Novel ISE Modified with Synthesized Magnetite Nanoparticles for Sulfates Determination

Abstract

Potentiometric ISEs are one of the fastest developing sensors in electrochemistry due to their wide range of applications. They are used in the food industry, agriculture, environmental and drug analysis as they offer numerous advantages: high selectivity and sensitivity, low LOD, small size, easy handling, portability and low cost. We have therefore developed a solid-state ISE for the potentiometric determination of sulfate ions. The membranes are based on a mixture of barium sulfate, silver sulfide, polymer and metal oxide nanoparticles. The mass ratio of BaSO₄, Ag₂S and PTFE in the membranes was 1 : 1 : 2, with the addition of various metal oxide NPs, such as Fe₃O₄, α-Fe₂O₃, Al₂O₃ or ZnO, to the membrane composition. The membrane containing magnetite NPs showed a positive effect on the linear response range for sulfate anions. In particular, the membrane containing 0.6% magnetite NPs showed a linear potential change with a slope of 28.5 mV dec⁻¹, which is very close to the theoretical Nernstian value (29.6 mV dec⁻¹), with a regression coefficient of 0.9978 in the concentration range between 4.88 ∙ 10⁻⁵ mol L⁻¹ and 1.00 ⸱ 10⁻² mol L⁻¹ with LOD 4.40 ∙ 10⁻⁵ mol L⁻¹. Finally, none of the membranes showed response to barium ions even at high concentrations (≥ 1.00 ∙ 10⁻³ mol L⁻¹). These results confirm that our newly developed potentiometric sensor has a high membrane selectivity for the determination of sulfate ions and, most importantly, that it is a fast, reliable and cost-effective tool.