Methyl mercury in-situ sampling device utilizing gas chromatography gas circuit

Abstract

The invention discloses a methyl mercury in-situ sample injection device utilizing a gas chromatography gas circuit, the device utilizes the gas chromatography gas circuit, and a gas phase detection device comprises a purging module (a sample injection needle, a gas flowmeter, a sample injection bottle with a polytetrafluoroethylene inner pad, a pressure stabilizing valve and a chromatography air circuit); the trapping module comprises a trapping trap, a quartz conduit, a heating coil with the resistance of about 11 ohm, a temperature control system and a heat dissipation system; the chromatography and sample injection module is based on a column oven, a chromatographic column and a carrier gas flow path flow control system of an old gas chromatograph. According to the device, accurate detection of methyl mercury is realized through an idle steady flow and steady pressure system and a gas path system of old gas chromatography. A water sample standard addition recovery experiment and a biological sample standard substance both show that the result meets the American EPA1630 standard.

Description

Technical Field

[0001] This invention belongs to the field of ecological and environmental monitoring, specifically to an in-situ sampling device for methylmercury determination. Economically, this device utilizes the pressure and flow stabilization equipment of older manual chromatographs as a gas path support, eliminating the need for expensive specialized equipment and complex components, significantly reducing production costs. Background Art

[0002] Methylmercury is highly bioaccumulative and biomagnifiable, and is also highly neurotoxic, posing a serious threat to human health (especially the nervous system) and ecosystems. Through the food chain, methylmercury concentrations in aquatic organisms accumulate and significantly amplify, leading to significant increases in methylmercury levels in organisms at higher trophic levels. This process not only exacerbates methylmercury pollution, seriously threatening human food safety, but also causes significant damage to aquatic ecosystems. Monitoring methylmercury is crucial for protecting human health and ecological security. Currently, the cost of complete methylmercury analysis equipment is high. For example, the US Tekran 2700 and Beijing Polytech Instrument Co., Ltd.'s MMA72 cost approximately 800,000 to 1,000,000 RMB and 300,000 to 500,000 RMB, respectively. This hinders the widespread use of methylmercury analysis and monitoring. Existing methylmercury determination methods mostly use purge and trap-gas chromatography-cold atomic fluorescence spectrometry detection. To save costs, researchers have attempted to build methylmercury sampling equipment based on the analytical principle. However, achieving stable pressure and flow in a home-built methylmercury determination system presents a technical challenge. Professional voltage and current stabilization equipment is not only expensive, but also has high requirements on the technical level of the operator.

[0003] With the development of equipment and the upgrading of gas chromatographs, a large number of old manual injection gas chromatographs have been left idle. However, their relatively complete and functional voltage and flow stabilization equipment can save costs and provide stable gas path support for methylmercury analysis. The present invention proposes a methylmercury in-situ injection device that utilizes the voltage and flow stabilization equipment and column oven of old manual injection gas chromatographs to provide stable gas path support for methylmercury analysis, significantly reducing costs. At the same time, by optimizing the gas path design, improving the temperature control module, and linking the control of the solenoid valve, the operational difficulty is reduced. Summary of the Invention

[0004] Purpose of the Invention

[0005] This device provides an economical and low-cost in-situ methylmercury injection device. This device uses the pressure and flow stabilization equipment of an old manual injection chromatograph to construct the gas path, eliminating the need to purchase an expensive new gas path system, significantly saving equipment costs.

[0006] Technical Solution

[0007] The core scheme of the present invention is as follows:

[0008] 1. Gas supply module:

[0009] A single gas source partial pressure design is adopted, and the gas flow in the chromatographic pipeline is uniformly controlled by the gas chromatographic pressure regulating valve (0.2MPa). The air flow is used as the purge flow, the chromatographic carrier gas I gas path is used as the carrier gas for the methylmercury test system, and the chromatographic carrier gas II is used as the injection gas to reduce gas path interference. The two-position three-way solenoid valve (V2, V3) and the solenoid switch V1 are linked to control the purge, capture and injection gas path switching ( Figure 1 ), green represents the purge gas flow, blue represents the chromatographic carrier gas flow, and red represents the injection gas flow, ensuring that the gas flows enter the chromatographic column synchronously.

