The main components of any chromatography system are the stationary phase, the mobile phase, and the analyte. The surface on which the compounds are separated is the stationary phase. The analytes are the solutes, and the solvent carrying the solute forward is the mobile phase. Chromatography is used to separate solutes in a mixture based on the time they spend in the stationary or mobile phases. Partition and adsorption chromatography are the two main types of chromatography. In liquid–liquid partition chromatography, separation occurs based on differences in solubility. In gas–liquid partition chromatography, or gas chromatography, separation depends on the solubility of the solutes in the viscous stationary phase and the system vapor pressure. In adsorption chromatography, the stationary phase is solid, and the separation occurs by the differences in the affinity of the solute molecules for the stationary phase. Adsorption chromatography methods include thin-layer and column chromatography.