I have setup a 1260 system with heptane as carrier. I always see a second peak come out even though it is a pure hydrocarbon. If I inject isooctane the sharp main peak shows up at 4 min and always a smaller broad peak shows up at 8 min. When I inject heptane as sample I don't see it (same as carrier eluent). Changing flow, temp, inj volume don't help. I am starting to believe that it is something in the ALS valving but need a little guidance.