Green chemistry approach for determination of ionization constant values of parabens by reversed phase liquid chromatography method

In this master's thesis, an environmentally friendly analytical method based on the principles of green chemistry was developed to determine the ionization constant (pKa) values of parabens using the reversed-phase liquid chromatography (RP-LC) method. In the study, an eco-friendly preliminary analysis protocol was developed, and analyses were performed using high-performance liquid chromatography (HPLC) with a UV detector. In this study, the determination of parabens (methylparaben, ethylparaben, propylparaben, and butylparaben) used in pharmaceuticals and cosmetics was carried out by reverse phase liquid chromatography (RPLC) method with a green chemistry approach. With the developed method, the ionization constant (pKa) values of parabens could be determined with high sensitivity, accuracy, and precision. In this thesis, the pKa values of selected parabens were determined in water-methanol binary mixtures containing 40%, 45%, 50% and 55% (v/v) methanol and in water-ethanol binary mixtures containing 30%, 35%, 40% and 45% (v/v) ethanol. Analyses were carried out on a Gemini NX (250x4.60 mm, 3.5 µm) column at 37°C. Mobile phases prepared with varying organic solvent concentrations and pHs in the range of 6-11.5 were used to determine the pKa values of the compounds. The flow rate in the study was set to 1 mL/min, and the wavelength of the compounds for determination was set to 254 nm. The pKa values of methylparaben, ethylparaben, propylparaben, and butylparaben, which are widely used in many areas today, in the aqueous environment were calculated using the mole fraction and dielectric constant values of the organic solvents used for determination. Additionally, the pKa values of parabens at 25 °C were estimated based on the Abraham solvation parameter model.