 This separation step is not mandatory and is often omitted in NMR and "shotgun" based approaches such as shotgun lipidomics.Gas chromatography (GC), especially when interfaced with mass spectrometry (GC-MS), is a widely used separation technique for metabolomic analysis.GC offers very high chromatographic resolution, and can be used in conjunction with a flame ionization detector (GC/FID) or a mass spectrometer (GC-MS).