High oven temperature on-column injection in capillary gas chromatography. I: Sample introduction

High oven temperature on-column injection, i.e., on-column injection at column temperatures well above the boiling point of the solvent, is highly attractive for rapid analysis at elevated temperatures. Two concepts are described, involving the use of a temporarily cooled column inlet at least 10 cm long such as is achieved by the extended secondary cooling (Carlo Erba), the movable on-column injector (J & W) and the oven-independently thermostated column inlet (Varian). According to the first concept, a relatively small sample volume (ca. 0.5 μl, depending on the length of the temporarily cooled inlet) is injected, the liquid coating the wall of the cooled inlet. The second concept accepts larger sample volumes and uses the cooled inlet as a buffer zone in order to prevent violet solvent evaporation from rejecting sample liquid into the injector. Movements of the sample material within the column inlet are described, from which technical requirements are derived.