Opt for the Easy Way: Determining Glycerol in Biodiesel Using Ion Chromatography

Current US and European standards stipulate gas chromatography to determine the glycerol content in biodiesel. However, this method is both tedious and rather expensive. Metrohm recommends ion chromatography (IC) as a simple, cost-efficient and highly accurate alternative. The free and total content of glycerol in vegetable oil methyl esters (biodiesel) is of paramount importance for the quality of biodiesel. Both free and bonded glycerols (= total glycerol) lead to serve operational problems such as injector deposits and filter clogging.

The US ASTM D 6751 and the European EN 14214 specify a maximum total glycerol content of 2400 ppm (0.24%) and 2500 ppm (0.25%), respectively. The maximum free glycerol content is limited to 200 ppm (0.02%) in both standards, which stipulate gas chromatographic (GC) analysis involving time and reagent-consuming derivitasations. In addition, GC methods encounter coelution problems with biodiesel samples produced from or containing lauric oils, such as coconut and palm kernel oil.

In contrast to GC, the presented method is applicable to all types of vegetable oil methyl esters. Prior to chromatographic separation, free glycerol and bound glycerol are isolated by a straightforward extraction and saponification-extraction technique, respectively. Integrated pulsed amperometric detection following chromatographic separation achieves an outstanding method detection limit (MDL) of 0.7 ppm for free and total glycerol and thus easily exceeds ASTM and EN performance specifications.