Organic amines separation

FIGURE 5-27. Effect of column surface upon retention of organic amines ( ) separation on a fully coated C]8 column, (b) Separation on a column with 50% coating level of C18. (c) Separation on a column of silica. The mobile phase is acetonitrile/ water (60 40) with 4 mM dibasic ammonium phosphate (pH 7.8). The sample components are (1) benzocaine, (2) lidocaine, (3) etidocaine, and (4) tetracaine. (Reprinted from reference 4 with permission.)... 

Figure 8.90 Chemiluminescent nitrogen detection of organic amines. Separator column Luna Cl 8,3 pm column dimensions ISOmmxl mm i.d. eluent (A) 0.15% TFA in water and (B) (75 25 v/v) MeOH/IPA with 0.15% TFA gradient 15-85% B in 30 min flow...

Experience in air separation plant operations and other ciyogenic processing plants has shown that local freeze-out of impurities such as carbon dioxide can occur at concentrations well below the solubihty limit. For this reason, the carbon dioxide content of the feed gas sub-jec t to the minimum operating temperature is usually kept below 50 ppm. The amine process and the molecular sieve adsorption process are the most widely used methods for carbon dioxide removal. The amine process involves adsorption of the impurity by a lean aqueous organic amine solution. With sufficient amine recirculation rate, the carbon dioxide in the treated gas can be reduced to less than 25 ppm. Oxygen is removed by a catalytic reaction with hydrogen to form water. 

Organic amine compounds can be separated successfully on silica gel columns with good peak symmetry using organic/aqueous mobile... 

B. A. Bildenmeyer, J. K. Del Rios, and J. Korpi, Separation of organic amine compounds on silica gel with reversed-phase eluents, Anal. Chem., 54 442 (1982). 

Zeolites and related aluminosilicates constitute a vital family of microporous materials with immense applications in catalysis, sorption and separation processes [1-3]. The discovery of aluminophosphates is an important landmark in the science of these materials [4], All these materials are, in general, synthesized under hydrothermal conditions by making use of template molecules [2]. The template molecules are usually organic amines and they are involved in the formation of these framework structures in more ways than one. While it is difficult to pinpoint the exact manner in which the amines participate or direct the formation of these inorganic structures, it is generally believed that their size and shape are crucial in determining the pore structure. In recent years, a variety of open-framework structures formed by divalent metal phosphates... 

The chromatograms in Figure 5-27 indicate that the surface silanols by themselves are not deleterious to the retention of organic amines when using organic, aqueous eluents containing an inorganic salt. In fact, silica gel itself appears to be the preferred adsorbent for the separation of these bases. The... 

When ion-pairing agents (surfactants, tetraalkylammonium salts, organic amines) are introduced into the system, their effects resemble those observed with ion-pairing chromatography. Urea (2-6 M) is known to increase the solubility in water of hydrophobic molecules in MEKC separation by very lipophilic compounds was reported improved by highly concentrated urea. 

Conventional IPC separations were achieved by adding organic amines and ammonium salts of varying chain lengths as cationic IPRs for anionic analytes and alkyl or aryl sulfonates and sulfates as anionic IPRs for cationic solutes. Since these IPRs exhibit good tensioactive properties, IPC was originally named soap chromatography [1]. 

Uncommon IPRs were tested recently. Polymerized acyl monoglydnate surfactant was found to be as effective as sodium dodecylsulfate for the resolution of organic amines [126]. For the analysis of pyridine-based vitamins in infant formnlas, dioc-tylsulfosuccinate produced a unique retention pattern [133], Among bizarre IPRs, tris(hydroxymethyl)aminomethane was used for the determination of cyclamate in foods. It was selected over different ion-pair reagents such as triethylamine and dibu-tylamine, based on sensitivity and time economies [134]. Hexamethonium bromide, a divalent IPR, was used successfully to separate sulfonates and carboxylates [135]. 

Bisphosphonates (bone resorption inhibitor drugs) were subject to many investigations. They can chelate to metal surfaces, producing chromatographic peak tailing. Different tetraalkylammonium salts, commonly selected as IPRs in separation of bisphosphonates [85], were replaced by volatile organic amines when ELSD was used [86]. 

