Spectrophotometry, potentiometry and HPLC in determination of acidity constant for Cabergoline and Tadalafil

Abstract

Acidic dissociation constant (pKa) is an important physicochemical parameter in absorption, dissociation and elimination mechanisms of drugs in body. Various analytical methods are utilized for the determination of pKa values of pharmaceutical active ingredients, and potentiometry, spectrophotometry and HPLC are the most common methods. Cabergoline is dopaminergic ergoline derivative having a powerful and long-term prolactin reducing effect, which is used for the treatment of Parkinson disease. Tadalafil leads an increasing cGMP level in Corpus cavernous, during secretion of nitric oxide in sexual arousal. In the presented study, detection of pKa values for Cabergoline and Tadalafil by using potentiometry, spectrophotometry and HPLC was investigated. The pKa value for Cabergoline was respectively found to be 6.42, 6.05 and 6.20 by spectrophotometry, potentiometry and HPLC. Spectrophotometric pKa value was significantly different (p>0.05) from others, and potentiometry and spectrophotometry were appropriate for pKa value determination of Cabergoline. The pKa values for Tadalafil by potentiometry and spectrophotometry were found to be 3.52 and 3.44, respectively. But, in HPLC, no differentiation was observed in retention times of Tadalafil by increasing pH value of mobile phase. Developed methods for determination of pKa values for Cabergoline and Tadalafil demonstrated high repeatability values (RSD<%1). In this study, experimental pKa values for Cabergoline and Tadalafil from developed methods were compared with the values calculated by the common softwares and high-level divergences were observed.

A Novel Analytical Method for Simultaneous Quantification of Silodosin and Tadalafil by RP-HPLC

“…The main objective of chromatographic method is to develop a single RP-HPLC method for accurate quantification of Silodosin and Tadalafil. After detailed literature survey Silodosin available with two pKa (pKa1: 4.03, Nindoline ring and pKa2: 8.53, N-ethylaminopropyl group) [15]. The pKa values for Tadalafil were found to be 3.52 by potentiometry and 3.44 by spectrophotometry [16].…”

Developing Metal Complexes for Captopril Quantification in Tablets Using Potentiometric and Conductometric Methods

“…As an analytical application of potentiometric studies, the equivalence point of the produced titration curves was identified using the Gran plot . Sundry Gran plot applications have been published in the literature. − The goal of this work was to create a potentiometric process for assessing CAP in tablets directly using a Gran plot which was designed using data from a potentiometric investigation of the complexation equilibrium of CAP with various metal ions, especially Cr 3+ , Fe 3+ , La 2+ , Th 4+ , Co 2+ , Mn 2+ , Pd 2+ , Sr 2+ , Ti 2+ , and Zr 2+ .…”