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Agilent InfinityLab LC Series Vialsamplers User Manual
167
5
Optimizing Performance
Optimization for Lowest Carryover
Optimization for Lowest Carryover
Several parts of an injection system can contribute to carryover:
•
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 (main path) of the injection valve
is always in the flowline. 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 carryover in some
instances. When using small injection volumes or when injecting samples of low
concentration immediately after samples of high concentration, carryover may
become noticeable. Using the automated needle wash enables the carryover to
be minimized and also prevents contamination of the needle seat.
Using the Automated Needle Wash (Wash Port)
The automated needle wash can be programmed either as method parameter
"enable 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 before the sample is drawn. By washing the needle before drawing a
sample, the sample is removed from the surface of the needle immediately.
For best results and to obtain minimum carryover, the wash port should contain
solvent in which the sample components are soluble. The wash port flapper is
located in the needle station and a peristaltic pump delivers the wash solvent. It
has a volume of ca. 0.5 mL and the peristaltic pump delivers ca. 5 mL/min, which
means the wash port volume is completely refilled with fresh solvent in ca. 6 s. If
the wash port is selected, the user can set the length of time for washing the
outside of the needle with fresh solvent. This may be as low as two or three
seconds in routine situations where carryover is less of a problem and 10 to 20 s
for more complete washing. It is recommended that washing the outside of the
needle in the flush port should be standard procedure to avoid contaminating the
needle seat.