Reliable identification and quantification of three diethylphenethylamines in a Dendrobium-based dietary supplement

Abstract

An analytical method has been developed for the identification and quantification of N,α-diethyl-phenylethylamine, N,N-diethyl-phenylethylamine and N,β-diethyl-phenylethylamine (N,α-DEPEA, N,N-DEPEA and N,β-DEPEA, respectively) in a pre-workout dietary supplement containing extract from orchids of the Dendrobium genus. UHPLC-MS/MS (QQQ) technology was utilized for identification and quantitation using custom synthesized external standards as references. In less than 9 minutes the method successfully identifies N,α-DEPEA, N,N-DEPEA and N,β-DEPEA down to 0.1 ng ml⁻¹ and quantifies the same substances down to 0.3 ng ml⁻¹. The method proved to be rapid, stable and reproducible with good separation and detection limits. N,β-DEPEA proved difficult to be separated from N,α-DEPEA both chromatographically and mass spectrometry-wise due to the notable differences in concentration and their structural similarity. The presence of N,β-DEPEA in the analyzed sample type has not been studied in previously published results, thus this study adds to the current scientific interest in characterizing the contents of certain pre-workout dietary supplements. The amounts found in the products vary between batches, but were found to be around 2 mg g⁻¹ for N,β-DEPEA, 0.3–4 μg g⁻¹ for N,α-DEPEA and 60–230 ng g⁻¹ for N,N-DEPEA.