Why does the baseline of HPLC samples become unstable during injection?
When injecting samples in HPLC, baseline instability may be caused by several factors. Here are some common causes and solutions:
1. Sample contamination or impurity: The presence of impurities or particulates in the sample, especially insoluble substances, may lead to baseline instability. It is recommended to filter or centrifuge the samples to ensure purity.
2. Mobile phase issues: Poor quality or inconsistency in the mobile phase (such as variations in pH, ionic strength, or inaccurate solvent mixing ratios) can lead to baseline instability. Use high-quality solvents and ensure they are degassed to avoid this issue.
3. Injection system issues: Aging or micro-cracks in the injection valve, tubing, or seals can cause leaks, leading to signal instability. Inspect and replace relevant components to ensure a good system seal.
4. Temperature fluctuations: Unstable column temperatures can cause baseline drift. Check the temperature control system to ensure a constant temperature is maintained.
5. Pump system issues: Unstable pump output or bubbles affecting flow rate stability can cause baseline fluctuations. Check the pump performance, ensure it's bubble-free, and perform regular maintenance.
6. Detector issues: Malfunctions in the detector (such as DAD) can also cause baseline fluctuations. Calibrate or clean the detector to ensure the light source and optical path are free of contamination.
It is recommended to check the sample, solvent quality, injection system, temperature control system, pump performance, and detector status in sequence to identify and resolve the cause of baseline instability.
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