Figure 4.10
SPME sampling device.Extraction is an equilibrium process that is affected by temperature, analyte and other sample
component concentrations, and the volume/thickness of the polymeric coating. Continuous stirring of
liquid samples greatly speeds up the equilibration process whilst the headspace sampling of liquids and
solids (p. 109) and gaseous samples require the shortest equilibration times. Detection limits are the
lowest with the thickest fibre coatings but equilibration times are correspondingly very long (up to
several hours). The desorption of analytes is also time and temperature dependent so that careful control
of these parameters is necessary in both the sampling and analysis stages. An advantage of SPME over
SPE is the avoidance of solvents, but good precision for quantitative determinations is more difficult to
achieve and automated systems are only just being developed.
Applications of SPE and SPME
The principal application is in the preparation or 'pretreatment' of samples for analysis where analytes
need to be separated from other sample components (the sample matrix), and in some cases to
concentrate trace or ultra-trace levels of analytes that would otherwise not be detectable or quantifiable.
Matrix components may cause interference with the subsequent determination of analytes and, where a
chromatographic analysis is required, they may be detrimental to the performance of a column. The
pretreatment of 'dirty samples', i.e. those containing high levels of matrix components such as salts,
proteins, polymers, resins, etc., and often described as 'sample clean-up', is necessary where there is a
likelihood of contamination of the column leading to rapid deterioration. SPE is versatile and rapid,
requires only small volumes of solvents (cf. solvent extraction, section 4.1), or none in the case of
SPME, and cartridges or disks are cheap enough to be discarded after use thus obviating the need for
regeneration. The analysis of environmental, clinical, biological and pharmaceutical samples have all
benefited from a rapid growth in the use of SPE where it has largely replaced solvent extraction.
Specific examples include the determination of pesticides and herbicides in polluted surface waters and
soils, polycyclic aromatic hydrocarbons (PAHs) in drinking water, polluted industrial and urban
atmospheres, and drugs in biological fluids. SPME is finding particular use in water analysis, in the
analysis of fragrances and