Development of a new sample pre-treatment procedure based on pressurized liquid extraction for the determination of metals in edible seaweed

A new, simple, fast and automated method based on acetic acid-pressurized liquid extraction (PLE) has been developed for the simultaneous extraction of major and trace elements (As, Ca, Cd, Co, Cr, K, Mg, Mn, Na, Pb, Sr and Zn) from edible seaweeds. The target elements have been simultaneously determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The influence of several extraction parameters (e.g. acetic acid concentration, extraction temperature, extraction time, pressure, number of cycles, particle size and diatomaceous earth (DE) mass/sample mass ratio) on the efficiency of metal leaching has been evaluated. The results showed that metal extraction efficiency depends on the mass ratio of the dispersing agent mass and the sample. The optimized procedure consisted of the following conditions: acetic acid (0.75 M) as an extracting solution, 5 min of extraction time, one extraction cycle at room temperature at a pressure of 10.3 MPa and addition of a dispersing agent (at a ratio of 5:1 over the sample mass). The leaching procedure was completed after 7 min (5 min extraction time plus 1 min purge time plus 1 min end relief time). Limits of detection and quantification and repeatability of the over all procedure have been assessed. Method validation was performed analysing two seaweed reference materials (NIES-03 Chlorella Kessleri and NIES-09 Sargasso). The developed extraction method has been applied to red (Dulse and Nori), green (Sea Lettuce) and brown (Kombu, Wakame and Sea Spaghetti) edible seaweeds.