Background: The most crucial factor in the production and enhancement of pharmaceuticals is the
dissociation constant since it enables us to comprehend a variety of chemical phenomena, such as
biological activity, absorption, and the degree of ionisation of a substance at different pH levels. The pKa
of a material is the pH at which it is 50% protonated.
Methods: The aim of this study is to have a better understanding of sitagliptine's molecular behavior. The
above study was performed by using UV-Visible Spectrophotometer. At first, alkaline buffer of different
pH range was prepared by adding 50.0 ml of 0.2M boric acid and potassium chloride in a 200-ml
volumetric flask. The volume was then raised to the necessary level with double-distilled water after
adding the prescribed quantity of 0.2M sodium hydroxide. The pH of the buffer was measured using a pH
metre. For Preparation of standard stock solution, 10mg of Sitagliptine was measured and transferred into
100ml volumetric flask containing 40ml of alkaline borate buffer at pH 8. Then it was sonicated for two
minutes to dissolve and then the volume was adjusted to 100 ml with same buffer to get 100?g/ml. 2ml of
the SSS were transferred into a second 10ml volumetric flask, and the volume was diluted with buffer pH
8 until the required concentration was achieved. Then this solution was scanned in the range of 200 to
Received 19th Oct. 2022; Revised 16th Nov. 2022; Accepted 1st April 2023; Available online 1st Dec. 2023 400nm with the help of UV-visible spectrophotometer (Pharmaspec-1700). The ?max was found to be
267nm. For Preparation of Tablet sample solution (TSS), 10 tablets of SGP was weighed and ground into
a fine powder. An accurately weighed portion of the powder equivalent to 10 mg was transferred into
different 12 nos of 100mlvolumetric flask containing 50ml of buffer and sonicated for 3 minutes and then
the volume was made up to the mark with 0.1 N HCl, 0.01 N HCl, 0.1 N NaOH, 0.01 N NaOH, alkaline
borate buffer pH 8, 8.4, 8.8 & 9.2. Then content of the flask was sonicated for 3minutes and then the
volume was made with the respective buffer. Whatmann filter paper 41 was used to filter the solutions.
Then 2ml of the tablet sample solution was transferred into different 12 nos 10ml volumetric flasks and
diluted up to the mark with the respective buffer to produce the sample solution strength of 20?g/ml.
Measure the absorbance reading of the tablet sample solution at 267nm. The Dissociation constant value
of the drug can be calculated by utilizing the below equation, i.e.,
pKa =pH +log
Where pH is the pH meter value, dm is the unionised molecule absorbance, di is the ionised molecule
absorbance, and d is the molecule absorbance in each of the tested buffers.
Results: The entire experiment was replicated on two different spectrophotometers by two different
people, along with the inter-day validation with same drug concentrations. The Log P experiment was
performed three times in order to acquire accurate and trustworthy data. Sitagliptine's pKa was roughly
calculated to be 9.2, since it is where the graph of the absorbance of the drug solution vs. pH's inflection
point was found to be at a pH value of 9.2. The presence of a single value of pKa for sitagliptine was
demonstrated by the absorbance curve at 267 nm. A single equilibrium in the Sitagliptine ionisation state
is supported by the absorbance diagram's typically linear appearance. The experiment also shows that
sitagliptine exhibits pH-dependent UV-absorption at buffers with a pH range of 8 to 12, which comprise
drugs at a concentration of 20 g/ml. The ruggedness of the investigation was confirmed in accordance
with the analytical method validation parameter.
Conclusion: The aforementioned experiment revealed that additional understanding of Sitagliptine's
(SGP) molecular behaviour was required. In the current work, the pKa and log P of sitagliptine were
calculated experimentally for the first time. pKa is the main physicochemical variable employed in drug
development. According to our findings, sitagliptine's pKa is inferred to be at 9.2. The fact that all of
these figures fall within a range of ± 0.25 shows that the data is accurate.
Keywords: Sitagliptine, pKa, Calibration Curve, Standard Stock Solution, Dissociation constant
Publication date: 01/12/2023
https://ijbpas.com/pdf/2023/December/MS_IJBPAS_2023_7626.pdf
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https://doi.org/10.31032/IJBPAS/2023/12.12.7626
