Chromatographic apparatus for online enrichment of trace and ultra-trace components and method for analyzing trace and ultra-trace components using same

A chromatographic apparatus for online enrichment of trace and ultra-trace components and an analytical method using the same. The apparatus includes an injection system, a vaporizing chamber, an enrichment system, a thermal box, a sample collection system, a focusing trap, a chromatographic analytical column system, a detector and an electronic control system. The method includes steps of sample enrichment, thermal desorption and back flushing, which are performed through a combination of a four-way valve and an electronic switch valve box.

TECHNICAL FIELD

This application relates to chemical analysis, and more particularly to a chromatographic apparatus for online enrichment of trace and ultra-trace components and a method for analyzing the trace and ultra-trace components using the same.

BACKGROUND

Considering the fact that it is difficult to achieve the analysis of trace and ultra-trace impurities only using a detector with high detection sensitivity and low detection limit, it is required to enrich such trace components prior to analysis. Currently, the solid-phase extraction technique, consisting of processes of enrichment, desorption and analysis, is considered as a powerful tool for the enrichment and analysis of gaseous, liquid and solid micro or trace impurities in the fields of environmental and petrochemical analysis. Impressively, this technique enables both the offline analysis and the online analysis of the trace components. However, the enrichment material and enrichment tube employed in the above method are often not readily available since they need to have a certain adsorption capacity and easy desorption without introduction of new impurities and irreversible adsorption. Additionally, numerous enrichment materials are required to be used together for complex matrices and mixtures, which will make it difficult to ensure a desired recovery for all components. At the same time, undue experimentation is required to determine conditions of thermal desorption and elution to obtain a reliable method, which is time- and labor-consuming.

Chinese patent No. 2038700780 discloses a gas chromatography system, in which an adsorption and desorption apparatus, a sampling pump and a micro chromatograph are connected through a six-way valve to realize the online analysis of gas samples. This system not only has fast response and good portability, but also can operate independently, and thus it is suitable for the handling of emergencies. However, in use, the sample is directly delivered to the adsorption and desorption apparatus (a key role in the enrichment of target components), so that the background interference cannot be eliminated. In addition, there are high requirements for adsorbent materials, optimization of conditions and temperature of the cold trap.

Chinese patent No. 207263702U first couples the online solid-phase extraction technique widely used in liquid chromatography (LC) to gas chromatography (GC) to design an online solid-phase extraction apparatus for gas chromatography, in which a solid-phase extraction trap is provided to enrich, focus and re-release the components separated by one-dimensional chromatography into a two-dimensional chromatographic column for separation and detection, allowing for good selectivity and high detection sensitivity for low-level compounds. Although the apparatus eliminates the background interference by using a one-dimensional chromatographic column, the trapping of different components is still greatly dependent on the selected filler due to the use of a solid-phase extraction trap. In addition, the apparatus has a high requirement for cooling.

For the analysis of a complex sample such as volatile organic compounds (VOCs) in atmosphere or water, the target components are prone to being interfered by adsorption materials, sample delivery and background factor. At the same time, the thermal expansion and contraction of the adsorbent materials during the repeated heating process will bring a poor reproducibility in the space between the adsorbent particles in the adsorbent tube. As a result, the analysis repeatability and reproducibility will not be satisfactory, rendering the results less reliable. In the analysis of a sample such as high-purity gas, high-purity solvent and polymer-grade monomer, when the background is air or purge carrier gas, since the adsorption performance of the background components is similar or close to that of the impurity components, the similar systems will fail to enable an effective detection.

Given the above, this disclosure directly uses a commercial/home-made gas chromatographic column/tube as a system for enriching impurities, which eliminates the sample background interference on the enrichment and analysis of the target components. With regard to the enrichment, desorption and analysis conditions, reference can be made to the use conditions of the corresponding chromatographic column without doing undue experimentation. The chromatographic column can be used repeatedly after back flushing, allowing for lowered cost. Moreover, the apparatus provided herein combines the direct injection with chromatographic column-based enrichment, which effectively avoids the loss of trace components caused by the strong and irreversible adsorption on the pretreatment system and cold trap. The apparatus has an ingenious design, which simplifies the installation and connection of the chromatographic column. The sampling system is optional, which enhances the compatibility of the apparatus to make it suitable for the analysis of trace and ultra-trace impurities in gaseous, liquid and solid high-purity samples that can be analyzed by gas chromatography. Currently, there is still no report about the online chromatographic enrichment apparatus and analytical method of trace and ultra-trace components.

