Contamination Or Carryover - Agilent Technologies 7697A Troubleshooting Manual

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Chromatographic Symptoms

Contamination or Carryover

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Carryover results when sample condenses on the flow path
or is trapped in any unswept areas of the flow path.
Normally, the HS reduces the possibility of carryover by
purging the sampling system between injections using with a
high flow rate of vial pressurization gas.
If your output has contamination or unexpected peaks:
1 Check for contamination in the lab air or on the sample
vials.
• Use new, clean vials, caps, and septa.
• Purge a vial with pure nitrogen or argon, then run a
standard.
• Consider the sample preparation process.
2 Check gas supplies. Check gas traps.
3 Check the GC.
• Check GC split vent trap (as applicable).
• Check the GC inlet flows. Verify there is enough
septum purge flow to sweep the inlet weldment.
• Check GC consumables. For example, When were the
inlet liner and septum last changed?
• If possible, mount an automatic liquid sampler (ALS)
over the inlet and inject a sequence of air blanks or
solvent blanks. (Use fresh solvent from a clean source.)
If the carryover disappears, check the headspace
sampler and original solvent source.
• If the problem is in the GC, perform GC maintenance
as needed (bakeout, inlet or detector maintenance,
column maintenance, and so forth). Refer to the GC's
documentation.
4 Check the HS.
5 Is the HS due for routine maintenance?
• Run a series of solvent blanks. Use fresh solvent from
a clean source. If the carryover in a series of solvent
blanks does not decay for each run, the carryover is
probably due to adsorbed or condensed sample in the
flow path. Replace flow path parts as needed (sample
loop, sample probe, transfer line, and so forth).
Agilent 7697A Troubleshooting