Design and Construction of a Novel and an Efficient Potentiometric Sensor for Determination of Sodium Ion in Urban Water Samples

Sodium ions are one of the essential cations for various activities in the human body to control fluid levels, blood pressure, and nerve and muscle functions. Sodium-ion is a highly soluble chemical that small amounts of it can be absorbed by the body through water intake. However, consuming an excess amount of sodium ions can cause problems in the body. Therefore, it is vital to measure sodium ions in water samples. A novel and cheap potentiometric sensor was developed to measure trace amounts of sodium ions in real water samples. For the purpose, four effective components in the Nernstian response of the sensor, including 1-Hexyl-3-methyl imidazolium hexafluorophosphate as an ionic liquid, 1, 4 Diaminoanthraquinone (DAQ) as an ionophore, graphene oxide nanosheets, and paraffin oil as a binder were optimized using a response surface methodology (RSM) based on central composite design. The optimum percentages of paraffin, ionic liquid, ionophore, and graphene oxide to prepare the sensor were 13.34, 11.40, 3.21, and 2.16 %, respectively. Under the best percentage of electrode components, the potentiometric sensor showed a suitable slope of 59.2 mV decade-1 over a wide Na+ concentration range (10^-6-10^-2 mol L^-1) with a proper detection limit of 8.97×10^-7 mol L^-1. The sensor can be applied to measure sodium ions in a pH range of 4 to 8. The optimized geometry of the complex formed between sodium ion and the ionophore was investigated using the density functional theory (DFT) methods.