What are the differences between Electrospray Ionization (ESI) and Atmospheric Pressure Chemical Ionization (APCI)?

1. Different ionization methods: APCI uses corona discharge gas-phase ionization; ESI uses ion evaporation liquid-phase ionization. 2. Suitable compounds for analysis: APCI is suitable for weakly polar, small molecular compounds with some volatility; ESI is suitable for polar compounds and biological macromolecules. 3. Different flow rates: ESI generally has a lower flow rate, while APCI has a relatively higher flow rate. 4. Different charges produced: APCI cannot generate a series of multiply charged ions; ESI can generate a series of multiply charged ions.

• Protein mass spectrometry identification