Ghost Peaks...

[mhof]

I run a Hewlitt-Packard 6890 GC with a 5793 MS. I see signigicant peaks in my solvent runs (we use ACS grade hexane as a solvent). I have cleaned the inlet, and the ion source, replaced the inlet liner, and base seal, and do not see these peaks when I run the method without making an injection. The air and water check for the system comes up clean (18/69 = 0.31, 28/69 = 1.12, 32/69 = 0.22, 44/69 = 0.19).

If I concentrate the hexane under a stream of nitrogen, and then inject it, the peak areas increase significantly, but I purchased a new lot of hexane, and the problem didn't go away.

I'm at a loss. Where could the contaminants be coming from?

[ods-at-pacific]

I assume you are talking about chromatograohic peaks. What is their retention time? What is the GC temperature program? What is the elution temperature? What do the mass spectra for these chromatographic peaks look like?