One blotter stamp: Identification of multiple phenethylamine new psychoactive substances and unambiguous differentiation of two isomers

Abstract In recent years, new psychoactive substances (NPSs) have emerged continuously, often concealed in carriers such as blotter stamps, tobacco, and beverages, posing serious challenges to drug control and forensic identification. In this study, seven phenethylamine substances were detected from a seized blotter stamp using liquid chromatography–high‐resolution mass spectrometry (LC‐HRMS). By comparison with an in‐house mass spectral library, six of them were identified as 25D‐NBOMe, 25E‐NBOH, 25C‐NBOMe, 2C‐E, 25B‐NBOMe, and 25I‐NBOH. The most abundant component exhibited a protonated molecular ion ([M + H] + ) at m/z 330.2068; the relative peak area percentage of this component among the seven identified analytes was approximately 94.6%. Further comparison with the in‐house library indicated that this substance could be either 25G‐NBOMe or 25E‐NBOMe, which were structural isomers of each other. Conventional liquid chromatography–tandem mass spectrometry (LC–MS/MS) methods relying primarily on retention time and selected parent/product ion pairs were insufficient to confidently distinguish these two structural isomers, posing a risk of misidentification. Therefore, this study employed HRMS combined with diagnostic fragment ion abundance ratio analysis. It was found that under identical collision energy conditions, the fragment ions at m/z 135.0804 and 193.1223 exhibited markedly stronger responses for 25E‐NBOMe than for 25G‐NBOMe. Based on this, we distinguished the two structural isomers and confirmed that the target substance in the seized blotter stamp was 25E‐NBOMe.