Okay, here's what I did:
The molecular weight of amphetamine-d2 dulfate is 372.52 g/mol, or 372.52 ng/nmol. Since there are 2 amphetamine molecules for every sulfate, I divided by 2 to get 186.26 ng/nmol. To calculate the number of nmols of amphetamine-d2 in 1.62 mg (or 1,620,000 ng), I divided 1,620,000 ng by 186.26 ng/nmol to get 8690 nmols. To determine the number of ul of solvent to reach 10 nmol/ul, I divided by 10 to get 869 ul. In summary, to get a final concentration of 10 nmol/ul of amphetmine-d2, dissolve 1.62 mg of amphetamine-d2 sulfate in 869 ul of solvent.
Thanks in advance for any comments and advice.
Sam