A headspace sampling device for a surface acoustic wave gas chromatograph

Abstract

This invention relates to the field of gas chromatography, specifically to a headspace sampling device for a surface acoustic wave gas chromatograph. The headspace sampling device includes: a heating sleeve, a heating element, a heat insulation layer, a guide seal, a heat tracing tube, an injection tube, a set screw, a shield, and a purge tube. The heating sleeve has a heating element on its outer wall, and a heat insulation layer is provided outside the heating element. The heating sleeve is fitted onto the heat tracing tube, and the injection tube is located inside the heat tracing tube. The inner wall of the heat tracing tube is in close contact with the outer wall of the injection tube for heat conduction. The guide seal includes a base, a step, and a guide post. The base has a step, and the guide post is located on the step. A through hole is provided between the base, the step, and the guide post for the heat tracing tube to pass through. A groove is provided on the step, and the groove has the same shape as the mouth of the sample vial. This invention significantly improves sample detection consistency and is simple to operate.

Description

Technical Field

[0001] This invention relates to the field of gas chromatography, and more specifically to a headspace injection device for a surface acoustic wave gas chromatograph. Background Technology

[0002] When performing headspace analysis using a surface acoustic wave gas chromatograph, the sample vial needs to be placed close to the injection device to capture the headspace sample gas. Traditional headspace injection devices include manual methods, gas-tight needle injection methods, and closed-tube / pressure-balanced injection methods. These methods have the following drawbacks: Manual method: Sampling depth is difficult to standardize, human error is large, detection repeatability is poor, and detection accuracy is affected. Its structure is as follows: Figure 1 As shown.

[0003] Airtight needle injection method: This method requires puncturing the sample vial while it is sealed, which places high demands on the materials of the sealing gasket and cap. Repeated punctures can easily generate debris and cause air leakage. Sample residue can easily remain on the puncture needle, causing cross-contamination, and cleaning and maintenance are complex.

[0004] Closed-loop / pressure-balanced injection method: Relies on tubing, valves, metering loops, etc., to form a closed flow path. The flow path is long and the dead volume is large, which easily adsorbs volatile components, resulting in a decrease in recovery rate. The system structure is complex, costly, and inconvenient for installation, commissioning, and maintenance. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a headspace sampling device for surface acoustic wave gas chromatographs. During testing, the sample vial is connected only to the injection device, enabling sealed headspace sampling and avoiding air interference. By incorporating a guide column, accurate positioning of the sample vial and injection port is achieved, facilitating operation and improving detection consistency. Sampling at a fixed position within the sample vial ensures good test repeatability. The addition of an isolation hood and purge tube enhances resistance to external interference. The application of a silanized inner liner reduces adsorption loss during sample transport, improving sensitivity and detection consistency.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A headspace sampling device for a surface acoustic wave gas chromatograph, the headspace sampling device comprising: a heating sleeve, a heating element, a heat insulation layer, a guide seal, a heat tracing tube, an injection tube, a set screw, an isolation hood, and a purge tube; Heating elements are provided on the outer wall of the heating sleeve, and an insulation layer is provided outside the heating elements; The heating sleeve is fitted onto the heat tracing pipe, and the heat tracing pipe contains an inlet pipe; the inner wall of the heat tracing pipe is in contact with the outer wall of the inlet pipe for heat conduction. The guide seal includes a base, a step, and a guide post. The base has a step, and the step has a guide post. A through hole is provided in the middle of the base, the step, and the guide post for passing through a heat tracing pipe. A groove is provided on the step, and the groove has the same shape as the mouth of the sample bottle. The top surface of the isolation cover is fixedly connected to the heating sleeve. An opening is provided on the top surface of the isolation cover, and a guide seal is fixedly installed in the opening. The guide seal is sealed to the heat tracing pipe. Through holes are provided at corresponding positions on the heat tracing pipe and the guide seal. A set screw is installed in the through hole. The set screw passes through the guide seal and the heat tracing pipe and abuts against the injection tube to adjust the extension length of the injection tube. Loosen the set screw to extend or shorten the injection tube to the appropriate position, and then tighten the set screw.

[0007] A purge tube is installed on the wall of the isolation hood, which can spray inert gas into the isolation hood; a silanized inner liner is installed inside the sample inlet tube.

[0008] Preferably, the heating sleeve is a cylindrical structure with flanges at both ends, and heating elements and an insulation layer are disposed on the cylindrical body between the flanges. The heating sleeve of the present invention is not limited to the above structure; it can also have a flange at one end and no flange at the other end, etc.

