Quantitative Investigations of Biodiesel Fuel Using Infrared Spectroscopy: An Instrumental Analysis Experiment for Undergraduate Chemistry Students

Biodiesel has gained attention in recent years as a renewable fuel source due to its reduced greenhouse gas and particulate emissions, and it can be produced within the United States. A laboratory experiment designed for students in an upper-division undergraduate laboratory is described to study biodiesel production and biodiesel mixing with conventional petroleum-based diesel fuel using Fourier transform infrared (FTIR) spectroscopy. The production of biodiesel from oil via a transesterification reaction is monitored by the intensity of the C-O ester peak (1098 cm(-1)), whereas the mixing of biodiesel and petroleum-based diesel is monitored by the C=O ester stretch (1746 cm(-1)). The impact of water on the precision of the biodiesel mixture is determined using a Karl Fischer titration to monitor water content. Students also gain experience with method validation using multiple sampling platforms (liquid cell, ATR-cell, and IR card). At the conclusion of the experiment, students are able to use FTIR to quantitatively monitor reactions and determine mixtures, determine the impact of water content on quantitation, and evaluate the strengths and weaknesses of different sampling platforms for various applications.