芯片液相色谱技术进展

微型化是现代分析仪器发展的重要趋势。微型化液相色谱仪器在提供与常规尺度液相色谱相同甚至更高分离效率的同时,可以有效减少溶剂和样品的消耗;在液相色谱-质谱联用中,低流速进样可以有效提高质谱离子源的离子化效率,提高质谱检测效率;对于极微量样品的分离,微型化的液相色谱可以有效减少样品稀释;液相色谱的微型化还有利于液相色谱仪器整体的模块化和集成化设计。芯片液相色谱是在微流控芯片上制备色谱柱并集成相应的流体控制系统和检测系统。芯片液相色谱是色谱仪器微型化的一种重要方式,受到学术界和产业界的普遍关注,但是这一方式也充满挑战。液相色谱微流控芯片需要在芯片基底材料、芯片色谱柱的结构设计、微流体控制技术、检测器技术等方面做出创新,使微流控芯片系统适配液相色谱分离技术的需要。目前芯片液相色谱领域面临的主要问题在于芯片基底材料的性质难以满足芯片液相色谱进一步微型化和集成化的需求;因此芯片液相色谱在未来的发展中需要着重关注新型微流控芯片基底材料的开发以及微流控芯片通道结构的统一设计。该文着重介绍了芯片液相色谱技术近年来的研究进展,并简要展示了商品化芯片色谱当前的发展情况。

Recent advances in microchip liquid chromatography

Miniaturization is an important trend in modern analytical instrument development, including miniaturized gas chromatography and liquid chromatography, as well as micro bore columns and capillary-to-microfluidics-based platforms. Apart from the miniaturization of the separation column, which is the core part of a chromatographic system, other parts of the system, including the sampler, pumping system, gradient generation, and detection systems, have been miniaturized. Miniaturized liquid chromatography significantly reduces solvent and sample consumption while providing comparable or even better separation efficiency. When liquid chromatography is coupled with mass spectroscopy, a low flow rate can increase the ionization efficiency, leading to enhanced sensitivity of the mass spectrometer. In contrast, normal-scale liquid chromatography suffers from its relatively high volumetric flow rate, which challenges the scanning frequency of the mass spectrometer. On the other hand because of the small sample size, other detection strategies such as spectrometric methods cannot provide sufficient sensitivity and limits of detection. In this sense, mass spectrometry has become the detection method of choice for micro-scale liquid-phase chromatography. Miniaturized liquid chromatography can diminish sample dilution efficiently when extremely small amounts of samples are used. The main driving force for this miniaturization trend, especially in liquid-phase separations, is the desperate need for microscale analyses of biological and clinical samples, given these samples are precious and the sample size is usually very small. At present, microscale liquid-phase chromatography is the only method of choice for such small, precious, and highly informative samples. The miniaturization of liquid chromatography systems, especially chromatographic columns, would be advantageous to the modularization and integration of liquid chromatography instrumental systems. Chip liquid chromatography is an integration of chromatography columns, liquid control systems, and detection methods on a single microfluidic chip. Chip liquid chromatography is an excellent format for the miniaturization of liquid chromatography systems, and it has already attracted significant attention from academia and industry. However, this attempt is challenging, and great effort is required on fundamental techniques, such as the substrate material of the microfluidic chip, structure of the micro-chromatography column, fluid control method, and detection methods, in order to make the chips suitable for liquid chromatography. Currently, the major problem in chip liquid chromatography is that the properties of the chip substrate materials cannot meet the requirements for further miniaturization and integration of chip liquid chromatography. The strength of the existing chip substrate materials is generally below 60 MPa, and the material properties limit further advances in the miniaturization and integration of chromatographic chips. Therefore, new chip substrate materials and the standard of chip channel design such as channel size and channel structure should be the key for further development of chip liquid chromatography. Mainstream instrumentation companies as well as new start-up innovation companies are now undertaking efforts toward the development of microchip liquid chromatographic products. Agilent, the first instrumentation company that introduced commercial microchip liquid chromatographic columns to the market, has led this field. Apart from microchip-based columns, Agilent introduced trap columns for different kinds of biological molecules as well as gradient generation systems for microchip-based liquid phase chromatography. Recently, another start-up company introduced microchip columns based on the in situ microfabrication of the column bed rather than packing the column with a particulate material. Such developments in microfabrication may further propel the advancement of micro-scale liquid-phase chromatography to an unprecedented level, which is beyond the conventional components and materials employed in normal-scale liquid chromatography. This review introduces the recent research progress in microchip liquid chromatography technologies, and briefly discusses the current state of commercialization of microchips for liquid chromatography by major instrumentation companies.