Inner Filter Effect and Energy Transfer Studies for Subsurface Contamination AnalysisEPA Grant Number: U915376
Title: Inner Filter Effect and Energy Transfer Studies for Subsurface Contamination Analysis
Investigators: Pagano, Todd Eric
Institution: Tufts University
EPA Project Officer: Michaud, Jayne
Project Period: September 8, 1998 through January 1, 2001
Project Amount: $67,111
RFA: STAR Graduate Fellowships (1998) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemistry and Materials Science
The objectives of this research project are to: (1) acquire information to assess the masking of fluorescence responses by inner-filter effects and resonance energy transfer in applications of fluorescence spectroscopy; and (2) understand and characterize subsurface JP-4 jet fuel contamination detected by laser-induced fluorescence (LIF) with fiber optic and cone penetrometer technology (CPT) sensor. Fluorescence spectroscopy has become a powerful tool in many fields of chemistry; in situ monitoring of subsurface environments using LIF-CPT has enormous potential. Despite the versatility and sensitivity of fluorescence spectroscopy, two phenomena—the inner-filter effect and resonance energy transfer—can prevent the reliable interpretation of data when the concentrations of fluorophores and chromophores are high. The integrity of most of the currently used data analysis algorithms requires that a fluorophore present in the sample display the same spectral signature, apart from a single concentration-dependent scaling factor, regardless of its concentration or the concentrations of other components of the sample. However, a given compound, or a typical mixture such as jet fuel, shows different spectral fingerprints at different concentrations in nonpolar solvents (e.g., cyclohexane). Therefore, it is imperative to investigate and characterize the phenomena that hinder qualitative and quantitative analysis of acquired data.
The assessment of the extent of inner filtering in the jet fuel JP-4 can be accomplished either experimentally or mathematically. The dual-pathlength method is a novel experimental technique developed by our group. The method quantifies separately the extent of spectral distortion by primary and secondary inner filtering, corrects for both inner-filter effects, and establishes an absolute "dilute limit" for a sample. The method avoids reliance on separate absorption measurements that add error by introducing a second instrument with different instrumental parameters/specifications and avoids the need for difficult absorption measurements of optically dense samples (especially fuels). Fluorescence data of a varying concentration range of JP-4 samples will be studied, and the results will be used as both a correction procedure and as a method of interpreting the reliability of established mathematical correction factors. Because sample absorption is the cause of inner filtering, the second part of the research project will involve the measurement of absorption spectra in addition to fluorescence spectra. Again, solutions of JP-4 at varying concentrations—ranging from the neat liquid to an optically dilute solution in cyclohexane—will be used. The measured absorption values will be plugged into the mathematical correction factors, and the measured fluorescence data will be adjusted to account for inner filtering. The reliability of the various mathematical correction factors can be compared to each other, as well as to our experimental results. Once the inner-filter effect is better understood in the JP-4 system, we will try to account for resonance energy transfer.