RAPID PARTIAL DIGESTION OF BIOLOGICAL TISSUES WITH NITRIC-ACID FOR THE DETERMINATION OF TRACE-ELEMENTS BY ATOMIC SPECTROMETRY

Determination of Cu, Fe, Mn and Zn in fresh bovine liver and BCR bovine liver and pig kidney reference materials, after digestion at 105-degrees-C with nitric acid for various times, showed that the trace elements were completely released after heating for only 20 min. Centrifugation of the sameples after digestion improved the separation from undigested fat. This partial-digestion method, based on heating about 0.2 g of sample with 2 ml of nitric acid for 20 min, was tested on a range of biological reference materials and on fresh bovine liver for the four elements. Comparison was made with results obtained after digestion by a recommended hydrogen peroxide-sulfuric acid digestion procedure. Results obtained by inductively coupled plasma atomic emission spectrometry or by flame and graphite-furnace atomic absorption spectrometry showed good agreement between the two digestion procedures, and results for the reference materials agreed well with the certified values. Between-batch precision was better than 4% for Cu, Fe and Zn at levels of 30 to 190,210 to 320 and 100 to 140 mug g-1, respectively. For Mn, the precision varied between 7 and 14% for measured concentrations of 8 to 12 mug g-1. The partial-digestion procedure offers simplicity, speed, low cost and the ability to handle a large number of samples at the same time.