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5 Optimizing Performance
Precise Injection Volume
Precise Injection Volume
Injection Volumes Less Than 2 µl
When the injection valve switches to the BYPASS position, the mobile phase in
the sample loop is depressurized. When the syringe begins drawing sample,
the pressureof the mobile phase is decreased further. If the mobile phase is
not degassed adequately, small gas bubbles may form in the sample loop
during the injection sequence. When using injection volumes < 2 µl, these gas
bubbles may affect the injection-volume precision. For best injection-volume
precision with injection volumes < 2 µl, use of the Agilent 1200 Infinity
degasser is recommended to ensure the mobile phase is adequately degassed.
Also, using the automated needle wash (see “Optimization for Lowest
Carry-over” on page 62) between injections reduces carry-over to a minimum,
further improving the injection volume precision.
Draw and Eject Speed
Draw Speed
The speed at which the metering unit draws sample out of the vial may have an
influence on the injection volume precision when using viscous samples. If the
draw speed is too high, air bubbles may form in the sample plug, affecting
precision. The default draw speed is 200 µl/min for the autosampler and
1000 µl/min for the preparative autosampler. This speed is suitable for the
majority of applications, however, when using viscous samples, set the draw
speed to lower speed for optimum results. A “DRAW” statement in an injector
program also uses the draw speed setting which is configured for the
autosampler.
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