Determination of Free Glycerol in Biodiesel by Molecularly Imprinted Polymer – Based Solid-Phase Extraction (SPE) Using an Enzymatic Spectrophotometric Assay

Abstract

The present work reports the development of a new analytical method for the determination of free glycerol in biodiesel samples using enzymatic-spectrophotometric assay combined with solid phase extraction (SPE) by molecularly imprinted poly(methacrylic acid) (MIP). The spectrophotometric method was performed using a commercial enzyme kit. The enzymatic-spectrophotometric method showed good analytical performance in terms of the linearity (0.998), limit of detection (7.70 × 10⁻⁶% w/w), limit of quantification (2.54 × 10⁻⁵% w/w), repeatability (0.42% to 7.91%), and recovery (99.4% to 112%). The analyses of several biodiesel samples by SPE and enzymatic-spectrophotometric method provided recovery values between 91.4% and 105%. Therefore, the high selectivity of molecularly imprinted polymer (MIP) was successfully applied to isolate free glycerol from biodiesel samples containing acylglycerols and methyl esters, and thereby allow enzymatic-spectrophometric based quantification. The developed method using SPE with MIP was efficient for the determination of free glycerol in biodiesel and the obtained results are in agreement with gas chromatrography (GC) that was used as a reference protocol.

Keywords:

• Biodiesel
• free glycerol
• gas chromatography
• molecularly imprinted polymers
• solid phase extraction
• spectrophotometry

Additional information

Funding

This work was supported by FAPERJ (Foundation for Research Support of the State of Rio de Janeiro) and Peugeot (E-26/111.159/2014), FAPERJ (E-26/203.353/2017 and E-26/201.892/2017), CAPES (Coordination for the Improvement of Higher Education Personnel) and CNPq (National Council for Scientific and Technological Development) (312005/2018-0 and 307432/2017-3). The authors also thank the Fuel and Oil Derivatives Laboratory of Federal University of Rio de Janeiro for the GC results.