Separation of enantiomers of N-acetylcysteine by capillary electrophoresis after derivatization by o-phthaldialdehyde

The optical purity of N‐acetyl‐L‐cysteine was tested by capillary electrophoresis. The D‐enantiomer can be found down to a ratio of 0.4:99.6 within 4 min without the use of the D‐form or the racemate as a standard. The efficiency was optimized during method development up to a theoretical plate number, N, of several hundred thousand. The migration order and the separation mechanism was explained. The assumed structure of the formed isoindole S‐[2‐(1‐carboxy‐2‐methylpropyl)isoindole‐1‐yl]‐N‐acetylcysteine diastereomers was confirmed and its stability was examined.