The organic amine extractants are the most commonly used anion exchangers. Secondary amines have been used to recover uranium from leach liquors (GlO) secondary and tertiary amines to recover molybdenum from uranium mill circuits (L13) a primary amine, diethylenetriamine-penta-acetic acid (DTPA) to extract cerium group lanthanides (B6) tri-,V-butylamine-3-methyl-2-butanonc to separate yttrium and rare earth nitrates (G13) tricaprylyl amine (Alamine 336) and methyltrioctyl-ammonium salt (Aliquat 336) to recover vanadium from acidic solutions (A3) and Aliquat 336 to extract vanadium from slightly acidic or alkaline leach liquor (S36). 

Similarly, Sano et al. [1994] added colloidal silica to a stirred solution of tetrapropylammonium bromide and sodium hydroxide to synthesize a hydrogel on a stainless steel or alumina support with a mean pore diameter of 0.5 to 2 pm. The composite membrane is then dried and heat treated at 500 C for 20 hours to remove the organic amine occluded in the zeolite framework. The silicalite membranes thus obtained are claimed to be free of cracks and pores between grains, thus making the membranes suitable for more demanding applications such as separation of ethanol/water mixtures where the compound molecules are both small. The step of calcination is critical for synthesizing membranes with a high permselectivity. 

Molecular design and rational synthesis of inorganic microporous crystalline materials are frontier subjects in the fields of zeolites science and molecular engineering. Zeolite synthesis is an active field of research because zeolites with uniform micropores are important in many industrial processes in catalysis, adsorption, and separation, and are finding new applications in electronics, magnetism, chemical sensors, and medicine, etc.12 91 Synthesis of such materials typically involves crystallization from a gel medium under hydrothermal/solvothermal conditions in the presence of organic amines as... 

In this type of separation the analyte cations compete with the eluent cation for ion-exchange sites and move down the eolumn at different rates. The ionic eluent selected depends on the cations to be separated, the type of separation column and on the detector. In many cases an aqueous solution of a strong acid such as hydrochloric, sulfuric or methanesulfonic acid is a satisfactory eluent. Sample cations commonly separated include the following alkali metal ions (Li, Na+, K", Rb, Cs ), ammonium, magnesium, alkaline earths (Ca, Sr +, Ba ), and various organic amine and alkano-lamine cations. Most other metal cations are separated with a weakly complexing eluent. 

In acidic solution organic amines can be separated by CE as the protonated cations. If necessary, some methanol or acetonitrile may be mixed with the aqueous BGE to enhance the solubility. For example, amino acids are zwitterions throughout much of the pH range but they have a net positive charge at very low pH values. The CE sepa-... 

In the case of acidic glycolipids the relative proton affinity of chemicals can shift the balance for negative ionisation in favor of co-eluted compounds. Pre-analytical separation under acidic conditions serves also to reduce as much as possible the dispersion in the MS spectrum of the metabolite into multiple m/ z representing the various adducts of counterions Na, K, NH4, organic amines, ... which improves sensitivity of the test. Sulfatides are lost during the partition between the hexane and the methanol/water phase. The analysis of sulfatides involves the isolation of the glycosphingolipid fraction and the subsequent separation of sulfatides from neutral lipids by chromatography on DEAE-sephadex or DEAE-cellulose column (the variety of methods are referenced in the website CyberLipid (http //www.cyberlipid.org/). 

The next step in purification is separation of uranyl nitrate from the other metallic impurities in the dissolver solution by solvent extraction. Practically aU uranium refineries now use as solvent tributyl phosphate (TBP) dissolved in an inert hydrocarbon diluent. The first U.S. refinery used diethyl ether as solvent and later refineries have used methyl isobutyl ketone or organic amines, but practically all have now adopted TBP. It is nonvolatile, chemically stable, selective for uranium, and has a uranium distribution coefficient greater than unity when the aqueous phase contains nitric acid or inorganic nitrates. 

Thoriuin recovery processes. Because of the many elements in the solution, their chemical similarity, and the presence of phosphoric acid, separation of thorium from this acid solution has proved to be difficult. Wylie [WS] has reviewed the numerous separatirm processes that have been developed. Figure 6.5 shows the principal steps in seven of these processes and gives references for more details. Processes 4 and 6 appear to be the most economic when thorium, rare earths, and uranium all are to be recovered. Process 4, involving separation of thorium and rare earths from phosphate and uranium by precipitation with oxalic acid, is described next. Process 6, involving separation by solvent extraction with organic amines, is described in Sec. 8.6. 

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