Recent Techniques

Microwave-assisted extraction (MAE) [45] is a simple technique that provides a novel way of extracting soluble products into a fluid, from a 

The first applications of MAE dealt with the extraction of essential oils from plant products was reported in 1994 [45]. Microwave heating was used for the isolation of essential oils. Solvent free microwave extraction (SEME) involves microwave heating involves dry distillation at atmospheric pressure for the isolation of the essential oils in fresh plant materials. SFME was used to obtain essential oils from different spices such as ajowan, cumin, and star anise [46,47], and three different aromatic herbs (basil, garden mint, and thyme) [47]. Using the SFME method, either solvent or water is needed if fresh plant material is used. However, in case of dry plant material, the sample should be rehydrated by soaking in water before the extraction. 

TABLE 7.1. Recent Applications of SCF Extraction for Natural Compounds. 

Sideritis raeseii subsp attica Phenolics and flavonoids 90-300 bar. Co-solvent ethanol (0-20%) [110] 

Sweet basil Eugenol, germacrene-D, epi-alpha-cadinol, malic acid, tartaric acid, ramnose, cafleic acid, quinic acid, kaempferol, caffeoylquinic acid, and kaempferol 3-0-glucoside CO2 and the cosolvent H20at1%, 10%, and 20% (w/w) [1111 

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Mass spectral analysis of quaternary ammonium compounds can be achieved by fast-atom bombardment (fab) ms (189,190). This technique rehes on bombarding a solution of the molecule, usually in glycerol [56-81-5] or y -nitroben2yl alcohol [619-25-0], with argon and detecting the parent cation plus a proton (MH ). A more recent technique has been reported (191), in which information on the stmcture of the quaternary compounds is obtained indirectly through cluster-ion formation detected via Hquid secondary ion mass spectrometry (Isims) experiments. 

Another relatively recent technique, in its own way as strange as Mossbauer spectrometry, is positron annihilation spectrometry. Positrons are positive electrons (antimatter), spectacularly predicted by the theoretical physicist Dirac in the 1920s and discovered in cloud chambers some years later. Some currently available radioisotopes emit positrons, so these particles arc now routine tools. High-energy positrons are injected into a crystal and very quickly become thermalised by... 

An alternative approach is the use of pH-sensitive fluorophores (Lichtenberg and Barenholz, lOSS). These probes are located at the lipid-water interface and their fluorescence behavior reflects the local surface pH, which is a function of the surface potential at the interface. This indirect approach allows the use of vesicles independent of their particle size. Recently, techniques to measure the C potential of Liposome dispersions on the basis of dynamic light scattering became commercially available (Muller et al., 1986). 

Recently techniques have been developed for x02 oxidations in zeolite cavities.174 The photosensitizer is absorbed in the zeolite and generation of l02 and reaction with the alkene occurs within the cavity. The reactions under these conditions show changes in both regiochemistry175 and stereoselectivity. The cis effect is reduced and there is a... 

Since it was proposed in the early 1980s [6, 7], spin-relaxation has been extensively used to determine the surface-to-volume ratio of porous materials [8-10]. Pore structure has been probed by the effect on the diffusion coefficient [11, 12] and the diffusion propagator [13,14], Self-diffusion coefficient measurements as a function of diffusion time provide surface-to-volume ratio information for the early times, and tortuosity for the long times. Recent techniques of two-dimensional NMR of relaxation and diffusion [15-21] have proven particularly interesting for several applications. The development of portable NMR sensors (e.g., NMR logging devices [22] and NMR-MOUSE [23]) and novel concepts for ex situ NMR [24, 25] demonstrate the potential to extend the NMR technology to a broad application of field material testing. 

Usually we talk about reactions in solution, but recently techniques have been developed to follow reactions that occur in a vacuum when a stream of reactant A and a stream of reactant B cross each other in a defined direction, as with molecular beams. From the direction in which the products are ejected and their energies, much fundamental information can be deduced about the details of the molecular processes. Lasers, which emit light-energy in a highly focused beam, are sometimes used to put energy into one of the reactants in a defined way. Such a technique reveals less about the nature of the transition state than about what is called the dynamics of the process—how molecules collide so as to react, and how the products carry away the energy of the overall reaction. The development and application of such techniques were recognized by a Nobel Prize in 1986 to Dudley Herschbach, Yuan Lee, and John Polanyi. 

