Secondary purging and trapping system and method for determination of alkyl mercury in liquid sample

Abstract

The invention discloses a two-stage purging and trapping system and method for determination of alkyl mercury in a liquid sample, and relates to the technical field of alkyl mercury determination equipment.The system comprises a purging bottle, a trapping trap, a blowing device and a switching valve, and secondary trapping and efficient purification of the sample are achieved by precisely controlling gas flow and heating analysis; by means of the eight-channel design of the switching valve mechanism, the system can flexibly switch different channels, and simultaneous or continuous treatment of multiple samples is achieved; by means of the design, the sample processing efficiency is improved, manual operation is reduced, and the automation degree is improved; when the first-stage trapping trap performs heating analysis and second-stage trapping, other channels can start the purging trapping process of a next sample, so that the continuous operation capability of the system is realized; the working efficiency of a laboratory is greatly improved, and the sample treatment period is shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of alkyl mercury determination equipment, and more particularly to a secondary purge trapping system and method for determining alkyl mercury in a liquid sample. Background Art

[0002] Alkyl mercury includes methyl mercury, ethyl mercury, dimethyl mercury, diethyl mercury, propyl mercury and other organic forms of mercury. Among them, methyl mercury and ethyl mercury are the most concerned organic forms of mercury at home and abroad. Their physiological toxicity, bioaccumulation and concentration levels in the environment are more prominent. The environmental protection standards related to alkyl mercury are all based on the purge and capture method. Methyl mercury and ethyl mercury in water or extract react with sodium tetrapropylborate to generate volatile methyl propyl mercury and ethyl propyl mercury. After purge and capture, thermal desorption and gas phase horizontal separation, they are then cracked at high temperature into mercury vapor and measured by cold atomic fluorescence spectrometry.

[0003] The Chinese patent with publication number CN108333380A discloses an automatic sampling device and an automatic sampling method thereof, which includes an automatic alternating sampling device and a first and a second capturing device; the purge gas inlet, the dry gas inlet and the carrier gas inlet of the automatic alternating sampling device are respectively connected to the purge gas source, the dry gas source and the carrier gas source, the two pairs of sample outlets of the automatic alternating sampling device are respectively connected to the first and the second capturing devices, and the sample detection port of the automatic alternating sampling device is connected to the detection device; the automatic alternating sampling device and the first and the second capturing devices are all controlled by the system control circuit. The invention has a simple structure and is easy to operate, and can be widely used in the field of sample analysis and processing, but the purge method in the invention cannot improve the efficiency of purge capture, and cannot backwash and drain the pipeline.

[0004] In order to improve the purge efficiency, the present invention provides a two-stage purge and capture system and method for determining alkyl mercury in a liquid sample. Summary of the invention

[0005] In view of the shortcomings of the background technology, the object of the present invention is to provide a two-stage purge and capture system and method for the determination of alkyl mercury in liquid samples.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A secondary purge trapping system for determining alkyl mercury in a liquid sample, comprising a purge bottle mechanism and a first air blowing device, wherein the purge bottle mechanism is respectively connected with a secondary three-way valve and a three-way valve, the first air blowing device is connected with the secondary three-way valve and is used to blow nitrogen into the secondary three-way valve, one end of the three-way valve is connected with a sample bottle, one end of the sample bottle is connected with a switching valve mechanism, the switching valve mechanism is connected with a primary three-way valve, the switching valve mechanism is connected with a primary trap and is used for primary trapping;

[0008] It also includes a second blowing device and a waste valve. The second blowing device is connected to the switching valve mechanism and is used to blow argon into the switching valve mechanism. The waste valve is connected to the switching valve mechanism and is installed. The switching valve mechanism is also connected to a secondary capture trap and is used for secondary capture.

[0009] Preferably, the purge bottle mechanism comprises a cylindrical bottle body, the two ends of the cylindrical bottle body are respectively connected to a spherical bottle body and a liquid inlet pipe, the spherical bottle body is also connected to a liquid outlet pipe, one end of the liquid inlet pipe is connected and installed on a secondary three-way valve, and one end of the liquid outlet pipe is connected and installed on the three-way valve.

