During the past two decades, considerable attention has been focused on electrochemical determination using chemically modified carbon paste electrodes, with the preconcentration agent mixed into a carbon paste matrix in order to react with and bind selectivity the target solute [1]. The resulting electroresponses are very stable and the electrodes can be easily renewed by removing an outer layer of the paste and resmoothing the surface. Yet, the applications of modified paste electrodes are mainly defined in the field of voltammetric determination and very few have been used in potentiometry [2]. Some potentiometric modified carbon paste electrodes are reported for the determination of chloride [3], chromium (VI)[4], perchlorate and floroborate[5]. In this work, we report a carbon paste electrode based on recently synthesized macrocyclic diamide 1,4-diaza-2,3,8,9-dibenzo-7,1o-dioxacyclodeca-5,12-dione was constructed for Ca2+ determination. The calibration graph was linear over a wide concentration range (1.3 x 10-6-3.2 x 10-6 mol/dm-3) with a near Nernstian slope of 32 mv decade-1. The limit of detection is 7.9 x 10-7 mol/dm-3 (0.032 ppm). Selectivity coefficients were tabulated and the working pH range was determined. It has a fast response time of <10 s and can be used for at least 3 months without any considerable divergence in potentials. The electro was successfully applied to the determination of Ca2+ ions in a pharmaceutical preparation References: [1] R.w. Murray, Chemically Modified Electrodes, in Electroanalytical Chemistry(Ed: A.j.Bard), vol.13, 13, Marcel Dekker, New York, 1984 [2] I. Stefan, H.Y. Aboul-Enein, Talanta, 48, 1139 (1999) [3] J.P. Sapio, J.F. Calaruotolo, J.M. Bobbitt, Anal. Chim. Acta, 67, 1433 (1997) [4] X.Y. Hu, Z.Z. Ieng, Anal, proc, 32 (1995) [5] J. Jezkova, J. Musilova, K. Vytras, Electroanalysis, 18, 1433 (1997)
