Chemistry, Third edition

23 · FORENSIC CHEMISTRY

cause many traffic accidents but the presence of such substances can only be con-

firmed by analysis of blood or urine. Such measurements cannot readily be con-

ducted by the roadside and drivers suspected of driving under the influence of drugs

are first arrested and taken to the police station where samples of blood or urine are

obtained for subsequent chromatographic analysis.

Analysis of drugs in hair

Many job applicants are required to provide blood or urine samples as part of an

interview. If a habitual drug user refrains from using drugs in the week before the

test, s/he will avoid detection because the drug has long passed through their bodies.

Analysis of hair avoids these difficulties, as hair retains within it tiny traces of

drugs that a person may have consumed for many months (Figure 23.5). Further,

since hair grows about 1 cm per month, the analysis of segments of hair allows an

estimate to be made of drug consumption over several months.

The analysis of arsenic in hair is discussed in Box 21.1 on p. 409.

23.7

428

Fig. 23.5Window of detection
of drug use or absence,
measured in days. Sweat
patches can detect drug use
for up to a week whilst they
are worn; sweat swabs will
detect drug use for up to
24 hours. (Reproduced with
permission from Tricho-tech,
Cardiff)

Hair

Sweat

Urine

Saliva

Blood

No. of days: 0.1 1 10 100 1000

1 week to

2+ years

2–3 days

2–3 days

24 hrs

24 hrs

Fig. 23.6A single hair. It has
long been known that
poisons, including heavy
meatals, are depositied in
the hair. The observation that
minute quantities of drugs
such as cocaine and ecstasy
are also stored in hair offers
the possibility of identifying
individuals with a history of
drug addiction. Photograph
reproduced courtesy of Dr
John Gray.