Which technique is the gold standard for drug testing?

• A. TLC
• B. HPLC
• C. GC-MS
• D. Paper chromatography

Answer: (C)

In drug testing, you need a method that can reliably identify a specific substance, not just indicate that something is present. Gas chromatography–mass spectrometry achieves this by combining separation with a definitive chemical fingerprint. The gas chromatography step separates the mixture’s components. As each compound exits the column, the mass spectrometer ionizes it and records a mass spectrum—a unique pattern of fragment masses that acts like a molecular fingerprint. By matching this spectrum to reference libraries, you get unequivocal identification and accurate quantification.

This high specificity is what makes it the preferred confirmatory technique. Other methods like TLC and paper chromatography are qualitative and less sensitive, so they’re prone to ambiguity. HPLC can be very sensitive and quantitative, but without mass spectral identification (or another confirmatory detector), it can’t definitively confirm the compound's identity. GC-MS provides both separation and a reliable identification, which is why it’s regarded as the gold standard for drug testing.