The acidity of boric acid solutions is greatly increased in the presence of cis-vicinal diols (organic compounds containing similarly oriented hydroxyl groups in adjacent carbon atoms, ) such as glycerol and mannitol.
The tetrahydroxyborate anion formed in the dissolution spontaneously reacts with these diols to form relatively stable anion esters containing one or two five-member  rings. For example, the reaction with mannitol , whose two middle hydroxyls are in cis orientation, can be written as
Giving the overall reaction 
The stability of these mannitoborate ester anions shifts the equilibrium of the right and thus increases the acidity of the solution by 5 orders of magnitude compared to that of pure boric oxide, lowering the pK from 9 to below 4 for sufficient concentration of mannitol. The resulting solution has been called mannitoboric acid.
The addition of mannitol to an initially neutral solution containing boric acid or simple borates lowers its pH enough for it to be titrated by a strong base as NaOH, including with an automated a potentiometric titrator.  This property is used in analytical chemistry to determine the borate content of aqueous solutions, for example to monitor the depletion of boric acid by neutrons in the water of the primary circuit of light-water reactor when the compound is added as a neutron poison during refueling operations.