Enhanced detection in capillary electrophoresis: example determination of serum mycophenolic acid

In order to overcome the poor absorbency detection limits in CE, two simple strategies were combined to increase the amount of the sample injected: a long capillary to hold extra sample while leaving adequate room for the separation and acetonitrile stacking, which concentrated the sample based on transient pseudo-ITP. The combination of these two strategies yielded sensitivity comparable or better than that of the HPLC with good separation and with better theoretical plate number. The analysis of mycophenolic acid, a common immunosuppressant drug, in serum was used here as an example to illustrate this enhanced detection and its applicability to therapeutic drug monitoring. Acetonitrile was used to remove serum proteins followed by direct injection filling 5-21% of the capillary volume and separation in a borate buffer. The overall CE method compared well to an assay by HPLC as far as sample preparation, correlation coefficient, and especially sensitivity of detection.