High temperature separations on hybrid stationary phases

This project has focused on the study of hybrid phases at low percentage of organic modifier and pure water using high temperature in liquid chromatography (HTLC). It examined the effect of temperature on the retention of a range of test solutes and phenol homologues. The hybrid columns all showed linear van't Hoff relationship at low percentages of methanol but at higher temperature non linear van't Hoff curves were observed. Non·linear van't Hoff curves were observed with pure water on hybrid phases. This was thought to be because the retention mechanism changed at a discontinuity point above 100 ·C due to change in the properties of the mobile phase as well as changes in the entropy. The methylene selectivity decreased with temperature and increase with increasing pressure. XTerra phenyl and XBridge phenyl columns were stable up to 200 ·C and also in different flow rates without distortion in peaks. The efficiency of both columns was significantly decreased at low linear velocities due the domination of the B-term but at higher linear velocities the C-term dominated the separation. XBridge phenyl showed a flattened van Deemter curve indicates that high flow rate enabled a better separation. The application of high temperature on hybrid phases was studied for the separation of the selected steroids on XTerra MS C18 at low percentages methanol and pure water. A high flow rate was used to decrease the retention on XTerra MS C18 column at low percentage of methanol. In this project, variable back-pressure was used as an external parameter at constant flow rate and temperature to study the effect of pressure on retention in liquid chromatography. Hydrophobicity and shape selectivity, which depend on retention factor, increased due to increases in the pressure.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

High temperature liquid chromatography of steroids on a bonded hybrid column

A hybrid stationary phase, XTerra MS C18, has been evaluated for the high temperature reversed phase liquid chromatography of selected hydrophobic steroids. The effects on the retention and efficiency at temperatures up to 130 °C and eluent compositions from methanol-water mixtures to superheated water were studied. The thermodynamic data of the separations were determined. It was shown that increasing the temperature enabled the percentage of methanol to be reduced. High mobile phase flow rates could be used but for these non-polar analytes the retention times with superheated water as the eluent were still high

Green method development approach of superheated water liquid chromatography for separation and trace determination of non-steroidal anti-inflammatory compounds in pharmaceutical and water samples and their extraction

Non-steroidal anti-inflammatory drugs (NSAIDs) are pharmaceutical compounds with anti-inflammatory, analgesic, and antipyretic effects. Herein, a simple and rapid high-temperature liquid chromatography and superheated water chromatography method was developed and validated for the trace determination of NSAID residues of ketoprofen, naproxen, sodium diclofenac, and ibuprofen in water samples. The NSAIDs were separated in less than five minutes using buffered distilled water as the mobile phase and ODS Zirconia RP-C18 column as the stationary phase. Linearity was observed in the van’t Hoff plots of the tested drugs by employing a low acetonitrile percentage (20% ACN) in the mobile phase, without any significant changes in their retention mechanisms. However, nonlinear van’t Hoff plots were obtained for the superheated water chromatography data of the tested drugs because of significant changes in their retention factors, transition stage of the stationary phase, or the mobile phase properties. The limits of detection for ketoprofen, naproxen, sodium diclofenac, and ibuprofen were 14, 2, 4.2, and 32 µg L−1, respectively, and their limits of quantification were 44, 8, 12, and 98 µg L−1, respectively. The accuracy and precision parameters were determined for selected drugs, where the relative standard deviations were in the range of ± 0.2179–2.6741%. In addition, these conditions were employed for the removal of NSAIDs from the water samples using carbon nanotubes. The proposed system was applied for the separation and analyses of drugs in water and pharmaceutical samples, and acceptable recoveries of 90.48–98.15% for the water samples and 99.9–100.08% for the pharmaceutical samples were obtained