![]() It can also be used as a purification tool, separating the components of a mixture for use in other experiments or procedures. Ion exchange chromatography separates the components of a mixture based on their charge, in addition to or instead of their size. In essence, positively (cations) or negatively (anions) charged ions are separated using different stationary phases and different pH mobile phases.Ĭhromatography can be used as an analytical tool, feeding its output into a detector that reads the contents of the mixture. ![]() Thin-layer chromatography comes with the advantage of photographing well, making its output easy to digitize. In thin-layer chromatography (TLC), the stationary phase is a thin layer of solid material, usually silica-based, and the mobile phase is a liquid in which the mixture of interest is dissolved.Several varieties of liquid chromatography exist, depending on the relative polarities of the mobile and stationary phases ( normal-phase versus reverse-phase) and whether the mobile phase is pressurized ( high-performance). In liquid chromatography, the mixture of interest is dissolved in a liquid and passed through a solid stationary phase, which is often made of a silica material.Larger molecules in the mixture take longer to pass through the column and reach the detector at the far end. In gas chromatography, the mixture of interest is vaporized and carried through a stationary phase (usually a metal or glass separation column) with an inert gas, usually nitrogen or helium.Some of the most common forms of chromatography are as follows. By dissolving a mixture of interest in a mobile phase and transporting it through a stationary phase, the components of the mixture can be separated from one another based on their different speeds of travel.īy altering the mobile phase, the stationary phase, and/or the factor determining speed of travel, a wide variety of chromatographic methods have been created, each serving a different purpose and ideal for different mixtures. In modern laboratories, the color aspect is no longer relevant, but the same principles apply. With time, it also spawned a unique branch of chemistry, and with it, the techniques used today to understand and purify mixtures. This gives the technique the name “chromatography” or “writing color.” From Art to ScienceĬhromatography was initially used by artists, color theorists and artisans hoping to perfect industrial dyes for textiles. The largest molecules of the mixture will travel more slowly while the smallest ones race ahead, causing the stationary phase to develop discrete bands of color corresponding to each component of the mixture. If a sheet of paper or cloth contacts a container filled with water or alcohol in which a complex pigment is dissolved, capillary action will carry the mixture up the paper or cloth, but the components of the pigment will not all travel at the same rate. “Writing Color”Ĭhromatography gets its name from a technique first used in the late 19 th century to separate pigments in a complex mixture. These different travel times are termed retention time. The nature of the specific mobile and stationary phases determines which substances travel more quickly or slowly, and is how they are separated. The different components of the mixture travel through the stationary phase at different speeds, causing them to separate from one another. To get the process started, the mixture is dissolved in a substance called the mobile phase, which carries it through a second substance called the stationary phase. Chromatography is a process for separating components of a mixture. ![]()
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