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 μL 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 1.0×10−5 and 1.0×10−1 mol L−1 with detection limits of 5.6×10−6 mol L−1 for calcium and 9.5×10−6 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.