Determination of Ionization Constant Value of Pravastatin in Water and Water-Acetonitrile Binary Mixtures by RPLC Method

Öz

Reverse phase liquid chromatography (RPLC) is preferred for the determination of ionization/protonation (pKa) constants of compounds containing acidic and basic functional groups. The pKa value is an important parameter to predict the absorption, distribution, metabolism, excretion, toxicity (ADMET) properties of drugs. In this study, RPLC method was developed for the determination of pKa value of pravastatin in water-acetonitrile binary mixture and the chromatographic behavior of pravastatin was determined by changing the amount of acetonitrile in the mobile phase. The study was carried out in Nucleosil C4 (250×4,6 mm, 5 µm) column, at 37°C and at a constant flow rate of 1 mL/min. With the obtained retention data, the pKa of the compound was determined using nonlinear model. The pKa value of hydrophilic pravastatin in water was calculated using the mobile phase pKa values determined in different organic modifier-water mixtures and the macroscopic constants (mole fraction, dielectric constant, etc.) of acetonitrile, specific solvation interaction parameters between the solvent and the solute. It has been observed that this important physicochemical parameter calculated is compatible with the literature data.

Anahtar Kelimeler

• RPLC
• Carboxylic acid group
• Ionization constant
• Hydrophilic compound

Pravastatinin Su ve Su-Asetonitril İkili Karışımlarında İyonlaşma Sabiti Değerinin RPLC Metoduyla Belirlenmesi

Öz

Ters faz sıvı kromatografi (RPLC) yöntemi asidik ve bazik fonksiyonel grup içeren bileşiklerin iyonlaşma/protonasyon (pKa) sabitlerinin tayini için tercih edilmektedir. pKa değeri, ilaçların absorpsiyon, dağılım, metabolizma, atılım, toksitite (ADMET) özelliklerini tahmin etmeye yarayan önemli bir parametredir. Sunulan bu çalışmada, pravastatinin su-asetonitril ikili karışımında pKa değerinin tayini için RPLC metot geliştirilmiş ve asetonitrilin mobil fazdaki miktarının değişimiyle pravastatinin kromatografik davranışı da belirlenmiştir. Çalışma Nücleosil C4 (250×4,6 mm, 5 µm) kolonda, 37°C’de ve 1 mL/dakika sabit akış hızında gerçekleştirilmiştir. Elde edilen alıkonma verileriyle doğrusal olmayan model kullanılarak bileşiğin pKa değeri belirlenmiştir. Hidrofilik özellikte olan pravastatinin su ortamındaki pKa değeri farklı organik modifiyer-su karışımlarında tayin edilen mobil faz pKa değerleri ve asetonitrilin makroskopik sabitleri (mol kesri, dielektrik sabiti, vs.), çözücü-çözünen arasındaki spesifik solvasyon etkileşim parametreleri kullanılarak hesaplanmıştır. Hesaplanan bu önemli fizikokimyasal parametrenin literatür verileriyle uyumlu olduğu görülmüştür.

Anahtar Kelimeler

• RPLC
• Karboksilik asit grubu
• İyonlaşma sabiti
• Hidrofilik bileşik

Kaynakça

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