ONLINE LIQUID BACKFLUSH OF AN UNCOATED PRECOLUMN FOR AUTOMATED GAS-CHROMATOGRAPHIC ANALYSIS OF COMPLEX-MIXTURES

A fully automated system for the GC analysis of samples containing non-volatile material, consisting of a double-oven on-line liquid backflush system, was constructed and evaluated. An uncoated precolumn is mounted in the first oven and the analytical column is housed in the second oven. It is possible to backflush the precolumn with both gases and liquids, via low-volume three-way connectors, while the analysis is proceeding in the coated column. The different events are controlled pneumatically by off-line valves, situated outside the GC ovens. The performance of the system was evaluated by repetitive injections of sample solutions containing crude oil, olive oil and shoe polish. It is shown that refocusing of high-boiling solutes from contaminated precolumns is enhanced when a faster temperature ramp of the precolumn is utilized. It is also shown that the useful lifetime of the precolumn is significantly extended by the on-line solvent rinsing of the precolumn.