Yeah, but I made sure that I did all the titrations before the milk's best-before-date. And other students in my class have been doing the same type of investigation (though using different brands of milk); out of the three I spoke to, two have gotten similar trends to mine, and one has gotten no trend.
Yeah, that last dude...he's the organic chemist of the bunch.
So, what I've to say doesn't deal with your titrations directly, but does answer some of the tangential quetions raised. The presence of phosphate along with calcium will hinder its absorbtion, and also calcium is absorbed by the body exclusively in the stomach. My assumption about the decreased absorption in the presence of phosphate is the insolubility of calcium phosphate, but in an acidic environment, one might expect to see solubilization. The other thing I know is that the presence of citrate with calcium aids in its absorbtion (the brandname of calcium suppliment Citrical utilizes this) compared to either calcium carbonate or calcium phosphate. So, drink some orange juice with your tums as opposed to pop
So in retrospect, this post is overall not really contributing to the thread, but whatever. It's neat stuff, perhaps you will find it interesting, even as an aside.