How And When Is Ion Chromatography Used In The Laboratory

Ion Chromatography is a system that separates ions (an electrically charged +/- particle) and polar molecules based on their charge

. A polar molecule is the divergence of charges at either pole that thus attracts its opposite. It is quite similar to a magnet that has different charges on either end. The use of aqueous sampling is called Ion Aqueous (or liquid) Chromatography and it is the most used technique in laboratories.

This process is generally used for separating proteins, nucleotides and amino acids. The separation process utilizes a buffered aqueous solution (usually carried by an autosampler) to a gel or resin matrix of agarose or cellulose beads used as a stationary phase. The beads are formed by covalently bonded functional groups (a cluster of atoms that replace hydrogen in an organic compound) that create a canvas with opposite charged ends. This allows the charges of the analytes (anions or cation) to separate according to the applied liquid sample.

For example, if the analytes are present on either the agarose or cellulose beads, the addition of anions will elute (wash out) the cations. This process is referred to as cation ion exchange chromatography and anion exchange chromatography and measure coulombic interactions. By collecting the eluted analytes, you can then measure the conductivity or UV/Visible light absorbency.

General applications of ion liquid chromatography are drinking water analysis for pollution and other constituents, determination of water chemistries in aquatic ecosystems, isolation of select proteins and the determination of sugar and salt content in foods. Other forms of chromatography include gas-liquid chromatography, column chromatography, high performance liquid chromatography and thin layer chromatography.

Gas-liquid chromatography is used in the lab when an element can be vaporized without the consequence of decomposition. This setup is used to test the purity of a substance or separating a mixture. The instruments needed for this are autosamplers (sometimes robotic), inlets (introduces the sample), columns (packed and capillary) and detectors (used to detect components other than gas).

Column chromatography is very similar to gas-liquid chromatography except the mobile phase is liquid, the stationary phase is solid and there is no temperature control. High performance liquid chromatography is also a form of column chromatography and uses high pressure to separate, identify, and quantify compounds. The stationary phase is usually hydrophobic carbon chains. A pump provides an increased pressure that pushes the mobile phase and analyte through the column resulting in better separation.

Thin layer chromatography is a process designed to separate mixtures. Unlike the other forms of chromatography, this process requires minimal instruments - just a sheet of glass, plastic, or aluminum foil, coated in adsorbent material (usually silica gel, aluminum oxide, or cellulose) that acts as the stationary phase. After the sample is applied a siphon or capillary action is administered that draws up the solvent (or a solvent mixture).

The application of this system is used to determine the constituents of a plant, analyze organic reactions/ceramides/fatty acids, identify the presence of pesticides or insecticides in food and water, determine dye composition of fibers, or identify unknown compounds present in a substance and appraising the level of chemical purity in radiopharmaceuticals.

Chromatography is a very useful tool for analysis and though there are many types, they all fundamentally act as separating techniques for organic compounds.

by:Andrew Long

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