Mass Spectrometry of Synthetic Polymers

Tandem Mass Spectrometry Reflects Architectural Differences in Analogous, Bis-MPA-Based Linear Polymers, Hyperbranched Polymers, and Dendrimers

The growing use of branched polymers in various industrial and technological applications has prompted significant interest in understanding their properties, for which accurate structure determination is vital. This work is the first instance where the macromolecular structures of dendrimers, linear polymers, and hyperbranched polymers with analogous 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) backbone groups were synthesized and analyzed via tandem mass spectrometry (MS/MS). When comparing the fragmentation pathways of these polymers, some unique and interesting patterns emerge that provide insight into the primary structures and architectures of each of these materials. As expected, the linear polymer undergoes multiple random backbone cleavages resulting in several fragment ion distributions that vary in size and end group composition. The hyperbranched polymer dissociates preferentially at branching sites; however, differently branched isomers exist for each oligomer size, thus giving rise again to several fragment distributions. In contrast, the dendrimer presents a unique fragmentation pattern comprising key fragment ions of high molecular weight; this unique characteristic stands out as a signature for identifying dendrimer structures. Overall, dendrimers, hyperbranched polymers, and linear polymers display individualized fragmentation behaviors, which are caused by differences in primary structure. As a result, tandem mass spectrometry fragmentation is a particularly useful analytical tool for distinguishing such macromolecular architectures.

The alarming link between environmental microplastics and health hazards with special emphasis on cancer

Microplastic contamination is a burgeoning environmental issue that poses serious threats to animal and human health. Microplastics enter the human body through nasal, dermal, and oral routes to contaminate multiple organs. Studies have advocated the existence of microplastics in human breast milk, sputum, faeces, and blood. Microplastics can find their ways to the sub-cellular moiety via active and passive approaches. At cellular level, microplastics follow clathrin and caveolae-dependent pathways to invade the sub-cellular environment. These environmental contaminants modulate the epigenetic control of gene expression, status of inflammatory mediators, redox homeostasis, cell-cycle proteins, and mimic the endocrine mediators like estrogen and androgen to fuel carcinogenesis. Furthermore, epidemiological studies have suggested potential links between the exposure to microplastics and the onset of various chronic diseases. Microplastics trigger uncontrolled cell proliferation and ensue tissue growth leading to various cancers affecting the lungs, blood, breasts, prostate, and ovaries. Additionally, such contamination can potentially affect sub-cellular signaling and injure multiple organs. In essence, numerous reports have claimed microplastic-induced toxicity and tumorigenesis in human and model animals. Nonetheless, the underlying molecular mechanism is still elusive and warrants further investigations. This review provides a comprehensive analysis of microplastics, covering their sources, chemistry, human exposure routes, toxicity, and carcinogenic potential at the molecular level.

Polystyrene Chain Geometry Probed by Ion Mobility Mass Spectrometry and Molecular Dynamics Simulations

Polystyrene (PS) is a thermoplastic polymer commonly used in various applications due to its bulk properties. Designing functional polystyrenes with well-defined structures for targeted applications is of significant interest due to the rigid and apolar nature of the polymer chain. Progress is hindered to date by the limitations of current analytical methods in defining the atomistic-level folding of the polymer chain. The integration of ion mobility spectrometry and molecular dynamics simulations is beneficial in addressing these challenges. However, data on gas-phase polystyrene ions are rarely reported in the literature. We herein investigate the gas phase structure of polystyrene ions with different end groups to establish how the nature and the rigidity of the monomer unit affect the charge stabilization. We find that, in contrast to polar polymers in which the charges are located deep in the ionic globules, the charges in the PS ions are rather located at the periphery of the polymer backbone, leading to singly and doubly charged PS ions adopting dense elliptic-shaped structures. Molecular dynamics (MD) simulations indicate that the folding of the PS rigid chain is controlled by phenyl ring interactions with the charge ultimately remaining excluded from the core of the globular ions, whereas the folding of polyether ions is initiated by the folding of the flexible polyether chain around the sodium ion that remains deeply enclosed in the core of the ions.

Mass spectrometry of dendrimers

Mass spectrometry (MS) has become an essential technique to characterize dendrimers as it proved efficient at tackling analytical challenges raised by their peculiar onion-like structure. Owing to their chemical diversity, this review covers benefits of MS methods as a function of dendrimer classes, discussing advantages and limitations of ionization techniques, tandem mass spectrometry (MS/MS) strategies to determine the structure of defective species, as well as most recently demonstrated capabilities of ion mobility spectrometry (IMS) in the field. Complementarily, the well-defined structure of these macromolecules offers major advantages in the development of MS-based method, as reported in a second section reviewing uses of dendrimers as MS and IMS calibration standards and as multifunctional charge inversion reagents in gas phase ion/ion reactions.

