Recent studies showed that injection of large volume of hydrophobic solvents used as sample diluents could be applied in reversed-phase liquid chromatography (RP-LC). This study reports a systematic research focused on the influence of a series of aliphatic alcohols (from methanol to 1-octanol) on the retention process in RP-LC, when large volumes of sample are injected on the column. Several model analytes with low hydrophobic character were studied by RP-LC process, for mobile phases containing methanol or acetonitrile as organic modifiers in different proportions with aqueous component. It was found that starting with 1-butanol, the aliphatic alcohols can be used as sample solvents and they can be injected in high volumes, but they may influence the retention factor and peak shape of the dissolved solutes. The dependence of the retention factor of the studied analytes on the injection volume of these alcohols is linear, with a decrease of its value as the sample volume is increased. The retention process in case of injecting up to 200 L of upper alcohols is dependent also on the content of the organic modifier (methanol or acetonitrile) in mobile phase.

A retention study on perfluorophenyl silicabased stationary phase was undertaken for some organic compounds containing different polar functionalities. The dependence of the retention factor on the content of organic modifier (acetonitrile, or methanol) in mobile phase was fitted by polynomial equations. The only exception was observed for adenine, which showed a sigmoidal dependence for the retention factor versus organic modifier content. The extrapolated values of retention factor for water as mobile phase (log kw) from these dependences were well correlated with octanol–water partition constants (log Kow), excepting the values for hexachlorocyclohexane isomers and adenine. Temperature dependences of the retention factor obeyed the van’t Hoff equation with thermodynamic parameters similar to those obtained in reversed phase on C8 or C18 stationary phases, excepting two statines whose dependences of ln k on the reciprocal value of absolute column temperature were nonlinear. Again, adenine had an atypical behavior with decrease in the retention factor with the increase in column temperature, due to possible tautomeric equilibria of this compound in presence of water, in accordance with theoretical models reported by literature. Charge modeling with MarvinSketch package program revealed charged centers from analyte molecule that could interact differently with charge centers from stationary phase.

Indole-3-acetic acid (IAA) is an important growth hormone for plants obtained by biosynthesis from tryptophan. In this paper was studied the competitive transport of two biologically active compounds, indole-3-acetic acid (IAA) and tryptophan (TRP), through a liquid membrane. The separation of the two compounds was obtained using a hybrid liquid membrane system having trioctylphosphine oxide (TOPO) as a carrier. The most important operational parameters of the system, and pH influence on the efficiency of the transport process, in correlation with the speciation diagrams of the two compounds: TRP and IAA, were studied. The evaluation of the ransport process was performed by calculating the composition of the phases at the end of the transport process and he organic substrate flow at the membranes exit.

Non-linear van’t Hoff plots were observed for several benzodiazepines over the usual temperature interval used in RP-LC (10–60 C), when acetonitrile was added in the mobile phase. Such deviation from linearity was not observed when methanol or isopropanol was added to the mobile phase. Polynomial regressions were applied to fit the experimental data when acetonitrile was used as organic additive in mobile phase. The second-order polynoms may allow finding out the maximum retention depending on temperature, which can be within or out of the normal temperature range used in RP mechanism. A thermodynamic model deriving from the partition of two or more tautomers of the same analyte was proposed to explain this deviation from linearity of van’t Hoff plots.