Determination of L-ascorbic acid with semi-differential voltammetry at chitosan modified graphite electrode

Graphite disc electrode modified with chitosan by drop-coating method was used to determine L-ascorbic acid (LAA) by semi-differential voltammetry. The effect of the type and acidity of electrolytes, the thickness of chitosan membrane, enrichment potential and time, scan rate and temperature on the voltammetric curve of LAA were investigated to acquire optimum conditions. En 0.20 mol/L NaH2PO4-Na2HPO4 buffer (pH 6.0), there was an excellent linearity between oxidation current and concentration of L-ascorbic acid in the range from 1.0 x 10(-6) to 6.0 x 10(-4) mol/L (r = 0.9997) with a detection limit of 6.7 x 10(-7) mol/L. Some ordinary biological substances such as nitrite, dopamine, glucose, etc, did not interfere with the determination of LAA, Relative standard deviation (RSD) of the oxidation peak currents obtained from 9 determinations of the same solution containing 5.0 x 10(-5) LAA was 3.6%. Recoveries of 96.4% similar to 102.8% were obtained from five determinations. This method has been applied to the determination of LAA in tablets and human serum successfully.