A Novel All-Solid-State Levocetirizine-Selective Potentiometric Microsensor

There are five commonly used antihistamines, i.e., cetirizine, loratadine, fexofenadine, desloratadine, and levocetirizine. Among them, levocetirizine has emerged as one of the most effective options for treating allergic conditions. It is known for its fast relief, long-lasting action, and minimal side effects, and has also become a preferred choice for managing both mild and chronic allergies. Recognizing its importance in allergy treatment, researchers have now developed a new all-solid-state levocetirizine-selective microsensor, marking a significant advancement in drug testing and quality control.

This all-solid-state, simple design is cost-effective and accurate even with limited samples. The fabrication of the all-solid-state levocetirizine-selective microsensor involves two main stages. In the first stage, the solid contact layer is prepared by mixing 50% graphite, 35% epoxy, and 15% hardener by weight in tetrahydrofuran (THF) and stirring for about 20 minutes to achieve a uniform consistency. Copper wires with a 0.5 mm diameter and an exposed tip length of 0.2 mm are dipped 4-5 times into this mixture and left to dry at room temperature for 24 hours, forming a stable, conductive solid contact that eliminates the need for an internal reference solution.

In the second stage, the ion-selective membrane is prepared using a PVC-based cocktail containing 4-6% Levocetirizine Tetraphenylborate (LEV-TPB) as the ionophore, 1% KTpClPB as an additive, 26–27% PVC for structural support, and 67-69% plasticizer in 2.5 mL THF. The solid-contact wires are coated with the membrane mixture and allowed to dry for 12 hours at room temperature, resulting in a uniform, selective layer that enables the sensor to detect levocetirizine with high sensitivity, stability, and reproducibility.

The experimental setup for developing the LEV-selective microsensor involved precise instruments. Potentiometric measurements were carried out using a multi-channel potentiometer, with a Jenway 3040 pH meter to control solution acidity, a Shimadzu analytical balance for accurate weighing, a Kubota 4200 centrifuge for sample separation, and a BASi Ag/AgCl reference electrode for stability.

For characterization, a Bruker Avance III 400 MHz NMR analyzed the molecular structure of the LEV-TPB ion-pair, a Jeol JSM-6610 SEM with EDX examined surface composition, a Shimadzu FT-IR spectrophotometer identified chemical bonds, and a Thermo Scientific Genesys 180 UV–Vis spectrometer measured optical properties. Deionized water (18.6 MΩ) ensured sample purity.

The all-solid-state levocetirizine-selective microsensor was tested under steady-state conditions and demonstrated excellent potentiometric performance, with a response time of less than 10 seconds, a detection limit of 3.5 × 10⁻⁷ mol/L, and a super-Nernstian slope of 59.9 ± 0.6 mV/decade over a linear range of 10⁻⁶ to 10⁻² mol/L. The sensor remained stable for over seven weeks, operated optimally in a pH range of 4.0–8.0, and showed high selectivity, reliably distinguishing levocetirizine from interfering substances.

The all-solid-state microsensor offers advantages such as miniaturization, low cost, low dead volume, and improved slope, linear range, response time, pH tolerance, and detection limit, making it a valuable tool for accurate antihistamine detection and quality control in pharmaceuticals. Its results were also highly consistent with UV-Vis spectroscopy measurements, confirming its accuracy, reliability, and suitability for pharmaceutical applications.