Estimation of the synthetic routes of seized methamphetamines using GC-MS and multivariate analysis.

•Seized methamphetamine samples were analyzed using GC-MS.•Eighteen unknown impurities were newly detected in methamphetamine crystalline.•Route specific impurities were selected for Nagai, Emde and Leuckart methods.•GC-MS data were deconvoluted using target component library of AMDIS software.•Synthetic routes were estimated by multivariate analysis.