Quality control by the Society of Hair Testing.

In contrast to urine and blood analyses the amount of hair samples lies in the order of 20-100 mg. Consequently at similar concentrations the absolute detection limit is about one order lower, increasing the relative deviation. The interlaboratory differences are correspondingly high. Concerning blood and urine, calibrators and controls are produced by adding certain amounts of the drug to the negative sample. Usually the single determinations are calibrated with spiked hair samples. These samples cannot be used as controls because in real hair the drug is bound to a solid phase surrounded by keratin, whereas in a spiked sample the drug is bound to the surface of the hair and can easily be washed away by any liquid phase. Recently some round robin surveys have been performed by several laboratories, some using drug soaked hair to detect contamination, the other using powdered hair of drug addicts to compare quantitative results. In this contribution the manufacturing of the hair pools and the results of the last international interlaboratory comparison will be described and future activities of the Society of Hair Testing are presented.