A generic strategy based on gas phase decomposition of protonated and ammoninted precursors producing predictable MRM-MS ion pairs and collision energies for direct analysis of plant triterpene glycosides

Optimization of multiple reaction monitoring mass spectrometry (MRM-MS) parameters of triterpene glycosides (TGs) using traditional infusion methods remains to be labor-intensive. However, it was found that mild gas phase decompositions of protonated and ammoninted precursors (DPAP) of TGs could produce a series of abundant dehydrated product ions of aglycones ([A+H-nH₂O]⁺ (n = 0, 1, 2, 3…)) with high efficiency and stability. Based on these considerations and findings, an innovative ESI⁺-MRM-DPAP-MS strategy was devised on a QTRAP 4000 instrument allowing for rapid the qualitative and quantitative analysis of plant TGs. A detailed study of 85 model compounds from 20 herbal medicines was implemented for validation and evaluation of the ESI⁺-MRM-DPAP-MS strategy proposed. The central composition design confirmed that collision energy (CE) played more significant roles than declustering potentials (DP) for the formation of these Q₁/Q₃ ion pairs based on MRM-DPAP-MS. It is also noted that Q₁ and M_w were the most important factors for the prediction of CE values by a partial least square regression model. Here, we demonstrated this generic workflow and its merits in: (1) early prediction and selection of MRM ion pairs, no matter which type of TGs, employing a new-found Q₁/Q₃ calculation formula (Q₁=[M+H/NH₄]⁺ and Q₃= [A+H-nH₂O]⁺ (n = 0, 1, 2, 3…)); (2) direct determination of practicable CE values using TGs-specific CE-estimating linear equations; (3) appearances of excellent sensitivity, stability and repeatability through real application in Aralia elata, Panax notoginseng and Caulophyllum robustum; (4) seamless application of optimal CE parameters in other triple quadrupole MS instruments such as Thermo TSQ Quantum Ultra. The ESI⁺-MRM- DPAP-MS may service as an effective and feasible approach for analytical characterization of biological TGs from herbal medicines.