Sensor-containing microspheres of chitosan crosslinked with 8-hydroxyquinoline-5-sulphonic acid for determination of Cu(II) in instant coffee

A novel carbon paste electrode containing chitosan microspheres for the determination of Cu(II) in instant coffee by anodic stripping voltammetry was developed. Chitosan was crosslinked with the chelating agent 8-hydroxyquinoline-5-sulphonic acid and glutaraldehyde. The microspheres of the crosslinked chitosan biopolymer were obtained by the spray drying technique and employed in the construction of the sensor. In acetate buffer solution (0.1 mol L−1, pH 6.0), the calibration curve obtained was linear for concentrations of 5.0 × 10−7 to 1.4 × 10−5 mol L−1 (r = 0.9990); the detection limit was 5.5 × 10−8 mol L−1. The relative standard deviation (n = 8) was lower than 3.0% for solutions containing 6.0 × 10−6, 5.0 × 10−5 and 1.5 × 10−4 mol L−1 of Cu(II). The method was successfully employed for determination of Cu(II) in instant coffee and the results obtained showed good agreement when compared with those using electrothermal atomic absorption spectrometry.