Multidimensional Mass Spectrometry of Multicomponent Nonionic Surfactant Blends

Ultraperformance liquid chromatography (UPLC) and ion mobility (IM) spectrometry were interfaced with mass spectrometry (MS) and tandem mass spectrometry (MS/MS) to characterize a complex nonionic surfactant mixture. The surfactant was composed of a glycerol core, functionalized with poly­(ethylene oxide) units (PEOn) that were partially esterified by caprylic and/or capric acid. Reversed-phase UPLC classified the blend based on polarity into four groups of eluates, corresponding to compounds with zero, one, two, or three fatty acid residues. Additional separation within each eluate group was achieved according to the length of the fatty acid chains. Coeluting molecules of similar polarity were dispersed in the gas phase by their collision cross section in the IM dimension. Performed in series, UPLC and IM allowed for the separation and detection of several isomeric and isobaric blend constituents, thereby enabling their isolation for conclusive MS/MS analysis to confirm or elucidate their primary structures and architectures (overall four-dimensional, 4D, characterization)

Supplemental material for Analysis of monodisperse, sequence-defined, and POSS-functionalized polyester copolymers by MALDI tandem mass spectrometry

Supplemental Material for Analysis of monodisperse, sequence-defined, and POSS-functionalized polyester copolymers by MALDI tandem mass spectrometry by Jialin Mao, Wei Zhang, Stephen ZD Cheng and Chrys Wesdemiotis in European Journal of Mass Spectrometry</p

Multidimensional Mass Spectrometry Coupled with Separation by Polarity or Shape for the Characterization of Sugar-Based Nonionic Surfactants

Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were interfaced with ultra-performance liquid chromatography (UPLC) and ion mobility (IM) separation to characterize a complex nonionic surfactant, consisting of a methylated glucose core (glucam) conjugated with poly­(ethylene oxide) (PEO_<i>n</i>) branches that were partially esterified with stearic acid to form ethoxylated glucam (PEO_<i>n</i>-glucam) stearates. Reverse-phase LC-MS afforded fast separation according to polarity into five major fractions. Accurate mass measurements of the ions in the mass spectra extracted from these fractions enabled conclusive identification of six components in the surfactant, including PEO_<i>n</i>-glucam mono-, di-, and tristearates as well as free and esterified PEO_<i>n</i> as byproducts. MS/MS experiments provided corroborating evidence for the fatty acid content in each fraction based on the number of stearic acid losses observed. With IM-MS, the total surfactant ions were separated according to charge and shape into four distinct bands. Extracted mass spectra confirmed the presence of two disaccharide stearates in the surfactant, which were undetectable by LC-MS. PEO_<i>n</i>-glucam tristearates were, however, not observed upon IM-MS. Hence, LC-MS and IM-MS unveiled complementary compositional insight. With each method, certain components were particularly well separated from other ingredients (by either polarity or shape), to be detected with confidence. Consequently, combined LC-MS and IM-MS offer a superior approach for the characterization of surfactants and other amphiphilic polymers and for the differentiation of similarly composed amphiphilic blends. It is finally noteworthy that NH₄⁺ charges minimized chemical noise in MS mode and Li⁺ charges maximized the fragmentation efficiency in MS/MS mode

Gradient Tandem Mass Spectrometry Interfaced with Ion Mobility Separation for the Characterization of Supramolecular Architectures

Traveling wave ion mobility mass spectrometry (TWIM MS) was combined with gradient tandem mass spectrometry (gMS2) to deconvolute and characterize superimposed ions with different charges and shapes formed by electrospray ionization (ESI) of self-assembled, hexameric metallomacrocycles composed of terpyridine-based ligands and CdII ions. ESI conditions were optimized to obtain intact hexameric cation assemblies in a low charge state (2+), in order to minimize overlapping fragments of the same mass-to-charge ratio. With TWIM MS, intact hexameric ions could be separated from remaining fragments and aggregates. Collisional activation of these hexameric ions at varying collision energies (gMS2), followed by TWIM separation, was then performed to resolve macrocyclic from linear hexameric species. Because of the different stabilities of these architectures, gMS2 changes their relative amounts, which can be monitored individually after subsequent ion mobility separation. On the basis of this unique strategy, hexameric cyclic and linear isomers have been successfully resolved and identified. Complementary structural information was gained by the gMS2 fragmentation pattern of the metallosupramolecules, acquired by collisionally activated dissociation after TWIM dispersion. TWIM MS interfaced with gMS2 should be particularly valuable for the characterization of a variety of supramolecular polymers, which often contain isomeric architectures that yield overlapping fragments and aggregates upon ESI MS analysis

Tandem Mass Spectrometry Characteristics of Silver-Cationized Polystyrenes: Backbone Degradation via Free Radical Chemistry

