Separation and detection of charged and neutral biomolecules in plants and food matrices by capillary zone electrophoresis

Capillary Zone Electrophoresis (CZE), also known as free solution capillary electrophoresis, is an electromigration separation technique that uses continuous electrolyte solution systems and constant electric field strength throughout the length of a capillary tube, usually of fused silica, filled with an aqueous or nonaqueous background electrolyte solution. It is generally employed for microscale analytical separations of charged compounds, based on their electrophoretic mobility, that is the velocity at which charged compounds migrate toward the electrode of opposite sign in a considered medium per unit of the applied electric field. The methods mostly employed to separate uncharged compounds by CZE includes the use of a derivatization reaction performed before the electrophoretic separation or the incorporation into the BGE of a proper reagent capable to convert the neutral analyte into another charged molecule or complex. This communication illustrates and discusses the results of the studies we have performed to investigate the use of selected additives, complexing agents, and organic solvents on the separation by CZE of biomolecules occurring in plants and food matrices. Both coated and bare fused-silica capillary tubes have been employed and the investigated additives, complexing agents, and organic solvents have been incorporated into the continuous background electrolyte solution (BGE) employed for the separations of biomolecules at various pH values. The observed effects on selectivity, resolution and separation efficiency of charged and neutral biomolecules of large interest in phytochemistry and food analysis are evaluated and discussed. Also reported and discussed are the effects of the investigated BGE compositions on the formation of the electric double layer at the interphase between the BGE and the inner surface of the fused-silica capillary tube employed for the separations, from which it originates the electroosmotic flow (EOF). All the investigated approaches have been carried out using continuous electrolyte solutions, whose optimal composition has been selected on the basis of experimental evidence. Examples of the discussed investigations include the study on the influence of trifluoroethanol incorporated into the BGE on the electrophoretic mobility of phenolic compounds separated by CZE as borate complexes. Also examined is the use of a strong alkaline BGE (pH 12-13) that allows neutral carbohydrates to be totally ionized, selectively separated as anions and directly UV detected as products of the photochemical reaction taking place in the detection windows. Applications of the discussed approaches to the separation of biomolecules in plant extracts and food matrices by CZE are illustrated and discussed.