Investigation Of Microwave-Assisted Extraction And Its Related Techniques In Application Of Pharmaceutical Analysis

Sample preparation is the most important and limiting step for qualitative and quantitative analysis in matrices. In the last two decades, there has been an increasing demand for new extraction techniques with the properties of amenable to automation, shortened extraction times and reduced organic solvent consumption which not only prevents pollution in analytical laboratories but also reduces sample preparation costs. Driven by these demands, several techniques such as microwave-assisted extraction (MAE), supercritical fluid extraction (SFE), and pressurized liquid extraction have been developed. Among these techniques, MAE, a process of using microwave energy to heat solvents in contact with a sample in order to partition analytes from the sample matrices into the solvent, has drawn more and more attention in recent years. In this study, we focused on developing new extraction methods for separation and determination of active component in plant materials, especially in TCMs (Traditional Chinese Medicine). The microwave-assisted extraction and its related techniques, combined with modern chromatographic methods, were applied for qualitation and quantitative study of different kinds of target compounds or target plant materials. This dissertation is divided into five parts.In Chapter 1, the significant impact of developing pre-preparation technique on modernization of TCM and several traditional methods were overviewed. The principle of MAE and its advantages in application were summarized in details. Then intention and meaning of this dissertation were explained.In Chapter 2, a gas chromatography mass spectrometry (GC-MS) following microwave distillation and solid-phase microextraction (MD-SPME) was developed for the analysis of essential oil compounds in both fresh ginger and safflower. In the proposed method, the isolation, extraction and concentration of volatile components in TCMs were carried out in one single step. Some parameters, including SPME fiber coating, volume of water, microwave power and irradiation time, were optimized. The MD-SPME method was compared with convertional SPME and steam distillation method. The results showed the method is simple, rapid and solvent-free. These two research papers were published in Journal of Pharmaceutical and Biomedical Analysis (2007,43(1):24-31) and Annali di Chimica (2007,10 (97):1075-1084).We further developed microwave-assisted liquid-phase extraction method followed with gas chromatography for quantitative determination of menthol, menthone and pulegone in Mentha haplocalyx Briq. Three MAE parameters, including concentration of extraction solvent, extraction time and microwave power, were studied. Compared with conventional ultrasonic extraction, the proposed method is simple, rapid, stable and efficient.In Chapter 3, the developed MAE-HPLC method was applied for analysis of involatile components in plants or TCMs. The concentration of flavone in orange peel was determined by the improved method which was also applied to fruits and juice. The MAE technique was again proved to be efficient and rapid. Despite the wide application, problems emerged when utilizing MAE for extraction of oxidizable compounds such as antioxidants, since they are easy to degrade under the circumstances of air and elevated temperature. Then, nitrogen-protected microwave-assisted extraction (NPMAE) in which MAE was performed under nitrogen protection, was initially developed for the first time and combined with HPLC separation for the determination of ascorbic acid, an oxidizable component, from fruit and vegetables. Compared with conventional MAE and solvent extraction methods, the oxidation of ascorbic acid was significantly reduced or prevented in the process of NPMAE. The study suggested the potential of NPMAE method for the extraction of oxidizable compounds from different spices of matrices. The result was established in Journal of Separation Science (2009,32 (23-24):4227-4233).In Chapter 4, a novel strategy for extracting active components from plant materials with Infrared-assisted extraction (IRAE) technique was applied to determine chlorogenic acid, rutin and galuteolin in lonicerae combined with HPLC-tandem MS spectrometry. Infrared ray is another important form of electromagnetic wave, which was employed as an efficient energy source in a wide range of applications. The parameters of extraction solvent, solid/liquid ratio, Infrared power and irradiation time were optimized. Compared with MAE and ultrasonic extraction, the developed IRAE method is rapid, efficient and safe as well. The results open up a possibility for IRAE's further application in plant material pre-processing and analysis. The research paper is being written and will be submitted to Talanta.In Chapter 5, we employed, for the first time, a multiple headspace single-drop microextraction (MHS-SDME) method coupled to gas chromatography with flame-ionization detection for direct determination of residual solvents in solid drug product. The MHS-SDME technique is based on extrapolation to an exhaustive extraction of consecutive extractions from the same sample which eliminates the matrix effect on the quantitative analysis of solid samples. In this work, a model drug powder was chosen and the amounts of residues of two solvents, methanol and ethanol were investigated. Influential factors affected in the process of extraction including extraction solvent, microdrop volume, extraction time, sample amount, thermostatting temperature and incubation time were studied. Validation of the improved method showed good agreement with the traditional dissolution method for analysis of residual solvents in drug product. The results indicated that MHS-SDME has a great potential for the quantitative determination of residual solvents directly from the solid drug products due to its low cost, ease to operate, sensitivity, reliability and environmental protection. The research paper was submitted to Journal of Chromatography A and is under revision.In summary, the main contributes of this dissertation is that we initially investigated several pretreatment methods on the basis of microwave assisted extraction and its related technique, and the developed methods were successfully applied to analysis of plant material of different species. We aimed at exploring and finding out new techniques in sample preparation of plant material analysis, so that more breakthroughs can be obtained in the quality control research study of TCMs.