Trace substance enrichment and rapid sample injection method and device

Abstract

The invention provides a trace substance enrichment and rapid sample introduction method and device, which is characterized in that a low Curie point alloy wire is coated with a coating for sample enrichment, after enrichment is completed, an induction coil is connected to a high-frequency alternating current to generate a high-speed changing magnetic field, and an eddy current is generated in the alloy wire, so that a heat effect is generated to realize rapid thermal desorption; the heating time is shortened; and overheating is prevented. The invention also provides a device which is divided into three layers of structures, namely the induction coil, the insulating tube and the alloy wire solid-phase extraction head from outside to inside. The device is simple in structure, small in size, high in desorption speed and low in energy consumption, and can be used for continuous online analysis and portable application.

Description

Technical Field

[0001] The invention belongs to the field of sample analysis, and in particular relates to a method and device for enriching and rapidly injecting trace substances. Background Art

[0002] In the early sample analysis and testing process, there were many challenges in detecting trace substances in certain complex samples. The traditional direct sampling method, because the concentration of the target component in the gas is usually low, direct detection is difficult to achieve the required sensitivity and accuracy requirements, and cannot meet the increasingly stringent environmental monitoring and quality control requirements.

[0003] In the field of research on enrichment methods of trace substances, solid phase extraction (SPE) technology has attracted much attention as a classic and widely used method. It separates the measured components from the matrix and interfering components based on the difference in the strength of the forces of different components in the sample on the solid phase filler, and then elutes and collects the measured components with the help of eluent to achieve the purpose of enrichment. SPE has many advantages such as low organic solvent consumption, high enrichment multiple, fast extraction speed, good selectivity and good reproducibility. It has a large number of application examples in environmental water samples, soluble solid environmental samples, and the capture of trace organic matter and aerosols in gases. However, this technology also has certain limitations. For example, the flow rate is limited. When facing relatively dirty samples, it is easy to cause column clogging problems, thereby increasing the sample processing time. In addition, the filler particle size is large, which is easy to cause uneven filling and affect the stability of the enrichment effect. This technology plays an important role in the wide application of environmental monitoring, chemical analysis, drug quality control, food testing and other fields. It is mainly used for the separation, enrichment, desorption and analysis of trace substances in solid, liquid or gas samples.

[0004] The emergence of extraction adsorption technology has brought new solutions for trace analysis of gases. By adding specific adsorbents and utilizing the physical or chemical adsorption between the adsorbent and the target component in the gas, trace target substances can be effectively enriched from a large amount of gas. Different types of adsorbents such as activated carbon, molecular sieves, polymer adsorbents, etc. can selectively adsorb targets of different properties (polarity, boiling point, molecular size, etc.), greatly improving the accuracy and sensitivity of subsequent analysis. After the trace analyte is enriched on the adsorbent, it needs to be desorbed so that the trace analyte can enter the instrument for analysis. Therefore, thermal desorption technology came into being. It is based on the principle of the difference in volatility of substances at different temperatures. By heating the device equipped with the adsorbent, the enriched trace analyte is volatilized from the adsorbent, and then it is transmitted to the subsequent analytical instruments such as ion mobility spectrometer, gas chromatograph, mass spectrometer, etc. for precise analysis using carrier gas.

[0005] The heating method currently used in thermal desorbers is mostly resistance wire heating. This heating method has the disadvantages of long desorption time, large device size, and high power consumption. It is not suitable for continuous online analysis and portable use. It is urgent to develop a rapid thermal desorption method and device. Summary of the invention

[0006] In view of the above-mentioned problems, the present invention provides a method and device for enriching and rapidly injecting trace substances.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention provides a method for enriching and rapidly injecting trace substances, comprising:

[0009] An appropriate adsorbent is selected according to the properties of the substance to be enriched, and then the adsorbent is coated on one end of the alloy wire to form a solid phase extraction head. The alloy wire solid phase extraction head coated with the selective adsorbent is placed in the sample solution or headspace to complete the enrichment of the sample under certain conditions.