General Experiments over several years by a variety of techniques had shown us that the concentration of -OH end-groups and that of tert-oxonium ions in polymerisation mixtures initiated by anhydrous HC104 depend critically upon the purity, especially the dryness, of solvent, monomer, and killing reagent. Our most recent techniques, described below, were developed out of this experience and we believe them to be a useful advance on those in use previously and elsewhere. 

Recently techniques have been developed to further reduce the sample volume required. Perhaps the most promising technique is SPME. This method consists of utilising high capacity adsorbents that are brought into contact directly with the sample (< 10 mL) or indirectly through a headspace above the sample. 

Many of the more established techniques have been validated through collaborative studies which becomes of greater importance as laboratories seek to become accredited via ISO, EN or related systems where the use of official or well validated methods is mandatory. New instrumental techniques are constantly being reported in the literature but it often requires many years before procedures are introduced, validated and then applied within the food industry. Recent techniques that can be included in this category are capillary electrophoresis and liquid chromatography-mass spectrometry (LC-MS). In time procedures based on these techniques will also become accepted as routine methods and are likely to be adopted by some of the official international bodies like the AOAC International, CEN, ISO, etc. 

These first three volumes are designed to serve as an advanced text. These volumes describe the more recent techniques and technologies (Volume 1), the principles governing fluorescence and the experimental observables (Volume 2), and applications in biochemistry and biophysics (Volume 3). 

Finally, in Chapter 5, the applied side of electrochemistry is served by Bech-Neilsen et al. in the review of recent techniques for automated measurement of corrosion. 

The determination of nitrogen in petroleum products is performed regularly by the Kjeldahl method (ASTM D3228), the Dumas method, and the microcoulomet-ric (ASTM D3431) method. The chemiluminescence method is the most recent technique applied to nibogen analysis for petroleum and is used to determine the amount of chemically bound nitrogen in liquid samples. 

CE is not yet as widespread as analytical techniques such as HPLC and GC. Especially as a more recent technique, it needs to demonstrate sufficient robustness to be considered as a conventional routine analytical technique. Robustness (see Chapter 9) of a method should always be tested before starting to calibrate. If the method is later found to be not robust, parameters have to be changed. Then the calibration and consequently its validation have to be repeated. 

Bures, M.G. Recent techniques and applications in pharmacophore mapping. In Practical Application of Computer-Aided Drug Design,... 

SAMDI as a merger of the rapidly growing field of SAMs and the established MALDI-MS is an even more recent technique. Interesting assay formats and applications have already been described combining the selectivity of SAMs with the efficiency of MALDI. Nevertheless, there are, up to now, too few applications in order to predict in which way SAMDI is going to develop. For future applications,... 

A recent technique to achieve a reuse of the thickener is the precipitation of the thickener by addition of organic solvent (e.g., methanol). After removal of the dyes and chemicals the thickener can be reused for the preparation of new pastes. The removed chemicals and dyes are collected and discarded [68]. By this method a considerable part of the COD-forming compounds can be recycled and the AOX and heavy metal content in the wastewater from textile printing can be reduced. 

Tritiated digoxin has been used as a tracer in most of the published procedures, but recently techniques employing [ I]tyrosine-labeled digoxin have been described. Such techniques not only are more sensitive, but have the added advantage of dispensing with the necessity to use scintillation counting. 

The three isomers of cresol are not as readily separated by HPLC, although recent techniques have been developed to accomplish this task. Reversed-phase chromatography columns have been used for the analysis of cresols with limited success. Recently, a new reversed-phase support has been developed that allows complete separation of the three cresol isomers (Bassler and Hartwick 1989). Inclusion complexes of the cresols with p-cyclodextrin cleanly separate the three isomers on commercially available columns (Yoshikawa et al. 1986). Detection limits down to 1 ppm can be obtained by this method. 

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