Chromatography

Introduction

Chromatography is a separations method that relies on differences in partitioning behavior between a flowing mobile phase and a stationary phase to separate the the components in a mixture.

A column (or other support for TLC, see below) holds the stationary phase and the mobile phase carries the sample through it. Sample components that partition strongly into the stationary phase spend a greater amount of time in the column and are separated from components that stay predominantly in the mobile phase and pass through the column faster.

As the components elute from the column they can be quantified by a detector and/or collected for further analysis. An analytical instrument can be combined with a separation method for on-line analysis. Examples of such "hyphenated techniques" include gas and liquid chromatography with mass spectrometry (GC-MS and LC-MS), Fourier-transform infrared spectroscopy (GC-FTIR), and diode-array UV-VIS absorption spectroscopy (HPLC-UV-VIS).

Specific chromatographic methods:

Gas chromatography (GC)

Applied to volatile organic compounds. The mobile phase is a gas and the stationary phase is usually a liquid on a solid support or sometimes a solid adsorbent.

High-performance liquid chromatography (HPLC)

A variation of liquid chromatography that utilizes high-pressure pumps to increase the efficiency of the separation.

Liquid chromatography (LC)

Used to separate analytes in solution including metal ions and organic compounds. The mobile phase is a solvent and the stationary phase is a liquid on a solid support, a solid, or an ion-exchange resin.

Size-exclusion chromatography (SEC)

Also called gel-permeation chromatography (GPC), the mobile phase is a solvent and the stationary phase is a packing of porous particles.

Thin-layer chromatography (TLC)

A simple and rapid method to monitor the extent of a reaction or to check the purity of organic compounds. The mobile phase is a solvent and the stationary phase is a solid adsorbent on a flat support.