CN105651910A - Enrichment-thermal desorption-chromatography separating unit - Google Patents

Abstract

The invention provides an enrichment-thermal analysis-chromatographic separation device, which is composed of a rapid enrichment thermal analysis device, a sampling device and a rapid separation device. Among them, the rapid enrichment thermal analysis device uses the adsorption tube equipped with adsorbent to enrich the target components in the gas sample at low temperature under the action of low-temperature carbon dioxide gas. The target components after collection and analysis enter the separation device through the sampling device. The separation device uses low-temperature carbon dioxide gas to cool the chromatographic column, and cooperates with the rapid heating module to achieve a low initial temperature of the chromatographic column and a high heating rate, thereby obtaining high separation effect, extremely fast analysis rate and high peak capacity. The device can realize online enrichment of trace components in gas samples, rapid analysis, and ultra-fast gas chromatography analysis.

Description

A kind of enrichment-thermal analysis-chromatographic separation device

technical field

The invention belongs to the field of analytical instruments, in particular to a gas sample rapid enrichment-thermal analysis-chromatographic separation device.

Background technique

The analysis of trace substances in gas samples is an important part of analytical chemistry and environmental analysis. Its main application areas include: 1) Monitoring of volatile organic compounds (Volatile Organic Compounds, referred to as VOCs) in the air; VOCs in the air are harmful to human health, and lead to photochemical pollution and odor problems, so online and fast , Highly sensitive detection is of great significance. 2) The detection of trace volatile organic compounds in exhaled breath has great guiding significance for early detection, early diagnosis and screening of diseases. 3) On-line detection of hazardous compounds in the working environment, which is an important guarantee for safe production.

Due to the complex composition, the content of trace substances in gas samples is generally very low, and it is difficult to detect directly, so sample pretreatment is required. The existing technology mostly adopts the cold trap adsorption concentration/thermal desorption method, filling the sampling adsorption tube with a certain volume of adsorbent, and utilizing the characteristics of the solid adsorbent to adsorb light component samples at a low temperature of liquid nitrogen or -70°C to achieve concentration For the purpose of enrichment, the thermal desorber heats up quickly, and the desorption of the component to be tested is made by using the characteristic of the adsorbent that the retention performance of the component to be tested is reduced at high temperature, and the volatiles are directly transported to the chromatograph by the carrier gas for analysis and determination .

Most of the existing adsorption concentration/thermal desorption devices use normal temperature to install adsorption tubes, and then heat-purge to inject samples. Since the thermal desorption of the sample is completed by placing the adsorption tube in the desorption chamber of the thermal desorption instrument for heating, the following problems arise:

1. The enrichment efficiency of low boiling point components is low at room temperature.

2. The heating rate of the heater is slow, the long-term desorption process and the transmission line of the thermal desorption component cause the peak broadening of the thermal desorption component, which reduces the resolution ability of the chromatographic column to the peak, making qualitative and quantitative difficulties. Therefore, commercialized devices all use secondary cold trap and secondary thermal analysis technology, which will lead to long analysis period and increase the cost and complexity of the device.

3. After the thermal desorption is completed, the time for the high-temperature thermal desorption tube to cool naturally to the initial enrichment temperature is too long, resulting in a long analysis period, generally more than 10 minutes.

4. The analysis period of the conventional chromatographic analysis method is too long, generally more than 15 minutes, which is not conducive to rapid analysis; while ordinary fast gas chromatography is difficult to ensure sufficient analysis rate, resolution and peak capacity at the same time, resulting in difficulty in balancing analysis speed and separation efficiency .

Contents of the invention

In order to solve the above problems, the present invention provides a kind of enrichment-thermal analysis-chromatographic separation device, which adopts low-temperature _CO2 gas to cool down the adsorption tube filled with adsorbent, so as to obtain a lower enrichment temperature, thereby improving the concentration of low-temperature Enrichment efficiency of boiling point components; use the heating wire wound outside the adsorption tube for direct thermal analysis to achieve rapid temperature rise to obtain a narrow sample band; after thermal analysis is completed, use low-temperature CO ₂ gas again Cool down to lower the low-temperature enrichment temperature as soon as possible to reduce the analysis period. At the same time, low-temperature CO ₂ gas is used to cool the chromatographic column, which further reduces the sampling band, improves the separation efficiency, and improves the resolution of low boiling point components _; cooling, thereby reducing the overall analysis cycle time.

