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Liquid Chromatography 1

● Adsorption chromatography • The stationary phase is an adsorbent (like silica gel or any other silica-based packing) • The separation is based on repeated adsorption-desorption steps. ● Normal-phase chromatography • The stationary bed is strongly polar in nature (e.g., silica gel), and the mobile phase is nonpolar (such as n-hexane or tetrahydrofuran). • Polar samples are retained on the polar surface of the column packing longer than less polar materials. | 4 30 2012 VILLANOVA UNIVERSITY Liquid Chromatography 1 and SolidPhase Extraction Lecture Date April 9th 2008 Reading Material Skoog Holler and Crouch Ch. 28 Cazes Ch. 22 26 For those using LC in their work see L. R. Snyder J. J. Kirkland and J. L. Glajch Practical HPLC Method Development 2nd Ed. Wiley 1997. 1 4 30 2012 Basic LC Terminology Adsorption chromatography The stationary phase is an adsorbent like silica gel or any other silica-based packing The separation is based on repeated adsorption-desorption steps. Normal-phase chromatography The stationary bed is strongly polar in nature e.g. silica gel and the mobile phase is nonpolar such as n-hexane or tetrahydrofuran . Polar samples are retained on the polar surface of the column packing longer than less polar materials. Reversed-phase chromatography The stationary bed is nonpolar hydrophobic in nature The mobile phase is a polar liquid such as mixtures of water and methanol or acetonitrile. The more nonpolar the material is the longer it will be retained. Basic LC Terminology Size exclusion chromatography SEC column filled with material having precisely controlled pore sizes and the sample is simply sieved or filtered according to its solvated molecular size. Larger molecules are rapidly washed through the column smaller molecules penetrate inside the pores of the packing particles and elute later. Also called gel permeation chromatography GCP although the stationary phase is not restricted to a gel Ion-exchange chromatography IC the stationary bed has a charged surface of opposite charge to the sample ions. Used almost exclusively with ionic or ionizable samples. The stronger the charge on the sample the stronger it will be attracted to the ionic surface and thus the longer it will take to elute The mobile phase is an aqueous buffer where both pH and ionic strength are used to control elution time 2 4 30 2012 Analytical Applications of LC The branches of the LC family Basic Mechanisms used in LC Separations