Chromatography retention mechanisms

J. R K. Huber and G. Lamprecht, Assay of neopterin in serum by means of two-dimensional high-performance liquid chromatography with automated column switching using tliree retention mechanism , 7. Chromatogr. B 666 223-232(1995). 

Virtually all interactive mechanisms that control retention in chromatography are, in fact, mixed interactions as shown by the previous application examples. It has already been suggested that reverse phases can exhibit almost exclusively dispersive interactions with solutes. However, as they are almost always employed with aqueous solvent mixtures then, polar and dispersive interactions will still be operative in the mobile phase. Consequently, the examples given here will be taken where the mixed interactions are either unique or represent a separation of special interest. 

General Description. Liquid chromatography encompasses any chromatographic method in which the mobile phase is a liquid (c.f. gas chromatography). A variety of stationary phases and retention mechanisms are available such that a broad range of modes of separation are possible. It is worthwhile to briefly describe the important modes that find use in clinical chemistry. 

Scheme 4.4 Classification of liquid chromatography according to the retention mechanism. After Weston and Brown [365], Reprinted from A. Weston and P.R. Brown, HPLC and CE. Principles and Practice, Academic Press, Copyright (1997), with permission from Elsevier...

S. Ahuja, Retention Mechanism Investigations on Ion-pair Reversed Phase Chromatography, American Chemical Society meeting, Miami, April 28, 1985. 

The data prove that the retention order of anthocyanins deviates from each other in HPLC and TLC suggesting the involvement of a different retention mechanism. It was stated that the preseparation of anthocyanins by size-exclusion chromatography is a prerequisite of the successful preparative separation by RP-HPLC [244],... 

The selection of the solvent is based on the retention mechanism. The retention of analytes on stationary phase material is based on the physicochemical interactions. The molecular interactions in thin-layer chromatography have been extensively discussed, and are related to the solubility of solutes in the solvent. The solubility is explained as the sum of the London dispersion (van der Waals force for non-polar molecules), repulsion, Coulombic forces (compounds form a complex by ion-ion interaction, e.g. ionic crystals dissolve in solvents with a strong conductivity), dipole-dipole interactions, inductive effects, charge-transfer interactions, covalent bonding, hydrogen bonding, and ion-dipole interactions. The steric effect should be included in the above interactions in liquid chromatographic separation. 

B. A. Bidlingmeyer, S.N. Deming, W.P. Price, Jr., B. Sachok, and M. Petrusek, Retention mechanism for reversed-phase ion-pair liquid chromatography , J. Chromatogr., 1979,186, 419. 

Several improved stationary phase materials have been synthesized for reversed-phase liquid chromatography. One material is vinyl alcohol copolymer gel. This stationary phase is quite polar and chemically very stable however, it demonstrated a strong retention capacity for polycyclic aromatic hydrocarbons.45 9 Although stable octadecyl- and octyl-bonded silica gels have been synthesized from pure silica gel50,51 and are now commercially available, such an optimization system has not yet been built. Further experiments are required to elucidate the retention mechanism, and to systematize it within the context of instrumentation. 

Gritti, F. and Guiochon, G, Critical contribution of nonhnear chromatography to the understanding of retention mechanism in reversed-phase hquid chromatography, J. Chromatogr. A, 1099, 1, 2005. 

Sentell, K.B. and Dorsey, J.G, Retention mechanisms in reversed-phase chromatography. Stationary-phase bonding density and solute selectivity, J. Chromatogr., 461, 193, 1989. 

Berendsen, GE. and de Galan, L., Role of the chain length of chemically bonded phases and the retention mechanism in reversed-phase liquid chromatography, J. Chromatogr., 196, 21, 1980. 

Lochmiiller, C.H., Jiang, C., Liu, Q., and Antonucci, V., High-performance liquid chromatography of polymers retention mechanisms and recent advances, Crit. Rev. Anal. Chem., 26, 29, 1996. 

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