In order to achieve the above object, the technical solution adopted in the present invention is:

An enrichment-thermal desorption-chromatographic separation device is composed of an enrichment thermal desorption device, a sampling device, a separation device and a cooling source, and is characterized in that:

The enrichment thermal desorption device is composed of an adsorption tube, a heating wire, a first cooling cover and a first cooling nozzle; the adsorption tube is filled with an adsorbent; the heating wire is wound on the outer surface of the adsorption tube; the two ends of the adsorption tube are respectively connected with The sample source is connected to the sampling device; the first cooling cover wraps the adsorption tube wrapped with the heating wire inside; the first cooling cover is provided with a first cooling spray head and a first gas outlet; the first cooling spray head and the cooling source There is a pipeline connection between them, so that the cooling substance in the cooling source can enter the inside of the first cooling cover through the first cooling nozzle, and be discharged from the first gas outlet on the first cooling cover.

The separation device is composed of a chromatographic column, a chromatographic column heating module, a second cooling nozzle and a second cooling cover; the front end of the chromatographic column is connected to the sampling device, and the rear end is connected to the detector; the chromatographic column heating module is in close contact with the chromatographic column; The second cooling cover wraps the chromatographic column and the chromatographic column heating module inside; the second cooling spray head and the second gas outlet are arranged on the second cooling cover; there is a pipeline connection between the second cooling spray head and the cooling source, so that the cooling The cooling material in the source can pass through the second cooling spray head into the second cooling cover and be discharged from the second gas outlet on the second cooling cover.

The sampling device is an airtight container, and the airtight container is provided with a sampling device outlet to communicate with the outside world, and the sampling device is connected to the adsorption tube through the first joint; the sampling device is connected to the chromatographic column through the second joint; the sampling device The device has two working states; in state 1, the gas passing through the adsorption tube enters the sampling device through the first joint and is directly discharged from the outlet of the sampling device; in state 2, after the gas passing through the adsorption tube enters the sampling device, it passes through the first The two adapters are transferred to the column.

The first cooling nozzle and the second cooling nozzle have variable diameter structures, and the inner diameter of the outlet becomes smaller, that is, the cross-sectional area of the outlet perpendicular to the fluid flow direction is smaller than the cross-sectional area of the inlet perpendicular to the fluid flow direction.

The outlet of the first cooling spray head faces the adsorption tube, and the distance between the outlet of the first cooling spray head and the adsorption tube is 1 mm to 50 mm.

The adsorption tube is a quartz tube, a glass tube or a metal tube with an inert treatment on the inner wall, and its inner diameter is 0.5mm-10mm; the end of the adsorption tube connected to the sampling device has a closing port with a smaller inner diameter; the inner diameter of the closing part is preferably 0.1-10 mm. 5mm to reduce the width of the sample band.

The sampling device is a two-position, three-way or more than three-way valve.

The two working states of the sampling device are realized by controlling the pressure difference between the first joint and the outlet of the sampling device, and the pressure difference between the outlet of the sampling device and the second joint.

The sampling device and the connecting pipelines with the chromatographic column and the adsorption tube are all heated and kept warm.

The second cooling spray head faces the chromatographic column.

The cooling source is high-pressure liquid carbon dioxide, and the cooling substance is low-temperature carbon dioxide gas.

The chromatographic column heating module is a direct heating electric heating block or an air bath heating module.

When the device is working, the adsorption tube is first cooled by the low-temperature _CO2 gas sprayed from the first cooling nozzle. After reaching the required cooling temperature, the gas sample passes through the adsorption tube, and the target components in it are enriched. At this time, after the gas sample enters the sampling device through the adsorption tube, it is discharged from the outlet of the sampling device. After the enrichment is completed, the heating wire wrapped around the adsorption tube is rapidly heated for thermal analysis, and the analyzed target components enter the separation device after passing through the sampling device. After the thermal analysis is completed, the first cooling nozzle sprays out low-temperature _CO gas again to rapidly cool down the adsorption tube, thereby reducing the enrichment time. At the same time, the second cooling nozzle can spray low-temperature _CO2 gas into the second cooling cover to cool down the chromatographic column, obtain a lower chromatographic initial temperature and a high heating rate, thereby obtaining high separation effect, extremely fast analysis rate and High peak capacity.

The variable-diameter structures of the first cooling nozzle and the second cooling nozzle can cause the high-pressure gas to expand and do work for cooling, thereby further improving the cooling efficiency.

