Simultaneous distillation/adsorption

Figure 1. Apparatus for simultaneous distillation/adsorption. (Reprinted with permission from ref. 11. Copyright 1984 de Gruyter.)...

Simultaneous distillation/adsorption Microwave extraction Accelerated solvent extraction (ASE)... 

Figure 12. Simultaneous steam-distillation adsorption (SDA) head. (Reproduced with permission from Ref. 30. Copyright 1981, Walter de Gruyter Co.).

The search of adequate extraction techniques allowing the identification and quantification of wine volatile compounds has attracted the attention of many scientists. This has resulted in the availability of a wide range of analytical tools for the extraction of these compounds from wine. These methodologies are mainly based on the solubility of the compounds in organic solvents (liquid-liquid extraction LLE, simultaneous distillation liquid extraction SDE), on their volatility (static and dynamic headspace techniques), or based on their sorptive/adsorptive capacity on polymeric phases (solid phase extraction SPE, solid phase microextraction SPME, stir bar sorptive extraction SBSE). In addition, volatile compounds can be extracted by methods based on combinations of some of these properties (headspace solid phase microextraction HS-SPME, solid phase dynamic extraction SPDE). 

Solid-phase microextraction is an adsorption/desorption technique used to analyze the volatile and non-volatile compounds in both liquid and gaseous samples used as an alternative to the headspace, purge-and-trap, solid-phase extraction, or simultaneous distillation/extraction techniques. Analytes are thermally desorbed and directly introduced into any gas chromatograph or GC/mass spectrometry (MS) system. When coupled to HPLC with the proper interface, the analytes are washed out of the fiber by the mobile phase. 

Three commonly used extraction techniques for the analysis of aroma are simultaneous distillation/extraction (SDE), dynamic headspace adsorption on Tenax TA (Buchem N.V., Apeldoorn, The Netherlands), and solid-phase microextraction (SPME) [1,2]. All of these techniques have positive aspects and drawbacks, and these are described. In SDE the sample is boiled for 1 to 2 hr and so precooking may not be necessary, although the meat is usually minced to maximize surface area for the extraction process. The other techniques can be used to examine either a chopped or a whole piece of cooked meat. 

Simultaneous distillation/extraction, headspace adsorption on Tenax TA, and SPME have all been widely described. The discussion here is confined to the merits and drawbacks of these techniques. 

In the desorption step, ammonia is passed downflow through the bed which has completed the adsorption cycle. The ammonia is heated to approximately the same temperature as that of the feed in the adsorption step in order to maintain a nominally isothermal operation. The first portion of the desorbate, although rich in n-paraffms, contains impurities and is recycled to the second bed which is simultaneously operating on the adsorption cycle. The remaining product is condensed and separated from ammonia. The product is freed of dissolved ammonia by distillation. 

Following crystallization, the solid was separated from the mother liquor by filtration, washed with distilled water, and air dried in an oven at 100 C to remove loosely bound water. Samples of the dried powder were sent routinely to the x-ray laboratory. The fact that we could obtain a strip chart recording of the x-ray powder pattern within 30 minutes was an important factor in the pace of our work. Adsorption evaluations were facilitated by use of multiple, quartz spring, McBain-Bakr balances connected in parallel. As many as 16 adsorbent samples could be evaluated simultaneously. 

Many wastes can be effectively purified by activated carbon,1 but the cost is generally higher than with other methods. The use of carbon often can be justified, however, when the process involves the simultaneous recovery of useful ingredients. Depending on the nature of the adsorbed substances, they may be extracted from the carbon by steam distillation, by elution with a suitable solvent, or by a combination of both. The desorption restores some adsorptive power to the carbon, but the regeneration is seldom complete because many impurities adsorbed from waste liquors cannot be removed either by steam or by a solvent. 

Oil displacement experiments were performed under different salinity conditions (1) constant salinity of pol3nner solution at 1.5% NaCl (i.e. optimal salinity of the soluble oil formulation), and variable connate water salinity (2) constant salinity of connate water at 1.5% NaCl and variable salinity of pol3mier solution and (3) the salinity of polymer solution equals the salinity of connate water, both varied simultaneously. Sand packs were chosen as the model porous media in order to avoid the effects of porous media heterogeneity, clays and surfactant adsorption loss. The compositions of aqueous formulation and soluble oils are specified in Figures 1 and 2. The difference between their compositions reflects the density difference between water and dodecane whereas the surfactant and alcohol concentrations (w/v) are the same in both types of formulations. The polymer solution used was 1000 ppm PUSHER-700 in brine. For polymer solution in distilled water, the polymer concentration was reduced to 250 ppm to avoid excessive viscosity. Several experiments were repeated and the reproducibility was established to be within 2% in tertiary oil recovery. 

The SDK procedure was performed using a micro-version of a Likens-Nickerson apparatus [33] in the configuration for heavier-than-water solvents. The aroma components were extracted by steam distillation and the aqueous distillate was simultaneously extracted with dichloromethane. The organic extracts were analyzed by GC-FID and GC-MS. The DHS technique was carried out with adsorption on Tenax traps and thermal desorption with ctyofocusing of the volatile substances into the GC capillary column. 

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