A mesoporous graphite material micro-structured with palladium-platinum deposits (mixed in the ratio of 70:30% Pd:Pt) has been used as a cost-effective electrode material for designing an amperometric biosensor for xanthine. The here reported biosensor shows significantly improved operational parameters as compared to previously published results. At a constant applied potential of −0.05 V (vs. Ag/AgCl) it is distinguished with enhanced selectivity of the determination: at the working potential the current from the electrochemical transformation of various electrochemically active substances usually attending biological fluids (incl. uric acid, L-ascorbic acid, glutathione and paracetamol) has been eliminated. The effect of both the temperature and buffer composition on the analytical performance of the sensor has been investigated. Under optimal operational conditions (25°C, −0.05 V vs. Ag/AgCl, phosphate buffer, pH 8.4), the following have been defined for the biosensor: sensitivity 0.39 µA µM−1, strict linearity of the response up to xanthine concentration 70 µM, detection limit of 1.5 µM (S/N=3) and a response time of at most 60 s. [...]
Electrochemical or chemical reduction of nitric acid is a well studied area in literature due to the importance of the products formed. The present work focuses on the effect of conventional cathode materials including PbO2, amalgamated Cu, graphite, Pb, Pt and a modified electrode material Ti/TiO2 on the reduction of nitric acid. Ammonia and hydroxylamine are the main products which are estimated by conventional titration methods. Other conditions being similar, the product distribution varies quite drastically as a function of the electrode material and Ti/TiO2 is found to favor a higher ratio of hydroxylamine to ammonia formation compared to other electrodes. The conditions have also been optimized based on the maximum yield of the product.
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