Q:

Why is NH4OH used in Polarimetric analysis?

Why is a sugar solution pre-treated with ammonium hydroxide before analyzing? And why is it specifically ammonium hydroxide instead of sodium hydroxide or calcium hydroxide? 

A:

If I'm not wrong, this is about polarimetry, not polarography. (No dripping mercury, but optical rotation).
If your sugar is a hexose, the following species will exist in aqueous solution:

open form (a bit)
furanose  (traces)
pyranoses (major amount)

The pyranoses will adopt the $\alpha$- and the $\beta$-form. Both rotate polarized light by a different angle. 
The interconversion between these forms (mutarotation) is facilitated by addition of acid or base. Thus, an equilibrium, resulting in a constant angle in polarimetry, is reached faster.

