Solid phase extraction for the analysis of organic compounds

Despite the implementation of high-performance separation techniques combined with increasingly sensitive and specific detection modes, the efficiency of the analytical procedure is still limited by the sample preparation stage. This is an important stage, since it is estimated that 30% of the errors made during the overall analysis are attributable to it, and that the analyst devotes 60% of his time to it. The strategies adopted at this stage are varied and depend on the nature of the solute, the nature of the sample and the level of concentration required.

However, it is important to develop methods that are fast, reliable (which implies a reduction in the number of intermediate steps: transfers, evaporations, derivations, etc.), easily automated and which limit the use of organic solvents, in compliance with current legislation. Based on these principles, a variety of methods applicable to one type of sample, or easily adaptable to samples of different origins, have emerged and shown great potential.

There is no longer any doubt that Solid-Phase Extraction (SPE) has become the most widespread technique for processing liquid samples prior to analysis, as demonstrated by the number of suppliers currently offering SPE products (phases available in various formats, robots...). This solid-phase extraction method is increasingly used for liquid samples, due to its ease of use, since it can be directly applied to water analysis (the filtration stage is often integrated with the extraction stage), or requires simple pre-treatment (dialysis, ultrafiltration), particularly for biological fluids.

Its emergence is particularly linked to regulations on organic solvents, but also to the fact that liquid-liquid extraction, long used, cannot be applied to the extraction of polar compounds from water, due to their low affinity for these solvents. Its evolution has been facilitated by the marketing of a wide variety of phases dedicated to very different compounds and samples, and supported by a rapid evolution in the formats available (cartridges of different capacities, disks, 96-well plates) as well as in the automated systems adapted to these different formats.

This SPE technique draws its richness from the diversity of supports currently available or under development, such as molecularly imprinted materials or immunoadsorbents, which increase the selectivity of the extraction step and thus facilitate the detection of compounds during analysis.

A derivative of liquid-solid extraction, Solid-Phase Micro-Extraction (SPME) has also produced highly promising results. In this method, organic compounds are extracted by a polymer-coated silica fiber, then directly transferred to the injector by gas chromatography...