## 5 Recent Applications Using Selective Enrichment
### Environmental Analysis
The PTFE disks were suspended in the headspace of test tubes containing the contaminated water samples and the assembly was placed in an oven to facilitate extraction. After the extraction phase, which lasted from 1 to 14 h, transmission spectra of the PTFE disks were obtained. The authors identified CH stretching bands in the spectra of the PTFE disks after extraction, and observed that the position of the maximum corresponding to the CH stretch changed according to the contaminant studied, thus allowing identification of the different oils studied. The effect of the water matrix was studied by using three different types of water (tap, Milli-Q and seawater) and it was reported that the water matrix did not cause any significant difference in detection ability. [PERSON] _et al._ reported in 2008 the use of a PVC sensing phase in combination with FTIR spectroscopy for the detection of BTEX compounds in water [92]. The PVC sensing phase was placed in a vial which was filled with the aqueous solution. The studied films reached saturation after 180 min; however, 60 min enrichment was sufficient to generate a signal strong enough to measure the selected analytes. The addition of a plasticiser to the film was shown to improve the sensitivity of the method and limits of detection ranging from 4 ppm (for xylene) to 9 ppm (for ethylbenzene) were reported. [PERSON] _et al._ in 1990 were among the first to demonstrate the potential of ATR-FTIR spectroscopy combined with polymer coatings generated directly on the IRE surface for quantification of organic compounds in aqueous solution [93]. Aqueous solutions of halogenated hydrocarbons (e.g., C\({}_{2}\)Cl\({}_{4}\), CHCl\({}_{3}\)) were obtained by injecting them into methanol to generate a solution. In the following distilled water was added. Both gaseous and liquid phase spectral measurements were obtained and a variety of polymer membranes were studied. Linear relationships were found between absorbance at characteristic wavenumbers and concentration of the analyte of interest. Limits of detection were generally lower for the liquid (ranging from 1 to 10 ppm) than for the gaseous (ranging from 4 to 740 ppm) phase. [PERSON] and [PERSON] developed in 2001 a sensor for detecting phenolic compounds in water using SPMEs combined with FT-IR spectroscopy [94]. The SPMEs were coated directly on to ZnSe IREs and poly(acrylonitrile-_co_-butadiene) was found to be the most suitable polymer among those tested. Standard aqueous solutions of phenols were used for calibration development and detection limits of lower than 200 ppb were reported, although sensitivity was lower for high polarity compounds, such as phenol, 3-hydroxylphenol and 2,4-dinitrophenol. This calibration technique was applied to environmental water samples and it was demonstrated that the variable water matrix in such samples did not significantly affect the detection ability. Soaking the SPME phase in water containing 5% methanol for 20 min was found to be sufficient for its regeneration. Polyisobutylene has shown promise as a membrane for enrichment of volatile organic compounds from aqueous solutions. [PERSON] and [PERSON] in 2002 used this polymer, coated on a ZnSe ATR crystal for determination of chloroform, trichloroethylene (TCE), toluene, chlorobenzene (CB) and 1-chloronaphthalene (1-CN) in aqueous solutions [95]. The solution was heated to liberate the volatile organic compounds from the sample and a cooling unit was integrated in the system to prevent warming up of the ATR crystal. Limits of detection in the ppm range were reported in this study. In 2004 [PERSON] _et al._ employed ethylene/propylene copolymer films coated onto Zn-Se crystals as an enriching phase for ATR-IR quantification of BTEX compounds in water. Aqueous solutions containing mixtures of BTEX compounds were passed through a flow cell in direct contact with the coated crystal.