@unpublished{pittir30892,
           month = {June},
           title = {IMPROVING LIQUID CHROMATOGRAPHY PERFORMANCE: NOVEL DEVELOPMENTS IN PRECONCENTRATION,INSTRUMENTATION AND OPTIMIZATION},
          author = {Stephen Groskreutz},
            year = {2017},
        keywords = {chromatography, temperature, optimization},
             url = {http://d-scholarship-dev.library.pitt.edu/30892/},
        abstract = {Maximizing performance when using real-world samples and small volume, high sensitivity columns which degrade the native chromatographic separation is a challenge. Loss in column performance is due to precolumn dispersion and volume overload. In this work a series of methods based on novel instrumentation and sound theory is presented to improve a chromatographic result for such samples in both isocratic and gradient elution modes. An approach called temperature-assisted solute focusing (TASF) was developed to improve sample focusing or preconcentration. TASF is designed to address precolumn dispersion in capillary scale LC. Volume overload is a common form of precolumn dispersion and degrades LC performance. TASF works by relying on the temperature dependence of solute retention and high power thermoelectric or Peltier elements (TECs) to actively heat/cool a short segment of the column near its inlet during sample loading. Cooling the head of the column transiently increases retention for solutes during injection, improving focusing and solving the volume overload problem. Following focusing rapid heating decreases retention releasing the compressed injection band to the downstream portion of the column. The TASF approach was assessed using a series of three instruments with well characterized solutes developing it into a robust platform capable of routine, unattended use. Three models for solvent-based on-column focusing in isocratic elution were experimentally investigated. Solvent-based on-column focusing is a well-known method to increase concentration sensitivity and combat precolumn dispersion by injecting samples made in weak elution solvents. Additionally, solvent-based focusing occurs naturally as a consequence of increased solute retention in the sample solvent and a step gradient generated by the difference between sample and mobile phase composition. Finally, a simple graphical method for rapid chromatographic optimization was developed. This plot was designed specifically to assist practitioners to determine experimental conditions to achieve a desired column efficiency or peak capacity in a defined time in both isocratic and gradient elution modes.}
}