Liquid chromatography/tandem mass spectrometry (LC/MS/MS) has become an important tool to complement traditional methodologies used in the clinical chemistry laboratory. In early 1970s, majority of the mass spectrometric analyses of clinical samples utilized the application of gas chromatography/mass spectrometry (GC/MS) which is particularly suitable for analytes that are small molecules and volatile. However, many biomolecules have high molecular mass, are thermolabile and/ or extremely polar. Sample extraction and derivatization required for GC/MS analysis of clinical samples is usually extensive, complicated as well as laborious. Not only such sample preparation is difficult, quite often it is not possible to perform on certain analytes of interest. On the other hand, LC/MS can be easily performed on biological samples (primarily body fluids such as blood, urine, cerebrospinal fluid) which are often extremely hydrophilic and include compounds with a wide range of molecular masses such as amino acids, fatty acids, bile acids that are less than 500 Da as well as peptides, proteins, glycoproteins and oligonucleotides with high molecular masses.