1. Investigación

An in-capillary sample preconcentration strategy based on solid phase extraction (SPE) technology coupled with capillary electrophoresis (CE) has been developed taking advantage of both techniques (SPE and CE). An in-line frit-free preconcentration device for capillary electrophoresis containing MCX beads, obtained from the corresponding Waters OASIS® cartridges, was prepared. The retention of the particles was based on the relative diameters of the particles, carefully selected, and the capillaries. An experimental preconcentration factor of 100 was found for the system. Conditions were optimised for 3-nitrotyrosine measurement in rat urine being 4.4 M spiked in the urine the lowest value detectable.

Capillary electrophoresis (CE) poses unique challenges in many different analytical applications, mainly to biological and complex samples and when only small amounts of sample are available, due to its low sample consumption. As a consequence, poor limits of detection are usually observed with this technique, especially with UV photodetectors. Minimal or no sample treatment is desirable in any analytical method to avoid external sources of contamination or errors and to provide a high throughput. On- and in-capillary sample pre-concentration strategies, based on solid-phase extraction (SPE) technology can take advantage of both techniques (SPE and CE), while avoiding sample contamination and tedious manipulations when the sample amount is an issue. Moreover, the combination can provide two-dimensional separations. This review collects the most recent strategies that merge SPE technology built on- and in-capillary pre-concentration for increasing sensitivity and/or selectivity.

Short chain organic acids play an important role in different areas such as biochemistry, clinical chemistry, or the food industry. The enantiomeric ratio of chiral metabolites is an important parameter for the understanding of metabolic processes and in many cases it can serve diagnostic purposes. On the other hand, the presence of racemates in food products could indicate the use of organic acids as additives; this is not always permitted and needs to be controlled. The short chain of these acids makes difficult the three point interaction generally accepted as necessary for chiral recognition. Relatively recent publications have demonstrated the feasibility of their direct chiral separation in capillary electrophoresis by various techniques utilizing exchange capillary electrophoresis, macrocyclic antibiotics, cyclodextrins, ion-pair method, and transition metal complexes. The present article describes existing methods and strategies proposed to advance these areas.

Fruit juices each have very distinct organic acids profiles that can be used as fingerprints for establishing authenticity. A method has been developed, optimised and validated for measuring by capillary electrophoresis citric, isocitric, malic and tartaric acids as authenticity markers in orange juices, without any sample treatment other than dilution and filtration. Final conditions were phosphate buffer 200 mM, pH 7.50, 214 kV as applied potential, and 57 cm length neutral capillary. Detection was direct UV at 200 nm. Different kinds and marks of orange juice, chosen from the great variety existent in the market, were analysed and clear differences could be found between them and just pressed orange juice.  2000 Elsevier Science B.V. All rights reserved.

This review article is a comprehensive survey of capillary electrophoresis methods developed for the measurement of short-chain organic acids and inorganic anions in a wide variety of matrices, such as food and beverages, environmental, industry, and other applications, as well as clinical applications in body fluids such as urine, plasma or cerebrospinal fluid. Details of sample pretreatment and of electrophoretic conditions have been collected in tables, arranged by the type of matrix. Strategies employed for method development for the analysis of these compounds by capillary electrophoresis in real samples are discussed.

A capillary electrophoresis method has been developed and validated for acetic, citric, fumaric, lactic, malic, oxalic, succinic, and tartaric acids plus the measurement of nitrate and sulfite ions in white and red wines. The separation was carried out in a neutral coated capillary. Separation was performed at 14 kV of applied potential. Temperature was maintained at 20 C. The background electrolyte used was 200 mM phosphate buffer at pH 7.50. Separation was obtained in less than 13 min. Validation parameters obtained for the method permit it to be considered adequate for routine analysis.

The control of degradation products is currently a critical issue to the pharmaceutical industry. A degradation product that appeared in alprazolam tablets during their stability assay, 7-chloro-1-methyl-5-phenyl-[1,2,4]triazolo[4,3-a]quinolin-4-amine, also named triazolaminoquinoline, was tested as possible candidate in the HPLC method employed for the study. The impurity showed the same retention time and spectra as the degradation product; but as all these compounds are very closely related, a confirmation with an independent technique was necessary, and CE was chosen for that purpose. Problems related to the adsorption of the analytes to the negatively charged silica surface were solved by employing a new polymeric capillary coating consisting of poly(3-aminopropylmethylsiloxane). The polymer provided EOF towards the anode, and the two compounds were separated in less than 8 min in a 60 cm total-length capillary, 75 mm id capillary with a BGE containing 50 mM phosphate buffer at pH 2.0 with 20% ACN. When the sample containing the degradation product was injected, the presence of triazolaminoquinoline was confirmed.