Oil-In-Water Microemulsion Liquid Chromatography

Diuretics in Different Samples: Update on the Pretreatment and Analysis Techniques

Diuretics are drugs that promote the excretion of water and electrolytes in the body and produce diuretic effects. Clinically, they are often used in the treatment of edema caused by various reasons and hypertension. In sports, diuretics are banned by the World Anti-Doping Agency (WADA). Therefore, in order to monitor blood drug concentration, identify drug quality and maintain the fairness of sports competition, accurate, rapid, highly selective and sensitive detection methods are essential. This review provides a comprehensive summary of the pretreatment and detection of diuretics in various samples since 2015. Commonly used techniques to extract diuretics include liquid-liquid extraction, liquid-phase microextraction, solid-phase extraction, solid-phase microextraction, among others. Determination methods include methods based on liquid chromatography, fluorescent spectroscopy, electrochemical sensor method, capillary electrophoresis and so on. The advantages and disadvantages of various pretreatment and analytical techniques are elaborated. In addition, future development prospects of these techniques are discussed.

Aqueous liquid chromatography with mobile phases of sodium dodecyl sulphate and ionic liquid

In conventional reversed-phase liquid chromatography (RPLC) with hydro-organic solvents, basic cationic solutes yield retained, broad, asymmetric peaks, owing to their interaction with free anionic silanols in the stationary phase. RPLC mobile phases to which the anionic surfactant sodium dodecyl sulphate (SDS), or an ionic liquid (IL) are added, have been proposed as solutions, since these additives are able to block the silanol effect thus improving the chromatographic performance. With these additives, it is however necessary to increase the elution strength by adding an organic solvent, such as an alcohol or acetonitrile. A novel aqueous liquid chromatographic mode (in the absence of organic solvent) is here proposed, where the mobile phases contain only a mixture of aqueous solutions of SDS and an IL derived from 1-alkyl-3-methylimidazolium associated to chloride, both environmentally friendly. When these reagents are added, the anionic surfactant adsorbed on the stationary phase is able to attract the cationic solutes, whereas the adsorbed IL cation repels them. The combination of both effects (attraction and repulsion) allows the modulation of retention, by varying the IL/SDS ratio. Given the character of the additives, a type of green liquid chromatography is achieved. In this work, the chromatographic behavior of six basic compounds of pharmaceutical interest, the β-adrenoceptor antagonists acebutolol, atenolol, carteolol, metroprolol, oxprenolol and propranolol, is examined. In order to assess the chromatographic behavior of the mixed mobile phases containing SDS and IL, changes in retention, peak profile and resolution of mixtures of the analytes were explored at varying concentration of the additives.

Pickering emulsion prepared by nano-silica particles - A comparative study for exploring the effect of various mechanical methods

Pickering emulsions are eco-friendly, stabilized by solid particles, and have an essential role in leading industries. Although Pickering emulations have found several applications, surprisingly few investigations have attempted to explore the effectiveness of various mechanical processes for its production. To fill these gaps, the present investigation comprehensively examined the application of various Pickering emulsion preparation processes such as rotor-stator homogenization emulsification (R-SH), ultrasonic emulsification, and their combined processes by using nano-silica particles. The influences of emulsification time and intensity on emulsion droplets' distribution were analyzed as indicative factors. The kerosene/water nano-silica Pickering emulsion was utilized for all assessments. The obtained results demonstrated that the main distribution peak of the emulsion prepared by R-SH occurred where the chord length was greater than 40 μm. Micro-scale nano-silica-aggregates generated large droplets, while the fine-emulsion fraction was significantly increased after ultrasonic treatment. The experimental results showed that the emulsion prepared only by ultrasound needed substantial power to form a Pickering emulsion since the oil phase was difficult to disperse in the water phase. Finally, it was concluded that preprocessing by R-SH could form a stable and uniform emulsion speedily, which is essential for ultrasound emulsion preparation.

