Optimizing Electrospray Ionization (ESI) source parameters can significantly enhance sensitivity and reproducibility in LC-MS analysis. Here are key factors to consider:
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Capillary Voltage (Ionization Potential) :
- Too low: Poor ionization efficiency.
- Too high: Can cause ion fragmentation and signal loss.
- Recommended range: 3–5 kV (positive mode), -2.5 to -4 kV (negative mode).
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Nebulizer Gas Pressure (e.g., Nitrogen ):
- Controls droplet formation at the ESI source.
- Low pressure → Larger droplets, less efficient ionization.
- High pressure → Small droplets, better desolvation but possible ion suppression.
- Recommended range: 20–60 psi.
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Desolvation Temperature:
- Higher temperature aids solvent evaporation and ionization efficiency.
- Too high can degrade thermally unstable compounds.
- Recommended range: 250–450°C.
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Flow Rate of Mobile Phase:
- Lower flow rates (e.g., 0.1–0.3 mL/min) improve ESI efficiency.
- High flow rates may require a split or post-column modifications.
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Solvent Composition:
- Increase organic content (e.g., acetonitrile, methanol) for better ionization in positive mode.
- Formic acid (0.1%) or ammonium acetate enhances protonation in positive mode.
- Ammonium hydroxide can improve deprotonation in negative mode.
To ensure accurate mass calibration and sensitivity optimization, using high-quality LC-MS Calibration Standards is essential.
