Bonded stationary phases for HPLC

Table 25-5 Selection of bonded stationary phases for HPLC...

The first chemically bonded stationary phases for HPLC were prepared by reacting the surface silanol groups of silica with an alcohol as shown below ... 

The commonly used chemically bonded stationary phases for HPLC, marketed under their trade names by various suppliers, are listed in Table 10.6 (Commercial products presently available under these trade names may have specifications which are different from those given in the Table). 

Zhong Q, He L, Beesley TE, Trahanovsky WS, Sun P, Wang C, Armstrong DW (2006) Optimization of 2,6-dinitro-4-trifluoromethylphenyl ether substituted cyclodextrin bonded stationary phases for HPLC separation of enantiomers. Chromatographia 64 147-155... 

Proteias, amino acids bonded through peptide linkages to form macromolecular biopolymers, used as chiral stationary phases for hplc iaclude bovine and human semm albumin, a -acid glycoproteia, ovomucoid, avidin, and ceUobiohydrolase. The bovine semm albumin column is marketed under the name Resolvosil and can be obtained from Phenomenex. The human semm albumin column can be obtained from Alltech Associates, Advanced Separation Technologies, Inc., and J. T. Baker. The a -acid glycoproteia and ceUobiohydrolase can be obtained from Advanced Separation Technologies, Inc. or J. T. Baker, Inc. 

Armstrong, D.W., Liu, Y., and Ekborg-Ott, K.H., A covalently bonded teico-planin chiral stationary phase for HPLC enantioseparations. Chirality, 7, 474, 1995. 

New concepts presented in this edition include monolithic columns, bonded stationary phases, micro-HPLC, two-dimensional comprehensive liquid chromatography, gradient elution mode, and capillary electromigration techniques. The book also discusses LC-MS interfaces, nonlinear chromatography, displacement chromatography of peptides and proteins, field-flow fractionation, retention models for ions, and polymer HPLC. 

Among more complex macrocycles, Li et al. [47-52] reported the preparation and characterization of stationary phases incorporating calixarenes or calix-crowns bonded to silica. With individual columns, high selectivity was observed in the separation of alkylated aromatics, aromatic carboxylic acids, sulfonamides, nucleosides, and water-soluble vitamins. In other work, Sokoliess et al. [53] have characterized calixarene- and resorcinarene-bonded stationary phases similar to those described in the previous section of this chapter. And Huai et al. [54] used an end-capped p-tert-butyl-calix[4]arene-bonded silica phase for HPLC separation of a number of organic compounds. Resorcinarenes have also found application in GC. [55-57] Recently, exotic macrocycles have been used in capillary electrochromatography, as reported by Gong et al. [58]... 

The thermodynamic and hydrogen-bond basicity of 1 have been reported by the group of Berthelot, Laurence and coworkers (04CJC1413). TB 1, TB 110 and another mixed crown ether TB have been reported in a communication dealing with a novel chiral stationary phase for HPLC (94JCS(CC)1811). 

The first class of sorbents used for modern-era SPE were bonded-phase silicas. In the early 1970s, bonded silica sorbents found popularity as a stationary phase for HPLC. HPLC was not commonly used until the early 1970s, nor SPE until the late 1970s, until the application of silanized, or bonded silica sorbents, was realized. May et al. [89] and Little and Fallick [90] are credited with the first reports of applying bonded phases to accumulate organic compunds from water [60], The first article about SPE on commercially available bonded-phase silica (an octadecyl, Cig, phase) was published by Subden et al. [91] and described the cleanup of histamines from wines. 

Eor the separation of alkaloids prior to MS analysis, perfluorinated stationary phases for HPLC columns can be a useful alternative to the reversed phase, alkyl-bonded silica-based stationary phases such as the C8 and C18 reversed phase columns [10]. 

For example, using non covalent bonding, Mossbach et al. have prepared a stationary phase for HPLC in order to resolve ( )-timolol [2). MIP s have fiinctional groups arranged in such a manner that they are complementary in shape and electronic features to the template. Therefore, Wulf et al. have selectively prepared L-Threonine with an enantiomeric excess of 36% by using a polymer which was imprinted with L-DOPA [3). 

