An Introduction to Chromatographic Separations：对色谱分离的介绍.ppt

An Introduction to Chromatographic Separations An Introduction to Chromatographic Separations It was Mikhail Tswett, a Russian botanist, in 1903 who first invented and named liquid chromatography. Tswett used a glass column filled with finely divided chalk (calcium carbonate) to separate plant pigments. He observed the separation of colored zones or bands along the column, hence name chromatography, where Greak chroma means color and graphein means write. The development of chromatography was slow for reasons to be discussed later and scientists waited to early fifties for the first chromatographic instrument to appear in the market (a gas chromatograph). However, liquid chromatographic equipment with acceptable performance was only introduced about two decades after gas chromatography. General Description of Chromatography In a chromatographic separation of any type, different components of a sample are transported in a mobile phase (a gas, a liquid, or a supercritical fluid). The mobile phase (also called eluent) penetrates or passes through a solid or immiscible stationary phase. Solutes (eluates) in the sample usually have differential partitioning or interactions with the mobile and stationary phases. Since the stationary phase is the fixed one then those solutes which have stronger interactions with the stationary phase will tend to move slower (have higher retention times) than others which have lower or no interactions with the stationary phase will tend to move faster. Therefore, chromatographic separations are a consequence of differential migration of solutes. It should be remembered that maximum interactions between a solute and a stationary phase take place when both have similar characteristics, for example in terms of polarity. However, when their properties are so different, a solute will not tend to stay and interact with the stationary phase and will thus prefer to stay in the mobile phase and move faster; a polar solvent and a non polar stationa