Selection, 693 nonionic

Modified carboxylates, in which the carboxylate moiety forms part of a carboxymethoxy group, are also available. These are made by reaction of selected nonionic surfactants with chloroacetic acid. The result is a useful hybrid range, lacking the sensitivity of simple... 

TABLE XVI. Summary of Structure of Some Selected Nonionic Surfactants and their CMC and Cloud Point Values ... 

Table 6.10 Critical micelle concentration (CMC) and cloud point temperatures for selected nonionic surfactants...

Properly selected nonionic surfactants can be good candidates to stabilize emulsions through steric repulsion. 

Table 2.7 Symbols and main components of selected nonionic surfactants.

Flotation reagents are used in the froth flotation process to (/) enhance hydrophobicity, (2) control selectivity, (J) enhance recovery and grade, and (4) affect the velocity (kinetics) of the separation process. These chemicals are classified based on utili2ation collector, frother, auxiUary reagent, or based on reagent chemistry polar, nonpolar, and anionic, cationic, nonionic, and amphoteric. The active groups of the reagent molecules are typically carboxylates, xanthates, sulfates or sulfonates, and ammonium salts. 

Emulsifiers. Removing the remover is just as important as removing the finish. For water rinse removers, a detergent that is compatible with the remover formula must be selected. Many organic solvents used in removers are not water soluble, so emulsifiers are often added (see Emulsions). Anionic types such as alkyl aryl sulfonates or tolyl fatty acid salts are used. In other appHcations, nonionic surfactants are preferred and hydrophilic—lipophilic balance is an important consideration. 

A detergent that is compatible with the remover formula must be developed for water rinse removers. Anionic or nonionic surfactants should be selected, depending on the pH and intended application of the remover. 

The method of action of the polymers is thought to be encapsulation of drill cuttings and exposed shales on the borehole wall by the nonionic materials, and selective adsorption of anionic polymers on positively charged sites of exposed clays which limits the extent of possible swelling. The latter method appears to be tme particularly for certain anionic polymers because of the low concentrations that can be used to achieve shale protection (8). 

Amino Alcohols. Reaction of chloroformate is much more rapid at the amino group than at the hydroxyl group (4—8). Thus the hydroxy carbamates, which can be cyclized with base to yield 2-oxazoHdones, can be selectively prepared (29). Nonionic detergents may be prepared from poly[(ethylene glycol) bis(chloroformates)] and long-chain tertiary amino alcohols (30). 

Properties. HydroxyethjIceUulose [9004-62-0] (HEC), is a nonionic polymer. Low hydroxyethyl substitutions (MS = 0.05-0.5) yield products that are soluble only in aqueous alkali. Higher substitutions (MS > 1.5) produce water-soluble HEC. The bulk of commercial HEC falls into the latter category. Water-soluble HEC is widely used because of its broad compatibiUty with cations and the lack of a solution gel or precipitation point in water up to the boiling point. The MS of commercial HEC varies from about 1.8 to 3.5. The products are soluble in hot and cold water but insoluble in hydrocarbon solvents. HEC swells or becomes pardy to mosdy soluble in select polar solvents, usually those that are miscible with water. 

At low temperature, nonionic surfactants are water-soluble but at high temperatures the surfactant s solubUity in water is extremely smaU. At some intermediate temperature, the hydrophile—Hpophile balance (HLB) temperature (24) or the phase inversion temperature (PIT) (22), a third isotropic Hquid phase (25), appears between the oil and the water (Fig. 11). The emulsification is done at this temperature and the emulsifier is selected in the foUowing manner. Equal amounts of the oil and the aqueous phases with aU the components of the formulation pre-added are mixed with 4% of the emulsifiers to be tested in a series of samples. For the case of an o/w emulsion, the samples are left thermostated at 55°C to separate. The emulsifiers giving separation into three layers are then used for emulsification in order to find which one gives the most stable emulsion. 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

Poloxamers are used primarily in aqueous solution and may be quantified in the aqueous phase by the use of compleximetric methods. However, a major limitation is that these techniques are essentially only capable of quantifying alkylene oxide groups and are by no means selective for poloxamers. The basis of these methods is the formation of a complex between a metal ion and the oxygen atoms that form the ether linkages. Reaction of this complex with an anion leads to the formation of a salt that, after precipitation or extraction, may be used for quantitation. A method reported to be rapid, simple, and consistently reproducible [18] involves a two-phase titration, which eliminates interferences from anionic surfactants. The poloxamer is complexed with potassium ions in an alkaline aqueous solution and extracted into dichloromethane as an ion pair with the titrant, tet-rakis (4-fluorophenyl) borate. The end point is defined by a color change resulting from the complexation of the indicator, Victoria Blue B, with excess titrant. The Wickbold [19] method, widely used to determine nonionic surfactants, has been applied to poloxamer type surfactants 120]. Essentially the method involves the formation in the presence of barium ions of a complex be-... 

Adsorption and ion exchange chromatography are well-known methods of LC. In adsorption, one frequently selects either silica or alumina as stationary phase for separation of nonionic, moderately polar substances (e.g. alcohols, aromatic heterocycles, etc.). This mode works best in the fractionation of classes of compounds and the resolution of isomeric substances (J). Ion exchange, on the other hand, is applicable to the separation of ionic substances. As to be discussed later, this mode has been well developed as a tool for analysis of urine constituents (8). 

To reduce or eliminate polymer solute/glass packing interactions the following parameters were optimized a) pH, ionic strength and concentrations of additives such as nonionic surfactants, b) selection of pore sizes in a column combination. 

The separations of some nonionic tensides having biological activity and consisting of ethyleneoxide oligomer mixtures were performed in many different TEC systems (silica and alumina as the stationary phase and single solvent or binary mixtures as the mobile phase). Selectivity was higher on alumina than on the silica layer. Both... 

An especially preferred product comprises about 2 parts Gilsonite HM, about 1 part Gilsonite Select, about 1 part causticized lignite and about 0.1 to 0.15 part of a nonionic surfactant [378-382]. 

Since poly(oxyethylene)-type nonionic surfactants have a capability of facilitating the transfer of cations [51,52], the above interphase complexation may be seen as an example of precomplex formation before the bulk transfer of ions, which is seen when Aq (p is sufficiently positive. The presence of such precomplex formation at the interface, which is detectable voltammetrically [53], may have significance in the rate of complex formation and the selectivity in the bulk facilitated transfer. 

Reviews of w/o-ME-based LLE of biomolecules are readily available [4,57,102-104]. However, new results have been generated in this field since the publication of the cited reviews. For instance, there has been a large amount of research involving new surfactant and surfactant systems, particularly those involving nonionic and natural surfactants such as phosphatidylcholine and bioaffinity surfactants (Table 1), in order to increase biocompatibility and selectivity and prevent denaturation that occurs using ionic surfactants. The more recent results along these lines will be presented here, along with an overview of the LLM process. 

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