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404 FORENSIC AND CLINICAL TOXICOLOGY

Thermal

Thermal

Desorption

Desorption

System

Controller

Mass Spec

GC Injection Port

 

Micro

Cryo-Trap

MS

Interface Capillary

Column

GC Oven

Figure 22.2 Thermal desorption system.

22.5.4Gas Chromotography (GC)

Involves a sample being vaporized and injected into the head space of the chromatographic column. The sample is transported through the column by the flow of an inert gas (mobile phase). The column itself contains a liquid stationary phase which is adsorbed onto the surface of an inert solid. Retention time with detection techniques (spectrophotometer, mass spectrometry, fluorescence) identifies the compound.

22.5.5High-PerformanceLiquid Chromatography (HPLC)

The mobile phase is a solvent that is pumped at high pressure through a packed column. As described for GC, retention time with various detection techniques identifies the compound.

22.5.6Enzymatic Immunoassay

An enzyme-linkeddrug derivative is added to the specimen to be tested. This competes with the drug in question for antibody. The more drug that binds to antibody, the less is bound toenzyme-linkeddrug. Enzyme activity is proportional to the amount of the drug that was already in the specimen.

22.6ANALYTICAL SCHEMES FOR TOXICANT DETECTION

The circumstances surrounding the case will usually determine the types of toxicological tests that are required. There are different screens specific for the type of substance