Aliphatic polyamine oxidation response variability and stability at boron-doped diamond thin-film electrodes as studied by flow-injection analysis

Abstract

Previously it was shown that four different aliphatic polyamines can be quantitatively electrooxidized at boron-doped diamond thin film electrodes without derivatization or the use of pulsed voltammetric waveforms [Anal. Chem. 71 (1999) 1188; Anal. Chem. 69 (1997) 4041]. The flow injection analysis (FIA-EC) investigation (amperometric detection mode) of cadaverine (CAD), putrescine (PUT), spermine (SPM) and spermidine (SPMD), reported previously [Anal. Chem. 71 (1999) 1188], are updated herein with particular emphasis on the electrode response variability and stability. Most of the measurements were made with a film deposited from a 0.50% methane-to-hydrogen (C/H) volumetric ratio. In general, films deposited with C/H ratios near this value tend to possess the requisite physicochemical properties to support anodic oxygen transfer reactions. The electrode performance was evaluated in terms of the linear dynamic range, limit of quantitation, response variability and response stability. A linear dynamic range from 1.0 μM to 1.0 mM and a limit of quantitation of 1.0 μM or 20 pmol injected (S/N≥3) were found for CAD, PUT, and SPMD. For SPM, a linear dynamic range from 0.32 μM to 1.0 mM and a limit of quantitation of 0.32 μM or 6.4 pmol were observed. The response variability, as low as 2–4%, was observed which is vastly improved over previous results. The improvement was achieved by introducing a 3–6 min delay period between injections. The long-term response stability was good with no evidence for any progressive response attenuation or complete fouling by the reaction product, even though a solid deposit was observed to accumulate on the electrode surface with extended use. The deposit appears to partially reduce the active electrochemical area for polyamine oxidation and to decrease the overpotential for water discharge. Preliminary chromatographic results demonstrated the possibility of separating and detecting the polyamines by a simple reverse-phase scheme at constant applied potential.