Sample stacking for charged phenol derivatives in capillary zone electrophoresis

10 selected phenol derivatives are separated by capillary zone electrophoresis in an alkaline phosphate/borate buffer at pH 10. Resolution and selectivity of the separation are increased using methanol as an organic modifier. The conductivity in the sample zone, mainly due to the high pH, needed for the formation of phenolates and the electroendosmotic flow are considerably lowered by adding about 40% methanol. Detection limits are improved by a specially optimized electrostacking procedure. The improvement is in the range of two orders of magnitude compared to hydrodynamic injection. Detection limits are found to be in the low ppb range. This optimization for electrostacking may also be used for other slow anionic analytes forming charged molecules only at a very high pH.