Fluorescence Sampling Targets Oil Spills
Michael D. Wheeler
DHAHRAN, Saudi Arabia -- Oil spills happen nearly every day throughout the world, but only a fraction are highly publicized. Lesser spills are far more frequent, most occurring when tankers discard oil during ballasting and other routine operations. Authorities have sought ways to identify the responsible tankers in the hope of recouping cleaning costs and of deterring such dumping in the future.
Oil tankers may discard crude during ballasting and other routine operations. A fluorescence detection system developed at King Fahd University for Petroleum and Minerals may enable authorities to tie samples of spilled oil to an offender.
Researchers at King Fahd University for Petroleum and Minerals have developed a variant of time-resolved fluorescence sampling that can identify subclasses of crude oil, making it possible to tie an oil sample to the offender. Unlike other time-resolved fluorescence methods that measure the fluorescence lifetimes at particular wavelengths, this approach targets the spectral profile of the emitted fluorescence bands as a function of time, which differs among types of crude oil.
The scientists assembled a YAG-pumped master oscillator power oscillator laser system emitting at 250 nm, a monochromator, a photomultiplier and a signal processor coupled with a gated integrator. This setup enables them to sample and to digitize the acquired fluorescence at specific points in time.
"Our approach is based on measuring the fluorescence spectra at particular time gates as in the former method, but with no consideration given to the relative intensities," said Ezzat Hegazi, the lead researcher on the project. Instead, the researchers monitor the variations in the shape of the spectra at different time gates.
The laser-pulse convolution thus depends on the shape of the laser pulse, which can be standardized, Hegazi explained, rather than on its intensity, which is difficult to predict when performing remote measurements. And by standardizing the spectral response of the detectors, the researchers are able to produce "fingerprints" of the crude oils.
"Because our 'standardized' fingerprints are independent of the laser-pulse intensity, they can be used to discriminate between not only different subclasses, but also between members belonging to the same subclass. We have been able to distinguish between closely similar crudes."
The fluorescence detection system is available for commercial applications. Hegazi and his colleagues, who published the results of their study in the February issue of Applied Spectroscopy, are working to patent the technique and to expand it to detect materials other than petroleum.
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