Liquid partition chromatography

Figure 7. Separation of eight biogenic amines using ion pair partition liquid chromatography. Conditions 30 cm column with 4 fim silica stationary phase, 0.1M HClO /0.9M NaClO mobile phase, ethylacetate/tributyl phosphate/hexane (72.5/10/17.5) velocity, 0.8 cm/sec (47).

Two types of system are used for ion-pair liquid chromatography. When polar stationary phase materials, such as silica gel, are used an ion-pair partition mechanism is applied. When non-polar stationary phase materials, such as octadecyl-bonded silica gel and polystyrene gel, are employed a paired-ion adsorption mechanism is involved. The former is called normal-phase ion-pair partition liquid chromatography, and the latter is called reversed-phase ion-pair liquid chromatography. 

Normal-phase Ion-pair Partition Liquid Chromatography... 

The molecular absorption intensity of polar compounds is usually small, but highly sensitive detection can be obtained after pre- or post-column derivatiza-tions. The use of ultraviolet absorption or fluorescence-active counter-ions makes it possible to achieve highly sensitive detection of polar compounds and enhance the capability of ion-pair liquid chromatography. For example, N,N-dimethylprotriptyline has been used as a counter-ion for carboxylic acids12 and picric acid for quaternary amines13 in normal-phase ion-pair partition liquid chromatography. Phenethylammonium, cetylpyridinium, l-phenethyl-2-pyco-linium, and naphthalene-2-sulfonic acid have been used for sulfonic acid and alkyl amines detection.14,15 Ion-pair post-column extraction was applied on-line for fluorescence detection.16... 

To increase Vs, the chromatographer can increase the surface area of the stationary phase materials in normal-phase liquid chromatography, increase the stationary phase volume in reversed-phase or partition liquid chromatography, or increase the ion-exchange capacity in ion-exchange liquid chromatography. In general, if the internal diameter of a column is constant, the retention time... 

The most important cleanup procedures are liquid-liquid partition, liquid chromatography in a column of silica, florisil, and/or alumina, gel permeation chromatography, and solid-phase extraction. 

Osterloh, J. Yu, S. Simultaneous ion-pair and partition liquid chromatography of acetsuninophen, theophylline and salicylate with application to 500 toxicologic specimens. Clin.Chim.Acta, 1988, 175, 239-248... 

Polymer surfaces, exposed to blood and blood plasma, can function like the stationary phase in partition liquid chromatography, that is, the molecular blood elements (lipids, proteins) cannot only adsorb on, but may dissolve into the surface layer of the polymer. 

Chapter 7 is devoted to important physicochemical —basically mechanistic — aspects of the direct enantioseparations, carried out by using either CSP or mobile phase. In such cases, the diversity of the involved separation mechanisms is much greater than the most of other chromatographic modes (and, particularly, when compared with the relatively simple physicochemical rules governing adsorption or partition liquid chromatography). Thus, the author of this chapter discusses enantioseparation in terms of the solute-chiral selector complexation constants, stoichiometry and selectivity of complexation, the nature of the binding sites on the stationary phase surface, and, finally, the supramolecular mechanisms of complexation. 

Liquid chromatography is complementary to gas chromatography because samples that cannot be easily handled in the gas phase, such as nonvolatile compounds or thermally unstable ones, eg, many natural products, pharmaceuticals, and biomacromolecules, are separable by partitioning between a Hquid mobile phase and a stationary phase, often at ambient temperature. Developments in the technology of Ic have led to many separations, done by gc in the past, to be carried out by Hquid chromatography. 

By modeling the substance behavior at the interface of two liquid phases, in particular, stationary and mobile phases in liquid chromatography, 1-octanol - water partition coefficients or partition coefficients in... 

In contrast to vapour phase chromatography, the mobile phase in liquid chromatography is a liquid. In general, there are four main types of liquid chromatography adsorption, partition, ion-chromatography, and gel filtration. 

In gas-liquid partition chromatography (GLPC), the stationary phase is a liquid that coats the particles in the tube or the walls of the tube. Often the tube itself is very narrow and long, perhaps 100 m, and has to be coiled (Fig. 4). Solutes are separated, as in liquid chromatography, by their relative solubility in the gas and liquid phases. In... 

Tswett s initial column liquid chromatography method was developed, tested, and applied in two parallel modes, liquid-solid adsorption and liquid-liquid partition. Adsorption ehromatography, based on a purely physical principle of adsorption, eonsiderably outperformed its partition counterpart with mechanically coated stationary phases to become the most important liquid chromatographic method. This remains true today in thin-layer chromatography (TLC), for which silica gel is by far the major stationary phase. In column chromatography, however, reversed-phase liquid ehromatography using chemically bonded stationary phases is the most popular method. 

Lipophilicity represents the affinity of a molecule or a moiety for a lipophilic environment. It is commonly measured by its distribution behavior in a biphasic system, either liquid-liquid (e.g. partition coefficient in 1-octanol-water) or solid-liquid (retention on reversed-phase high-performance liquid chromatography or thin-layer chromatography system). 

Sangster, J. Octanol-Water Partition Coefficients Fundamentals and Physical Chemistry, Wiley, Chichester, 1997. n Valko, K. Application of high-performance liquid chromatography based measurements of lipophilicity to model biological distribution. J. Chromatogr. A 2004, 1037, 299-310. 

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