Direct detection of aromatic amines and observation of intermediates of Schiff-base reactions by reactive desorption electrospray ionization mass spectrometry

Abstract

The fast, sensitive detection for 6 aromatic amines and direct observation of intermediates of Schiff-base reactions were achieved through reactive desorption electrospray ionization mass spectrometry (reactive DESI-MS). Pure acetone was electrosprayed to impact the aromatic amines on the paper, allowing two reactions, a proton-transfer reaction and a Schiff-base reaction, to occur in these experiments. The former was used to detect the aromatic amines, and the protonated analytes generated were selected for the qualitative and quantitative analysis. The false-positive signals were excluded by tandem mass spectrometry. For the 6 analytes, linear signal responses were obtained, and each had a dynamic range of 5 orders of magnitude. The relative standard deviation (RSD) and limit of detection (LOD) for all the measurements were in 1.5–5.3% and 0.03–0.2pg/mm2 range, respectively. The latter is a nucleophilic addition reaction that occurred between the aromatic amines and the acetone. The carbinolamine intermediates of these reactions were directly detected and identified by reactive DESI-MS. The data show that reactive DESI-MS is not only a reliable, sensitive tool for chemical analysis, but also a valid and promising method for studying organic reactions simultaneously, especially for heterogeneous reactions that occurred at a solution/solid interface.