Surface Concentration Of Functional Groups Research Articles

Preparation and retention characteristics of different phenyl phases for reversed-phase liquid chromatography

Three different phenyl phases were prepared. The amount of organic moiety bound on silica support was determined from thermogravimetric curves of the modified silica gel. The specific surface areas of gels were obtained from nitrogen sorption measurement at −196°C. The effect on separation and selectivity of the different bonded-phenyl functional groups was studied. The selectivity of the phenyl-bonded silica gels was examined and compared with octadecyl (ODS) silica in liquid chromatography. Corresponding to the high surface concentration of functional groups, the capacity factors of solutes, normalized to unit surface area of the adsorbent, k′/SBET were found to decrease in the sequence phenylmethyl>diphenyl>triphenyl. Polar solutes are retained in greater extent on the phenyl phases than on the ODS phase.

Modification of carbon surfaces in cold plasmas

Various forms of carbon, including carbon black, carbon fibre and pyrolytic graphite, have been surface-modified in a cold-plasma reactor. Plasma fluorination of the carbon surfaces was performed using variable flow rates, treatment times, and types of gas. The plasma-modified carbon surfaces were characterized using electron spectroscopy (ESCA), contact angle measurements, and scanning electron microscopy (SEM). The surface chemical structure of the plasma-fluorinated carbon blacks appeared to be similar to that of commercial Fluorographite. Nitrogen-containing groups were introduced into the surfaces of carbon blacks and carbon fibres by exposure to glow discharges in mixtures of ammonia and N2-H2. The surface concentration of functional groups containing nitrogen decreased with time. Several mechanisms for this degradation have been proposed. Plasma-modified carbon blacks and carbon fibres have potential for improving the properties of composites by achieving appropriate levels of adhesion between filler and matrix through physical compatibility and/or chemical bonding.

Monomeric vs. polymeric bonded iminodiacetate silica supports in high-performance ligand-exchange chromatography

The synthesis of monomeric and polymeric bonded iminodiacetate-groups on silica supports is described. The polymeric support offers advantages over the monomeric, such as (i) preparation is much simpler, (ii) higher surface concentration of functional groups can be achieved without loss of efficiency and (iii) hydrolytic stability. Cu2+ loaded supports were examined for their kinetic performance, in particular for the C-parameter of the Knox equation, and for their hydrolytic stability. Calculation of the surface coverage shows that only a rather thin polymeric layer is formed; this is in agreement with the results of the kinetic performance. The retention of α-amino acids on the Cu2+ loaded polymeric support demonstrates its use in HPLEC.

Influence of the Amount of Bonded Non-Polar Phase and of the Length of Attached Alkyl Chains on Retention Characteristics of Silica-Based Sorbents for Reversed-Phase High Performance Liquid Chromatography

Abstract The retention characteristics of two sets of chemically bonded non-polar silica packings with a high surface concentration of functional groups have been compared in the reversed-phase mode of liquid chromatography: (i) the conventional packings prepared by chemical modification with trimethylsilyl, heptyl, dodecyl and octadecyl groups, and (ii) mixed-phase materials where differences in the amount of organic bonded phase were achieved by bonding octadecyl and trimethylsilyl groups in different proportions. The retention data of two homologous series of solutes show that these two classes of packings are distinctly different; in particular, the capacity factors and selectivities are always higher on the mixed-phase bonded silica packings at the same percentage of carbon.

Recent developments in the evaluation of chemically bonded silica packings for liquid chromatography

The basic variables and conditions in the synthesis of chemically bonded silica packings (CBSPs), obtainable by means of a surface reaction between porous silica and an organochlorosilane or organoethoxysilane as a modifier, yielding a dense monolayer of bonded functional groups, are discussed. The CBSPs can also be prepared by a novel procedure termed bulk modification, which involves a co-hydrolysis and co-condensation of tetraethoxysilane or poly(ethoxysiloxane) and a corresponding organotriethoxysilane. In this way, the organic functional groups become a constituent of the bulk phase as well as of the surface. The retention behaviour of solutes on columns packed with both types of packings was examined in normal and reversed-phase liquid-solid chromatography. Corresponding to the high surface concentration of functional groups, the capacity factors of solutes normalized to unit surface area of the adsorbent, k′/ S BET, were found to be relatively larger on bulk- than on surface-modified silica packings for a given bonded group. For n-alkyl bonded phases in reversed-phase chromatography, the plot of log k′/ S BET versus the number of carbon atoms in the n-alkyl chain was linear for each solute. Further, it is shown that the selectivity of solutes on polar modified packings is largely controlled by the type of polar functional groups substituting the silanol groups.