Determination of Alkyl Esters Content by Gas Chromatography: Validation of Method Based on Short Column and Response Factor

Abstract

In this study an analytical method, based on gas chromatography with flame ionization detection, using a short column and response factor (GCSCRF), was validated for the quantification of fatty acid alkyl esters (methylic or ethylic). During the validation process, the proposed method was employed to analyze twenty samples of fatty acid methyl esters and fatty acid ethyl esters. Biodiesel samples were produced from soybean oil and the validated method was found to be selective, being able to separate and identify every ester species present in the samples according to its carbon number. When the method was submitted to some variations in the sample preparation procedure, it remained robust. Limits of detection and quantification were 6.76 and 20.4 mg mL -1 , respectively. The suggested method also showed great precision when successive analyses were carried out for different analysts, with standard deviation (SD) 0.6 for repeatibility and relative standard deviation (RSD) percentage 7.3% for intermediate precision, excellent accuracy when compared to other reference methods (EN 14103 and high-performance liquid chromatography with ultraviolet dection (HPLC-UV)) and recovery studies.Keywords: biodiesel, gas chromatography, chromatografic column, response factor IntroductionThe growing energy crisis, caused by a high consumption of fossil fuels and environmental degradation, has influenced the development of renewable fuels as alternative energy sources. Biodiesel, produced by the transesterification or esterification of vegetable or animal oils and fats or fatty acids, in the presence of an alcohol such as methanol or ethanol, 1-3 is one of the most promising alternative fuels. Besides being renewable, nontoxic and biodegradable, biodiesel can be added to petrodiesel due to its similar physico-chemical properties. 4Pure biodiesel is represented by B100 (100% fatty acid alkyl esters (FAAE)). However, in the case of biodiesel/petrodiesel blends the abbreviation BX indicates the percentage volume of B100 in these blends. 5 Nowadays, a B7 mixture (7% B100 and 93% diesel oil) is marketed in Brazil. 6 Biodiesel is composed of a mixture of fatty acid methyl esters (FAME) or ethyl esters (FAEE). 7 The quantification of these esters is conducted using several analytical techniques, particularly gas chromatography (GC) and high-performance liquid chromatography (HPLC).8-14 GC with flame ionization detection (FID) shows excellent selectivity in biodiesel analysis and is the main technique used for this purpose. 8,11,15,16 In Brazil, the production and use of biodiesel is regulated and supervised by the Brazilian National Petroleum, Natural Gas and Biofuels Regulatory Agency (ANP) through Resolution No. 45/2014, 17 in which the European Standard EN1410318 is adopted for the determination of methyl esters by the GC technique. In this case, the external calibration method is used, based on a comparison of the analyte peak area with the peak area of some external standards, analyzed at different concentrations. 17In the ...

Studies on Inter- and Transesterification: Different Oils with the Same Fatty Acid Composition and Their Reaction Behaviors

“…The amount of fatty acid methyl esters (FAMEs) was determined by gas chromatography (GC) using the short column methodology, and the determined error is 0.6%. 20…”

“…Aliquots were removed from the reaction medium at 0.5, 1, 2, 3, 4, 5, 10, 20, and 30 min, and the sample was deposited in a separation system, neutralized with 5% phosphoric acid solution (v/v), and washed with saturated sodium chloride solution to obtain products with neutral pH values that were free of impurities. The amount of fatty acid methyl esters (FAMEs) was determined by gas chromatography (GC) using the short column methodology, and the determined error is 0.6% …”