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The Injector

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  132

2026-07-05

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The Injector

The injector is a heated chamber where the analyte mixture is introduced and combined with the mobile phase. The mobile phase continually passes through the injector under pressure. In a typical GC experiment, the analyte mixture is dissolved in a volatile solvent. For the cocaine/caffeine/sugar analyte, methyl alcohol is a good choice for the solvent. Cocaine, caffeine, and sugar are all solids at room temperature. Sugar is mostly insoluble in methanol so it must be filtered out before the experiment is run. This leaves only the cocaine and caffeine to be separated. The injector is generally heated to about 250 °C. At this temperature at least some of the cocaine and caffeine will vaporize as will all of the alcohol. The solution is introduced into the injector using a syringe, through an airtight septum. The vaporized mixture is mixed immediately with the flowing mobile phase and carried into the capillary column. Injectors can be configured as split or splitless. Capillary columns are very narrow and easily overloaded with analyte so the mobile phase will be split so that some of it is vented away and only part of it goes through the column. If the analytes are very dilute or there is very little, then the entire amount is sent through the column in a splitless configuration.