Stationary Phases in HPLC

Fig. 3.1a shows the different sizes and shapes of particles that have been used as stationary phases in hplc. The particles are usually silica, although in ion exchange and exclusion chromatography polymeric gels or resins are common. 

Albert, K. 1988. Correlation between chromatographic and physicochemical properties of stationary phases in HPLC C30 bonded reversed-phase silica. Trends Anal. Chem. 17 648-658. 

Kempe M. Antibody-mimicking polymers as chiral stationary phases in HPLC. Anal Chem 1996 68 1948-1953. 

One unique challenge in using SCILs as stationary phases in HPLC is the determination of the column-void or mobile-phase volume. Accurate determination of retention factors, k, requires measurement of fg, the void volume. 

In a contribution published in 2005 the group of Sellergren compared the performance of composite MIPs imprinted with propazine and prepared from the same porous silica support using the pore-filling technique (with and without final removal of the silica) as well as the layer grafting approach with an immobilised iniferter [148], The MIP composite prepared by layer grafting was found to exhibit the best performance when employed as stationary phase in HPLC, although extensive optimisation of the imprinted layer thickness was required. 

MIP beads or microspheres are also widely used for sensing purposes [166]. They are prepared by precipitation polymerization and then they are embedded in a dedicated matrix, which is immobilized on the transducer surface. Moreover, the MIP beads are used to serve as stationary phases in HPLC [167] and for catalytic purposes. Other systems, such as self-assembled monolayers, SAMs [168], sol-gel matrices [169] and preformed polymers [170] have also been utilized for fabrication of MIP constructs. 

MIPs have been frequently used as stationary phases in HPLC. It is useful to distinguish two types of HPLC experiments with MIPs ... 

H. Kaga, Precision synthesis of (1 —> 6)-o -D-glucopyranan by cationic ring-opening polymerization of l,6-anhydro-tri-0-allyl-/8-D-glucopyranose, Macromol. Symposia, 181 (2002) 101-106 (b) A. Kusuno, M. Mori, T. Satoh, M. Miura, H. Kaga, and T. Kakuchi, Enantioseparation properties of (1 - 6)- -i)-glucopyranan and (1 - 6)-a-D-mannopyranan tris(phenylcarbamate)s as chiral stationary phases in HPLC, Chirality, 14 (2002) 498-502. 

Chirality of derivatized cyclodextrin was used for recognition of stereoisomers. Phenylazobenzoyl modified y-cyclodextrin was anchored onto silica gel used as stationary phase in HPLC and photoresponsive chromatographic behavior of dansyl amino acid enantiomers was studied [64],... 

Since the discovery of ordered mesoporous materials, researchers have explored many possible applications that can take advantage of the unique compositional or structural features of mesoporous materials. In addition to apphcations in traditional areas such as catalysis, separation, and ion exchange, new applications that might involve mesoporous materials include stationary phases in HPLC, bio and macromolecular separations, low dielectric constant materials, enzyme immobilization, optical host materials, templates for fabrication of porous carbons, and reactions in confined enviromnents. 

The stationary phase in HPLC is the solid support contained in within a specified column over which the mobile phase flows effecting the separation of the individual components. The HPLC column is normally fabricated using 100- to 300-mm long stainless steel tubes with an internal diameter of 2-5 mm. They are packed with porous, microporous, spherical, or irregularly shaped particles, or particles with specific coatings with the following characteristics. 

Octadecyl-polyvinylalcohol copolymer gel, ODP, offers an alternative as a nonpolar stationary phase in HPLC. With this material, no silanophilic interactions take place and there are no pH limitations. Drawbacks of ODP columns are the large retention times observed and the longer equilibration time required. 

The dominant stationary phase in HPLC is modified silica and, to be more specific, octadecyl silica (ODS). It should be pointed out that there could be great differences between various types of ODS materials or even between different batches of the same material. Carbon load, free silanol content, endcapping, type of silica, and coupling chemistry to the Cig moiety, not to mention the several physical characteristics of the packing material all involve the behavior of an ODS column. However, a rather safe generalization is that, in such material, hydrophobic interactions are a dominant mechanism of separation [3-7]. 

Raw material can be injected into the column without any previous sample treatment, which simplifies the purification procedure. Oka et al. [1] have gathered antibiotics purification by CCC from crude extract and fermentation broth. They have shown that CCC has been successfully applied to the separation of macrolides and of various antibiotics, including various peptide antibiotics which are generally strongly adsorbed to silanol groups on silica gel used in the stationary phase in HPLC. Several CCC types are used, such as DCCC (droplet countercurrent chromatogra-... 

Alumina The common name for aluminum oxide. In a finely divided state, used as a stationary phase in adsorption chromatography also finds application as a support for a liquid stationary phase in HPLC. 

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