Determination of free and total glycerol in biodiesel by spot analysis

Abstract The importance of alternative fuel production has increased in the lately years, and so has the need of methods of analysis to evaluate their quality. Biodiesel fuel is a valuable substitute to petrodiesel fuel. Among the side and byproducts that have to be determined as an indicator of biodiesel quality are free glycerol and mono-, di-, and tri-acylglycerol. A simple, economic, friendly, and green method to quantify free and total glycerol in biodiesel has been developed. Novelty of the approach is related to the new extraction method proposed and its combination with the further steps that allow to accomplish the determination fully in the field, with the results being read without any sophisticated equipment other than a smartphone. The method is based on two extractions, i.e., the conventional aqueous extraction and another one with detergent, both followed by four consecutive enzymatic reactions to produce a colored product, which can be quantified with a free downloadable smartphone application for digital image analysis. The methodology was assayed to determine free and total glycerol content in commercial biodiesel samples. The results obtained using the proposed method have been compared with those acquired by the standard, normalized gas chromatography-FID one, and turned out to be equivalent (P