Voltammetric analysis of europium at screen-printed electrodes modified with salicylamide self-assembled on mesoporous silica

Mercury-free sensors for europium (Eu³⁺) assay based on the chemical modification of screen-printed carbon electrodes (SPCEs) with self-assembled salicylamide on mesoporous silica (Sal-SAMMS) have been developed. The preconcentration of Eu³⁺ at SAMMS-based sensors utilizes the binding affinity of the salicylamide and Eu³⁺, accomplished at open circuit potential without electrolyte and solution de-gassing. Optimal Eu detection was obtained after 3-5 min preconcentration in Eu solution (pH 2-6), electrolysis at -0.9 V for 60 s in a new medium (0.1-0.2 M NH₄Cl, pH 3.5), followed by a square-wave voltammetric detection of Eu in the same electrolyte. Attributed to the strong covalent bonding of the functional groups on mesoporous silica and silane cross-linking, the SAMMS-modified SPCEs with a built-in 3-electrode system can be re-used for tens of measurements with minimal degradation, enabling the establishment of the calibration curve and lowering the costs. A linear calibration curve was found in the range of 75 to at least 500 ppb Eu³⁺ after 5 min preconcentration. The experimental detection limit was 10 ppb after 10 min preconcentration, which can be improved with increased preconcentration time. Reproducibility (% RSD) of 100 ppb Eu²⁺ was 10% for a single sensor and 10% for 5 sensors, which can be improved through the precision of sensor manufacturing, in which SAMMS modification can be made in-situ.