Comparison of Classical and Green RPLC Methods in the Determination of pK Values of Some Piperazine Group Antihistamines.

In this study, protonation constant values and liquid chromatographic behaviors of hydrophobic cyclizine, chlorcyclizine, hydroxyzine, cinnarizine, cetirizine, meclizine, and buclizine in some water-organic solvent binary mixtures were examined for the first time using classical and green reverse phase liquid chromatography methods. In the isocratic study, the relationship of the retention time and mobile phase pH in water-organic solvent binary mixtures containing acetonitrile (45, 50, 55, 60, 65%, v/v), methanol (60, 65, 70, 75%, v/v) and ethanol (45, 50, 55, 56, 59, 60, 62, 65%, v/v) were determined at 37 °C. In the study, XBridge C18 and Gemini NX C18 columns suitable for the chemical properties of basic compounds were used.

Development of liquid chromatographic and UV-visible spectrophotometric methods for determination of pK values of folic acid antimetabolites.

In this study, the values of ionization/protonation constants (pK) of pemetrexed and raltitrexed, which are folic acid antimetabolites, were determined by reversed-phase liquid chromatography (RPLC) and UV-visible spectrophotometric methods at 25 °C. The pKass values were evaluated by retention time (t) in binary acetonitrile-water mixtures with acetonitrile (ACN) contents of 13%, 15%, 17% and 20% (v/v) for the RPLC method and 13%, 15% and 17% (v/v) for the spectrophotometric method. The aqueous pK values (pKaww) of the studied compounds were calculated from the pKass value using the macroscopic parameters (mole fraction and dielectric constant), which play an important role in solvent properties.

Estimation of thermodynamic acidity constants of some penicillinase-resistant penicillins.

In this work, thermodynamic acidity constants (pssKa) of methicillin, oxacillin, nafcillin, cloxacilin, dicloxacillin were determined with reverse phase liquid chromatographic method (RPLC) by taking into account the effect of the activity coefficients in hydro-organic water-acetonitrile binary mixtures. From these values, thermodynamic aqueous acidity constants of these drugs were calculated by different approaches. The linear relationships established between retention factors of the species and the polarity parameter of the mobile phase (ET(N)) was proved to predict accurately retention in LC as a function of the acetonitrile content (38%, 40% and 42%, v/v).

Determination of chromatographic dissociation constants of some carbapenem group antibiotics and quantification of these compounds in human urine.

The dissociation constant values (s (s) pKa ) of some carbapenem group drugs (ertapenem, meropenem, doripenem) in different percentages of methanol-water binary mixtures (18, 20 and 22%, v/v) were determined from the mobile phase pH dependence of their retention factor. Evaluation of these data was performed using the NLREG program. From calculated pKa values, the aqueous pKa values of these subtances were calculated by different approaches.

Determination of chromatographic and spectrophotometric dissociation constants of some beta lactam antibiotics.

In this work, dissociation constants values of seven beta lactam antibiotics in water and acetonitrile-water mixtures using spectrophotometric and reversed phase liquid chromatography methods were determined. The dissociation constant values of these compounds were calculated by NLREG and STAR programs. Aqueous pK(a) values of beta lactam antibiotics were calculated with extrapolation by means of the Yasuda-Shedlovsky and mole fraction equations.