Biomedical Engineering Reference
In-Depth Information
However, urine has no great relevance in quantitative analysis because the
analyte concentrations vary depending on the dose, means of administration,
physiological status (urinary pH, sex, age, weight, etc.), the time lag between intake
and analysis, the addition of adulterants. So the analytical data of urine may only
indicate the presence of a substance up to a defined cutoff point; the monitoring
window (time interval in which a substance can be detected by ordinary analytical
methods) varies from a few days for cocaine, amphetamine, methoxyamphetamine
to 2-3 weeks for cannabinoids.
In order to prevent tampering, investigations are planned on the assessment of
creatinine, specific gravity, pH, and the presence of oxidizing adulterants [
41
] .
6.4
Hair
The hair matrix possesses a large monitoring window (months/years) that allows a
retrospective analysis and the study of past history. Hair is also characterized by a
high stability and a minimum possibility of adulteration [
41,
42
] . The structure of
the hair can be considered as a repeated network of keratin fibers. There are also
melanins, lipids, and all the compounds of cells that led to the formation of the stem.
The growth of hair is in the range of 0.6-1.4 cm/month [
43,
44
] .
6.4.1
Incorporation Mechanism
The most widely accepted model for the incorporation of substances into hair has
been proposed by Henderson [
45
]: the incorporation of substances inside hair is
primarily dependent on the diffusion of molecules from blood in the capillaries to
the cells in growth. The drugs can also enter the hair fiber during its formation by
spreading from the deep skin strata. Sebum and sweat, which themselves contain
the substances, can carry them within the hair structure [
46-
51
] .
Moreover, substances from the environment can be absorbed in the hair surface
and then sweat facilitates their spread within the hair.
7
LC-MS Analysis
The toxicological analysis is essential in the clinical and medicolegal process, aimed
at seeking evidence of the presence of psychoactive substances in biological fluids
and tissues. The fields of intervention of a clinical toxicology laboratory are mainly
two:
Clinical toxicology
, where the analysis is made with a therapeutic purpose.
Forensic toxicology
, which performs analysis for administrative and forensic
purposes.
