Stability evaluation method of thermogravimetry-instillation microextraction combined system

Abstract

The invention discloses a stability evaluation method of a thermogravimetry-instillation microextraction combined system, and belongs to the technical field of chemical analysis and testing. According to the method, a target compound and an internal standard compound with volatility are utilized to realize stable and constant-speed volatilization under an optimal test condition of a thermogravimetric-instillation microextraction combined system, a parallel experiment is carried out through instillation microextraction according to the optimal test condition, a plurality of liquid drops containing the target compound and the internal standard compound at the same time are collected, and the target compound and the internal standard compound are obtained. Measuring the concentration of the compound in the liquid drop by using a gas chromatography-hydrogen flame ionization detector to obtain a plurality of groups of concentration values, respectively calculating the relative standard deviations SD1 and RSD2 of the concentration of the target compound and the internal standard compound, calculating the concentration ratio of the target compound to the internal standard compound in each group and the relative standard deviation RSD3 of the target compound and the internal standard compound in each group, and taking the three RSD values as an evaluation index of the stability of the thermogravimetry-instillation microextraction combined system, and indicating that the stability of the combined system is good if the RSD1 is less than or equal to 10%, the RSD2 is less than or equal to 10% and the RSD3 is less than or equal to 5% in a required range.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis and testing, and particularly relates to a stability evaluation method for a thermogravimetric-drip microextraction combined system. Background Art

[0002] Thermal analysis technology is a very important analytical test method that studies various transformations and reactions of materials under temperature program control, such as dehydration, crystallization, melting, evaporation, phase change, and thermal decomposition processes and reaction kinetics of various inorganic and organic materials. As a traditional thermal analysis technology, thermogravimetric / differential thermal analysis is a thermal analysis technology that uses a thermobalance to measure the relationship between material mass, heat change mass increase, mass loss or heat absorption, heat release and temperature under program-controlled temperature. It has the advantages of simple instrument operation, high accuracy, sensitivity and speed, and sample micro-quantification. It is now widely used in inorganic, organic, chemical, metallurgical, pharmaceutical, food, tobacco, energy and biological fields.

[0003] Single-drop microextraction is a new, environmentally friendly sample pretreatment technology that integrates extraction and enrichment. It has the characteristics of low cost, simple device, easy operation, low organic solvent usage and high enrichment efficiency. The thermogravimetric-drip microextraction system developed on this basis is easy to operate, fast in extraction speed, and highly automated. It realizes the online simultaneous extraction and enrichment of thermogravimetric escaped compounds and internal standard compounds, providing technical support for the application of single-drop microextraction technology in the field of qualitative and quantitative analysis of thermogravimetric escaped substances. However, there are no reports on the stability evaluation method of the thermogravimetric-drip microextraction system. Summary of the invention

[0004] In view of the problem that there is no specific stability evaluation method for the current thermogravimetric-drip microextraction combined system, the present invention provides a stability evaluation method for the thermogravimetric-drip microextraction combined system.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for evaluating the stability of a thermogravimetric-drip microextraction system is disclosed. The method utilizes a volatile target compound and an internal standard compound to achieve stable and uniform volatilization under the optimal test conditions of the thermogravimetric-drip microextraction system. Parallel experiments are carried out through drip microextraction according to the optimal test conditions to collect multiple droplets containing both the target compound and the internal standard compound. The concentration of the compound in the droplets is measured by a gas chromatography-hydrogen flame ionization detector to obtain multiple groups of concentration values. The relative standard deviations RSD1 and RSD2 of the concentrations of the target compound and the internal standard compound are calculated respectively. The concentration ratio of each group of target compounds and internal standard compounds and their relative standard deviation RSD3 are calculated and used as evaluation indicators for the stability of the thermogravimetric-drip microextraction system. When the three RSD values ​​RSD1≤10%, RSD2≤10% and RSD3≤5%, it indicates that the thermogravimetric-drip microextraction system has good stability.

[0006] Furthermore, by controlling the magnetic stirring speed, water bath temperature and purge carrier gas flow rate of the internal standard solution, the stable and uniform volatilization of the internal standard compound in the internal standard addition unit is achieved.

