Extraction and concentration

The next step is to obtain the compounds of interest free of interferences. This has traditionally been done by extracting only interfering compounds from the solution, leaving all others behind, an ideal, but seldom realized goal. 

Extraction of nonpolar compounds using equal volumes of sample and the Folsch mixture (2 1, chloroform/MeOH) gives a very broad polarity cut. Everything from steroids to triglycerides is pulled down into the bottom chloroform-rich layer. Extraction with methylene chloride from a sample acidified with sulfuric acid is more specific, pulling in steroids, fat-soluble vitamins, and free fatty acids. The triglyceride fraction can be extracted using i-PrOH/ hexane (1 9) with little emulsification. 

After extraction, these fractions should be dried to remove water. When dry, the extraction solvent is removed by evaporation and the sample is reconstituted with a solvent or mobile phase before injection. Care must be taken that these evaporated samples go completely back into solution. Sonicating the sample with your starting mobile phase is usually sufficient. However, at least the first time you perform an extraction, it is always good technique to sonicate the dry-down tube with a strong solvent and reinject this wash as a check that everything redissolved. For gradient work, the stronger of the two mobile phases is an excellent choice for this second sonication solvent. 

It is always a good idea to make sure particulates are removed from these sonicates, or for that matter from any sample. Using centrifugation or filtration as a last step before injection protects the column filter from plugging and the system from pressure build-up. 

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EXTRACTATION AND CONCENTRATION OF DIFFERENT-CHARGED COMPLEXES OF SOME PLATINUM METALS WITH... 

On-line LC-GC has frequently been used as a clean-up technique for the analysis of trace levels of contaminants (pesticides, plasticizers, dyestuffs and toxic organic chemicals) in water and food products. Several different approaches have been proposed for the analysis of contaminants by on-line LC-GC. Since pesticide residues occur at low concentration in water, soil or food, extraction and concentration is needed before GC analysis is carried out. 

The procedure followed entails the removal of gross interferences by solvent extraction, and the selective extraction and concentration of the trace metal by use of a chelating agent. The alloy used should not contain more than 0.1 g of copper in the sample weighed out. 

It is seen that there are a large number of compounds capable of dispersive interactions with the reverse phase, contained in the serum that have been extracted and separated. Again the results have been obtained, partly as a result of the extraction and concentration properties of the sampling system, and partly as a result of the high mass sensitivity of the small bore columns. 

Solid phase extraction systems have a wide range of application whether operated manually or automatically. Wherever materials are present in solution at very low concentrations they offer a means of extraction and concentration that is simple, efficient and fast. 

This sample preparation required both extraction and concentration and this was carried out in the traditional manner with the use of an appropriate solvent. The separation was again achieved exploiting the dispersive interactions between the components of the mixture and the strongly dispersive hydrocarbon chains on the reversed phase. 

The mobile phases that are most effective for use with reverse phases are aqueous mixtures of methanol or acetonitrile and for subtle adjustments, ternary mixtures of water, methanol and acetonitrile or tetrahydrofuran can be used. The greater the water content the more the solutes with dispersive groups will be retained and in fact, in pure water, many substances are irreversibly held on a reverse phase. As already discussed, this characteristic make reverse phases very useful for solute extraction and concentration from aqueous solutions prior to analysis. 

A major consequence of the activities associated with the exploitation of mineral deposits (i.e., exploration, the development of mines and processing facilities, the extraction and concentration, which is also called beneficiation, of ores containing the desired minerals, and the decommissioning or abandonment of mine facilities) is the production of extremely large volumes of unwanted materials. Waste volumes vary from ca. 30% of the mass of the ore in the case of gypsum and other non-metals, to about 50% for base metals to more than 80% for strip-mined... 

Using a solution of water-containing reversed micelles of di(2-ethylhexyl)phospho-rothioic acid in isooctane, hemoglobin was extracted and concentrated. Desolubilization of the protein entrapped in the reversed micelles by weak alkahne solution was realized by adding small amounts of n-octanol [167]. 

Purification of anthocyanin-containing extracts is often necessary for further structural identification. Since none of the solvents used for extraction is specific for anthocyanins, considerable amounts of other compounds may be also extracted and concentrated. The variety and concentration of other compounds will depend on the solvent and methodologies used. The presence of extraneous materials could affect the stability and/or analysis of anthocyanins. Therefore, the next step toward anthocyanin characterization is the purification of those extracts. 

Specific extraction methods are used to prepare the analyte for immunoassay by freeing the analyte fromboth specific and nonspecific interferences. Supercritical fluid extraction has been used to decrease the amount of solvent waste generated. Solid-phase extraction has gained popularity, and many different supports are available. One promising extraction and concentration method is immunoaffinity chromatography, which will be addressed later. 

Joarmon S, Pin C (2001) Ultra-trace determination of Ra in thermal waters by high sensitivity quadrapole ICP-mass spectrometry following selective extraction and concentration using radium-specific membrane disks. J Anal At Spectrom 16 32-37... 