SUMMARY

An object of this application is to provide a chromatographic apparatus for online enrichment of trace and ultra-trace components and a method for analyzing the trace and ultra-trace components using the same to overcome the defects in the thermal desorption applied in the existing analysis of the composition of trace and ultra-trace impurities in high-purity gaseous, liquid and solid samples, for example, the enrichment apparatus is complicated; there is great difficulty in seeking a selective adsorption material; the steps of extraction and desorption (thermal desorption/elution) have harsh conditions and low efficiency; the background interference cannot be eliminated; and the detection has a narrow linear range and a poor stability and repeatability.

Technical solutions of this application are specifically described as follows.

In a first aspect, this application provides a chromatographic apparatus for online enrichment of trace and ultra-trace components and a method for analyzing the trace and ultra-trace components using the same, comprising:an injection system;a column compartment;a vaporizing chamber;a chromatographic analytical column system;a detector;an electronic pressure controller;an enrichment system;a focusing trap;a thermal box;a sample collection system;a four-way valve; andan electronic control system;wherein the injection system is connected to the column compartment; the vaporizing chamber, the chromatographic analytical column system and the detector are connected to the column compartment; and the chromatographic analytical column system is connected to the detector;the injection system is connected to the vaporizing chamber through the column compartment; the injection system is configured to inject a sample into the vaporizing chamber for vaporization; the enrichment system is connected to the vaporizing chamber through the column compartment and is also connected to the focusing trap; the enrichment system is configured to trap target components in a vaporized sample, and desorb and transfer the target components to the focusing trap; the four-way valve is provided in the thermal box; the four-way valve is connected to the enrichment system, the focusing trap, the electronic pressure controller and the sample collection system through the thermal box, respectively; the focusing trap is connected to the chromatographic analytical column system through the column compartment; the focusing trap is configured to focus the target components desorbed from the enrichment system and transport the focused target components to the chromatographic analytical column system for separation; and the target components separated by the chromatographic analytical column system are transferred to the detector for detection;the electronic control system is connected to the injection system, the column compartment, the vaporizing chamber, the chromatographic analytical column system, the detector, the electronic pressure controller, the enrichment system, the thermal box, the sample collection system, the focusing trap and an electronic switch valve box; andthe chromatographic apparatus comprises an enrichment mode, a thermal desorption mode and a back flushing mode, which are performed by means of a combination of the four-way valve and the electronic switch valve box.

In an embodiment, the four-way valve comprises a port A and a port D; the electronic switch valve box comprises a first electronic switch valve provided between the electronic pressure controller and the four-way valve, and a second electronic switch valve provided between the sample collection system and the four-way valve; the enrichment system is a trap column system which is configured to trap the target components in the vaporized sample under a first preset temperature; and the sample collection system is configured to collect and discharge background components in the vaporized sample;the enrichment mode is performed through steps of:after the sample is vaporized in the vaporizing chamber, communicating the port D with the port A of the four-way valve; andclosing the first electronic switch valve and opening the second electronic switch valve;wherein the target components in the vaporized sample are trapped by the trap column system under the first preset temperature, and the background components in the vaporized sample are collected by the sample collection system and discharged.

In an embodiment, the four-way valve further comprises a port B; the thermal desorption mode is performed through steps of:after the target components are enriched, closing the second electronic switch valve, and rotating the four-way valve to communicate the port A with the port B; andraising a temperature of a trap column of the trap column system to perform desorption of the target components;wherein the target components trapped by the trap column system are heated to be desorbed from the trap column system to enter the focusing trap.

In an embodiment, the four-way valve further comprises a port C; the focusing trap is a focusing chromatographic column system configured to focus the target components desorbed from the trap column system; and the back flushing mode is performed through steps of:rotating the four-way valve to communicate the port A with the port D again and communicate the port C with the port B;closing the second electronic switch valve and opening the first electronic switch valve;closing a pressure of the vaporizing chamber;raising a temperature of the focusing chromatographic column system to focus the target components desorbed from the trap column system; andtransferring the focused target components to the chromatographic analytical column system;wherein heavy components in the sample are back flushed out; the target components separated from the chromatographic analytical column system are delivered to the detector for detection.

