Simple gas chromatographic analysis of plasma dopa and dopamine

A method for gas chromatographic analysis of plasma dopa and dopamine is described. Deproteinized plasma was shaken with acid washed aluminium oxide at pH 8.8. Dopa and dopamine were eluted from alumina with weak acids and evaporated to dryness. The pentafluoropropionic derivative of dopamine and the trifluoroacetic derivate of dopa were made and injected into a gas chromatograph equipped with a 63Ni electron capture detector. Alpha-methyl derivatives of each substance were used as internal standards. Linearity of plasma working curves of each substance was good. This method was applied to the assay of plasma samples from Parkinsonian patients under treatment with L-dopa with or without peripheral dopa decarboxylase inhibitors. The method described is sensitive and simple enough to monitor the blood levels of dopa and dopamine of these patients.