| Summary: | 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. === Science, Faculty of === Chemistry, Department of === Graduate
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