Polarography, hydrogen peroxide

The product of the one-electron reduction of O2, the superoxide ion, Oi, is highly unstable in acidic-aqueous solutions where its protonated form, the peroxyl radical H02(pA = 4.8), decomposes to ozone, oxygen, and hydrogen peroxide experiments have shown that the two latter compounds are produced almost quantitatively, when only traces of ozone are found. In alkaline solutions, the superoxide ion is more stable even if it decomposes spontaneously to O2 and H02 (AG-6-=—51.13 kj mol ), it has been studied by polarography in NaOH solutions, in the presence of compounds that adsorb at the surface of the electrode and slow down the protonation of 02 . From these electrochemical experiments... 

The most useful application of polarography in biochemistry is the determination of oxygen. The reduction of oxygen proceeds in two steps at a mercury dropping electrode. In the first wave oxygen is reduced to hydrogen peroxide and in the second, more negative wave, the peroxide formed is reduced to water. 

Finally, among inorganic molecules, polarography can be used to determine oxygen, hydrogen peroxide, elemental sulfur, some sulfur oxides, and oxides of nitrogen, as well as some undissociated acids. 

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