Flow-injection electrochemical determination of citric acid using a cobalt(II)–phthalocyanine modified carbon paste electrode

The electrocatalytic activity of cobalt(II)–phthalocyanine immobilized in a carbon paste electrode for citric acid oxidation under a diffusion-controlled electrochemical process was employed to develop a selective flow injection amperomettric analysis method. Under optimized conditions, rapid and reliable determinations of citric acid (65 samples per hour) were achieved for analyses of commercial fruit juices with minor pretreatment of the samples. A linear response was accomplished ranging from 0.25 to 15 mmol L−1 (r2=0.9979) with an estimated detection limit of 0.117 mmol L−1. Alternatively, a very sensitive and selective assay was developed for the micromolar range, obtaining a linear response ranging from 3.81 to 91.2 μmol L−1 (r2=0.9993) with an estimated detection limit of 2.54 μmol L−1, by using square wave voltammetric methodology. The speed and simplicity of the proposed approaches compares advantageously to the all other citric acid determination methods.