title: The influence of salt chaotropicity, column hydrophobicity and analytes' molecular properties on the retention of pramipexole and its impurities.
abstract: The aim of this study was to examine the interaction of the chaotropic salts of different position in Hofmeister series (CF3COONa, NaClO4, NaPF6) added to the mobile phase with the stationary phases of different hydrophobicity (C8 and C18 XTerra(®) columns), as well as their common influence on the retention behavior of pramipexole and its structurally related impurities. The extended thermodynamic approach enabled the understanding of the underlying separation mechanism. Comparing six different column-salt systems it was observed that general system hydrophobicity presented by salt chaotropicity and column hydrophobicity favors stationary phase ion-pairing over the ion-pair formation in the eluent. Further, an attempt was made to describe the influence of analytes' nature on their retention behavior in such chromatographic systems. An analysis is performed in order to select and elucidate the molecular descriptors (electrostatical, quantum-chemical, geometrical, topological, and constitutional) that best explain the experimental evidence and findings obtained by the thermodynamic approach. The results of this analysis suggest that analytes' charge distribution and its complementarity to the structure of the electric double layer formed on the surface of the stationary phase upon the addition of chaotropic additives can be useful for understanding the differences in retention of structurally related analytes. These findings provide a novel understanding of the interactions between all the components of the chromatographic system containing chaotropic additive and a good basis for further investigations suggesting the development of generally applicable predictors in structure-retention relationship studies in related chromatographic systems.
authors: University of Belgrade-Faculty of Pharmacy, Department of Drug Analysis, Vojvode Stepe 450, Belgrade, Serbia.
authors: Ana
authors: A
authors: Vemić
authors: University of Belgrade-Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Vojvode Stepe 450, Belgrade, Serbia.
authors: Marko
authors: M
authors: Kalinić
authors: University of Belgrade-Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Vojvode Stepe 450, Belgrade, Serbia.
authors: Slavica
authors: S
authors: Erić
authors: University of Belgrade-Faculty of Pharmacy, Department of Drug Analysis, Vojvode Stepe 450, Belgrade, Serbia. Electronic address: andja@pharmacy.bg.ac.rs.
authors: Anđelija
authors: A
authors: Malenović
authors: University of Belgrade-Faculty of Pharmacy, Department of Physical Chemistry and Instrumental Methods, Vojvode Stepe 450, Belgrade, Serbia.
authors: Mirjana
authors: M
authors: Medenica
mesh_terms: D052160:Benzothiazoles / Q000032:analysis* / Q000302:isolation & purification; D002853:Chromatography, Liquid; D005463:Fluoroacetates / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D010472:Perchlorates / Q000737:chemistry; D000077487:Pramipexole; D011789:Quantum Theory; D012492:Salts / Q000737:chemistry*; D017670:Sodium Compounds / Q000737:chemistry; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D052160:Benzothiazoles; D005463:Fluoroacetates; D010472:Perchlorates; D012492:Salts; D017670:Sodium Compounds; D000077487:Pramipexole; C031068:sodium perchlorate; C014815:fluoroacetic acid
keywords: Chaotropic salts; Column hydrophobicity; Molecular descriptors; Pramipexole; Thermodynamic approach