WATERS CORPORATION 2424, Руководство оператора

Страница: 153 / 196

Chromatography troubleshooting 5-27
Erratic or incorrect retention times
When you troubleshoot retention time problems, determine whether the
retention times:
• Change from run to run or are constant from run to run but outside the
allowable range for the assay
• Vary 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 fall
within range after a few minutes, which can indicate that the column
was not equilibrated or that the solvent is not properly degassed and
sparged
Spiking (continued) Mobile phase
contaminated or
made of low quality
material.
Check make up of mobile
phase.
Gas flow set too low. Increase gas flow.
Troubleshooting general chromatography problems
Symptom Possible cause Corrective action
Erratic retention
times
Air bubble in pump
head
Degas all solvents, prime
pump (see page 6-7 ).
Malfunctioning
pump check valves
Clean, replace, or rebuild
pump check valves.
Leaking pump seals Replace pump seals.
Separation
chemistry
Check mobile phase and
column.
Abnormal baseline troubleshooting (Continued)
Symptom Possible cause Corrective action