Colorimetric Assay of Alditols in Complex Biological Samples

A colorimetric assay for the determination of alditols in complex extracts from biological sources, showing negligible interferences by other carbohydrates, has been worked out. The method involves mild oxidation of alditols by sodium periodate under acidic conditions, followed by reaction of the resulting formaldehyde with ammonia and acetylacetone (Hantzsch reaction) to yield a colored heterocycle amenable to spectrophotometric measurement. The assay is completed within a few minutes, and mannitol and other alditols can be detected down to the nanomolar range. The method is convenient in that it uses inexpensive chemicals of low potential hazard and requires only few minutes to complete. The method has been used for the determination of mannitol in aqueous extracts from olive leaves and fruits and has been validated by parallel determinations carried out by HPLC and enzymatic analysis with mannitol dehydrogenase.