Direct and simultaneous recognition of the positional isomers of aminobenzenesulfonic acid by TIMS-TOF-MS.

Positional isomer recognition is a challenging scientific issue. Fast and accurate detection of isomers is required for understanding their chemical properties. Here, we describe a method for simultaneous recognition of three positional isomers of 2-aminobenzenesulfonic acid (2-ABSA), 3-ABSA, and 4-ABSA using trapped ion mobility spectroscopy-time-of-flight mass spectrometry (TIMS-TOF-MS). The three ABSA positional isomers were recognized by measuring the different ion mobility of the ternary complexes of [ß-cyclodextrin (CD)+ABSA + Li]+ or [λ-CD + ABSA + Na]+, because their different collision cross-sections or different spatial conformations. The collision-induced dissociation mechanism of the different complexes of [ß-CD + ABSA + Li]+ and [λ-CD + ABSA + Na]+ using tandem mass spectrometry exhibited the same dissociation process with slightly different dissociation energies, which the smaller cross-section requires higher collision energy that means the smaller complex with tighter and more stable conformation than a larger complex for the ABSA complexes. In addition, relative quantification of the ABSA isomers was studied by measuring any two of the three ABSA isomer complexes at different molar ratio of 10:1 to 1:10 in the µM range, good linearity (R2 > 0.99) with precision between 2.14% and 2.58%, and accuracy ≥ 97.1% were obtained. The method for fast determination and recognition of ABSA positional isomers by combination with CD and alkali metal ions possesses the advantages of being simple, direct, rapid, sensitive, cost-effective, and needs no chemical derivatives or chromatographic separation before analysis. Therefore, the proposed method would be a powerful tool for the analysis of ABSA isomers or even other positional isomers.