Baseline problems
Nico Vonk, Avans+, Breda, The NetherlandsLevelBasic
Baseline noise.
| Possible causes | Solutions | |
| Electrical problem. | Take care that the pump, detector and data system are all set at the correct values and are functioning well. | |
| Pump not functioning pulse free (pressure fluctuations?!). | Check the pump or connect a pulse dampener between pump and injector | |
| Bubbles in detector cell. |
First degas the mobile phase solvents properly and check your degassing system.
Connect detector directly to the pump and flush out the bubble. It is also possible to compress the bubble by increasing the pressure at the detector outlet with a restrictor or simply with a finger. Be careful and do not apply a high pressure when the flow cell is not strong enough. | |
| Contaminated detector cell. | Flush cell with appropriate solvent or clean the cell (see manual). | |
| Detector lamp old. | Replace the lamp. | |
| Leaking connection. | Check all fittings. | |
| Eluent not sufficiently degassed. | Continually degas the eluent. | |
| Detection wavelength too low for the eluent used. | Use cleaner or different organic solvent in mobile phase. Otherwise change method to higher UV wavelength. | |
| Spikes caused by bubbles coming forth out of heat development by mixing two solvents, like methanol and water. | Check / improve solvent degassing. |
Unstable baseline.
| Possible causes | Solutions | |
| Unstable gradient or mixing. | Check gradient pump, degassing, propotional valves and mixing chamber. | |
| Temperature fluctuations. | Use column thermostat. Column temperature > 5 ° above ambient. | |
| Bubbles in the detector cell | Degas mobile phase properly. Apply back pressure behind detector cell (check manual if possible!) to avoid bubble formation behind the column. | |
| Poor gradient mixing. | Run an blank gradient with methanol (+ 0.1 % acetone ) to locate the problem. |
Baseline drift.
| Possible causes | Solutions | |
| Eluent impurities | Replace solvents. Use HPLC grade only. | |
| Column equilibration with the mobile phase. | Purge thee pump system and re-equilibrate the column. Refer to the column manual if your method does not result in fast equilibration of the column. | |
| Temperature fluctuations. | Use or check the column oven. Adjust the oven temperature at least 5 degrees above room temperature. | |
| Bubbles in detector cell. | Degas the mobile phase properly. Apply a detector cell back pressure ot prevent bubble formation. Refer to your detector maual if this set-up is allowed! | |
| A change in the equilibrium inside the column (impurities). | Regenerate column and use fresh eluent. | |
| A change in flow rate. | Check flow adjustment and stability of flow and pressure. | |
| Gradient elution. | Detection level of eluent changes with change in composition. | |
| Stabilisation of the detector. | Allow the detector to warm up for half an hour before injection. |
