Low - Pressure , Continuous - Flow Systems for Automated Sample Preparation

Introduction Capillary gas chromatography (GC) is a mature technique commonly used in routine analysis laboratories. Despite the performance of modern chromatographs, sample preparation is still a vital step of the analytical process as it ensures samples are suitable for chromatographic determination (1). Figure 1 summarizes some of the pretreatment steps employed prior to gas chromatographic analysis. The actual techniques used depend on the aggregation state of sample to be analysed and the nature of the analytes (e.g., volatility and thermal stability). However, almost all determinations performed by GC require several extraction, clean-up and preconcentration steps. These are often hazardous for both the operator and the environment because of the high levels of organic solvents used. The drawbacks of sample pretreatment prior to GC are well known (Figure 1), but they can be overcome with an increasing degree of automation (2). Among the different extraction/ clean-up/preconcentration alternatives, solid-phase extraction (SPE) is the preferred choice for the pretreatment of environmental, food and biological samples. This mainly stems from the availability of disposable extraction columns in a broad range of column sizes and sorbents. The advantages of SPE include highly purified extracts, high analyte recoveries, effective concentration, the ability to extract analytes of varying polarities, easy automation, an absence of emulsion and reduced organic solvent consumption. In recent years, low-pressure, continuous-flow (CF) systems have emerged as a simple, robust alternative for sample preparation. They provide clear advantages over conventional manual procedures through automation, simplification and miniaturization of the analytical process (3). This article reports on the use of several CF systems based on SPE for the automated preparation of environmental, food and biological samples, in both off-line and on-line modes. There are commercially available modules based on SPE (Prospekt (Spark Holland Instrumenten, Emmen, The Netherlands), ASPEC (Gilson, Villiers-le-Bel, France )), a detailed discussion of which is beyond the scope of this article as they use high pressure. Their main field of application is, therefore, on-line coupling to high performance liquid The potential of low-pressure, continuous-flow (CF) systems based on solid-phase extraction (SPE) for automated sample preparation prior to gas chromatography is discussed. The most salient features of these systems are presented and current challenges and future trends in CF–SPE are outlined. Soledad Cárdenas, Mercedes Gallego and Miguel Valcárcel, Analytical Chemistry Division, University of Córdoba, Córdoba, Spain. Low-Pressure, Continuous-Flow Systems for Automated Sample Preparation