Available electrons and equivalents

Atoms that are not present in a substance are ignored. For substances such as glucose not containing N, P, or S, AE = eq. On the other hand, for the biomass represented by formula (B) eq = 4.577, which is considerably higher than 4.079 AE. This is because of the further oxidation of nitrogen and sulfur. Phosphorous is already in its highest oxidation state in biologically important substances. Ions such as Mg , Ca, and do not contribute electrons since they do not become further oxidized. 

The difference between the idea of eq and AE is sometimes not recognized, and can lead to differences in the interpretation of data. 

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