ABSTRACT
Near-IR surface plasmon resonance is used to characterize Teflon AF films for refractive index-based detection of the aromatic hydrocarbon contaminants benzene, toluene, and xylenes in water. The technique requires no sample preparation, and film sensitivity is found to be enhanced by oxygen plasma etching. A diffusion equation model is used to extract the diffusion and partition coefficients, which indicate film enrichment factors exceeding two orders of magnitude, permitting a limit of detection of 183, 105 and 55 ppb for benzene, toluene, and xylenes, respectively. The effect of other potential interfering contaminants is quantified.
Subject(s)
Benzene/analysis , Polytetrafluoroethylene , Spectroscopy, Near-Infrared/methods , Surface Plasmon Resonance/methods , Toluene/analysis , Water Pollutants, Chemical/analysis , Xylenes/analysisABSTRACT
Sinusoidally structured illumination is used in concert with a phantom-based lookup-table (LUT) to map wide-field optical properties in turbid media with reduced albedos as low as 0.44. A key advantage of the lookup-table approach is the ability to measure the absorption (mu(a)) and reduced scattering coefficients (mu(s) (')) over a much broader range of values than permitted by current diffusion theory methods. Through calibration with a single reflectance standard, the LUT can extract mu(s) (') from 0.8 to 2.4 mm(-1) with an average root-mean-square (rms) error of 7% and extract mu(a) from 0 to 1.0 mm(-1) with an average rms error of 6%. The LUT is based solely on measurements of two parameters, reflectance R and modulation M at an illumination period of 10 mm. A single set of three phase-shifted images is sufficient to measure both M and R, which are then used to generate maps of absorption and scattering by referencing the LUT. We establish empirically that each pair (M,R) maps uniquely to only one pair of (micro(s) ('),micro(a)) and report that the phase function (i.e., size) of the scatterers can influence the accuracy of optical property extraction.
