A test for tainted blood.

Thanks to the murder trial of football star O.J. Simpson, crime investigators now have another forensic tool. A new study describes a method of analyzing blood and urine for an anticoagulant called EDTA, often used to preserve crime-scene blood samples. During the Simpson trial, defense lawyers seized on the presence of the compound in unpreserved blood samples found long after the day of the murder to suggest that police had planted evidence.

For the prosecution team, the argument hinged on whether any EDTA is present naturally in human blood. People ingest EDTA all the time because it is a water softener and is used to maintain color and flavor in foods such as mayonnaise, canned vegetables, and salad dressing. "It wasn't known before if there were nominal levels in everyone's blood," says study coauthor Robin L. Sheppard, an analytical chemist at Xerox Corp. in Webster, MY

Spurred by the issues raised during the trial, Sheppard and her colleague Jack Henion of Cornell University developed an analytical technique to measure EDTA in a nanoliter of blood. Their tests showed that EDTA does not occur in significant amounts in human blood unless the person is being treated with EDTA for heavy metal poisoning, Sheppard says. The researchers' report appears in the Aug. I Analytical Chemistry.

These results suggest that if EDTA is found in blood, it was most likely added--one way or another--after collection. The FBI now suspects that the low concentrations present in the Simpson blood evidence came from EDTA-containing water run through the testing device just before the blood.

If the blood had been deliberately mixed with EDTA, much higher concentrations would have been detected, even by FBI's less sensitive technique, the researchers say. Crime investigators often add EDTA to fresh blood samples to bind calcium ions and stop the formation of a protein involved in coagulation.

The trial highlighted this particular application of the technique, called capillary electrophoresis-mass spectrometry, but the study was also "the first validation that it can be used for routine quantitative analysis," Sheppard notes. She and Henion also have shown that it accurately measures EDTA in urine and environmental water samples.