Alkyl-silica columns

Gilroy, J. J., Dolan, J. W. and Snyder, L. R., Column Selectivity in Reversed-phase Chromatography IV. Type-B Alkyl-silica Columns,/. Chromatogr. A, 1000 757—778, 2003. 

J. Gilroy, J. Dolan, and L. Snyder, Column selectivity in reversed-phase liquid chromatography IV.Type-B alkyl silica columns,/. Chromatogr. A1000 (2003),757-778. 

Figure 4.12 shows the separation of a pharmaceutical agent on an analytical alkyl-silica column (Purospher Star RP18e, 100mm long, internal diameter 4mm). The sample was dissolved in pure methanol and between 5 and 250 pi was injected, while the mobile phase consists of methanol and water (60 40 volumetric ratio). At small injection volumes no peak distortion is observed, but with 30 pi the chromatogram shows a distortion of the main peak and band splitting. A small part of the sample... 

The present chapter describes the hydrophobic-subtraction model of RP-LC column selectivity, for characterizing columns in terms of five fundamental column properties (H, S, A, B, C). Because the hydrophobic-subtraction model can predict retention (values of k) within a few percent, coltunns with sufficiently similar values of H, S, etc. should provide equivalent separation for any sample. Similarly, columns with very different values of H, S, etc. should provide quite different separation. Several examples of the use of values of H, S, etc. for the selection of similar columns have been reported, some of which are discussed below. The present chapter also compares the selectivity of different column types (e.g., alkyl-silica columns, phenyl columns, cyano columns, etc.) and summarizes values of H, S, etc. for several commercial Cjg columns. 

Equation (2) has also been extended to other commonly used kinds of RP LC columns (a) older alkyl-silica columns made from impure (type A) silica, (b) columns with polar groups such as amide or carbamate, which are either embedded into the column ligands or used to end-cap unreacted silanols after a conventional bonding, (c) cyano columns, (d) phenyl columns, (e) columns with... 

This section provides an overview of properties of polymer monolith columns related to 2D-HPLC. Monolithic organic polymer columns, having longer history than silica monoliths, have been reviewed in detail recently by S vec and by Eeltink including their preparation methods and performance (Eeltink et al., 2004 Svec, 2004a). Polymer monolith columns commercially available include polyfstyrene-co-di vinyl benzene) (PSDVB) columns and poly(alkyl methacrylate) columns. 

Ethoxylated alkyl amines in pesticide formulations were separated using two different columns a cyano-modified silica column to determine the alkyl distribution and an amino-modified column to determine the ethylene oxide distribution [88]. The detection, specific for ethoxylated amine, was performed with a post-column ion-pair extraction system and fluorescence detection. 

Myelin galactolipid analysis by HPLC. Fig. 2 and 3 show HPLC chromatograms obtained from myelin lipids on Silica column and reverse phase column, respectively. Reverse phase HPLC of mono-galactosyl diglyceride and its 1-0-alkyl ether homolog was not examined but typical chromatograms of these lipids obtained from calf brain stem were presented previously (11 ). Myelin was obtained from 25 day-old rat brains. 

The authors compared this aqueous silica method with alkyl-bonded procedures by testing 12 different corticosteroids on 8 different silica sorbents and on 6 different reversed-phase sorbents. The variations in selectivity of the 12 corticosteroids among the silica columns were found to be substantially less than those based on the reversed-phase sorbents. Based solely on this comparison, silica-based separations using aqueous mobile phases would be preferred over reversed-phase sorbents for assay of steroids [328]. The arguments on which sorbent is best for the assay of steroids will more than likely continue. 

N-alkyl silica-based stationary phases typically employed in HPLC separation of peptides and proteins have been investigated to a large extent in CEC mode. In most cases, gradient elution was required to optimize the resolution and analysis time. Tryptic digests maps of cytochrome c by pressurized CEC were better resolved than by pHPLC [93], The experiments were conducted at low pH in the presence of trifluoroacetic acid (TFA) to prevent tailing of basic peptides, on a column packed with 1,5-pm C18 silica particles. It has been... 

Column. Alkyl-silica (SAS-Hypersil, 5 qm, 12.5 cm X 4.5 mm internal diameter). 

The use of low concentrations (0.1-5%) of acetic, formic, or trifluoroacetic acid, generally with gradient elution, has been reported for the separation of tryptic or CNBr peptides on alkyl silicas. For example, the CNBr peptides of the C-1 chymotryptic fragment of bacteriorhodopsin have been separated 78) on a ja-Bondapak Cig column using 5% formic... 

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