Chromatographic part included the determination of sitagliptin in plasma using fluorimetric detection and in its ternay mixture with metformin and sitagliptin alkaline degradation product using ultraviolet detection, and the determination of vildagliptin in its binary mixture with its impurity, and the determination of pioglitazone in its binary mixture with metformin. Spectrofluorimetric part included the determination of sitagliptin in its binary mixture with metformin and in its ternary mixture with metformin and sitagliptin alkaline degradation product. Spectrophotometric part included the determination of sitagliptin in its binary mixture with metformin using zero order and first derivative methods and the determination of metformin in its binary mixture with sitagliptin using first derivative and derivative of the ratio spectra methods. Spectrophotometric part also included the determination of sitagliptin and vildagliptin using charge transfer reactions. Statistical comparison