1. Investigación

The complexity of the chemical composition of synthetic macromolecules has increased the need for more reliable analytical methodologies for characterizing these materials. CE has emerged as a powerful analytical tool able to provide useful information about the chemical properties of these complex molecules. Interestingly, such information can be in some cases complementary to that provided by other classical techniques. Thus, in this revision it has been demonstrated that CE is being used in their different modes (FSCE, CGE, MEKC, etc.) to successfully face the tremendous diversity that can be found analyzing synthetic polymers. One of the main characteristics of CE is that this technique makes possible to develop uniquely tailored separation procedures to analyze synthetic macromolecules of very different nature.

This review article addresses the different chiral capillary electrophoretic methods that are being used for the study and characterization of foods and food compounds (e.g., amino acids, organic acids, sugars, pesticides). An updated overview, including works published till December 2002, on the principal applications of enantioselective procedures together with their main advantages and drawbacks in food analysis is provided. Some anticipated applications of chiral electromigration methods in food characterization are also discussed.

A new physically adsorbed capillary coating for capillary electrophoresis-mass spectrometry (CE-MS) of basic proteins is presented, which is easily obtained by flushing the capillary with a polymer aqueous solution for two min. This coating significantly reduces the electrostatic adsorption of a group of basic proteins (i.e., cytochrome c, lysozyme, and ribonuclease A) onto the capillary wall allowing their analysis by CE-MS. The coating protocol is compatible with electrospray inonlzation (ESl)-MS via the reproducible separation of the standard basic proteins (%RSD values (n = 5) < 1 % for analysis time reproducibility and < 5% for peak heights, measured from the total ion electropherograms (flEs) within the same day). The LODs determined using cytochrome c with total ion current and extracted ion current defection were 24.5 and 2.9 fmol, respectively. Using this new coating lysozymes from chicken and turkey egg white could be easily distinguished by CE-MS, demonstrating the usefulness of this method to differentiate animal species. Even after sterilization at 1200C for 30 min, lysozyme could be detected, as well as in wines at concentrations much lower than the limit marked by the EC Commission Regulation. Adulteration of minced meat with 5% of egg-white could also be analysed by our CE-MS protocol.

Antioxidants from orange juice were determined by the combined use of countercurrent supercritical fluid extraction (CC-SFE) prior to reverse-phase liquic chromatography (RP-LC) or micellar electrokinetic chromatography (MEKC). The separation of antioxidants found in the SFE fractions was achieved by using a new MEKC method and a published LC procedure, both using diode array detection. The characterization of the different antioxidants was further done by LC-mass spectrometry. Advantages and drawbacks of LC and MEKC for analyzing the antioxidants found in the different orange extracts are discussed. Although LC yields higher peak area and slightly better reproducibility than MEKC, the latter technique provides information about the CC-SFE extracts in analysis times 7 times faster than by LC. This analysis advantage can be used for the quick adjustment of CC-SFE conditions, thus providing a fast way to obtain orange fractions of specific composition.

In this work a new method to detect the existence of chiral amino acids in orange juice is presented. The method employs â-cyclodextrins and micellar electrokinetic chromatography with laser-induced fluorescence (MEKC-LIF) to separate and detect L- and D-amino acids (L-aa and D-aa) previously derivatized with fluorescein isothiocianate (FITC). A systematic optimization of the chiral-MEKC conditions is done bringing about in less than 20 min a good separation of the main amino acids found in orange juice (i.e., Pro, Asp, Ser, Asn, Glu, Ala, Arg, and the nonchiral GABA, i.e., ç-aminobutyric acid). Using this procedure, the analysis time reproducibility for the 15 standard compounds (L-aa, D-aa, and GABA) has been determined to be better than 0.2% (n ) 5) for the same day and better than 0.7% (n ) 15) for three different days. Corrected peak area reproducibility is somewhat lower, providing values better than 3.3% (n ) 5) for the same day and 6.9% (n ) 15) for three different days. The limit of detection using this procedure was determined to be 0.86 attomoles for L-Arg. The optimized FITC derivatization method allows the easy and straightforward detection of amino acids in orange concentrates and juices (i.e., only centrifugation of diluted samples for 5 min is needed prior to their derivatization). D-Ala, D-Asp, D-Arg, and D-Glu were determined in orange juices and orange concentrates from different geographical origins using this new method. Moreover, the effect of different temperature treatments (50, 92, and 150 °C) on the content of D-aa in orange juice was evaluated.