[0007] Furthermore, by controlling the carrier gas flow rate, circulating water temperature and furnace temperature of the thermogravimetric analyzer and adding a crucible cover with vent holes, the stable and uniform volatilization of the target compound in the crucible of the thermogravimetric analyzer is achieved.

[0008] A method for evaluating the stability of a thermogravimetric-drip microextraction system comprises the following steps: Step 1, selecting isopropanol as an internal standard compound to prepare an internal standard solution; Step 2, pipette 300 mL of internal standard solution and add it into the reagent bottle of the internal standard addition unit of the drip microextraction device; Step 3, selecting sec-butanol as the target compound, weighing 200 mg of sec-butanol into a crucible of a thermogravimetric analyzer, and covering the crucible with a crucible cover having a 1 mm vent hole, which is conducive to the stable volatilization of the target compound in the crucible and prevents interference from the thermogravimetric carrier gas; Step 4, setting various parameters of the thermogravimetric analyzer according to the optimal test conditions; Step 5, setting various parameters of drip microextraction according to the optimal experimental conditions; Step 6, after the thermogravimetric furnace is heated to 50°C and maintained for 20 minutes, drip microextraction is started to collect droplets, one droplet is collected every 2 minutes, and new droplets are automatically replenished after each collection. The droplet collection and replenishment process takes 5 seconds and ends after 15 droplets are collected; Step 7, discarding the first 5 droplets, injecting the last 10 droplets into a gas chromatography-hydrogen flame ionization detector for detection, and measuring 10 groups of concentration data of sec-butyl alcohol and isopropyl alcohol in the droplets; Step 8, respectively calculating the relative standard deviations RSD1 and RSD2 of the concentrations of sec-butyl alcohol and isopropyl alcohol, and calculating the ratio of the concentrations of sec-butyl alcohol and isopropyl alcohol in each group and its relative standard deviation RSD3; Step 9: If RSD1≤10%, RSD2≤10%, and RSD3≤5%, it indicates that the combined system has good stability.

[0009] Further, the preparation of the internal standard solution in step 1 is specifically to add 5 g of isopropanol into a 1 L volumetric flask, and make up the volume with ethanol to obtain an internal standard solution with an isopropanol concentration of 5 g / L.

[0010] Furthermore, the preferred experimental conditions of the internal standard addition unit of the drip microextraction device include: the magnetic stirring speed of the internal standard solution is 200r / min, the water bath temperature is controlled at 10°C, the carrier gas for purging the internal standard solution is high-purity nitrogen, and the carrier gas flow rate is 300mL / min.

[0011] Further, in step 4, various parameters of the thermogravimetric analyzer are set according to the preferred experimental conditions; the thermogravimetric carrier gas is high-purity nitrogen, the carrier gas flow rate is 200 mL / min, the circulating water temperature outside the thermogravimetric furnace is 22°C, the furnace is set at 30°C and maintained for 5 minutes, then increased to 50°C at 2°C / min and maintained for 60 minutes.

[0012] Furthermore, in step 5, various parameters of the drip microextraction are set according to the preferred experimental conditions; the extraction liquid is chromatographically pure ethanol, the droplet volume is controlled to be 35±5 μL, the extraction chamber temperature is 40°C, the purge carrier gas is a mixture of the internal standard solution carrier gas and the thermogravimetric carrier gas, and the total carrier gas flow rate is 500 mL / min.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This evaluation method is used to examine the stability of the thermogravimetric-drip microextraction system. It is easy to operate, has a fast inspection speed, and high evaluation accuracy, providing a stable guarantee for the subsequent use of the thermogravimetric-drip microextraction system.

[0014] 2. Drip microextraction is a microextraction process in which a continuously flowing carrier gas carrying the components to be measured continuously sweeps the droplets, and the components to be measured achieve dynamic equilibrium between the carrier gas and the droplets. It is a process in which the droplets are continuously volatilized by the carrier gas sweep and are constantly replenished by the controller. RSD1 and RSD2 in the evaluation method of the present invention can effectively examine the effect of this volume change process on the enrichment effect of the compounds in the droplets.

