Application of microwave induced combustion in closed vessels for carbon black-containing elastomers decomposition

A rapid digestion procedure for the determination of Al, Fe, Mn, Sr and Zn in carbon black-containing elastomers (30%) has been developed using sample combustion in closed quartz vessels. Microwave radiation was used for ignition. Combustion takes place in the presence of oxygen under pressure using ammonium nitrate (50 μl of 6 mol l− 1) as aid for ignition. Samples of nitrile-butadiene rubber and ethylenepropylene-diene monomer were decomposed. A quartz device was used simultaneously as a sample holder and for the protection of vessel cap. The influence of the absorption solution (nitric acid or water) and the necessity of an additional reflux step were evaluated. Determination of Al, Fe, Mn, Sr and Zn was performed by inductively coupled plasma optical emission spectrometry. A reference method (ASTM D 4004-06) based on conventional dry ashing and flame atomic absorption spectrometry was used for comparison (Mn and Zn). Results were also compared to those obtained by using wet acid digestion in closed systems. Concentrated and diluted (4 mol l− 1) nitric acid, with 5 min of reflux after the combustion, gave best recoveries for all analytes (from 97 to 101%). For dry ashing quantitative recoveries were found only for Zn whereas for Al, Fe, Mn and Sr the recoveries were only 14, 37, 72 and 37%, respectively. With the proposed procedure the residual carbon content was below 0.5% and further determination of analytes was feasible with only the combustion step (for Fe a reflux with diluted HNO3 was necessary). Complete sample digestion is obtained in less time using the proposed procedure than with other procedures and no concentrated acids were necessary.