Forensics laboratory investigation using fluorometry to detect nitrated explosives and materials labeled with fluorophores

The two part general chemistry laboratory in forensics was developed to illustrate the use of fluorometry for tracing materials tagged with fluorophores and the detection of nitrated explosive residues. The laboratory uses UV-light sources for detection and identification of single fluorophore makers present in various materials. This analysis is extended to the detection and identification of very low concentrations of fluorophore mixtures with the use of a fluorometer. Fluorescent markers are identified by comparing both the emission and excitation spectra to the spectra of known fluorophore standards. The second part of the experiment makes use of fluorescent quenching to detect residual amounts of nitrated explosive residues. Materials collected from a blast site are processed to remove explosive residue. The residue is then mixed with standard solutions of selected fluorophores and the resultant fluorescent quenching is measured with a fluorometer. Both the amount of explosive residue found and locations of materials with the contamination are used to reconstruct the blast scene. For laboratories without a fluorometer, concentrations of fluorophores and nitrated explosive residues can be manipulated to allow for analysis using UV-light sources only. The experiment illustrates differences in the emission and excitation spectra, molar extinction coefficients, quenching and detection limits for selected fluorophores in addition to providing an introduction to the theory and operation of a fluorometer.
Authors: 
Eric Schurter