Establishment Of A Self-heating Gas-liquid Microextraction Technique And Its Application To The Analysis Of Plant Components

At present,the analysis and testing of samples in a variety of fields such as the detection of pollutants in the environment,plant composition analysis and pesticide residues in food safety is becoming more and more precise,miniaturised and on-site.Take the analysis of volatile components in plants as an example,some of them are chemically unstable,volatile and degraded under the influence of light.Changes in the composition or loss of volatile components during sample collection,transfer and storage inevitably result in incomplete information on chemical composition and the need to ensure the timeliness and accuracy of analytical results.The sample analysis process consists of two main components:sample pre-treatment and instrumental testing.Amongst other things,detection technology has undergone rapid development and at this stage can meet the needs of peak capacity,detection limits and timeliness,with the development and preparation of portable detection instruments tending towards maturity.However,at this stage,common sample pre-treatment techniques such as soxhlet extraction,hydrodistillation and ultrasonic extraction are commonly used with the assistance of borrowed energy,cumbersome construction of experimental apparatus,long extraction time and other limitations,which cannot be matched to the portable rapid test performance applied to field testing.Therefore,there is a need to establish a simple,green,efficient and portable on-site pre-treatment method.In this thesis,a self-heating gas-liquid microextraction method is developed to address these issues.Based on the self-heating material’s own exothermic properties,a portable on-site pre-treatment method is proposed that does not require external energy.Applying this method to plant samples,the extraction of volatile plant components can be achieved by using the release of heat from the hydration reaction of calcium oxide as an energy source for desorption of volatile components from plant samples,and coupled with gas chromatography-mass spectrometry.A highly efficient and low-energy method for the in situ extraction of volatile components from plants was developed.The aim is to provide a novel portable sample pre-treatment method for the accurate analysis and exploitation of volatile components in botany and pharmacology.The main work is from the following aspect:Firstly,established a self-heating gas-liquid microextraction device.Use of self-heating materials,exothermic properties of the reaction of calcium oxide with water combined with an inert gas flow purge to obtain an experimental apparatus that enables field extraction.Secondly,the theoretical system of self-heating gas-liquid micro-extraction method is established and the method parameters are optimised for the volatile components in plants,so that the extraction process can be completed without external energy borrowing by taking advantage of the exothermic nature of the reaction between calcium oxide and water to achieve field extraction.The optimum extraction efficiency was achieved with a calcium oxide to water ratio of 1:2,a water droplet acceleration of 0.5 m L s^-1,a sample volume of 300 mg,an extraction time of 15 min,an airflow rate of 10.0 m L min^-1,an extraction solvent of dichloromethane and a receiver phase solvent height of 4 cm.Comparing this method with the traditional extraction technique of water distillation of volatile components of plants,the composition and content of the compounds obtained are similar.A three-dimensional comparison in terms of energy consumption and suitability for on-site extraction shows that self-heating gas-liquid microextraction has clear advantages.The precision of the method was verified by intra-day inter-day stability experiments and the relative standard deviation obtained was less than 10%.Third,the method was applied to the extraction of phytovolatile components from six natural medicinal plants.The preliminary qualitative results and the relative content of each component were obtained by comparison with the NIST spectral library,and six samples were extracted to obtain 33,29,26,43,27 and 34 volatile components respectively.In summary,this method is expected to provide a theoretical basis and technical support for the accurate analysis and exploitation of volatile components in botany and pharmacology as a rapid detection method without the need for external energy.