Microporous particles 3-10 pm particles used as a solid stationary phase or as the inert support for bonded stationary phases in HPLC, usually made from synthetic silica gel by a proprietary process involving the hydrolysis of SiCl4 to form particles with a controlled pore size ca 5-50 nm). 

D. W. Armstrong, Y. Liu and K. H. Ekborgott, A Covalently Bonded Teicoplanin Chiral Stationary Phase for HPLC Enantioseparations, Chirality, 7(1995)474. 

Self-assembled structures are supramolecular assemblies of covalent backbones structured through intra- and interchain noncovalent interactions. These secondary structures arise from steric constraints and a network of weak interactions (i.e., hydrogen or Van der Waals bonding, dipole-dipole or amphiphilic interactions). Helical morphologies are stiU rarely represented in these artificial species but the control of the heHx sense, and a better knowledge of the chiral amplification mechanism, is highly desirable due to their potential use in many applications. For example, helically chiral polymers can be used as chiral stationary phases for HPLC or for catalysis. 

Okamoto Y, Aburatani Y, Miura S, Hatada K (1987) Chiral stationary phases for hplc Cellulose tris(3,5-dimethylphenylcarbamate) and tris(3,5-dichlorophenylcarbamate) chemically bonded to silica gel. J Liq Chromatogr 10(8 9) 1613-1628... 

The following table provides, for comparative and interpretive purposes, eluotropic values on bonded octadecylsilane (ODS) and octylsilane (OS) for common solvents used in HPLC (Refs. 1-3). For additional information on common, specific and chiral stationary phases for HPLC, and for solvents, derivatizing reagents, and detectors, see Ref. 3. 

With the development of HPLC, a new dimension was added to the tools available for the study of natural products. HPLC is ideally suited to the analysis of non-volatile, sensitive compounds frequently found in biological systems. Unlike other available separation techniques such as TLC and electrophoresis, HPLC methods provide both qualitative and quantitative data and can be easily automated. The basis for the HPLC method for the PSP toxins was established in the late 1970 s when Buckley et al. (2) reported the post-column derivatization of the PSP toxins based on an alkaline oxidation reaction described by Bates and Rapoport (3). Based on this foundation, a series of investigations were conducted to develop a rapid, efficient HPLC method to detect the multiple toxins involved in PSP. Originally, a variety of silica-based, bonded stationary phases were utilized with a low-pressure post-column reaction system (PCRS) (4,5), Later, with improvements in toxin separation mechanisms and the utilization of a high efficiency PCRS, a... 

Chiral stationary phases for the separation of enantiomers (optically active isomers) are becoming increasingly important. Among the first types to be synthesized were chiral amino acids ionically or covalently bound to amino-propyl silica and named Pirkle phases after their originator. The ionic form is susceptable to hydrolysis and can be used only in normal phase HPLC whereas the more stable covalent type can be used in reverse phase separations but is less stereoselective. Polymeric phases based on chiral peptides such as bovine serum albumin or a -acid glycoproteins bonded to... 

Packings for HPLC can be further described as either pellicular or porous. Pellicular particles are made from spherical glass beads, which are then coated with a thin layer of stationary phase. For example, a porous layer can be deposited onto the glass bead to produce a porous layer or a superficially porous particle. The porous layer can in turn be coated with liquid stationary phase or reacted to give a bonded stationary phase. Pellicular particles are generally less efficient than the porous layer of superficially porous particles. 

The great versatility of HPLC lies in the fact that the stability of the chemically bonded stationary phases used in partition chromatography allows the use of a wide range of liquids as a mobile phase without the stationary phase being lost or destroyed. This means that there is less need for a large number of different stationary phases as is the case in gas chromatography. The mobile phase must be available in a pure form and usually requires degassing before use. The choice of mobile phase (Table 3.6) is influenced by several factors. 

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