ONLINE MICROWAVE-ASSISTED DIGESTION OF SOLID SAMPLES FOR THEIR FLAME ATOMIC SPECTROMETRIC ANALYSIS

A new procedure has been developed for the on-line digestion of solids in a microwave oven. The direct injection in a water carrier flow of dispersions of solid samples in concentrated nitric acid, the merging of these slurries with 30% (v/v) H2O2 and the microwave-assisted diges tion in a Teflon coil of 100 cm permit a fast and quantitative extract ion of Cu and Mn from different solid matrices, such as vegetables, po wdered dietary products and sewage sludges. The development of an appr opriate interphase, in which digested samples are cooled and degassifi ed, previous to their introduction into the nebulizer of a flame atomi c absorption spectrometer, makes possible the full automatization of t he digestion and measurement steps of the elemental analysis of solids and it provides a sample frequency of 180 injections per hour. The de veloped procedure has also been applied for Pb and Zn determination in certified sewage sludge samples, with accurate results obtained for P b but low results found for Zn.