Compared to other techniques such as LC or GC, where the retention of the analyte can be used to identify the unknows along with other properties such as the accurate mass or the fragmentation pattern, the use of migration times in CE presents the disadvantage of being a much less robust parameter. Many factors account for this lack of robustness, such as different experimental setups, matrix adsorption on the capillary walls, or changes in the suction caused by ESI sources at the capillary outlet when hyphenated to MS. To mitigate this issue, some alternatives to migration times have been proposed. Relative migration times expressed as ratios to a reference compound can be useful, but they are unable to adequately cope with the effect of constant parameters such as the application of a pressure to assist the electroosmotic flow (EOF) during the separation. Effective electrophoretic mobility is a much more robust parameter, and it constitutes a better option for the identification of metabolites since it is a molecular property which only depends on the nature of the chosen BGE and separation temperature .