[0010] 2. In-situ purge and trap module: This module primarily includes the injection needle, trap, and thermal desorption system. The injection needle and trap are supplied by a third party. The thermal desorption system utilizes a built-in quartz tube (8mm outer diameter, 5mm inner diameter) and a chromium-nickel heating wire (11Ω resistance). The thermal desorption system (150°C) is equipped with an independent temperature control system (K-type bare-end thermocouple + PID temperature controller + DC-to-DC fixed relay) to monitor and regulate temperature fluctuations in real time.

[0011] 3. Cracking chamber module: This section primarily includes the quartz cracking tube, high-temperature cracking chamber, and temperature control system. The cracking chamber (750°C) is equipped with an independent temperature control system (K-type bare-end thermocouple + PID temperature controller + DC-to-DC fixed relay) to monitor and regulate temperature fluctuations in real time.

[0012] 4. Operation procedure: The equipment operation procedure mainly consists of five processes: purge and capture, dry purge, thermal desorption, headspace sampling, and standby.

[0013] (1) Purge and trap process: The trap temperature was set at 25°C. The two-position three-way solenoid valves (V2 and V3) were kept in the trapping position (NO), and the solenoid switch V1 was in the closed position (NO). After the sample was added to the pretreatment, the injection needle was inserted and the gas flowmeter FR3 was adjusted to control the airflow. The purge time was specifically controlled to be 5 min.

[0014] (2) Dry blow: Insert the injection needle directly into the headspace bottle with a cap, consistent with the purge process, and the trap dry blow time is 5 minutes.

[0015] (3) Thermal desorption: After the dry blow is completed, turn on the thermal desorption switch.

[0016] (4) Headspace injection: When the trap temperature reaches 130°C, first adjust the two-position three-way solenoid valve (V2, V3) to the injection position (NC) in sequence. At this time, the gas flow meter FR1 will have airflow due to the air pressure but will automatically return to zero. After the gas flow meter FR1 returns to zero, adjust the solenoid switch V1 to the open position (NC). After the methylmercury peak is completely eluted, the trap temperature drops below 80°C, and the solenoid switch V1 is adjusted to the closed position (NO). At this time, the gas flow meter FR2 resumes the chromatographic gas supply, and then adjust the two-position three-way solenoid valve (V3, V2) to the capture position (NO) in sequence.

[0017] (5) Standby: Keep the two-position three-way solenoid valves (V2, V3) in the trap position (NO); adjust the solenoid switch V1 to the closed position (NO). Follow the injection procedure once to purge the trap.

[0018] Beneficial effects

[0019] Low economic cost: The old manual injection chromatography group's pressure and flow stabilization equipment is used to provide a stable gas supply for methylmercury analysis, eliminating the need to purchase expensive new gas systems and significantly reducing costs.

[0020] Easy to operate: Solenoid valve linkage realizes full process control of purging, capturing, sampling and detection, effectively reducing manual operation and lowering the difficulty of operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings and tables used are briefly introduced below.

[0022] Figure 1 This is a schematic diagram of the assembly of the methylmercury equipment described in the technical solution (blue represents the chromatographic carrier gas flow, red represents the injection gas flow, and green represents the purge gas flow; NC represents the gas flow control end, and NO represents the gas flow normally open end).

[0023] Figure 2 This is the effect of the purge time on the determination in Example 1 (dosage is 50 pg, stable purge flow rate is 40 mL / min).

[0024] Figure 3 This is the effect of the drying time on the determination in Example 1 (dosage is 50 pg, stable purge flow rate is 40 mL / min, and purge time is 5 min).

