This paper illustrates the simultaneous determination of riboflavin (RB), ascorbic acid (AA) and folic acid (FA) at physiological pH by electrochemical method for the first time using the electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole modified glassy carbon (p-AMTa) electrode. Bare GC electrode fails to show stable voltammetric signals for AA, RB and FA in a mixture due to the surface fouling caused by the oxidation products of them. In contrary, the p-AMTa electrode shows stable voltammetric signals for RB, AA and FA in a mixture with potential differences of 670 mV and 530 mV between RB-AA and AA-FA, respectively. Further, the p-AMTa electrode was used to selectively determine either of the vitamins individually in the presence of high concentrations of other two vitamins. When the concentration of RB was increased from 10 mu M to 90 mu M, M was increased from 30 mu M to 270 mu M and FA was increased from 20 mu M to 180 mu M, the oxidation currents of the respective compounds increased linearly. The detection limit was found to be 4.54 x 10(-8) M for RB, 7.14 x 10(-7) M for AA and 2.5 x 10(-7) M for FA (S/N = 3). The practical application of the present modified electrode was demonstrated by determining the concentrations of RB, AA and FA in human plasma samples. (C) 2012 Elsevier Ltd. All rights reserved.