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The use of aluminum substrate as an electrode and the modi®cation of its surface by means of the thin ®lm of nickel pentacyanonitrosylferrate (NiPCNF) was developed. The modi®cation conditions of aluminum surface including the electroless deposition of metallic nickel on the electrode surface from NiCl 2 NH 4 Cl solution and chemical derivatization of deposited nickel to NiPCNF ®lm in solution of 10 mM sodium pentacyanonitrosylferrate (PCNF) 0.5 M NaNO 3 0.03 M HNO 3 are described. The modi®ed Al electrode prepared under optimum conditions, shows a well-de®ned redox couple due to [Ni II Fe III/II (CN) 5 NO] 0/71 system. The effect of pH and radius of the hydrated alkali-metal cation of supporting electrolyte on the electrochemical characteristics of the modi®ed electrode were studied in detail. Diffusion coef®cients of alkali-metal cations in the ®lm (D),transfer rate constant for electron (k s ) and transfer coef®cient (a) were calculated. The electrocatalytic activity of the modi®ed electrode on the oxidation of hydrogen peroxide and ascorbic acid was demonstrated as a typical example of applications.

Nickel hexacyanoferrate (NiHCNF) film modified Al electrode prepared by simple and rapid electroless dipping procedure was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic or linear sweep voltammetry was linearly dependent on the ascorbic acid concentration. At a fixed potential under hydrodynamic conditions (stirred solutions), the calibration plot was linear over the ascorbic acid concentration range 2×10−6–2×10−4 M. The detection limit of the method is 2×10−6 M, low enough for trace ascorbic acid determination in various real samples. The proposed method was used for determination of ascorbic acid in fresh fruit juices, vegetables, pharmaceutical preparations and blood plasma. The results obtained are in good agreement with those obtained by the official standard methods. The analysis with NiHCF‐film‐modified Al electrode was selective for ascorbic acid from the various concomitant reducing compounds in real samples.