Chemistry Reference
In-Depth Information
possibilities of microfabrication technology, the unique behaviour of
microfluidics
, and the possibilities of
accurate fluidic manipulation.
In two broad parts, this chapter reviews the current state-of-the-art regarding miniaturization in sample
preparation and discusses most recent developments and achievements in the field on the basis of selected
examples. In particular, attention will focus on the analysis of trace organic compounds due to the difficulty
associated to this type of determination. Nevertheless, if relevant, examples will also be taken from other
application areas. In all cases, emphasis will be on techniques that have already demonstrated their practicality
by the analysis of real-life samples.
17.2
Non-integrated approaches for miniaturized sample preparation
In this section, the different analytical approaches will be revised on the base of sample preparation techniques
best suited for each type of matrix. Nevertheless, many of these techniques can be used at different stages of
sample pre-treatment for most matrices.
17.2.1
Gaseous and liquid samples
17.2.1.1
Thermal desorption-based techniques
Purge-based techniques have successfully been used for years in combination with gas chromatography (GC)
for the analysis of volatile components in liquid, semi-solid and solid samples. There are solvent-free
approaches among which the most significant and widely used is the so-called Purge-and-Trap (P&T). During
the last decades, several automatic systems have been commercialized for this already mature and well
established technique. Thereby, research in this field remains essentially in the development of novel sorbents
for improved analyte retention and of new electronics allowing faster heating and cooling of the different
parts of the instrumentation. Probably one of the most interesting recent achievements regarding this technique
has been the introduction of a direct thermal desorption (DTD) liner-exchange unit for determination of
(semi-)volatile analytes in solid samples with subsequent GC analysis. The system, introduced by de Koning
et al
. [3], enables complete sample preparation to be performed in an automated, on-line and miniaturized
fashion. The feasibility of the approach for obtaining information from sample sizes which could hardly be
handled with other extraction techniques has been illustrated, for example, by determination of wood
preservatives using only 10 mg of pine sapwood powder, or by obtaining paleontogical information from
1-20 pollen grains (pollen size ca. 20
m). The possibility of performing reactions directly in the liner and/
or using a fresh liner-plus-vial for each sample with automatic exchange of both opens new application
possibilities to be exploited in future and that certainly will contribute to further simplify sample handling.
μ
17.2.1.2
Solvent-based extraction techniques
In principle, the simplest strategy to miniaturize a procedure is reducing the dimensions of the systems used
in earlier approaches. This approach has been used in the case of liquid-liquid extraction (LLE) yielding
different modern miniaturized techniques.
When the volumes of the aqueous sample and the extractant are small enough, LLE can be performed in a
chromatographic vial and the analytical approach is called in-vial LLE. The experimental parameters affecting
the analytes partition process, and so to be optimized, are similar to those of LLE. Salting out of the mixture
and in-vial derivatization of the analytes can also be used to improve the extraction efficiency. However, apart
from its simplicity, probably the most interesting features of the techniques include the significant reduction
