I am having an issue with our backflush with our hydrocarbon analysis. We running hydrocarbon analysis from C1-C20. Our back flush kicks in at about 19 minutes retention time and dumps the heavier hydrocarbons (C13-C20) on to the column.These hydrocarbons seem to carry over into the next runs/injections on the GC but only at the 19 minute mark. Nothing else carries over....the run lasts for 50 mintues. So basically what im saying is there is large peak carrying over at the point of the backflush kicking and only at that point nothing else carries over. Why is this? and how can get rid of this carryover/contamination?