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Gas Liquid Chromatography
A gas chromatograph is a chemical analysis instrument for separating chemicals in a complex sample. It is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition.
A gas chromatograph uses a sample flow-through narrow tube known as the column, through which different chemical constituents of a sample pass in a gas stream (carrier gas, mobile phase) at different rates depending on their various chemical and physical properties and their interaction with a specific column filling, called the stationary phase.
Gas chromatography is typically used in testing the purity of a particular substance, or in separating the different components of a mixture. It can also be used to prepare pure compounds from a mixture.
Gas chromatography, utilizes the principle of partitioning between molecules in the mobile phase or “moving phase” and the stationary phase. The mobile phase, is usually an inert carrier gas, such as helium or unreactive gas eg nitrogen.The stationary phase is a microscopic layer of liquid on an coated or suspended on inert solid support placed inside a long piece of glass or metal tubing called a column
The gaseous compounds being analyzed interact with the walls of the column, which is coated with a stationary phase. This causes each compound to elute at a different time, known as the retention time of the compound. The comparison of retention times is what gives GC its analytical usefulness.
Components of Gas chromatograph
Gas chromatography consist with a carrier gas supply, an injection port, a column, an oven and a detector. The detector output will be received by an integrator which is an instrument that will integrate the output signal. And the integrated signal is then recorded from a recorder as shown in the diagram below
Preventive maintenance of gas liquid chromatograph includes replacing consumable items and performing maintenance procedures on a regular basis. Important periodic maintenance includes the following items.
Autosampler syringe: Inspect when adding vials. Clean every 200 injections. Replace when contaminated or leaking.
Septa: Replace every 50-100 injections.
Inlet liners: Replace with every other septum, or when dirty (100-200 injections).
Columns: Evaluate performance every month. Replace when it falls below performance requirements, or every 6 months of use.
Ferrules: Replace whenever making a connection, new, or old.
Detector: Evaluate performance at least every month. Bake out or clean only when contaminated or noisy. Replace consumables as required. Perform electron-capture detector wipe test as required.
Gas filters (including split vent filter): Replace or regenerate every two to four tanks, or as indicating trap requires.
Electronic pressure control (EPC) pressure zero: Check every month.
NB: Repair and maintenance work should only be left to expert persons.
Electrophoresis
Electrophoresis is a laboratory technique used to used to separate macromolecules in a fluid or gel based on their electric charge, binding affinity, and size under an electric field.. An electric current is used to move molecules to be separated through a gel. The pores in the gel work like a sieve, allowing smaller molecules to move faster than larger molecules. The conditions used during electrophoresis can be adjusted to separate molecules in a desired size range.
Anaphoresis is the electrophoresis of negative charge particles or anions whereas cataphoresis is electrophoresis of positive charge ions or cations. Electrophoresis has a wide application in separating and analysing biomolecules such as proteins, plasmids, RNA, DNA, nucleic acids.
Charged macromolecules are placed in the electric field move towards the negative or positive pole based on their charge. Nucleic acid has a negative charge and therefore it migrates towards the anode.
This technique is divided into two types viz slab electrophoresis and capillary electrophoresis.