Waters Prep Series Installation And Maintenance Manual page 94

Erratic or incorrect retention times
Retention time changes
Determine whether the retention times behave like this:
• Change from run to run
• Remain constant from run to run but extend beyond the allowable assay
range
Examining pressure fluctuations and changes
When troubleshooting retention time problems, examine system pressure
first. Look for these behaviors:
• Pressure fluctuations – Are they short term (with each pump cycle) or
long term (over several minutes)?
• Absolute pressure change – Is the pressure higher or lower than the
normal operating pressure?
Also, it is important to observe whether the retention time changes act like
this:
• They appear suddenly at the end of a series of runs, indicating air is
dissolving in the mobile phase, the mobile phase is degrading, or the
column is contaminated.
• They occur early in a run and tend to become constant or within range
after 3 or 4 minutes, indicating the column is not equilibrated, or that
the solvent is improperly degassed and/or sparged.
See the figure "Erratic retention time troubleshooting" on page 3-11
figure "Incorrect retention time troubleshooting" on page 3-12
what can cause a retention time problem.
3-10 Troubleshooting, Testing, and Maintenance
and the
to determine