[0010] Furthermore, after the enrichment is completed, the alloy wire is fixed in an electromagnetic induction coil, and a carrier gas with a constant flow rate is introduced into the coil through the air hole.

[0011] Furthermore, a high-frequency alternating current is applied to the coil, thereby generating a high-speed changing induced magnetic field.

[0012] Furthermore, the hysteresis loss and eddy current loss generated by the alloy wire will produce a thermal effect, thereby achieving rapid heating to achieve the purpose of rapid thermal desorption.

[0013] Furthermore, the carrier gas introduced during the desorption process brings the desorbed substances into the analytical instrument for analysis.

[0014] Furthermore, when the heating temperature reaches the Curie point of the alloy wire material, the alloy wire stops being heated to prevent the coating from being overheated and lost and decomposed.

[0015] The second aspect of the present invention provides a trace substance enrichment and rapid sample injection device, comprising:

[0016] A device for enriching and rapidly injecting trace substances based on electromagnetic induction heating, the structure of which is shown in Figure 1 , Figure 2 As shown, it includes: an alloy wire 1, an insulating tube 2, a first ferrule 3, a second ferrule 4, an induction coil 5, a solid phase extraction head 6, a carrier gas inlet 7, a sample gas outlet 8, a septum 9, and a needle tube 10.

[0017] The alloy wire 1 is made of a special alloy having a low Curie point.

[0018] The insulating tube 2 has internal threads of a certain depth at both ends thereof, which are used for threaded connection with the first ferrule 3 and the second ferrule 4 to achieve good air tightness.

[0019] The first ferrule 3 has a septum 9 inside. The needle tube 10 enters from the through hole on the first ferrule 3, pierces the septum and enters into the induction coil. The septum can play an airtight role.

[0020] The needle tube 10 has an alloy wire 1 fixed inside it. When injecting a sample, the needle tube 1 pierces the alloy wire 1 protected by the septum. After piercing, the solid phase extraction head 6 on the alloy wire 1 is pushed into the induction coil for desorption.

[0021] The solid phase extraction head 6 has a layer of adsorbent on it. The adsorbent is fixed on the alloy wire 1 by coating and solidification to form the solid phase extraction head 6.

[0022] The second ferrule 4 has a sealing ring (not shown) inside, and the carrier gas pipeline passes through the sealing ring and then exits from the sample gas outlet 8 .

[0023] The sample gas outlet 8 is a channel for the carrier gas to carry out the desorbed trace amount of the substance to be tested, and can be directly connected to the sample inlet of the analytical instrument.

[0024] The induction coil 5 is arranged in a spiral shape, and both ends are electrically connected to a high-frequency alternating power source through a cable.

[0025] The carrier gas inlet 7 is a passage for the carrier gas pipeline to pass through. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the internal device structure of the second embodiment of the present invention.

[0027] Figure 2 It is a side view of the internal device of the second embodiment of the present invention.

[0028] Figure 3 This is the ion migration spectrum of 5 ppb chlorpyrifos obtained by sampling using the device of Example 2 of the present invention.

[0029] Figure 4 This is the ion migration spectrum of 5 ppb chlorpyrifos obtained by direct injection. DETAILED DESCRIPTION

[0030] In the description of the present invention, all directional indications (such as "front", "rear", "left", "right", "upper", "lower", etc.) are based only on the positions shown in the drawings. The descriptions of "first", "second", etc. in the present invention are only used to describe the features and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features.

[0031] Embodiment 1

[0032] This embodiment provides a method for enrichment and rapid injection of trace substances.

