Bioequivalence and Bioavailability Forum

Dear all,
I have done one study in which the lable claim of the Drug tablet is of Bivalent salt of Zolpidem (Zolpidem Tartarate). For the preparation of stock solution I have considered Monovalent molecular weight.
The analysis was done on HPLC (with UV detector).
1. The counterpart (sponsor) is asking us to consider the bivalent molecular weight. But as per the FDA recommondations parent ion should be measured and
we have done the same. So, what is the right method?
2. This was the case with the UV-HPLC as a detector. If it would have been LC-MS/MS, as per the basics of Mass spectometry I had to consider actual molecular weight of the Monovalent.
So, should we consider Monovalent weight irrespective of the analytical technique?
Best regards,
Prashant