An H.P.L.C.-Fluorimetric analysis for L-dopa, noradrenalin and dopamine

A rapid (10 min) and sensitive determination of 3,4-dihydroxyphenyl-L-alanine (L-dopa), noradrenalin and doparmine has been developed. The assay involves the separation of the compounds with a strong cation-exchange resin, followed by post-column derivatization with o-phthalaldehyde. The fluorescence of the derivative is measured in a flow-through fluorimeter and is linear over a concentration range of 500 times the lower detection limit (4.6 ng for L-dopa, 7.5 ng for noradrenalin and 9.3 ng for dopamine). The assay does not require the stringent removal of oxidizing materials which is necessary for electrochemical detection, and may be useful in the analysis of biological samples.