Subject: I.V. vitamins must be reduced to pH close to blood, HOW?

I make TPN IV bags for a hospital.  IV vitamins come in two vials that must be 
mixed before use.  One contains vitamins, the other a buffer.  If I know mg/mcg 
amounts of each vitamin, how would I calculate the amount of buffer needed to 
bring pH to about 7.4 (that of blood)?  In practice, the total volume of IV 
solution is 5ml vitamin & 5ml buffering agent injected into no less than 500ml 
IV bag.  

My question boils down to (1) how do I calculate "acidity" for each vitamin, 
then (2) how do I calculate amount of buffer (citric acid, sodium citrate, NaOH, 
ect) needed to bring pH up to 7.4?

Thanks

Re: I.V. vitamins must be reduced to pH close to blood, HOW?