Bio analytical techniques, as the name suggests, are the analytical tools to study the biological molecules; non-biological molecules involved with life, such as drugs; and biological processes. These tools are routinely used to identify, estimate, purify, and characterize the biomolecules. Quantification of molecules in biological samples is at the heart of bio analysis and is routinely used to diagnose various diseases and metabolic disorders. For example, estimation of thyroxin and triodothyronine concentrations in blood provides information about the activity of thyroid gland. Home pregnancy test kits look for the human chorionic gonadotropin (HCG) hormone in the urine, presence of which above a threshold concentration is an indicator of pregnancy. Bio analytical methods are also used to detect drugs and their metabolites in biological samples. Initially, nonspecific assays were used to quantify the drugs in biological samples. Evolution of the existing assays, advancement in instrumentation, and introduction of newer techniques have made it possible to distinguish the drug molecules and their closely related metabolites in complex biological specimens.