Retention behavior of ginsenosides on a poly(vinyl alcohol)-bonded stationary phase in hydrophilic interaction chromatography

Abstract

The influences of the organic component of the mobile phase and the column temperature on the retention of ginsenosides on a poly(vinyl alcohol) (PVA) bonded stationary phase operated under hydrophilic interaction chromatographic mode were investigated. The retention of the ginsenosides was found to increase with increasing amount of acetonitrile (MeCN) in the mobile phase, which is typical of hydrophilic interaction chromatographic behavior. It was also found that the retention of the analytes was highly affected by the type of the organic modifier used. Aqueous MeCN (75-90%) gave the most satisfactory retention and separation of ginsenosides Rf, Rg1, Rd, Re, Rc, Rb2 and Rb1 compared with aqueous methanol, isopropyl alcohol or tetrahydrofuran at the same composition levels. The effects of the different types of organic modifiers on the retention of the analytes were attributed to their solvent strength and hydrogen-bond accepting/donating properties. The effect of temperature on the retention of ginsenoside on the PVA-bonded phase was assessed by constructing van't Hoff plots for two temperature ranges: subambient (273-293 K) and ambient-elevated (298-333 K) temperatures. van't Hoff plots for all analytes were linear at the two temperature intervals; however, the slopes of the lines corresponding to ginsenosides Rg1 and Re were completely different from those for the rest of the analytes especially in the subambient temperature range. Enthalpy-entropy compensation (EEC) studies were conducted to verify the difference in thermodynamics observed for ginsenosides Rg1 and Re compared with the other analytes. EEC plots showed that Rf, Rd, Rc, Rb2 and Rb1 were possibly retained by the same retention mechanism, which was completely different from that of Rg1 and Re at subambient temperatures. Retention prediction models were derived using multiple linear regression to identify solute attributes that affected the retention of the analytes on the PVA-bonded phase. The mathematical models derived revealed that the number of hydrogen-bond donors and the ovality of the molecules are important molecular properties that govern the retention of the compounds on the chromatographic system.

Retention Prediction Modeling of Ginsenosides on a Polyvinyl Alcohol-bonded Stationary Phase at Subambient Temperatures Using Multiple Linear Regression and Artificial Neural Network

“…However, this linearity slightly deteriorates as the temperature of the system is decreased (R 2 values for 40, 25, 10 and 0˚C are 0.9860, 0.9825, 0.9671 and 0.9437, respectively). 49 These results indicate that hydrogen bonding is a predominant retention mechanism at elevated temperatures, and that at subambient temperatures mechanisms other than hydrogen bonding are present. Shape selectivity could be one of these mechanisms as explained by the incorporation of Ov in the MLR equations.…”

“…48 As mentioned earlier, hydrogen bonding interaction can occur between the hydroxyl groups of both the stationary phase and the analytes. In a report by our group, 49 it was found that the retention (log k) of the ginsenosides on the same chromatographic system showed a linear dependency on HBD, especially at temperatures above 25˚C. However, this linearity slightly deteriorates as the temperature of the system is decreased (R 2 values for 40, 25, 10 and 0˚C are 0.9860, 0.9825, 0.9671 and 0.9437, respectively).…”

Miniaturization for the Development of High Performance Separation Systems

“…Development of novel fibrous extraction/separation media having different chemical structures and then different functionalities on the surface could be realized in the near future based on the concept of molecular shape recognition [3][4][5][6][7][8] and the systematic retention mechanism analysis with a help of various modern computational data calculations in LC [106][107][108][109][110][111][112][113][114][115][116][117][118]. Miniaturization of packed columns in GC [119][120][121][122][123] is also possible for high speed analysis with a unique selectivity but without a loss of sample loading capacity.…”

Theory and Practice of UHPLC and UHPLC–MS

“…Acetonitrile, an aprotic solvent, which does not show protonedonor interactions, shows the best retention and separation selectivity among all water-miscible organic solvents in HILIC (or in ANP) chromatography. Methanol and other lower alcohols are protic solvents that provide significant hydrogen bonding interactions and compete with water for solvation of the polar adsorbent surface, decreasing the amount of adsorbed water layer on polar stationary phases (Quiming et al, 2007b). Theoretically, it is possible to substitute water by an organic solvent and to employ, e.g., a methanoleacetonitrile mobile phase in "nonaqueous HILIC chromatography," but usually the retention is weaker than that in conventional HILIC separations .…”