On-line Combinations of Pressurized Hot-Water Extraction and Microporous Membrane Liquid–Liquid Extraction with Chromatography

298 Introduction Environmental and biological analyses are especially challenging for the analyst because sample matrices tend to be very complex and the analytes are present at very low levels. Selective and sensitive methods are needed for both sample preparation and analysis. Typically, extraction and clean-up are needed in the sample preparation, and the analyses are performed by chromatographic methods. Of the two steps, sample preparation is the most time-consuming, tedious and error-prone part of the whole analytical procedure, and often large amounts of hazardous organic solvents and reagents are consumed. Furthermore, all sample-preparation steps substantially increase the risks of sample loss and contamination, and the reliability of the analysis is accordingly decreased. With solid samples, analytes must be extracted from the solid matrix into a suitable solvent. Thus, especially for solid samples, extraction is typically the first step of the analytical procedure. Clean-up of the extract will then usually be required because extracts typically contain an abundance of matrix compounds that may co-elute with the analytes and obscure the quantitative analysis. After clean-up, reconcentration is often necessary to obtain satisfactory sensitivity of the analysis. Unfortunately, during the concentration step, even relatively non-volatile compounds may be totally or partially lost making the analysis less reliable. The risks for sample loss and contamination are major problems in multistep samplepretreatment methods. This means that the whole samplepretreatment procedure must be carefully optimized and the recovery must be checked with reference to standard compounds. Special emphasis has recently been given to the development of faster and more environmentally friendly samplepretreatment methods. At the same time, on-line combinations of sample pretreatment and analytical systems are being studied intensively. The idea behind such systems is to perform sample extraction, clean-up and concentration as an integral part of the analysis in a closed system. Manual sample preparation is then minimized or even totally avoided. Another benefit is that the sample clean-up tends to be much more effective. In this article, we look at two methods of sample preparation: pressurized hot-water extraction (PHWE) and microporous membrane liquid–liquid extraction (MMLLE), which can be combined with liquid chromatography (LC) or gas chromatography (GC).