Complex Spectroscopy Studies of Nifedipine Photodegradation

The aim of this work is to highlight the influence of UV light on the hydrolysis reaction of nifedipine (NIF) in the presence of alkaline solutions. In this context, the photodegradation of NIF in the absence of alkaline solutions caused (a) a change in the ratio between the absorbances of three bands in the UV-VIS spectra localized at 224-240 nm, 272-276 nm and 310-340 nm, assigned to the electronic transitions of -COOCH3 groups, -NO2 groups and a heterocycle with six atoms; (b) a red-shift of the photoluminescence (PL) band from 458 nm to 477 nm, simultaneous with an increase in its intensity; (c) a decrease in the ratio of the Raman line intensities, which peaked at 1224 cm-1 and 1649 cm-1, associated with the vibrational modes of -C-C-O in the ester group and C=C stretching; and (d) a decrease in the ratio between the absorbances of the IR bands, which peaked at 1493 cm-1 and 1223 cm-1, associated with the vibrational modes of the -NO2 group and C-N stretching. These changes were explained considering the NIF photodegradation reaction, which leads to the generation of the compound 4-(2-nitrosophenyl)-2.6-dimethyl-3.5-dimethoxy carbonyl pyridine. The interaction of NIF with NaOH in the absence of UV light was demonstrated to induce changes in the vibrational mode of the -C-C-O bond in the ester group. The photodegradation of NIF after its reaction with NaOH induces significant changes highlighted in its (a) UV-VIS spectra, by the shift of the absorption band at 238 nm; (b) PL spectra, by the supraunitary value of the ratio between the emission band intensities at 394-396 nm and 450 nm; (c) Raman spectra, by the change in the ratio between the intensities of the lines that peaked at 1224 cm-1 and 1649 cm-1 from 0.61 to 0.49; and (d) FTIR spectra, by the lowered absorbance of the IR band at 1493 cm-1 assigned to the vibrational mode of the -NO2 group as a result of the generation of the nitroso compound. These changes were explained considering the hydrolysis reaction products of NIF, as the nitroso compound is converted to a lactam-type compound. The photodegradation reaction rate constants of NIF and NIF after interaction with NaOH were also reported. The decrease in thermal stability of NIF samples after interaction with NaOH, as well as of NIF after exposure to UV light compared to NIF prior to exposure to UV light, was demonstrated by thermogravimetry, and the key fragments were confirmed by mass spectrometry.

Gas-phase structure of polymer ions: Tying together theoretical approaches and ion mobility spectrometry

An increasing number of studies take advantage of ion mobility spectrometry (IMS) coupled to mass spectrometry (IMS-MS) to investigate the spatial structure of gaseous ions. Synthetic polymers occupy a unique place in the field of IMS-MS. Indeed, due to their intrinsic dispersity, they offer a broad range of homologous ions with different lengths. To help rationalize experimental data, various theoretical approaches have been described. First, the study of trend lines is proposed to derive physicochemical and structural parameters. However, the evaluation of data fitting reflects the overall behavior of the ions without reflecting specific information on their conformation. Atomistic simulations constitute another approach that provide accurate information about the ion shape. The overall scope of this review is dedicated to the synergy between IMS-MS and theoretical approaches, including computational chemistry, demonstrating the essential role they play to fully understand/interpret IMS-MS data.

Mechanical and Structural Properties of Polyhydroxybutyrate as Additive in Blend Material in Additive Manufacturing for Medical Applications

Today, additive manufacturing (AM) is considered one of the vital tenets of the industry 4.0 revolution due to its high productivity, decentralized production and rapid prototyping. This work aims to study the mechanical and structural properties of polyhydroxybutyrate as an additive in blend materials and its potential in medical applications. PHB/PUA blend resins were formulated with 0 wt.%, 6 wt.%, 12 wt.% and 18 wt.% of PHB concentration. Stereolithography or an SLA 3D printing technique were used to evaluate the printability of the PHB/PUA blend resins. Additionally, from FESEM analysis, a change was observed in PUA's microstructure, with an additional number of voids spotted. Furthermore, from XRD analysis, as PHB concentration increased, the crystallinity index (CI) also increased. This indicates the brittleness properties of the materials, which correlated to the weak performance of the tensile and impact properties. Next, the effect of PHB loading concentration within PHB/PUA blends and aging duration towards the mechanical performance of tensile and impact properties was also studied by using analysis of variance (ANOVA) with a two-way method. Finally, 12 wt.% of PHB/PUA was selected to 3D print the finger splint due to its characteristics, which are compatible to be used in finger bone fracture recovery.

Analytical methods for microplastics in the environment: a review

Microplastic pollution is a recently discovered threat to ecosystems requiring the development of new analytical methods. Here, we review classical and advanced methods for microplastic analysis. Methods include visual analysis, laser diffraction particle, dynamic light scattering, scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, thermal analysis, mass spectrometry, aptamer and in vitro selection, and flow cytometry.

Progress on the development of a metal salt-assisted ionization source for the mass spectrometric analysis of polymers

The mass spectrometric analysis of polymers has been addressed as a challenging research topic due to poor ionization and complicated analysis using conventional mass spectrometry. The ionization source has demonstrated a promising future in rapid mass spectrometric analysis. Soft ionization techniques, such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) are the most ionization sources appeared to be a powerful tools for polymer characterization when combined with MS. However, they always need metal salts to be introduced during the ionization protocol for polymers due to the crucial role played by their ions (cations and anions). The current review focuses on the progress in the development of metal ion-assisted-ionization sources for the mass spectrometric analysis of polymers. Different ionization systems are comprehensively reviewed. The application of metal ion-assisted ESI, nanoESI, PSI, and MALDI-MS for polymer sample analyses is systematically discussed. The future research trends and challenges in this cutting-edge research field are summarized. It also aims to provide the current state-of-the-art of metal salts as a platform for ionization systems for the mass spectrometric characterization of polymers and offers the current challenges and perspectives on the promising future to improve analytical performance in this field. Finally, this mini-review provides a comprehensive handbook to researchers from different research backgrounds wishing to work in this area.

Correlated studies of photoluminescence, vibrational spectroscopy and mass spectrometry concerning the pantoprazole sodium photodegradation

In this work, new optical evidences concerning the changes induced of the UV light on pantoprazole sodium (PS), in solid state and as aqueous solution, are reported by UV-VIS spectroscopy, photoluminescence (PL), Raman scattering and FTIR spectroscopy. New evidences concerning the products of the PS photodegradation pathways are reported by the correlated studies of thermogravimetry and mass spectrometry. The influence of the excipients and alkaline medium on the PS photodegradation is also studied. New aspects regarding the chemical mechanism of the PS photodegradation in the presence of the water vapor and oxygen form air and the alkaline medium are shown. Our results confirm that the PS photodegradation induced of the water vapors and oxygen from air leads to the generation of 5-difluoromethoxy-3H-benzimidazole-2-thione sodium, 5-difluoromethoxy-3H-benzimidazole sodium, 2-thiol methyl-3, 4-dimethoxypyridine and 2-hydroxymethyl-3, 4-dimethoxypyridine, while in the alkaline medium, compounds of the type of the 2-oxymethyl-3,4-dimethoxypyridine sodium salts are resulted.

