Chemistry Reference
In-Depth Information
8
Green Sample Preparation with Non-
Chromatographic Separation Techniques
María Dolores Luque de Castro and Miguel Alcaide Molina
Department of Analytical Chemistry, Campus of Rabanales, University of Córdoba, Spain
8.1
Sample preparation in the frame of the analytical process
The analytical process involves preliminary operations that can be dealt with as a whole in relation to the
concept ''sample preparation'' (SP). This term is widely used at present, but is occasionally confused with
'sample pretreatment'' because the boundary between the two (i.e. where sample pretreatment ends or what
precedes and follows sample preparation), if any, is rather ill-defined. In the authors' opinion, sample
preparation includes every step required to make a sample, or rather, the target analytes it contains, ready for
insertion into a measuring instrument and may involve more than one step; this is consistent with IUPAC's
statement that 'sample preparation is intended to transfer or transform the analytes into measurable forms' [1].
On the other hand, sample pretreatment can be envisaged as the first step in a sample preparation process
or as one preceding some specific action (e.g. a pretreatment for either subsequent liquid-liquid extraction or
insertion of a solution into a chromatograph). From this point of view, it is unclear when such a step finishes
and detection starts (e.g. ionization in methods using MS detection or vaporization and atomization treatments
in atomic detectors).
Sample preparation is most often a necessity since even the simplest samples are frequently unsuitable for
direct analysis. In most cases, the need arises from excessive dilution or concentration of the target analytes
in the sample or from incompatibility with the standard operational procedures for some instruments. A large
number of SP approaches have been devised to enable the detection of analytes that range from classical
operations - many of which including calcination, wet digestion or Soxhlet leaching have been in use for
centuries - to modern operations developed less than two decades ago (e.g. supercritical fluid leaching). In
any case, both classical and modern SP operations are being continuously improved.