[0010] Preferably, the switching valve mechanism includes a total of eight passages, namely passage one, passage two, passage three, passage four, passage five, passage six, passage seven and passage eight, and the switching valve mechanism is used to switch the connecting paths between the eight passages.

[0011] The secondary purge-and-trap method for determining alkyl mercury in a liquid sample is implemented based on the secondary purge-and-trap system for determining alkyl mercury in a liquid sample, and uses a sampling needle, a GC separation chromatography analysis device and a waste liquid bucket to perform the following steps:

[0012] S1: Channel selection, the switching valve mechanism switches the required capture channel to the offline purge capture state, disconnects it from the secondary capture trap, and the sampling needle pierces through the septum into the purge bottle mechanism. The second blowing device is turned on, and the liquid is transferred to the purge bottle mechanism and starts purge capture. The target is adsorbed on the primary capture trap;

[0013] S2: After the purge is completed, open the first-level three-way valve to blow air, and open the three-way valve. The first-level three-way valve purges the air to dry the first-level trap while emptying the purge bottle mechanism. The liquid in the purge bottle mechanism is discharged into the waste liquid barrel through the three-way valve;

[0014] S3: The switching valve mechanism switches again, switching the primary trap to the main flow path to connect with the secondary trap, releasing the purge bottle mechanism, and the other channels connected to the primary trap can start to purge the next sample;

[0015] S4: The primary trap starts heating and desorption, and the argon gas blown out by the second blowing device transfers the target released by thermal desorption to the secondary trap to start secondary trapping;

[0016] S5: The secondary trap starts to heat and desorb, and the argon gas blown out by the second blowing device transfers the released target substance to the GC separation chromatography analysis device for separation and detection.

[0017] Preferably, the specific steps of S1 are:

[0018] S1.1: Open the secondary three-way valve and the first blowing device, and blow air into the purge bottle mechanism through the guide of the secondary three-way valve.

[0019] S1.2: After 7-9 minutes of continuous blowing, the substances in the purge bottle mechanism are continuously adsorbed by gas.

[0020] S1.3: By switching passage eight and passage seven in the valve mechanism, the substances carried in the gas are collected through a primary trap.

[0021] Preferably, the specific steps of S2 are:

[0022] S2.1: Switch the passages of the secondary three-way valve and the primary three-way valve, open the three-way valve, and continue blowing through the first blowing device;

[0023] S2.2: The gas passes through the secondary three-way valve, the primary three-way valve, the switching valve mechanism, the primary trap, the sample bottle and the three-way valve in sequence. The gas path in the switching valve mechanism passes through passage three, passage four, passage eight and passage seven in sequence.

[0024] Preferably, the specific steps of S3 are:

[0025] S3.1: The switching valve mechanism switches the internal passages so that passage 8 is connected to passage 1, passage 2 is connected to passage 3, passage 4 is connected to passage 5, and passage 6 is connected to passage 7;

[0026] S3.2: connecting the passages of the primary trap and the secondary trap by switching the switching valve mechanism;

[0027] S3.3: Prepare for the next purge.

[0028] Preferably, the specific steps of S4 are:

[0029] S4.1: Turn on the second blowing device, and the second blowing device takes air into the switching valve mechanism;

[0030] S4.2: The gas passes through the second blowing device, passage 5, passage 4, primary trap, passage 8, passage 1 and secondary trap in sequence;

[0031] S4.3: The gas is heated and desorbed when passing through the primary trap, and adsorbed when passing through the secondary trap.

[0032] Preferably, the specific steps of S5 are:

[0033] S5.1: The secondary trap starts heating and desorption to blow out the substances in the gas;

[0034] S5.2: The blown gas is passed through a GC separation chromatography analysis device for GC separation chromatography analysis.

[0035] Preferably, the specific steps of S5.1 are:

[0036] S5.11: The second blowing device starts blowing, and the gas enters the switching valve mechanism;

[0037] S5.12: The gas repeats the S4.2 process in the switching valve mechanism and blows the desorbed substances in the primary trap into the secondary trap;

[0038] S5.13: The secondary trap adsorbs the material brought in by the gas and desorbs it again by heating;

[0039] S5.14: Blow out the desorbed material from the secondary trap.

