SWIM has an imaginary report:

Datura metel seeds were harvested when pods opened. They were brown. Datura metal is the kind with deep purple flowers. The stem was also deep purple.

SWIM bashed up some seeds with liquid N2 and weighed out 100mg. 100mg of powdered material mixed with 1ml 0.1N NaOH and 5mL chloroform. Let stand overnight. Next day filtered material through PTFE membrane. Basic water was seperated from chloroform and discarded. Chloroform was partitioned with clean distilled water to remove any excess base. Again seperated chloroform.

Chloroform layer was then dried under N2 stream. Redissolved white residue in methanol and analyzed by GC-MS.

Scopolamine was the major alkaloid. Hyoscyamine was minor. According to total ion chromatogram (rough qualitative estimate) 24% hyoscyamine and 76% scopolamine. There were some minor peaks perhaps also alkaloids but SWIM didn't investigate.

Note this Datura did get infected with bugs which were killed a few weeks before pods opened. Could effect alkaloid ratios who knows.

Interesting, thank you a lot for that analysis!

My notes says this about Datura metel seeds:

From herbarium in India: 1250 mg/kg scopolamine, 650 mg/kg hyoscyamine (Shah & Khanna, 1964)
Seeds from 2000, Poland: 756 mg/kg scopolamine, 914 mg/kg hyoscyamine (Mroczek, 2006)
Seeds from 2002, Poland: 425 mg/kg scopolamine, 1214 mg/kg hyoscyamine (Mroczek, 2006)

Var. fastuosa:
From herbarium in India: 3700 mg/kg scopolamine, 420 mg/kg hyoscyamine (Shah & Khanna, 1964)
From Poland, 773 mg/kg scopolamine, 1027 mg/kg hyoscyamine (Mroczek, 2006)
Unknown location, 76 % scopolamine, 24 % hyoscyamine (Bucher, 1989)

As it shows very clearly here, the alkaloid make-up seems to vary greatly. Note especially the great difference in the seeds from year 2000 and 2002, where you can see that the hyoscyamine content increases with age while scopolamine content drop, just as it is noted with other Daturas.

The general trend, however, seems to be that Datura metel seeds is scopolamine based. I wonder if you grew this plant yourself, or have any other way of determining the age of the plant the seeds originated from?