Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined).
In gas chromatography, the mobile phase (or “moving phase”) is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen.
The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a 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.
High-performance liquid chromatography/ High-pressure liquid chromatography (HPLC)
It is used to separate the components in a mixture, to identify each component, and to quantify each component.
It relies on pumps to pass a pressurized liquid solvent containing the sample mixture through a column filled with a solid adsorbent material.
Each component in the sample interacts slightly differently with the adsorbent material, causing different flow rates for the different components and leading to the separation of the components as they flow out the column.
Chromatography can be described as a mass transfer process involving adsorption. HPLC relies on pumps to pass a pressurized liquid and a sample mixture through a column filled with a sorbent, leading to the separation of the sample components.
Atomic Absorption Spectroscopy
Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in the gaseous state.
In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyzed.
AAS can be used to determine over 70 different elements in solution or directly in solid samples used in pharmacology, biophysics and toxicology research.
The absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved.
UV/Vis spectroscopy is routinely used in analytical chemistry for the quantitative determination of different analytes, such as highly conjugated organic compounds, and biological macromolecules.
A UV/Vis spectrophotometer may be used as a detector for HPLC. The presence of an analyte gives a response which can be assumed to be proportional to the concentration. For more accurate results, the instrument’s response to the analyte in the unknown should be compared with the response to a standard as in the case of calibration curve.