Extraction Procedures for Organic Pollutants Determination in Water

Abstract

The European Water Framework Directive 2000/60 is one of the key legislations introduced for many years in water management and protection fields. The model of water management established by this directive is the river basin. There are a variety of indicators to define the good ecological and chemical status, including a list of priority and emerging pollutants to monitor. Compounds in the directive list are organic pollutants, e.g. hydrocarbons, organochlorine compounds, organic solvents, pesticides and chlorophenol, toxic metals (Hg, Ni, Cd and Pb) and one organometallic compound (tributyltin). Other chemical compounds such as pharmaceuticals, hormones and endocrine disruptor have also become important emerging contaminants due to their presence in environmental waters, the threat for drinking water sources and the concern about their possible estrogenic and other effects. For these reasons, some of them have been included as emerging pollutants in the directive. Although this directive does not specify the analytical methods and procedures to be used, the results should come to an agreement no matter which method is used and regardless in which lab the analysis is carried out. Therefore, a large effort to validate and harmonize analytical methods is very required to assure the quality of the results. Consequently, the implementation of robust analytical methods is still a challenging requirement. Among the different steps of the analytical procedure sample preparation is not only the a major source of uncertainties but also where the risk of artifacts and contamination is the highest. Different extraction techniques for the analysis of organic pollutants in water samples are being developed and optimized in order to automate and miniaturize the extraction step, using low volumes of solvents or even solventless procedures in order to pre-concentrate the analytes in the final acceptor phase. We review recent strategies for the analysis of organic pollutants in environmental water samples as alternative choices against the most classical liquid-liquid extraction or solid-phase extraction. Revised extraction techniques are classified in two main groups: (i) sorptive extractions and (ii) liquid-liquid microextraction. Among sorptive extractions, solid-phase microextraction, stir-bar sorptive extraction and microextraction by packed sorbent are described. Cloud point extraction, single drop microextraction, membrane liquid-phase microextraction and dispersive liquid-liquid microextraction are included in the group of liquid-liquid microextraction techniques. Among membrane liquid-phase microextraction the use of both porous and non-porous membranes is described. During the description of liquid-liquid microextraction techniques the use of ionic liquids is also mentioned due to the high number of applications found for both single drop microextraction and dispersive liquid-liquid microextraction. We discuss the basics, advantages, drawbacks and applications of the techniques for the analysis of organic pollutants in environmental water samples, including river, estuarine water, seawater or wastewater.