A forensic toxicologist analyzing a blood sample uses the principle of hapten-antibody competition. No chromatographic separation is performed. The assay produces a color change inversely proportional to the concentration of the analyte. Which analytical technique is being described?
- A Enzyme-multiplied immunoassay technique (EMIT) ✓
- B Gas chromatography–mass spectrometry (GC-MS)
- C High-performance liquid chromatography (HPLC)
- D Thin-layer chromatography (TLC)
Correct answer: A. Enzyme-multiplied immunoassay technique (EMIT)
Explanation
EMIT (Enzyme-Multiplied Immunoassay Technique) uses a labeled drug-enzyme conjugate competing with free drug for antibody binding sites. When antibody binds the enzyme-labeled drug, enzyme activity is inhibited; free drug displaces this conjugate, restoring enzyme activity. Color change (via enzyme substrate) is therefore proportional to free drug concentration — an inverse competition relationship. GC-MS is the confirmatory gold standard but requires separation. TLC separates by migration; no antibody competition is involved.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
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