GC/MS or gas chromatography/mass spectrometry involves the coupling of a GC column to separate mixture components and a mass spectrometer to detect them by matching spectra obtained during the MS analysis with that from a computer library. In the GC portion of the analysis, the sample is injected into a GC inlet, vaporized and carried onto the column by a carrier gas where it is separated into individual compounds on the basis of boiling points and interactions with the stationary phase of the column. The separated components then flow into an ionization chamber of the mass spectrometer where they are ionized using a beam of electrons in a process known as electron impact ionization. The ion produced is the M+ ion or molecular or parent ion. In the resulting mass spectrum, this ion is used to determine the molecular weight of the compound. Another process known as chemical ionization can also be used by ionizing methane to create radicals that ionize the target analytes. A mass analyzer, most commonly a quadrupole or ion trap, then separates the particles according to their mass. They are then measured using a detector. A computer is used to compare the spectrum of the compounds in the sample to that of a library, made easier by the fact that most compounds have unique fragmentation patterns. The resulting matches are displayed to the analyst.