Fe(CN)₆⁴⁻‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Electrode. Part 2: Stability Improvement and Selective Detection of Dopamine in the Presence of Ascorbic Acid

Highly stable Nafion‐covered hexacyanoferrate‐doped‐glutaraldehyde‐cross‐linked poly‐ L ‐lysine (PLL‐GA‐Fe(CN) 6 4− /Naf) film modified glassy carbon electrode (GCE), for the selective detection of dopamine (DA) in the presence of ascorbic acid (AA), was prepared by first ion‐exchanging Fe(CN) 6 4− into PLL‐GA coating on GCE then sealing it with a Nafion outer layer. The Nafion over layer is crucial in preventing leaching of Fe(CN) 6 4− ions from the inner layer. The first layer was acting as electrocatalyst for DA oxidation and the outer coating acted as discriminating layer for selective permeation of DA in the presence of interfering anionic species. More than 90% of the initial response was retained after coating with the Nafion protecting layer compared to a huge loss (>60%) without Nafion outer layer. 5% Nafion coating was identified as optimum thickness for the selective detection of DA in the presence of AA.