Evolution of the metal and metalloid content along the bioethanol production process

Abstract

Metal and metalloid concentration has been determined through inductively coupled plasma - mass spectrometry (ICP-MS) in bioethanol samples, raw materials employed to obtain this biofuel and samples taken from different critical points of the manufacture method. In this way, it was possible to study the evolution of the metal and metalloid content all along the bioethanol production process, allowing to establish the origin of the elements determined in the final samples. Moreover, the steps of the production process where they were either removed from the biomass or accumulated in the biofuel were successfully identified. Four different acid assisted protocols were compared through the analysis of two biomass certified reference materials (CRMs). The results revealed that, for the most suitable method (nitric acid assisted MW digestion), recoveries for the analytes of interest went from 90% to 110%. Furthermore, good short-term and long-term precision and acceptable limits of detection (LODs) were obtained. Two different production lines were studied, and our results show that slight differences in terms of the minor elements concentration (Cd, Co, Sb, Pb and V) were identified. The most important source of metals and metalloids in the whole process can be attributed to the raw material. Meanwhile the distillation step caused 1000 to 10,000 times decrease in elemental concentration in the final bioethanol as compared to the initial biomass.