Analytical and bioactivity-based evaluation of Callistemon citrinus: HPTLC fingerprinting, marker quantification, and...

Callistemon citrinus is a medicinal plant with recognized antioxidant and therapeutic potential; however, comparative phytochemical standardization of its vegetative remains limited. The present study aimed to establish an analytical-bioactivity correlation through HPTLC fingerprinting, marker quantification, and antioxidant evaluation of hydroalcoholic extracts of C. citrinus leaves (CLE) and flowers (CFE). Total phenolic and flavonoid contents were determined using colorimetric methods, while quercetin and gallic acid were quantified by validated HPTLC analysis following ICH Q2(R1) guidelines. Antioxidant potential was assessed using DPPH, ABTS, and FRAP assays. Distinct chromatographic fingerprints demonstrated organ-specific phytochemical variation. CLE showed higher total phenolic (18.19 ± 0.10 mg GAE/g) and flavonoid content (16.35 ± 3.91 mg QE/g) than CFE. Quercetin was detected in both extracts with higher concentration in leaves, whereas gallic acid was observed primarily in flowers. Consistent with these findings, CLE exhibited stronger antioxidant activity in chemical assays. The validated HPTLC method demonstrated satisfactory linearity, precision, accuracy, and sensitivity, providing a reliable approach for phytochemical standardization. These findings highlight the relevance of integrating chromatographic profiling with bioactivity evaluation and suggest that C. citrinus leaves may represent a promising source of antioxidant phytoconstituents for future pharmaceutical and nutraceutical applications.