1. Increase or decrease solvent ionic strength, pH, or additive concentration (especially affects ionic solutes).

2. Column changed, new column has different selectivity from that of old column.

3. Sample injected in incorrect solvent or excessive amount (100-200 μL) of strong solvent.

4. Column temperature change.

1. Check make-up of mobile phase.

2. Confirm identity of column packing. For reproducible analyses, use same column type. Establish whether change took place gradually. If so, bonded phase may have stripped. Column activity may have changed, or column may be contaminated.

3. Adjust solvent. Whenever possible, inject sample in mobile phase.

4. Adjust temperature. If needed, use column oven to maintain constant temperature.