Polymer membranes are becoming ever more attractive for trace analysis based on ionophore-impregnated; offering a wide variety of potential for an even wider variety of applications. Here we report a series of macrocyclic compounds with different substituents; which have been examined for their potential to detect potassium phosphate in the presence of other potassium counter ions. The ion selective electrode based on dibenzo-18-crown-6 exhibited a near Nernstian response for potassium phosphate over a wide concentration range of 5 × 10-5 mol/l-1 to 1 × 10-1 mol/l-1 with a low limit of detection of 3.2 × 10-6 mol/l-1. The resulting electrode exhibited a shelf life of 40 days with negligible drift. The ensemble was use used to determine K+ ions in a range of real samples the results of which showed a strong correlation with the data obtain from the same samples via atomic absorption spectroscopy. The use of dibenzo-18-crown-6 showed the potential towards a method for the quantitative determination of potassium phosphate in water samples.