Development of a peak extraction method using the high-resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and machine learning techniques: Analysis of peak shapes

RATIONALE

Combining matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and Kendrick mass defect (KMD) analysis is a powerful tool for visualizing polymers in complex mass spectra. The identification of minor polymers by KMD analysis requires reduction of the broad noise peaks often observed in the low-mass region.

METHODS

A machine-learning model was created using pix2pixHD. It converts an original mass spectrum into a pseudo-mass spectrum that contains only the original peaks at m/z positions that the model judges as sharp single-component peaks. It reduces noise by selecting only the m/z and intensity values from the original spectrum's peak list that correspond to peaks in the pseudo-mass spectrum.

RESULTS

A machine-learning model was applied to a low-concentration polymer mass spectrum observed at m/z <2000. Extracting single-component peaks from the mass spectrum made the minor polymer series appear clearly in the KMD plot. The technique facilitated mass spectrometric imaging of the ultraviolet degradation of polyethylene terephthalate by plotting the polymers' spatial distributions. It could also distinguish between polymer series (before and after degradation) to identify their separate spatial distributions.

CONCLUSIONS

A machine-learning method for peak extraction from high-resolution MALDI-TOFMS was developed. Single-component peaks of the mass spectrum were distinguished from noise peaks by their peak shapes. Combining with KMD analysis facilitated the identification of minor polymer series in complex mass spectra.

End group analysis of poly(methylmethacrylate)s using the most abundant peak in electrospray ionization-ion mobility spectrometry-tandem mass spectrometry and Fourier transform-based noise filtering

RATIONALE

We recently developed the characterization method for synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization-ion mobility spectrometry-tandem mass spectrometry, in which the m/z value of the most abundant peak was used for characterization. However, the identification of the most abundant peak from the isotopic peaks was often difficult due to the background noise.

METHODS

Here, we employed a noise reduction method using Fourier transform (FT) filtering. In the power spectrum obtained using FT of the mass spectrum of the multiple charged analytes, the significant signals in the low-frequency region and at frequency z are observed for the analytes of z charges. When the signals in both regions were used for inversed FT (i.e., the signals in other regions were zero padded), a noise-filtered mass spectrum was obtained.

RESULTS

In the analysis of poly(methylmethacrylate)s weighing 13-17 kDa, mass spectra without noise filtering with relatively high-intensity noise (than signal) were complicated to identify the most abundant peak. On the contrary, the most abundant peak was clearly identified from the mass spectra after FT-based noise filtering, and end group composition was estimated successfully.

CONCLUSIONS

The proposed FT-based noise filtering for the mass spectrum is effective to characterize multiply charged synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization-ion mobility spectrometry-tandem mass spectrometry.

Characteristics, Toxic Effects, and Analytical Methods of Microplastics in the Atmosphere

Microplastics (MPs) (including nanoplastics (NPs)) are pieces of plastic smaller than 5 mm in size. They are produced by the crushing and decomposition of large waste plastics and widely distributed in all kinds of ecological environments and even in organisms, so they have been paid much attention by the public and scientific community. Previously, several studies have reviewed the sources, occurrence, distribution, and toxicity of MPs in water and soil. By comparison, the review of atmospheric MPs is inadequate. In particular, there are still significant gaps in the quantitative analysis of MPs and the mechanisms associated with the toxic effects of inhaled MPs. Thus, this review summarizes and analyzes the distribution, source, and fate of atmospheric MPs and related influencing factors. The potential toxic effects of atmospheric MPs on animals and humans are also reviewed in depth. In addition, the common sampling and analysis methods used in existing studies are introduced. The aim of this paper is to put forward some feasible suggestions on the research direction of atmospheric MPs in the future.

Identification and removal of micro- and nano-plastics: Efficient and cost-effective methods

Microplastics (MPs) and nanoplastics (NPs) have gained much attention in recent years because of their ubiquitous presence, which is the widely acknowledged threat to the environment. MPs can be <5 mm size, while NPs are <100 nm, and both can be detected in various forms and shapes in the environment to alleviate their harmful effects on aquatic species, soil organisms, birds, and humans. In efforts to address these issues, the present review discusses about sampling methods for water, sediments, and biota along with their merits and demerits. Various identification techniques such as FTIR, Raman, ToF-SIMS, MALDI TOF MS, and ICP-MS are critically discussed. The detrimental effects caused by MPs and NPs are discussed critically along with the efficient and cost-effective treatment processes including membrane technologies in order to remove plastics particles from various sources to mitigate their environmental pollution and risk assessment.

Side-chain fluorotelomer-based polymers in children car seats

Fabric and foam samples from popular children car seats marketed in the United States during 2018 were tested for fluorine content by particle-included gamma ray emission spectroscopy (PIGE, n = 93) and X-ray photoelectron spectroscopy (XPS, n = 36), as well as for per- and polyfluoroalkyl substances (PFAS) by liquid and gas chromatography mass spectrometry (LC/MS and GC/MS, n = 36). PFAS were detected in 97% of the car seat samples analyzed with MS, with total concentrations of 43 PFAS (∑PFAS) up to 268 ng/g. Fabric samples generally had greater ∑PFAS levels than foam and laminated composites of foam and fabric. The three fabric samples with the highest total fluorine content as represented by the highest PIGE signal were also subjected to ultraviolet (UV) irradiation and the total oxidizable precursor (TOP) assay. Results from these treatments, as well as the much higher organofluorine levels measured by PIGE compared to LC/MS and GC/MS, suggested the presence of side-chain fluorotelomer-based polymers (FTPs), which have the potential to readily degrade into perfluoroalkyl acids (PFAAs) under UV light. Furthermore, fluorotelomer (meth)acrylates were found to be indicators for the presence of (meth)acrylate-linked FTPs in consumer products, and thus confirmed that at least half of the tested car seats had FTP-treated fabrics. Finally, extraction of selected samples with synthetic sweat showed that ionic PFAS, particularly those with fluorinated carbons ≤8, can migrate from fabric to sweat, suggesting a potential dermal route of exposure.

