ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Nano-level fluorimetric determination of tizanidine via quenching of Acid Red 51 native fluorescence: application to tablet formulation and content uniformity study

Ahmed A. Abu-Hassan

Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Assiut Branch, Al-Azhar University, Assiut, Egypt

E-mail: Ahmedabuhassan@azhar.edu.eg

Received: 21 December 2025  Accepted: 2 April 2026

Abstract:

Tizanidine (TZN) is a centrally acting α2-adrenergic receptor agonist primarily prescribed for the management of spasticity related to multiple sclerosis and spinal cord injuries. The development of robust, sensitive, and cost-effective analytical methods for its quantification in pharmaceutical formulations and content uniformity remains a significant objective in pharmaceutical analysis. This study introduces a novel spectrofluorimetric approach for the determination of TZN, based on a quenching-based spectrofluorimetric method. This approach utilizes the intrinsic fluorescence of Acid Red 51 (AR51), which emits at a characteristic wavelength. The method is founded on the principle that the addition of TZN to an AR51 solution results in a quantifiable quenching of the dye’s native fluorescence intensity. This quenching effect is proportional to the concentration of TZN present, providing a reliable basis for its quantification. This strategy offers a distinct mechanistic pathway for analysis, bypassing the need for a derivatization reaction while maintaining the desired analytical performance for the determination of TZN in various samples. The strategy was rigorously validated by the directives of ICH guidelines. The calibration curve demonstrated excellent linearity over a concentration range of 50–1200 ng/mL. The limits of detection (LOD) and quantification (LOQ) were established at 15.6 and 47.0 ng/mL, respectively, indicating high sensitivity. The procedure was successfully applied to the determination of TZN in its commercial tablet formulations, the assessment of content uniformity, and the analysis yielding accurate and precise results.

Keywords: Tizanidine; Acid red 51; Spectrofluorimetric; Tablets; Content uniformity

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04871-w

Chemical Papers 80 (7) 8031–8039 (2026)