Structural elucidation of an uncommon phenylethylamine analogue in urine responsible for discordant amphetamine immunoassay results.

The present paper describes investigations following the analysis of a urine specimen containing important amounts of an unknown substance detected by gas chromatography-mass spectrometry (GC-MS) analysis. FPIA analysis was positive (cutoff 0.3 mg/L) and Triage 8 rapid test was negative (cutoff 1 mg/L) for amphetamines. Considering the GC-MS spectrum, two different molecules, for example, N-ethyl-1-(3,4-methylenedioxyphenyl)ethylamine (1) or N-ethyl-4-methoxyamphetamine (2), have been suspected. Synthesis of these two compounds was carried out together with spectral (MS, 1H and 13C NMR, IR, UV) and chromatographic (GC) characterization as well as determination of immunological cross reactivities (FPIA and Triage 8). The unknown compound present in the urine specimen has been finally identified as N-ethyl-4-methoxyamphetamine (2), an uncommon amphetamine analogue.