The [M + Ag]+ ions of polystyrene (PS) oligomers are formed by matrix-assisted laser desorption/ionization, and their fragmentation characteristics are determined by tandem mass spectrometry experiments in a quadrupole/time-of-flight mass spectrometer. Collisionally activated dissociation (CAD) of [M + Ag]+ starts with random homolytic CC bond cleavages in the PS chain, which generate radical ions carrying either the initiating (an•, bn•) or the terminating (yn•, zn•) chain end and primary (an•, yn•) or benzylic (bn•, zn•) radical centers. The fragments ultimately observed arise by consecutive, radical-induced dissociations. The primary radical ions mainly decompose by monomer evaporation and, to a lesser extent, by β-H• loss. The benzylic radical ions primarily decompose by 1,5-H rearrangement (backbiting) followed by β C−C bond scissions; this pathway leads to either closed-shell fragments with CH2 end groups, internal fragments with 2−3 repeat units, or truncated benzylic bn•/zn• radical ions that can undergo anew backbiting. The same internal fragments are produced in all backbiting steps; hence, these fragments and small benzylic radical ions (which cannot undergo backbiting) dominate the low-mass region of the CAD spectra, while the less abundant closed-shell fragments with CH2 end groups (an/yn) dominate the medium- and high-mass regions. The latter fragments are suitable for determining the individual initiating and terminating end groups, whereas the internal ions could be valuable in sequence analyses of styrene copolymers

Separation of Perfluorooctanoic Acid from Water Using Meso- and Macroporous Syndiotactic Polystyrene Gels

Per- and polyfluoroalkyl substances are an emerging class of contaminants that are environmentally persistent, bioaccumulative, and noxious to human health. Among these, perfluorooctanoic acid (PFOA) molecules are widely found in ground and surface water sources. A novel high surface area, meso- and macroporous syndiotactic polystyrene (sPS) wet gel is used in this work as the adsorbent of PFOA molecules from water at environmentally relevant PFOA concentrations (≤1 μg/L) and cleanse water to below the U.S. EPA’s 2023 health advisory limit of 4 parts per trillion (ppt). The sigmoidal shape of the PFOA adsorption isotherm indicates a two-step adsorption mechanism attributed to the strong affinity of PFOA molecules for the sPS surface and molecular aggregation at solid–liquid interfaces or within the pores of the sPS wet gel. The adsorption kinetics and the effects of sPS wet gel porosity, pore size, and pore volume on the removal efficiency are reported. The adsorption kinetics is seen to be strongly dependent on pore size and pore volume

Sequence Analysis of Styrenic Copolymers by Tandem Mass Spectrometry

Styrene and smaller molar amounts of either <i>m</i>-dimethylsilylstyrene (<i>m</i>-DMSS) or <i>p</i>-dimethylsilylstyrene (<i>p</i>-DMSS) were copolymerized under living anionic polymerization conditions, and the compositions, architectures, and sequences of the resulting copolymers were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS²). MS analysis revealed that linear copolymer chains containing phenyl–Si­(CH₃)₂H pendants were the major product for both DMSS comonomers. In addition, two-armed architectures with phenyl–Si­(CH₃)₂–benzyl branches were detected as minor products. The comonomer sequence in the linear chains was established by MS² experiments on lithiated oligomers, based on the DMSS content of fragments generated by backbone C–C bond scissions and with the help of reference MS² spectra obtained from a polystyrene homopolymer and polystyrene end-capped with a <i>p</i>-DMSS block. The MS² data provided conclusive evidence that copolymerization of styrene/DMSS mixtures leads to chains with a rather random distribution of the silylated comonomer when <i>m</i>-DMSS is used, but to chains with tapered block structures, with the silylated units near the initiator, when <i>p</i>-DMSS is used. Hence, MS² fragmentation patterns permit not only differentiation of the sequences generated in the synthesis, but also the determination of specific comonomer locations along the polymer chain

Conformational Characterization of Polyelectrolyte Oligomers and Their Noncovalent Complexes Using Ion Mobility-Mass Spectrometry

Poly-l-lysine (PLL), polystyrenesulfonate (PSS), and a mixture of these polyelectrolytes were investigated by electrospray ionization ion mobility mass spectrometry. The IM step confirmed the formation of noncovalent (i.e., supramolecular) complexes between these polyelectrolytes, which were detected in various charge states and stoichiometries in the presence of their constituents. Experimental and theoretical collision cross sections (CCSs) were derived for both PLL and PSS oligomers as well as their noncovalent assemblies. PSS chains showed higher compactness with increasing size as compared to PLL chains, indicating that the intrinsic conformations of the polyelectrolytes depend on the nature of the functional groups on their side chains. The CCS data for the noncovalent complexes further revealed that assemblies with higher PLL content have higher CCS values than other compositions of similar mass and that PLL–PSS complex formation is accompanied by significant size contraction

Poly(ethylene glycol) Hydrogel Crosslinking Chemistries Identified via Atmospheric Solids Analysis Probe Mass Spectrometry

Hydrogels are hydrophilic, crosslinked polymer networks that can absorb several times their own mass in water; they are frequently used in biomedical applications as a native tissue mimic. The characterization of hydrogels and other covalently crosslinked networks is often limited by their insolubility and infinite molecular weight conferred by crosslinking. In this study, chemically crosslinked hydrogel materials based on poly­(ethylene glycol) (PEG) have been characterized directly, without any sample preparation, by mild thermal degradation using atmospheric solids analysis probe mass spectrometry (ASAP-MS) coupled with ion mobility (IM) separation and tandem mass spectrometry (MS/MS) characterization of the degradants. The structural insight gained from these experiments is illustrated with the analysis of oxime-crosslinked PEG hydrogels formed by the click reaction between 4-arm PEG star polymers with either ketone or aminooxy end group functionalities and PEG dimethacrylate (PEGDMA) copolymeric hydrogel networks formed by photopolymerization of PEGDMA. The ASAP-MS, IM, and MS/MS methods were combined to identify the crosslinking chemistry and obtain precursor chemistry information retained in the end-group substituents of the thermal degradation products