Solvent systems contamination

Supercritical fluid extraction — During the past two decades, important progress was registered in the extraction of bioactive phytochemicals from plant or food matrices. Most of the work in this area focused on non-polar compounds (terpenoid flavors, hydrocarbons, carotenes) where a supercritical (SFE) method with CO2 offered high extraction efficiencies. Co-solvent systems combining CO2 with one or more modifiers extended the utility of the SFE-CO2 system to polar and even ionic compounds, e.g., supercritical water to extract polar compounds. This last technique claims the additional advantage of combining extraction and destruction of contaminants via the supercritical water oxidation process."... 

The purity of the product is determined not only by the inherent selectivity of the solvent system for the component sought, but also on the phase ratio, the concentration of the contaminants, and the performance of any scrubbing of the extract. 

Non-volatile buffers such as phosphates, borates, perchlorates and phosphoric acid should be avoided at all costs because of high background ion current, source contamination and blockages, and in the case of perchlorates, explosions. Figure 6.4 shows the mass spectrum of typical background when using phosphoric acid in the eluent. If the solvent system for a particular analysis does not assist the electrospray process, it is possible to enhance ionisation by postcolumn addition of a suitable volatile buffer. 

The CleanSoil process is an ex situ treatment technology that uses steam to remove hydrocarbons and chlorinated solvents from contaminated soils. The steam vaporizes the contaminants from the soil and carries them to a condenser for recovery. The water is converted back into steam and reused in the system. The remaining vapors pass through an activated carbon filter and are released into the atmosphere. The technology has been applied full-scale at multiple sites and is commercially available. 

Trans Coastal Marine Services (formerly Envirosystems, Inc.) and Louisiana State University (LSU) have developed several bioreactor systems to facihtate petroleum hydrocarbon mineralization and the bioremediation of organic wood preservatives utilizing an immobilized microbe bioreactor (IMBR) technology. These technologies can treat petroleum hydrocarbons, chlorinated solvents, pesticide-contaminated soils, and contaminated groundwater. 

In their test system, the researchers used the ionic liquid l-butyl-3-methylimidazol-ium hexafluorophosphate (bmim)(PF6), which is stable in the presence of oxygen and water, with naphthalene as a low-volatility model solute. Spectroscopic analysis revealed quantitative recovery of the solute in the supercritical CO2 extract with no contamination from the ionic liquid. They found that CO2 is highly soluble in (bmim)(PF6) reaching a mole fraction of 0.6 at 8 MPa, yet the two phases are not completely miscible. The phase behavior of the ionic liquid-C02 system resembles that of a cross-linked polymer-solvent system (Moerkerke et al., 1998), even though... 

Water-based solvent systems originally developed for the separation and purification of proteins and other biomaterials (Walter et al., 1985) have been suggested for the treatment of contaminated aqueous waste-streams. Certain pairs of water-soluble polymers are incompatible in solution together, and this can lead to phase separation in which two phases are formed. Both phases are predominantly water, and each contains only one of the two polymers. Similar phase behavior results with some polymers and high concentrations of organic salts. The properties of the two phases ensure that the environment-afforded targeted species is different in the two phases. 

Methylene chloride was selected primarily on the basis of the following criteria (1) It is commonly referred to as the universal solvent or the one used most frequently in the extraction of semivolatile organics sorbed on polymeric sorbent media. Hence, the contaminant chemistry associated with this solvent system would be of the most use to resin users. (2) The physical and chemical properties of methylene chloride make it ideally suited for the extraction of semivolatile organics sorbed on polymeric sorbent media. 

A reconstructed ion chromatogram (GC-MS) containing extractable contaminants isolated from a typical lot of foam is shown in Figure 4. The qualitative composition of the extractable contaminants was provided by GC-MS. Contaminant profiles were identical for each of the two solvent systems employed, methylene chloride (1003 ) and ethyl ether/hexane (5/95). The contaminant chemistry shown here and again in Figure 5 in several instances is consistent with the manufacturing process data shown in the box, most notably the presence of residual toluene diisocyanate (starting materials, see Scheme II) and an aliphatic amine (possible reaction catalyst). 

The extraction and measurement of lipids may require several steps, these include (1) Pretreatment, including drying, size reduction, and possibly acid hydrolysis to release lipids. (2) Homogenization of the tissue in the presence of a sol vent/solvent system. (3) Separation of liquids from solids. (4) Removal of nonlipid contaminants. (5) Removal of solvent and drying. (6) Calculating the content of lipids by weight difference. 

