order to further discharge the evaporated mixed gas, a waste discharge fan can also be installed at the outlet end of the gas detection gas path 3, so that the evaporated mixed gas can be discharged and diffused through the waste discharge fan after being discharged through the gas detection gas path 3.

[0022] Since the VOC sensor 3-4 takes a relatively long time to recover after detecting an evaporation mixed gas with a high concentration of volatile organic compounds, in order to facilitate the reset of the VOC sensor 3-4, the system is also provided with a VOC sensor 3-4 recovery gas path 2. The VOC sensor 3-4 recovery gas path 2 is connected in parallel between the nitrogen gas source 1-1 and the total nitrogen input control valve 1-2. At the same time, a gas path switching valve 3-3 is also installed on the gas detection gas path 3. The gas path switching valve 3-3 is located between the vacuum pump 3-2 and the VOC sensor 3-4. The other end of the VOC sensor 3-4 recovery gas path 2 is connected in parallel to the gas path switching valve 3-3. When the gas path switching valve 3-3 connects the VOC sensor 3-4 recovery gas path 2 to the sampling tube, the nitrogen gas provided by the nitrogen gas source 1-1 can enter the gas detection gas path 3 through the VOC sensor 3-4 recovery gas path 2, and after passing through the VOC sensor 3-4, it can be blown through the sampling needle 3-5. When the nitrogen gas entering the gas detection gas path 3 passes through the VOC sensor 3-4, the VOC sensor 3-4 is reset. In order to facilitate the flow rate of nitrogen gas through the VOC sensor 3-4 recovery gas path 2, a flow valve 2-1 is also installed on the VOC sensor 3-4 recovery gas path 2.

[0023] In the present invention, since the object collected by the sampling needle 3-5 must be the evaporation mixed gas generated by the sample nitrogen blown by the nitrogen blowing needle 1-4, therefore, in order to ensure the accuracy of the evaporation mixed gas collection, during the concentration process of the sample in the centrifuge tube, the sampling needle 3-5 and the nitrogen blowing needle 1-4 need to be inserted into the centrifuge tube at the same time. In order to facilitate the simultaneous insertion of the sampling needle 3-5 and the nitrogen blowing needle 1-4 into the centrifuge tube, when designing the sampling needle 3-5 and the nitrogen blowing needle 1-4, the sampling needle 3-5 and the nitrogen blowing needle 1-4 can be fixed together, that is, the sampling needle 3-5 can be fixed on one side of the nitrogen blowing needle 1-4, or the sampling needle 3-5 and the nitrogen blowing needle 1-4 can be arranged coaxially and radially spaced apart. Further, in order to prevent the sampling needle 3-5 from directly collecting the nitrogen gas blown by the nitrogen blowing needle 1-4 during collection and affecting the detection result, the hole for the evaporation mixed gas to enter on the sampling needle 3-5 is higher than the outlet of the nitrogen blowing needle 1-4.

[0024] Since a nitrogen blower generally blows nitrogen for multiple samples simultaneously, in this system, there are multiple nitrogen blowing needles 1-4, sampling needles 3-5, VOC sensors 3-4, and nitrogen blowing independent valves 1-3. The multiple nitrogen blowing independent valves 1-3 are connected to the multiple nitrogen blowing needles 1-4 one by one, so that each nitrogen blowing independent valve 1-3 controls the nitrogen blowing of one nitrogen blowing needle 1-4. The inlet ends of the multiple nitrogen blowing independent valves 1-3 are commonly connected in parallel to the outlet end of the total nitrogen input control valve 1-2, so that after nitrogen is sent out through the total nitrogen input control valve 1-2, it enters each nitrogen blowing needle 1-4 through each nitrogen blowing independent valve 1-3 respectively. At the same time, the inlet end of the gas detection gas path 3 is connected in parallel with multiple branch pipelines. The outlet ends of the minute pipelines are commonly connected in parallel to the gas path switching valve 3-3. The inlet ends of the multiple branch pipelines are connected to the multiple sampling needles 3-5 one by one, and the multiple VOC sensors 3-4 are installed on the multiple branch pipelines one by one, so that the evaporation mixed gas collected by each sampling needle 3-5 can be detected by an independent VOC sensor 3-4, and the sample liquid level and sample concentration degree in each centrifuge tube can be monitored separately. Since the inlet ends of the multiple branch pipelines are commonly connected in parallel to the gas path switching valve 3-3, the nitrogen gas in the gas path 2 restored by the VOC sensor 3-4 can enter each branch pipeline respectively, and after passing through the multiple VOC sensors 3-4, it is discharged from each sampling needle 3-5, so that the multiple VOC sensors 3-4 can all be reset.

