98 Agilent 1260 Infinity II Preparative Autosampler User Manual
6
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 (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 carry-over, 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
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