Comparative analysis of a bulk optode based on a valinomycin ionophore and a nano-optode in micelles with pluronic F-127 for the quantification of potassium in aqueous solutions.

Abstract

In this work, two types of optical sensors were prepared for the quantification of potassium: the bulk optode (BO) and nano-optode (NO). The BO was prepared using three main components: the ionophore valinomycin, the ion exchanger tetrakis(4-chlorophenyl) potassium borate (K-TCPB), and the chromoionophore ETH 5294 (CHI). The optimal composition was found to be in a ratio of [1 : 1 : 1]. The NO was prepared by miniaturizing the BO through sonication in surfactant Pluronic F-127. The working range for the linear calibration model of BO was from 10^-6 to 1.0 M K⁺ with a LOD_BO = 0.31 μM, meanwhile for NO was from 10^-4 to 1.0 M K⁺ with a LOD_NO = 30.3 μM. Both optodes were tested for selectivity towards K⁺ in the presence of alkaline and alkaline earth ions, with a selectivity coefficient > 1.0. Furthermore, precision and stability studies of BO and NO were performed for three levels of K⁺ concentrations, 10^-6, 10^-3, 1.0 M for BO and 10^-4, 10^-2, 1.0 M for NO, showing a good homogeneity of the NO in the whole concentration range. However, an excessive variability was obtained for BO at 1.0 M K⁺. Therefore, the NO represents a potential tool for quantification of K⁺.