Chromatography Short Notes

Introduction Several techniques are available for detecting and identifying chemical compounds. Analytical chemistry employs specialised instruments such as gas-liquid chromatography, nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry to analyze sample constituents. These instruments have high sensitivity, allowing the detection of chemical substances even at very low concentrations. One example of chemical detection methods utilized at airports is gas chromatography-mass spectrometry (GC-MS), which screens for drugs or other prohibited substances in baggage or on individuals. GC-MS combines both gas chromatography and mass spectrometry techniques. GC-MS is frequently used to separate and identify individual compounds within a mixture in forensic and toxicology analyses.. Chromatography Chromatography is a commonly used laboratory method that allows for the separation and analysis of intricate mixes of chemical compounds. The technique is vital in many scientific areas, including chemistry, biology, pharmaceuticals, and environmental science. Chromatography involves separating a blend of substances into separate components based on their unique physical and chemical characteristics. By isolating each constituent, scientists can identify and analyze compounds in a sample. Some Types of Chromatography There are various chromatography techniques, each with its specific uses. The most frequent chromatography types are: Gas Chromatography (GC): Gas is the mobile phase, and liquid or solid is the stationary phase. GC analyzes volatile compounds in gas or liquid form. Liquid Chromatography (LC): A liquid is used as the mobile phase in liquid chromatography, while a liquid loaded on a solid acts as the stationary phase. Liquid chromatography is extensively used in pharmaceutical, biological, and environmental analysis. Thin-Layer Chromatography (TLC): The technique uses a thin layer of a solid or liquid adsorbed on a glass or metal surface to act as the stationary phase adsorbent. The mobile phase is a liquid. TLC is frequently used in analyzing plant pigments, lipids, and other biomolecules. Paper chromatography is a type of thin-layer chromatography where the stationary phase is a piece of special filter paper or cellulose material. Ion Chromatography (IC): Ion chromatography is a type of liquid chromatography that separates ions based on their interactions with a charged stationary phase. Water and other environmental samples can be analyzed using IC. Size-Exclusion Chromatography (SEC): The stationary phase of size-exclusion chromatography (SEC) is a porous resin or gel that separates molecules according to size and shape. Affinity Chromatography: It's a technique that separates molecules by exploiting their attraction to specific ligands or molecules. Paper Chromatography Paper chromatography is a commonly used technique in analytical chemistry for separating and identifying different elements of a mixture, including inks, dyes, amino acids, sugars, and other small molecules. It is a kind of thin-layer chromatography where the stationary phase is a liquid supported on a solid. The solid support could be a piece of special filter paper or cellulose material. Capillary action is the principle of paper chromatography, in which a mobile phase (a liquid or solvent) moves up the paper, transporting the mixture at diverse rates on the solid phase. Sample elements are separated based on their distinctive chemical properties. Separated elements are distinguished based on their colors or by staining chemicals or UV light if colorless. Paper Chromatography: Principle Paper chromatography is based on the attraction of solute to captured water molecules (the stationary phase). Small spots of solute (e.g. hydrolysed protein or peptide) are applied to paper that supports the stationary phase. When submerged in a mobile phase, the solute molecules are carried along the paper by the mobile phase. Sample mixture components move at varied rates based on their attraction for the stationary phase. After measuring the distance travelled by each component, we compare it with the distance covered by the solvent. This ratio of the distance traveled by the component to that of the solvent is known as the Rf value, or retention factor, used to identify components present in the sample. The Rf or retention factor is then compared to pure reference compounds to identify sample components. The Rf values are compared to Rf reference values obtained from reference tables at identical conditions (same temperature and solvent). The investigated substances can be coloured and easily spotted on the paper, but other colourless substances must be stained to be observed.