[0015] 3. The relative standard deviation (RSD3) of the concentration ratio of each target compound and internal standard compound in parallel experiments is the most important indicator for evaluating the stability of the combined system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the concentration curve of sec-butanol of the present invention, and the ordinate is concentration (mg / L).

[0017] Figure 2 : isopropanol concentration curve of the present invention, and the ordinate is concentration (mg / L).

[0018] Figure 3 It is a curve of the concentration ratio of sec-butyl alcohol and isopropyl alcohol of the present invention, and the ordinate is the concentration ratio. DETAILED DESCRIPTION

[0019] In order to gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description of the present invention. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the comprehensive understanding of the disclosure of the present invention.

[0020] Example 1

[0021] Stability evaluation method of thermogravimetric-drip microextraction system Step 1, weigh 5 g of isopropanol and add it to a 1 L volumetric flask, and dilute to volume with ethanol to obtain a solution with an isopropanol concentration of 5 g / L as an internal standard solution; Step 2, pipette 300mL of internal standard solution into the reagent bottle of the internal standard addition unit of the drip microextraction device, set the magnetic stirring speed of the internal standard solution to 200r / min, the water bath temperature to 10°C, and the carrier gas for purging the internal standard solution to high-purity nitrogen with a carrier gas flow rate of 300mL / min; Step 3, select sec-butanol as the target compound, weigh 200 mg of sec-butanol into the crucible of the thermogravimetric analyzer, and cover the crucible with a crucible cover with a 1 mm vent hole to prevent interference from the thermogravimetric carrier gas; Step 4, setting various parameters of the thermogravimetric analyzer, the thermogravimetric carrier gas is high-purity nitrogen, the carrier gas flow rate is 200 mL / min, the temperature of the circulating water outside the thermogravimetric furnace is 22°C, the furnace is set at 30°C for 5 minutes, then raised to 50°C at 2°C / min and maintained for 60 minutes; Step 5, setting various parameters of drip microextraction, the extraction liquid is chromatographic pure ethanol, the droplet volume is controlled to be about 35±5 μL, the extraction chamber temperature is 40°C, the purge carrier gas is a mixture of the internal standard solution carrier gas and the thermogravimetric carrier gas, and the total carrier gas flow rate is 500 mL / min; Step 6, after the thermogravimetric furnace is heated to 50°C and maintained for 20 minutes, drip microextraction is started to collect droplets, one droplet is collected every 2 minutes, and new droplets are automatically replenished after each collection. The droplet collection and replenishment process takes 5 seconds and ends after 15 droplets are collected; Step 7, discarding the first 5 droplets, injecting the last 10 droplets into a gas chromatography-hydrogen flame ionization detector for detection, and measuring 10 groups of concentration data of sec-butyl alcohol and isopropyl alcohol in the droplets; Step 8, calculate the relative standard deviations (RSD1 and RSD2) of the concentrations of sec-butyl alcohol and isopropyl alcohol, respectively, and calculate the ratio of the concentrations of sec-butyl alcohol and isopropyl alcohol in each group and their relative standard deviation (RSD3), RSD1=8.72%, RSD2=8.52%, RSD3=1.61%; In step 9, RSD1≤10%, RSD2≤10%, and RSD3≤5%, indicating that the combined system has good stability.

[0022] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A method for evaluating the stability of a thermogravimetric-drip microextraction system, characterized in that: Using volatile target compounds and internal standard compounds, stable and uniform volatilization was achieved under the optimal experimental conditions of the thermogravimetric-drip microextraction system. Parallel experiments were carried out through drip microextraction according to the optimal experimental conditions, and multiple droplets containing both the target compound and the internal standard compound were collected. The concentration of the compound in the droplets was measured by gas chromatography-hydrogen flame ionization detector, and multiple groups of concentration values ​​were obtained. The relative standard deviations RSD1 and RSD2 of the concentrations of the target compound and the internal standard compound were calculated respectively. The concentration ratio of each group of target compounds and internal standard compounds and their relative standard deviation RSD3 were calculated and used as the evaluation index of the stability of the thermogravimetric-drip microextraction system. When the three RSD values ​​RSD1≤10%, RSD2≤10%, and RSD3≤5%, it indicates that the thermogravimetric-drip microextraction system has good stability.