Assessing the Structural Heterogeneity of Isomeric Homo and Copolymers: an Approach Combining Ion Mobility Mass Spectrometry and Molecular Dynamics Simulations

Synthetic polymers occupy a unique place in the field of ion mobility mass spectrometry (IMS-MS). Indeed, due to their intrinsic dispersity, they have the asset to offer a broad range of homologous ions with different lengths that can be detected in several charge states. In addition, the gas-phase structure of polymer ions mostly depends on their ability to screen the adducted charges. Several works dealing with linear, cyclic, and star-shaped polymers have already shown that the gas-phase structure of polymer ions heavily relies on the polymer architecture, i.e., the primary structure. In the present work, we move a step further by evaluating whether a relationship exists between the primary and secondary structures of synthetic homo and copolymers. The IMS-MS experiments will be further complemented by MD simulations. To highlight the effectiveness of IMS separation, we selected isomeric homo and copolymers made of lactide (LA) and propiolactone (PL) units. In this way, the mass analysis becomes useless since isomeric comonomer sequences can coexist for any given chain length. An UPLC method was implemented in the workflow to successfully separate all PL-LA comonomer sequences before infusion in the IMS-MS instrument. The analysis of doubly charged copolymers showed that the comonomer sequence has an impact on the IMS response. However, this only holds for copolymer ions with precise sizes and charge states, and this is therefore not a rule of thumb.

Application of a novel cyclic ion mobility-mass spectrometer to the analysis of synthetic polymers: A preliminary evaluation

RATIONALE

Mass spectrometry (MS) is often employed in the characterisation of synthetic polymers. As polymer architecture becomes more complex, ion mobility (IM) is increasingly being coupled with MS to provide an additional dimension of separation, along with structural information. In this study, we explore the use of a novel cyclic ion mobility (cIM) mass spectrometer for the analysis of a co-polymer sample.

METHODS

A solution of poly(ethylene glycol)-poly(propylene glycol) random co-polymer (PEG-ran-PPG) was used as a representative polymer sample. The solution was infused into a cIM-enabled quadrupole time-of-flight mass spectrometer. An m/z region of interest, selected using the quadrupole, was passed around the cIM device multiple times. Subsequently, regions of an arrival time distribution were 'sliced' and subjected to tandem mass spectrometric (MS/MS) analysis.

RESULTS

Typical, multiply charged series were observed for the polymer under electrospray ionisation. Multiple passes of the cIM device resulted in the separation of otherwise-overlapping charge states within a narrow m/z window (~3 m/z units), allowing individual selection of ions. These isolated ions were then subjected to post-mobility fragmentation resulting in clean, high-resolution product ion spectra, with a significant reduction in interference.

CONCLUSIONS

Scalable IM separation (IMS), brought about by passing ions multiple times around the cIM device, was demonstrated to provide increased IM resolution for ions in the selected m/z window. After multiple passes, deconvoluted high-resolution MS/MS product ion spectra were successfully acquired for ions that previously had interfering overlapping species present.

A mass spectrometry imaging method for visualizing synthetic polymers by using average molecular weight and dispersity as indices

RATIONALE

Matrix-assisted laser desorption/ionization mass spectrometric imaging (MSI) is considered to be a powerful tool for visualizing the spatial distribution of synthetic polymers. However, a conventional method extracting an image of a specific m/z value is not suitable for polymers, which have a mass distribution. It is necessary to develop the visualization method to show the spatial distribution of entire polymer series.

METHODS

The mass peaks included in polymer series were specified from the average mass spectrum of the entire MSI measurement region by using Kendrick mass defect analysis. The images of those mass peaks were extracted and the number average molecular weight (M_n ), the weight average molecular weight (M_w ) and dispersity (Đ) were calculated for each pixel. Finally, the spatial distribution of the polymer series was summarized to images using M_n , M_w and Đ as indices.

RESULTS

The effects of the methods were investigated by (i) polymers with different mass distributions and (ii) polymers with different repeat units and end-groups. In both cases, the spatial distribution of specific polymer series including several dozens to hundreds of mass peaks was summarized into three images related to M_n , M_w and Đ, which are familiar indices in polymer analysis. The results are able to provide an overview of the spatial variation of each polymer more intuitively.

CONCLUSIONS

The visualization of M_n , M_w and Đ will help provide an overview of the spatial distribution of polymer series combined with ion intensity distribution made by conventional methods. It can be also applied to other mass spectrometric imaging methods such as desorption electrospray ionization (DESI) or time-of-flight secondary ion mass spectrometry (TOF-SIMS).

Characterization of microstructures and reaction mechanisms of Tröger's base polymers of intrinsic microporosity

RATIONALE

Tröger's base polymers of intrinsic microporosity (PIMs) are receiving increasing attention for applications such as polymer molecular sieve membranes. Development of novel membrane materials requires microstructure analysis in order to overcome processing and applications challenges. This study aims to address these challenges and overcome some of the solubility/aggregation issues that hinder the analysis of these materials.

METHODS

A combination of matrix-assisted laser desorption/ionization mass spectrometry and collision-induced dissociation was used to examine the reaction products of unfunctionalized Tröger's base PIMs.