The first cooling nozzle can reduce the temperature of the adsorption tube to -30°C, which greatly improves the ability of the adsorption tube to enrich low boiling point components, and reduces the equilibrium time for the adsorption tube to return from the high temperature state after thermal analysis to the low temperature state during enrichment , reducing the analysis cycle.

The heating wire wrapped around the adsorption tube can provide a heating rate up to 40°C/s to ensure a sufficiently narrow sample band.

The column heating module in the separation unit is in close contact with the column to provide a high heating rate. Using low-temperature _CO2 gas to cool down, the initial column temperature of the chromatographic column can be reduced to -30°C, so as to increase the retention capacity and peak capacity of low-boiling components; greatly shorten the equilibration time of the chromatographic column, and reduce the analysis cycle.

The present invention has the following advantages:

1. The present invention uses low-temperature _CO2 gas to cool the adsorption tube, which can effectively improve the enrichment efficiency of low boiling point components, shorten the cooling time for the adsorption tube to return to the initial temperature after thermal analysis is completed, thereby reducing the enrichment thermal analysis time. total time.

2. The present invention adopts the structure of the adsorption tube with closed mouth and the direct heating of the heating wire, which improves the thermal analysis speed, reduces the chromatographic sampling band, and improves the separation efficiency.

3. The present invention adopts low-temperature _CO2 gas to cool the chromatographic column, which can effectively improve the resolution of low-boiling components and increase the peak capacity; and utilize the cold column head effect to compress the chromatographic sampling band and improve the separation efficiency; Cooling the gas after the analysis also reduces the equilibration time of the column, thereby reducing the overall analysis cycle time.

4. The present invention adopts the method of heating the chromatographic column heating module in close contact with the chromatographic column, which can obtain a higher programmed temperature rise rate and further improve the separation speed, thereby ensuring that the device can simultaneously obtain high resolution, separation speed and peak capacity.

Description of drawings

Figure 1 is a schematic structural view of the device of the present invention. Among them, 100-enrichment thermal desorption device; 101-adsorbent; 102-adsorption tube; 103-heating wire; 104-cooling source; 105-first cooling nozzle; 106-first cooling cover; 107-first gas outlet 200-sampling device; 201-first joint; 202-exit of sampling device; 203-second joint; 304-second cooling cover; 305-second gas outlet.

Fig. 2 is the temperature change curve of the adsorption tube when the device described in Example 1 is used for enrichment thermal analysis and cooling of the adsorption tube.

Fig. 3 is the temperature change curve of the chromatographic column when the device described in Example 1 is used for separation.

Fig. 4 is the chromatograms of 39 kinds of TO14 standard samples whose concentration is 100ppb using the device described in Example 1.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments, where the schematic embodiments and descriptions of the present invention are used to explain the present invention, but not as a limitation to the present invention.

Example 1

An enrichment-thermal desorption-chromatographic separation device, as shown in FIG.

The enrichment thermal desorption device 100 is composed of an adsorption tube 102 , a heating wire 103 , a first cooling cover 106 and a first cooling nozzle 105 . The adsorption tube 102 is a quartz tube with a main body diameter of 3 mm, which is filled with an adsorbent 101, which is a mixture of 5 mg of graphitized carbon black and 4 mg of Carbosieve SIII. The adsorption tube 102 is wound with a heating wire 103. The heating wire 103 is a Ni-Cr alloy with a wire diameter of 0.4 mm, a resistance of 10 ohms, and a heating rate of 40° C./s. Both ends of the adsorption tube 102 are respectively connected to the sample source and the sampling device 200 ; the end of the adsorption tube 102 connected to the sampling device 200 has a narrowing opening with a reduced inner diameter, and the diameter of the shrinking part is 0.6 mm.

The first cooling cover 106 wraps the heating wire 103 and the adsorption tube 102 inside; the first cooling cover 106 is provided with a first cooling nozzle 105 and a first gas outlet 107; between the first cooling nozzle 105 and the cooling source 104 There are plumbing connections. The cooling source 104 is high-pressure liquid carbon dioxide, the inner diameter of the nozzle of the first cooling nozzle 105 is 1.5 mm, and the distance between the outlet and the adsorption tube is 3 mm. The pressure of CO ₂ is 0.8MPa. During operation, the liquid CO ₂ gasifies, absorbs a large amount of heat, produces low-temperature and high-pressure CO ₂ gas, and cools down the adsorption tube 102 . When the gas passes through the first cooling nozzle, the pressure decreases sharply and expands to do work, and throttling refrigeration further reduces the temperature, thereby obtaining higher refrigeration efficiency.