[0025] Figure 4 The chromatogram (A) and the methylmercury standard curve (B) of the methylmercury detection equipment in Example 1 are shown.

[0026] Figure 5 This is the methylmercury spike recovery experiment in freshwater samples in Example 2 (n=3).

[0027] Figure 6This is the determination and recovery verification of the methylmercury standard substance in Example 2 (n=5). DETAILED DESCRIPTION

[0028] Example 1: Equipment parameter optimization

[0029] The present invention is based on the above device to analyze the main parameters affecting sample determination, purge time ( Figure 2 ) and dry blowing time ( Figure 3 ) has been optimized.

[0030] The experiment determined that when the stable purge flow rate was 40 mL / min, the purge and capture time was set to 5 minutes, and the capture well drying time was set to 5 minutes.

[0031] Using the equipment built, the experiment obtained a complete MeHg analysis chromatogram ( Figure 4 A) and MeHg standard curve ( Figure 4 B). The chromatographic conditions used in the experiment were as follows: column length × inner diameter: 500 mm × 1.6 mm (stationary phase: 15% OV-1, support: ChromW-AW (DMCS) 80 / 100 mesh, outer diameter: 3 mm); flow rate: 35 mL / min, column temperature: 50°C, MeHg peak time: 0.85 min. Good linearity (R) was observed for MeHg in the range of 5 pg to 100 pg. 2 =0.9998), which meets the analysis requirements.

[0032] Example 2: Accurate qualitative inspection of equipment

[0033] The present invention uses the aforementioned device to perform analyses and verify the accuracy of analytical equipment and methods. The accuracy of aqueous media analysis methods is primarily verified using the spike recovery method; the accuracy of biological sample analysis methods is primarily verified by comparison with fish tissue standards (TORT-2) and mussel tissue standards (SRM-2976).

[0034] Verification of freshwater sample analysis method. Two freshwater samples were collected in the experiment. 25mL of water sample was added to a 40mL injection bottle, and 0, 10pg, 25pg, and 50pg of MeHg were added respectively; the pH value was adjusted to 4.8 using 225μL of 2 mol / L acetate buffer; and 30μL of 1% sodium tetraethylborate / potassium hydroxide solution (200mg of sodium tetraethylborate dissolved in 20mL of 2% potassium hydroxide solution) was added. The results are as follows Figure 5 The recovery rate is 80.9%-109.3%, which meets the requirement of EPA 1630 method 75%-125%.

[0035] Validation of the biological sample analysis method. Weigh 0.1g of TORT-2 and RM-2976 standard substances respectively. Digest with 2mL of 25% KOH methanol solution at 70℃ for 8h, then dilute to 10mL. Pipette 50μL of the digestion solution into the injection bottle and add 25mL of ultrapure water. Inject according to the above process, the results are as follows Figure 6 The TORT-2 recovery rate was calculated to be 82.8%-99.2%, and the SRM-2976 recovery rate was 83.5%-91.4%, meeting the EPA 1630 method requirement of 75%-125%.

Claims

1. A methylmercury in-situ sampling device using a gas chromatography gas line, characterized in that: The old gas chromatography gas system was used to establish an in-situ purge and trap module and an integrated injection module.

2. The device according to claim 1, wherein the methylmercury in-situ sampling device adopts a single gas source partial pressure design, and controls the switching of the chromatographic carrier gas and the injection gas path through a two-position three-way solenoid valve (V2, V3) and an electromagnetic switch V1.

3. according to the device described in claim 2, the in-situ purge and trap module adopts the chromatographic air gas path as the purge gas flow and the chromatographic carrier gas I gas path as the methylmercury test system carrier gas; the purge and trap process is controlled by controlling the two-position three-way solenoid valve (V2, V3). Specifically, the purge time is controlled to be 5min and the trap dry purge time is 5min.

4. The device according to claim 1, wherein the integrated injection module uses chromatographic carrier gas II as the injection gas path; and the injection process is controlled by controlling the two-position three-way solenoid valve (V2, V3).

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