[0009] Preferably, the heat tracing pipe is configured as an upper pipe body and a lower pipe body, with an annular protrusion between the upper pipe body and the lower pipe body; The upper tube is disposed within the heating sleeve, and the lower tube passes through the guide seal. A sealing groove is provided on the annular protrusion, and a sealing ring is disposed within the sealing groove. This sealing ring serves as a sealing connection between the base surface of the guide seal and the heat tracing pipe. The heat tracing pipe of this invention is not limited to the above structure; it can also be an integral cylindrical tube, with the upper part disposed within the heating sleeve and the lower part disposed within the guide seal, etc. The diameters of the upper and lower tubes can be the same or different.

[0010] Preferably, the orifice of the guide post is chamfered or rounded.

[0011] Preferably, the heating sleeve is made of aluminum alloy; the heat tracing tube is made of copper; the guide seal is made of ETFE material; the injection tube is made of stainless steel; and the isolation cover is made of PEEK material.

[0012] Preferably, the purge pipe is connected to a nitrogen or helium source via a solenoid valve.

[0013] Preferably, the main body of the injection tube is cylindrical, and the lower end is tapered. The cylindrical end of the injection tube of the present invention can be sealed to the corresponding pipeline of the chromatograph through a compression fitting, and the tapered end can be configured to connect to other sampling connectors as needed, such as a Luer connector.

[0014] Compared with the prior art, the advantages of the present invention are: This invention eliminates the need for complex pretreatment and special sample introduction devices, lowering the barrier to entry and maintenance costs. It significantly improves sample detection consistency, is simple to operate, and is easy to promote. Attached Figure Description

[0015] Figure 1 It is an existing technology sample introduction device; Figure 2 This is a schematic diagram of the headspace sampling device of the present invention; Figure 3 This is an exploded view of the headspace sampling device of the present invention; Figure 4 This is a cross-sectional view of the headspace sampling device of the present invention; Figure 5 This is a schematic diagram of the structure of the guide seal of the present invention; Figure label: 1. Heating sleeve; 2. Insulation layer; 3. Heating element; 4. Heat tracing pipe; 5. First sealing ring; 6. Second sealing ring; 7. Sample inlet tube; 8. Guide seal; 8-1. Base; 8-2. Step; 8-3. Guide post; 8-4. Groove; 9. Set screw; 10. Purge tube; 11. Isolation hood; 11-1. Top of the hood; 11-2. Wall of the hood; 12. Silanized inner liner tube. Detailed Implementation

[0016] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0017] Example 1 like Figure 2-5 As shown, a headspace sampling device for a surface acoustic wave gas chromatograph includes: a heating sleeve 1, a heat insulation layer 2, a heating element 3, a guide seal 8, a heat tracing tube 4, an injection tube 7, a set screw 9, a purge tube 10, and an isolation cover 11. The heating sleeve 1 is a cylindrical structure with flanges at both ends. A heating element 3 and an insulation layer 2 are provided on the cylinder between the flanges. The insulation layer 2 is provided on the heating element 3. The heating sleeve 1 is fitted onto the heat tracing pipe 4, and the heat tracing pipe 4 is provided with a sample inlet pipe 7; the inner wall of the heat tracing pipe 4 is in contact with the outer wall of the sample inlet pipe 7 for heat conduction. The guide seal 8 is integrally formed and includes a base 8-1, a step 8-2, and a guide post 8-3. The step 8-2 is provided on the base 8-1, and the guide post 8-3 is provided on the step 8-2. A through hole is provided in the middle of the base 8-1, the step 8-2, and the guide post 8-3 for the heat tracing pipe 4 to pass through. A groove 8-4 is provided on the step 8-2, and the groove 8-4 has the same shape as the mouth of the sample bottle. The opening of the guide post 8-3 is chamfered. The heat tracing pipe 4 is integrally formed and can be configured as an upper pipe body and a lower pipe body, with an annular protrusion between the upper pipe body and the lower pipe body. The upper pipe body is set inside the heating sleeve 1, and the lower pipe body passes through the guide seal 8. A sealing groove is provided on the annular protrusion, and a second sealing ring 6 is provided in the sealing groove. The second sealing ring 6 is used for the sealing connection between the base 8-1 surface of the guide seal 8 and the heat tracing pipe 4. The top 11-1 surface of the isolation cover 11 is fixedly connected to the heating sleeve 1. An opening is provided on the top 11-1 surface of the isolation cover 11, and a guide seal 8 is fixedly provided in the opening. The guide seal 8 is sealed to the heat tracing pipe 4. Through holes are provided at corresponding positions on the heat tracing pipe 4 and the guide seal 8. Set screws 9 are installed in the through holes to adjust the extension length of the sample inlet pipe 7. A purge tube 10 is installed on the wall 11-2 of the isolation hood 11. The purge tube 10 is connected to a nitrogen source or a helium source through a solenoid valve. A silanized inner liner tube 12 is installed inside the sample injection tube 7. The main body of the sample injection tube is cylindrical and the lower end is conical.

