Phosphates have recently received special attention with respect to their impact on the global environment. The availability of mined phosphate for fertilizers is rapidly fading and the inability of soil to hold the phosphates has led to eutrophication in natural waters. Thus, efforts have been made to recover phosphates from waste water and solid biowaste. These recovery efforts rely on the ability to detect/quantify the amount of phosphate in water and therefore, many electrochemical and optical sensors have been explored. In particular, there is growing interest in H2PO4- specific molecular sensors because the mono-anion is the dominant species in aqueous media at neutral and moderately acidic pH. The citric acid/phosphate buffer systems present an excellent opportunity to study the pH-dependence of phosphate concentrations in aqueous solution. The dynamical approach is employed to determine equilibrium species concentrations for the buffer system comprised of citric acid (H3Cit) and dibasic sodium phosphate (Na2HPO4). The dynamical approach entails the solution of a system of ordinary differential equations describing the kinetic rate equations and considers ionic strength (IS) dependence using Debye-Hückel Theory. The results are compared to two experimental data sets and demonstrate that the dynamical approach is a convenient, flexible, and accurate method for the calculation of all species concentrations in a complex acid/base equilibrium at various acidities and ionic strengths. We report the simulated pH profile and the equilibrium concentrations of the non-hydrogen species (Figure 1) and discuss the effects of ionic strength (IS) on the equilibrium distribution.

Toward quantitative H2PO4- sensing: Simultaneous determination of all species concentrations in multi-equilibria of aqueous solutions containing dihydrogen phosphate

255th National Meeting (2018)

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