Microwave digestion of tree foliage for multi-element analysis

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 HNO 3 (10 mL), H 2 O 2 (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, HClO 4 , an extreme laboratory hazard, has been replaced in the digestion procedure by H 2 O 2 . 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.