In recent years the nutritional and bioactive properties of foods are being intensively investigated with a view to control, in addition to food quality, their possible influence on human health. Because of this, there is a growing demand for rapid, selective, sensitive, and validated methods for analysis and quantification. Bioactive plant compounds include those with weak estrogenic activity (phytoestrogens), among which are the isoflavones. Some of the beneficial activities that have been attributed to isoflavones are anticarcinogenic activity, the prevention of cardiovascular disease, the improvement of bone health, and antioxidant activity. The objective of this work is to provide an updated review of the methods used in sample preparation and subsequent analysis for the determination of isoflavones in food samples, including both soybean and soy products, as well as other foods with low isoflavone contents. The review focuses on the most common sample preparation techniques used during the last 10 years, including both conventional solvent extraction and other more recent extraction techniques. Separation and detection methods, including current trends in liquid chromatography analysis, such as the use of monolithic columns or ultra-high-pressure liquid chromatography, are also discussed.

Capillary zone electrophoresis (CZE) in nonaqueous media and in the presence of ionic additives has been successfully applied to the determination of compounds that differ only slightly in their electrophoretic mobilities. Triazine herbicides of environmental interest were chosen as test compounds because they behave as very weak bases. CZE separation of these analytes (especially chlorotriazines) in aqueous solution is difficult due to the low pH required for their conversion into protonated cationic form (HA(+)). However, in mixed nonaqueous solvents, 50% (v/v) acetonitrile-methanol, the acid-base characteristics of these compounds are modified, yielding the protonated ionic species that is susceptible to migration when subjected to an electric field. A noteworthy increase in separation selectivity and resolution can be achieved by using ionic additives. Thus, in this mode of capillary zone electrophoresis, separation is based on ionic interactions between the charged analytes and the ionic additive present in the separation medium. These interactions contribute to enhancing mobility differences and to improving analyte separation. For the separation of chloro- and methylthiotriazines, 10 mM perchloric acid in 50% (v/v) acetonitrile-methanol and 20 mM SDS proved to be satisfactory, providing high resolution in short analysis times. The selectivity achieved was found to depend on the degree of association of the analyte with the ionic additive in the nonaqueous medium. This permits manipulation of the selectivity of the electrophoretic separations as a function of the type and concentration of the ionic additive and of the nature of the nonaqueous medium employed.

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CZE was assayed for the separation of carbamate pesticides susceptible to protonation (Pirimicarb, Carbendazim). Different electrophoretic media with high organic contents were explored, adequate separation and resolution being achieved when a BGE based on ACN with acetic acid in the presence of SDS as an ionic additive was used. With a view to increasing the sensitivity of the method, an in-capillary SPE step prior to the electrophoretic separation was developed. We employed a monolithic polymer formed in situ within the capillary as a medium for analyte retention. The synthesized monolithic bed exhibited high porosity and allowed samples to be loaded at flow rates of about 65 microL/min by applying a pressure of 12 bar. A 5-cm length of monolithic sorbent was used to preconcentrate the target analytes from aqueous samples. The analytes retained were eluted from the polymeric phase directly in the separation capillary with the same electrophoretic medium used for their further separation by CZE. For a 15-min preconcentration time, the in-line SPE-CZE approach proposed here permitted the determination of these pesticides in drinking water at a concentration level of 0.1 microg/L, as demanded by current EU legislation.