Prior to phospholipid analysis, it is imperative to extract the lipids from their matrix and free them of any nonlipid contaminants. Phospholipids are generally contained within the lipid fraction, which may be recovered by the traditional Bligh and Dyer or Folch extraction procedure (9,22). In any phospholipid extraction method it is recommended to include a rather polar solvent in addition to a solvent with high solubility for lipids. The former is needed to break down lipid-protein complexes that prevent the extraction of the lipids in the organic phase. Traditionally, mixtures of chloroform and methanol (especially 2 1, v/v) have been recommended. These are washed with water or aqueous saline to remove nonlipid contaminants. Comparing the recovery of phospholipids, Shaikh found that the neutral phospholipids PC, PE, SPH as well as DPG were nearly quantitatively extracted by all solvent systems studied (Table 1), although Bligh and Dyer, in which the lower phase was removed only once, was somewhat worse (23). 

In order to prevent the formation of a stable emulsion at any stage of the extraction procedure, the water content of the hydrated WPC has to be controlled so as not to obtain a biphasic solvent system during extraction with mixtures of chloroform and methanol. Besides, nonlipid contaminants are removed from the extract by gel filtration on nonlipophilic Sephadex G-25 instead of traditional aqueous washing total lipids were eluted with a 19/1 (v/v) mixture of chlo-roform/methanol, saturated with water, whereas a 1/1 (v/v) mixture of water and methanol eluted nonlipid contaminants. The method yields a similar total lipid content to the Folch method, but it is about four times faster (24). 

Using this solvent system, serine is not completely separable from glycine (RF 0.58) which is a possible contaminant. The latter may be distinguished, however, by the characteristic brownish-pink spot which it gives on spraying with ninhydrin that of serine is purple. 

The isolation of pure bases by repeated chromatography with varied solvent systems is often tedious and sometimes not possible for example, zizyphine-B and zizyphine-C showed identical Rt values in a dozen different solvent systems. The isolation of pure zizyphine-C was only achieved when the contaminant zizyphine-B was acetylated (29). Similarly, the sensitive mucronine-G and mucronine-H were only obtained pure as acetyl derivatives (28). Presumably, the problem of the separation of these alkaloids could be rendered more facile by the high pressure liquid chromatographic technique. 

This process is characterized by its high C02 retention under pressure and by low steam requirements for regeneration. According to U.S. Patent 3,347,621, a sidestream regenerator is required to remove by-products that build up in the system. Mild steel is suitable in much of the process, but stainless steel is preferred where C02 concentrations are high. The process must be carefully engineered to protect the downstream nickel catalysts from sulfur that may carry-over from the absorber. Likewise, the C02 that is produced must be protected from entrainment of the solvent and contamination with sulfur260. 

In the analysis of metals in petroleum and petroleum products one of the most common sample preparation procedures is the dilution of the sample with an organic solvent such as xylene, methyl isobutyl ketone (MIBK) or white spirit. It is of great importance that the solvent system chosen is as free as possible from metallic contamination. Elements such as sodium and zinc are commonly found in many organic solvents. Similarly, other reagents such as mineral acids must be investigated for metal content before use. Where ultra-trace level determinations are to be attempted the reagents used may need to be purified. For solvents, the use of redistillation or extraction with mineral acid may improve the blank levels. 

This solvent system is convenient to separate less polar contaminants such as tert-butyl acetate or unchanged di-tert-butyl dicarbonate. 

Bonded stationary phases for NPC are becoming increasingly popular in recent years owing to their virtues of faster column equilibration and being less prone to contamination by water. The use of iso-hydric (same water concentration) solvents is not needed to obtain reproducible results. However, predicting solute retention on bonded stationary phases is more difficult than when silica is used. This is largely because of the complexity of associations possible between solvent molecules and the chemically and physically heterogeneous bonded phase surface. Several models of retention on bonded phases have been advocated, but their validity, particularly when mixed solvent systems are used as mobile phase, can be questioned. The most commonly accepted retention mechanism is Snyder s model, which assumes the competitive adsorption between solutes and solvent molecules on active sites... 

High speed countercurrent chromatography (HSCCC) produces highly efficient chromatographic separations of solutes without the use of solid supports Thus the method eliminates all complications caused by the solid support, such as adsorptive loss and deactivation of samples, tailing of solute peaks, contamination, etc. As with other CCC schemes, HSCCC utilizes two immiscible solvent phases, one as a stationary phase and the other as a mobile phase, and the separation is highly dependent on the partition coefficient values of the solutes, i.e., the ratio of the solute concentration between the mobile and stationary phases. Therefore the successful separation necessitates a careful search for the suitable two-phase solvent system that provides an ideal range of the partition coefficient values for the applied sample. 

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