Reversed Phase Liquid Chromatography of Organic Hydrocarbons with Water as the Mobile Phase

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Abstract
Reversed phase high-performance liquid chromatography (RP-HPLC) is demonstrated for hydrophobic analytes such as aromatic hydrocarbons using only water as the mobile phase. Achievement of reasonable capacity factors for these types of compounds without the need for toxic and costly organic modifiers in the mobile phase is accomplished by substantially decreasing the phase volume ratio of stationary phase relative to the mobile phase volume and by increasing the polarity of the stationary phase relative to stationary phase materials commonly used for RP-HPLC. Applying a stationary phase of trifluoropropylsiloxane, which is a common gas chromatographic stationary phase material, to nonporous glass microspheres yields a stationary phase with a phase volume ratio reduced by about 2 orders of magnitude as compared to common liquid chromatographic packing materials. As a result, a separation was obtained for hydrophobic organic analytes such as benzene, toluene, ethylbenzene, and isopropylbenzene using a water mobile phase at ambient temperature. A separation of sodium benzoate, benzaldehyde, benzene, and butyrophenone is shown in less than 3 min using a water mobile phase and UV/visible absorbance detection. Additionally, the separation of the ionic surfactant species octyl sulfate and dodecyl sulfate in water in less than 3 min, using unsuppressed conductivity detection, is achieved with a separation mechanism based on interactions with the hydrophobic portion of the surfactant. A water mobile phase offers many potential advantages over traditional mixed aqueous/organic solvent systems. In addition to saving on the cost and expense of buying and disposing of toxic solvents and waste, there is less exposure of the operator to potentially harmful solvents. Increased consistency in reproducing retention times can be expected, since there will not be any variability in solvent strength due to slight variations in mobile phase composition. A water mobile phase produces an environment that should provide an inherent advantage of increased signal-to-noise ratio for detection. Additionally, excellent predictions of the octanol/water partitioning coefficient and aqueous solubility for hydrophobic analytes are obtained from a single measurement of the capacity factor in the water mobile phase.

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