Chemistry Reference
In-Depth Information
As an example of the latest research in this field, Moreda-Piñeiro
et al.
proposed the use of a pressurized
enzymatic-assisted hydrolysis extraction for arsenic speciation in seafood samples prior to HPLC-ICP-MS
determination together with a simultaneous in situ clean up procedure that speeds up the sample treatment [42].
11.2.1.5
Extraction-preconcentration approaches with nanotubes
Carbon nanotubes have been mentioned before in another context (as potential target sample). It is also
becoming trendy to evaluate the potential of these materials for the simultaneous extraction and
preconcentration of trace metals and also, for the separation of one metal from another one, as performed
elsewhere [43-46]. All the methods of extraction-preconcentration based on the use of nanotubes do not
exempt the use of different reactants, but the required volumes are very small and, in the case of their
combustion, there are no significant residues.
11.2.1.6
Cloud point extraction
A new sample pre-processing procedure with a methodology that agrees with the Green Analytical Chemistry
principles is the cloud point extraction. This is a solventless solvent extraction, in which the solvent phase is
replaced by a surfactant in which preconcentration and separation of the analytes from the sample takes place
[47-49]. The small volume of surfactant phase used confers good characteristics to this technique, although
these surfactants are not always innocuous. However, the more eco friendly tendency is based on the use of
non toxic surfactants [50].
11.2.2 Slurry methods
Slurry sampling techniques are used in atomic spectrometry as a means to carry out the (quasi) direct
determination of metals in solid samples, and provide some good analytical features, including some
advantages over conventional procedures based on sample digestion, such as:
increased sample throughput,
●
prevention of analyte losses and/or contamination,
●
the same automated device used for liquid dosing may also be applied for slurry introduction.
●
Most of these features are shared with truly direct solid sampling techniques that will be discussed later on
this chapter. However, it should be mention that slurries techniques still require the use of reagents that can
be considered as contaminants for acid leaching (e.g., HNO
3
) or as surfactants (Triton X-100, for example).
Drawbacks in the past associated with sedimentation of particles or flotation of light material of the slurry
are avoided with the addition of surfactant agents to the medium. With respect to the liquid media used to
generated the slurry, in some occasion water can be a good choice, working in that case with an environmental
friendly reactant but, as stated before, the use of acids is very frequent, which a priori causes the same
problems as sample digestion related to waste generation. However, it has to be remarked that the amounts of
acids used are normally much lower than those used for wet digestions.
Most of the applications of slurry sampling techniques are designed for atomic absorption spectrometry
(AAS). There are two recent works of Ferreira
et al.
[51] and Resano
et al.
[52] that review the state-of-the-art
of this technique. Recent trends in this context involved the use of high-resolution continuum source AAS,
which has been demonstrated to offer relevant advantages in conjunction with the slurry sampling approach
for the direct analysis of yogurt samples [53] or for the simultaneous determination of Cd and Fe in sewage
sludge. More comments on this technique will be provided later on this chapter [54].
