Simultaneous determination of calcium and potassium in coconut water by a flow-injection method with tubular potentiometric sensors

In the present work, a simultaneous determination of calcium and potassium in coconut water samples using a flow-injection system with tubular ion-selective electrodes (ISEs) in series is described. The samples were injected into a 0.1 mol L-1 HEPES (pH = 6.0) carrier solution, using an injection volume of 100 mu L and a flow of 2.0 mL min(-1) in the FIA system. The electrodes developed exhibited nernstian response for calcium and potassium in the concentration range between 1.0 x 10(-5) and 1.0 x 10(-1) mol L-1 with detection limits of 5.6 x 10(-6) mol L-1 for calcium and 9.5 x 10(-6) mol L-1 for potassium. And no significant interference between both ions was observed. The flow-injection analysis (FIA) system with tubular ISEs was suitable for the simultaneous calcium and potassium on-line monitoring. The determination of potassium presented good results when compared to the reference method. And the recovery results were 95 +/- 1% for calcium and 102 +/- 2% for potassium, showing a good evidence of the accuracy of the method. (c) 2005 Elsevier Inc. All rights reserved.