Modification of a novel polymer inclusion membrane sensor for sensitive and selective detection of holmium in diverse real samples

A novel bulk sensor membrane with exceptional selectivity and sensitivity has been designed for detecting trace levels of holmium ions (Ho3+) through the application of a polymer-based inclusion membrane (PIM). This innovative membrane has been examined for its effective-ness in analyzing Ho3+ in biological, and environmental samples. The polymer inclusion membrane (PIM) is composed of 30% di(2-ethylhexyl)phosphoric acid (D2EHPA) as the transport carrier, 60% poly(vinyl chloride) (PVC) serving as the structural polymer, 7.0% o-nitrophenyl octyl ether (o-NOPE) functioning as the plasticizer, and 3.0% Solochrome Black T (SBT) as the colorimetric reagent specifically for Ho3+ detection. In this research, Ho3+ ions are absorbed into the PIM forming an Ho3+-D2EHPA complex, which then interacts with SBT, resulting in a pink Ho3+-SBT complex (λmax = 587 nm). The impact of various parameters on the fabrication of the PIM was utilized such as pH levels, the quantity of additives and SBT, and response time, all of which significantly influence the sensor's performance. Under optimal conditions, the sensor membrane demonstrates a quantification limit (LOQ) of 6.0 ng mL−1 and a detection limit (LOD) of 1.8 ng mL−1. The developed membrane sensor demonstrates outstanding durability, consistency, and an extended operational lifespan, making it highly suitable for the precise and reliable measurement of Ho³+ ion levels. It was efficiently regenerated using a 0.1 M HCl solution, ensuring a reversible and repeatable response with a relative standard deviation (RSD) of at least 1.90%. Moreover, the SBT-integrated PIM sensor was effectively utilized for identifying Ho3+ ions in actual biological and environmental specimens.