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 backflu sh system, was constructed and evaluated. An uncoated precolumn is mou nted in the first oven and the analytical column is housed in the seco nd oven. It is possible to backflush the precolumn with both gases and liquids, via low-volume three-way connectors, while the analysis is p roceeding in the coated column. The different events are controlled pn eumatically by off-line valves, situated outside the GC ovens. The per formance of the system was evaluated by repetitive injections of sampl e solutions containing crude oil, olive oil and shoe polish. It is sho wn that refocusing of high-boiling solutes from contaminated precolumn s is enhanced when a faster temperature ramp of the precolumn is utili zed. It is also shown that the useful lifetime of the precolumn is sig nificantly extended by the on-line solvent rinsing of the precolumn.