Independent optimization of capillary electrophoresis separation and native fluorescence detection conditions for indolamine and catecholamine measurements.

Separation conditions in capillary electrophoresis with native fluorescence detection often represent a compromise in terms of the separation and detection figures of merit. As both the separation and fluorescence properties greatly depend on pH, the ability to independently optimize pH in the separation capillary and the detection region can improve many complex separations. When using a sheath flow cell, the pH at the detection zone can be adjusted independently of the electrophoresis buffer pH. Using capillary electrophoresis with 257-nm excitation and native fluorescence detection, more than an order of magnitude improvement in the limits of detection for dopamine (from 1400 to 120 nM) and epinephrine (from 850 to 60 nM) is achieved by maintaining the basic separation conditions and an acidified sheath buffer. The detection of dopamine in an individual Aplysia californica cerebral ganglion neuron is demonstrated.