Negative ESI spectrum of water and methanol acidified with acetic acid

FIGURE 4.15 Negative ESI spectrum of water and methanol acidified with acetic acid. 

The corona discharge ionizes the solvent molecules in the tiny droplets as they pass by a tip held at very high voltage. In turn, the charge is transferred to any analyte molecules present in the solvent stream. 

A positive APCI mass spectrum usually contains the quasi-molecular ion, [M + H]+. However, APCI is a less-soft ionization technique compared to ESI and generates more fragment ions. 

This technique is used as an LCMS (liquid chromatographic-mass spectrometric) interface because it can accommodate very high (1 mL/min) liquid flow rates. 

---