Solvent Extraction - Infrared Spectrometry

Udris [53] has described two schemes, based on chromatography and infrared spectroscopy, for the identification, in PVC extracts of  

R = alkyl stabilisers in which the dialkyltin group is combined with both thiol and carboxyl groups. 

It is first of all necessary to prepare an extract of the PVC in which the organotin stabiliser 

For the extraction of the first set of compounds, i) the polymer is refluxed with acetone and the silver salts precipitated by the addition of aqueous silver nitrate. After drying the residue is examined by infrared spectroscopy to identify alcohols, thioacids, thiols, and alkyl groups attached to tin. For the extraction of the second set of compounds ii) the polymer is refluxed with 10% aqueous sodium hydroxide prior to the identification of alcohols by gas chromatography then the alkyl groups attached to tin and carboxylic acids are identified. 

Udris [53] examined methods for the recovery and identification of tin stabilisers in excess plasticiser (90 to 95%). The plasticisers included diisooctyl phthalate and mixtures of diisooctyl phthalate and tritolyl phosphate in various proportions. 

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A predictive macromolecular network decomposition model for coal conversion based on results of analytical measurements has been developed called the functional group, depolymerization, vaporization, cross-linking (EG-DVC) model (77). Data are obtained on weight loss on heating (thermogravimetry) and analysis of the evolved species by Eourier transform infrared spectrometry. Separate experimental data on solvent sweUing, solvent extraction, and Gieseler plastometry are also used in the model. 

The conventional approach to solvent extraction is the batch method. Early work with this method was hampered by the low concentration of the compounds present and the relative insensitivity of the methods of characterization. Thus lipids and hydrocarbons have been separated from seawater by extraction with petroleum ether and ethyl acetate. The fractionation techniques include column and thin-layer chromatography with final characterisation by thin-layer chromatography, infrared, and ultra-violet spectroscopy and gas chromatography. Of these techniques, only gas chromatography is really useful at levels of organic matter present in seawater. With techniques available today such as glass capillary gas chromatography and mass spectrometry, much more information could be extracted from such samples [20]. 

Commonly used methods for the determination of petroleum hydrocarbon contamination in soil are modifications of Environmental Protection Agency method 418.1, which use sonication or a Soxhlet apparatus for analyte extraction and either infrared spectrometry [5] or gas chromatography with flame ionization detection [6-7] for extract analysis. Regardless of the analytical method following the extraction, both modifications use Freon-113, which has been implicated as a cause of ozone depletion. Therefore, alternative methods are being sought for the determination of hydrocarbon contamination in environmental samples that reduce the need for this halogenated solvent. 

With the demonstration of supercritical fluid extraction, an obvious extension would be to extract or dissolve the compounds of interest into the supercritical fluid before analysis with SFC.(6) This would be analogous to the case in HPLC, where the mobile phase solvent is commonly used for dissolving the sample. The work described here will employ a system capable of extracting materials with a supercritical fluid and introducing a known volume of this extract onto the column for analysis via SFC. Detection of the separated materials will be by on-line UV spectroscopy and infrared spectrometry. The optimized SFE/SFC system has been used to study selected nonvolatile coal-derived products. The work reported here involved the aliphatic and aromatic hydrocarbon fractions from this residuum material. Residua at several times were taken from the reactor and examined which provided some insight into the effects of catalyst decay on the products produced in a pilot plant operation. 

If the analyte is organic in nature, these oxidizing methods cannot be used. Rather, the analyte may be extracted away from the sample or dialyzed, or the sample dissolved in an appropriate solvent. It may be possible to measure the analyte nondestructively. An example is the direct determination of protein in feeds by near-infrared spectrometry. 

Biphenyl is usually determined by chromatographic analysis of an extract prepared using an organic solvent. In the TLC method, biphenyl is located under UV radiation, extracted with methanol, and determined spectrophotometrically at 248 nm. If the silica gel layer is impregnated with the fluorescent indicator GF254, biphenyl can be detected by densitometry. LC analysis with UV detection at 254 nm and fluorimetric detection at 350 nm with excitation at 285 nm are good alternatives. Derivative infrared spectrometry has also been developed as an alternative procedure. 

See also Extraction Solvent Extraction Principles Solid-Phase Extraction. Fluorescence Environmental Applications. Gas Chromatography Mass Spectrometry Environmental Applications. Gravimetry. Headspace Analysis Static Purge and Trap. Immunoassays Overview. Infrared Spectroscopy Overview. Liquid Chromatography Overview. Sampling Theory. 

Two general methods of plasticiser determination were distinguished between by Guiochon and Henniker [82] with and without preliminary extraction. Either may precede infrared spectrometry or GC. The most common method is to use ether to extract the plasticisers to be determined. If a quantitative analysis is required, the sample should be thin (0.1 mm or less) and should be extracted for several hours (usually 10 hours) to ensure that extraction is complete. If extraction is to be followed by spectrometry, care must be taken to eliminate all solvent by drying for 2-3 hours at 80 "C. If the analysis is to be done by chromatography, drying is unnecessary since the solvent is much more volatile than the plasticiser and will be well separated. 

Freon-extractable material is reported as total organic material from which polar components may be removed by treatment with silica gel, and the material remaining, as determined by infrared (IR) spectrometry, is defined as total recoverable petroleum hydrocarbons (TRPHs, or total petroleum hydrocarbons-IR). A number of modifications of these methods exist, but one particular method (EPA 418.1 see also EPA 8000 and 8100) has been one of the most widely used for the determination of total petroleum hydrocarbons in soils. Many states use or permit the use of this method (EPA 418.1) for identification of petroleum products and during remediation of sites. This method is subject to limitations, such as interlaboratory variations and inherent inaccuracies. In addition, methods that use Preon-113 as the extraction solvent are being phased out and the method is being replaced by a more recent method (EPA 1664) in which n-hexane is used as the solvent and the n-hexane extractable material (HEM) is treated with silica gel to yield the total petroleum hydrocarbons. 

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