Separation of D/L-carnitine enantiomers by capillary electrophoresis

Carnitine is an essential component of the tissue of animals, higher plants and many microorganisms. Whereas the L-carnitine enantiomer plays an important role during the metabolism of long chained fatty acids, D-carnitine has a considerably toxic influence on biochemical processes. The analytical separation of D/L-carnitine is possible only after derivatization with UV- or fluorescence active substances, e.g. FMOC (9-fluorenylmethyl chloroformate) and (+)/(-)-FLEC ((+)-1-(9-fluorenylethyl)chloroformate). The capillary electrophoretic separation of enantiomeric FMOC derivatives was performed using acidic buffers and different cyclodextrins as chiral selectors. Baseline separation as well as detection limits in the micromolar range could be achieved using UV detection. The migration order of both enantiomeric derivatives was reversed by the application of substituted cyclodextrins (CDs), thus making the analysis of low amounts of D- or L-carnitine in high concentrations of the other enantiomeric form possible. Different kinds of coated capillaries are compared with respect to separation time and resolution. Examples for the analysis of pharmaceuticals with high L- and low D-carnitine contents and of serum samples spiked with D/L-carnitine are shown.