High Performance Liquid Chromatography (HPLC) is a technique used to separate compounds dissolved in solution using high pressure to push a mobile phase through a column containing a stationary phase. HPLC instruments consist of pumps to deliver the mobile phase, an injector to introduce the sample, a separation column, and detectors. Compounds are separated based on differences in how they partition between the mobile and stationary phases. HPLC provides high resolution separation of complex mixtures and is characterized by its reproducibility, high pressure operation, and ability to use small particle sizes in the column.