Spectrophotometric and spectrofluorimetric methods for the determination of saxagliptin and vildagliptin in bulk and pharmaceutical preparations

New simple and sensitive spectrophotometric and spectrofluorimetric methods have been developed and validated for the determination of saxagliptin (SAX) and vildagliptin (VDG) in bulk and pharmaceutical preparations. The spectrophotometric methods were based on derivatization of the investigated drugs with two reagents: 1,2-naphthoquinone-4-sulfonic acid sodium salt (NQS) and 4-chloro-7-nitrobenzofurazan (NBD-Cl). For further increase in the sensitivity, the D1 spectra of the reactions products were also recorded. For NQS reaction, Beer’s law was obeyed over the ranges of 5–30 and 7–45 μg mL^-1 for the absorbance readings; and 3–32 and 5–50 μg mL^-1 for the derivative readings of SAX and VDG, respectively. For NBD-Cl reaction, Beer’s law was obeyed over the ranges of 3–20 and 4.5–35 μg mL^-1 for the absorbance readings; and 1.5–25 and 2.5–40 μg mL^-1 for the derivative readings of SAX and VDG, respectively. Spectrofluorimetric methods were developed based on the fact that the derivatized investigated drugs with NBD-Cl reagent are highly fluorescent products. The fluorescence concentration plots were linear over the ranges of 0.02–0.25 and 0.03–0.37 μg mL^-1 for SAX and VDG, respectively. The fluorescence measurement enabled the detection of SAX and VDG at concentrations of about 3 and 7 ng mL^-1, respectively. The proposed methods have been validated and successfully applied to the determination of the investigated drugs in their pharmaceutical preparations. The results obtained were statistically compared to those obtained from reference methods.