Simultaneous analysis of endogenous neurotransmitters and neuropeptides inbrain tissue using capillary electrophoresis - microelectrospray-tandem mass spectrometry

Capillary electrophoresis was combined with highly sensitive microelectrosp ray-tandem mass spectrometry to simultaneously detect classical small molec ule neurotransmitters as well as neuropeptides from discrete regions of the marmoset brain. A mixture of four classical neurotransmitters (glutamate, gamma-aminobutyric acid, acetylcholine, dopamine) and four neuropeptides (n eurotensin, methionine-enkephalin, leucine-enkephalin and substance P 1-7) was studied to optimize the capillary electrophoresis conditions for separa tion, injection volume, and analysis time. gamma-Aminopropyltriethoxysilane -coated capillaries and acetic acid electrolytes were used to avoid interac tions between the sample and the capillary surface and to obtain a high ano dic electroosmotic flow, which resulted in a short analysis time. Detection was performed using tandem mass spectrometry in the selected reaction moni toring mode using a triple quadrupole mass spectrometer. Samples were disso lved in ammonium acetate to achieve a transient-isotachophoretic concentrat ion step at the beginning of the separation and to make it possible to inje ct larger sample volumes, up to 140 nL. Small amounts of tissue from specif ic regions of the marmoset monkey brain were pretreated using solid-phase e xtraction as a clean-up and concentrating step. In the striatum we could de tect endogenous glutamate, gamma-aminobutyric acid (GABA), acetylcholine an d dopamine, as well as the neuropeptides methionine-enkephalin and substanc e P 1-7 in the same analysis, using only 58 mm(3) of brain tissue.