Sensitive screening of methamphetamine stimulant using potential-modulated electrochemiluminescence

Methamphetamine (MA) is one of the most commonly abused recreational stimulants; thus, rapid and sensitive screening methods for MA are of great importance in forensic analytical chemistry. In the present work, potential modulation was combined with electrochemiluminescence (ECL) for the sensitive determination of MA. The potential modulated (PM) technique involved applying a signal to electrodes by superimposing an alternating current potential on the direct current potential. When tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) was used as an ECL emitter, the sensitivity of MA detection by PM-ECL was over 100 times that obtained with in conventional potential sweep mode. The radical on the α-carbon of the amine moiety is thought to play an important role in the ECL reaction mechanism involving amine-containing species. However, in the case of MA-type stimulants, density functional theory calculations suggest that the generated α-carbon radicals induce further intramolecular proton transfer. On the basis of the proposed ECL reaction route, we clarified the conditions under which MA could be selectively detected in the presence of the similar substance methoxyphenamine. The proposed method was applied to MA determination in a spiked human urine sample and showed good linearity with a low detection limit (100 nM, ca. 15 ng mL^-1).