Nonaqueous reversed-phase liquid

FW Quackenbush, RL Smallidge. Nonaqueous reverse phase liquid chromatographic system for separation and quantitation of provitamins A. J Assoc Off Anal Chem 69 767-772, 1986. 

HJCF Nelis, AP De Leenheer. Isocratic nonaqueous reversed-phase liquid chromatography of carotenoids. Anal Chem 55 270-275, 1983. 

Fnhanced-fluidity liquid reversed-phase chromatography has numerous applications including the separation of nonpolar and polar compounds. For example, EFLC and nonaqueous reversed-phase HPLC are the common means of achieving effective separations of high molecular weight homologous compounds. 

Most HPLC is based on the use of so-called normal-phase columns (useful for class separations), reverse-phase columns (useful for homolog separations), and polar columns (used in either the normal- or reverse-phase mode). Since reverse-phase HPLC columns are generally easier to work with, almost all authors use high-performance reverse-phase liquid chromatography with octade-cyl chemically bonded silica as the stationary phase and nonaqueous solvents as mobile phases (so-called NARP, or nonaqueous reverse-phase chromatography). 

A nonaqueous reversed-phase high-performance liquid chromatography (NARP-HPLC) with refractive index (RI) detection was described and used for palm olein and its fractions obtained at 12.5°C for 12-24 h by Swe et al. (101). The objective of their research was to find the optimum separation for analysis of palm olein triglycerides by NARP-HPLC, and to find a correction factor to be used in calculating CN and fatty acid composition (FAC). The NARP-HPLC method used to determine the triglyceride composition was modified from the method of Dong DiCesare (88). Palm olein was melted completely at 70°C in an oven for 30 min prior to crystal-... 

WO Landen Jr, RR Eitenmiller. Application of gel permeation chromatography and nonaqueous reverse phase chromatography to high pressure liquid chromatographic determination of retinyl palmitate and /3-carotene in oil and margarine. J Assoc Off Anal Chem 62 283-289, 1979. 

Abbott, T, Peterson, R., McAlpine, J., Tjarks, L., and Bagby, M. (1989) Comparing centrifugal countercurrent chromatography, nonaqueous reversed phase HPLC and Ag ion exchange HPLC for the separation and characterization of triterpene acetates. J. Liquid Chromatogr. 12, 2281-2301. 

Nonaqueous suspension agents such as paraffin oils have been developed to polymerize polar monomers, such as acrylic acid. The so-called water-in-oil (W/O) suspension polymerization (reversed phase suspension polymerization) comprises an aqueous solution containing the hydrophilic monomer(s) and initiator(s), which are dispersed in a liquid paraffin oil or other nonpolar hydrocarbon media and polymerized. The use of perfluorocarbon fluids has extended the scope of the suspension polymerization method to monomers and initiators that cannot be used, due to their high solubility and reactivity, in conventional suspension media [249]. 

Reverse osmosis is applicable for the separation, concentration, and/or fractionation of inorganic or organic substances in aqueous or nonaqueous solutions in the liquid or the gaseous phase, and hence it opens a new and versatile field of separation technology in chemical process engineering. Many reverse osmosis processes are also popularly called "ultrafiltration", and many reverse osmosis membranes are also practically useful as ultrafilters. 

Prior to this discovery, in 1954 Silberberg and Kuhn (62) were first to study the polymer-in-polymer emulsion containing ethylcellulose and polystyrene in a nonaqueous solvent, benzene. The mechanisms of polymer emulsification, demixing, and phase reversal were studied. Wetzel and Hocks discovery would then equate the pressure-sensitive adhesive to a polymer-polymer emulsion instead of a polymer-polymer suspension. Since the interface is liquid-liquid, the adhesion then becomes one type of R-R adhesion (35, 36). According to our previous discussion, diffusion is not operative unless both resin and rubber have an identical solubility parameter. The major interfacial interaction is physical adsorption, which, in turn, determines adhesion. Our previous work on the wettability of elastomers (37, 38) can help predict adhesion results. Detailed studies on the function of tackifiers have been made by Wetzel and Alexander (69), and by Hock (20, 21), and therefore the subject requires no further elaboration. 

Countercurrent chromatography is based on the distribution of substances in two liquid phases [128,129]. The liquid is fed into a coiled tube that is moved along an orbital trajectory. Due to centrifugal power, the liquids move in a counter-current. For proteins and many other biomolecules, this method is not practical because of denaturation in a nonaqueous phase. In aqueous two-phase systems, at least one phase exhibits high viscosity and, therefore, mass transfer between the two phases is limited. Similar problems occur with reversed micelle extraction as were observed with the aqueous two-phase extraction [130]. CCC has not been used for large-scale purification of proteins and other biopolymers. 

The evolution of the two-phase system may, however, be more complex. Solubilization of some hydrocarbons in the micellar aqueous phase can take place. Surfactant molecules can migrate across the water-liquid hydrocarbon interface and form structures that have been called reversed micelles, providing the surfactant concentration in the whole system is high enough to reach the critical aggregation concentration in the considered hydrocarbon solvent. Reversed micelles have an aqueous core ensuring the hydration of hydrophilic head group, whereas hydrophobic tails orient toward the nonpolar liquid. It is not our purpose to discuss surfactant behavior in nonaqueous media. 

In this chapter, latest advancements in solvent engineering in bioreductions and greener needs for bioreaction media have been discussed in depth with recent examples. Solvents for bioreductions may be categorized as (i) aqueous (ii) water/water-miscible (monophasic aqueous-organic system) (iii) water/ water-immiscible (biphasic aqueous-organic system) (iv) nonaqueous (mono-phasic organic system, including solvent-free system) and (v) nonconventional media (e.g., ionic liquids, supercritical fluids, gas-phase media, and reverse micelles). 

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