• Energy Research

Bioethanol real samples have been directly analyzed through ICP-MS by means of the so called High Temperature Torch Integrated Sample Introduction System (hTISIS). Because bioethanol samples may contain water, experiments have been carried out in order to determine the effect of ethanol concentration on the ICP-MS response. The ethanol content studied went from 0 to 50%, because higher alcohol concentrations led to carbon deposits on the ICP-MS interface. The spectrometer default spray chamber (double pass) equipped with a glass concentric pneumatic micronebulizer has been taken as the reference system. Two flow regimes have been evaluated: continuous sample aspiration at 25 μL min− 1 and 5 μL air-segmented sample injection. hTISIS temperature has been shown to be critical, in fact ICP-MS sensitivity increased with this variable up to 100–200 °C depending on the solution tested. Higher chamber temperatures led to either a drop in signal or a plateau. Compared with the reference system, the hTISIS improved the sensitivities by a factor included within the 4 to 8 range while average detection limits were 6 times lower for the latter device. Regarding the influence of the ethanol concentration on sensitivity, it has been observed that an increase in the temperature was not enough to eliminate the interferences. It was also necessary to modify the torch position with respect to the ICP-MS interface to overcome them. This fact was likely due to the different extent of ion plasma radial diffusion encountered as a function of the matrix when working at high chamber temperatures. When the torch was moved 1 mm plasma down axis, ethanolic and aqueous solutions provided statistically equal sensitivities. A preconcentration procedure has been applied in order to validate the methodology. It has been found that, under optimum conditions from the point of view of matrix effects, recoveries for spiked samples were close to 100%. Furthermore, analytical concentrations for real samples following the preconcentration method and the direct determination were not significantly different. The quantification method was finally based on external calibration with standards containing 50% (v/v) ethanol content. C. Sánchez would like to thank the Ministry of Education, Culture and Sports, Spain for the grant FPU 13/01438.

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.

A method has been developed for the direct (no sample pretreatment and/or isolation of the target element from the sample matrix) Pb isotopic analysis of bioethanol via multi-collector ICP-mass spectrometry (MC-ICP-MS).

Biofuel quality control involves the determination of metal and metalloid content.

Forty-one bioethanol real samples and related fractions, together with a biobutanol sample, have been analyzed with gas chromatography coupled to either mass spectrometry (GC-MS) or flame ionization detection (GC-FID). Bioethanol with different water contents, samples originated from several sources of biomass, first- as well as second-generation specimens, distillation fractions, samples stocked in containers made of four different materials, and, finally, a biobutanol sample have been analyzed. The number of the compounds found through GC-MS has been 130, including alcohols, aldehydes, ketones, esters, ethers, nitrogen compounds, organic acids, furane derivates as well as other species (e.g., limonene). Afterward, a quantitative determination of major components of bioethanol has been carried out. The achieved results have revealed that, besides ethanol and, in some cases, water, species such as acetaldehyde, methanol, and higher alcohols, as well as 1,1-diethoxyethane, may be present at concentrations above 500 mg L-1. While the source of bioethanol (nature of the raw material, ethanol generation, or water content) has a direct impact on its volatile organic compound (VOC) profile, the material of the container where the biofuel has been stored does not play a significant role. Finally, the results have demonstrated that, for a given production process, different distillation fractions contain unequal VOC profiles.

A new method to carry out the elemental determination of metals in bioethanol through ICP-OES has been developed. The procedure is based on the use of a heated torch integrated sample introduction system (hTISIS) to directly introduce the vaporized sample into the plasma. Two injection modes (continuous liquid aspiration and air-segmented flow injection analysis) have been evaluated. In a first step, the matrix effects caused by several ethanol–water mixtures were removed by operating the hTISIS at 400 °C in segmented injection. Meanwhile, the results also proved that the system could be operated in continuous mode at 200 °C with the complete interference removal. Finally, twenty-eight real samples with bioethanol contents between 55% and 100% were analyzed with the methods previously developed. Regarding validation, recoveries from 80% to 120% were obtained for 18 analytes and the concentrations found with the proposed method were in agreement with those encountered with a preconcentration method, taken as a reference procedure. Limits of detection went from 3 ng mL− 1 for manganese to about 500 ng mL− 1 for calcium. This allowed to quantify Cr, Fe, Mg, Mn and Zn in segmented flow injection and Al, Cd, Cr, Cu, K, Mg, Mn, Na and Zn in continuous sample aspiration mode in bioethanol samples. The authors wish to acknowledge the IFPEN for the financial support and samples provided and the UNGDA for the samples provided to carry out this work. C. Sánchez would like to thank the Ministry of Education, Culture and Sports, Spain for the grant FPU 13/01438.

A total sample consumption system (hTISIS) was used for the first time to evaluate the plasma spatial ion profile for ethanolic samples in ICP-MS.