In order to purchase the most appropriate analytical system, some details of the desired analysis must be considered. One of the most versatile systems is the gas chromatograph/mass spectrometer system (GC/MS), which can provide data necessary for both quantitative and qualitative analyses-often in the same experiment. Further, the GC/MS system is capable of being a highly general detector (useful for a wide variety of analytes) as well as highly selective (suitable to eliminate interferences). Combined with a thorough understanding of chemistry and analytical techniques, the GC/MS system is a true workhorse, and is itself the mainstay technique in a wide variety of laboratories.