MICROWAVE-ASSISTED DILUTE-ACID EXTRACTION OF TRACE-METALS FROM BIOLOGICAL SAMPLES FOR ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION

A microwave extraction method with dilute nitric acid for biological s amples was developed using a pressure feedback microwave extraction sy stem, The concentration of nitric acid, pressure setting and extractio n time were optimized by a mixed level orthogonal array design, The in teractions among the selected parameters for the extraction were inves tigated, The effect of sample mass was also studied, Six replicate ana lyses of MST SRM 1515 Apple Leaves were performed under the optimized extraction conditions (5 ml of 14% v/v nitric acid; pressure setting, 1104 kPa; extraction time, 30 min; sample mass, 0.3 g), Eight elements , viz., Ca, Cu, Fe, K, Mg, Mn, Ni and Zn, were determined by FAAS or E TAAS, Recoveries of 96-103% mere achieved for all the elements, The RS Ds of the test elements were less than 3.8%, except for Ni, The extrac tion method was also employed to extract four other biological SRMs an d CRMs. With the exception of Ni, the recoveries of the eight test ele ments were 91-107% in all the reference materials.