Microwave digestion of tree foliage for multi-element analysis

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Abstract
A microwave digestion procedure was developed for multi-element determinations in tree foliage by inductively coupled plasma–atomic emission spectrometry. The procedure involved the sequential digestion of 0.500 g of plant material with HNO3 (10 mL), H2O2 (1 mL), and HCl (2 mL) at 90% power for 30 min, 90% power for 15 min, and 30% power for 10 min, respectively. The proposed method gave Ca, Mg, K, Na, Mn, P, and S results in good agreement with the National Institute of Standards and Technology plant reference materials. Iron and aluminum concentrations were 20 to 30% lower than the certified National Institute of Standards and Technology values. Recovery of standard additions of the elements tested (including iron and aluminum) ranged from 93 to 105%. The proposed digestion method provides accurate and precise results for multi-element analysis on one solution. In addition, HClO4, an extreme laboratory hazard, has been replaced in the digestion procedure by H2O2. The microwave digestion method has been used successfully in our laboratory for over 1 year for routine analysis and for a quality assurance program using a variety of plant materials. With this method 36 to 48 samples per person per day can be prepared for inductively coupled plasma–atomic emission spectrometry analysis.