Liquid-adsorption chromatography

When the predominant functional group of the stationary phase is more polar than the commonly used mobile phases, the separation technique is termed normal-phase HPLC (NPLC), formerly also called adsorption liquid chromatography. In NPLC, many types... 

The elution volumes of polystyrene and benzene in the size-exclusion mode were 0.98 and 1.78 ml, respectively (Figure 1.4A). This means that separations by molecular size can be achieved between 0.98 and 1.78 ml in this system. In the normal phase mode the elution volumes of octylbenzene and benzene were 1.98 and 2.08 ml, respectively, in n-hexane solution (Figure 1.4B). This type of chromatography is called adsorption or non-aqueous reversed-phase liquid chromatography. These are adsorption liquid chromatography and non-aqueous reversed-phase liquid chromatography. The elution order of the alkylbenzenes in the reversed-phase mode using acetonitrile was reversed... 

Ballschmiter K, Bacher R (1989), Fresenius J. Anal Chem. 333 732-733.. .Adsorption liquid chromatography of PCDD and PCDF on the polyphenol- phase unique structural effects"... 

From the literature there is evidence that in GC on polar phases and in normal-phase (adsorption) liquid chromatography (HPLC and TLC) the chemically specific, molecular size-independent intermolecular interactions play the main retention-determining role. For example, the HPLC retention parameters determined for substituted benzenes on porous graphite are described by QSRR equations comprising polarity descriptors but containing no bulk descriptors [93-95]. Because, in general, it is difficult to quantify the polarity properties precisely, the QSRR for GC on polar phases and for normal-phase HPLC are usually of lower quality than in the case of GC on non-polar phases and in the case of reversed-phase liquid chromatography. 

Lefebvre, P. Agadir, A. Comic, C. Gourmel, B. Hue, B. Dreux, C. Degos, L. Chomienne, C. Simultaneous determination of all-frans and 13-cis retinoic acids and their 4-oxo metabolites by adsorption liquid chromatography after solid-phase extraction. J.Chromatogr.B, 1995, 666, 55-61... 

Fig. 2 Mixed solvent strengths on silica gel after Saunders. Source From Solvent selection in adsorption liquid chromatography, in Anal. Qiem. ...

FIGURE 7.12 Comprehensive normal-phase (adsorption) liquid chromatography (LC) x reversed-phase LC separation of the oxygen heterocyclic fraction of a lemon oil sample (for peak identi cation, see Ref. [133]). (From Dugo, P. et al., Anal. Chem., 73, 2525, 2004. With permission.)... 

K. Ballschmiter, M. Wossner Recent developments in adsorption liquid chromatography (NP-HPLC), Fresmius J. Anal. Chem. 361 (1998), 743-755. 

M. D. Palamareva, V. R. Meyer New graph of binary mixture solvent strength in adsorption liquid chromatography,... 

Further, the chiral discrimination model via the formation of ionic diastereomers, as proposed by Bhushan and Parshad [8] in Scheme 13.1, was viewed by Kowalska and coworkers [11] in terms of the energy difference for ion-pair formation (i.e., in the formation of the two diastereomeric salts). Ibuprofen is a carboxylic acid and, therefore, apt to dissociate (and form an organic anion) and the separation of the two enantiomers of ibuprofen can be achieved only because the thermodynamic equilibrium constants (K) for the ion-pair formation process for the two enantiomers (Ki and K2, respectively) have different numerical values. From the theory of adsorption liquid chromatography, it is well known [15] that the thermodynamic equilibrium constant of adsorption, K, can be defined as follows ... 

Liquid chromatography is a separation technique based on the selective adsorption on a solid, siiica or alumina for example, or a mixture of the two, of the different components of a liquid mixture. 

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. 

Lab method with high performance liquid chromatography after collection in an impinger containing water Charcoal adsorption tube and gas chromatography... 

Lab method using porous polymer adsorption tube and thermal desorption with gas chromatography Lab method using porous polymer diffusive samplers with thermal desorption and gas chromatography Lab method using pumped acid-coated filters, desorption and liquid chromatography... 

There are a number of causes of peak asymmetry in both gas and liquid chromatography, including heat of adsorption, high activity sites on the support or absorbent, and nonlinear adsorption isotherms. Assuming that good quality supports and adsorbents are used, and the column is well thermostatted, the major factor causing peak asymmetry appears to result from nonlinear adsorption isotherms. 

R. E. Boehm and D. E. Martiie, A unified theory of retention and selectivity in liquid chromatography. 1. Eiquid-solid (adsorption) clrromatography , J. Phys. Chem. 84 3620-3630(1980). 

Nieoud R. M., Euehs G., Adam P, Bailly M., Kusters E., Antia E, Reuille R., Sehmid E. (1993) Preparative Seale Enantioseparation of a Chiral Epoxide Comparison of Liquid Chromatography and Simulated Moving Bed Adsorption Teehnology, Chirality 5 267-271. 

High-pressure liquid chromatography (HPLC) is a variant of the simple column technique, based on the discovery that chromatographic separations are vastly improved if the stationary phase is made up of very small, uniformly sized spherical particles. Small particle size ensures a large surface area for better adsorption, and a uniform spherical shape allows a tight, uniform packing of particles. In practice, coated Si02 microspheres of 3.5 to 5 fxm diameter are often used. 

A more complex but more versatile separation method is chromatography, a technique widely used in teaching, research, and industrial laboratories to separate all kinds of mixtures. This method takes advantage of differences in solubility and/or extent of adsorption on a solid surface. In gas-liquid chromatography, a mixture of volatile liquids and gases is introduced into one end of a heated glass tube. As little as one microliter (10-6 L) of sample may be used. The tube is packed with an inert solid whose surface is coated with a viscous... 

The consideration made above allows us to predict good chromatographic properties of the bonded phases composed of the adsorbed macromolecules. On the one hand, steric repulsion of the macromolecular solute by the loops and tails of the modifying polymer ensures the suppressed nonspecific adsorptivity of a carrier. On the other hand, the extended structure of the bonded phase may improve the adaptivity of the grafted functions and facilitate thereby the complex formation between the adsorbent and solute. The examples listed below illustrate the applicability of the composite sorbents to the different modes of liquid chromatography of biopolymers. 

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