Effect of acid concentration on closed-vessel microwave-assisted digestion of plant materials |
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Authors: | Gergia C L Araújo Mrio H Gonzalez Antnio G Ferreira Ana Rita A Nogueira Joaquim A Nbrega |
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Institution: | a Grupo de Análise Instrumental Aplicada, Embrapa Pecuária Sudeste, Caixa Postal 339, 13560-970, São Carlos SP, Brazil b Departamento de Química, Universidade Federal de São Carlos, São Carlos SP, Brazil |
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Abstract: | 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 l?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 l?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 l?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. |
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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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