[0040] Beneficial effects of the present invention:

[0041] 1. The present invention adopts a dual capture mechanism of a primary capture trap and a secondary capture trap. This design can more effectively enrich and purify the target (alkyl mercury) and reduce background interference and impurity effects. The primary capture trap initially captures and removes most impurities, while the secondary capture trap further purifies the target, thereby significantly improving the sensitivity and accuracy of detection. By precisely controlling the purge and capture process, the stability and consistency of the target during the capture process can be ensured, further improving the reliability of the test results.

[0042] 2. The eight-channel design of the switching valve mechanism enables the system to flexibly switch between different channels to achieve simultaneous or continuous processing of multiple samples. This design not only improves the efficiency of sample processing, but also reduces manual operations and improves the degree of automation. While the primary trap is performing heating analysis and secondary trapping, other channels can start the purge trapping process of the next sample, realizing the continuous operation capability of the system. This greatly improves the work efficiency of the laboratory and shortens the sample processing cycle.

[0043] 3. By precisely controlling the purge and capture process, the system can minimize the generation of waste liquid. The waste liquid is discharged into the waste liquid barrel through the waste valve, which is convenient for subsequent treatment and reduces pollution to the environment. At the same time, nitrogen and argon are used as purge gases, and the efficient use of gas resources is achieved by precisely controlling the gas flow and usage time. At the same time, the secondary capture mechanism also reduces gas waste and improves resource utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the structure of the purge bottle mechanism in the two-stage purge-and-trap system for the determination of alkyl mercury in liquid samples;

[0045] Figure 2 The working flow diagram of the two-stage purge and trap system for the determination of alkylmercury in liquid samples is shown in FIG.

[0046] Figure 3 It is a flow chart of the primary capture process;

[0047] Figure 4 Flow chart of the secondary capture process.

[0048] Figure numerals: 100, purge bottle mechanism; 101, cylindrical bottle body; 102, spherical bottle body; 103, liquid inlet pipe; 104, liquid outlet pipe; 200, switching valve mechanism; 201, primary trap; 202, waste valve; 203, secondary trap; 204, primary three-way valve; 205, secondary three-way valve; 206, sample bottle; 207, three-way valve. DETAILED DESCRIPTION

[0049] Example 1

[0050] See also Figure 1-Figure 2 This embodiment introduces a secondary purge trapping system for determining alkyl mercury in a liquid sample, comprising a purge bottle mechanism 100 and a first air blowing device, wherein the purge bottle mechanism 100 is respectively connected with a secondary three-way valve 205 and a three-way valve 207, the first air blowing device is connected with the secondary three-way valve 205 and is used to blow nitrogen into the secondary three-way valve 205, one end of the three-way valve 207 is connected with a sample bottle 206, one end of the sample bottle 206 is connected with a switching valve mechanism 200, the switching valve mechanism 200 is connected with a primary three-way valve 204, the switching valve mechanism 200 is connected with a primary trap 201 and is used for primary trapping;

[0051] It also includes a second blowing device and a waste valve 202. The second blowing device is connected and arranged on the switching valve mechanism 200 and is used to blow argon into the switching valve mechanism 200. The waste valve 202 is connected and installed on the switching valve mechanism 200. The switching valve mechanism 200 is also connected and provided with a secondary capture trap 203 and is used for secondary capture.

[0052] The purge bottle mechanism 100 includes a cylindrical bottle body 101, and the two ends of the cylindrical bottle body 101 are respectively connected to a spherical bottle body 102 and a liquid inlet pipe 103, and the spherical bottle body 102 is also connected to a liquid outlet pipe 104. One end of the liquid inlet pipe 103 is connected and installed on a secondary three-way valve 205, and one end of the liquid outlet pipe 104 is connected and installed on a three-way valve 207.

[0053] The switching valve mechanism 200 includes eight passages, namely, passage 1, passage 2, passage 3, passage 4, passage 5, passage 6, passage 7 and passage 8. Figure 2 , Figure 3 , Figure 4 In the figure, they are represented by numbers 1-8 respectively, and the switching valve mechanism 200 is used to switch the communication paths between the eight passages. Figure 2 , Figure 3 , Figure 4 In the figure, V1 is the channel selection valve. The primary trap 201 and the secondary trap 203 are connected to the channel selection valve. The primary trap 201 performs H1 heating and C1 cooling, and is connected to the channel selection valve positions 8 and 4, i.e., channel eight and channel four; the exhaust valve 202 performs H2 heating and C2 cooling, and is connected to the channel selection valve positions 2 and 6. H1 heating is the first heating, C1 cooling is the first cooling, and the subsequent H2 / C2 / H3 / C3 are analogous.

