MLT GlobeForensic Science: Forensic toxicology – page 3
45 Forensic Science MCQs on Forensic toxicology with answers and explanations.
Which medication is a well-known cause of false-positive results on amphetamine immunoassays?
Sympathomimetic amines such as pseudoephedrine share structural features with amphetamine and can cross-react with some immunoassays. Mass spectrometric confirmation distinguishes them from amphetamine or methamphetamine.
Raised zinc protoporphyrin in lead poisoning mainly results from lead inhibiting which enzyme?
Ferrochelatase inserts iron into protoporphyrin to form heme. When lead inhibits it, zinc is incorporated instead, raising zinc protoporphyrin. Lead also inhibits delta-aminolevulinic acid dehydratase.
Why is urine often treated with beta-glucuronidase before chromatographic analysis of opioids?
Opioids such as morphine are largely excreted as glucuronide conjugates. Enzymatic or acid hydrolysis releases the free drug, increasing sensitivity when an assay targets the parent compound.
Which urinary microscopy finding supports ethylene glycol poisoning?
Ethylene glycol is metabolized to glycolic acid and then oxalic acid, which combines with calcium, forming calcium oxalate crystals in urine and renal tubules. Absence of crystals does not exclude poisoning.
During LC-MS/MS method validation, reduced analyte signal caused by co-eluting components of the specimen is called:
Co-eluting matrix components compete for ionization in the source, suppressing or enhancing analyte signal. Validation must assess matrix effects, typically using post-extraction spikes, and isotope-labelled internal standards help compensate.