In an embodiment, the trap column of the trap column system is a cooling-type trap column or a heating-type trap column; the focusing chromatographic column of the focusing chromatographic column system is a cooling-type focusing chromatographic column or a heating-type focusing chromatographic column; and the trap column system and the focusing chromatographic column system both are a cooling-type capillary chromatographic column, a heating-type capillary chromatographic column or a combination, and are independently temperature controlled;the electronic control system further comprises a chromatographic workstation and a display screen; and the injection system, the vaporizing chamber, the chromatographic analytical column system and the detector are connected to the chromatographic workstation, respectively; andafter introduced by the injection system, the sample is sequentially enriched and desorbed by the trap column system, focused by the focusing chromatographic column system, separated by the chromatographic analytical column system and detected by the detector; and detection results are displayed on the display screen by the electronic control system.

In an embodiment, models of the injection system, the vaporizing chamber, the chromatographic analytical column system and the detector are adjustable; andthe injection system is a gas sampling valve or an automatic liquid injector; and the vaporizing chamber is a split or splitless inlet for a chromatographic instrument.

In an embodiment, the sample collection system is connected to the electronic pressure controller; the sample collection system is configured to measure the sample by cooperation with the electronic pressure controller or using a precision electronic flow meter, or to perform a cumulative measurement on the sample after multiple injections.

In an embodiment, in the enrichment and thermal desorption working modes, interference of the background components is eliminated through large-volume continuous injection and repeated injection, and by separating the background components with the help of the enrichment system; and the target components trapped by the enrichment system are transferred to the focusing trap.

In an embodiment, in an analytical cycle, a switch among the enrichment, thermal desorption and back flushing working modes is performed through the combination of the four-way valve and the electronic switch valve box; and the electronic control system is configured to control the analytical cycle through a time sequence program.

In a second aspect, this disclosure also provides a method of analyzing trace and ultra-trace components using the above chromatographic apparatus, comprising:injecting the sample into the vaporizing chamber through the injection system;vaporizing the sample in the vaporizing chamber;trapping, by the enrichment system, the target components in the vaporized sample;subjecting the target components to desorption from the enrichment system followed by transferring to the focusing trap, and subjecting the enrichment system to back flushing to remove heavy components;focusing the target components by the focusing trap;subjecting the focused target components to separation through the chromatographic analytical column system; anddetecting the target components by the detector.

In an embodiment, the four-way valve comprises a port A and a port D; the electronic switch valve box comprises a first electronic switch valve provided between the electronic pressure controller and the four-way valve, and a second electronic switch valve provided between the sample collection system and the four-way valve; the enrichment system is a trap column system which is configured to trap the target components in the vaporized sample under a first preset temperature; and the sample collection system is configured to collect and discharge background components in the vaporized sample; andthe step of “trapping, by the enrichment system, the target components in the vaporized sample” comprises:communicating the port D with the port A of the four-way valve; andclosing the first electronic switch valve and opening the second electronic switch valve to perform the trapping of the target components at the first preset temperature.

In an embodiment, the four-way valve further comprises a port B; andthe step of “subjecting the target components to desorption from the enrichment system” comprises:closing the second electronic switch valve, and rotating the four-way valve to communicate the port A with the port B; andraising a temperature of the trap column system to desorb the target components from the trap column system.

In an embodiment, the four-way valve further comprises a port C; and the focusing trap is a focusing chromatographic column system configured to focus the target components desorbed from the trap column system; andthe step of “subjecting the enrichment system to back flushing to remove heavy components” comprises:rotating the four-way valve to communicate the port A with the port D again and communicate the port C with the port B;closing the second electronic switch valve and opening the first electronic switch valve; andclosing a pressure of the vaporizing chamber to perform back flushing on the enrichment system.

In an embodiment, the step of “focusing the target components by the focusing trap” comprises:raising a temperature of the focusing chromatographic column system to focus the target components.

Compared to the prior art, this application has the following beneficial effects.(1) The apparatus provided herein has simple installation and assembly and excellent versatility, and thus can be applied to the analysis of trace and ultra-trace impurities in high-purity gaseous, liquid and solid samples that are suitable for GC analysis.(2) In the analysis cycle, the entire enrichment system can independently work with respect to a chromatographic analysis system through its own electronic control system.(3) The apparatus and method provided herein can be used for on-site automatic collection and on-site online enrichment and analysis of samples.

