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

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 sys tem with six reaction vessels, one magnetron, one waveguide and six slots t o control the transfer of the microwave radiation to each one of the six ca vities. The digestion efficiency was correlated with the residual carbon co ntent, 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 v ariation in the effective power is similar to the variation observed in the residual carbon content of digested oil samples that was found to be betwe en 2.37 and 9.71%, depending if all cavities were used simultaneously or ea ch one individually. These aspects should be taken into account in the eval uation of possible effects on sample introduction and atomization/excitatio n conditions in inductively coupled plasmas (C) 2001 Elsevier Science B.V. All rights reserved.