A Sensitive Nitrate Ion-Selective Electrode from a Pencil Lead. An Analytical Laboratory Experiment

Abstract

Nitrate ion is an important environmental and human health analyte and thus its detection and quantification is considered essential. This article summarizes a simple procedure for preparing and testing a nitrate ion-selective electrode based on doped polypyrrole films. Everyday pencil leads were used as a substrate for the electrochemical deposition of polypyrrole. Nitrate-doped polypyrrole electrodes, tested potentiometrically for their response to varying NO3–concentrations, exhibited Nernstian behavior (slopes of 54–55 mV per log cycle of nitrate concentration at T = 22°C), with a linear response to nitrate concentrations spanning three orders of magnitude (0.1–1× 10–4 M of NO3–) and a detection limit of 5 ± 1 × 10–5 M of nitrate. The procedure outlined here has the potential to initiate and motivate students with interests in sensor development, micro-fabrication procedures, advanced monitoring of environmental problems, and creating solutions to those problems.