Journal
SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY
Volume 57, Issue 12, Pages 2121-2132Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0584-8547(02)00164-7
Keywords
acid digestion; closed vessel; microwave-assisted digestion; plant materials; residual carbon content; inductively coupled plasma optical emission spectrometry (ICP-OES)
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The efficiency of microwave-assisted acid digestion of plants using different concentrations of nitric acid (2.0, 3.0, 5.0, 7.0 and 14 mol 1(-1)) with hydrogen peroxide (30% v/v) was evaluated by measuring the residual carbon content (RCC) using inductively coupled plasma optical emission spectrometry (ICP-OES) with axial viewing. Certified reference materials were used for evaluating the accuracy attained when 2 mol 1(-1) HNO3 was employed for digestion. Under all experimental conditions RCC values were always lower than 13% w/v, and even the highest concentration did not cause any interference with element recovery. It seems that the high pressure reached for closed-vessel operation improved the oxidative action of nitric acid due to consequent temperature increase, even when this reagent was not used at high concentrations. According to acid-base titration data, residual acid in the digestates varied from 1.2 to 4.0 mol 1(-1), depending on the acid concentration initially added. It can be concluded that for plant materials, microwave-assisted acid digestion can be carried out under mild conditions, which implies that digestates do not need extensive dilution before introduction by pneumatic nebulization to ICP-OES. An additional advantage is the lower amount of residue generated when working with less concentrated acid solutions. (C) 2002 Elsevier Science B.V. All rights reserved.
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