Studying the suitability of hybrid micelle liquid chromatography for estimating the lipophilicity of some partial dopamine agonists used to attain the reward circuit

Three micellar-based mobile phases were developed and optimized for the simultaneous determination of certain partial dopamine agonists that are used to overcome the withdrawal symptoms of abused drugs, namely aripiprazole, pramipexole and piribedil. The studied drugs were separated using micellar liquid chromatography, hybrid micellar liquid chromatography (HMLC) and microemulsion liquid chromatography (MELC). The three developed mobile phases were studied to estimate their suitability for the measurement of log p-values of the studied drugs. Experimental determination of log Pm/w values using the three mobile phases demonstrates that HMLC is the mobile phase of choice since the obtained practical log Pm/w values were in accordance with the reported log P values, and calculated log P and log D values. An explanation of the obtained results was presented based on the separation retention mechanism for each chromatographic technique. Furthermore, the effect of the pH and the column temperature in HMLC on the practical log Pm/w values was studied. To verify its suitability for experimental measurement of log Pm/w , HMLC was subjected to full validation according to the United States Pharmacopeia.

Performance and modelling of retention in microemulsion liquid chromatography

The capability of liquid chromatography with microemulsions (MEs) as mobile phases was studied for the analysis of four parabens (butylparaben, ethylparaben, methylparaben, and propylparaben) and seven β-adrenoceptor antagonists (acebutolol, atenolol, carteolol, metoprolol, oxprenolol, propranolol, and timolol). MEs were formed by mixing aqueous solutions of the anionic surfactant sodium dodecyl sulphate, the alcohol 1-butanol that played the role of co-surfactant, and octane as oil. In order to guarantee the formation of stable MEs, a preliminary study was carried out to determine the appropriate ranges of concentrations of the three components. For this purpose, mixtures of variable composition were prepared, and the possible separation of two phases (formation of an emulsion) was visually detected. The advantage offered by the addition of octane to micellar mobile phases, inside the concentration range that allows the formation of stable MEs, was evaluated by comparing the retention behaviour, peak profile and resolution of mixtures of the probe compounds, in the presence and absence of octane. The final aim of this work was the proposal of a mathematical equation to model the retention behaviour in microemulsion liquid chromatography. The derived global model that considered the three factors (surfactant, alcohol and oil) allowed the prediction of retention times at diverse mobile phase compositions with satisfactory accuracy (in the 1.1‒2.5% range). The behaviour was compared with that found with mobile phases without octane. The model also yielded information about the retention mechanism and revealed that octane, when inserted inside the micelle, modifies the interaction between solutes and micelles.

Comparison of surfactant-mediated liquid chromatographic modes with sodium dodecyl sulphate for the analysis of basic drugs

In reversed-phase liquid chromatography (RPLC), basic drugs are positively charged at the usual working pH range and interact with free anionic silanols present in conventional silica-based stationary phases. This translates into stronger retention and tailed and broadened peaks. This problem can be resolved by the addition of reagents to the mobile phase that are adsorbed on the stationary phase, avoiding the access of solutes to silanols. Among these additives, surfactants under micellar conditions have provided good silanol suppressing potency through the technique known as micellar liquid chromatography (MLC). The most common example of this is anionic sodium dodecyl sulphate (SDS). When SDS is at moderate concentration in the presence of high organic solvent content, micelles are not formed and the chromatographic mode is known as high submicellar liquid chromatography (HSLC). In contrast, the addition of an oil to an aqueous solution of SDS containing micelles gives rise to microemulsions in a chromatographic mode known as microemulsion liquid chromatography (MELC). A comprehensive comparison of the chromatographic behaviour of a set of basic β-adrenoceptor antagonists analysed by MLC, HSLC and MELC is carried out in this work, in terms of retention, peak shape and organic solvent consumption. The study shows that high submicellar eluents reduce retention and enhance efficiency with respect to conventional RPLC and MLC. Meanwhile, MELC allows reduced analysis times with less organic solvent with respect to HSLC. The narrower and more symmetrical peaks in MLC, HSLC and MELC, with respect to conventional RPLC, reveal the presence of silanol masking.