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In this work new designed, highly sensitive electrochemical method is developed for the determination of nitrites in tap water using glassy carbon electrode modified with graphene nanoribbons (GNs/GCE). Graphene nanoribbons (GNs) have been newly synthetized and aligned to the surface of glassy carbon electrode (GCE) and exhibited excellent electrocatalytic activity for nitrite oxidation with a very high peak currents. Studies about electrochemical behavior and optimization of the most important experimental conditions were done using cyclic voltammetry (CV), while quantitative studies were done with amperometric detection. Nitrite provides a well-defined, oxidation peak at +0.9V (vs. Ag/AgCl, 3.0M KCl) in Britton-Robinson buffer solution (BRBS) at pH 3. The influence of most possible interferent ions has been examined and was found to be negligible. Under optimized experimental conditions in BRBS at pH 3 linear calibration curves were obtained in the range from 0.5 to 105µM with the detection limit of 0.22µM. Reproducibility of ten replicate measurements of 1µM of nitrite was estimated to be 1.9%. Proposed method and constructed sensor is successfully applied for the determination of nitrite present in tap water samples without any pretreatment. This developed method represents inexpensive analytical alternative approach compared to other analytical methods.

Rhenium(IV)-

Tin (IV) oxide was used as a bulk mediator in carbon paste and carbon ink screen-printed electrodes to improve the better performance of the carbon electrodes for the detection of hydrogen peroxide in comparison with unmodified electrodes. A new glucose biosensor developed from modified carbon paste electrode and coated with glucose oxidase entrapped in Nafion was investigated with a flow injection system. The biosensor could be operated under physiological conditions (pH 7.5, 0.1 M phosphate buffer), with an operating potential of −200 mV (vs. Ag/AgCl), a flow rate of the carrier of 0.2 mL/min. and an injection volume of 100 μL. The amperometric response of the biosensor showed good linearity up to 200 mg/L with a detection limit (3σ) of 6.8 mg/L. The relative standard deviation for the repeatability of measurements for 100 mg/L glucose was 2.9% (n = 10 measurements) and the corresponding reproducibility was 12% (n = 5 sensors). The effect of all investigated interferences (uric acid, paracetamol, xanthine, hypoxanthine and ascorbic acid) was not fatal and could be eliminated by the use of the standard addition method. The new biosensor was successfully applied to the determination of glucose in human blood plasma.

No abstract