Accuracy Improvement When Determining Copper(II) Ions With Zincon at Acidic Condition

摘要

2-Carboxy-2'-hydorxy-5'-sulfoformazylbenzene has been widely used to determine Cu(II) ions. In general, basic pH condition is preferred to enhance the reactivity between metal ions and zincon. But acidic condition can be applied for copper determination because Cu(II) cannot lose reactivity at acidic condition. Also, pH = 5 condition can minimize the interference from zinc which is found together with copper in many samples. However, zincon can be precipitated at acidic condition. We minimized precipitation problem by adding cyclohexanone or the use of lower buffer concentration. Using this approach, accuracy was improved from -17.7 to 242.5% to -0.4% to 22.0%. A very linear calibration curve (r~2 = 0.9999) was obtained for the copper concentration range of 30-2002 ng/mL. This method was successfully applied to determine copper concentration from discharged water samples. No significant interference was observed and the estimated LOD (S/N = 3) is 5.5 ng/mL.