Waters 2707 Operator's Manual page 22

chromatography (HPLC) mobile phase. Sample enters the column, and
analysis starts.
Syringe
After each injection, a wash routine of programmable volume occurs.
Air segment with full loop injections
A 5-µL air segment that is at the front of the flush volume but not injected can
minimize sample dilution caused by dispersion during aspiration.
With a standard needle, recommended flush volumes are 30 µL for injections
that incorporate air segments and 35 µL for injections that do not. To enhance
performance with highly viscous samples, larger flush volumes and reduced
syringe speeds may be needed.
Needle injection loop
With
air
Without
air
1-12 Understanding Operating Principles
Buffer tubing
INJECT
Needle
Sample
Buffer tubing
Sample
Sample
Sample loop
Eluent Flush Air
Eluent Flush
Pump
Column