HP 5890 Series II Plus Reference Manual page 210

Chromatographic Troubleshooting
Peak symptoms
2. Additional peaks appear when pure sample is injected:
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stationary phase with trace levels of O , H O, and/or other
materials present in the carrier gas.
A contaminated inlet may also produce ghost peaks. Residues in
the inlet are volatilized or pyrolyzed and swept onto the head of
the column. Try reducing inlet temperature; if this eliminates or
reduces ghosts, the inlet should be cleaned.
These might be ghost peaks as described above. Make a blank run;
if the peaks persist, they are not sample related.
A common cause of extra peaks, assuming the sample is pure, is
degradation of one or more components by an overheated inlet.
Test this by reducing inlet temperature.
Operate the inlet at as low a temperature as possible without
causing peak broadening due to slow vaporization. Also, perhaps a
more volatile solvent can be used. In extreme cases, derivatize the
sample before analysis.
Metal columns may also degrade the sample. Extra peaks in this
case are usually broader than their immediate neighbors since
they are generated along the entire length of the column. If this is
the cause, changing to an all•glasssystem may be necessary.