Low-volume microwave digestion of marine biological tissues for the measurement of trace elements

The use of low-volume (7 ml) Teflon vessels and microwave heating is described for the digestion of three marine biological tissues representing a mollusc, a fish and a crustacean. Freeze-dried samples (< 0.1 g dry mass) and 1 ml of nitric acid were placed in 7 ml screw-topped Teflon vessels and treated using a programmed three-stage digestion. The first two stages were kept consistent (600 W, 2 min; 0 W, 2 min) and the third stage was varied from 150 to 450 W over 15-60 min to find the optimum microwave digestion conditions. Trace elements were determined using flame atomic absorption spectrometry, or electrothermal atomic absorption spectrometry when analysing samples containing very low concentrations of cadmium. Quantitative recoveries of copper, zinc and cadmium were obtained from the five marine reference materials under the following conditions: 600 W, 2 mins; 0 W, 2 min; 450 W, 45 mins.