Liquid chromatographic separation and sensing principles with a water only mobile phase

Abstract

Two separate subjects will be developed in this work. The first subject is a novel chemical analyzer based on a polymer clad optical fiber inserted into a transparent capillary tube. This configuration is referred to as an annular column. A light source is directed into the end of the fiber optic. When a small sample volume is injected into a mobile phase flowing through the annular column, selective partitioning of an analyte into the fiber optic polymer cladding causes a local change in the cladding refractive index, and a consequent change in the amount of light emerging from the side of the optical fiber is detected. The result is a low volume chemical sensor that temporally separates, as well as detects, chemical species that partition into the fiber cladding. The sensor is both theoretically and experimentally characterized in terms of the sensitivity dependencies upon several parameters. The sensor can be used for the simultaneous separation and detection of organics in water and yields a detection limit of 500 parts-per-billion for cumene at 1 $\mu$L/min flow rate. This detection limit corresponds to an effective refractive index change in the mobile phase of $8\times10\sp{-8}$ in a detection volume of 17 nL.The second subject is the development of reversed phase high performance liquid chromatography columns for the separation of hydrophobic analytes such as aromatic hydrocarbons, using only water as the mobile phase. Achievement of reasonable capacity factors for hydrophobic species without organic modifier in the mobile phase is accomplished by substantially decreasing the phase volume ratio of stationary phase relative to the mobile phase volume, and also by increasing the polarity of the stationary phase relative to stationary phase materials commonly used for RP-HPLC. Using only water as the mobile phase results in the elimination of toxic organic solvent waste from HPLC analysis. Also, a water mobile phase provides an environment offering an improved signal-to-noise ratio for UV detection. Additionally, excellent prediction of the octanol/water partitioning coefficient (P$\sb0)$ and aqueous solubility (X$\sb0)$ for hydrophobic analytes are obtained from a single measurement of the capacity factor in the water mobile phase.