Solid phase extraction for micropollutant sampling

Although separation and detection techniques are becoming increasingly efficient, the analysis of environmental samples generally requires a pre-treatment step. This can serve a variety of purposes, such as pre-concentration of pollutants at levels too low to be detected directly, or sample purification when the matrix is too complex or contains interferents.

The methods used involve very different principles, depending on the physico-chemical properties of the compounds to be extracted and the sample matrix (water, air, soil, etc.). By way of example, figure 1 shows a classification of micropollutants according to their polarity and volatility, as well as several aqueous phase extraction/concentration techniques related to the compounds' physico-chemical properties.

Many of these methods are based on older technologies, such as liquid/liquid solvent extraction. This technique is still widely used, however, as it is subject to numerous standards. However, it has a number of drawbacks, such as the need to maintain glassware, the use of sometimes toxic solvents, and the number of extraction stages that can lead to losses. These features also make it difficult to automate analysis, as it is difficult to couple with separation and detection techniques.

The current trend is towards rapid, inexpensive and automatable protocols. This would make it easier to move towards routine methods, but also to envisage on-site measurement systems for monitoring industrial effluents.

Another important point is to reduce the volume of solvents used to minimize health and environmental risks.

Given these different objectives, solid-phase extraction (SPE), which developed rapidly from the 1980s onwards, emerged as an attractive alternative. Since then, it has been widely used for the pre-concentration of traces in highly diluted media, such as natural waters, and for sample purification. A wide variety of phases, often...