DETAILED DESCRIPTION OF EMBODIMENTS

The technical solutions of this disclosure will be further described in detail below with reference to the accompanying drawings and embodiments.

As shown inFIG.1, provided is a chromatographic apparatus for online enrichment of trace and ultra-trace components and a method for analyzing the trace and ultra-trace components using the same, including: an injection system1, a column compartment2, a vaporizing chamber21, a chromatographic analytical column system22, a detector23, an electronic pressure controller24, an enrichment system3, a focusing trap4, a thermal box5, a sample collection system6, a four-way valve51, and an electronic control system8. The injection system1is a gas sampling valve or an automatic liquid injector, where the gas sampling valve can be connected to a headspace sampler or a purge-trap device.

The injection system1is connected to the column compartment2through pipelines. The vaporizing chamber21, the chromatographic analytical column system22and the detector23are connected to the column compartment2. The chromatographic analytical column system22is connected to the detector23. The detector23can be any commercially-available detector or a combination thereof, and the electronic pressure controller24is a flow controller or a pressure controller.

Specifically, in this embodiment, the vaporizing chamber21and the chromatographic analytical column system22are provided in the column compartment2, to be controlled for the temperature during the operation. The detector23and the electronic pressure controller24are provided on the column compartment2and are connected to the column compartment2.

In another embodiment, the vaporizing chamber21, the chromatographic analytical column system22, the detector23and the electronic pressure controller24are provided independently and are connected to the column compartment2, which facilitates the on-site sampling for subsequent analysis.

The injection system1is connected to the vaporizing chamber21through the column compartment2. The injection system1is configured to inject a sample into the vaporizing chamber21for vaporization. The enrichment system3is connected to the vaporizing chamber21through the column compartment2and is also connected to the focusing trap4. The enrichment system3is configured to trap target components in a vaporized sample, and desorb and transfer the target components to the focusing trap4. The enrichment system3is a trap column system31, which is selected from any commercially-available trap columns and a combination thereof. Moreover, the trap column system31can be independently cooled and rapidly heated.

The four-way valve51is provided in the thermal box5. The four-way valve51is connected to the enrichment system3, the focusing trap4, the electronic pressure controller24and the sample collection system6through the thermal box5, respectively. The four-way valve51in the thermal box5can independently control for the temperature. The focusing trap4is connected to the chromatographic analytical column system22through the column compartment2and includes a focusing chromatographic column system41. The focusing trap4is configured to focus the target components desorbed from the trap column system31and transport the focused target components to the chromatographic analytical column system22for separation. The target components separated by the chromatographic analytical column system22are transferred to the detector23for detection. The sample collection system6is configured to collect and discharge background components in the vaporized sample.

The sample collection system6is configured to measure the sample by cooperation with the electronic pressure controller24or using a precision electronic flow meter, or to perform a cumulative measurement on the sample after multiple injections. Specifically, the sample collection system6is connected to the electronic pressure controller24. The sample collection system6is an insulation cavity for measuring gas injection volume, and at this time, the sample collection system6can be used to collect the vaporized sample and independently controlled for the temperature, so that the total amount of the sample can be measured according to the pressure change in the sample collection system6at a second preset temperature recorded by the electronic pressure controller24, or using the precision electronic flowmeter, where a temperature of the sample collection system6is controlled at 20-350° C.

The electronic control system8is connected to the injection system1, the column compartment21, the vaporizing chamber22, the chromatographic analytical column system22, the detector23, the electronic pressure controller24, the enrichment system3, the thermal box5, the sample collection system6, the focusing trap4and an electronic switch valve box7to control their working states.

The electronic control system8further comprises a chromatographic workstation81and a display screen82. The injection system1, the vaporizing chamber21, the chromatographic analytical column system22and the detector23are connected to the chromatographic workstation81, respectively. After introduced by the injection system1, the sample is sequentially enriched and desorbed by the trap column system31, focused by the focusing chromatographic column system41, separated by the chromatographic analytical column system22and detected by the detector23; and detection results are displayed on the display screen82by the electronic control system8. Specifically, the chromatographic workstation81is connected to the vaporizing chamber21, the chromatographic analytical column system22and the detector23through the column compartment2, respectively.