RESULTS

Enhanced data mining, using ultrahigh-resolution mass spectrometry and statistical analysis, yielded a wealth of information on the molecular mass, chemical connectivity, and end groups of species generated during synthesis. Modifications of interest include N-methyl, N-methanimine, N-formyl, and N-methylol end-capping moieties, as well as incomplete backbone methanodiazocine rings with missing bridging methylene linkages. Most importantly, a general fragmentation mechanism, supported by computational modeling, was developed to assist in the rapid identification of main-chain and end-group modifications in Tröger's base PIMs.

CONCLUSIONS

Unfunctionalized Tröger's base polymers were selected as a model system, to thoroughly study their end-group modification chemistry. This model system could then be used to gain insights into complex hydroxy-functional PIM materials.

New mass spectrometry concepts for characterization of synthetic polymers and additives

RATIONALE

New ionization processes have been developed for biological mass spectrometry (MS) in which the matrix lifts the nonvolatile analyte into the gas phase as ions without any additional energy input. We rationalized that additional fundamental knowledge is needed to assess analytical utility for the field of synthetic polymers and additives.

METHODS

Different mass spectrometers (Thermo Orbitrap (Q-)Exactive (Focus); Waters SYNAPT G2(S)) were employed. The formation of multiply charged polymer ions upon exposure of the matrix/analyte(/salt) sample to sub-atmospheric pressure directly from the solid state and surfaces facilitates the use of advanced mass spectrometers for detection of polymeric materials including consumer products (e.g., gum).

RESULTS

Astonishingly, using nothing more than a small molecule matrix compound (e.g., 2-methyl-2-nitropropane-1,3-diol or 3-nitrobenzonitrile) and a salt (e.g., mono- or divalent cation(s)), such samples upon exposure to sub-atmospheric pressure transfer nonvolatile polymers and nonvolatile salts into the gas phase as multiply charged ions. These successes contradict the conventional understanding of ionization in MS, because can nonvolatile polymers be lifted in the gas phase as ions not only by as little as a volatile matrix but also by the salt required for ionizing the analyte through noncovalent metal cation adduction(s). Prototype vacuum matrix-assisted ionization (vMAI) and automated sources using a contactless approach are demonstrated for direct analyses of synthetic polymers and plasticizers, minimizing the risk of contamination using direct sample introduction into the mass spectrometer vacuum.

CONCLUSIONS

Direct ionization methods from surfaces without the need of high voltage, a laser, or even applied heat are demonstrated for characterization of detailed materials using (ultra)high-resolution and accurate mass measurements enabled by the multiply charged ions extending the mass range of high-performance mass spectrometers and use of a split probe sample introduction device. Our vision is that, with further development of fundamentals and dedicated sources, both spatial- and temporal-resolution measurements are within reach if sensitivity is addressed for decreasing sample-size measurements.

Weighing synthetic polymers of ultra-high molar mass and polymeric nanomaterials: What can we learn from charge detection mass spectrometry?

Advances in soft ionization techniques for mass spectrometry (MS) of polymeric materials make it possible to determine the masses of intact molecular ions exceeding megadaltons. Interfacing MS with separation and fragmentation methods has additionally led to impressive advances in the ability to structurally characterize polymers. Even if the gap to the megadalton range has been bridged by MS for polymers standards, the MS-based analysis for more complex polymeric materials is still challenging. Charge detection mass spectrometry (CDMS) is a single-molecule method where the mass and the charge of each ion are directly determined from individual measurements. The entire molecular mass distribution of a polymer sample can be thus accurately measured. Described in this perspective paper is how molecular weight distribution as well as charge distribution can provide new insights into the structural and compositional studies of synthetic polymers and polymeric nanomaterials in the megadalton to gigadalton range of molecular weight. The recent multidimensional CDMS studies involving couplings with separation and dissociation techniques will be presented. And, finally, an outlook for the future avenues of the CDMS technique in the field of synthetic polymers of ultra-high molar mass and polymeric nanomaterials will be provided.

Mass spectrometry in bioresorbable polymer development, degradation and drug-release tracking

A detailed characterization of polymeric matrices and appropriate degradation monitoring techniques are required to sustain the development of new materials as well as to enlarge the applications of the old ones. In fact, polymer analysis is essential for the clarification of the intrinsic relationship between structure and properties that ascertains the industrial applications in diverse fields. In bioresorbable and biodegradable polymers, the role of analytical methods is dual since it is pointed both at the polymeric matrices and at degradation tracking. The structural architectures, the mechanical and morphological properties, and the degradation rate, are of outstanding importance for a specific application. In some cases, the complexity of the polymer structure, the processes of decomposition or the low concentration of the degradation products need the concurrent use of different complementary analytical techniques to give detailed information of the reactions taking place. Several analytical methods are used in bioresorbable polymer development and degradation tracking. Among them, mass spectrometry (MS) plays an essential role and it is used to refine polymer syntheses, for its high sensitivity, to highlight degradation mechanism by detecting compounds present in trace amounts, or to track the degradation product profile and to study drug release. In fact, elucidation of reaction mechanisms and polymer structure, attesting to the purity and detecting defects as well as residual catalysts, in biodegradable and bioresorbable polymers, requires sensitive analytical characterization methods that are essential in providing an assurance of safety, efficacy and quality. This review aims to provide an overview of the MS strategies used to support research and development of resorbable polymers as well as to investigate their degradation mechanisms. It is focused on the most significant studies concerning synthetic bioresorbable matrices (polylactide, polyglycolide and their copolymers, polyhydroxybutyrate, etc.), published in the last ten years.

