Retention mechanisms in reversed-phase liquid chromatography

1 Retention mechanisms in reversed-phase liquid chromatography 

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Sentell, K.B. and Dorsey, J.G., Retention mechanisms in reversed-phase liquid chromatography. Stationary-phase honding density and partitioning, Anal. Chem., 61, 930, 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. 

Rafferty, J.L. et al.. Retention mechanism in reversed-phase liquid chromatography molecular perspective. AnaZ. Chem. 2007, 79, 6551-6558. 

It seems that the recent investigations made on the AED have resulted in the development of an important new tool for the investigation of mildly heterogeneous surfaces such as modern packing materials used in HPLC. This method has already allowed the derivation of important new results regarding retention mechanisms in reversed phase liquid chromatography [61,117] and on molec-ularly imprinted polymers [56,118]. Its application in preparative liquid chromatography should be fruitful. 

Dorsey, J.G and DiU, K.A., The molecular mechanism of retention in reversed-phase liquid-chromatography, Chem. Rev., 89, 331, 1989. 

Gritti, F. and Guiochon, G. Role of the buffer in retention and adsorption mechanism of ionic species in reversed-phase liquid chromatography I analytical and overloaded band profiles on Kromasil-C18. J. Chromatogr. A. 2004, 1038, 53-66. 

K. A. Dill, The mechanism of solute retention in reversed-phase liquid chromatography, /. Phys. Chem. 91 (1987), 1980-1988. 

QSRR Eqs. (11.15) and (11.16) clearly demonstrate that the organic modifier of binary aqueous eluents used in reversed-phase liquid chromatography also modifies the stationary phase. The hydrocarbon brush on the silica matrix adsorbs the modifier and gets to some extent its properties 117]. QSRR enables differences in the mechanism of reversed-phase retention in individual HPLC. systems employing the. same stationary phase material, are characterized in a numerical manner. 

Micelles and cyclodextrins are the most common reagents used for this technique. Micellar electrokinetic capillary chromatography (MECC or MEKC) is generally used for the separation of small molecules [6], Sodium dodecyl sulfate at concentrations from 20 to 150 mM in conjunction with 20 mM borate buffer (pH 9.3) or phosphate buffer (pH 7.0) represent the most common operating conditions. The mechanism of separation is related to reversed-phase liquid chromatography, at least for neutral solutes. Organic solvents such as 5-20% methanol or acetonitrile are useful to modify selectivity when there is too much retention in the system. Alternative surfactants such as bile salts (sodium cholate), cationic surfactants (cetyltrimethy-lammonium bromide), nonionic surfactants (poly-oxyethylene-23-lauryl ether), and alkyl glucosides can be used as well. 

The mechanism of reversed phase chromatography can be understood by contrast with normal phase chromatography. Normal phase liquid chromatography (NPLC) is usually performed on a polar silica stationary phase with a nonpolar mobile phase, while reversed phase chromatography is performed on a nonpolar stationary phase with a polar mobile phase. In RPLC, solute retention is mainly due to hydrophobic interactions between the solutes and the nonpolar hydrocarbon stationary surface. The nonpolar... 

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