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Fiber optic infrared reflectance probe for detection of hydrocarbon fuels in soil

The acquisition of fiber optic reflectance spectra of diesel fuel marine (DFM) dispersed on sea sand is described. Reflectance spectra are acquired by collection of the diffusely scattered light from a black body source imaged onto a specially designed sample cell. Samples of DFM were prepared by diluting a stock standard containing 10 wt% DFM on sea sand. Interactive band analysis is used to remove the background absorption due to residual water on the sand. Results indicate a linear relationship between the band depth at 3.68 microns and the concentration of DFM. Statistical analysis of ten replicate measurements of a 0.02 wt% DFM on sea sand gives the average band depth and 95% confidence interval of 0.02875 +/- 0.000654. An instrumental detection limit of 0.0033 percent reflectance is calculated from the standard deviation of the replicate measurements.