Page 162 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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Figure 7.1
Flow injection manifold for coupling with atomic spectrometry. The column can be used
for preconcentration, matrix removal or chromatography.
and the advantages described for pulse nebulization. The introduction of organic solvents into plasma
instruments can lead to high reflected power (i.e. power that is reflected back to the generator and
which can cause damage), plasma cooling, interference effects and possible plasma extinction. The use
of flow injection enables only very small volumes to be introduced and hence the deleterious effects
are minimized. For some samples, e.g. sea-water, the matrix constituents are very high (e.g. 3.5% w/v
salt) and many of the analytes of interest are at very low concentration (ng ml level or below). By
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using a micro-column containing an appropriate ion or chelating exchange resin, the analytes may be
retained while the bulk matrix is allowed to pass to waste. The analytes may then be eluted to detection
by the introduction of a small volume of eluent. If 20 ml of sample are passed through the column and,
after washing with de-ionized water to remove the remnants of the matrix, the analytes are eluted to
detection by 0.5 ml of eluent, a preconcentration factor of 40 is achieved. The use of such mini-columns
of exchange media is becoming more popular as it facilitates the analysis by both preconcentrating the
sample while simultaneously removing potential interferences. Such a technique enables ultra-trace
analytes to be determined using simpler and cheaper instrumentation, e.g. a flame spectrometer. If it is
coupled with ICP-MS, detection limits substantially below the ng ml level may be obtained, even for
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very complex samples. A typical flow injection manifold that would permit preconcentration or matrix
removal is depicted in Fig. 7.1.

7.5 Vapour Generation

7.5.1 Hydride Generation
The elements Ge, Sn, Pb, As, Sb, Bi, Te and Se, form covalent gaseous hydrides. A number of these
elements are now routinely determined by