Composition and charge state influence on the ion-neutral collision cross sections of protonated N-linked glycopeptides: an experimental and theoretical deconstruction of coulombic repulsion vs. charge solvation effects

Ion mobility spectrometry (IMS) is of significant interest as a platform for glycoanalysis. While much attention has been focused on the resolution of isomeric carbohydrates and glycoconjugates, another appealing aspect of IMS is the ability to sort different classes of biomolecules into distinct regions of mass vs. mobility space. This capability has potential to greatly simplify glycoproteomic analyses, as glycosylated and non-glycosylated peptides can be rapidly partitioned in the gas phase. Nevertheless, the physical and chemical characteristics of glycopeptides that dictate their mass vs. mobility loci have yet to be systematically investigated. This report presents an IMS study of model protonated glycopeptide ions with systematically varied oligosaccharide topologies, polypeptide sequences, and charge states. In all, over 110 ion-neutral collision cross sections (CCSs) were measured and analyzed in the context of the physicochemical characteristics of the analytes. Glycan size and composition emerged as a decisive factor in dictating the CCS space occupied by the glycopeptides and exerted this influence in a charge state dependent fashion. Furthermore, elongation of the glycan group was found to either increase or decrease glycopeptide CCSs depending on the ion charge state and the size of the glycan. Molecular dynamics (MD) simulations of the gas phase structures and CCSs of selected glycopeptides revealed that the experimental observations were consistent with a glycan size and charge state dependent interplay between destabilizing coulombic repulsion effects (tending to result in more extended structures) and stabilizing charge solvation effects in which the glycan plays a major role (tending to result in more compact structures). Taken together, these IMS and MD findings suggest the possibility of predicting and delineating glycopeptide-enriched regions of mass vs. mobility space for applications in glycoproteomics.

Easily readable palindromic sequence-defined polymers built by cascade thiol-maleimide Michael couplings

The rational combination of cascade thiol-maleimide Michael couplings (CTMMC) with iterative exponential chain growth was demonstrated as an efficient way to synthesize palindromic sequence-defined polymers.

Metal salt assisted electrospray ionization mass spectrometry for the soft ionization of GAP polymers in negative ion mode

Glycidyl azide polymers (GAP) are one of the most important energetic polymers, but it is still a challenge to elucidate their structures using mass spectrometry due to their fragility upon ionization. Herein we developed a soft metal salt assisted electrospray ionization (MSAESI) to characterize directly GAP polymers using mass spectrometry. This technique combines paper spray ionization and the complexing effect of anions from metal salts with GAP in the negative ion mode to softly ionize GAP polymers prior to mass spectrometry analysis. The effects of experimental parameters (e.g., ion mode, applied voltage, and type and concentration of metal salts) have been investigated in detail. In contrast to the positive ion mode, a softer ionization was observed for GAP polymers when the negative ion mode was applied. The radius and average charge of cations and anions in metal salts were found to play crucial roles in determining the performance of the MSAESI analysis of GAP. For a given charge number, a smaller radius of cations favored the soft ionization of GAP polymers (e.g., Na+ > K+ > Rb+), whereas a larger radius of anions led to a preferred performance (e.g., F- < Cl- < Br- < I-) due to variation in dissolution ability. For anions with multiple charges, the ones with fewer charges gave a more favorable ionization to the GAP sample because of their better complexing to GAP molecules than those with more charges in the structure of anions (e.g., NO3- > SO42- > PO43-). According to the experimental observation and evidence from mass spectrometry, we proposed the plausible electrospray mechanisms of MSAESI for GAP analysis with the involvement of metal salts. Moreover, the developed protocol has been applied successfully to the analysis of various GAP samples, and works for other types of sources such as nanoelectrospray ionization.

Mass Spectrometry of Polyurethanes

This review covers the applications of mass spectrometry (MS) and its hyphenated techniques to characterize polyurethane (PU) synthetic polymers and their respective hard and soft segments. PUs are commonly composed of hard segments including methylene bisphenyl diisocyanate (MDI) and toluene diisocyanate (TDI), and soft segments including polyester and polyether polyols. This literature review highlights MS techniques such as electrospray ionization (ESI), matrix assisted laser/desorption ionization (MALDI), ion mobility-mass spectrometry (IM-MS), and computational methods that have been used for the characterization of this polymer system. Here we review specific case studies where MS techniques have elucidated unique features pertaining to the makeup and structural integrity of complex PU materials and PU precursors.

Electrospray ionization-ion mobility spectrometry-high resolution tandem mass spectrometry with collision-induced charge stripping for the analysis of highly multiply charged intact polymers

Polymers with large molecular weight are difficult to interpret using electrospray ionization-mass spectrometry (ESI-MS) due to the generation of various highly multiply charged analytes. Although ESI-ion mobility spectrometry (IMS)-MS is effective in reducing the complexity of the mass spectrum, this approach is insufficient for analyzing highly multiply charged polymers. In this study, we propose a method combining tandem mass spectrometry (quadrupole and high-resolution time-of-flight MS, QMS/TOFMS), IMS, and collision-induced charge stripping (CICS) for analyzing large intact polymers (∼40 kDa), which are highly multiply charged. The number of charges can be estimated from a Fourier transform power spectrum of a mass spectrum when the charge number is less than approximately 20. Interpretations of the spectra of poly(ethylene oxide)s (PEOs) weighing 20 kDa, poly(methyl methacrylate)s weighing 22 kDa, and methoxy-PEO-maleimide weighing 40 kDa were successfully demonstrated with isotope level and polymerization degree level separations, respectively. In the proposed method, a mixture can be analyzed for relatively small (a few kDa) and large (a few tens of kDa) polymers simultaneously without any sample pretreatment.

Subtle End Group Functionalization of Polymer Chains Drives Surface Depletion of Entire Polymer Chains

The surface of a blend of 6 kDa polystyrene and 6 kDa polystyrene functionalized with hydroxymethyl ends not only is depleted of the higher energy end groups but also is depleted of any segments belonging to the functionalized chains. This is demonstrated using the emerging technique of surface layer matrix-assisted laser desorption ionization time-of-flight mass spectrometry (SL-MALDI-ToF-MS), which detects entire chains that have any repeat unit at the outer surface, and requires no labeling. Detecting entire chains provides information about the relationship of chain functionalization to surface segregation behavior of entire chains. That the surface is depleted of interior segments of functionalized chains as well as of the ends is remarkable, since the functionality at the single chain end involves less than 0.5 wt % of the functionalized polymer chain.