The separation device 300 is composed of a chromatographic column 301, a chromatographic column heating module 302, a second cooling nozzle 303, and a second cooling cover 304; the front end of the chromatographic column 301 is connected to the sampling device 200, and the rear end is connected to the detector; the chromatographic column heating module 302 In close contact with the chromatographic column 301; the second cooling cover 304 wraps the chromatographic column 301 and the chromatographic column heating module 302 in its interior; the second cooling cover 304 has a second cooling nozzle 303 and a second gas outlet 305; the second cooling There is a pipeline connection between the spray head 303 and the cooling source 104 . The structure of the second cooling spray head 303 is the same as that of the first cooling spray head 105 .

The sampling device 200 is a two-position six-way valve, and the first joint 201 and the second joint 203 are respectively two valve port joints of the six-way valve. Another valve hole on the six-way valve communicates with the atmosphere as the outlet 202 of the sampling device. Two working states are realized by switching between two positions of the valve: one is enrichment state. The remaining gas after the sample gas is enriched through the adsorption tube 102 enters the sampling device 200 and is discharged to the outside from the outlet. The other is the sample injection state, in which the target components adsorbed on the adsorbent during thermal analysis will be transferred to the chromatographic column 301 through the adsorption tube 102 and the sample injection device 200 .

As shown in Figure 2, the enrichment thermal analysis device 100 can cool down to -25°C when the first cooling nozzle 105 is working to improve the enrichment efficiency; The adsorption tube 102, the VOCs therein are adsorbed and enriched by the adsorbent 101. After the enrichment is completed, the first cooling nozzle 105 stops working, and the heating wire 103 applies a heating voltage to raise the temperature of the adsorption tube 102 to 320° C. at a heating rate of 40° C./s. At this time, the sampling device 200 is in a sampling state, and the thermally desorbed VOCs enter the chromatographic column 301 through the sampling device 200 . Thermal analysis injection 5s, in order to reduce the injection band. After the sample injection is completed, the first cooling nozzle 105 starts to work, and rapidly lowers the temperature of the adsorption tube 102 to -25° C. within 10-30 seconds to continue the enrichment, and completes an enrichment thermal desorption cycle.

The sampling end of the adsorption tube 102 is connected to the sampling device 200 through a connecting tube, and the sampling device 200 is also connected to the chromatographic column 301 through the connecting tube. The connecting tube was kept at 80°C, and the sampling device 200 was kept at 70°C to reduce analysis residues. The chromatographic column 301 is 10m×0.10mmi.d.×5μm OV-17. When the separation starts, the second cooling nozzle 303 works, and the chromatographic column is lowered to the initial column temperature -20°C to improve the resolution and peak capacity of the low-boiling components, and then enters the temperature programming stage; the second cooling nozzle 303 stops working, and the chromatographic column The heating module 302 starts to work and heats up rapidly to accelerate the separation speed. After the separation is completed, the second cooling nozzle 303 works to reduce the temperature of the chromatographic column from high temperature to the initial temperature of -20° C., and start the next analysis. Figure 3 shows the change of column temperature in one analysis cycle under this condition. It can be seen that the entire analysis period is 130s, which is much lower than the analysis period (generally 15-30min) of the conventional enrichment/thermal desorption-chromatographic separation system.

The results of rapid enrichment thermal analysis and gas chromatographic separation of 39 TO14 standard samples at 100 ppb are shown in Figure 4. The data in the figure is the data of the hydrogen flame ionization detector, and other gas chromatographic detectors can also be used.

Example 2

The device as described in Embodiment 1, wherein the sampling device 200 is a three-way two-position solenoid valve.

Example 3

The device as described in Example 1, wherein the adsorption tube 102 is a stainless steel tube with an inert inner wall, and the adsorbent 101 is 10 mg carbon molecular sieve TDX-1. The sampling device 200 and its connecting pipes are in room temperature environment. The device can realize rapid enrichment-thermal analysis-chromatographic separation of low-carbon hydrocarbons (such as ethane, ethylene, propane, etc.), and the entire analysis period is less than 2 minutes.

Example 4

The device as described in Embodiment 1, wherein the sampling device 200 is a pressure control device adopting a Deanswitch structure.

