2.2. Standard solutions
Stock solutions (10 mM of each) of L-Dopa, dopamine, 3-
O-methyldopa and a-methyldopa were prepared fresh daily,
dissolving pure standards in 2 M perchloric acid (HClO4).
The solutions were stored in ice in the dark. Serial dilutions
of the standard mixture with 2 M HClO4 were also made;
the ranges being 62.5 pmole200 nmol/ml for native fluorimetric
assay, 50 pmole5 nmol/ml for fluorescence detection after
derivatisation and 25e400 nmol/ml for UV assay.