Reversed-phase liquid chromatography of 5-fluoro-uracil nucleosides and nucleotides in the presence of quaternary ammonium ions

Cation exchange characteristics of silica-based reversed-phase liquid chromatographic stationary phases

“…The small number of higly acidic sites can perhaps explain the irregular chromatographic behavior of certain solutes. Because of the small number of ion-exchange sites, solute molecules such as amines (9)(10)(11)(13)(14)(15)(16)(17)(18)(19)(20)(21) may overload these sites under normal conditions leading to band broadening. This band broadening is especially evident at high mobile phase organic modifier concentrations where hydrophobic retention is reduced.…”

“…Studies on naked silica have supported the view that the retention of amines may be due to an ion-exchange process (14,22,23). The addition of amines to the mobile phase in RPC has the effect of causing the "regular" (i.e., governed by hydrophobic interactions) retention of amines and amino acids (9)(10)(11)18). A recent study on the ion-exchange behavior of stationary phases used in RPC showed that tetraalkylammonium bromides were retained by both ion-exchange and hydrophobic interactions (24).…”

“…When alkyl bonded phases are used with low polarity mobile phases, it has been shown that silica deactivation has occurred because of the surface modification (activity = 0.50) but that certain solutes which are electron acceptors or donors adsorb at localized "sites" as on naked silica (12). Solute molecules containing the amine group seem to be affected more than other solutes by residual silica hydroxyls (9)(10)(11)(13)(14)(15)(16)(17)(18)(19)(20)(21).…”

“…One of the ways in which silica can interact with solutes is felt by some to be ion exchange (15)(16)(17)(18)(19). This has been 1 Present address: Galgón Corp., P.O.…”

Electrical double-layer model for sorption of ions on octadecylsilyl bonded phases including the role of residual silanol groups

“…Effect of Silanols on TBA+. Other workers have reported that the amount of TBA+ sorbed on reversed-phase bondedphase packings, such as Cig, increases with increasing mobile-phase pH (40,46,47,50). It has been suggested that this phenomenon is related to the fact that cationic samples sorb more strongly onto anionic silanolate sites by the process of cation exchange than they sorb onto silanol sites or onto ODS groups and that the number of silanolate sites increases with pH.…”