Eli5: Why do vitamins mg not match their true weights?

Question

Eli5: Why do vitamins mg not match their true weights?

In: Chemistry

Answer 1

Be careful of things like salt forms, for example something like iron (not a vitamin, but close enough) can be present as iron gluconate in a supplement.

1 mole of iron gluconate weighs 446.1 grams, but only contains 55.8 grams of iron.

If you get vitamin C as sodium ascorbate, it will only contain ~89% ascorbic acid by weight due to the presence of sodium.

So you have to account for that difference when weighing it out for a supplement.