The trap column of the trap column system31is a cooling-type trap column or a heating-type trap column. The focusing chromatographic column of the focusing chromatographic column system41is a cooling-type focusing chromatographic column or a heating-type focusing chromatographic column. The trap column system31and the focusing chromatographic column system41both are a cooling-type capillary chromatographic column, a heating-type capillary chromatographic column or a combination, and are independently temperature controlled. Injection structures of the injection system1, the vaporizing chamber21, the chromatographic analytical column system22, the detector23and the chromatographic workstation81are respectively a gas sampling valve, an automatic liquid injector or a pressure-controlled structure.

Referring toFIG.1, the apparatus also includes the electronic switch valve box7. The electronic switch valve box7includes a first electronic switch valve71provided between the electronic pressure controller24and the four-way valve51, and a second electronic switch valve72provided between the sample collection system6and the four-way valve51. The first electronic switch valve71and the second electronic switch valve72are configured to perform a switch among the enrichment, desorption and back flushing working modes.

Models of the injection system1, the vaporizing chamber21, the chromatographic analytical column system22and the detector23are adjustable and may be any commercially-available chromatographic accessory. The injection system1is a gas sampling valve or an automatic liquid injector. The vaporizing chamber21is a split or splitless inlet for a chromatographic instrument.

The enrichment, thermal desorption and back flushing working modes can be implemented through the combination of the four-way valve51including a port A511, a port B512, a port C513and a port D514, and the first electronic switch valve71and the second electronic switch valve72of the electronic switch valve box7. The above apparatus can perform an online enrichment and analysis of purities in high-purity gas, HPLC-grade and food-grade solvents and polymer-grade monomers, such as ethylene and propylene. For gas samples, a flow can be adjusted by a vacuum pump and a pressure controller/flow meter under normal pressure to obtain the optimal enrichment effect. Moreover, under pressure, the gas sample can directly pass through the trap column of the trap column system31, and the flow rate can be controlled through the flow meter provided after the trap column to obtain an enhanced enrichment effect. Moreover, it is also feasible to cumulatively measure the volume of multiple injections with the help of a sample loop. For liquid samples, the volume of multiple injections can be cumulatively measured using an automatic sampler. The trap column applied in the trap column system31can be a single chromatographic column or a combination of more chromatographic columns to ensure that all target components are trapped. Similarly, an analytical column of the chromatographic analytical column system22can be also a single chromatographic column or a combination of more chromatographic columns. The detector23should be selected in terms of the characteristics of the target components to ensure the accurate qualitative and quantitative analysis. Each analysis program has functions of back flushing the trap column and the analytical column and purging the pipeline to ensure that it is free of background interference, and the heavy components are completely removed. As validated by measurement of standards and test samples, the analytical method using the apparatus has a detection limit less than 0.1 nmol/mol, an accuracy within ±10% and a precision greater than 90%. The guide sample and practical sample are performed a measurement, where each component is less than, is less than is less than 10%. The measured contents of the target components are extremely identical to the actual contents.

The analysis method provided herein has the following three working modes.

The enrichment mode is performed as follows.

After the sample is vaporized in the vaporizing chamber21, the port D514and the port A511of the four-way valve51are communicated. The first electronic switch valve71is closed and the second electronic switch valve72is opened. The target components in the vaporized sample are trapped by the trap column system31under the first preset temperature, and the background components in the vaporized sample are collected by the sample collection system6and discharged.

Regarding the thermal desorption mode, the specific steps are described as follows.

After the target components are enriched, the second electronic switch valve72is closed, and the four-way valve51is rotated to communicate the port A511with the port B512. A temperature of a trap column of the trap column system31is raised to allow the target components to be desorbed from the trap column system31, and then the target components are transferred to the focusing trap4.

The back flushing mode is performed through the following steps.

The four-way valve51is rotated to communicate the port A511with the port D514again and communicate the port C513with the port B512. The second electronic switch valve72is closed and the first electronic switch valve71is opened. A pressure of the vaporizing chamber21is closed. A temperature of the focusing chromatographic column system41is raised to focus the target components desorbed from the trap column system31. The focused target components are transferred to the chromatographic analytical column system22. The heavy components in the sample are back flushed out. The target components are sequentially separated by the chromatographic analytical column system22and detected by the detector23.

Further, the heavy components are components in the sample that may interfere with the enrichment and analysis of the target components.

