Decision Tree: Poor Repeatability
Symptom: repeat injections vary; unstable component readings or peak areas.
Field tip: If peak area varies → injection/sample issue. If peak timing varies → flow/temperature issue.
Step-by-step isolation
1) Check sample pressure stability and fast loop flow. Unstable sample pressure causes volume variation.
2) Inspect sample conditioning: filters, regulators, condensation, liquid carryover, heat tracing.
3) Valve/injection loop check:
- Listen/confirm valve switching sequence is consistent.
- Inspect valve wear, sticking, solenoid response.
- Check for contamination in sample loop.
4) Carrier flow stability: verify pressure/flow does not fluctuate (no regulator hunting).
5) Detector stability: if baseline is noisy, fix baseline first (see baseline tree).
6) Validation:
- Run a calibration standard 3 times. If standard repeats OK but process does not → process/sample variability.
- If standard also varies → instrument/sample system problem.
7) Corrective actions:
- Stabilize sample regulators and repair conditioning system.
- Service/replace injection valve components if sticking or worn.
- Replace contaminated filters and verify with repeats.