Preparation Of Chromatographic Materials Using Droplet Microfluidic Technologies

High performance liquid chromatography (HPLC) is an important branch of modern chromatography science. HPLC, with its high speed, high efficiency and high sensitivity is widely used in petroleum and chemical, life science, pharmaceutical industry, environmental monitoring and other fields. Chromatographic column is one of the most important components of HPLC. The packing, i.e., the stationary phase within the column, is the core of chromatographic separation, as high quality particulate packing is the key to obtain a high quality separation for HPLC. High performance liquid chromatographic techniques need chromatographic particles having narrow size distributions and ideally, mono-dispersive. Mono-dispersive spherical particles can lead to good permeability, significantly improved reproducibility and excellent separation efficiency. Highly monodispersed chromatographic particles have always been a goal of chromatography. In recent years, droplet microfluidics provides new strategies for prepartion of monodisperse chromatography material. The technique uses two-phase immiscible solutions, which can form droplets at the interface. Such droplets have fast thermal transfer, fast mass transfer, high surface area, high mono-dispersion etc. Microfluidic systems can generate droplets at high speed with a frequency up to thousands hertz. In addition, the volume of the droplet can be flexibly controlled by regulating the size of chip channels, surface chemical properties, two-phase flow velocities and other conditions, in order to produce highly uniform micro-droplets. By controlling the droplet generation frequency, size and reproducibility, one can quickly prepare size controlled, narrow size distribution (monodisperse) chromatographic particles.In this thesis, we use droplet microfluidic technology to prepare monodisperse lysine-silica hybrid microspheres, by adjustting the flow rate ratio of continuous phase and dispersed phase to precisely control the size of the spherical particles. The thesis consists of four chapters as following: In chapter one, traditional methods for preparing chromatographic particles and the application of droplet microfluidic technology were reviewed. The chapter also discussed the importance of monodisperse chromatographic particles in improving the permeability and column efficiency. It also pointed out that the purpose of this thesis is to study the preparation of monodisperse chromatography particles to meet the requirements of narrow particle size distribution in chromatographic materials.In chapter two, we prepared a microfluidic chip for droplets generation, by simply assembling with a three-way valve, PEEK fittings, FEP adapter sleeve, cylindrical capillary and tapered cylindrical capillary. The method was simple, easy to disassemble and there is no need for the photolithographic process or experimental equipment.The preparation of microfluidic chips was conducted in an ordinary chemical laboratory, rather than in a super-clean room. With such a chip, we can stably generated oil-in-water droplets and the coefficient of variation (CV) of the diameter was less than4%, showing excellent monodispersity. Moreover, by adjusting flow rate ratio of the continuous and dispersed phases, we can precisely control the droplet size. For a fixed flow rate of the dispersed phase, gradually increasing the flow rate of the continuous phase lead to decreasing of, the droplet size. After hydrophobic modification, the chip can also be used to prepare water-in-oil droplets.In chapter three, we used droplet microfluidic technology to prepare monodispersive, size-controllable, lysine-silica hybrid porous microspheres, which were characterized with SEM, IR methods. The size of particles can be accurately controlled in the range of tens of microns to several hundred microns by adjusting the dimension of chips and the ratio of the dispersed phase and continuous phase flow rate, the CV of the microspheres is less than5%, indicating good monodispersity.In chapter four, a summary of this thesis was concluded and future work was outlooked.