Introduction To Forensic Science Practice Test

GC-MS confirms a drug’s identity by using both separation and a distinctive spectral fingerprint. The gas chromatography step separates the drug from other components, and the mass spectrometry step produces a fragmentation pattern that is highly specific to that compound. When this observed retention time and its mass spectrum match a reference standard, the result is considered confirmatory rather than just a screening signal. This is crucial because immunoassays can yield false positives due to cross-reactivity, so a definitive spectral match proves the compound’s identity beyond the initial screening. Relying only on retention time isn’t sufficient because different substances can share similar times, and a mass spectrum without a library match isn’t definitive. The notion that GC-MS cannot confirm identity is incorrect, as the spectral match to a known standard is what provides the confirmation. And while sample purity or interfering substances can affect results, a properly performed GC-MS analysis uses the characteristic fragmentation pattern to distinguish the target compound, leading to a reliable confirmation.