Isolation volatiles

Various gas chromatographic techniques combined with plentiful detection methods were used to separate and quantify volatile V-nitrosamines. Preconcentration methods were usually applied for separating these compounds. Thus, a method was developed for determination of V-nitrosodimethylamine (278a) in minced fish or frankfurters, based on SPE followed by GC-CLD-TEA RSD was 0.56 to 2.25%569. This method has been adopted by AOAC. A similar GC method using NPD was described for the determination of 278a in fish products570. Steam distillation can also be used to isolate volatile... 

Various sample enrichment techniques are used to isolate volatile organic compounds from mammalian secretions and excretions. The dynamic headspace stripping of volatiles from collected material with purified inert gas and trapping of the volatile compounds on a porous polymer as described by Novotny [3], have been adapted by other workers to concentrate volatiles from various mammalian secretions [4-6]. It is risky to use activated charcoal as an adsorbent in the traps that are used in these methods because of the selective adsorption of compounds with different polarities and molecular sizes on different types of activated charcoal. Due to the high catalytic activity of activated charcoal, thermal conversion can occur if thermal desorption is used to recover the trapped material from such a trap. 

The key intermediates in the process are the silylenes and the radical fragments, both of which should be amenable to trapping experiments. With this in mind, two representative, polysilane derivatives 6 and 9, were irradiated (254 nm) in the presence of excess triethylsilane, and the results of this experiment are shown in Figure 6. Since the polysilane 9 was not soluble in the trapping reagent, it was dissolved in cyclohexane which contained a 100 fold molar excess of triethylsilane. In each case, the major isolable volatile products... 

You need to decide the goal of an analysis before developing a chromatographic method. The key to successful chromatography is to have a clean sample. Solid-phase microextraction, purge and trap, and thermal desorption can isolate volatile components from complex matrices. After the sample preparation method has been chosen, the remaining decisions for method development are to select a detector, a column, and the injection method, in that order. 

Headspace Sampling Technique. The method used a new gas chromatographic desorption - concentration - GC introduction device (D.C.I.) based on dynamic headspace analysis and available from Delsi Instruments (Paris, France). This apparatus made it possible to isolate volatiles from both solid and liquid samples (4). 

The headspace technique developed in the present study to isolate volatiles from canned black truffles performed satisfactorily. The aroma isolate obtained was described as typical, and 36 compounds were identified for the first time as canned clack truffle constituents. The formation of the major part of them could be correlated to the thermal treatment applied. 

Distillation techniques, such as steam distillation, are typically carried out in a rotary evaporator after the sample has been solubilized in an organic solvent. The distillate is injected directly onto a suitable GC column. This method is used widely due to its simplicity and because components with high boiling points are recovered easily. High-vacuum distillation is used widely to isolate volatile components from solvent extracts. This procedure often requires an extraction step to remove water. 

Next, In agreement with the work of Bateman and Morton (76) on the Queensland fruit fly, we found that increasing the pH of the hydrolysate from its normal 4.2 to 8.5 to 9 increases the attrac-tancy of the bait for our test species. Gas chromatography (Figure 4) and gc/mass spectrometry (Flnnigan/Incos model 4500X GC/MS with OV-101 fused silica capillary column) on the isolated volatiles of pH 4.2 and pH 9 hydrolysate show considerable differences. 

This process can be used to separate water-insoluble covalent compounds from crude reaction mixtures or to isolate volatile natural products, e.g. terpenes from plant tissue. The crude mixture is heated with water and steam and the steam-volatile material co-distils with the steam and is then condensed with the water and collected. You will then need to carry out an extraction (p. 102) to separate the water and the insoluble component. 

Sample injection in gas chromatography often seems deceptively simple a microlitre aliquot is rapidly injected into an inlet system, and elution and detection follow. Samples containing substantial amounts of non-volatile material, however, require one or more preparation steps in order to isolate volatile analytes from non-volatiles that would otherwise contaminate the inlet system and column, eventually leading to impaired chromatographic performance. Examples of such procedures include liquid-liquid extraction, solid-phase extraction and filtration. The use of a pre-column (viz. a retention gap or a guard column) is often required, even if prepared samples are used. 

