Chromatography: Detecting volatile organic compounds

CHROMATOGRAPHY is a method or analytical process for separating mixtures based on differences in the speed at which they migrate over or through a stationary phase. This process can separate complex mixtures of chemicals or proteins into their various different components.

- Paul Thottian

To initiate the process, a mixture of unknown components is dissolved in a substance known as mobile phase, which carries it through a solid second substance called the stationary phase. This mixture of unknown components travels through the stationary phase at variable speed, causing them to separate from one another. These different travel times are popularly known as the retention time.

Retention time is time that passes between the sample injection and peak maximum is known as or called the retention time, or it is the time between the sample's injection and the maximum response for the solute's peak. The retention time is one of the most basic characteristics of a peak. Its most elementary application is the qualitative identification of a known compound by means of reference information.

The speed of the mixture is based on the polarity of the components in the mobile and stationary phases. The higher the polarity of the components, the faster it moves through the mobile phase and vice versa. The stationary phase constrains many of the components in a mixture, slowing them down to move slower than the mobile phase.

Polarity has a huge effect on how attracted a chemical is to other substances. Some molecules have a positively charged side and a negatively charged side. For example, the positive side is attracted to the negative side of another molecule. The larger the charge difference, the more polar a molecule is. When increase the polarity of the solvent, all the components of the mixture move faster.

Polarity scales are used to determine how polar a solvent is. These scales rank a solvent's polarity according to the polarity index. The solvent used for chromatography will be selected based on the polarity of the substances in the mixture which we want to separate.