SAMPLE PREPARATION TECHNIQUES

Evidentiary false positives are caused by passive exposure to drugs in the environment rather than by active use of drugs. The avoidance of such positives is essential for both hair and urine analysis. Hair ana lysis enjoys the advantage over urinalysis in having a number of appro aches for making this distinction. These include: methylene blue stain ing of the hair specimen for selecting the appropriate wash solvent; a pplication of hair digestion techniques for the complete release of ch emically unaltered analytes; the determination of three diagnostic rat ios from wash and digestion data; the measurement of metabolite:drug r atios; the use of cut-off levels setting the limits for passive endoge nous drug exposure; reproducibility of results (including segmental an alysis) with a newly collected hair specimen; and the reporting of res ults as either negative, positive, or contaminated. Our sample prepara tion procedures have been effectively applied to the analyses of nearl y 200 000 specimens, i.e. to approximately one million drug analyses f or cocaine, opiates, methamphetamine, phencyclidine or marijuana. On t he basis of this experience we conclude that hair analysis is a safe a nd effective method for workplace drug testing.