The retention time (tR) is a reflection of the substance's
affinity for the stationary phase. The longer the retention time, the higher the substance's affinity for the stationary phase.
The purity of a sample can be assessed using gas chromatography. The number of peaks present can indicate how many components are in the mixture. Chromatography should be used in conjunction with other techniques before a statement about purity is made. (A single peak could be several components that have not been separated. What other techniques could be used to confirm purity?)
The sizes of the peaks also give useful information. The ratio of the sizes of the peaks gives the ratio of the relative amounts of substances in the sample. The sizes of the peaks may be found by calculating the areas under the peaks or by carefully cutting out the peaks and weighing them on an accurate balance.