## 5 Recent Applications Using Selective Enrichment
### Environmental Analysis
Solid-phase extraction (SPE) using synthetic materials in combination with NIRS has been demonstrated for detection of a variety of organic compounds in water. [PERSON] _et al._ in 2004 measured BTEX compounds in water using a silicone rod attached to an NIR transflectance probe [102]. The probe assembly was placed in an aqueous solution containing BTEX compounds, which was mechanically stirred during measurements. Limits of detection of 8, 7, 2.6 and 3 ppm were reported for benzene, toluene, ethylbenzene and \(m\)-xylene, respectively. The sensor was used on gasoline and diesel fuel contaminated water samples and it was possible to discriminate between the contaminant sources using first derivative spectra. In another study [PERSON] _et al._ pre-extracted by means of a solid PDMS disk placed in an aqueous solution containing BTEX compounds. After agitation of the solution, the disk was removed and its NIR spectra obtained. Limits of detection of 0.080, 0.12, 0.14 and 0.27 ppm were reported for benzene, toluene, ethylbenzene and xylenes, respectively [103]. [PERSON] _et al._ reported in 2009 about the implementation of a new flow-through FT-IR sensor for oil in water analysis based on SPE employing silica C28 particles as a stationary phase. For this on-line approach no chlorinated solvents are required, reducing the environmental impact. Additionally, this method benefited from the minimal sample preparation steps. Spectra were recorded by co-adding 32 scans at a resolution of 4 cm\({}^{-1}\). The vibrational band located at 1462 cm\({}^{-1}\) due to the CH(2) bending was integrated from 1475 to 1450 cm\({}^{-1}\) and following baseline correction was established between 1485 and 1440 cm\({}^{-1}\) using the areas as analytical signal. It was reported that the technique provides a limit of detection (LOD) of 22 mg L\({}^{-1}\) and a precision expressed as relative standard deviation (RSD) lower than 5%. The major advantages of this novel approach are the speed and its high level of automation [104]. [PERSON] _et al._ introduced in 2008 a completely different strategy for determining subnanomolar iron concentrations in ocean seawater. The introduced device uses an iron-specific chelating biomolecule, desferrioxamine B (DFB), covalently immobilized on a mesoporous silica film. Changes in infrared spectral signatures of the immobilized DFB upon Fe(III) complexation provided an reproducible and exact measure of iron on the surface of a chip that has been exposed to seawater. The LOD found was 50 pM for a 1 L sample at pH 1.7 and was used to measure dissolved iron in subarctic Pacific waters without any interference from other elements. This analytical technique provides an autonomous research platform being helpful to better understand the iron distribution and chemistry in seawater [105]. ClearSamplerTM (Richland, WA, USA) offers a wide range of kits consisting of a swab or scoop to pick up the sample and a collection vial with buffer to solubilize or suspend the sample [106]. Several different kits are available for analysing proteins, DNA, but also hazardous materials including anthrax, bacteria (e.g., Salmonella, _etc._). In ASTM D7575-11 a standard test method for solvent-free membrane recoverable oil and grease by IR determination is described following this measurement principle [107].