The scale of preparative HPLC is normally larger than that of conventional HPLC. Therefore, a practical starting point is to develop an analytical separation that optimizes the isolation conditions. Optimization of the analytical method implies seeking conditions that combine maximum resolution of the peak of interest and minimum elution time, under the restriction of a limited pressure drop. The optimized conditions determine the column, mobile phase, flow rate, and sample loading capacity for the particular column. The conditions may be either normal phase or reverse phase. The mobile phase should be chosen carefully to avoid salt complexation with the compound to be isolated. Volatile acid salts such as trifluoroacetic acid, formic acid, and acetic acid are acceptable mobile phase additives, and the ammonium counterion is preferred for pH adjustment to any of these acids. 

In 1993, Surburg et al. used two different headspace techniques to isolate volatile constituents of lily of the valley. The first method,... 

Film-forming properties, low flow when softened. Easily plasticized and cross-linked at above 150°C, isolating volatiles. 

Neither soxhlet extraction nor steam distillation is designed to isolate volatiles from solids for subsequent determination. Slurrying the solids in water and then applying the PaT procedure has been reported A vacuum extractor with cryogenic concentration has been applied to both fish and sediment samples for determination of volatile priority pollutants PaT, LLE, and static headspace techniques have all been applied to the determination of volatiles in sludges from municipal waste treatment plants... 

Pfab and Noffz [53] have described two methods, both based on GC, for the determination of styrene monomer and other volatiles in polystyrene. In one method an or /70-dichlorobenzene solution of the polymer is distilled to isolate volatiles as a concentrate in the distillate. The ortho-dichlorobenzene used to dissolve the polymer contains a known amount of toluene which is used as an internal standard. The distillate is chromatographed on a polyethylene glycol column using helium as a carrier gas and a katharometer detector. 

Methods for the study of grape flavour have often been employed in flavour analysis of other fruits and beverages. Techniques such as solvent extraction (Cacho et al. 1992) or headspace methods (Kallio 1991) may be used to isolate volatiles, and analysis usually involves gas-liquid chromatography (Cronin 1982), coupled with mass spectrometry (Merritt and Robertson 1982). Such methods have provided qualitative and some quantitative assessment of grape aroma composition, usually as part of research on wine flavour (Strauss et al. 1986 Rapp 1988 Eti vant 1991). 

FIGURE 3.4 Distillation equipment used to isolate volatiles from foods (left high vacuum distillation of volatiles from an aqueous food right simultaneous distillation/extraction apparatus). (Reproduced from Guntert, M., G. Krammer, H. Sommer, P. Werkhoff, Flavor Analysis, C.J. Mussinan, M.J. Morello, Eds., Amer. Chem. Soc., Washington, D.C., 1998, p. 38. With... 

Many foods contain components that are thermo-sensitive or labile and are changed by the application of heat resulting in artefact formation. One of the most commonly used extraction methods is simultaneous distillation-extraction (SDE). This method was first proposed by Likens and Nickerson in 1964 (16). Due to the high temperature used in atmospheric SDE, thermal artefacts may be generated during the extraction process and thus vacuum SDE systems have been developed to overcome the generation of thermal artefacts. One of the more recent vacuum SDE systems was developed by Maignial et al (10). This Static Vacuum SDE apparatus is an "easy-to-use device to isolate volatile... 

Several approaches are used to isolate and eoneentrate volatile analytes from waste samples for subsequent measurement. Some of these based on headspace analysis involve evaporation of volatile substanees into the space above the sample (headspace) in a closed container. Method 5021, Volatile Organic Compounds in Soils and Other Solid Matrices Using Equilibrium Headspace Analysis, is used to isolate volatile organic compounds, such as benzene, bromomethane, chloroform, 1,4-dichlorobenzene, dichloromethane, styrene, toluene, vinyl chloride, and the xylene isomers, from soil, sediment, or solid waste samples for determination by gas chromatography or gas chromatography/mass spectrometry. 

In addition to headspace analysis, purge-and-trap procedures can be employed that drive volatile anal 4 es from a sample and collect them on an adsorbent colunm for subsequent analysis. Distillation techniques, including azeotropic distillation and vacuum distillation are also used to isolate volatile analjdes. 

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