Troubleshooting and Maintenance
Troubleshooting and Maintenance
This domain tests systematic diagnosis. The exam rewards a logical order - is the problem pressure, retention, peak shape, or signal? - and knowledge of which component owns each symptom.
Symptom to likely cause
- High or rising pressure: a blockage in the flow path. Change one item at a time, starting at the detector end. A steady climb during a run suggests precipitation (buffer meeting high organic) or a clogging frit; a sudden spike suggests the column inlet or a check valve.
- Low or unstable pressure: air in the pump, a failing check valve, a leak, or a seal-wash problem. Purge first.
- Retention drift: mobile phase evaporation or pH drift, insufficient equilibration, temperature fluctuation, or reliance on a volatile modifier.
- Peak shape: tailing often means secondary interactions (silanol, metal contamination) or a partly blocked frit; fronting often means column overload or a strong diluent; split peaks point to a void at the column inlet.
- Ghost peaks and carryover: contaminated water or buffer, microbial growth in aqueous mobile phase, needle or loop carryover, or a previous sample.
Preventive maintenance
Replace pump seals and check valves on schedule, change inline filters and guard columns, keep aqueous buffers fresh (refrigerated, discarded within days), filter and degas everything, and log lamp hours.
Worked example
A gradient method shows retention times drifting 0.15 min later each injection while resolution falls slightly and pressure stays flat. Unchanged pressure argues against a blockage, so the mobile phase composition is probably shifting - an aging aqueous buffer or an open bottle losing organic by evaporation. Prepare fresh mobile phase and re-equilibrate; if retention returns, the method needs capped bottles and a defined mobile phase expiry.
Traps
Changing the column first; adjusting integration to hide tailing; using buffer past its microbial life; assuming a new column lot is identical.