A new phosphate ion selective electrode

This project describes the development of a new dibasic phosphate ion selective electrode. A series of neutral ion carriers that selectively complex phosphate ions were synthesized and tested for use in a phosphate ion selective electrode. The best phosphate ionophore was the macrocyclic polyamine (3-decyl-1,5,8-triazacyclodecane-2,4-dione, N$\sb3$-cyclic amine). The linear range of the phosphate ion selective electrode made with this ionophore is from 1 $\times$ 10$\sp{-6}$ to 0.1 mol/L, with a limit of detection of 2 $\times$ 10$\sp{-7}$ mol/L. The slope of response curve is near-Nernstian at $\sim$29 mV per concentration decade. Further, this electrode is not affected at all by changes in pH between 6 and 8, and is not greatly affected by changes in pH between 5 and 11. The selectivity pattern for this electrode is: HPO$\sbsp{4}{2-}$ $\gg$ Cl$\sp- >$ NO$\sbsp{3}{-} >$ SO$\sbsp{4}{2-}$ = Lac$\sp- \gg$ Ace$\sp-$. Benefits arising from this study are: (1) the development of a new orthophosphate selective electrode that has superior selectivity and sensitivity for dibasic orthophosphate (HPO$\sbsp{4}{2-}$); (2) a comprehensive review of the literature relevant to phosphate ion selective electrodes, including construction and response characteristics; (3) the evaluation of some of the phosphate ion selective electrodes described in the literature, including their construction and response characteristics; (4) the measurement of the activity of dibasic phosphate ions in hydroxyapatite solutions; (5) and, for the first time, the direct measurement of dibasic phosphate activities in complex biological fluids.