Liquid Chromatographic Sensing in Water on a Thin-Clad Optical Fiber by Mode-Filtered Light Detection

Abstract

An improved annular column sensor is reported. The sensor is made by applying a thin polymeric film cladding of trifluoropropylpolysiloxane (TFPS), nominally 0.1 μm thick, to a 200 μm diameter bare glass fiber core and inserting the fiber into a short section of 250 μm i.d. fused silica capillary tubing, producing an annular column. A He/Ne laser is directed into the end of the fiber optic. When a small sample volume is injected into a mobile phase flowing along the sensor, selective partitioning of an analyte into the thin polymeric film, i.e., the stationary phase, causes a local change in the cladding refractive index, and thus the aperture of the fiber, and a consequent change in the amount of light emerging from the side of the optical fiber is sensitively detected. Temporal selectivity is simultaneously obtained as there is some chromatographic separation of analytes flowing through the annular column sensor. The sensor is both theoretically and experimentally characterized in terms of the sensitivi...