Fluorescence detection of proteins and amino acids in capillary electrophoresis using a post-column sheath flow reactor

A simple laser-induced fluorescence detection method for proteins and amino acids in capillary electrophoresis is reported. A sheath flow cell is utilized as a post-column reactor for fluorescence derivatization of proteins and amino acids by addition of o-phthaldialdehyde-2-mercaptoethanol to the sheath fluid. With the use of a 50 microns I.D. capillary, the limits of detection for carbonic anhydrase are 0.73 nM or 1.8 amol which represents a five- and two-fold improvement, respectively, over the best results previously reported for post-column detection. In addition, separation efficiencies up to 8.07 x 10(5) are achieved and the detector response is linear over three-orders of magnitude. These results demonstrate that mixing is adequate and the reaction kinetics are rapid enough to provide sensitive detection with this approach. Also, because this post-column derivatization scheme requires no instrumental changes to a typical sheath flow cell detector, the system can be used for detection of pre-column labeled analytes and for native fluorescence detection.