Different strategies for the preconcentration and separation of parabens by capillary electrophoresis

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Progress in on-line, at-line, and in-line coupling of sample treatment with capillary and microchip electrophoresis over the past 10 years: A review

The review presents an evaluation of the development of on-line, at-line and in-line sample treatment coupled with capillary and microchip electrophoresis over the last 10 years. In the first part, it describes different types of flow-gating interfaces (FGI) such as cross-FGI, coaxial-FGI, sheet-flow-FGI, and air-assisted-FGI and their fabrication using molding into polydimethylsiloxane and commercially available fittings. The second part deals with the coupling of capillary and microchip electrophoresis with microdialysis, solid-phase, liquid-phase, and membrane based extraction techniques. It mainly focuses on modern techniques such as extraction across supported liquid membrane, electroextraction, single drop microextraction, head space microextraction, and microdialysis with high spatial and temporal resolution. Finally, the design of sequential electrophoretic analysers and fabrication of SPE microcartridges with monolithic and molecularly imprinted polymeric sorbents are discussed. Applications include the monitoring of metabolites, neurotransmitters, peptides and proteins in body fluids and tissues to study processes in living organisms, as well as the monitoring of nutrients, minerals and waste compounds in food, natural and wastewater.

In-line molecularly imprinted polymer solid phase extraction-capillary electrophoresis coupled with tandem mass spectrometry for the determination of patulin in apple-based food

We present a simple and sensitive method for the determination of patulin at µg·kg^-1 level in apple-based products. Our method relies on the application of an in-line molecularly imprinted polymer solid-phase extraction microcartridge in capillary electrophoresis coupled with mass spectrometry. Capillary zone electrophoresis method has been developed and parameters affecting the in-line process have been carefully optimized. Validation parameters were assessed for patulin, giving LOQ of 1 µg·kg^-1 and linearity range 1-100 µg·kg^-1 with R² ≥ 0.997. The LOQ was below the maximum content of patulin requested by the European Union in this type of products. The precision of the peak area and the migration time were less than 14.9 and 1.6%, respectively. Patulin has been analyzed in the presence of 5-hydroxymethylfurfural, which is the main interference in this kind of matrix. The method was applied to assay patulin content in various apple-based products.

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.

Trace determination of tetracyclines in water samples by capillary zone electrophoresis combining off-line and on-line sample preconcentration

In this work, a sensitive and reliable method using capillary zone electrophoresis with UV detection has been developed for trace determination of tetracycline antibiotics in river, spring, and ground waters. A solid-phase extraction method using Oasis HLB was applied for off-line preconcentration and cleanup of water samples, in combination with an on-line preconcentration methodology named large volume sample stacking with polarity switching. Different parameters were optimized in order to obtain an adequate separation combined with the highest sensitivity, using 75 mM sodium carbonate (pH 10) and 1 mM EDTA as separation buffer, applying a voltage of 25 kV at 25°C. The samples were injected in water at 1 bar for 1 min, applying then -25 kV and starting the sample stacking. Sample matrix removal from the capillary was controlled by monitoring the electric current (when the 95% of the separation current is reached the stacking process is completed). The applied voltage was then switched from negative to a positive value of 25 kV in order to separate the compounds. Under optimum conditions, sensitivity enhancement factors ranged from 303 to 428 for the studied compounds. The combination of both off-line and on-line preconcentration procedures provided a total sensitivity enhancement factor about 20 000, obtaining detection limits from 67 to 167 ng/L. The precision (intra- and interday), expressed as %RSD was below 12%. Recoveries obtained from river, spring, and ground waters ranged from 87 to 96%. Thus, this procedure is suitable for monitoring these compounds in water samples.

Simultaneous determination of multiclass preservatives including isothiazolinones and benzophenone-type UV filters in household and personal care products by micellar electrokinetic chromatography

In this work, a simple and reliable micellar electrokinetic chromatography method for the separation and quantification of 14 preservatives, including isothiazolinones, and two benzophenone-type UV filters in household, cosmetic and personal care products was developed. The selected priority compounds are widely used as ingredients in many personal care products, and are included in the European Regulation concerning cosmetic products. The electrophoretic separation parameters were optimized by means of a modified chromatographic response function in combination with an experimental design, namely a central composite design. After optimization of experimental conditions, the BGE selected for the separation of the targets consisted of 60 mM SDS, 18 mM sodium tetraborate, pH 9.4 and 10% v/v methanol. The MEKC method was checked in terms of linearity, LODs and quantification, repeatability, intermediate precision, and accuracy, providing appropriate values (i.e. R(2) ≥ 0.992, repeatability RSD values ˂9%, and accuracy 90-115%). Applicability of the validated method was successfully assessed by quantifying preservatives and UV filters in commercial consumer products.