Forensic Applications of Gas Chromatography - Forensic Applications of Gas Chromatography - page 101

There are a number different ways in which to classify drugs that may be
investigated in toxicology. ( Note: The classification used in this chapter is not
the same as the one used in the previous chapter. Here we will use the clas-
sification for the way that the drug acts when it enters the body.)
Central nervous system stimulants: This group of drugs will increase
the rate of mental and physical responses. Examples include cocaine,
amphetamine, MDMA, caffeine and methylphenidate.
Central nervous system (CNS) depressants: This group of drugs
reduces the activity of the brain. The most commonly encountered
CNS depressant in the UK and United States is ethanol (or alcohol).
Other examples of CNS depressants are benzodiazepines (e.g., alpra-
zolam, diazepam and flunitrazepam) and barbiturates (e.g., pheno-
barbitone, pentobarbital and amylobarbitone).
Narcotic analgesics: This group of drugs is used to relieve moderate to
severe pain. Examples include opioids such as morphine, diacetylmor-
phine, codeine, propoxyphene, oxycodone, fentanyl and tramadol.
Hallucinogens: These drugs will produce hallucinations in an individ-
ual. Examples include lysergic acid diethylamide (LSD), psilocybin,
mescaline, ketamine and phencyclidine (PCP).
Other: This may include inhalants such as carbon monoxide and
organic solvents such as those found in glues and aerosols.
8.3.4 Sample Pretreatment
Due to the nature of samples in toxicology, it is necessary to carry out sample
pretreatment to clean up the sample prior to analysis by GC. If this is not
carried out, it is possible that the GC liner (see Chapter 2) and column will
be contaminated with the sample matrix, thus reducing the sensitivity of the
detection (if not impeding detection altogether). The type of pretreatment
chosen depends upon the matrix being analysed.
8.3.4.1 Protein Precipitation
Protein precipitation is a technique used in toxicology that is used to remove
the protein content of human body fluids and tissues before they are analysed.
The reason for this is that in these samples, the protein content can vary from
6% to more than 50%, by weight, in some tissues. This can greatly affect the
possibility of detecting and quantifying drug or metabolite concentrations.
Generally, a precipitation reagent will be used, such as an organic solvent
(e.g., acetonitrile or methanol) or a salt and an acid (e.g., ammonium sul-
phate and hydrochloric acid). Once the proteins have been precipitated, the
solid protein will then be removed by filtering or by centrifuging. The rest of