An alternative spectrophotometric method for the determination of free glycerol in biodiesel

The presence of small amounts of free glycerol in fatty acid methyl esters used as diesel fuel or as heating fuel may represent the reason for some failures in engines and heating systems as well. Several methods are actually available for the determination of free-glycerol traces in biodiesel, and most on them are based on gas-chromatographic techniques. After a review of the existing methods, a new procedure based on periodate oxidation of glycerol, leading to the preparation of formaldehyde, on reaction with acetylacetone and on spectrophotometric measurement at 410 nm is illustrated. This method is simple, quick and economic and seems to be sufficiently reliable. Data related to recovery tests and analyses of real samples are shown, also in correlation with the existing reference method.