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8 Sources of error
It is unnecessary to go through all the
troubleshooting, but it is important to
distinguish some of the most common
sources of error. Most of the trouble is
caused by contamination. Impurities in
the column or in the liner are visible in
noise and/or drifting baseline. Even
ghost peaks may appear when running
a sample or a standard. Ghost peaks
mean peaks appearing at positions
where peaks are not expected. Briefly,
be aware of avoiding contamination.
When running samples or standards,
every other run should be plain water,
because it
avoids samples
to
contaminate each other. To maintain Picture 12. In the back, there is a liner, septums and o-rings from
the column clean, the helium flow must left to right. In front of them are tools for replacing them in the
inlet and for maintaining the column.
to be on all the time. It also helps to
“bake out” the impurities from the
column increasing the oven temperature to 200-230 °C for ten minutes every day. The
column won’t last very long if it’s baked continuously in its maximum temperature, but short
baking at times purifies it. Every time when there are no samples to run, the time can be
spent to purify the column by baking the oven and/or running water.
Organic acids consume the stationary phase so the retention times change slightly within
time, but that can be corrected with calibration. If the ghost peaks keep continuously
appearing, it may be necessary to cut a little piece from the beginning of the column (a cutter
and explanation in the Picture 13), because most of the contamination piles up there.
Regular
maintenance
will
help
avoiding
chromatographic issues. Other supplies that have to be
replaced from time to time are the liner, septum and oring (Picture 12) especially if problems occur. It is
Picture 13. Used for cutting a piece from
the column tubing. Use the side with
black stripes to scratch it a couple of
times and bend the column tubing off.
recommended to replace the o-ring and septum after a
hundred injections. A new liner is needed when the old
one is dirty (glass wool turns black) and it depends on
how much impurities there are in samples. Remember
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