[0033] For a certain type of trace substance that needs to be enriched, a specific adsorbent is fixed at one end of the alloy wire to form a solid phase extraction head, and then the solid phase extraction head is placed in the environment of the trace substance that needs to be enriched, and adsorption and enrichment are carried out under certain conditions. After the enrichment is completed, the alloy wire solid phase extraction head is placed in an induction coil, and high-frequency alternating current is passed through the induction coil to heat the alloy wire solid phase extraction head and simultaneously pass a carrier gas to achieve the purpose of rapid desorption. Specifically, the following steps are included:

[0034] 1. Coating of solid phase extraction head on alloy wire: Taking the coating of polydimethylsiloxane (PDMS) adsorbent as an example, prepare high-purity polydimethylsiloxane (PDMS) and curing agent (10:1), and suitable organic solvents (such as toluene, n-hexane, etc.). Prepare clean alloy wire, and its surface is pretreated including grinding, cleaning (cleaning with organic solvents such as acetone to remove oil and impurities) and drying to ensure that the surface is flat and clean. The cleaned alloy wire is surface treated with low-temperature plasma to facilitate the adhesion of PDMS. Slowly immerse the pretreated alloy wire in the PDMS solution, and then slowly withdraw it at a uniform speed so that the PDMS solution is evenly coated on the surface of the alloy wire. Place the alloy wire coated with PDMS solution in a well-ventilated environment to allow the organic solvent to evaporate naturally. Then cure it at a certain temperature (according to the curing requirements of PDMS, such as placing it in an oven at 60-80°C for several hours) to form a stable coating of PDMS. The curing time and temperature should be adjusted according to factors such as the type of PDMS and the thickness of the coating. The solidified alloy extraction head was placed at a high temperature of 180° C. and aged for 5 hours under nitrogen protection.

[0035] 2. Trace substance enrichment: Place the alloy wire solid phase extraction head above the sample or in the liquid where the gas needs to be enriched, and the trace substances inside are adsorbed on the adsorbent, thereby achieving the purpose of enriching the trace substances.

[0036] 3. Induction heating desorption: After completing the enrichment of trace substances, place the alloy wire solid phase extraction head into the induction coil, turn on the high-frequency alternating power supply to power the induction coil, and the current frequency on the induction coil can reach 10-30kHZ. When these currents pass through the induction coil, they will generate a high-speed changing alternating magnetic field. The alloy wire relies on hysteresis loss and eddy current loss to generate heat to achieve the purpose of heating. This process is very short. Generally, according to the needs of actual analysis, the heating time is about 5s, and the thermal conversion rate is as high as 95%, which can be quickly heated to a certain temperature. When the material temperature of the alloy wire reaches its Curie point, the metal changes from ferromagnetism to paramagnetism, the magnetic domain structure is destroyed, and the hysteresis loss almost disappears. Then the power supply of the induction coil is cut off, the heating process is terminated, and the thermal desorption is completed. In different analysis processes, the temperature required for desorption of different substances is different. The desorption temperature can be controlled by selecting the material of the alloy wire.

[0037] Embodiment 2

[0038] This embodiment provides a device for enriching and rapidly injecting trace substances.

[0039] The device is divided into three layers of structure. The innermost structure is that the needle tube 10 enters through the fine hole at the center of the first ferrule 3, pierces the septum and enters the induction coil. The solid phase extraction head 6 on the alloy wire 1 is pushed into the induction coil. The middle layer structure is the insulating tube 2. The two ends of the insulating tube 2 are punched with internal threads of a certain depth. One end of the first ferrule 3 has an external thread of corresponding size. The first ferrule 3 is fixed to the upper end of the insulating tube 2 by threaded fit, and the second ferrule 4 is fixed to the lower end of the insulating tube 2 by threaded fit. There is a carrier gas inlet 7 on the first ferrule 3 for the passage of the carrier gas pipeline, and there is a sample gas outlet 8 on the second ferrule 4. The outermost structure is the induction coil 5, which is arranged in a spiral shape, and the two ends of the coil are connected to high-frequency alternating current.

