ASTM D7637

Glycerin Assay by Titration (Sodium Metaperiodate)

Applicability: Applies to glycerin (glycerol) and glycerin/water mixtures with glycerol concentrations greater than 75% by mass. The method is not suitable for samples containing compounds with two or more hydroxyl groups on adjacent carbon atoms (such as sugars, glycols, or other polyols) because these interferents also react with periodate, producing erroneously high results.

Purpose: Quantitatively determines glycerol content by cold oxidation with sodium metaperiodate in acidic medium, which cleaves the glycerol molecule and produces stoichiometric amounts of formic acid; the formic acid is then titrated to a pH 8.1 endpoint with standardized sodium hydroxide solution. Results expressed as percent glycerol by mass are used for quality control in pharmaceutical, food, cosmetic, and industrial glycerin production and procurement to confirm purity and compliance with product specifications.