Desenvolvimento e validação de metodologia analítica para determinação simultânea dos teores de éster e metanol em biodiesel

Abstract

This work aimed to develop and validate an analytical method for the simultaneous determination of contents of ester and methanol in soybean methyl biodiesel, based in the derivatization of the methanol with acyl chlorides to form methyl esters. The method was optimized for direct use in EN14103:2003 determination of ester content. We tested the reactions with heptanoyl, octanoyl, nonanoyl and decanoyl chlorides. The derivatization reaction was optimized with total time of 21 minutes, excess of nonanoyl chloride, pyridine as catalyst and 2-propanol in order to react with the excess of the acyl chlorides. To quantify the amount of ester was used methyl heptadecanoate solubilized in dichloromethane as internal standard. The identification and quantification of ester and methanol contents in biodiesel was performed by gas chromatography (GC) using polar phase column of polyethyleneglycol of 30 m x 0.25 mm id x 0.25 μm and flame ionization detector (FID). The peak of methyl nonanoate derivatized showed excellent resolution and gas chromatography-mass spectrometry (GC-MS) was used to assess the selectivity of the proposed method. The correlation coefficient obtained for evaluation of linearity was greater than 0.999. The limits of detection and quantification adopted were 0.010% (w/w). Recovery in samples with methanol concentration of 0.0198, 0.2053 and 0.4458% (w/w) was between 78 and 111% and the relative standard deviation was less than 4%. The results show that the proposed method can be used for simultaneous determination of ester and methanol, contents in biodiesel facilitating and reducing significantly the cost of chromatographic analysis for quality control of soybean biodiesel.