[KRuland]

I have been assigned to determine how much Calcium is in this (http://www.walgreens.com/store/c/caltrate-600%2Bd-calcium-supplement-tablets/ID=prod3427006-product) Calcium + Vitamin D supplement tablet. We know that the tablet is supposed to contain 600mg of Ca, the objective is to recalculate the amount of Ca and compare the actual content with the advertised content.

At first I thought would be easy if the tablet only contained Calcium (the medium is CaCO₃) and Vitamin D (C₂₇H₄₄O). I could react the dissolved tablet with an excess of Na₂SO₄ and the solutions would precipitate CaSO₄.

The problem lies in that there are dozens of other substances (binders, color, preservatives) in the tablet notably including Silicon Dioxide, Sodium Ascorbate, Sucrose, Talc, Titanium Dioxide, and corn starch, which I believe at least some of which are insoluble.

How can I measure the actual amount of Calcium in this tablet without having my results skewed by the extra ingredients. Thank you for any help in advance.

[Arkcon]

I don't think that reaction will work, for just the reasons you described.  You'll have to think of another one.

[curiouscat]

Would a titration against EDTA work? Or are there impurities that might bind to EDTA?

[Borek]

No need to reinvent the wheel - go to a library, find any decent classical analytical chemistry text and look for methods there. Or google for pharmacopoeia analytical methods.