Determination of Free Glycerol in Biodiesel via Solid‐Phase Extraction and Spectrophotometric Analysis

Abstract

AbstractTo date, the standardized method for glycerol quantification in biodiesel production utilizes gas chromatography (GC); however, availability to manufacturers and instrumentation cost limits GC as an analytical method for general quality enforcement among producers. The method developed here is a bench top technique for quantitative determination of glycerol in biodiesel, with practical application in pharmaceutical and environmental quality control. The method extracts the glycerol contaminant from biodiesel using a normal phase solid phase extraction column (SPE). The protocol proceeds by rinsing with hexane to remove residual methyl esters, then collecting the glycerol with water. The aqueous extract is analyzed spectrophotometrically by an anthrone coloring reagent. Use of 2‐g SPE columns and the solvent system developed has achieved 85% glycerol recovery. The assay applied has a detection range of 0.004–0.400% free glycerol, comparable to the established American Society of Testing and Materials (ASTM) D 6584‐07 GC technique. Results were confirmed by GC and high‐pressure liquid chromatography (HPLC). The bench top technique reduces the costs of operation relative to current methods, completes analysis in proficient time, requires minimal labor, and has analytical limits comparable to existing standard methods of biofuel analysis.