Method development and validation for estimation of capsaicin in topical formulations by gas chromatography

This study presents, a novel, simple, rapid, and highly sensitive Gas Chromatography–Flame Ionization Detection (GC-FID) method developed for capsaicin estimation in marketed semi-solid topical analgesic formulations and validated according to ICH Q2 (R1). Capsaicin, an alkaloid of Capsicum species shows its analgesic effect through selective activation of the transient receptor potential vanilloid 1 (TRPV1) channel on nociceptive neurons. Sustained stimulation leads to desensitization and depletion of neuropeptides, resulting in attenuation of pain signalling. Accurate quantification of capsaicin in topical formulations is essential to ensure therapeutic consistency, especially in semi-solid matrices that contain multiple co-actives and potential analytical interferents. Although GC-based methods have been reported for capsaicin in food matrices and multi-component topical analyses, no rapid, dedicated GC-FID method has been described for selective quantification of capsaicin in commercial balm and gel formulations using conventional instrumentation. Chromatographic separation using an HP-5 capillary column yielded a sharp, well-resolved capsaicin peak having a tailing factor of 1.21, with a total run time 9.5 min. The method demonstrated excellent specificity, with no matrix interference, and exhibited linearity across 50–1000 µg/mL (R² = 1.000). The method has high sensitivity, with LOD of 7.2 µg/ml and LOQ of 21.8 µg/ml. Assay of commercial topical balm and gel formulation reveals a concentration of 0.015% to 0.018%. The proposed GC-FID method minimizes matrix interference, simplifies sample preparation, and enables rapid, cost effective analysis with a short run time, making it suitable for routine quality control and stability assessment of capsaicin-containing topical formulations.