Chemical bonding, of stationary-phase

Deactivation of solid support by chemical bonding of stationary phase. 11... 

Chemical bonding of stationary phases has been shown to increase the stability of the stationary phase compared with conventionally coated films. A chemically bonded phase may be regarded as one that is not extractable by solvents that do not attack the phase. 

Silica particles have surface silanol groups, — SiOH. These are used for chemical bonding of stationary phases by silination reactions with chlorosilanes ... 

Buszewski, B., Gadza-la-Kopciuch, R. M., Markuszewski, M. L, Kaliszan, R. Chemically bonded silica stationary phases synthesis, physicochemical characterization, and molecular mechanism of reversed-phase HPLC retention. Anal. Chem. 1997, 69, 3277-3284. 

Yang, W.-H., Chen, I-L., and Wu, D.-H., Chemically bonded phenylsilicone stationary phases for the liquid chromatographic separation of polycyclic aromatic hydrocarbons and cyclosiloxanes, /. Chromatogr. A, 722, 97, 1996. 

Sandoval, I.E. and Pesek, I.I., Synthesis and characterization of a hydride-modified porous silica material as an intermediate in the preparation of chemically bonded chromatographic stationary phases, AnaZ. Chem., 61, 2067, 1989. 

S. N. El-Gizawy, A. N. Ahmed, and N. E. El-Rabbat, High performance liquid chromatographic determination of multivitamin preparations using a chemically bonded cyclodextrin stationary phase, Anal. Lett., 24 1173 (1991). 

Selection of Ionic and Neutral Specie Which at pH < 7.0 Modify the Retention Characteristics of Unprotected Peptides on Chemically Bonded Hydrocarbonaceous Stationary Phases"... 

S. A. Wise, S. N. Chesler, H. S. Hertz, L. R. Hilpert, and W. E. May, Chemically-bonded aminosilane stationary phase for the high-performance liquid chromatographic separation of polynuclear aromatic compounds. Anal. Chem. 49 (1977), 2306-2310. 

Figure4.3 Formation of chemically bonded silica stationary phases.

Gfeller et al.25 1 used a microparticulate chemically bonded diol stationary phase in combination with an exclusively aqueous mobile phase. It allowed post-column ion-pair derivatiza-tion of the separated alkaloids. By changing the pH and the ionic strength of the buffer, the capacity factors of the alkaloids could be varied. 

Szepesi et al. reported an ion-pair separation of eburnane alkaloids on a chemically bonded cyanopropyl stationary phase. As counter-ion, di-(2-ethyl hexyl)phosphoric acid or (+)-10-camphorsulfonic acid were used in a mobile phase consisting of hexane - chloroform -acetonitrile mixtures (Table 8.8, 8.9). Because of the poor solubility of the latter pairing ion, diethylamine (Table 8.9) was added to the mobile phase. Addition of diethylamine considerably reduced the k1 of the alkaloids, due to suppression of the ionization of the alkaloids. However, due to the strong acidic character of the pairing ion, ion-pairs were still formed under these conditions. The camphorsulfonic acid containing mobile phases were found to be very useful for the separation of optical isomers (Table 8.10, 8.11, Fig.8.8) 6. It was also found that the selectivity of the system could be altered by choosing different medium-polarity solvents (moderator solvents) as dioxane, chloroform or tetrahydrofuran. The polar component of the solvent system affected peak shape. Based on these observations, a method was developed to analyze the optical purity of vincamine and vinpocetine. For the ana-... 

Lumley, B., Khong, T.M. and Perrett, D. (2004) The characterisation of chemically bonded chromatographic stationary phases by thermogravimetry. Chromatographia, 60 (1-2), 59-62. 

Ahmed, A.N. El-Gizawy, S.M. Use of chemically-bonded cyclodextrin stationary phase for high performance liquid chromatographic determination of Feldene capsules. J.Chromatogr.Sci., 1987, 25, 424-426 [column temp 35]... 

