injection device bypass injector true bypass injector valve injector A device in which the sample is first introduced into a chamber (loop), temporarily isolated from the mobile phase system by valves, which can be switched to make an instantaneous diversion of the mobile phase stream through the chamber to carry the sample to the column. [IUPAC] sampling valve L.S. Ettre, "Nomenclature for Chromatography", Pure & Appl. Chem. 1993, Vol. 65, No. 4, pp. 819-872