Page 150 - Inorganic Mass Spectrometry - Fundamentals and Applications

140 Olesik

cient information. For example, a high concentration of arsenic in blood could be
due to a lethal ingestion of inorganic arsenic or of shellfish that contain seemingly
unhardul arsenobetaene.
The evolution and trends in elemental speciation have recently been as-
sessed [386-3881. Speciation is essential in many developing areas, including
biomedical, food, environmental, industrial processes, and industrial hygiene.
Among the elements for which species dete~nation can be necessary are M, As,
Br, Cd, Cr, Cu, Fe, Hg, I, P, Pb, Pt, Se, Sb, Sn, and the actinides [386].
Elemental speciation presents many analysis challenges. Often species are
important at very low concentrations. Stable storage is a problem as often the
speciation changes over time after the sample is collected. The elemental specia-
of
tion could be changed by processing the sample. ICP-MS has become popular
as a detector for separation techniques in order to identify and quantify diEerent
species, as described in a recent review [389]. Different species are separated and
introduced into the ICP-MS as a function of time. Time-resolved ICP-MS signals
then provide information on the species containing each detected element (from
the
the time the signal appears) as well as specifically identifying elements present
and quantitatively measuring their concentration. Among the separation tech-
[390,
niques that have been used with ICP-MS detection are gas c~o~a~ograp~y
39 l] , liquid extractions [ 3921, ~gh-pe~ormance liquid c~omatography [ 393 ,
3941, size exclusion chro~atography [395,396], and capillary electrophoresis
[24,397].
The choice of TCP-MS is mainly due to the low detection limits and high
elemental specificity. Because the sample must be physically transported from the
separation column or capillary into the plasma, the interface is important. High
analyte transport efficiency is desirable to obtain low detection limits, but care
must also be taken in designing the interface so that the separation is not degraded.
Dead volume and induced laminar Bow due to the interface E3981 must be
considered.
Although there is clear agreement on the importance of elemental specia-
tion, routine applications have not grown as quickly as predicted [386]. mar-
The
ket for commercial instruments for elemental speciation has not risen significantly.
There are several reasons for this. The initial groups interested in speciation are
researchers who have put together their own inst~ments. Sample preservation and
measurement without changes in speciation can be problems; therefore, court
cases based on evidence from elemental speciation measurements have not been
successful. Recently, an approach using isotope dilution has been described to
assess quantitatively and correct for changes in speciation during sample storage
it
and analysis [399,400]. Standards are lacking, in part because may be difficult to
ensure their stability. Elemental speciation typically requires much more knowl-
edge about the sample chemistry than does total elemental analysis. Separation
systems for specific sample and analyte types must often developed. Therefore,
be
there is not a method that is as “universal” as for total elemental analysis.