On-line SFE coupled to GC or SFC, according to the thermal stability of the analytes, are both very competitive with classical methods of analysis in terms of sensitivity and analysis time. Since all of the extracted analytes are transferred to the GC system, much higher method sensitivities can be obtained. Several modes of operation are possible utilising on-line SFE-GC, including quantitative extraction of all analytes from a sample matrix quantitative extraction and concentration of trace analytes selective extractions at various solvating powers to obtain specific fractions and periodic sampling (multiple-step extractions) of the effluent at various pressures for qualitative characterisation of the sample matrix. 

Human coronary plaque Plaque gruel is solvent extracted and concentrated fractionation on silica gel columns Capillary GC/MS Not specified Not specified Ferrario et al. 1985a... 

Isotope dilution gas chromatography-mass spectrometry has also been used for the determination of ppb of total chromium in seawater [181-183]. The samples were reduced to ensure Cr111 and then extracted and concentrated as tris (l,l,l-trifluoro-2,4-pentanediono) chromium (III) [(Cr(tfa)3>] into hexane. The Cr(tfa)2 mass fragments were monitored into a selected ion monitoring (SIM) mode. 

Many studies have been reported on extractability and concentration of protein from leafy plants (13, 14). While it is more efficient to consume the leafy vegetable or fruit directly, considerable quantities of less available protein can be made available through extraction and concentration into LPC. As pointed out by Pirie (13) and Kohler Knuckles (14), an LPC processing plant could be oriented near packinghouses for leafy vegetables so that leaves, stems, and stalks trimmed from these vegetables before being sent to market, could subsequently be extracted for protein. Leaf protein processes are covered in more detail in another chapter. 

Goldberg and Weiner [9] have described methods for the extraction and concentration of phenolic compounds from sediment. Lopez-Avila et al. [8]... 

High polarity is one of the reasons why both the ionic and amphoteric surfactants, and especially their metabolites, are difficult to detect. This property, however, is important for the application tasks of surface-active compounds, but is also the reason for their high water solubility. Due to this fact, their extraction and concentration from the water phase, which can be carried out in a number of very different ways, is not always straightforward. Furthermore, they are often not volatile without decomposition, which thus prevents application of gas chromatographic (GC) separation techniques combined with appropriate detection. This very effective separation method in environmental analysis is thus applicable only for short-chain surfactants and their metabolites following derivatisation of the various polar groups in order to improve their volatility. 

The sample pretreatment steps for surfactant analysis such as extraction and concentration can be carried out in a variety of ways. Most of the common and well tested procedures have been described by Schmitt [46]. Solid phase extraction (SPE) with C2, Cg or Cis and divinyl benzene resins as well as special phases, e.g. graphitised carbon black (GCB), can be adequate methods, especially for SPE of metabolites from... 

In environmental analytical applications where analyte concentrations, e.g. surfactants or their metabolites, are quite low, extraction and concentration steps become essential. Solid phase extraction (SPE) with cartridges, disks or SPME fibres (solid phase micro extraction) because of its good variety of SP materials available has become the method of choice for the analysis of surfactants in water samples in combination with FIA as well as LC—MS analysis. SPE followed by sequential selective elution provides far-reaching pre-separations if eluents with different polarities and their mixtures are applied. The compounds under these conditions are separated in the MS spectrometer by their m/z ratios providing an overview of the ionisable compounds contained in a sample. Identification in the sense it has been mentioned before, however, requires the generation of fragments. 

The present chapter provides an overview of methods currently used for extracting and concentrating surfactants from aqueous matrices. Some of the techniques will be addressed only briefly, because they are discussed elsewhere in this book more extensively. 

An analytical procedure that quantifies the total AE concentration resolved by alkyl chain length for various environmental matrices (influent, effluent, and river water) was developed by Di Corcia et al. [41]. The method utilises a reverse-phase column to extract and concentrate AE from surface waters and wastewaters and utilises strong anionic and cationic exchange columns to remove potential interferences. Samples are passed through the RP extraction column (Ci). AE and potential anionic and cationic interferences are eluted from the Ci column and passed directly through the SAX and SCX. The SAX and SCX columns retain anionic and cationic materials while non-ionic AE are not retained. Recovery of AE from influent, treatment plant effluent, and river water is quantitative (65—102%) over a range of concentrations for all matrices. 

Potable water and raw source water Sample acetylated in situ by addition of acetic anhydride, solvent extracted and concentrated alternatively, extracted acidic sample derivatized by pentafluorobenzyl bromide and cleaned up by column chromatography HRGC-ECD (for pentafluorobenzyl derivative) HRGC-MS (for acetyl derivative) <50 ng/L (pentafluorobenzyl) <50 ng/L (acetyl derivative) 10-64% (pentafluorobenzyl derivative) 70-132% (acetyl derivative) Sitholeetal. 1986... 

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