Chromatographic Troubleshooting
Baseline symptoms
203
It can also result from valve operations: If valves are being
switched during a run, examine the valve time program to see if
the change coincides with a valve operation.
This symptom also can occur if the septum suddenly begins to
leak; Avoid the problem by changing septa regularly.
Offset•see troubleshooting procedure for the particular detector
in use.
Wander and drift
Baseline wander or drift may occur when a flow or temperature setting is
changed. If the system is not stabilized at the new conditions before
starting a run, some baseline changes are to be expected. Cases following
assume that sufficient stabilization time has elapsed since the last
change in operating conditions.
Wander and drift are often accompanied by noise, discussed below.
1. Baseline moves steadily upscale or downscale (drift) during the run:
This is most frequently seen during temperature programming:
Operation with a single column (no column compensation) at
moderate to low attenuation causes this. If dual columns are used,
check that the signal mode is correct for column compensation.
It is also possible the compensation is insufficient (upscale
movement) or too great (downscale movement).
This cause of drift is minimized by thorough column conditioning.
Operating at lower oven temperature also helps but prolongs the
analysis. Use of a chromatographically equivalent column with
higher temperature limit is also possible.
