Comments
To
flush the needle port: Use from 0.1 to 1 mL of mobile phase. Use a Needle
Port Cleaner (Rheodyne Part Number 7125-054) attached to a luer tip
syringe. Flush only when the handle is in INJECT, so flow goes directly
out vent tube #5 and bypasses the loop. This cleans the entire length
of the needle port guide, tube, and needle seal. The cleaner does
this because it seals against the front of the guide. A fully inserted
needle flushes none of these parts.
If you have
no cleaner, use a luer tip syringe. See the illustration in Symptom
#5. In routine operation, remove the syringe after turning to INJECT,
but keep the handle in this position so the loop is continuously flushed
with mobile phase. Flushing after every injection is rarely needed, but,
if necessary, do it just before the next analysis. It is usually sufficient
to flush after every ten or twenty injections. This keeps liquid in the
needle port tube, which baths the syringe needle and dilutes contaminating
sample. See Appendix E for more information on
when to flush the injector.
There are
non-injector sources of sample carryover. These include residual sample
in the syringe, contamination in the blank solvent, and contamination
in the solvent used for flushing.
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Symptom
#4
A
miniature chromatogram of the previous sample is produced by injecting
a blank. Flush the needle port (see comments). Load and inject a blank,
using the loading method you have been using partial-filling
or complete-filling (see Fig. 15):
- If the
peaks are now absent, see Cause A.
- If the
peaks are still present, see Cause B.
Fig.
15. Droplets of sample remaining in the needle port tube and needle
seal. These are absent in normal operation.
Cause
A
The needle port was contaminated with previous sample. It was pushed
into the loop when the syringe was inserted during loading. The flushing
step has cleaned the port (see Fig. 16).
Solution
If the contamination reappears, make sure you are inserting the syringe
properly. You may need to flush the needle port routinely. See Appendix
E.
Fig. 16. When
the syringe is inserted under the conditions shown in Fig. 15, droplets
of previous sample are pushed into the loop.
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