In the enrichment and thermal desorption working modes, interference of the background components is eliminated through large-volume continuous injection and repeated injection, and by separating the background components with the help of the enrichment system3. The target components desorbed from the enrichment system3are transferred to the focusing trap4to achieve the enrichment of the trace and ultra-trace components.

In an analytical cycle, a switch among the enrichment, thermal desorption and back flushing modes is performed through the combination of the four-way valve51and the electronic switch valve box7. The electronic control system8is configured to control the analytical cycle through a time sequence program.

The analytical method using the above apparatus will be further described with reference to the following examples.

A high-purity hydrogen sample was analyzed herein by the above method using the chromatographic apparatus provided herein for online enrichment of trace and ultra-trace components. Specifically, conditions of enrichment, desorption and back flushing, including type and size of the trap column and the analytical column, pressure of individual pressure control points, switching time of the valve, temperature and switching time of individual temperature control points, programmed temperature rate and flow of each flow control point, were selected and optimized. The impurities in the sample were enriched and then subjected to separation and analysis, and the optimized chromatographic conditions were presented in Table 1.

The online enrichment and analysis method of trace and ultra-trace components using the chromatographic apparatus provided herein was evaluated for accuracy, repeatability and stability system under the optimized conditions using a reference sample 1 as calibration reference and a reference sample 2 as an analyte. The obtained gas chromatogram was presented inFIG.2, and the data results were displayed in Table 2.

It can be seen from Table 2 that when applied to the analysis of impurities in the high-purity hydrogen sample, the method of this disclosure had a relative standard deviation (RSD, calculated by 5 consecutive tests) less than 7.1% and a recovery rate of 95.6%-120.8%, indicating that it was suitable for the analysis of trace and ultra-trace components.

TABLE 2Testing results of impurities in high-purity hydrogenContent, mg/m3AverageRecoveryComponents12345valueRSD/%rate/%O20.630.670.710.580.730.667.1115.2N210.710.210.510.810.210.482.1120.8CO0.0430.0480.0440.0410.0370.0436.8100.8CO20.0330.0320.0360.0320.0350.0344.595.6CH40.0590.0580.0650.0610.0590.0603.498.7

A commercially-available 1,3-butadiene product was analyzed herein by the above method using the chromatographic apparatus provided herein for online enrichment of trace and ultra-trace components. Specifically, conditions of enrichment, desorption and back flushing, including type and size of the trap column and the analytical column, pressure of individual pressure control points, switching time of the valve, temperature and switching time of individual temperature control points, programmed temperature rate and flow of each flow control point, were selected and optimized. The impurities in the sample were enriched and then subjected to separation and analysis, and the optimized chromatographic conditions were presented in Table 3.

The online enrichment and analysis method of trace and ultra-trace components using the chromatographic apparatus provided herein was evaluated for accuracy, repeatability and stability system under the optimized conditions using 1,3-butadiene samples added with different concentrations of dimethyl ether, methyl tert-butyl ether (MTBE), methanol and Tert-/Sec-/Iso-butyl alcohol respectively as calibration reference and analyte. The obtained gas chromatogram was presented inFIG.3, and the data results were displayed in Table 4.

It can be seen from Table 4 that when applied to the analysis of impurities in the 1,3-butadiene product, the method of this disclosure had a relative standard deviation (RSD, calculated by 5 consecutive tests) less than 8.7% and a recovery rate of 90.5%-102.3%, indicating that it was suitable for the analysis of trace and ultra-trace components.

TABLE 4Testing results of impurities in 1,3-butadieneContent, mg/m3AverageRecoveryComponents12345valueRSD/%rate/%Dimethyl0.1850.1880.1830.1860.1930.1871.2593.6etherMethyl1.921.811.881.891.921.901.4798.3tert-butylether(MTBE)Methanol0.2150.2260.2220.2250.2260.2241.35110.5Tert-/ Sec-/0.2110.2120.2060.2130.2150.2181.33107.8Iso-butylalcohol

A commercially-available polymer-grade ethylene glycol was analyzed herein by the above method using the chromatographic apparatus provided herein for online enrichment of trace and ultra-trace components. Specifically, conditions of enrichment, desorption and back flushing, including type and size of the trap column and the analytical column, pressure of individual pressure control points, switching time of the valve, temperature and switching time of individual temperature control points, programmed temperature rate and flow of each flow control point, were selected and optimized. The impurities in the sample were enriched and then subjected to separation and analysis, and the optimized chromatographic conditions were presented in Table 5.

