[samuraifiction]

Hey folks,

I have a standard for amphetamine-d2 sulfate (there are 2 moles of amphetamine-d2 for every 1 mol of H2SO4). If I weigh 1.62 mg of the powder into a vial, how much solvent do I need to add to reach a concentration of 10 nanograms of amphetamine-d2 per microliter of solution? Thanks in advance for your help. (amphetamine 135; amphetamine-d2 137; sulfate 98)

Sam

[Borek]

You have to show your attempts at solving the problem to receive help, this is a forum policy.

Use definition of concentration - it is just plug and chug. Just don't forget conversion so that mass and volume are always expressed in the same units.

[samuraifiction]

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

[Borek]

In you first post you told us you need a 10 ng/μL solution, now you attempted to calculate amounts for 10 nmol/μL concentration. Which one is right?

[samuraifiction]

Oops, you're right. Well, assuming I was correct in my previous calculation, for ng/ul I would just have to convert from nmols back to nanograms using the mw of amphetamine-d2, which is 137 ng/nmol, so 10 nmol/ul x 137 ng/nmol = 1370 ng/ul. Then just dilute to get down to 10 ng/ul.

[Borek]

In general for ng you don't need to go through the moles path.

Note: I have not checked numbers, I just wrote what caught my attention.