Erratic Or Incorrect Retention Times; Retention Time Troubleshooting - Waters 2410 Operator's Manual

7.2.2 Erratic or Incorrect Retention Times

When you troubleshoot retention time problems, check if retention times:
• Change from run to run or are constant from run to run, but are outside the allowable range
for the assay
• Are due to pressure fluctuations that are short-term (with each pump cycle) or long-term
(over the course of several minutes)
• Are associated with an absolute pressure change, that is, if the pressure is constant but higher
or lower than the normal operating pressure
• Change suddenly at the end of a series of runs, which may indicate that air is dissolving in
the mobile phase, that the mobile phase is degrading, or that the column is contaminated.
• Change early in a series of runs and tend to become constant or within range after 3 to 4
minutes, which may indicate that the column was not equilibrated, or that the solvent is not
properly degassed and sparged.
To troubleshoot problems with retention times, refer to Table 7-2.
Table 7-2 Retention Time Troubleshooting
Symptom
Erratic retention times
Possible Cause
Air bubble in pump head
Malfunctioning pump check
valves
Leaking pump seals
Separation chemistry
Clogged solvent filters
Corrective Action
Degas all solvents, prime pump
(see Section 4.3.2, Solvent
Degassing Methods).
Clean/replace/rebuild pump
check valves.
Replace pump seals.
Check mobile phase and column.
Replace filters.
Chromatography Troubleshooting
7
7-7