|
 |
Department of Chemistry
E D U C A T I O N University of Minnesota, DuluthMajors: BS Chemistry (1994) BS Biochemistry and Molecular Biology (1994) Minor: Mathematics (1994) Abstract The basic concept of my work is to use high temperature eluents and high column temperatures in HPLC. In comparison to GC, it is well known that HPLC is much slower, has lower plate counts and smaller peak capacities. These all result from the lower analyte diffusivities in the high viscosity fluids used in HPLC and the higher viscosity of liquids relative to gases. Maximum eluent velocity is severely limited by excessive peak broadening which results from slow diffusion transport in high viscosity fluid and eluent viscosity limits the flow rate and separation speed because pressure generated by conventional pumps is limited to about 6000 psi. One of the major goals of this work is to overcome limitations to speed of HPLC by heating eluent fluids well above typical temperatures (e.g. 200oC vs 40oC). This will enable use of higher (3-10 fold) linear velocities. We will also attempt to improve plate counts and peak capacities at high temperature using longer columns (3-10 fold) but at conventional velocities. Our overall goal is to understand the long over looked role of temperature in establishing the performance limitations (speed, plate count, resolution, peak capacity) of HPLC. In order to do high temperature HPLC, it is evident that sample, eluent and column must be heated. It is true that most common types of detectors used in HPLC (absorbance, refractive index) cannot tolerate hot (>40-50oC) column eluents. Thus, as shown in the diagram above, the column effluent must be cooled prior to the detector. These heating and cooling steps are the two chief general problems that must be overcome to allow the implementation of high temperature HPLC. Due to (1) significant resistances to heat transfer, primarily in the flowing eluent, (2) high heat capacities of aqueous eluents, and (3) high pressure drops encountered in using long (> 10 cm), very narrow (<0.004? ID) heating and cooling tubes, adjusting temperature of eluent without simultaneously introducing overwhelming extra-column band broadening and excessive pressure drops in the tubing is quite complicated. Proper design of the overall system (column dimensions, flow rates, thermal equilibration tubes) is the first critical step in achieving the overall goals. There are also many additional issues which must be considered including the stability of the analyte, eluent and stationary phase at high temperature, but these are less general and less ubiquitous.
Last updated: 6/30/99 |