The online enrichment and analysis method of trace and ultra-trace components using the chromatographic apparatus provided herein was evaluated for accuracy, repeatability and stability system under the optimized conditions using polymer-grade ethylene glycol samples added with different concentrations of 1,2-propanediol, 1,2-butanediol, ethylene carbonate, 1,4-butanediol and 1,2-hexanediol respectively as calibration reference and analyte. The obtained gas chromatogram was presented inFIG.4, and the data results were displayed in Table 6.

It can be seen from Table 6 that when applied to the analysis of impurities in the ethylene glycol product, the method of this disclosure had a relative standard deviation (RSD, calculated by 5 consecutive tests) less than 8.7% and a recovery rate of 90.5%-102.3%, indicating that it was suitable for the analysis of trace and ultra-trace components.

TABLE 6Testing results of impurities in ethylene glycolContent, mg/kgAverageRecoveryComponents12345valueRSD/%rate/%1,2-propanediol0.460.470.510.580.530.0517.192.11,2-butanediol0.270.290.350.340.320.03148.798.6Ethylene7.98.37.58.17.70.0793.0102.3carbonate1,4-butanediol0.360.380.340.410.330.3646.899.41,2-hexanediol0.0230.0210.0260.020.0270.02348.790.5

A commercially-available HPLC-grade methanol was analyzed herein by the above method using the chromatographic apparatus provided herein for online enrichment of trace and ultra-trace components. Specifically, conditions of enrichment, desorption and back flushing, including type and size of the trap column and the analytical column, pressure of individual pressure control points, switching time of the valve, temperature and switching time of individual temperature control points, programmed temperature rate and flow of each flow control point, were selected and optimized. The impurities in the sample were enriched and then subjected to separation and analysis, and the optimized chromatographic conditions were presented in Table 7.

The online enrichment and analysis method of trace and ultra-trace components using the chromatographic apparatus provided herein was evaluated for accuracy, repeatability and stability system under the optimized conditions using HPLC-grade methanol samples added with different concentrations of dimethyl ether, ethanol, methyl formate and acetone respectively as calibration reference and analyte. The obtained gas chromatogram was presented inFIG.5, and the data results were displayed in Table 8.

It can be seen from Table 8 that when applied to the analysis of impurities in the methanol product, the method of this disclosure had a relative standard deviation (RSD, calculated by 5 consecutive tests) less than 6.4% and a recovery rate of 91.3%-108.4%, indicating that it was suitable for the analysis of trace and ultra-trace components.

TABLE 8Testing results of impurities in methanolContent, mg/kgAverageRecoveryComponents12345valueRSD/%rate/%Dimethyl0.370.410.450.440.390.596.491.3etherMethyl0.2110.2180.2060.2230.2350.2193.8103.8formateEthanol0.520.470.540.480.530.495.2108.4Acetone0.0550.0570.0610.0580.0630.00414.494.6

Considering the problems in the prior art that the enrichment apparatus is complicated; there is great difficulty in seeking a selective adsorption material; the steps of extraction and desorption (thermal desorption/elution) have harsh conditions and low efficiency; the background interference cannot be eliminated; and the detection has a narrow linear range and a poor stability and repeatability, this application provides a chromatographic apparatus in which a chromatographic column/tube that can be rapidly cooled and heated is used as the enrichment system; an electronic pressure controller is provided to measure the pressure change; a precision flow meter is employed to accurately measure the total amount of samples; and a focusing chromatographic column that can be electrically cooled or cooled with low-temperature liquid is employed to re-focus the desorbed target components. In addition, the apparatus provided herein has an excellent compatibility with multiple detectors, simple assembly and desirable versatility, rendering it suitable for the enrichment and analysis of trace and ultra-trace impurities in HPLC-grade, food-grade and medical-grade solvents, high-purity gases and polymer-grade monomers. The entire enrichment system can work independently with respect to the chromatographic analysis system through its own electronic control system, so that it can be directly applied to the on-site sampling or to the on-site enrichment and analysis through coupling with a micro-chromatography.

Described above are merely preferred embodiments of this disclosure, which are not intended to limit the disclosure. It should be understood that any change, modification and replacement made by those skilled in the art without departing from the spirit of the disclosure should fall within the scope of the disclosure.