High-performance liquid chromatography (HPLC) is a method used to separate compounds. It's composed of a column with a stationary phase or the adsorbent and a mobile phase or eluent (usually a pure solvent). A pump is used to pump the eluent or the chemical you want to purify, separate or quantify through the stationary phase. The time it takes for the compound to travel down the column depends on the size of the compound, the solvent used, and how the compound(s) interacts with the adsorbent. There are different types of HPLC such as reverse phase chromatography, partition chromatography, ion exchange chromatography, size exclusion chromatography, etc.  Size exclusion chromatography separates compounds based on their size. The bigger compounds take longer to flow down the column through the stationary phase while the smaller compounds take less time.