LC-MS is a technique that combines liquid chromatography with mass spectrometry. It separates components in a mixture using HPLC and then uses an ion source like ESI or APCI to ionize the molecules and a mass analyzer like a quadrupole or time-of-flight to separate the ions by mass-to-charge ratio. The separated ions are then detected to identify and quantify each component. Validation of LC-MS systems includes tests of vacuum, mass accuracy, linearity, precision, carryover, and signal-to-noise ratio to ensure proper separation, ionization, detection, and quantification capabilities.