SOLVING CRIMES WITH 3-D FLOURESCENCE SPECTROSCOPY
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The Santa Barbara channel off the coast of California is choked with oil tankers waiting to unload their car goes of crude oil for refining. Suddenly the water becomes fouled with crude leaking from one of the vessels. But which one? An old car pulls into the driveway of an expensive home. The driver of the car commits a burglary in the home and leaves the scene, but his car leaves a deposit of motor oil that has leaked from the crankcase. Can the oil spill be matched to the oil of the car? An arsonist is hired by the owner of a failing business to torch the build ing. He shows up at the building in the middle of the night and tosses a Molotov cocktail, a bottle containing gaso line and a cloth wick that is ignited, through the window. After the fire is put out, an investigator finds the broken bottle still containing a small amount of gasoline. Did the gasoline come from a five-gallon can of gasoline found in the suspect's car? These incidents have certain as pects in common. They occur fre quently in the United States today, and they involve a petroleum-based hydrocarbon product as a critical piece of evidence. These cases require comparisons of a hydrocarbon whose source is known (such as the crude oil in the tankers, the engine oil in the crankcase, and the gasoline in the fivegallon can) with one whose source is not known and which is found at the scene of the incident (the oil slick on the water, the motor oil spill on the driveway, and the remains of the Molotov cocktail). The goal of the chemical analysis in each case is to de
934 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 8, JULY 1986
termine to a standard of reasonable scientific certainty whether the known samples and the scene samples could have had a common source. The simi larities among various types and brands of hydrocarbon products cre ate formidable analytical problems that may call for unconventional methodologies. Present methods of analysis The conventional methods used to analyze petroleum products in foren sic cases are usually some variation of gas-liquid chromatography (GLC). The more volatile products such as gasoline are usually analyzed by headspace techniques, perhaps after con centration by a purge-and-trap meth od. The less volatile oils and lubri cants are solvent extracted and/or directly injected. Although GLC can easily determine what type of petrole um product is present, i.e., gasoline vs. motor oil vs. petroleum jelly, it is not discriminating enough to determine reliably what brand or type of a par ticular hydrocarbon product is pres ent. Thus, GLC cannot, by itself, be used to determine if two samples could have had a common source. Al though capillary column GLC has im proved resolution significantly and uses smaller samples, it still cannot overcome the fundamental weakness of this method. Fluorescence spectroscopy in hydrocarbon analysis In recent times, the possibility of using fluorescence spectroscopy in the analysis of petroleum products has re ceived increased attention. Virtually 0003-2700/85/0357-934Α$01.50/0 © 1985 American Chemical Society