Claims (10)

1. An enrichment-thermal desorption-chromatographic separation device is composed of an enrichment thermal desorption device (100), a sampling device (200), a separation device (300) and a cooling source (104), characterized in that: The enrichment thermal desorption device (100) is made up of adsorption tube (102), heating wire (103), first cooling cover (106) and first cooling nozzle (105); the adsorption tube (102) is filled with adsorption agent (101); the heating wire (103) is wound on the outer surface of the adsorption tube (102); the two ends of the adsorption tube (102) are respectively connected with the sample source and the sampling device (200); the first cooling cover (106) will wrap the The adsorption tube (102) of the heating wire (103) is wrapped in it; the first cooling cover (106) is provided with a first cooling nozzle (105) and a first gas outlet (107); the first cooling nozzle (105) There is a pipeline connection between the cooling source (104), so that the cooling substance in the cooling source (104) can enter the inside of the first cooling cover (106) through the first cooling spray nozzle (105), and from the first cooling cover (106) The first gas outlet (107) on the top is discharged; The separation device (300) is composed of a chromatographic column (301), a chromatographic column heating module (302), a second cooling nozzle (303) and a second cooling cover (304); the front end of the chromatographic column (301) and the sampling device ( 200), and the rear end is connected to the detector; the chromatographic column heating module (302) is in close contact with the chromatographic column (301); the second cooling cover (304) wraps the chromatographic column (301) and the chromatographic column heating module (302) Inside it; there are second cooling nozzles (303) and second gas outlets (305) on the second cooling cover (304); there is a pipeline connection between the second cooling nozzles (303) and the cooling source (104), so that The cooling substance in the cooling source (104) can enter the second cooling cover (304) inside through the second cooling nozzle (303), and be discharged from the second gas outlet (305) on the second cooling cover (304); The sampling device (200) is an airtight container, and the airtight container is provided with a sampling device outlet (202) to communicate with the outside world, and the sampling device (200) is connected to the adsorption tube (102) through the first joint (201); The sampling device (200) is connected to the chromatographic column (301) through the second joint (203); the described sampling device (200) has two kinds of working states; in state 1, the gas passing through the adsorption tube (102) passes through the first joint (201) is directly discharged from the outlet of the sampling device (202) after entering the sampling device (200); in state 2, after the gas through the adsorption tube (102) enters the sampling device (200), it passes through the second joint (203) is transferred to the chromatographic column (301). 2. The enrichment-thermal desorption-chromatographic analysis device according to claim 1, characterized in that: the first cooling nozzle (105) and the second cooling nozzle (303) have variable diameter structures, and the inner diameter at the outlet becomes smaller , that is, the cross-sectional area perpendicular to the fluid flow direction at the outlet is smaller than the cross-sectional area perpendicular to the fluid flow direction at the inlet. 3. The enrichment-thermal desorption-chromatographic analysis device according to claim 1 or 2, characterized in that: the outlet of the first cooling spray head (105) faces the adsorption tube (102), and the first cooling spray head (105) The distance between the outlet and the adsorption tube (102) is 1 mm to 50 mm. 4. The enrichment-thermal desorption-chromatographic analysis device according to claim 1 or 2, characterized in that: the adsorption tube (102) is a quartz tube, a glass tube or a metal tube with an inert treatment on the inner wall, and its inner diameter is 0.5mm-10mm; the end of the adsorption tube (102) connected to the sampling device (200) has a closing opening with a smaller inner diameter. 5. The enrichment-thermal desorption-chromatographic analysis device according to claim 1 or 2, characterized in that: the sampling device (200) is a two-position, three-way or more than three-way valve. 6. The enrichment-thermal desorption-chromatographic analysis device according to claim 1 or 2, characterized in that: the two working states of the sampling device (200) are controlled by the first joint (201) and the sampling device The pressure difference between the outlet (202) and the pressure difference between the outlet (202) of the sampling device and the second joint (203) are realized. 7. The enrichment-thermal desorption-chromatographic analysis device according to claim 1 or 2, characterized in that: the sampling device (200) and its connecting pipe with the chromatographic column (301) and the adsorption tube (102) Roads are heated and insulated. 8. The enrichment-thermal desorption-chromatographic analysis device according to claim 1, characterized in that: the second cooling nozzle (303) faces the chromatographic column (301). 9. The enrichment-thermal desorption-chromatographic analysis device according to claim 1, characterized in that: the cooling source (104) is high-pressure liquid carbon dioxide, and the cooling substance is low-temperature carbon dioxide gas. 10. The enrichment-thermal desorption-chromatographic analysis device according to claim 1, characterized in that: the chromatographic column heating module (302) is a direct heating electric heating block or an air bath heating module.