[0054] The V2 carrier gas valve (one in and one out, a switch) is connected to the channel selection valve position 5, and the secondary trap 203 (H3 heating, C3 cooling) is connected to the channel selection valve position 1.

[0055] The outlet of the purge pipe is connected to position 7 of the channel selection valve.

[0056] V3 purge air valve (one in and one out, a switch).

[0057] V4 represents two two-position three-way valves, com at V4 represents the common end of V4, NO at V4 represents the normally open end of V4, and NC at V4 represents the normally closed end of V4.

[0058] V5 represents a two-position three-way valve. com at V5 represents the common end of V5, which is connected to the lower end of the purge tube. NO at V5 is connected to the sampling needle. NC at V5 is the normally closed end connected to the waste liquid barrel.

[0059] In summary, first, the liquid sample to be tested is introduced into the cylindrical bottle body 101 of the purge bottle mechanism 100 through the liquid inlet pipe 103. The design of the spherical bottle body 102 helps to reduce the evaporation loss of the sample during the purge process, while the liquid outlet pipe 104 reserves the possibility of subsequent processing.

[0060] Next, the first blowing device is started to blow nitrogen into the secondary three-way valve 205. Nitrogen, as a carrier gas, enters the purge bottle mechanism 100 through the secondary three-way valve 205 to preliminarily purge the sample in the sample bottle 206. This step is intended to take the volatile components (including alkyl mercury) in the sample out of the sample bottle 206 and enter the subsequent capture process.

[0061] The gas after the preliminary purge (containing volatile components such as alkyl mercury) enters the primary three-way valve 204 through the guidance of the switching valve mechanism 200. At this time, the switching valve mechanism 200 adjusts the channel connection according to the preset program to make the gas flow to the primary trap 201.

[0062] The primary trap 201 uses a highly selective adsorption material that can specifically capture target compounds such as alkylmercury, while allowing most non-target compounds to pass through, thereby achieving preliminary purification.

[0063] After the primary trapping, the switching valve mechanism 200 adjusts the channel connection again to release the target compound enriched in the primary trap 201 and enter the secondary trap 203 through the three-way valve 207 .

[0064] During this process, the second blowing device is activated to blow argon as a purge gas into the switching valve mechanism 200. The inert property of argon helps to reduce the loss and contamination of the target compound during the transmission process.

[0065] The secondary capture trap 203 uses a more efficient adsorption material to further enrich and purify target compounds such as alkyl mercury, remove residual impurities, and improve analytical sensitivity.

[0066] Non-target compounds and some impurities that are not completely adsorbed are discharged from the system through the waste valve 202 to reduce interference with subsequent analysis.

[0067] When the secondary capture is completed, the switching valve mechanism 200 adjusts the channel connection again to introduce the enriched and purified target compound into an analytical instrument (such as a gas chromatography-mass spectrometer) for quantitative analysis.

[0068] Example 2

[0069] See also Figure 1-Figure 4 Another embodiment provided by the present invention is a two-stage purge-and-trap method for determining alkyl mercury in a liquid sample, which is performed based on the two-stage purge-and-trap system for determining alkyl mercury in a liquid sample, using a sampling needle, a GC separation chromatography analysis device and a waste liquid bucket, and performing the following steps:

[0070] S1: Channel selection is performed, the switching valve mechanism 200 switches the required capture channel to the offline purge capture state, disconnects from the secondary capture trap 203, and the sampling needle pierces through the septum into the purge bottle mechanism 100. The second blowing device is turned on, the liquid is transferred to the purge bottle mechanism 100 and starts purge capture. The target object is adsorbed on the primary capture trap 201;

[0071] S2: After the purge is finished, the primary three-way valve 204 is opened for purge, and the three-way valve 207 is opened. The primary three-way valve 204 purges the primary trap 201 with purge gas and empties the purge bottle mechanism 100 at the same time. The liquid in the purge bottle mechanism 100 is discharged into the waste liquid bucket through the three-way valve 207;

