Abstract

Quantification of particulate (>0.45 µm) and dissolved (<0.45 µm) trace elements in seawater is imperative for understanding geochemical cycling in the marine environment. Suspended particulate trace element concentrations are typically <10% of total element concentrations in seawater. To overcome analytical difficulties associated with low analyte concentrations, it is common to filter large volumes (tens to thousands of litres) of seawater. We report a novel method for the rapid quantification of Al (324 ppb), P (159 ppb), V (2.02 ppb), Cr (2.85 ppb), Mn (22.3 ppb), Fe (304 ppb), Co (0.129 ppb), Ni (0.817 ppb), Cu (1.68 ppb), Zn (3.25 ppb), Mo (0.264 ppb), Ag (0.079 ppb), Cd (0.029 ppb), Ba (3.54 ppb), Pb (1.13 ppb) and U (0.053 ppb) in digest solutions of suspended matter, filtered from 0.2 to 5.0 L of seawater. Filter digest solutions, consisting of a complex matrix of filter residue, sea salt, dissolved solids and strong acids, are analyzed on the ELEMENT, a high resolution, inductively coupled plasma mass spectrometer (Finnigan-MAT, Bremen, Germany). High sensitivity (>1 × 10⁶ counts s⁻¹ ppb⁻¹ In; with shielded torch) combined with low flow rates (μFlow nebulizer, Elemental Scientific) provide excellent absolute detection limits (0.4 to 720 pg depending on the element). A resolution of 300 (low resolution) is appropriate for interference-free high mass analytes of interest (Ag, Cd, Pb, Ba and U), whereas 4300 (medium resolution) is sufficient to resolve all plasma-, water- and matrix-based polyatomic interferences on low mass analytes (Al, P and first row transition metals). The precision of the method is better than ±4% for most analytes. Accuracy could not be determined conventionally using a certified reference material (not available), but was estimated from spiked samples to be <±4% when calculated using a standard additions curve and <±10% for most elements if using an external standard curve.