Base drift in HPLC is the low-frequency signal deviation that occurs in the baseline due to column stationary phase bleed, background ionization, and low-frequency fluctuations in the detector and/or instrument-controlled parameters (such as temperature or flow). Baseline rise is the gradual increase in baseline found in temperature-programmed or gradient elution separations. It is categorized as a form of long-term noise and characterized as a shift in the baseline position Chandrakant, R., Malwade. Lars, P., Christensen. 2013. Computer Aided Chemical Engineering, 32, pp 49-54..
The Cause of Baseline Drift in HPLC
This form of drift is primarily caused by the following:
- Column temperature fluctuations. (Even minor variations allow the cyclic baseline to rise and fall. Refractive index and conductivity detectors, UV detectors at high sensitivity or indirect photometric mode are most commonly affected.)
- The non-homogeneous mobile phase. (Drift from temperature fluctuation to higher absorbance, rather than a cyclic pattern.)
- Contaminant or air build-up in the detector cell.
- Connected outlet line to the detector. (High-pressure gaps in the cell window, creating a noisy baseline.)
- Mobile phase mixing problem or alteration in flow rate.
- Slow column balancing, particularly when adjusting the mobile step.
- Polluted, degraded or unprepared mobile phases of high-quality chemicals.
- Strongly preserved materials in the sample can be elucidated as very broad peaks which tend to be rising baseline. (The gradient analysis can make the problem worse.)
- Detector (UV) not mounted at the highest absorbance but the curve angle.
Control procedure of Baseline Drift in HPLC
- Use a heat exchanger before the detector to control the temperature of the column and mobile process.
- Use HPLC-grade solvents, high-purity salts, and additives. Mobile process degasses before use, store with helium during use.
- Flush cell with methanol or other potent solvents. Clean cell with 1N HNO3 if possible (never with HCl and never use nitric acid with PEEK tubing or fittings.)
- Unplug or replace the row. Refer to the Window Replacement Detector Manual.
- Correct rate of composition/flow. To prevent problems, regularly track the composition and flow rate.
- Flush column with moderate intensity solvent, run 10-20 column volumes of the current mobile phase across the column before the examination.
- Examine the mobile phase’s make-up
- Use column guard. If required, flush the column with a strong solvent between injections or at regular intervals in the study.
- Set the wavelength to the optimum UV absorbance Chau, F., Leung, A.K. 2000. Data Handling in Science and Technology, 22, pp 205-223..