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Optimizing Performance
Optimization for Lowest Carry-over
Optimization for Lowest Carry-over
Several parts of an injection system can contribute to carry-over:
• needle outside
• needle inside
• needle seat
• sample loop
• seat capillary
• injection valve
The autosampler continuous flow-through design ensures that sample loop,
needle inside, seat capillary, and the mainpass of the injection valve is always
in the flow line. These parts are continuously flushed during an isocratic and
also during a gradient analysis. The residual amount of sample remaining on
the outside of the needle after injection may contribute to carry-over in some
instances. When using small injection volumes or when injecting samples of
low concentration immediately after samples of high concentration,
carry-over may become noticeable. Using the automated needle wash
enables the carry-over to be minimized and prevents also contamination of
the needle seat.
Using the Automated Needle Wash
The automated needle wash can be programmed either as “injection with
needle wash” or the needle wash can be included into the injector program.
When the automated needle wash is used, the needle is moved into a wash
vial after the sample is drawn. By washing the needle after drawing a sample,
the sample is removed from the surface of the needle immediately.
Uncapped Wash Vial
For best results, the wash vial should contain solvent in which the sample
components are soluble, and the vial should not be capped. If the wash vial is
capped, small amounts of sample remain on the surface of the septum, which
may be carried on the needle to the next sample.
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