CAPILLARY ZONE ELECTROPHORESIS WITH LASER-INDUCED FLUORESCENCE DETECTION FOR THE DETERMINATION OF NANOMOLAR CONCENTRATIONS OF NORADRENALINEAND DOPAMINE - APPLICATION TO BRAIN MICRODIALYSATE ANALYSIS

Determination of catecholamines by capillary zone electrophoresis with laser-induced fluorescence detection was performed on low-concentrati on samples, which were derivatized with naphthalene-2,3-dicarboxaldehy de to give highly fluorescent compounds. When the berate concentration in the derivatization medium was decreased from 130 to 13 mM, sensiti vity for noradrenaline (NA) and dopamine (DA) was greatly enhanced whi le resolution between these two compounds decreased. A 50 mM berate co ncentration in derivatization medium was chosen since it provided maxi mal resolution between NA and DA, together with a high separation effi ciency (3.1 million theoretical plates per meter for DA). The injectio n of 2.4 nL of a NA and DA solution derivatized at 10(-9) M produced p eaks with signal-to-noise ratio of 8:1 and 3:1, respectively, correspo nding to 1.8 amol of each catecholamine. The calibration curves were l inear when NA and DA solutions were derivatized at concentrations rang ing from 10(-6) to 10(-9) M. This method was used to determine NA in b rain extracellular fluid: a peak corresponding to a basal level of 5 x 10(-9) M endogeneous NA was observed in microdialysates from the medi al frontal cortex of the rat, and its nature was confirmed by both ele ctrophoretic and pharmacological validations.