The extraction and analysis of dissolved trace metals from seawater using on-line flow injection inductively coupled mass spectrometry
Creators: name: Nicolidakis, Helen
Publisher: name: University of British Columbia
Year: 2009

description: A method utilizing flow injection (Fl) for on-line preconcentration with inductively coupled plasma mass spectrometry (ICP-MS) detection has been developed for analyzing dissolved zinc, cadmium, nickel, copper, lead, manganese, gallium and niobium in seawater. This method was used to investigate the distributions of these trace metals in the western, central and sub-Arctic North Pacific Ocean. Using on-line Fl methods to replace conventional preconcentration/separation techniques results in significant decreases in sample and reagent volumes and sample work up and analysis time. This method used a column filled with 8-hydroxyquinoline on silica resin to preconcentrate up to 18 millilitres of seawater for a minimum sample throughput of six per hour. Concentrations of these elements ranged between 0.01 and 12 nmol/kg, with analytical precision being better than 12 % for all elements except Cu, and detection limits in the low picomolar range (1 - 90 pmol/kg). The accuracy of the technique was verified by analysis of standard reference material from the National Research Council of Canada for Zn, Cd, Ni, Cu, Pb and Mn. This Fl method was also incorporated into the design of a prototype sampler with multi-sampling capabilities which was developed to preconcentrate trace metals from seawater remotely. The sampler was submerged in-house for a period of one week, and operated successfully. Before collecting contaminant-free seawater samples, a second generation sampler is required. The results obtained for Zn, Cd, Ni, Cu, Pb and Mn using the on-line Fl-ICP-MS method developed here showed the expected distributions, agreeing well with profiles previously determined using the same samples and with profiles measured by other labs in the same region of the North Pacific. The first set of dissolved Ga data from the western North Pacific are presented here. When coupled with published data from the sub-Arctic North Pacific Current and from the central gyre, the new information yields a better understanding of the controls of dissolved Ga behaviour in the North Pacific. At all stations, Ga shows high surface concentrations, a minimum at ~1000 m and increases at greater depth. Sub-surface maxima at ~ 500 m are observed in the central gyre and in the sub-arctic North Pacific Current, but not in the western North Pacific. Dissolved Ga in surface waters is highest in the central gyre (14 to 19 pmol/kg), an area with low dust input from the Asian continent and low productivity. In the western Pacific, where dust input and productivity are both high, surface water Ga values are lower (9 to 12 pmol/kg). This indicates that the high levels of Ga in the central gyre and the presence of the sub-surface maximum in this region are not due to advection from the western North Pacific. The lowest surface concentrations (4 to 10 pmol/kg) are found in the sub-Arctic North Pacific Current, an area with low dust input and high productivity. The first full depth profiles of niobium in the ocean are reported in this dissertation. The Nb distributions in the North Pacific show low surface concentrations and sub-surface and mid-depth maxima coincidental with the boundaries of the O₂ minimum. Nb concentrations range between 10 and 80 pmol/kg in surface waters, 40 and 100 pmol/kg in the upper boundary of the O₂ minimum zone, 40 and 200 pmol/kg in the lower boundary of the O₂ minimum zone and 10 and 100 pmol/kg in deep waters. The concentrations decrease with distance from the Asian continent, and increase in the North Equatorial Current, suggesting horizontal advection of high Nb waters from both the western and eastern Pacific boundaries. The distribution of Nb may also be affected by Mn and nutrient cycling and pH changes in the O₂ minimum zone, though the extent of these cannot be ascertained at present.