Web Date: April 28, 2011
A Strand Of Hair Tells Tales Of Cocaine Use
Addicts may lie about their recent drug use, but their hair records the truth. Swiss researchers report that mass spectrometry can spot cocaine that hid in a strand of human hair as it grew, providing a timeline of a person's drug use (Anal. Chem., DOI: 10.1021/ac200610c).
Either body fluids or hair can reveal recent drug use, but only hair provides information about long-term behavior, says Gérard Hopfgartner at the University of Geneva. Still, he says, techniques that reveal the user's history of intake from their hair are slow and cumbersome. The methods take days because technicians must chop up the hair into dozens of 1-mm-long segments, pulverize each segment, and then analyze them by mass spectrometry separately, in order from root to tip.
Hopfgartner and colleagues turned to mass spectrometric imaging, which creates a picture of an object, such as a piece of hair, using information about the masses of molecules within that object. Imaging, Hopfgartner says, takes just a couple of hours and doesn't require tedious hair cutting. Instead, the researchers collected whole strands of hair from frequent cocaine users and affixed each to a small metal plate. They then coated the strand with a protective matrix, a chemical that facilitates ionization in mass spectrometry. The researchers aimed and fired an ultraviolet laser at one end of the hair, then directed the laser to follow a zigzag path down the length of the strand, crossing the 60-mm-long hair every millimeter to take a measurement. The laser ionized the molecules in the hair, which then traveled through a series of filters that removed all but the ions of cocaine and its derivatives.
The resulting hair image showed when, within a margin of a few days, a person had used cocaine over the past six months or so. The relative intensity of the signal at each millimeter-long segment also showed how much drug the person had consumed in comparison to his or her use at other times.
The cocaine users who had supplied the hair for the study were on the road to recovery; the results showed that cocaine concentrations in their hair fell over time. The researchers found that they could detect 5 ng of cocaine per milligram of hair. That sensitivity works well for regular cocaine consumers but not for one-time users, whose hair may only contain a tenth of that amount, Hopfgartner says. He plans to improve sensitivity.
Another limitation on the method's use is that "the instrumentation is certainly not routine in drug testing facilities," says Christine Moore, the vice president of toxicology research and development for Immunalysis, a company that develops reagents for drug screening. Even so, she will consider investing in the instrumentation because the easy sample preparation offers a "distinct advantage over traditional hair analysis".
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