The retention time is the amount of time it takes for the analyte to elute and is unique in each sample. The linear velocity that is enhanced by the high pressure that is used gives the components minimal time to diffuse inside the column. This is necessary because it allows for a higher resolution of the chromatogram that is used to deduce results. In a typical HPLC, various miscible organic liquids are used and the modern units have the capacity to generate a maximum pressure of 6000psi. HPLC units are available commercially and the buyer selects a type that is most suitable for their need. Different types come with different detectors, for example, UV absorption detector, refractive index detector, conductivity detector, evaporative light scattering detector, fluorescence detector, and electrochemical detector.

Generally, there are two types of HPLC units, one being the preparative HPLC and the other an analytical HPLC. In the preparative type, compounds are usually isolated and purified whereas the analytical mainly gets detailed information about a sample that is passed through it. This means that the sample can be identified, quantified and its resolution obtained. The main uses of HPLC, however, are identification and purification of samples. HPLC is highly preferred by many professionals because it is accurate, sensitive, simple to use and can analyze nonvolatile samples that are sensitive to temperature changes. Furthermore, HPLC can easily be used in combination with mass spectrophotometry as a means of validating the data collected. Most chemists use the technique in the analysis of amino acids, hydrocarbon, proteins, pesticides, pharmaceuticals, among other products.

A combination of 0.7mg/ml phenol, 4.0mg/ml toluene and 5.0mg/ml ethylbenzene is dissolved in 10ml isopropanol. The amount of each of the above components is then calculated accordingly to allow for later calculations.