Biomedical Engineering Reference
In-Depth Information
[ 130, 131 ]. It is also possible to operate a segmentation of the hair to distinguish
different temporalities; however, the variability of growth from person to person
will never allow to assign the exact time of illicit drugs assumption.[ 42 ] .
An analytical method for determining illicit drugs in the hair should include
before analysis a proper washing procedure to eliminate possible external contami-
nation, or traces of drugs that can be deposited on the outside of the hair, thus limit-
ing the possibility of interference and false positives. The washes also remove
residues of shampoo and cosmetics as well as sweat and sebum, which can cause
problems of interference in the subsequent analytical procedures and increase the
background noise recorded in instrumental analysis of the sample [ 42, 132 ] .
10.4.1
Decontamination
The solvents can be divided between solvents that swell the keratin structure (swell-
ing solvent), which penetrate the hair such as water and methanol, and solvents that
do not swell the keratin structure (nonswelling solvent), failing to cross the cuticle
and therefore not penetrating inside the hair. The washing procedure in most cases
requires more than one step (2-3) [ 48, 133- 146 ] generally processed through the
subsequent use of different solvents or solutions. Only rarely is a washing procedure
including a single step [ 51 ] .
The used solvents, in subsequent steps or in mixtures, are as follows: ultrapure water
[ 136, 138, 144 ], aqueous solutions of surfactants (dodecylsulphate [ 138 ] , polysorbate
[ 136, 140 ] , generic surfactant [ 144 ]), and organic solvent (dichloromethane [ 51, 133,
141- 143 ] , acetone [ 137, 138, 143 ] , methanol [ 134, 139, 143, 145 ] , ethanol [ 146 ] ,
hexane [ 137 ] , isopropanol [ 135, 142, 147 ] , petroleum ether [ 139 ] ).
Aprotic solvents such as dichloromethane and acetone have the advantage of not
possessing extractive capabilities [ 42 ], being unable to penetrate into the keratin
structure. Extraction tests with conventional techniques, for dichloromethane,
showed that the analytes were not found in the extracts [ 51 ] .
10.4.2
Extraction and Digestion of the Keratin Matrix
The extraction methods are divided between those using the solvent and those pro-
viding for the dissolution of the keratinic matrix.
Solvent Extraction
This process allows to provide contact of hair, chopped or shredded to increase
surface development, with an appropriate extracting solvent. Methanol is the most
used as the extraction solvent and is often supported by the use of an ultrasonic bath
to reduce the extraction time. The extraction times are usually between 16 and 20 h
[ 51, 137, 148- 150 ]; the use of ultrasonic bath shortens the extraction time up to 4 h
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