The catecholamines dopamine, norepinephrine, and epinephrine comprise an important class of neurotransmitters, which serve to maintain homeostasis of the autonomic nervous system. Dysregulation these neuroactive compounds and their metabolites in the L-3,4-dihydroxyphenylalanine (L-DOPA) metabolic pathway is a key process in neurodegenerative diseases (e.g., Parkinson’s) and behavioral disorders. The development of highly sensitive and selective analytical tools for simultaneous in vivo monitoring of multiple neurotransmitters in the brain would help deduce the roles of these compounds in aberrant neurochemical processes, while providing a platform for evaluating potential therapeutic drugs. In this study, capillary electrophoresis with UV detection was first used to separate a mixture of four neurotransmitters (dopamine, norepinephrine, epinephrine, serotonin), two metabolites (homovanillic acid, 3,4-dihydroxyphenylacetic acid), and an internal standard (hydroquinone). Baseline resolution of all analytes was obtained within 10 minutes upon optimizing the concentrations of the components of the background electrolyte: 15 mM phosphate at pH 7.4, 2.5 mM boric acid, 1 mM sodium dodecyl sulfate, 5 mg/mL sulfated β-cyclodextrin, and 10% dimethyl sulfoxide v/v. Next, the separation conditions were transferred to a microchip electrophoresis with electrochemical detection (ME-EC) platform. ME was conducted on a hybrid device where polydimethylsiloxane (PDMS) made up 3 walls of a "simple t" microchip with a 7 cm long separation channel, and the fourth wall was made up by a quartz glass plate containing a pyrolyzed photoresist film electrode in order to carry out electrochemical detection. Via ME-EC, the above reported analytes and ascorbic acid were separated within 110 s using a modified background electrolyte consisting of 15 mM phosphate at pH 7.4, 5 mM boric acid, 15 mM SDS, and 10% DMSO. Moving forward, various electrode configurations and sample preconcentration procedures will be probed with the goal of achieving nanomolar limits of detection for all target analytes. Subsequently, the ME-EC device will be coupled to a microdialysis interface for continuous in vivo monitoring of neurotransmitters in rat brains upon L-DOPA administration.

Optimization of the separation of catecholamine neurotransmitters and their metabolites present in brain microdialysis samples by capillary and microchip electrophoresis

ACS Fall 2021

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