## Extraction methods using organic solvents
### Liquid samples preparation
developed an off-line solid-phase extraction procedure to extract priority pesticides and priority organic pollutants, including some phenolic compounds, from river waters using this type of cartridge. Recoveries for the majority of compounds were between 70 and 130% with standard deviations below 30%. All the compounds were studied in a concentration range from 0.05 to 2 mg\(\cdot\)L\({}^{\text{-1}}\) for 200 mL of river water [35]. The same type of cartridges was used by [PERSON] _et al_. to extract the U.S. EPA eleven priority pollutants phenols from spiked river water samples [36]. The recoveries obtained with the on-line SPE HPLC-APCI-MS technique were ranged between 90 and 105%. Limits of detection ranged from 40 to 280 ng\(\cdot\)L\({}^{\text{-1}}\) and relative standard deviation below 8% were obtained for 10 mL of water samples for concentrations about one order of magnitude above of LODs. Another polymeric cartridge, LiCholut EN, has been used successfully to extract phenolic compounds from aqueous samples [37]. [PERSON] _et al_. used them for the extraction of eight phenolic compounds in effluent from various tertiary sewerage treatment plants with good recoveries for analytes investigated which differed widely in polarity. Recoveries were found to remain high, even for samples consisting of large amounts of organic matter. The SPE procedure described in this work was able to provide detection limits at ppt levels for phenol and the chlorophenols tested [38]. Graphitised carbons are the third kind of sorbent used in SPE of phenolic compounds [39]. In this case, it is not necessary to acidify water samples to extract phenols, because of the strong interactions of phenolates with the positively charged sites on the carbon surface. [PERSON] _et al_. developed a procedure for determining the U.S. EPA eleven priority pollutant phenols in natural waters [40]. The method involves passing 1 and 4 L, respectively, of drinking and river waters through a reversible cartridge filled with 0.5 g of graphitized carbon black (Carbograph 4) at flow-rates of about 100 mL\(\cdot\)min\({}^{\text{-1}}\). Phenols were separated and quantified by ion-suppression, reversed-phase LC with UV detection. Recoveries of phenols, including phenol itself, were higher than 90%. Although SPE is widely accepted, as an alternative extraction and clean-up method to LLE, has certain limitations, especially for analytes such as phenolic derivatives, which exhibit different behaviour in terms of polarity and acidity. Solid phase micro-extraction (SPME) has been developed to resolve some of the drawbacks that present the SPE technique. This extraction method, introduced by [PERSON] in 1990 [41], accomplishes the sampling, extraction and enrichment in a single step process. This approach consists of a fused-silica fiber coated with different polymers, which is housed in the needle of a syringe. SPME is based on equilibrium between the analyte concentration on the sample and that in the fiber coating. For SPME, two possible approaches have been evaluated: headspace exposure and direct immersion of the fiber on the aqueous sample [42-44]. However, although SPME of phenols from the water headspace minimises fiber contamination by adsorption of non volatile matrix components, this approach is limited to volatile compounds, typically up to tri-chlorinated phenols. Desorption of analytes can be carried out by placing the fiber in the hot injector of the gas chromatograph, where the analytes are thermally desorbed. In liquid chromatography, a SPME-HPLC interface or desorption chamber can be used to desorb the analytes. Two modes of desorption are possible: dynamic desorption and static desorption. In the dynamic mode, analytes are desorbed from the fiber by the moving stream of the mobile phase. In the static mode, the fiber is kept in the desorption chamber, filled with an organic solvent or the mobile phase, for a period of time. These both procedures are called on-line desorption mode.