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The SiO2/SnO2/Phosphate composite, SSF, was prepared by the sol-gel process. The redox dye methylene blue was immobilized on the SSF surface. This new material was utilized in the preparation of a modified carbon paste electrode (SSFAM) and its electrochemical characteristics were studied by the cyclic voltammetry technique. The SSFAM sensor presented a formal potential of -90 mV vs SCE, excellent stability regarding the number of cycles and regarding the pH of electrolyte support solution ranging from 2.0 to 8.0. The SSFAM sensor was utilized for the determination of ascorbic acid (Vitamin C), utilizing the chronoamperometry technique, and presented a response time of 1.5 s, a linear response range between 2.0 x 10-4 and 3.0 x 10-3 mol L-1, with a detection limit of 7.8 x 10-6 mol L-1, considering a relation signal/noise = 3. The results obtained for real samples by the SSFAM sensor were compared with those from the standard method for determination of ascorbic acid by the 2,6-dichlorophenilindophenol. The comparison of the obtained results by the two methods demonstrated that the SSFAM sensor has great utilization potential.