The antagonistic role of chaotropic hexafluorophosphate anions and imidazolium cations composing ionic liquids applied as phase additives in the separation of tri-cyclic antidepressants

Phase Behavior of Ionic Liquid-Based Aqueous Two-Phase Systems

As an environmentally friendly separation medium, the ionic liquid (IL)-based aqueous two-phase system (ATPS) is attracting long-term attention from a growing number of scientists and engineers. Phase equilibrium data of IL-based ATPSs are an important basis for the design and optimization of chemical reactions and separation processes involving ILs. This article provides the recent significant progress that has been made in the field and highlights the possible directions of future developments. The effects of each component (such as salting-out agents and ILs) on the phase behavior of IL-based ATPSs are summarized and discussed in detail. We mainly focus on the phase behavior of ATPSs by using ILs, expecting to provide meaningful and valuable information that may promote further research and application.

Control of retention mechanisms on an octadecyl-bonded silica column using ionic liquid-based mobile phase in analysis of cytostatic drugs by liquid chromatography

This study assesses the potential of using ionic liquids (ILs) as mobile phase additives to control the retention mechanism of four cytostatic drugs: doxorubicin hydrochloride (DOX), epirubicin hydrochloride (EPI), daunorubicin hydrochloride (DAU) and idarubicin hydrochloride (IDA). Chromatographic separations were performed on a C18 analytical column (Discovery C18 150 × 4.6 mm, 5 µm) using six IL anions and four methyl-substituted IL cations with different alkyl chain lengths (alone or with the additional methyl group on the aromatic ring), or with an allyl group added as a cationic substituent. Thus, a total of 17 different ILs were assessed. The aqueous formic acid solution and phosphate buffer were used to compare how mobile phase composition affected the behavior of the analyzed cytostatic agents in the presence of ILs. In addition, the impacts of IL concentration, phosphate buffer concentration, and phosphate buffer pH on the final results were also considered. The ability to change analyte retention without negatively impacting peak shape or analytical efficiency was also controlled via the tailing factor and number of theoretical plates. Based on the results, the tested ILs were classified as either effective or ineffective mobile phase additives for separation of anthracyclines and identification by LC-FL technique.

Ultra-high performance separation of basic compounds on reversed-phase columns packed with fully/superficially porous silica and hybrid particles by using ultraviolet transparent hydrophobic cationic additives

The use of the tetrabutylammonium additive was investigated in the ultra-high performance reversed-phase liquid chromatographic elution of basic molecules of pharmaceutical interest. When added to the mobile phase at low pH, the hydrophobic tetrabutylammonium cation interacts with the octadecyl chains and with the residual silanols, thus imparting a positive charge to the stationary phase, modulating retention and improving peak shape of protonated basic solutes. Two sources of additive were tested: a mixture of tetrabutylammonium hydroxide/trifluoroacetic acid and tetrabutylammonium hydrogen sulfate. Retention and peak shape of 11 basic pharmaceutical compounds were evaluated on commercially available ultra-fast columns packed with octadecyl stationary phases (Ascentis Express C18 2.0 µm, Acquity BEH C18 1.7 µm, Titan C18 1.9 µm). All columns benefit from the use of additive, especially tetrabutylammonium hydrogen sulfate, providing very symmetric peaks with reasonable retention times. Focusing on the probe compounds amitriptyline and sertraline, efficiency and asymmetry values were investigated at increasing retention factor. The trend is very different to that obtained in reversed-phase conditions and the effect lies in the complex molecular interaction mechanisms based on hydrophobic and ion exchange interactions as well as electrostatic repulsion.

The Influence of Ionic Liquids on the Effectiveness of Analytical Methods Used in the Monitoring of Human and Veterinary Pharmaceuticals in Biological and Environmental Samples-Trends and Perspectives

Recent years have seen the increased utilization of ionic liquids (ILs) in the development and optimization of analytical methods. Their unique and eco-friendly properties and the ability to modify their structure allows them to be useful both at the sample preparation stage and at the separation stage of the analytes. The use of ILs for the analysis of pharmaceuticals seems particularly interesting because of their systematic delivery to the environment. Nowadays, they are commonly detected in many countries at very low concentration levels. However, due to their specific physiological activity, pharmaceuticals are responsible for bioaccumulation and toxic effects in aquatic and terrestrial ecosystems as well as possibly upsetting the body's equilibrium, leading to the dangerous phenomenon of drug resistance. This review will provide a comprehensive summary of the use of ILs in various sample preparation procedures and separation methods for the determination of pharmaceuticals in environmental and biological matrices based on liquid-based chromatography (LC, SFC, TLC), gas chromatography (GC) and electromigration techniques (e.g., capillary electrophoresis (CE)). Moreover, the advantages and disadvantages of ILs, which can appear during extraction and separation, will be presented and attention will be given to the criteria to be followed during the selection of ILs for specific applications.

Analysis of antisense oligonucleotides with the use of ionic liquids as mobile phase modifiers

The main goal of this study was the investigation of the impact of several ionic liquids, commonly used as free silanol suppressors, on the retention and separation of phosphorothioate oligonucleotides. Three various stationary phases (octadecyl, octadecyl with embedded polar groups and pentafluorophenyl) as well as ionic liquids with the concentration range of 0.1-7 mM were used for this purpose. The results obtained during this study showed that the increase in concentration of ionic liquids results in increasing retention of the oligonucleotides. Such an effect was observed regardless of the stationary phase used. Moreover, elongation of the alkyl chain in the structure of ionic liquids caused an increase of antisense oligonucleotide retention factors. The results obtained during retention studies confirmed that addition of ionic liquids to the mobile phase influences antisense oligonucleotide retention in a way similar to the case of commonly used ion pair reagents such as amines. A method of oligonucleotide separation was also developed. The best selectivity was obtained for the octadecyl stationary phase since separation of mixtures of antisense oligonucleotides and their metabolites differing in sequence length was successful. It has to be pointed out that ionic liquids were used for the first time as mobile phase additives for oligonucleotide analysis.