Direct determination of chlorine in the glycerin by-product of biodiesel production: A green approach using energy dispersive X-ray fluorescence spectrometry

Glycerin, by-product of biodiesel, is produced in large amounts and it contains several contaminants, including chorine (due to the neutralization stage using HCl). When using this glycerin as biomass to produce energy, the presence of alkaline chlorides may lead to the formation of corrosive fumes at high temperatures. In this sense, the knowledge of chloride content is important in order to decide the fate of this raw by-product. The direct spectrometric determination of chlorine is an analytical challenge. In this context, energy-dispersive X-ray fluorescence spectrometry provided direct and accurate determination, relying on external calibration based on sample dilution and matrix matching with mixture of pure glycerin and water and using NaCl as the analytical (primary) standard. Method limit of quantification was 50 mg kg⁻¹, with analytical curve up to 1000 mg kg⁻¹ (R² = 0.9992), and repeatability below 5% were found to be adequate for such application in such highly salty samples (original concentrations at mg g⁻¹). In addition to sample directly analysis, without any previous treatment but homogenization and dilution, not requiring chemical derivatization and the not using of toxic reagents are in consonance to the analytical green chemistry requirements, allowing direct analysis of sample with no chemical derivatization with toxic reagents.