Focused microwave-assisted acid digestion of oils: an evaluation of the residual carbon content

Abstract

A focused-microwave oven was applied for acid digestion of oil samples. The aim was to evaluate the efficiency of the decomposition performed on a system with six reaction vessels, one magnetron, one waveguide and six slots to control the transfer of the microwave radiation to each one of the six cavities. The digestion efficiency was correlated with the residual carbon content, which was determined by inductively coupled plasma optical emission spectrometry with an axial view configuration. It was demonstrated that the effective power can vary up to 42% employing water for calibration. This variation in the effective power is similar to the variation observed in the residual carbon content of digested oil samples that was found to be between 2.37 and 9.71%, depending if all cavities were used simultaneously or each one individually. These aspects should be taken into account in the evaluation of possible effects on sample introduction and atomization/excitation conditions in inductively coupled plasmas