Why is NH4OH used in Polarimetric analysis?
Do you see a potential corresponding to the sugars, or to their Schiff bases, or to said imines' trimers?  Perhaps ammonia gives you a nice pH buffer, as opposed to alkali hydroxides that will wildly swing pH and allow Cannizzaro disproportionation of reducing sugars' aldehyde groups at high pH. Ammonia does not reduce at the cathode.