Capillary electrophoresis (CE) has been proven to be a highly efficient and rapid analytical technique for various applications. However, an important limitation which hampers the use of CE is that the limit of detection is generally poor. Furthermore, its application to real samples may require special care in order to deal with interfering matrix components, such as salts in high concentration and particulate matter. Solid phase extraction (SPE) can be used to avoid these two main drawbacks associated with CE, simultaneously enriching the trace analytes and removing potentially interfering compounds. This review details the most recent strategies that employ SPE technology in order to increase the sensitivity and/or selectivity of capillary electrophoresis. We highlight solid-phase extraction, as a sample preparation technique suitable for trace enrichment and matrix simplification, in combination with CE. Although methods involving coupling with CE are reviewed in the literature, specific considerations required for certain sample matrices, including techniques to clean up the interfering matrix of a real sample and enrich the analytes of interest, merit further discussion. In order to understand the adsorption process, attention is paid to the chemical aspects, as well as to important requirements associated with the conditions employed. We also highlight the most important advantages and disadvantages of the different methodologies and briefly outline new trends, such as the coupling of sorbent preconcentration with CE. The present review focuses on the sample pretreatment techniques for biological and environmental samples prior to analysis by CE.
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