Retractable-pen-based renewable silver amalgam film electrode for microliter sample analysis of electrochemically reducible environmental pollutants

Abstract

A novel, inexpensive, and simple construction of a retractable-pen-based renewable silver amalgam film electrode (RAE) was introduced in this study for electrochemical sensing of electrochemically reducible compounds in small sample volumes. This electrode is based on a mechanical renewal of the amalgam film achieved by using mechanisms found in a common retractable ballpoint pen. Cadmium(II) and two model environmental pollutants (4-nitrophenol (NP) and 3-nitrobiphenyl (NB)) were used to evaluate the performance of the novel RAE and its utilization in the electrochemical microcell. In order to decrease the high variability of observed reduction potentials of NP and NB on RAE, the influence of the content of silver in the amalgam used for the renewal of the film was investigated. It was found that 4 % of Ag in the amalgam improved the repeatability of peak potentials. Obtained limit of quantification (LOQ) for Cd(II) was 54 nmol L–1 (6.1 ppb) in acetate buffer (pH 4.8); LOQ for NP was 1.2 μmol L–1 in Briton-Robinson (BR) buffer (pH 4.0). LOQ for NB was 2.5 μmol L–1 in BR buffer (pH 6.0) – methanol (8:2, v/v) medium. The possibility of further decrease of LOQ of NB to a nanomolar range with the help of the microcell was demonstrated by the liquid-liquid extraction (LLE) to hexane with the preconcentration factor of 1000. Moreover, RAE offers portability, long-term stability, simple renewal of the surface, a wide cathodic potential window, and it can be considered as an inexpensive, robust, and safe alternative to other mercury-based electrochemical sensors.