The surface concentration of nitrophenyl (NP) films is commonly calculated from the charge associated with its redox reactions in aqueous solution. Reduction is usually carried out in acidic or basic solution and is assumed to proceed by either four electrons, or a mixed four and six electron process. Here, we reproducibly graft NP films of different thicknesses to glassy carbon electrodes from the corresponding diazonium ion and examine the reduction of the films in strongly acidic and basic solutions. We demonstrate that in most, if not all, cases, assumption of a four‐electron reduction of NP groups coupled with use of the redox reaction of the hydroxylamine product will lead to an underestimation of the surface concentration of NP groups. Use of acidic media with the assumption of a mixed four and six electron reduction of NP groups is shown to be an electrochemically and chemically sensible approach to estimating surface concentrations of NP groups.

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