[0072] S3: The switching valve mechanism 200 is switched again, and the primary trap 201 is switched to the main flow path to connect with the secondary trap 203, and the purge bottle mechanism 100 is released, and other channels connected to the primary trap 201 can start to purge the next sample;

[0073] S4: The primary trap 201 starts heating and desorption, and the argon gas blown out by the second blowing device transfers the target released by thermal desorption to the secondary trap 203 to start secondary capture;

[0074] S5: The secondary trap 203 starts heating and desorption, and the argon gas blown out by the second blowing device transfers the decomposed and released target substances to the GC separation chromatography analysis device for separation and detection.

[0075] The specific steps of S1 are:

[0076] S1.1: Open the secondary three-way valve 205 and the first blowing device to blow air into the purge bottle mechanism 100 through the guidance of the secondary three-way valve 205 .

[0077] S1.2: After 7-9 minutes of continuous blowing, the substances in the purge bottle mechanism 100 are continuously adsorbed by the gas.

[0078] S1.3: By switching passage eight and passage seven in the valve mechanism 200 , the substances carried in the gas are collected through the primary trap 201 .

[0079] The specific steps of S2 are:

[0080] S2.1: Switch the passages of the secondary three-way valve 205 and the primary three-way valve 204, and open the three-way valve 207, and continue blowing through the first blowing device;

[0081] S2.2: The gas passes through the secondary three-way valve 205, the primary three-way valve 204, the switching valve mechanism 200, the primary trap 201, the sample bottle 206 and the three-way valve 207 in sequence. The gas path in the switching valve mechanism 200 passes through passage three, passage four, passage eight and passage seven in sequence.

[0082] The specific steps of S3 are:

[0083] S3.1: The switching valve mechanism 200 switches the internal passages so that passage 8 is connected to passage 1, passage 2 is connected to passage 3, passage 4 is connected to passage 5, and passage 6 is connected to passage 7;

[0084] S3.2: connecting the passages of the primary trap 201 and the secondary trap 203 by switching the switching valve mechanism 200;

[0085] S3.3: Prepare for the next purge.

[0086] The specific steps of S4 are:

[0087] S4.1: Turn on the second blowing device, and the second blowing device takes air into the switching valve mechanism 200;

[0088] S4.2: The gas passes through the second blowing device, passage 5, passage 4, primary trap 201, passage 8, passage 1 and secondary trap 203 in sequence;

[0089] S4.3: The gas is heated and desorbed when passing through the primary trap 201 , and is adsorbed when passing through the secondary trap 203 .

[0090] The specific steps of S5 are:

[0091] S5.1: The secondary trap 203 starts heating and desorption to blow out the substances in the gas;

[0092] S5.2: The blown gas is passed through a GC separation chromatography analysis device for GC separation chromatography analysis.

[0093] The specific steps of S5.1 are:

[0094] S5.11: The second blowing device starts blowing, and the gas enters the switching valve mechanism 200;

[0095] S5.12: The gas repeats the S4.2 process in the switching valve mechanism 200 and blows the desorbed substances in the primary trap 201 into the secondary trap 203;

[0096] S5.13: The secondary trap 203 adsorbs the substances brought in by the gas and desorbs them again by heating;

[0097] S5.14: Blow out the desorbed substances in the secondary trap 203.

[0098] In summary, the main flow path is the gas blown into the second blowing device, first entering the passageway 5, and then passing through the passageway 4, the passageway 8 and the passageway 1 in sequence; first, the required capture channel is switched to the offline purge capture state through the switching valve mechanism 200 to ensure that it is disconnected from the secondary capture trap 203 to avoid interference. The sampling needle pierces the septum and enters the purge bottle mechanism 100, and at the same time, the second blowing device (usually using argon) is opened to start transferring the liquid sample to the purge bottle mechanism 100.

[0099] As the second blowing device continues to blow (about 7-9 minutes), the liquid sample in the purge bottle mechanism 100 is heated and evaporated, and the volatile components (including alkyl mercury) flow out with the gas and are guided to the primary trap 201 through specific channels (such as channel eight and channel seven) of the switching valve mechanism 200. The adsorbent material in the primary trap 201 specifically captures these target substances to achieve preliminary enrichment.

