Amperometric flow injection analysis of hydroquinone in dermatological creams using a porous diamond-like carbon electrode

A porous diamond-like carbon film deposited on vertically aligned multi-walled carbon nanotubes (DLC: VAMWCNT) was evaluated as an electrode material in flow injection analysis (FIA) with amperometric detection. The redox behavior of hydroquinone (H2Q) was carried out as proof of concept. From cyclic voltammetry tests, H2Q gave a heterogeneous electron transfer rate constant (k0) of 4.9 x 10-3 cm s- 1, which is comparable or better than those obtained with conventional electrodes. For the H2Q determination with the FIA-amperometry system, optimizations were performed regarding the supporting electrolyte, applied potential and FIA parameters (flow rate and sample injection volume). Under optimal conditions, the amperometric response of the DLC: VAMWCNT electrode was linear in the H2Q concentration range from 1.0 x 10-6 to 1.0 x 10-4 mol L-1, with a limit of detection (LOD) of 7.7 x 10-7 mol L-1. Interestingly, the DLC:VAMWCNT electrode displayed a very stable response under hydrodynamic conditions, with no memory effect while retaining accuracy towards the analysis of commercial H2Q-based dermatological creams. From these findings, DLC:VAMWCNT appears to be an outstanding candidate for flow injection analysis systems coupled to electrochemical detection.