Probing Polyester Branching by Hybrid Trapped Ion-Mobility Spectrometry–Tandem Mass Spectrometry

Abstract

Trapped ion-mobility spectrometry combined with quadrupole time-of-flight mass spectrometry (TIMS-QTOFMS) was evaluated as a tool for resolving linear and branched isomeric polyester oligomers. Solutions of polyester samples were infused directly into the ion source employing electrospray ionization (ESI). TIMS-MS provides both mobility and m / z data on the formed ions, allowing construction of extracted-ion mobilograms (EIMs). EIMs of polyester molecules showed multimodal patterns, indicating conformational differences among isomers. Subsequent TIMS-MS/MS experiments indicated mobility differences to be caused by (degree of) branching. These assignments were supported by liquid chromatography-TIMS-MS/MS analysis, confirming that direct TIMS-MS provided fast (500 ms/scan) distinction between linear and branched small oligomers. Observing larger oligomers (up to 3000 Da) using TIMS required additional molecular charging to ensure ion entrapment within the mobility window. Molecular supercharging was achieved using m -nitrobenzyl alcohol (NBA). The additional charges on the oligomer structures enhanced mobility separation of isomeric species but also added to the complexity of the obtained fragmentation mass spectra. This complexity could be partly reduced by post-TIMS analyte-decharging applying collision-induced dissociation (CID) prior to Q1 with subsequent isolation of the singly charged ions for further fragmentation. The as-obtained EIM profiles were still quite complex as larger molecules possess more possible structural isomers. Nevertheless, distinguishing between linear and symmetrically branched oligomers was possible based on measured differences in collisional cross sections (CCSs). The established TIMS-QTOFMS approach reliably allows branching information on isomeric polyester molecules up to 3000 Da to be obtained in less than 1 min analysis time.

Sequence distribution determination by SWAMP‐MS a systematic way of analyzing multiple fragmented polymers with mass spectrometry

“…Macromolecules (Mw = 5–10 kDa) were visualized using charge states of z = 1 and z = 4 32 . Voeten et al performed direct infusion and included trapped ion mobility spectrometry (TIMS)‐MS to elucidate complex sequences of branched, low molecular weight polyesters 33 . Recently, Nitsche et al investigated the ionization of carboxylic acid containing polystyrene generating [M‐H] − and [M‐H] 2− ions with m/z values of 8 kDa 34 .…”

“…32 Voeten et al performed direct infusion and included trapped ion mobility spectrometry (TIMS)-MS to elucidate complex sequences of branched, low molecular weight polyesters. 33 In this present work, a copolymerization model system (see Figure 1) was studied containing polyamide 4,6 (also named A: PA-4,6, consisting of diamino butane (DAB) and adipic acid (ADP)) and polyamide 4,10 (also named B: PA-4,10 consisting of DAB and sebacic acid (SEB)).…”