Submitted to: Chromatographia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2004
Publication Date: 9/1/2004
Citation: Foglia, T.A., Jones, K.C., Nunez, A., Phillips, J.G., Mittelbach, M. 2004. Comparison of chromatographic methods for the determination of bound glycerol in biodiesel. Chromatographia. 60:305-311.
Interpretive Summary: Simple alkyl ester derivatives of animal fats and vegetable oils, primarily methyl esters, are actively being promoted as diesel fuel alternatives both domestically and in Europe. When used as diesel fuels these esters are commonly referred to as biodiesel. Before biodiesel can be used as a fuel, however, it must meet established standards of identity. One important identity criterion for biodiesel is alkyl ester content, because high levels of impurities (such as residual fat or oil, glycerol and free fatty acids) can cause problems in the fuel system, or engine fouling or higher engine emissions. The current analytical method specified for this measurement, however, is time consuming, labor intensive, and not suited for routine monitoring of biodiesel fuels. In this paper we describe an alternative approach for measuring the alkyl ester content of biodiesel and the minor lipid impurities that may be present. Analysis of variance showed that there was no statistical difference between the two methods. Operationally, the method reported herein is superior to the current method in that it requires no chemical modification of the sample before analysis, has shorter analysis time, and is directly applicable to most biodiesel fuels. The method provides researchers and trade organizations who are promoting alternative fuel technology with a valuable alternative tool for assuring biofuel quality.
Technical Abstract: An important fuel criterion for biodiesel is bound glycerol, which is a function of the residual amount of triglycerides and partial glycerides in the biodiesel. Either high-temperature gas chromatography (HTGC) or high performance liquid chromatography (HPLC) can be used for determining these minor but important components in biodiesel. We report in this paper a statistical study on the accuracy of the two methods for ascertaining the bound glycerol in biodiesel fuels obtained from different feedstocks. Analysis of variance showed that with one exception there was no statistical difference in bound glycerol for the biodiesel samples analyzed or a difference between methods. Operationally, the HPLC method described herein is superior to the HTGC method in that it requires no sample derivatization, has shorter analysis time, and is directly applicable to most biodiesel fuels. The HPLC method uses a cyanopropyl column (250 x 4.6 mm i.d., 5 micron), a binary mobile phase of hexane and methyl-t-butyl ether each fortified with acetic acid (0.4%), a simple linear gradient profile at a flow rate of 1 ml per minute, and an evaporative light scattering detector for quantitation of analytes. Total separation time of the neutral lipid classes is less than 30 minutes.