Microwave-assisted dilute acid extraction of trace metals from biological samples for atomic absorption spectrometric determination

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Abstract
A microwave extraction method with dilute nitric acid for biological samples was developed using a pressure feedback microwave extraction system. The concentration of nitric acid, pressure setting and extraction time were optimized by a mixed level orthogonal array design. The interactions among the selected parameters for the extraction were investigated. The effect of sample mass was also studied. Six replicate analyses of NIST 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 ETAAS. Recoveries of 96–103% were achieved for all the elements. The RSDs of the test elements were less than 3.8%, except for Ni. The extraction method was also employed to extract four other biological SRMs and CRMs. With the exception of Ni, the recoveries of the eight test elements were 91–107% in all the reference materials.

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