An adapter for releasably securing a probe to a reaction vessel. Embodiments of the adapter include a cover plate for mating with a reaction vessel, a body portion extending from the cover plate, and a probe gripping portion secured to the body portion. A collet and at least one anvil resides within the body portion/probe gripping portion assembly. The collet has at least one split conical end that may be divided into a plurality of flexible gripping fingers, the conical end of the collet adapted to mate with the at least one anvil. An o-ring is preferably located in the body portion and surrounds a probe when the probe is passed through the adapter. Pressure from the reaction vessel exerts an axial force on the o-ring which, in turn, exerts a like force on the anvil, thereby causing the gripping fingers of the collet to exert a gripping force on the probe.