Chromatography is a method of analysing different compounds in a sample through separation.
There are many different types of chromatography: Paper Chromatography (PC), Thin Layer Chromatography (TLC), Column Chromatography, High Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC, sometimes referred to as GLC).
Paper Chromatography (PC)
Paper chromatography is considered to be the least accurate method of chromatography. It is through the use of running a sample up a piece of paper via a solvent (usually water) to separate the components in order for them to be determined. It is qualitative, however, good separation and resolution is required to obtain a reliable result.
Components in the sample are determined by its Rf value (retardation factor) by determining the distance travelled by the component divided by the distance travelled by the mobile phase. A standard will have to be used.Thin Layer Chromatography (TLC)
It is similar to paper chromatography, however, instead of using paper to separate the components, a glass coated with a thin layer of tightly packed alumina is used. This enables the use of determining corrosive substances which would not have been possible with PC. Like PC, TLC is also qualitative. Components in the sample are determined by its Rf value (retardation factor) by determining the distance travelled by the component divided by the distance travelled by the mobile phase. A standard will have to be used.
Column Chromatography
This method is relatively slow in comparison to other techniques. It is a qualitative technique, consisting of a column packed with alumina (as a stationary phase) and pouring the solvent (as a mobile phase) down the column. Bands of colours will appear on the column, thus enabling the determination of components in the sample (solvent). Eluent (waste coming out of the bottom of the column) will flow out of the column at the same rate that the solvent was added. It is also depended upon its Rf value.
High Performance Liquid Chromatography (HPLC)
It is both
qualitative and quantitative. HPLC is a advanced version of Column Chromatography. It uses the Rt (retention time) to identify components and is a lot quicker. This technique is rather sensitive, however, it is not as sensitive as GC. HPLC consists of a column packed very small particles. In this technique, both adsorption onto the stationary phase and desorption into the mobile phase is used in the separation of components in the sample. A detector and recorder will record the results and produce a chromatogram. These results may be used in the determination of the substance, as well as used to produce a calibration curve to determine the quantity of each component in the sample tested. The downside to this technique is that it’s very expensive, the equipment can be quite costly.Gas Chromatography (GC/GLC)
It is both qualitative and quantitative. GC is extremely sensitive, it can be accurate up to ppm (parts per million). It consists of a gaseous mobile phase containing an inert gas that is pumped through the column at a constant pressure. The gas acts as a mobile phase, whilst the column is used as a stationary phase. The column is packed with a porous solid that is usually coated with a hydrocarbon or ester. There is an injection port where the sample is quickly injected into the column so that the analysis may begin. The detector and recorder will record the results, the results are used to produce a calibration curve in order to determine the quantity of each component. This technique is very fast, however it is also very expensive as the equipment is very costly.
