Determination of trace elements in marine plankton by inductively coupled plasma mass spectrometry (ICP-MS)

A method has been developed for the determination of 23 elements in marine plankton in which inductively coupled plasma (ICP) source mass spectrometry (MS) was used to quantify the elements in the solution after digestion in a mixture of hydrofluoric and nitric acids in sealed PTFE vessels in a micr owave field. The procedure was validated by the analysis of a standard refe rence soil (SRM 2709 San Joaquin Soil) and a standard reference fresh water plankton (CRM 414). The method was applied to the analysis of several mari ne plankton samples grown under controlled conditions including several who se growth media had been enriched with selenium. Matrix induced signal supp ressions and instrumental drift were corrected by internal standardization. The suitabilities of germanium, indium, rhodium, scandium and yttrium as i nternal standard elements were evaluated. Neither scandium nor yttrium coul d be used due to the presence of these el elements in the samples, germaniu m was used for the determination of As, Co, Cu, Fe, Ni, Se, Si and Zn, indi um was used for Al, Ba, Ca, Eu, Sr, and Tl, and rhodium was used for Cd, Cr , Hg, Mg, Pb, Sb, Sn, and V. For Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Sr, V, and Zn internal standardization did not completely compensate for the supp ressive effect of the heavier elements and the solutions were diluted. Howe ver, for As, Ba, Cd, Co, Eu, HE, Pb, Sb, Se, Sn and T1, it was possible to obtain accurate results despite the 35-40% suppression in the signals. Isob aric overlap was only a problem in the cases of Ca-42 and Se-78; Ca-44 and Se-77, respectively, were used. Memory effects were only observed with Hg f or which a nitric acid-sodium chloride solution was the most effective wash -out solution. The marine plankton samples were able to tolerate a higher c oncentration of Hg as the selenium concentration increased.