Cocaine-laced locks tell hairy story.

Forensic scientists and toxicologists can read a history of chronic drug use from a person's hair. Unlike urine and blood, which carry remnants of recent drug use, hair preserves those clues from the moment it grows out of a person's head.

One problem limits its usefulness as legal evidence, however. Current analytical methods can't tell for sure how a (1rug such as cocaine made its way into a strand of hair. The person in question could have ingested it or just happened to be in the room when other people were smoking crack cocaine. Vapors can coat the outside of the hair shaft and show up in a laboratory test.

Scientists at the National Institute of Standards and Technology in Gaithersburg, Md., are testing a new method that may solve this problem. Instead of rinsing the hair with liquid solvents, as labs do now, they dissolve cocaine out of hair with supercritical carbon dioxide (SN: 8/16/97, p. 108).

Their preliminary results, which appear in the Jan. 1 Analytical Chemistry, show that pure carbon dioxide removes cocaine only from the surface, but a mixture of carbon dioxide, water, and the organic chemical triethylamine removes drug traces bonded inside the hair shaft.

The water and triethylamine molecules "kick off the cocaine" from its binding sites in hair, says study coauthor Janet F. Morrison, now at Trinity College in Hartford, Conn. The method can be tuned to extract only what the researcher wants.

Cocaine can penetrate hair in other ways, too. Perspiration on a person's scalp, for example, might absorb cocaine vapors and then bind inside the hair. Morrison and her coworkers are now treating hair samples with "fake sweat" to test that possibility.