## 5 Recent Applications Using Selective Enrichment
### Environmental Analysis  
[PERSON] _et al._ reported the application of NIR spectroscopy to detect residues of the pesticide phoxim [87]. Phoxim is an organophosphate insecticide produced by the Bayer Corporation. It is allowed for use in limited applications in the European Union. It is banned for use on crops in the EU since 2007 and is applied in veterinary medicine to treat ectoparasitic acarids, which belong to the mite family. Silica gel was employed as absorbent to extract and enrich the low concentration samples, which were subsequently analyzed in diffuse reflection mode. Calibration models were established based on PLSR and leave-one-out cross validation in a range between 0.25 and 1.15 mg/mL and allowed the analysis of the organophosphate insecticide in real samples with an r for calibration being 0.924. [PERSON] _et al._ already reported in 1996 on the determination of pesticides in water using ATR-FTIR spectroscopy on PVC/chloroparaffin coatings [88]. The objective of the described study was the development of a novel _in situ_ optical sensor consisting of PVC with a chloroparaffin plasticizer capable of enriching chlorinated pesticides and concentrating them within the penetration depth of the evanescent region of the ATR crystal of optical fiber. Measurements were performed by filling the sample cell with the aqueous pesticide solutions and recording a series of spectra over a period of time. Absorbance spectra were recorded for atrazine at 1577 cm\({}^{-1}\) and alachlor at 1104 cm\({}^{-1}\). Limits of detection in the region of 2 ppm have been achieved for atrazine and alachlor using a polymer-coated ATR element. [PERSON] _et al._ published in 2015 an article about the application of NIR spectroscopy coupled with fluidized bed enrichment and chemometrics to detect low concentration of \(\beta\)-naphthalenesulfonic acid in water [89]. D301 resin was used as an adsorption material to pre-concentrate in solutions in a concentration range of 2.0-100.0 ug/mL. NIR spectra were measured directly relative to the \(\beta\)-naphthalenesulfonic acid adsorbed on the material. An improved partial least squares (PLS) model was attained with the aid of multiplicative scatter correction pretreatment and stability competitive adaptive reweighted sampling wavenumber selection method. The root mean square error of cross validation was 1.87 ug/mL at PLS factor of 7. An independent test set was used to assess the model, with the relative error (RE) in an acceptable range of 0.46 to 10.03% and mean RE of 3.72%. This study confirmed the viability of the proposed method for the measurement of a low content of \(\beta\)-naphthalenesulfonic acid in water. SPME coupled with MIR spectroscopy has been investigated for the determination of volatile organic compounds in water [90]. Standard solutions of benzene, chlorobenzene, toluene, chloroform, and \(p\)-chlorootuene were prepared by spiking into methanol and diluting in water. In this study, Parafilm was used as a solid phase; it was suspended in the headspace of jars containing the aqueous solution which was then stirred. After this extraction process, FT-IR spectra of the films were obtained. Limits of detection in the range 66 ppb-1.3 ppm were reported, and reproducible extractions were achieved with a 30 min extraction time. In order to validate the procedure, the method was also applied to real water samples spiked with benzene-toluene-xylene (BETX) compounds. It was reportedthat solid matter within the real water samples did not significantly affect the extraction and detection of the tested compounds. SPME has been employed in combination with FTIR for estimation of the oil and grease content in water [91]. In this study, several oils and greases were examined including \(n\)-hexadecane, \(n\)-tetradecane, \(n\)-nonadecane and \(n\)-docosane. Contaminated water samples were made by adding oil or grease samples to distilled water in a test tube, and polytetrafluoroethylene (PTFE) disks were used as a solid phase.