[0018] The headspace sampling device consists of a heating sleeve 1, an insulation layer 2, a heating element 3, a sampling tube 7 (with an embedded silanized inner liner tube 12), a guide seal 8, a heat tracing tube 4, a first O-ring seal 5, a second O-ring seal 6, a set screw 9, a purge tube 10, and an isolation cover 11.

[0019] The guide seal 8 of this invention is made of ETFE material, which has good temperature resistance and inertness, preventing corrosion by the sample. While ensuring a certain strength, it has a low elastic modulus, allowing for slight elastic deformation under low pressure. The guide seal 8 is designed with guide posts 8-3 and grooves 8-4, as shown... Figure 5 As shown. During sample injection, the sample vial is inserted from below the headspace injection device. The sample vial first contacts the guide post 8-3 of the guide seal 8 (the end of the guide post 8-3 is chamfered to ensure smooth insertion into the sample vial opening). The guide post 8-3 guides the sample vial upwards while preventing it from tilting. Subsequently, the sample vial opening contacts the groove 8-4. The upper half of the outer periphery of the groove 8-4 is sloped, and it undergoes elastic deformation due to pressure against the outside of the sample vial, forming a tight seal and improving the consistency of sample detection.

[0020] Above the guide seal 8 is the heating sleeve 1, which can be made of aluminum alloy, possessing certain strength and good thermal conductivity. An external heating element 3 uniformly heats the heating sleeve 1, transferring heat to the heat tracing tube 4. A 3.1mm diameter through-hole is provided on the heating sleeve for placing a thermocouple to monitor the real-time temperature of the injection device. The heat tracing tube 4 is made of copper, offering good thermal conductivity while remaining relatively flexible. Through the heat tracing tube 4, the heating sleeve 1 and the injection tube 7 can be well-fitted and thermally conductive, maintaining the injection tube 7 at a high temperature of 150~200℃. The injection tube 7 protrudes from the guide seal 8, and by adjusting the set screw 9, the injection tube 7 can extend to different lengths, enabling headspace sample injection at different depths within the sample vial. The injection tube 7 is made of stainless steel, offering corrosion resistance while ensuring certain mechanical strength. The main body of the injection tube 7 is cylindrical; the beginning can be sealed to the corresponding tubing of the chromatograph via a compression fitting, the middle section is tightly fitted with the heat tracing tube 4 for thermal conductivity, and the end is tapered, compatible with Luer connector sampling. The injection tube 7 is lined with a silanized inner liner 12, which significantly reduces adsorption loss during sample transport. An O-ring 5 is placed between the heating tube 4 and the injection tube 7, and an O-ring 6 is placed between the guide seal 7 and the heating tube 4 to prevent air from entering the injection tube 7. Both O-rings 5 ​​and 6 are made of fluororubber, which is heat-resistant and prevents contamination release. To avoid interference from the external environment during testing, an isolation cover 11 is installed. The isolation cover 11 is made of PEEK material, which has good temperature resistance and inertness, preventing corrosion from the sample, and is also lightweight. A purge tube 10 is installed on the isolation cover 11, connected to an external nitrogen or helium gas source via a solenoid valve. When sampling begins, the external solenoid valve is closed, and the headspace injection device is not purged. After sampling, the external solenoid valve is opened, and clean nitrogen or helium is blown in to remove residual sample between the injection device and the sample vial.

[0021] The functions of each part of this invention are described below: O-ring 5: Seal to prevent air from entering the injection tube 7 from inside the injection device.

[0022] O-ring 6: Seal to prevent air from entering the injection tube 7 from inside the injection device.

