In the past two decades, green analytical chemistry has started to become a more prominent subarea of green chemistry, particularly in the area of sample preparation such as extraction. In typical reversed phase liquid chromatography (LC) methods, organic solvents such as acetonitrile (MeCN) or methanol are used as mobile phase modifiers due to their low viscosity and low UV cutoff. However, these solvents are hazardous and therefore cause environmental concerns and costly disposal. In our previous work, it has been shown that the separation of short chain carboxylic acid mixtures can be performed in a totally aqueous low pH mobile phase with the use of an amino acid surfactant (N-Lauroyl-L-glutamate) coated C18 stationary phase. In this work, we have coated a typical C18 column with the zwitterionic synthetic inexpensive surfactant Cocamidopropyl Betaine (CAPB) in order to generate a mixed mode reversed phase ion exchange column. The surfactant loading on the column was calculated to be 0.29mmoles. To ensure good retention time reproducibility for the analytes, 8.8 x 10-4M of the surfactant was added to the totally aqueous dilute H2SO4 mobile phase. At low pH, the carboxyl group is unionized and the overall charge of the surfactant is positive. This allowed for the separation of a four component sulfonamide mixture in under 11 mins with nearly baseline separation for all components. Using the C18 column with just the dilute sulfuric acid mobile phase and no surfactant on the stationary phase, the total retention time was excessive, reaching nearly an hour. Future work will use a mixture of short chain carboxylic acids to examine the retention mechanism of the column in different pH environments which will control the anion exchange – zwitterion charge of the surfactant coated column. This will be important in preventing excessive retention of highly charged biological macromolecules.
Author: Krista Wilson
Faculty Advisor: Neil Danielson, Chemistry and Biochemistry
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