Nanoemulsion supported microemulsion electrokinetic chromatography coupled with selected preconcentration techniques as an approach for analysis of highly hydrophobic compounds.

In this paper, an oil-in-water (O/W) nanoemulsion (NE) prepared by water cold dilution of an O/W microemulsion (ME) was introduced as a sample matrix in microemulsion electrokinetic capillary chromatography (MEEKC) for the highly hydrophobic compounds analysis. Several model compounds with log PO/W values in the 4.1-10.9 range, from different chemical groups, including retinol, α-tocopherol, cholecalciferol, phylloquinone, menaquinone-7, dichlorodiphenyltrichloroethane, ivermectin have been tested. As a proof of the concept of NE formation, a dynamic light scattering technique was employed to determine the size distribution profile of NE particles. Moreover, due to relatively low conductivity of the NE matrix (50-100 times lower in comparison to the separation buffer) and a negative electric charge provided to hydrophobic compounds through NE dispersed phase, NE matrices have been combined with preconcentration techniques based on electrokinetic dosing, namely field amplified sample injection (FASI) and pressure assisted electrokinetic injection (PAEKI). The detection limits for vitamin K1 and K2-MK7 in the NE matrix in combination with FASI (NE-MEEKC-FASI) as well as PAEKI (NE-MEEKC-PAEKI) were up to 42.9 and 12.1 ng mL-1, respectively. In comparison to standard hydrodynamic injection for microemulsion sample matrix NE-MEEKC-PAEKI grant 45-fold improvement in signal sensitivity. The study presents an innovative approach, as it enables the use of preconcentration techniques for highly hydrophobic compounds (log PO/W > 4), which was not previously possible for implementation in the electromigration techniques. Likewise, the use of organic solvents has been reduced by using ME as a solvent for stock solutions and diluting with water prior to the analysis. The application to real samples was investigated using a dietary supplement containing vitamin K2-MK7 obtained from the fermentation product of soybeans.

Simultaneous determination of mitotane, its metabolite, and five steroid hormones in urine samples by capillary electrophoresis using ß-CD2 SDS1 complexes as hydrophobic compounds solubilizers.

Mitotane is a cytotoxic drug used in the treatment of inoperable adrenocortical carcinoma, it inhibits steroidogenesis as well, and therefore monitoring the level of steroid hormones in patients treated with mitotane is a crucial point of therapy. Hence, we have developed a simple, fast, and efficient electrophoretic method combined with reverse polarity sweeping as online preconcentration technique and dispersive liquid-liquid microextraction for the simultaneous determination of mitotane, its main metabolite DDA, and five steroid hormones (progesterone, testosterone, epitestosterone, cortisol, and corticosterone) in urine samples. In addition, a new sample matrix consisting of ß-CD2 SDS1 complexes for a high hydrophobic compounds solubilization was developed. Approach based on the application of ß-cyclodextrin and SDS complex of a ratio 2:1 allowed for hydrodynamic injection into the capillary of a solution containing both mitotane and other analytes. The detection limits of the analytes for the reverse polarity sweeping-dispersive liquid-liquid microextraction method were found to be in the range of 1.5-3 ng/mL, which were approximately 1000 times lower than in the conventional hydrodynamic injection (5 s, 0.5 psi) without any preconcentration procedure. All analytes were completely resolved in less than 13 min by uncoated silica capillary with an inner diameter of 75 µm (ID) × 60 cm. Electrophoretic separation was performed in reverse polarity with a voltage of -25 kV with a background electrolyte (BGE) consisting of 100 mM SDS, 25% ACN, 25 mM phosphate buffer (pH 2.5), and 7 mM ß-cyclodextrin.

Combination of large volume sample stacking with polarity switching and cyclodextrin electrokinetic chromatography (LVSS-PS-CDEKC) for the determination of selected preservatives in pharmaceuticals.

In this study, a large volume sample stacking (LVSS) with polarity switching (PS) and cyclodextrin electrokinetic chromatography (CDEKC) method has been developed for the simultaneous separation and determination of 8 preservatives: methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), isobutylparaben (IBP), sorbic acid (SA), benzoic acid (BA), p-hydroxybenzoic acid (PHBA) in pharmaceuticals. The effects of some typical parameters such as sample volume, applied voltage, composition and pH of the running buffer and organic modifier concentration were examined and optimized. Moreover, the impact of type and concentration of cyclodextrin as electrolyte modifiers was also investigated. The detection limits of analytes for the elaborated LVSS-PS-CDEKC method were found to be in 0.8-5 ng mL-1 range, which were around 500 times lower than normal CDEKC without preconcentration technique. All analytes were completely resolved in less than 11 min in an uncoated fused-silica capillary of 75 µm internal diameter (I.D) x 50 cm length. The electrophoretic separation was performed in a 2 mM α-cyclodextrin and 25 mM tetraborate system (pH = 9.3) with an applied voltage of 25 kV. The established method was validated and confirmed to be applicable for the determination of the preservatives in a quality control of pharmaceuticals.

Combination of field amplified sample injection and hydrophobic interaction electrokinetic chromatography (FASI-HIEKC) as a signal amplification method for the determination of selected macrocyclic antibiotics.

In this study, a field amplified sample injection (FASI) and hydrophobic interaction electrokinetic chromatography (HIEKC) method has been developed for the separation of five macrolide antibiotics: spiramycin, ivermectin, tylosin, josamycin, rapamycin, and one ansamycin drug - rifamycin. By the manipulation of both the sample and separation buffer compositions, their pH values and molarity, a systematic approach has been achieved to maximize analyte differential electrophoretic mobility and signal amplification. The impact of the sample solution composition and the injection mode on the signal amplification effect of the six tested antibiotics was also investigated. Moreover, the influence of the injection of the sample and the water plug on the quantity, symmetry and height of the analyte signal was demonstrated. All the analytes were completely resolved in less than 8 min in an uncoated fused-silica capillary of 75 µm internal diameter (I.D.) x 50 cm length. The electrophoretic separations were performed in a 60% (v/v) acetonitrile and 20 mM phosphate electrolyte system (pH 7.1) with an applied voltage of 25 kV. The established method was validated and confirmed to be applicable for the determination of the active ingredients in a quality control analysis.