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A new procedure for the speciation of chromium by means of differential pulse voltammetry using screen-printed carbon electrodes (SPCEs) has been proposed. Two different modified carbon working, a Ag/AgCl reference and a carbon counter screen-printed electrodes have been connected in array mode for the simultaneous determination of Cr(III) and Cr(VI). Mercury films or gold nanoparticles have been ground onto the SPCEs in order to improve their selectivity to each chromium species. The quantification of the peak currents observed at À1.25 V in Hg-SPCE and À0.1 V in AuNPs-SPCE were carried out. The method has been applied to the speciation of chromium in waste water from a tannery factory.

This work reports the development of horseradish peroxidase based biosensors using screen‐printed carbon electrodes for the determination of tyramine (tyr). A novel procedure based on the insertion of the enzyme in the screen‐printing process (SPCHRPEs) has been compared with the cross‐linked immobilization into the carbon working electrode (HRP/SPCEs). Both biosensors were characterized obtaining good capability of detection (2.1±0.2 and 0.2±0.01 µM for SPCHRPEs and HRP/SPCEs, respectively). The reproducibility was 3.4 % and 6.8 % for SPCHRPEs and HRP/SPCEs, respectively. The repeatability was 2.2 % and 7.1 % for SPCHRPEs and HRP/SPCEs, respectively. The specificity towards different biogenic amines was analyzed. The developed biosensors were applied to the determination of tyr content in cheese samples.