Amperometric determination of calcium ion with an alizarin/Nafion modifiedelectrode

Determination of Ca2+ ions with 4 mu L -5.0 x 10(-3) M alizarin and 5 % Naf ion-modified electrode was studied employing cyclic voltammetry and chronoa mperometry. The Nafion film fabricated in different humidities gave differe nt responses for the Ca2+ ion, of which morphology was characterized with a tomic force microscope. Various experimental parameters, which influenced t he sensitivity of the modified electrode to Ca2+ ions, were optimized. The modified electrode covering the Nafion film at the low humidity of 40 % was stable in all experiments. The electrodes were stable over pH 4-12 and cat ion interference could be avoided by controlling the pH of the sample solut ion. The linear response range for Ca2+ ions employing double potential chr onoamperometry was 2.0 x 10(4)-1.5 x 10(6) M. Least square analysis provide d two equations I [mA] = - 0.668 -0.136 C [10(5) M] and I [mA] = - 0.566 -0 .0185 C [10(5) M]. The correlation coefficients were 0.997 for both cases. The relative standard deviation was +/- 4.7 % at 1.0 x 10(-5) M for five de terminations. From the signal-to-background characteristics of the response , the detection limit was about 1.0 x 10(-6) M. Satisfactory results were a cquired for the determination of the Ca2+ ion in the certified standard uri ne reference material (SRM's 2670) and in tap water.