[0100] After the purge is completed, the passages of the secondary three-way valve 205 and the primary three-way valve 204 are switched, and the three-way valve 207 is opened, and the first blowing device (usually nitrogen gas) is used for purge to dry the primary trap 201 and empty the purge bottle mechanism 100. The gas passes through each component in turn, and finally the residual liquid in the purge bottle mechanism 100 is discharged into the waste liquid bucket.

[0101] During this process, the path of the gas in the switching valve mechanism 200 is carefully designed to ensure effective exhaustion and reduce the loss of the target object.

[0102] The switching valve mechanism 200 adjusts the internal passage again, connects the primary trap 201 with the secondary trap 203, and releases the purge bottle mechanism 100 to prepare for the purge of the next sample. The other channels of the primary trap 201 can be used for the purge and capture of other samples, thereby improving the processing efficiency of the system.

[0103] Make all preparations for the next purge, including adjusting valve status, preheating equipment, etc.

[0104] The second blowing device is turned on to allow air to enter the switching valve mechanism 200. The gas enters the primary trap 201 through a specific channel, and the primary trap 201 is heated to release the adsorbed target. The released target flows with the gas to the secondary trap 203 for secondary enrichment and purification. This step further improves the concentration and purity of the target, providing high-quality samples for subsequent analysis.

[0105] The secondary trap 203 starts heating and desorbing, releasing the adsorbed target into the gas. The second blowing device continues blowing, sending the desorbed gas into the GC separation chromatography analysis device. In this process, the path of the gas in the switching valve mechanism 200 is similar to S4.2, but in the opposite direction, ensuring that the target is effectively transferred.

[0106] In the GC separation chromatography analysis device, the target substances are separated according to their adsorption and desorption characteristics on the chromatographic column and detected by the detector. The resulting chromatogram of the target substances can be used to quantitatively analyze the alkyl mercury content in the liquid sample.

[0107] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A two-stage purge-and-trap system for the determination of alkyl mercury in liquid samples, characterized in that: The invention comprises a purge bottle mechanism (100) and a first air blowing device, wherein the purge bottle mechanism (100) is respectively connected with a secondary three-way valve (205) and a three-way valve (207), the first air blowing device is connected with the secondary three-way valve (205) and is used to blow nitrogen into the secondary three-way valve (205), one end of the three-way valve (207) is connected with a sample bottle (206), one end of the sample bottle (206) is connected with a switching valve mechanism (200), the switching valve mechanism (200) is connected with a primary three-way valve (204), and the switching valve mechanism (200) is connected with a primary trap (201) and is used for primary trapping; It also includes a second blowing device and a waste valve (202), wherein the second blowing device is connected to the switching valve mechanism (200) and is used to blow argon into the switching valve mechanism (200), and the waste valve (202) is connected to the switching valve mechanism (200), and the switching valve mechanism (200) is also connected to a secondary capture trap (203) and is used for secondary capture.

2. The two-stage purge-and-trap system for determining alkylmercury in liquid samples according to claim 1, characterized in that: The purge bottle mechanism (100) comprises a cylindrical bottle body (101), the two ends of the cylindrical bottle body (101) are respectively connected to a spherical bottle body (102) and a liquid inlet pipe (103), the spherical bottle body (102) is also connected to a liquid outlet pipe (104), one end of the liquid inlet pipe (103) is connected and installed on a secondary three-way valve (205), and one end of the liquid outlet pipe (104) is connected and installed on a three-way valve (207).

3. The two-stage purge-and-trap system for determining alkylmercury in liquid samples according to claim 2, characterized in that: The switching valve mechanism (200) comprises a total of eight passages, namely passage one, passage two, passage three, passage four, passage five, passage six, passage seven and passage eight. The switching valve mechanism (200) is used to switch the communication paths between the eight passages.