C.H. LochmHller, S.F. Marshall and R.W. Wilder. Photoacoustic Spectroscopy of Chemically Bonded Chromatographic Stationary Phases, Anal. Chem.. 52 19-23 (1980). 

A.H.N. Ahmed and S.M. El-Gizawy, Chemically Bonded Cyclodextrin Stationary Phase for the High-performance Liquid Chromatographic Separation and Determination of Sulphonamides, Analyst, 11(1989)4571. 

The inertness of stainless steel columns matches that of fused silica and is derived from a multistep process which utilizes a multilayer pretreatment of the inner surface of the stainless steel. Each layer is chemically stable at elevated temperatures and has the same or higher mechanical properties as the steel tubing. The layers are chemically bonded together. Stationary phases are easily bonded to this stable inert surface, resulting in high-performance columns. 

On the other hand, chiral separation of some fiavonoids was also carried out by HPLC using a chemically bonded chiral stationary phase or more often by the addition of chiral additives in the mobile phase facilitating separation of enantiomers on conventional stationary phases [8, 22, 86]. For the separation of different polyphenols, chromatographic conditions involve almost exclusively the use of a RP C18 column and a binary solvent system containing acidified water using acetic acid, phosphoric acid, or sulfuric acid and a less polar solvent such as methanol or acetonitrile [113-121]. 

Since the early nineties, column manufactures have devoted extensive resources to acquiring technology for the development of chemically bonding a stationary-phase... 

Chiral separation of flavonoids has also been carried out by chromatographic systems by using a chemically bonded chiral stationary phase or by the addition of chiral mobile phase additives (reviewed by Yanez et al. ). These chiral polymer phases can be further subdivided into polysaccharide-derived columns, and cyclodextrin and mixed cyclodextrin columns. With regard to chiral mobile phase additives, the addition of an optically active molecule to the mobile phase can facilitate separation of enantiomers on conventional stationary phases. Cyclodextrin as a chiral additive is widely used to separate enantiomers mainly by capillary electrophoresis (CE), as discussed in Section 3.6.2.I. Table 3.7 summarizes the most habitual HPLC procedures employed for the analysis of various classes of food flavonoids. 

Bonded-phase chromatography (BPC). To overcome some of the problems associated with conventional LLC, such as loss of stationary phase from the support material, the stationary phase may be chemically bonded to the support material. This form of liquid chromatography, in which both monomeric and polymeric phases have been bonded to a wide range of support materials, is termed bonded-phase chromatography . 

The problems of stationary phase erosion can be largely overcome by solvent-generated LLC, where the stationary liquid phase is generated dynamically by the mobile phase, in this approach, one of the phases of an equilibrated liquid-liquid system is applied as a mobile phase to a solid support which is better wetted by the other phase of the liquid-liquid system. The support is usually silica when the stationary phase is aqueous or a polar solvent and a reversed-phase chemically bonded support when the stationary phase is a nonpolar solvent. Under these Conditions a multimolecular layer is formed on the surface of the solid support which has the properties of the liquid phase in... 

Selection of columns and mobile phases is determined after consideration of the chemistry of the analytes. In HPLC, the mobile phase is a liquid, while the stationary phase can be a solid or a liquid immobilised on a solid. A stationary phase may have chemical functional groups or compounds physically or chemically bonded to its surface. Resolution and efficiency of HPLC are closely associated with the active surface area of the materials used as stationary phase. Generally, the efficiency of a column increases with decreasing particle size, but back-pressure and mobile phase viscosity increase simultaneously. Selection of the stationary phase material is generally not difficult when the retention mechanism of the intended separation is understood. The fundamental behaviour of stationary phase materials is related to their solubility-interaction... 

The mobile phase must not react chemically with the stationary phase or break the bond linking it to the supporting material. For this reason extremes of pH and strong oxidizing agents should normally be avoided. The working pH range of a medium will be quoted by the supplier. 

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