Micro electrochemical sensor with copper nanoclusters for nitrate determination in freshwaters

A microsensor chip was fabricated by micro electromechanical system technology, and a portable electrochemical system for nitrate determination in freshwaters was developed. As the electrocatalyst material, copper was electrodeposited onto the working-electrode of the microsensor by the cyclic voltammetry method. It was found that the deposited layer was porous and constructed by copper nanoclusters. The electrochemical response of the modified microsensor for nitrate under acidic conditions (pH=2.0) was characterised by linear sweep voltammetry. Calibration in standard nitrate samples in the range of 6.25=300==mol/l yielded straight lines: y₁ [μA]μμ0.0526x-3.905 (R₁²=0.9993), while in the range of 300=3500==mol/l yielded straight lines: y₂ [μA]μμ0.0353x-13.653 (R₂²=0.9918). It was found that the modified microsensor performed at higher sensitivity in nitrate detection than previous works and the limit of detection is 5==mol/l (S/N≥3). Interference analysis with nine kinds of ions (NO₂^-, Cl^-, HPO₄^2-/PO₄^3-, SO₄^2-, HCO₃^-/CO₃^2-, Na⁺ and K⁺) commonly found in water indicated that only NO₂^- causes reasonable interference (i.e. 10% signal distortion). Based on the modified microsensor, the developed portable electrochemical system was employed for nitrate determination in three freshwater samples. The results were in good agreement with the data obtained by the ultraviolet spectrophotometric method.