A novel carbon paste electrode containing modified clinoptilolite nano-particles with hexadecyltrimethylammonium surfactant (or surfactant modified zeolite (SMZ)) was constructed and used for selective voltammetric determination of ascorbic acid (AA) in the presence of dopamine (DA), because the SMZ present in the modified electrode adsorbs anionic AA species and repels cationic DA species. This caused to increase the over-voltage of electro-oxidation of DA by similar to 600 mV with respect to AA in square wave voltammetry (SqW). Hence, AA and DA can be effectively determined by the modified electrode in their aqueous mixture. Comprehensive CV, SqW and chronoamperometry (ChA) studies were done on AA using the proposed electrode. The widest linear responses with detection limits of 6.1 x 10(-8) mol dm(-3) and 5.9 x 10(-12) mol dm(-3) were respectively obtained for AA in SqW and ChA techniques. The diffusion coefficient of ascorbic acid was equal to 4.1 x 10(-5) cm(2) s(-1). The proposed method was successfully applied for the determination of AA in different pharmaceutical and food samples which of their AA contents were obtained as: 497.4 +/- 1.2 mg per Chewable tablet, 246.9 +/- 1.4 mg per Vitamin C tablet, 501.3 +/- 0.8 mg per Vitamin C ampoule, 45.2 +/- 1.1 mg per 100 g of Sweet lemon, 50.6 +/- 0.7 mg per 100 g of Orange, 36.9 +/- 0.9 mg per 100 g of Grapefruit, 31.2 +/- 1.3 mg per 50 g of Sour lemon, 9.5 +/- 1.0 mg per 250 mg of Lemonade. (C) 2015 Elsevier Ltd. All rights reserved.