50 Agilent 1200 Series Autosampler Reference Manual
2 Optimizing Performance
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 mobile phase is further subjected to decreasing pressure. If the mobile
phase is not adequately degassed, 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 Series 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 44) between injections reduces
carry-over to a minimum, improving injection-volume precision further.
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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