Experimental Design Methodologies for the Optimization of Chiral Separations: An Overview.

In this chapter, the application of design of experiments (DoE) for chiral separation optimization using supercritical fluid chromatography (SFC), liquid chromatography (LC), capillary electrophoresis (CE), and capillary electrochromatography (CEC) methods is reviewed. Both screening and optimization steps are covered, including a discussion of each aspect, such as factor-, level-, and response selection. Different designs are also presented, highlighting their applications.

Open-tubular capillary electrochromatography for the simultaneous determination of cadmium and copper in plants.

We discuss the separation and determination of cadmium and copper in plant samples such as Triticum durum (wheat) and Helianthus annuus (sunflower) using open tubular capillary electrochromatography with indirect detection. Before performing the analysis, the samples were digested by microwave-assisted methods using HNO3 . Regarding the electrophoretic system, several experimental parameters were previously evaluated such as the capillary surface, mobile phase composition, buffer, pH, and voltage applied. The baseline resolution of the studied metals was obtained within 8 min by using a capillary immobilized with carboxylic multi-walled carbon nanotubes and a background electrolyte composed of 6 mM imidazole, pH 4.0. The applied voltage and the temperature were set at 20 kV and 25°C, respectively. Precision, detection, and quantification limits, along with linearity were investigated. The limits of detection and quantification were 2.20 and 7.40 µg/kg, for Cu2 ⁺ and 0.05 and 0.20 µg/kg in the case of Cd2 ⁺. A good linearity was achieved over a concentration working range of 7.5-100 and 0.2-25 µg/kg for Cu2 ⁺ and Cd2 ⁺ accordingly. Recovery data for validation studies were found in a range of 98.2-101.5% for both analytes.

Photografted methacrylate-based monolithic columns coated with cellulose tris(3,5-dimethylphenylcarbamate) for chiral separation in CEC.

A chiral capillary monolithic column for enantiomer separation in capillary electrochromatography was prepared by coating cellulose tris(3,5-dimethylphenylcarbamate) on porous glycidyl methacrylate-co-ethylene dimethacrylate monolith in capillary format grafted with chains of [2(methacryloyloxy)ethyl] trimethylammonium chloride. The surface modification of the monolith by the photografting of [2(methacryloyloxy)ethyl] trimethylammonium chloride monomer as well as the coating conditions of cellulose tris(3,5-dimethylphenylcarbamate) onto the grafted monolithic scaffold were optimized to obtain a stable and reproducible chiral stationary phase for capillary electrochromatography. The effect of organic modifier (acetonitrile) in aqueous mobile phase for the enantiomer separation by capillary electrochromatography was also investigated. Several pairs of enantiomers including acidic, neutral, and basic analytes were tested and most of them were partially or completely resolved under aqueous mobile phases. The prepared monolithic chiral stationary phases exhibited a good stability, repeatability, and column-to-column reproducibility, with relative standard deviations below 11% in the studied electrochromatographic parameters.

Recent applications of nanomaterials in capillary electrophoresis.

Nanomaterials have found an important place in Analytical Chemistry and, in particular, in Separation Science. Among them, metal-organic frameworks, magnetic and non-magnetic nanoparticles, carbon nanotubes and graphene, as well as their combinations, are the most important nanomaterials that have been used up to now. Concerning capillary electromigration techniques, these nanomaterials have also been used as both pseudostationary phases in electrokinetic chromatography (EKC) and as stationary phases in microchip capillary electrophoresis (CE) and capillary electrochromatography (CEC), as a result of their interesting and particular properties. This review article pretends to provide a general and critical revision of the most recent applications of nanomaterials in this field (period 2010-2017).