2. The method for evaluating the stability of a thermogravimetric-drip microextraction system according to claim 1, characterized in that: By controlling the magnetic stirring speed, water bath temperature and purge carrier gas flow rate of the internal standard solution, the stable and uniform volatilization of the internal standard compound in the internal standard addition unit is achieved.

3. The method for evaluating the stability of a thermogravimetric-drip microextraction system according to claim 1, characterized in that: By controlling the carrier gas flow rate, circulating water temperature and furnace temperature of the thermogravimetric analyzer and covering the crucible with a vent hole, the stable and uniform volatilization of the target compound in the crucible of the thermogravimetric analyzer is achieved.

4. The method for evaluating the stability of a thermogravimetric-drip microextraction system according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1, selecting isopropanol as an internal standard compound to prepare an internal standard solution; Step 2, pipette 300 mL of internal standard solution and add it into the reagent bottle of the internal standard addition unit of the drip microextraction device; Step 3, selecting sec-butanol as the target compound, weighing 200 mg of sec-butanol into a crucible of a thermogravimetric analyzer, and covering the crucible with a crucible cover having a 1 mm vent hole; Step 4, setting various parameters of the thermogravimetric analyzer according to the optimal test conditions; Step 5, setting various parameters of drip microextraction according to the optimal experimental conditions; Step 6, after the thermogravimetric furnace is heated to 50°C and maintained for 20 minutes, drip microextraction is started to collect droplets, one droplet is collected every 2 minutes, and new droplets are automatically replenished after each collection. The droplet collection and replenishment process takes 5 seconds and ends after 15 droplets are collected; Step 7, discarding the first 5 droplets, injecting the last 10 droplets into a gas chromatography-hydrogen flame ionization detector for detection, and measuring 10 groups of concentration data of sec-butyl alcohol and isopropyl alcohol in the droplets; Step 8, respectively calculating the relative standard deviations RSD1 and RSD2 of the concentrations of sec-butyl alcohol and isopropyl alcohol, and calculating the ratio of the concentrations of sec-butyl alcohol and isopropyl alcohol in each group and its relative standard deviation RSD3; Step 9: If RSD1≤10%, RSD2≤10%, and RSD3≤5%, it indicates that the combined system has good stability.

5. The method for evaluating the stability of a thermogravimetric-drip microextraction system according to claim 4, characterized in that: The internal standard solution in step 1 is prepared by adding 5 g of isopropanol into a 1 L volumetric flask and fixing the volume with ethanol to obtain an internal standard solution with an isopropanol concentration of 5 g / L.

6. The method for evaluating the stability of a thermogravimetric-drip microextraction system according to claim 4, characterized in that: The preferred experimental conditions of the internal standard addition unit of the drip microextraction device include: the magnetic stirring speed of the internal standard solution is 200r / min, the water bath temperature is controlled at 10°C, the carrier gas for purging the internal standard solution is high-purity nitrogen, and the carrier gas flow rate is 300mL / min.

7. The method for evaluating the stability of a thermogravimetric-drip microextraction system according to claim 4, characterized in that: In step 4, various parameters of the thermogravimetric analyzer are set according to the preferred experimental conditions; the thermogravimetric carrier gas is high-purity nitrogen, the carrier gas flow rate is 200 mL / min, the circulating water temperature around the thermogravimetric furnace is 22°C, the furnace is set at 30°C and maintained for 5 minutes, then increased to 50°C at 2°C / min and maintained for 60 minutes.

8. The method for evaluating the stability of a thermogravimetric-drip microextraction system according to claim 4, characterized in that: In step 5, various parameters of drip microextraction are set according to the preferred experimental conditions; the extraction liquid is chromatographic pure ethanol, the droplet volume is controlled to be 35±5 μL, the extraction chamber temperature is 40°C, the purge carrier gas is a mixture of the internal standard solution carrier gas and the thermogravimetric carrier gas, and the total carrier gas flow rate is 500 mL / min.

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