Toxicology: analytical methods: practice question

A Forensic Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Forensic Medicine · Toxicology: analytical methods

Sample item

A forensic laboratory must give court-admissible confirmation of an unknown drug in a viscera extract after a thin-layer chromatography screen was positive. Which technique is the best confirmatory method?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Gas chromatography coupled with mass spectrometry

GC-MS separates compounds by chromatography and identifies each from its mass spectrum, which acts as a molecular fingerprint, so it is regarded as a confirmatory method. TLC, colour tests and immunoassays are screening or presumptive tests and can give false positives through cross-reaction.

Option by option

  • A. A repeat of the thin-layer chromatography run

    Repeating TLC remains a screening test and is not specific.

  • B. Gas chromatography coupled with mass spectrometry (correct)

    Correct. Mass-spectral identification gives specific confirmation.

  • C. A colour spot test on the extract

    Colour tests are presumptive and react with related compounds.

  • D. An immunoassay on urine

    Immunoassays cross-react with similar structures and need confirmation.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is B, Gas chromatography coupled with mass spectrometry. GC-MS separates compounds by chromatography and identifies each from its mass spectrum, which acts as a molecular fingerprint, so it is regarded as a confirmatory method.

Why is "A repeat of the thin-layer chromatography run" not the answer?

Repeating TLC remains a screening test and is not specific.

Why is "A colour spot test on the extract" not the answer?

Colour tests are presumptive and react with related compounds.

Why is "An immunoassay on urine" not the answer?

Immunoassays cross-react with similar structures and need confirmation.

What concept does this question test?

It tests Toxicology: analytical methods in Forensic Medicine. TLC, colour tests and immunoassays are screening or presumptive tests and can give false positives through cross-reaction.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Toxicology: analytical methods?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.