The metabolome reflects the interaction between an organism's genome and its environment. As a result, an organism's metabolome can serve as an excellent probe of its phenotype (i.e. the product of its genotype and its environment). Metabolites can be measured (identified, quantified or classified) using a number of different technologies including NMR spectroscopy and mass spectrometry. Most mass spectrometry (MS) methods must be coupled to various forms of liquid chromatography (LC), gas chromatography (GC) or capillary electrophoresis (CE) to facilitate compound separation. Each method is typically able to identify or characterize 50-5000 different metabolites or metabolite "features" at a time, depending on the instrument or protocol being used. See Figure 2 for an illustration of the relationship between different analytical methods and their sensitivity. Currently it is not possible to analyze the entire range of metabolites by a single analytical method.