Capillary electrophoresis with on-line enrichment for the analysis of biological samples

“On-Line” preconcentration in capillary electrophoresis (CE) is a good strategy to overcome the low concentration sensitivity of the technique, which is the main limitation when trace-level compounds are to be determined in complex matrices such as biological samples. Here we discuss the use of at-, on-, and in-line preconcentration procedures in combination with CE in the analysis of biological fluids. The preconcentration strategies discussed are classified into two groups depending on the mechanism involved: chromatographic or electrophoretic techniques. Recent applications are included and the advantages and drawbacks of the techniques are examined.