Approaches to novel analytical extraction and concentration using hollow fiber membranes

The current trend is to develop analytical techniques that provide simple, fast and automated analysis of trace components in different matrices. A typical analytical method is comprised of several steps; extraction, concentration, and detection. The objective of this research was to develop novel membrane extraction and concentration methods for sample preconcentration, microextraction, and on-line analysis. Three topics covered here are, sample concentration by membrane pervaporation, on-line analysis using this technique, and development of microscale supported liquid-membrane extraction and using this approach to monitor phenols in air.; Solvent removal by membrane pervaporation is presented as a method for on-line preconcentration of environmental and pharmaceutical model analytes. Development of a one-step, on-line, concentration process using a microporous composite hydrophobic membrane, or a polar solvent-permeable Nafion membrane is shown. Both polar and non-polar hollow fiber membranes were effective in concentrating trace analytes, thereby increasing analyte enrichment factors (EF). Solvent reductions greater than 90% and EF as high as 18.9 were observed and monitored using HPLC with UV detection. Residence time and operating temperature were found to be important parameters. Interaction with membrane-bound sulfonic acid residues resulted in the loss of reactive analyes such as 1,2-diphenylhydrazine and atrazine. This method was modified for on-line monitoring of trace level pharmaceutical compounds.; Supported liquid membrane micro-extraction (SLMME) from methanol showed very low EF and enrichment efficiencies (EE), partly due to the low partition coefficient from methanol to the supported liquid membrane. Moreover, the di-hexyl ether (DHE) was soluble in methanol and was lost from the membrane. A strategy of adding water to the methanol increased KD and also reduced the loss of DHE. Consequently, EF and EE increased to as high as 1250. As the percentage of water in the donor increased, the extraction performance improved. Overall, this appears to be a viable method for extraction of organic acids from methanolic solutions.; Trace nitrophenols in air were monitored by SLMME by a process of impinger sampling to capture the nitrophenols in an aqueous phase, followed by SLMME and analytical detection. The high enrichment of nitrophenol in SLMME allowed low detection limits even with UV detection.