[0025] The method for detecting that the concentrated sample is nearly dry by adopting the above system includes the following steps: S1. Open the nitrogen blowing independent valve 1-3: Open the nitrogen blowing independent valve 1-3 corresponding to the sample selected to be blown to nearly dry, so as to concentrate the selected sample. S2. Adjust the input nitrogen gas volume: According to the number of the selected samples to be concentrated, set the average flow rate of nitrogen gas blown into each centrifuge tube by each nitrogen blowing needle 1-4, calculate and set the magnitude of the total nitrogen blowing flow rate, and control the opening degree of the total nitrogen input control valve 1-2 according to the calculated magnitude of the total flow rate, so as to meet the nitrogen gas requirements for different tasks. S3. Reset the VOC sensor 3-4: Control the gas path switching valve 3-3 to connect the gas path 2 for restoring the VOC sensor 3-4 with the sampling needle 3-5, so that the VOC sensor 3-4 is connected to the nitrogen gas adjusted by the flow valve 2-1. When the nitrogen gas passes through the VOC sensor 3-4 on the branch pipeline, the VOC sensor 3-4 is quickly reset. After the VOC sensor 3-4 is reset, control the gas path switching valve 3-3 to connect the sampling needle 3-5 with the vacuum pump 3-2, and control the movement module to move. The movement module drives the nitrogen blowing needle 1-4 and the sampling needle 3-5 to move above the liquid level of the sample. S4. Concentrate the sample: Set the operating speed of the motion module so that the nitrogen blowing needles 1-4 and the sampling needles 3-5 track the sample liquid level, and keep the distance between the nitrogen blowing needles 1-4, the sampling needles 3-5 and the solvent liquid level within a fixed height range to improve the speed of nitrogen blowing concentration; and here, the distance between the nitrogen blowing needles 1-4, the sampling needles 3-5 and the solvent liquid level can be adjusted according to the nitrogen gas flow rate blown out by the nitrogen blowing needles 1-4 to improve the speed of sample concentration; and the nitrogen gas source 1-1 provides nitrogen gas, and the nitrogen gas is discharged from the nitrogen blowing needles 1-4 through the total nitrogen input control valve 1-2 and the nitrogen blowing independent valve 1-3, so that the nitrogen blowing needles 1-4 perform nitrogen blowing on the samples in the centrifuge tubes. During the nitrogen blowing of the samples, the vacuum pump 3-2 is started, and the evaporation mixed gas generated during the nitrogen blowing of the samples is pumped into the sampling needles 3-5 and discharged after passing through the gas path switching valve 3-3 and the vacuum pump 3-2 in the gas detection gas path 3. During the process of the evaporation mixed gas passing through the gas detection gas path 3, the VOC sensor 3-4 detects the content of volatile organic compounds in the evaporation mixed gas; S5. Detection of nearly dry sample: Calculate the liquid level height and the concentration degree of the sample in the centrifuge tube according to the content of volatile organic compounds in the evaporation mixed gas detected by the VOC sensor 3-4. During the calculation process, the VOC sensor 3-4 detects the evaporation mixed gas during the concentration process of the sample in the centrifuge tube in real time to determine whether the sample in the centrifuge tube is nearly dry; S6. Close the nitrogen blowing independent valve 1-3: When it is calculated that the liquid level of the sample is nearly dry, close the nitrogen blowing independent valve 1-3 corresponding to the nearly dry sample, so that the nitrogen blowing needles 1-4 corresponding to the nearly dry sample cannot continue to blow nitrogen gas to prevent over-blowing of the sample from affecting the subsequent re-dissolution.

[0026] Those skilled in the art should understand that the above embodiments are only for clearly illustrating the present invention, rather than limiting the scope of the present invention. For those skilled in the art, other changes or modifications can be made based on the above disclosure, and these changes or modifications are still within the scope of the present invention.