Poly(ethylene glycol) and Cyclodextrin-Grafted Chitosan: From Methodologies to Preparation and Potential Biotechnological Applications

Chitosan, a polyaminosaccharide obtained by alkaline deacetylation of chitin, possesses useful properties including biodegradability, biocompatibility, low toxicity, and good miscibility with other polymers. It is extensively used in many applications in biology, medicine, agriculture, environmental protection, and the food and pharmaceutical industries. The amino and hydroxyl groups present in the chitosan backbone provide positions for modifications that are influenced by factors such as the molecular weight, viscosity, and type of chitosan, as well as the reaction conditions. The modification of chitosan by chemical methods is of interest because the basic chitosan skeleton is not modified and the process results in new or improved properties of the material. Among the chitosan derivatives, cyclodextrin-grafted chitosan and poly(ethylene glycol)-grafted chitosan are excellent candidates for a range of biomedical, environmental decontamination, and industrial purposes. This work discusses modifications including chitosan with attached cyclodextrin and poly(ethylene glycol), and the main applications of these chitosan derivatives in the biomedical field.

Multidimensional Mass Spectrometry of Synthetic Polymers and Advanced Materials

Multidimensional mass spectrometry interfaces a suitable ionization technique and mass analysis (MS) with fragmentation by tandem mass spectrometry (MS² ) and an orthogonal online separation method. Separation choices include liquid chromatography (LC) and ion-mobility spectrometry (IMS), in which separation takes place pre-ionization in the solution state or post-ionization in the gas phase, respectively. The MS step provides elemental composition information, while MS² exploits differences in the bond stabilities of a polymer, yielding connectivity and sequence information. LC conditions can be tuned to separate by polarity, end-group functionality, or hydrodynamic volume, whereas IMS adds selectivity by macromolecular shape and architecture. This Minireview discusses how selected combinations of the MS, MS² , LC, and IMS dimensions can be applied, together with the appropriate ionization method, to determine the constituents, structures, end groups, sequences, and architectures of a wide variety of homo- and copolymeric materials, including multicomponent blends, supramolecular assemblies, novel hybrid materials, and large cross-linked or nonionizable polymers.

Polylactides-Methods of synthesis and characterization

Polylactides with various molar masses, microstructures and crystallinities are used as degradable and biocompatible polymers suitable for preparation of drug carriers and temporary medical implants. This paper presents state of current knowledge on synthesis of lactic acids, high purity lactide monomers and their polymerization. Syntheses of high molar mass polylactides by polycondensation of lactic acid and by ring-opening polymerization of lactides are described and their advantages and disadvantages are discussed. Mechanisms of lactide polymerization initiated by metal alkoxides are described. There are presented also results of more recent studies of polymerization initiated with the so-called "no metal" organocatalysts; both anionic and cationic. Presented are advantages and limitations of synthesis of PLA by all the major polymerization processes until now. Some properties of PLA and most important methods used for PLA characterization are also described.

Matrix-Assisted Ionization-Ion Mobility Spectrometry-Mass Spectrometry: Selective Analysis of a Europium-PEG Complex in a Crude Mixture

The analytical utility of a new and simple to use ionization method, matrix-assisted ionization (MAI), coupled with ion mobility spectrometry (IMS) and mass spectrometry (MS) is used to characterize a 2-armed europium(III)-containing poly(ethylene glycol) (Eu-PEG) complex directly from a crude sample. MAI was used with the matrix 1,2-dicyanobenzene, which affords low chemical background relative to matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI). MAI provides high ion abundance of desired products in comparison to ESI and MALDI. Inductively coupled plasma-MS measurements were used to estimate a maximum of 10% of the crude sample by mass was the 2-arm Eu-PEG complex, supporting evidence of selective ionization of Eu-PEG complexes using the new MAI matrix, 1,2-dicyanobenzene. Multiply charged ions formed in MAI enhance the IMS gas-phase separation, especially relative to the singly charged ions observed with MALDI. Individual components are cleanly separated and readily identified, allowing characterization of the 2-arm Eu-PEG conjugate from a mixture of the 1-arm Eu-PEG complex and unreacted starting materials. Size-exclusion chromatography, liquid chromatography at critical conditions, MALDI-MS, ESI-MS, and ESI-IMS-MS had difficulties with this analysis, or failed. Graphical Abstract ᅟ.

Characterization of Metallosupramolecular Polymers by Top-Down Multidimensional Mass Spectrometry Methods

Top-down multidimensional mass spectrometry, interfacing electrospray ionization (ESI) with ion mobility mass spectrometry (IM-MS), and energy resolved (gradient) tandem mass spectrometry (gMS(2) ) are employed to characterize the stoichiometries, architectures, and intrinsic stabilities of coordinatively bound supramolecular polymers containing terpyridine functionalized ligands. As a soft ionization method, ESI prevents or minimizes unwanted assembly destruction. The IM dimension affords separation of the supramolecular ions by charge and collision cross-section (a function of size and shape). The mobility separated ions are subsequently identified by their mass-to-charge-ratios and isotope patterns in the orthogonal MS dimension. Finally, the gMS(2) dimension reveals bond breaking proclivities and disintegration pathways of the assemblies. The described methodology does not require high sample purity due to the dispersive nature of the IM and MS steps. Its utility is demonstrated with the comprehensive analysis of bisterpyridine-based metallomacrocycle mixtures and a tristerpyridine based complex with 3-D nanosphere-like architecture.

