Toxicological analyses are performed to detect toxic and illegal substances and diagnose, follow up and evaluate the treatment of related disorders. Urine, serum, plasma, blood, hair, saliva, sweat, nails, stomach aspirates, and any solid or liquid in which a foreign substance is sought are used as a sample type. While the screening methods in these analyzes are fast, inexpensive, susceptible, and lowly specific, validation methods are slow, expensive, susceptible, and specific.
Screening methods are mainly immunoassays and chromatographic techniques, which are used to distinguish negative samples from positive samples, while confirmation methods are used to confirm positive results in screening tests. The gold standard confirmation method is mass spectrometry.
Since the immunoassays are not specific, cross-reactions may occur. High-pressure liquid chromatography is suitable for polar and non-volatile samples, while gas chromatography is suitable for volatile samples. Gas chromatography-mass spectrometry is more sensitive than immunoassay and high-pressure liquid chromatography, while sample preparation time is longer. Because substances and their metabolites are usually converted to less polar and more volatile derivatives for separation. On the other hand, liquid chromatography-tandem mass spectrometry has high specificity and sensitivity, but its analysis is complex, requires experienced personnel, and is costly.
There is no single analytical technique sufficient for toxicological analysis. It is recommended to combine more than one technique.