• Heath, Charles
• Myers, Matt

Abstract

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy using a polymer coated internal reflection element/waveguide is a proven sensor platform for the detection of a range of organic and hydrocarbon molecules dissolved in water. The polymer coating serves two purposes: to absorb the hydrocarbon from the aqueous phase and to exclude water along with other interfering molecules from the surface of the ATR crystal/waveguide. Although hydrocarbon quantification measurements have been performed in water mainly under mild ambient conditions, there is a need to monitor environmental and industrial processes/events that occur at high pressures and temperatures. Using a ruggedized optical fiber probe with a diamond-based ATR, we have conducted mid-infrared sensor experiments to understand the influence of high pressure (up to 207 bar) and temperature (up to 80 °C) on the detection of toluene and naphthalene dissolved in water. Using a poly(isobutylene)film, we have shown that the IR response is relatively unaffected by changes in pressure; however, a diminished response was observed with increasing temperature. The variations in sensor sensitivity with temperature are consistent with an exothermic partitioning process in which hydrocarbons are thermodynamically more favored to dissolve into the polymer film relative to the water phase. This paper shows that the hydrocarbon-polymer partition process is temperature dependent and that the ATR-FTIR sensor needs to account for thermal variations during the quantification of hydrocarbons in water.

Topics

• impedance spectroscopy
• surface
• polymer
• phase
• experiment