Investigations of micellar-stabilized room temperature phosphorescence:pH effects on intensity and potential for HPLC detection.

摘要

The objective of this work was to improve micellar room temperature phosphorescence sensitivity and micellar liquid chromatography column efficiencies. This was performed on the premise of combining the techniques to increasing the overall performance of micellar stabilized room temperature phosphorescent (MSRTP) detection when used as a detection mode for micellar chromatography.; MSRTP was performed using sodium dodecyl sulfate (SDS) and thallium nitrate. Oxygen removal was performed by nitrogen purging or chemical reaction with sodium sulfite. When sodium sulfite was used for deoxygenation, the phosphorescence intensity and the time required to obtain a peak phosphorescent signal (rise time) were pH dependent. A pH range of 6-9 was determined to be optimal with respect to rise times and intensity. Attempts were made to eliminate factors that may have contributed to the attenuation of the phosphorescence intensity when the pH was changed. Results indicated that the pH dependent phenomena are related to the use of sodium sulfite deoxygenation.; An oxygen electrode was used to monitor concentrations of dissolved oxygen in bulk solution, while adjusting the pH and monitoring phosphorescence intensities. The absence of a substantial signal below pH 5 was explained by a decrease in the equilibrium concentration of sulfite, and inefficient oxygen removal at these lower concentrations. When the solution was adjusted above pH 9, the results became more difficult to interpret. The concentration of dissolved oxygen in bulk solution was not reduced and the analyte was still able to phosphoresce after a substantial period of time. Possible explanations for this behavior are discussed.; Micellar chromatography has been limited by low column efficiency when compared to reversed phase liquid chromatography mobile phases. Some improvements in efficiency have been gained by the addition of alcohols to the micellar mobile phases. Attempts were made to determine the effects of the alcohol concentrations on micellar efficiency. Two factorial designs were performed using micellar mobile phases (SDS) on C1, C6 and C18 three micron stationary phases. The first factorial design, (butanol) x (SDS), was performed by varying butanol and sodium dodecyl sulfate concentrations and measuring the column efficiency. The second factorial design, (R-OH) x (R-OH chain length), was performed using normal alcohols of various chain lengths and varying their concentration. The addition of alcohols to the micellar mobile phase, within the concentration range used, did not improve the efficiency. When comparing 70/30 MeOH/H{dollar}sb2{dollar}O to SDS mobile phases, three micron packing material was better at maintaining column efficiency than 5 and 10 micron materials.