L-tyrosine can be used indeed. The background in comparison to L-dopa will be much better, but the oxidation of L-tyrosine would be slower because the lag period of the tyrosine hydroxylase activity of tyrosinase. Alternatively, you can use L-tyrosine adding also a catalytic amount of L-dopa (let me se for instance a ratio L-tyrosine/L-dopa around 20-50)

Yes sir, the lag was in fact very long. I shall try with L-DOPA.

Thank you.