Response Factor in GC-FID Methyl Ester Analysis in Several Biodiesels: A Comparative Study of the EN 14103:2011 and ABNT 15764:2015 Methods versus a Proposed GC-FID Procedure for Individual Ester Determination

Willian Da Silva,Arnaldo Oliveira Jr,Matthieu Tubino

doi:10.21577/0103-5053.20210144

Abstract

A gas chromatography method with a flame ionization detector enabled by relative response factor was developed to determine the individual and the total content of esters in biodiesel. This method accounts for different response factors of the detector for a homologous series of esters that may be present in biodiesel. In this way, the determination of the total ester content of a reference sample (100.5%) was done with more accuracy by the proposed procedure (100.2%) than by official analytical methods: EN (74.68%) and ABNT (118.2%). Another advantage of the developed method is the possibility of determining individual ester concentrations, which provides information on several important biodiesel properties such as oxidative stability and cold flow properties. The mean absolute error in the determination of the individual ester content was ca. 1.1%.

Highlights

The chromatographic method presented in this work accounts for the differences observed in the flame ionization detection (FID) signal related to each methyl ester in the biodiesel samples by including relative response factor (RRF) with respect to intrinsic internal standards
This approach allows a more accurate determination of the concentration of each ester and the total ester content determination in biodiesel samples with accuracy. By using this approach, was determined, with acceptable relative error, each individual ester content in a standard reference sample. This is an important advantage of the proposed method, over the officials (EN 14103:2011 and ABNT NBR 15764:2015) methods with which it is not possible to quantify each single methyl ester contained in biodiesel
With respect to the total methyl ester content, it was performed the analysis of a certified reference material using the proposed method

Summary

Introduction

Biodiesel is defined as mono-alkyl esters mixture of long chain fatty acids derived from the reaction of vegetable oils or animal fats and an alcohol in presence of a catalyst.[1,2] It can be used as a green alternative to mineral diesel fuels for motors and heating systems.[3,4,5,6] The main physical-chemical properties of this kind of fuel are highly dependent on a number of structural molecular factors like the number of double bonds in the fatty acid chain as well as the amount and position of allylic and bis-allylic carbons adjacent to the unsaturated ones.[7]The chemical compositions of some potential oil sources for biodiesel production have been previously reviewed allowing a more realistic analysis of their feasibility as raw materials without compromising any of the fuel’s properties.[8,9] Some of them are so well behaved that it is possible to estimate some of the physical-chemical properties of the fuel, like iodine value, cetane number, and cold filter plugging point (CFPP), from their ester composition determined by chromatographic analysis.[8,10] Serrano et al.,[11] for instance, reported that the amount of polyunsaturated esters in a biodiesel sample shows a good correlation with the oxidative stability measured through. Another reference standard mixture of methyl ester solution (12.5 mg L-1) with 800 μL of methyl tridecanoate (internal standard) was prepared in order to validate the quantitative determination of the proposed method by comparison with the content values provided by the supplier.

Results

Conclusion