I've just raised a thread "Do lentils contain levodopa?" which contains this reference:

"Determination of levodopa by capillary zone electrophoresis using an acidic phosphate buffer and its application in the analysis of beans."

Zhang, Zhai and Hu write:

"A simple capillary zone electrophoresis method has been developed for the quantification of levodopa in broad bean and lentil."

http://openagricola.nal.usda.gov/Record/IND43708486

Unfortunately, I can't get through the pay wall to get to the details of their methods. But it led me to look at electrophoresis.

If I understand it correctly (and there's a good chance that I don't, I am not a chemist and I have never been a member of the chemist party) this involves:
- filling a container with gel, potato starch will do,
- putting electrodes at both ends of the container, ensuring that the electric field is equal across the width of the container;
- fitting a battery
- dripping a baseline solution of levodopa in the container
- next to it put a solution of the substance under test.
- the electrical current causes the molecules to move, the distance travelled being, in part, a function of the mass of the molecule
- wait some time and there should be streaks at a number of places, one for each molecule in the substance;
- comparing position shows whether levodopa is present, determining the intensity of the streak shows concentration.

I bet the devil is in the detail. Do we have any chemists who could comment on whether we could get this to work in the "kitchen sink"?

I see these benefits:
- it helps those using levodopa containing foods to judge how much to take;
- it allows people to breed plants that contain more levodopa;
- it allows us to judge the consistency of levodopa containing drugs.
- it allows us to separate all the molecules, pointing to other useful substances.

John