Claims

1. A method for detecting that a concentrated sample is nearly dry by a nitrogen blowing instrument, characterized in that, It includes a nitrogen blowing needle (1-4) and a sampling needle (3-5) installed on a motion module (4), and also includes a nitrogen blowing gas path (1) communicated with the nitrogen blowing needle (1-4) and a gas detection gas path (3) communicated with the sampling needle (3-5). The inlet end of the nitrogen blowing gas path (1) is connected to a nitrogen gas source (1-1), and a total nitrogen input control valve (1-2) and a nitrogen blowing independent valve (1-3) are sequentially installed on the nitrogen blowing gas path (1); a VOC sensor (3-4) and a vacuum pump (3-2) are sequentially installed on the gas detection gas path (3).

2. The method for detecting that a concentrated sample is nearly dry by using a nitrogen evaporator according to claim 1, wherein It further includes a VOC sensor (3-4) recovery gas path (2). The inlet end of the VOC sensor (3-4) recovery gas path (2) is connected in parallel between the nitrogen gas source (1-1) and the total nitrogen input control valve (1-2), and a gas path switching valve (3-3) is installed between the VOC sensor (3-4) and the vacuum pump (3-2). The outlet end of the VOC sensor (3-4) recovery gas path (2) is connected to the gas path switching valve (3-3); a flow valve (2-1) is also installed on the VOC sensor (3-4) recovery gas path (2).

3. The method for detecting nearly dry concentrated samples by a nitrogen blowing instrument according to claim 1 or 2, characterized in that, The sampling needle (3-5) is located on one side of the nitrogen blowing needle (1-4), or the sampling needle (3-5) and the nitrogen blowing needle (1-4) are arranged coaxially with a radial interval.

4. The method for detecting that the concentrated sample is nearly dry by a nitrogen evaporator according to claim 1 or 2, characterized in that, The nitrogen blowing needles (1-4), sampling needles (3-5), VOC sensors (3-4) and nitrogen blowing independent valves (1-3) are all multiple. The multiple nitrogen blowing independent valves (1-3) are connected to the multiple nitrogen blowing needles (1-4) one by one, and the inlet ends of the multiple nitrogen blowing independent valves (1-3) are commonly connected in parallel to the outlet end of the total nitrogen input control valve (1-2); the inlet end of the gas detection gas path (3) is connected in parallel with multiple branch pipelines. The inlet ends of the multiple branch pipelines are connected to the multiple sampling needles (3-5) one by one, and the multiple VOC sensors (3-4) are installed on the multiple branch pipelines one by one.

5. It is characterized in that, It includes the following steps: S1. Open the nitrogen blowing independent valve (1-3): Open the nitrogen blowing independent valve (1-3) corresponding to the sample to be blown to nearly dry. S2. Adjust the input nitrogen gas volume: According to the number of samples to be concentrated selected, set the average flow rate of nitrogen gas blown into the centrifuge tube, and calculate and set the magnitude of the total nitrogen blowing flow rate. S3. Sample concentration: Set the running speed of the motion module to make the nitrogen blowing needle (1-4) and the sampling needle (3-5) track the sample liquid level, so that the distance between the nitrogen blowing needle (1-4), the sampling needle (3-5) and the solvent liquid level is kept within a fixed height range. S4. Nearly dry detection of the sample: The VOC sensor (3-4) detects in real time the content of volatile organic compounds in the evaporation mixed gas during the concentration process of the corresponding sample, and calculates the liquid level height and the concentration degree of the sample in the centrifuge tube according to the content of the volatile organic compounds in the evaporation mixed gas detected by the VOC sensor (3-4), and determines whether the sample in the centrifuge tube is nearly dry. S5. Close the nitrogen blowing independent valve (1-3): When it is calculated that the liquid level of the sample is nearly dry, close the nitrogen blowing independent valve (1-3) corresponding to the nearly dry sample.

6. The method for detecting that the concentrated sample is nearly dry by a nitrogen blowing instrument according to claim 5, characterized in that, Reset the VOC sensor (3-4) before step S3: Control the gas path switching valve (3-3) to connect the VOC sensor (3-4) to the nitrogen gas source (1-1) adjusted by the flow valve (2-1) for a quick reset of the VOC sensor (3-4); after the VOC sensor (3-4) is reset, control the gas path switching valve (3-3) to connect the sampling needle (3-5) to the vacuum pump (3-2), control the motion module to move, and the motion module drives the nitrogen blowing needle (1-4) and the sampling needle (3-5) to move above the liquid surface of the sample, and then start the vacuum pump (3-2).

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