Improved detection of Coptidis alkaloids by field-amplified sample stacking in capillary electrophoresis. 
To improve the on-line detection of Coptidis alkaloids in capillary electrophoresis the field-amplified sample stacking was studied for them.  In this work the peak height enhancements of stacking with hydrodynamic and electrokinetic injections were compared with respect to the conventional sample injection.  It was found that the stacking efficiency of electrokinetic injection was more than ten times greater than that of hydrodynamic injection.  No peak height enhancement was observed with the pre-injection of a short water plug before sample injection with electrokinetic injection.  The concentration limits of detection of berberine, coptisine and palmatine obtained with electrokinetic injection were about 5 ng/ml (ppb), which was approximately 240 times lower than those from conventional sample injections.  Baseline separation was also achieved for the main alkaloids.  After validation the developed method was applied to determine the quantity of berberine, coptisine and palmatine in a Coptidis Rhizoma sample.  The method is simple, rapid and should be able to be used in identification and quantitative evaluation of the crude drugs.