Electrospray Ionization Mass Spectrometry: A Technique to Access the Information beyond the Molecular Weight of the Analyte

Table 1

Typical redox reactions of the solvents expected to occur in the electrospray emitter and their corresponding standard potentials.

Solvent systems	Positive-ion mode		Negative-ion mode
	Oxidation reactions	E ^0 (V)	Reduction reactions	E ^0 (V)
Water	2H2O = O2 + 4H^++ 2e^−	1.23	2H2O + O2 + 4e^− = 4OH^−	0.40
	2H2O = H2O2 + 2H^++ 2e^−	1.77	H2O + O^−2 + e^− = HO^−2 + OH^−	0.20
	H2O = HO* + H^++ e^−	2.72	H2O + HO^−2 + e^− = HO* + 2OH^−	0.18
			2H2O + 2e^− = H2 + 2OH^−	0.07
			2H2O + O2 + 2e^− = H2O2 + 2OH^−	−0.13
			H2O + O2 + 2e^− = HO^−2 + OH^−	−0.83
Methanol	CH3OH = HCHO + 2H^+ + 2e^−	0.23	CH3OH + H2O + 2e^− = CH4 + 2OH^−	−0.25
	CH3OH + H2O = HCOOH + 4H^+ + 4e^−	0.10	CH3OH + 2H^+ + 2e^− = CH4 + H2O	0.58
	HCOOH = CO2 + 2H^+ + 2e^−	−0.20