Simultaneous determination of tryptophan, uric acid and ascorbic acid at iron(III) doped zeolite modified carbon paste electrode

A new chemically modified electrode is constructed based on iron(III) doped zeolite modified carbon paste electrode (Fe3+Y/ZCME). The electrode was evaluated as a sensor for sub-micromolar determination of tryptophan (Trp), uric acid (UA) and ascorbic acid (AA) in aqueous solutions. The measurements were carried out by application of the differential pulse voltammetry (DPV) method in phosphate buffer solution with pH 3.5. Iron(III) loaded in zeolite can increase anodic peak currents by adsorption of Trp, UA and AA on electrode surface The analytical performance was evaluated with respect to the carbon paste composition, pH of solution, accumulation time and accumulation potential. The prepared electrode shows voltammetric responses with high sensitivity and selectivity for Trp, UA and AA in optimal conditions, which makes it very suitable for simultaneous determination of these compounds. The linear calibration range for AA in the presence of 50 μM UA and 50 μM Trp was 0.6 μM to 100 μM, with a correlation coefficient of 0.9992, and a detection limit of 0.21 μM (S/N = 3). A linear relationship was found for UA in the range of 0.3–700 μM containing 10 μM AA and 50 μM Trp, with a correlation coefficient of 0.9990 and a detection limit of 0.08 μM. The linear calibration range for Trp in the presence of 10 μM AA and 50 μM UA was 0.2–150 μM, with a correlation coefficient of 0.9996, and a detection limit of 0.06 μM. The proposed method was successfully applied for determination Trp, UA and AA in biological systems and pharmaceutical samples.