Green spectrophotometric methods for the determination of metformin–curcumin combination: ICH validation and preliminary bioanalytical applications

Abstract The combined therapeutic use of Metformin and Curcumin has attracted growing interest in diabetes management, owing to metformin’s glucose-lowering effect and curcumin’s antioxidant and anti-inflammatory activities. This clinical relevance necessitates reliable analytical methods for their simultaneous determination. In this study, three simple, selective, and cost-effective complementary spectrophotometric methods were developed and validated for the analysis of metformin and curcumin in dosage forms and human plasma. A zero-order spectrophotometric method enabled the selective determination of curcumin, while a first-derivative method allowed simultaneous quantification of both analytes with improved spectral resolution. A ratio subtraction method was also established for selective metformin determination in the presence of curcumin, effectively resolving spectral overlap without prior separation. All methods exhibited excellent linearity over the concentration range of 0.5–20.0 µg mL − 1 ( r ≥ 0.999). The methods also demonstrated high analytical sensitivity, with limits of detection and quantitation ranging from 0.08 to 0.15 µg mL − 1 and 0.23 to 0.45 µg mL − 1 , respectively. Validation following ICH guidelines confirmed satisfactory accuracy, precision, and selectivity. Statistical comparison with reference methods using Student’s t-test and F-test showed no significant differences at the 95% confidence level. The proposed methods were successfully applied to the determination of both drugs in raw materials, metformin pharmaceutical formulations spiked with curcumin, and spiked human plasma, demonstrating excellent accuracy and precision, with recoveries ranging from 98.73% to 101.06% and RSD values not exceeding 1.50%. Greenness assessment demonstrated environmental compatibility, supporting their use as sustainable analytical tools for routine quality control and bioanalytical applications.