[0040] Polydimethylsiloxane (PDMS) adsorbent is coated on the invar alloy wire, and a solid phase extraction head is formed after the adsorbent is dried and solidified. The alloy wire solid phase extraction head is placed in a bottle containing 5ppb chlorpyrifos, and adsorption extraction is performed at a certain temperature and time. After the adsorption is completed, the alloy wire 1 is taken out and loaded into the needle tube 10, and the solid phase extraction head 6 and the needle tube 10 on the alloy wire 1 are inserted through the fine hole at the center of the first ferrule 3, and the needle tube 10 pierces the septum and enters the induction coil, and the solid phase extraction head 6 is pushed into the induction coil, and the air outlet of the micro air pump is connected to the pipeline at the carrier gas inlet 7 at the upper end of the device, and the air inlet of the micro air pump is connected to the atmospheric environment, so that the gas direction is from top to bottom. The pipeline at the sample gas outlet 8 at the lower end of the device is connected to a small ion migration spectrometer. Turn on the gas source and power supply, the alloy wire is heated in the device, the substance adsorbed by the adsorbent will volatilize and be carried into the ion mobility spectrometer by the carrier gas. Turn on the ion mobility spectrometer to collect data for analysis, and the spectrum obtained is as follows Figure 3 As shown, Figure 4 This is the spectrum of direct injection without adsorption and desorption. It can be seen that Figure 4 No signal from the substance to be tested is obtained. Figure 3 Obvious peaks of the substance to be detected can be obtained, indicating that the present invention has a very good enrichment effect in the analysis process of trace substances.

[0041] The above description is only a preferred embodiment of the present invention and does not limit the present invention. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for enriching and rapidly injecting trace substances, characterized in that: include: The substance to be tested is first enriched on the alloy wire with adsorbent, and then the alloy wire is quickly heated by electromagnetic induction. The power-on time is controlled at about 5s to achieve rapid thermal desorption. During the desorption process, carrier gas is continuously blown in to bring the desorbed substance to be tested into the instrument for analysis.

2. The method for enriching and rapidly injecting trace substances according to claim 1, characterized in that: The alloy wire is provided with an adsorbent, which can enrich trace substances. The adsorbent can be preferably selected from materials such as polydimethylsiloxane (PDMS), polyacrylate (PA), polystyrene-divinylbenzene copolymer (PS-DVB), C18, etc. according to the target substance to be enriched. The length of the coating can be preferably selected from 5 mm to 30 mm, and the thickness can be preferably selected from 10 μm to 50 μm.

3. The method for enriching and rapidly injecting trace substances according to claim 1, characterized in that: The alloy wire is made of an alloy material with a specific Curie point. The heating temperature can be controlled by optimizing the alloy material, including Invar alloy, 1J30 soft magnetic alloy, Kovar alloy, high magnetic permeability Permalloy, etc., and its diameter is preferably between 0.5mm and 1.5mm.

4. A device for enriching and rapidly injecting trace substances, characterized in that: include: Alloy wire, insulating tube, induction coil, carrier gas inlet, adsorbent, sample gas outlet, septum and needle.

5. The device for enriching and rapidly injecting trace substances according to claim 4, characterized in that: The adsorbent is fixed on the alloy wire by coating and curing.

6. The device for enriching and rapidly injecting trace substances according to claim 4, characterized in that: The insulating tube plays a role of isolating the alloy wire and the coil in the device, and its material can be silicon dioxide, polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK) and other materials.

7. The device for enriching and rapidly injecting trace substances according to claim 4, characterized in that: The septum is nested inside the ferrule. After the needle passes through the small hole at the center of the ferrule and pierces the septum to enter the induction coil, the alloy wire is quickly pushed into the coil, and the septum quickly returns to its original state, effectively preventing the leakage of the sample and the carrier gas. The septum can be optimized among silicone rubber septum, fluororubber septum and graphite septum according to actual needs.

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