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Contamination is usually identified by excessive background in the mass spectra. It can
come from the GC or from the MSD. The source of the contamination can sometimes be
determined by identifying the contaminants. Some contaminants are much more likely to
originate in the GC, others are likely to originate in the MSD.
Contamination Sources in the GC
• Column or septum bleed
• Dirty injection port
• Injection port liner
• Contaminated syringe
• Poor quality carrier gas
• Dirty carrier gas tubing
• Fingerprints
• Air leaks
• Cleaning solvents and materials
MSD Contamination
Column bleed generally appears as
a continuous and increased rise in
the baseline at higher column
temperatures, especially at or near
the upper temperature limit of the
GC column. Septum bleed usually
appears as discrete peaks, and can
occur at any temperature.
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