Page 144 - Inorganic Mass Spectrometry - Fundamentals and Applications

134 Olesik

Seawater

Analysis of seawater by ICP-MS is complicated by low concentrations of many
elements of interest, sensitivity reductions due to the high salt concentrations, and
[3
C1 containing molecular ion spectral overlaps 14.1. Standard reference seawaters
are available from the National Research Council (Canada).
Several different approaches to preconcentration and matrix elimination
have been reported. A commercially available chelation system based on silica-
immobilized 8-hydroxyquinoline has been used for on-line preconcentration and
matrix separation [3 15,3 161. Detection limits using a 90-fold concentration were
0.04 ng/dm3 for U to 6.3 ng/dm3 for Zn.
Off-line dicarbamate solvent extraction and ICP-MS analysis [317] pro-
vided p~-per-trillion detection limits: Cd (0,2 ppt), CO (0.3 ppt), Cu (3 ppt), Fe
(21 ppt), Ni (2 ppt), Pb (0.5 ppt), and Zn (2 ppt). Off-line matrix removal and
preconcentration using cellulose-immobilized ethylenediaminetetraacetic acid
(EDTA) have also been reported [3 1 S]. Transition metals and rare earth elements
were preconcentrated and separated from the matrix using on-line ion chroma-
tography with a NTA chelating resin [3 191. Isotope-dilution-based concentration
measurement has also been used after matrix separation with a Chelex ion-
exchange resin [320]. The pH, flow rate, resin volume, elution volume, and time
required for isotope equilibration were optimized. A controlled-pore glass immo-
also
bilized iminodiacetate based automated on-line matrix separation system has
been described [321]. Recoveries for most metals were between 62% and 113%.
~lectrothermal vaporization has also been used for seawater sample intro-
duction into an ICP-MS. Trace metals were complexed and then vaporized as
dithiocarbamate complexes in one study [322]. Addition of a matrix modifier
of
[~d(N03)~-Mg(NO~)~] enhanced analyte sensitivity. Addition a matrix modifier
to act as a physical carrier in ETV-ICP-MS has become common. Seawater was
used as a matrix modifier for ETV-ICP-MS in one report [323].
Sector-based ICP-MS instruments have recently been used for seawater
analysis. These instruments can provide high resolution to minimize spectral
The
overlaps or high sensitivity when used in a low-resolution mode. sample can
be diluted to reduce sample-dependent variations in sensitivity while maintaining
sufficient detection limits, Diluted seawater was introduced into the ICP without
further sample preparation in one recent report 113241. Nonspectral matrix effects
due to seawater for quadrupole and sector-based ICP-MS instruments have been
compared [325].

Soils and Sediments
The use of ICP-MS for trace analysis in sediments has recently been reviewed
[326]. The advantages and disadvantages of acid digestion versus fusion-based
of
sample dissolution were discussed. The problems involved in ICP-MS analysis