In the second case, the signal corresponds only to the interfering components. The calculated difference is compared with the calibration plot. Preliminary Staurosporine supplier tests employing palladium-modified electrodes showed an interesting behaviour in the presence of ascorbic acid. Cyclic voltammograms

of the bare gold electrode and of the same electrode after palladium deposition, after increasing concentrations of AA, were obtained. The current enhancement was remarkable when the electrode is modified (Fig. 1). Probably, part of the increase in the current may be attributed to the growth of the effective area of the electrode. Observations with a microscope showed the formation of a very porous surface after the palladium deposition. The influence of parameters, such as flow rate and sample volume, was studied. Fig. 2a shows the amperometric responses of a gold electrode modified with palladium for injections of 150 μL of AA 50 μmol L−1, as a function of the flow rate (1–4 mL min−1). For high flow rates, the ascorbate oxidase immobilised in the tubular reactor was unable to oxide the AA completely into DAA, and for low flow rates a larger dispersion for the current signal of ascorbic acid is observed. Thus a flow rate of 2.5 mL min−1 was chosen as the most favourable, since it combines good reproducibility, high efficiency (180-samples h−1), and low consumption of carrier

solution, Trichostatin A also providing the complete oxidation of AA into DAA. The influence of the sample volume on the analytical signal was also evaluated. Fig. 2b shows the amperometric responses of a gold electrode modified with palladium for injections of AA 50 μmol L−1 and a flow rate of 2.5 mL min−1, as a function of the loop (50–300 μL). When the volume of the sample is increased, the amperometric signal increases such as well as the time required for each Protein tyrosine phosphatase analysis. A volume of 150 μL was chosen as the working volume

for the subsequent experiments. For all the studied volumes, the ascorbate oxidase immobilised in the tubular reactor was sufficient to oxidise AA completely in DAA. To examine the efficiency of the rector containing immobilised ascorbate oxidase on amberlite IRA-743, amperometric responses of a gold electrode modified by electrodeposition of palladium involving 50 injections of 150 μL of ascorbic acid 50 μmol L−1 for a channel with and without immobilised ascorbate oxidase were performed. The precision for injections of ascorbic acid without immobilised ascorbate oxidase on tubular reactor was 3%. An important characteristic observed in the immobilised enzymes was its storage stability of at last 1 week under intense use with ascorbic acid standard. After this period, a decrease on the order of 50–60% of the enzymes activity was observed. When applied in the determination of ascorbic acid in honey, the enzymatic reactors showed a loss in the enzyme activity after 50 injections, requiring construction of new reactors.