Use of Ion Mobility Spectrometry-Mass Spectrometry to Elucidate Architectural Dispersity within Star Polymers

The power of ion mobility spectrometry-mass spectrometry (IMS-MS) as an analytical technology for differentiating macromolecular architecture is demonstrated. The presence of architectural dispersity within a sample is probed by sequentially measuring both the drift time and the mass-to-charge ratio for every component within a polymer sample. The utility of this technology is demonstrated by investigating three poly(ethylene glycol) (PEG) architectures with closely related average molecular weights of about 9000 Da: a linear PEG, an unevenly branched miktoarm star PEG, and evenly branched homoarm star PEGs. The three architectures were readily distinguished when analyzed separately as "pure" architectures or when analyzed as mixtures. IMS-MS results are contrasted with matrix-assisted laser desorption/ionization-MS and viscometry measurements.

MALDI of synthetic polymers with labile end-groups

Mass spectrometry is increasingly used in the field of synthetic polymers as a fast and accurate technique for end-group analysis. More particularly, matrix-assisted laser desorption/ionization (MALDI) has gained much popularity because it allows quite simple mass spectra to be obtained, displaying a single distribution for each polymeric species present in the sample, in contrast to electrospray ionization (ESI) which readily promotes multiple charging for most polymers. A soft ionization process, ensuring the integrity of the species upon transfer into gas phase ions, is however mandatory for polymer end-group analysis since information about the chain terminations mainly rely on the m/z values measured for polymer adducts. As compared to ESI, MALDI is sometimes suspected to be a quite "hard" ionization technique, leading to spontaneous dissociation of ionized species either in the source or during their flight time. This issue is of particular concern for polymers carrying so-called fragile end-groups arising from their mode of synthesis. In particular, controlled radical polymerization (CRP) processes, one of the most important advances in the field of polymer science during the last 20 years, allow the production of polymers with well-defined molecular distribution and low polydispersities, but they are all based on the low dissociation energy of the chemical bond between the last monomer and the terminating group. As a result, if macromolecules are activated while being ionized, this end-group is prone to fragmentation and ions measured in the mass spectra do no longer reflect the original chain composition. However, different results are reported in the literature about the ability of MALDI to generate intact ions from CRP synthetic polymers. This article reviews MALDI MS data reported for synthetic polymers produced by atom transfer radical polymerization (ATRP), reversible addition-fragmentation transfer polymerization (RAFT), and nitroxide-mediated polymerization (NMP), the three most studied CRP techniques. The general principle of each polymerization process, which defines the structure of the end-groups in both targeted macromolecules and species arising from eventual side-reactions, is first briefly presented. An overview of MALDI data reported for samples obtained upon polymerization of different monomers are then commented for each polymerization techniques with regards to the success of the ionization method to generate intact cationic adducts and its propensity to distinguish in-source fragments from polymerization side-products.

Characterizing synthetic polymers and additives using new ionization methods for mass spectrometry

RATIONALE

New inlet and vacuum ionization methods provide advantages of specificity, simplicity and speed for the analysis of synthetic polymers and polymer additives directly from surfaces such as fibers using mass spectrometry (MS) on different commercial mass spectrometers (Waters SYNAPT G2, Thermo LTQ Velos).

METHODS

We compare inlet ionization methods with the recently discovered vacuum ionization method. This method, termed matrix assisted ionization vacuum (MAIV), utilizes the matrix 3-nitrobenzonitrile (3-NBN) for the analysis of synthetic polymers and additives without additional energy input by simply exposing the matrix:analyte:salt to the vacuum of the mass spectrometer. Matrix:analyte:salt samples can be introduced while dry (surfaces, e.g. glass slides, pipet tips) or slightly wet (e.g. filter paper, pipet tips).

RESULTS

Compounds ionized by these methods can be analyzed in both positive and negative detection modes through cationization or deprotonation, respectively. The dynamic range of the experiment can be enhanced, as well as structural analysis performed, by coupling the vacuum ionization method with ion mobility spectrometry mass spectrometry (IMS-MS) and tandem mass spectrometric (MS/MS) fragmentation.

CONCLUSIONS

The specificity of 3-NBN matrix to ionize small and large nonvolatile analyte molecules by MAIV makes this matrix a good choice for observing low-abundance additives in the presence of large amounts of synthetic polymer using MS.

Synthesis, characterization and applications of a perdeuterated amphipol

Amphipols are short amphipathic polymers that can substitute for detergents at the hydrophobic surface of membrane proteins (MPs), keeping them soluble in the absence of detergents while stabilizing them. The most widely used amphipol, known as A8-35, is comprised of a polyacrylic acid (PAA) main chain grafted with octylamine and isopropylamine. Among its many applications, A8-35 has proven particularly useful for solution-state NMR studies of MPs, for which it can be desirable to eliminate signals originating from the protons of the surfactant. In the present work, we describe the synthesis and properties of perdeuterated A8-35 (perDAPol). Perdeuterated PAA was obtained by radical polymerization of deuterated acrylic acid. It was subsequently grafted with deuterated amines, yielding perDAPol. The number-average molar mass of hydrogenated and perDAPol, ~4 and ~5 kDa, respectively, was deduced from that of their PAA precursors, determined by size exclusion chromatography in tetrahydrofuran following permethylation. Electrospray ionization-ion mobility spectrometry-mass spectrometry measurements show the molar mass and distribution of the two APols to be very similar. Upon neutron scattering, the contrast match point of perDAPol is found to be ~120% D2O. In (1)H-(1)H nuclear overhauser effect NMR spectra, its contribution is reduced to ~6% of that of hydrogenated A8-35, making it suitable for extended uses in NMR spectroscopy. PerDAPol ought to also be of use for inelastic neutron scattering studies of the dynamics of APol-trapped MPs, as well as small-angle neutron scattering and analytical ultracentrifugation.