Biomedical Engineering Reference
In-Depth Information
The knowledge of the plasmatic concentration is very useful in legal testing,
where it is necessary to correlate a person's actions with the effect of a substance
(impairment).
Illicit drugs are usually quickly metabolized so it is necessary to perform testing
a few hours after intake. In plasmatic analysis the possibility for adulteration is very
low and so blood samples have always been considered for forensic analysis.
The problems related to the use of these matrices are the invasiveness of testing,
the reduced volume of the sample, the need for specialized staff, and suitable stor-
age until analysis [
33
] .
6.2
Oral Fluids
6.2.1
Anatomy and Physiology
The glandular apparatus produces from 500 to 1,500 ml of saliva per day: this secre-
tion, however, is not constant, being higher in the digestive phase (0.05 ml/min
during sleep, at rest 0.3-0.6). There are several inorganic compounds, such as
sodium, potassium, or bicarbonate, while organic molecules are mainly proteins,
such as a-amylase and mucine, a glycoprotein which gives high viscosity to OF,
even if the total protein concentration is 1 % than the plasmatic one (10-50 mg/ml).
Most of the plasmatic substances are affected by a transcellular passive diffusion
mechanism in the saliva in a concentration gradient [
36
] . The transfer between
blood and OF depends on both their pH and on the p
K
a of the molecule: the OF pH
is usually lower than the plasmatic one, so basic substances, which are unionized in
plasma, can cross the membrane and remain in the salivary compartment at lower
pH in ionized form [
27
] .
The growing interest in the use of OF is due to the strict correlation between
plasmatic concentration [
28-
30
] and pharmacokinetics [
31,
32
] ; furthermore, OF is
easily available and its testing is absolutely noninvasive, fast, cheap and can be per-
formed by untrained staff even on the road.
In OF, like in blood, the parent drugs are more concentrated than the metabolites:
that is, cocaine is itself the target analyte and THC is the predominant cannabis
product [
37-
39
] .
6.3
Urine
Urine is the matrix of choice in the analysis of drugs of abuse, as it allows noninva-
sive testing, the ability to analyze both the substance itself and the metabolites after
several days, a large amount of sample, the concentration of analytes (up to 100
times than plasma) [
40
] .
