Cathodic electrochemical detection of nitrophenols at a bismuth film electrode for use in flow analysis

The bismuth film electrode (BiFE) is presented for use in both batch voltammetric and flow injection (FI) amperometric detection of some nitrophenols (2-nitrophenol, 2-NP; 4-nitrophenol, 4-NP; 2,4-dinitrophenol, 2,4-DNP). The bismuth film was deposited ex situ (batch measurements) and in-line (FI) onto a glassy carbon substrate electrode. Batch analysis of the nitrophenols was carried out in 0.04 M Britton Robinson (BR) buffer pH 4, while for FI measurements, a carrier/electrolyte solution composed of 0.1 M BR buffer pH 4 mixed with methanol (20 + 80, v/v%) was employed to resemble media used in preconcentration/clean-up and flow separation sample pretreatment procedures. Under batch conditions, the voltammetric behavior of the nitrophenols was examined for dependence on medium pH in the range of 2 to 10. Employing the square-wave voltammetry mode, the limits of detection were 0.4 mug L-1, 1.4 mug L-1, and 3.3 mug L-1 for 2-NP, 4-NP, and 2,4-DNP, respectively. Under flow conditions, a simple in-line electrochemical bismuth film renewal procedure was tested and shown to provide very good inter- and intra-electrode reproducibility of the current signals at low mug L-1 analyte concentrations. The limits of detection for 2-NP, 4-NP and 2,4-DNP obtained using FI and amperometric detection at -1.0 V (vs. Ag/AgCl) were 0.3 mug L-1, 0.6 mug L-1 and 0.7 mug L-1, respectively, with linear ranges extending up to 20 mug L-1. The attractive performance of the BiFE under flow analysis conditions offers great promise with respect to its detection capability and to its use for a prolonged period of time with no need for inconvenient removal of the electrode from the system for mechanical surface treatment.