Extraction from solids

Classical solvent extraction is a phase transfer of solute from the solid phase to solution. All analytical extractions from solid matrices undergo three processes ... 

Work is in progress to validate the MAE method, proposed for EPA, in a multi-laboratory evaluation study. Nothing similar has been reported for additives in polymeric matrices. Dean el al. [452] have reviewed microwave-assisted solvent extraction in environmental organic analysis. Chee et al. [468] have reported MAE of phthalate esters (DMP, DEP, DAP, DBP, BBP, DEHP) from marine sediments. The focus to date has centred on extractions from solid samples. However, recent experience suggests that MAE may also be important for extractions from liquids. 

Liquids can be extracted from solids by leaching. As the name implies, the soluble liquid contained in a solid is leached out by contacting the solid with a suitable solvent. A principal application of leaching is in the extraction of valuable oils from nuts and seeds such as, palm oil and rape seed oil. 

Figure 5.6. Relationship between Co and Mn contents extracted from solid-phase of six Israeli arid-zone soils with sequential dissolution procedures (after Han et al., 2002b. Reprinted from J Environ Sci Health, Part A, 137, Han F.X., Banin A., Kingery W.L., Li Z.P., Pathways and kinetics of transformation of cobalt among solid-phase components in arid-zone soils, p 184, Copyright (2002), with permission from Taylor Francis)...

Figure 19 Antioxidative qualities of wines (white rectangles) in comparison to watery extracts from solid grape constituents skins (gray rectangles) and pips (black rectangles) in equivalent concentrations of ascorbic acid (mmol/L, mmol/g).

Finally, extractions from solids can be performed by heating followed by solvent trapping. Such a procedure is known as thermal extraction. 

In Section 2.5, we described separation procedures in which analytes are extracted from solid samples via contact with liquid solvents that selectively dissolve the analyte and leave other components undissolved or unextracted. There are several methods by which analytes can be extracted from liquid matrices as well. 

A single-stage extraction using the same total volume of solvent achieves only 92% extraction, and the extract concentration is only 0.23, vs. nearly 0.25 for the cross-flow extraction. The use of four cross-flow extraction stages is clearly preferable to a single extraction. Equally, of course, the use of more than four extraction stages, each with a proportionately smaller volume, would improve the performance. In the limit, one would seek a differential contacting process similar to the Soxhlet extractor employed for extraction from solid phases, but such a contactor has not found use in solvent extraction. 

In this Chapter, fundamentals of design criteria in relation to processes and equipment are reviewed for dense-gas-extraction from solid matrices. Although, as mentioned in previous chapters, numerous dense gases can be used as solvents. In the following discussion we concentrate on the most extensively used gas-carbon dioxide. The reason for this is its nontoxic, non-flammable and inert nature, the possibility of gentle treatment of thermally sensitive materials, and the fact that it is inexpensive and an environmentally acceptable material. 

The problems connected-with separation processes, units, and equipment are treated in the Sixth Chapter, focusing the reader s attention on high-pressure distillation and on dense-gas extraction from solids and liquids. 

Coal and Coal-Tar Hydrogenation. If paraffinic and olefinic liquids are extracted from solid fuel substances, the hydrogen content of the residual material is reduced even further, and the residues become more refractory. The yields of liquids so derivable are generally low, even when a significant fraction of the hydrogen is extractable. Thus production of fuel liquids from nonliquid fuel substances such as coal and coal tars may be enhanced only by the introduction of additional hydrogen in a synthesis process. The principal differences in the processes are from the modes in which hydrogen is introduced and the catalysts used. 

The information that can be extracted from solid-state NMR spectra is encoded via spin interactions such as the chemical shielding, the quadrupolar interaction and the homo-and hetero-nuclear dipolar interactions [1,9-10]. Some knowledge of the spin interactions that determine the features of the spectra are thus of prime importance. 

Sodium and potassium are extracted from solid samples by wet digestion or dry ashing followed by acid dissolution of residue, and are determined by flame AAS using an air—acetylene flame. Liquid samples are aspirated after dilution. 

Special aspects of extraction from solid samples... 

For extraction from solid samples, e.g., biological materials and homogenates (planf tissue, food), liquid extraction can be applied using for instance acetone, methanol, or acetonitrile. Often, extracts are filtered prior to injection to LC-MS. 

Supercritical Fluids (SFs) allow analytes to be extracted from solid samples, i.e., marine sediments, faster and more efficiently since they have lower viscosity and higher diffusivity than liquid solvents (56). CO2 is the most widely used supercritical fluid with or without a modifier, e.g. methanol and toluene. A very exhaustive discussion on the role of a modifier in the enhancement of the extraction efficiency was recently published (39). Few procedures have been described in the literature based on SFE of organic pollutants from environmental samples, including PCBs and PAHs (39, 41, 56-59). Generally, the extraction is performed... 

In addition to extraction from solids, supercritical fluids can be used to extract aromatic molecules from liquids. Senorans et al. have utilized carbon dioxide to extract high-quality brandy aroma using a countercurrent supercritical fluid extractor. The aroma quality is influenced by the extraction conditions. Medina and Martinez studied alcohol removal from beverages using supercritical carbon dioxide, to produce beverages with low-alcohol content but sufficient flavor, because of three key benefits 1) water and salts are not appreciably removed by the carbon dioxide 2) proteins and carbohydrates are not extracted or denatured and 3) there is a good control in the aroma recovery. The alcohol removal efficiency increases with the extraction pressure raffinate alcohol concentration can be reduced up to 3 wt.% at 250 bar and 40°C, from 6.2 wt.% in the feed. " ... 

The overlapping CSA patterns often hide the isotropic information and then the main NMR parameter cannot be extracted from solid state spectra. 

---