4. A two-stage purge-and-trap method for determining alkyl mercury in a liquid sample, which is implemented based on the two-stage purge-and-trap system for determining alkyl mercury in a liquid sample according to any one of claims 1 to 3, characterized in that: Using a sampling needle, GC separation chromatography device and waste liquid bucket, perform the following steps: S1: channel selection is performed, the switching valve mechanism (200) switches the required capture channel to the offline purge capture state, disconnects from the secondary capture trap (203), the sampling needle pierces through the septum and enters the purge bottle mechanism (100), the second blowing device is turned on, the liquid is transferred to the purge bottle mechanism (100) and purge capture is started, and the target object is adsorbed on the primary capture trap (201); S2: After the purge is completed, the primary three-way valve (204) is opened for purge, and the three-way valve (207) is opened. The primary three-way valve (204) purges the primary trap (201) with purge gas and empties the purge bottle mechanism (100) at the same time. The liquid in the purge bottle mechanism (100) is discharged into the waste liquid bucket through the three-way valve (207); S3: the switching valve mechanism (200) is switched again, the primary trap (201) is switched to the main flow path to connect with the secondary trap (203), the purge bottle mechanism (100) is released, and other channels connected to the primary trap (201) can start to purge the next sample; S4: the primary trap (201) starts heating and decomposing, and the argon gas blown out by the second blowing device transfers the target released by thermal desorption to the secondary trap (203) to start secondary capture; S5: The secondary trap (203) starts heating and desorption, and the argon gas blown out by the second blowing device transfers the target substance released by the analysis to the GC separation chromatography analysis device for separation and detection.

5. The two-stage purge and capture method for determining alkyl mercury in a liquid sample according to claim 4, characterized in that: The specific steps of S1 are: S1.1: Open the secondary three-way valve (205), and open the first blowing device to blow air into the purge bottle mechanism (100) through the guidance of the secondary three-way valve (205); S1.2: After 7-9 minutes of continuous blowing, the substances in the purge bottle mechanism (100) are continuously adsorbed by the gas; S1.3: By switching passage 8 and passage 7 in the valve mechanism (200), the substances carried in the gas are collected through the primary trap (201).

6. The two-stage purge and trap method for determining alkyl mercury in a liquid sample according to claim 4, characterized in that: The specific steps of S2 are: S2.1: Switch the passages of the secondary three-way valve (205) and the primary three-way valve (204), and open the tertiary valve (207), and continue blowing through the first blowing device; S2.2: The gas passes through the secondary three-way valve (205), the primary three-way valve (204), the switching valve mechanism (200), the primary trap (201), the sample bottle (206) and the three-way valve (207) in sequence. The gas travels through passage three, passage four, passage eight and passage seven in sequence in the switching valve mechanism (200).

7. The two-stage purge and capture method for determining alkyl mercury in a liquid sample according to claim 4, characterized in that: The specific steps of S3 are: S3.1: The switching valve mechanism (200) switches the internal passages so that passage 8 is connected to passage 1, passage 2 is connected to passage 3, passage 4 is connected to passage 5, and passage 6 is connected to passage 7; S3.2: connecting the passages of the primary trap (201) and the secondary trap (203) by switching the switching valve mechanism (200); S3.3: Prepare for the next purge.

8. The two-stage purge and capture method for determining alkyl mercury in a liquid sample according to claim 4, characterized in that: The specific steps of S4 are: S4.1: Turning on the second air blowing device, the second air blowing device intakes air into the switching valve mechanism (200); S4.2: The gas passes through the second blowing device, passage five, passage four, primary trap (201), passage eight, passage one and secondary trap (203) in sequence; S4.3: The gas is heated and desorbed when passing through the primary trap (201), and adsorbed when passing through the secondary trap (203).

9. The two-stage purge and trap method for determining alkyl mercury in a liquid sample according to claim 8, characterized in that: The specific steps of S5 are: S5.1: The secondary trap (203) starts heating and desorption to blow out the substances in the gas; S5.2: The blown gas is passed through a GC separation chromatography analysis device for GC separation chromatography analysis.

10. The two-stage purge and trap method for determining alkyl mercury in a liquid sample according to claim 9, characterized in that: The specific steps of S5.1 are: S5.11: The second blowing device starts blowing, and the gas enters the switching valve mechanism (200); S5.12: The gas repeats the S4.2 process in the switching valve mechanism (200) and blows the desorbed substances in the primary trap (201) into the secondary trap (203); S5.13: The secondary trap (203) adsorbs the substances brought in by the gas and desorbs them again by heating; S5.14: Blow out the desorbed substances in the secondary trap (203).

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