[0023] Purge tube 10: Connected to an external nitrogen or helium gas source to form a purge gas path. After sampling, the gas source is turned on via an external solenoid valve to remove any residual sample between the injection device and the sample vial. At the start of sampling, the gas source is turned off via the external solenoid valve.

[0024] Heat tracing tube 4: Maintains the sample injection device at a certain temperature (150~200℃) to prevent condensation and adsorption of the sample during collection. The inlet of the heat tracing tube is inside the orifice of the guide column, lower than, flush with, or slightly higher than the orifice of the guide column.

[0025] Injection tube 7: Protrudes from the guide column 8-3 structure (the protrusion length can be adjusted by 1~5mm via the set screw 9; injection tube 7 extends 9~13mm into the sample vial), collecting sample gas at different depths within the sample vial. It can achieve a sealed connection with the corresponding tubing of the chromatograph via a compression fitting, and is also compatible with Luer tube sampling methods.

[0026] Silanized inner liner 12: Reduces adsorption during sample transport.

[0027] Guide seal 8: A guide post 8-3 is provided to guide the sample vial towards the injection device and position the sample vial. A groove 8-4 is provided, and the inclined surface around the groove 8-4 presses against the sample vial, which achieves a sealing effect and helps improve the consistency of sample testing.

[0028] Set screw 9: Adjust the length of the injection tube 7 to achieve headspace sample injection at different depths inside the sample vial.

[0029] Isolation shield 11: to prevent interference from the external environment during the testing process.

[0030] Heating element 3: Heating headspace injection device, which can be connected to the temperature control component of the chromatograph.

[0031] Insulation layer 2: Insulation.

[0032] Heating sleeve 1: Provides structural support for the heating element and ensures uniform heat conduction.

[0033] In addition to the parts described above, this invention can also include various conventional auxiliary components on the headspace sampling device, such as thermocouples for temperature detection or fixing components between various parts and between the headspace sampling device and the chromatograph. A sealed connection is maintained between the heating tube and the injection tube. A through-hole is provided on the heating sleeve to accommodate thermocouples and monitor the real-time temperature of the sampling device.

[0034] Sample injection method: Open-cap headspace injection. During testing, the original injection device of the surface acoustic wave gas chromatograph is disassembled, and the headspace injection device of this invention is directly installed in the corresponding position. For example, a fixing hole is provided on the top surface of the heating sleeve, and it is fixed to the chromatograph through corresponding fixing screws. A clamping structure is used to achieve a sealed connection between the injection tube and the chromatograph tubing, etc. The surface acoustic wave gas chromatograph injection device is placed vertically downwards, and the sample vial is placed open and directly in the corresponding position of the bracket for sampling. The bracket mentioned above can be the original bracket of the chromatograph.

[0035] Example 2: Sample Consistency Test Using a Headspace Sampling Device 1) Sample preparation: A certain fragrance sample was dispensed into a 20 mL brown headspace vial. 10 mL of the fragrance sample was added to the vial. The vial was stirred well, sealed, and stored for testing. 2) Test conditions: A surface acoustic wave gas chromatograph was used, with the probe inverted, the injection port temperature at 200℃, the valve box temperature at 160℃, and an MXT-5 column (1 m × 0.25 mm × 0.25 μm) with an initial column temperature of 45℃ and a programmed temperature increase to 180℃ at 8℃ / s. The carrier gas was N2 at a flow rate of 5 mL / min. The detector temperature was 65℃, and the sampling (pump aspiration) time was 10 s. Tests were conducted using both the existing injection device and the headspace injection device of this invention.

[0036] During headspace testing, the original injection device of a certain type of surface acoustic wave gas chromatograph had poor sealing between itself and the sample vial, resulting in gaps when the cap was opened (e.g., Figure 1 Previously, sample vials needed to be held by hand for injection analysis, and differences in injection angle or sealing could lead to poor consistency in sample testing. After replacing the headspace sampling device with the one of the present invention, the consistency of testing the same fragrance sample was significantly improved. The relative standard deviation (RSD) of the main chromatographic peak response values ​​decreased from 29.60% and 45.10% to 4.39% and 3.95%, as shown in Table 1.

[0037] Table 1. RSD values ​​of the main chromatographic peaks in the original chromatographic injection device / headspace injection device of this invention.

[0038] Example 3: Intra-day and inter-day repeatability evaluation of the detection device 1) Sample preparation: A certain fragrance sample was dispensed into six 20 mL brown headspace vials, with 10 mL of the fragrance sample in each vial. After stirring well, the vials were sealed and stored for testing. 2) Test conditions: The surface acoustic wave gas chromatograph has an inverted probe and uses the headspace injection device of this invention. The injection port temperature is 200℃, the valve box temperature is 160℃, the chromatographic column is an MXT-5 column (1 m × 0.25 mm × 0.25 μm), the column initial temperature is 45℃, and the temperature is programmed to rise to 180℃ at 8℃ / s. The carrier gas is N2, the flow rate is 5 mL / min, the detector temperature is 65℃, and the sampling (pump aspiration) time is 10s.

[0039] 3) Intraday repeatability testing: Six parallel samples were headspace sampled and tested. Each sample was measured three times, and the average value was taken. The response values ​​of the main aroma substances, such as the solvent propylene glycol peak (retention index 745), β-phenylethanol (retention index 1124), and citronellol (retention index 1227), were recorded. The relative standard deviation (RSD) of the response values ​​of the six samples was calculated. The relative standard deviation of the main chromatographic peak response values ​​of the six parallel samples was <10%, and the specific data are shown in Table 2.

[0040] Table 2. Daily stability test data of fragrances

[0041] 4) Daytime stability test: Under the same chromatographic conditions, the relative standard deviation of the same fragrance sample was ≤11% when repeated tests were performed continuously for 6 days.

[0042] Table 3. Fragrance daytime repeatability test data

[0043] Through intra-day and inter-day repeatability tests of the headspace sampling device, it was found that when using the headspace sampling device of the present invention for headspace sampling, the intra-day and inter-day stability of the chromatographic peak response values ​​of the main aroma substances during sample testing is good, with RSD < 11%.

[0044] All aspects not described in detail in this invention can be covered using conventional technical knowledge in the field.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A headspace sampling device for a surface acoustic wave gas chromatograph, characterized in that, The headspace sampling device includes: a heating sleeve, a heating element, a heat insulation layer, a guide seal, a heat tracing tube, a sampling tube, a set screw, an isolation cover, and a purge tube; Heating elements are provided on the outer wall of the heating sleeve, and an insulation layer is provided outside the heating elements; The heating sleeve is fitted onto the heat tracing pipe, and the heat tracing pipe contains an inlet pipe; the inner wall of the heat tracing pipe is in contact with the outer wall of the inlet pipe for heat conduction. The guide seal includes a base, a step, and a guide post. The base has a step, and the step has a guide post. A through hole is provided in the middle of the base, the step, and the guide post for passing through a heat tracing pipe. A groove is provided on the step, and the groove has the same shape as the mouth of the sample bottle. The top surface of the isolation cover is fixedly connected to the heating sleeve. An opening is provided on the top surface of the isolation cover, and a guide seal is fixedly installed in the opening. The guide seal is sealed to the heat tracing pipe. Through holes are provided at corresponding positions on the heat tracing pipe and the guide seal. Set screws are installed in the through holes to adjust the extension length of the sample inlet tube. A purge pipe is installed on the wall of the isolation enclosure; A silanized inner liner is installed inside the injection tube.

2. The headspace sampling device according to claim 1, characterized in that, The heating sleeve is a cylindrical structure with flanges at both ends, and heating elements and insulation layers are installed on the cylinder between the flanges.

3. The headspace sampling device according to claim 1, characterized in that, The heat tracing pipe is configured as an upper pipe body and a lower pipe body, with an annular protrusion between the upper pipe body and the lower pipe body; The upper tube is installed inside the heating sleeve, and the lower tube passes through the guide seal. A sealing groove is provided on the annular protrusion, and a sealing ring is provided in the sealing groove. The sealing ring is used for the sealing connection between the base surface of the guide seal and the heat tracing pipe.

4. The headspace sampling device according to claim 1, characterized in that, The orifice of the guide post is chamfered.

5. The headspace sampling device according to claim 1, characterized in that, The heating sleeve is made of aluminum alloy; the heat tracing tube is made of copper; the guide seal is made of ETFE material; the injection tube is made of stainless steel; and the isolation cover is made of PEEK material.

6. The headspace sampling device according to claim 1, characterized in that, The purge tube is connected to a nitrogen or helium source via a solenoid valve.

7. The headspace sampling device according to claim 1, characterized in that, The main body of the injection tube is cylindrical, and the lower end is conical.

8. The headspace sampling device according to claim 1, characterized in that, The injection tube protrudes from the guide post, with a protrusion length of 1~5mm.

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