Tandem mass spectrometry of lithium-attachment ions from polyglycols

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.

Development of an Efficient On-Tissue Epoxidation Reaction Mediated by Urea Hydrogen Peroxide for MALDI MS/MS Imaging of Lipid C═C Location Isomers

Unsaturated lipids containing different numbers and locations of C═C bonds are significantly associated with a variety of cellular and metabolic functions. Although matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) has been used to visualize the spatial distribution patterns of various lipids in biological tissues, in situ identification, discrimination, and visualization of lipid C═C location isomers remain challenging. Herein, an efficient and fast on-tissue chemical derivatization (OTCD) approach was developed to pinpoint the locations of C═C bonds in complex lipids in situ via methyltrioxorhenium (MTO)-catalyzed epoxidation of C═C with a urea hydrogen peroxide (UHP)/hexafluoroisopropanol (HFIP) system. The efficiency of OTCD could reach 100% via one-step spray deposition of the solution mixture of MTO/UHP/HFIP at room temperature. The developed OTCD method provided rich structural information on lipid C═C location isomers, and their accurate spatial distribution patterns were resolved in mouse brain tissues. Tissue-specific distributions and changes of lipid C═C location isomers in the liver sections of obese ob/ob and diabetic db/db mice were further investigated, and their correlation in two animal models was revealed. The simplicity and high efficiency of the OTCD method developed for MALDI tandem MSI of lipid C═C location isomers possess great potential for functional spatial lipidomics.

Rapid Characterization of Polymer Materials Using Arc Plasma-Based Dissociation-Mass Spectrometry

Fingerprinting spectra of polymer materials containing information of monomers' molecular weight and detailed structure, constituents, and sequences were obtained by a direct analytical process using arc plasma-based dissociation (APD)-mass spectrometry. The thermal arc plasma generated using a simple arc discharge device induces the dissociation of the polymeric backbone, producing mass spectra with strong regularity within seconds. The molecular weight of the repeating unit was revealed by equal intervals between peak series and protonated monomer ions in the mass spectra. Meanwhile, lots of secondary fragment ions were produced to provide abundant structural information. For polyethers, it is even possible to decipher (read) the "sequence" directly from their spectra. Polymers composed of isomers or only differing in their initiator moieties were easily distinguished with their characteristic APD mass spectra. The spectra were highly reproducible according to the results of similarity calculation. Unlike pyrolysis mass spectrometry, in the APD device, polymers in liquid, solid, powder, and crude samples can be analyzed directly without any pretreatment, and the regular spectra are easier to interpret. Compared with other direct analytical methods, more structural informative spectra can be acquired owing to the high energy, high temperature, and unique chemical reactivity of arc plasma. Thus, this technique is promising to be a valuable tool in rapid elucidation of polymer materials.

Unveiling spatial metabolome of Paeonia suffruticosa and Paeonia lactiflora roots using MALDI MS imaging

Paeonia suffruticosa (PS) and Paeonia lactiflora (PL) belong to the only genus in the family Paeoniaceae. Comparative analysis of the spatial metabolomes of PS and PL has rarely been performed. In this work, combined with multiple matrixes and dual-polarity detection, high mass resolution matrix-assisted laser desorption/ionization MS imaging (MALDI MSI) and MALDI tandem MSI were performed on the root sections of the two Paeonia species. The spatial distributions of many metabolites including monoterpene and paeonol glycosides, tannins, flavonoids, saccharides and lipids were systematically characterized. The ambiguous tissue distribution of the two isomers paeoniflorin and albiflorin were distinguished by tandem MSI using lithium salt doped 2,5-dihydroxybenzoate matrix. In addition, the major intermediates involved in the biosynthetic pathway of gallotannins were successfully localized and visualized in the root sections. High-mass resolution MALDI full-scan MSI provides comprehensive and accurate spatial distribution of metabolites. The analytical power of the technique was further tested in the tandem MSI of two isomers. The ion images of individual metabolites provide chemical and microscopic characteristics beyond morphological identification, and the detailed spatiochemical information could not only improve our understanding of the biosynthetic pathway of hydrolyzable tannins, but also ensure the safety and effectiveness of their medicinal use.

Tandem Mass-Remainder Analysis of Industrially Important Polyether Polyols

The characteristics of the polyalkylene oxide polyether polyols highly influence the properties of final polyurethane products. As a novel approach, in order to gain structural information, the recently invented data mining procedures, namely the Mass-remainder analysis (MARA) and the Multistep Mass-remainder analysis (M-MARA) are successfully applied for the processing of tandem mass spectrometry (MS/MS) data of various industrially important polyether polyols. M-MARA yields an ultra-simplified graphical representation of the MS/MS spectra and sorts the product ions based on their double bond equivalent (DBE) values. The maximum DBE values unambiguously differentiate among the various polyether polyols. Accordingly, the characteristic DBE values were 0, 1 for the linear diol polyethers, 0, 1, 2 for the three-arm, and 0, 1 2, 3, 4 for the six-arm polyether polyols. In addition, it was also found that the characteristic collision energy necessary for the optimum fragmentation yield depended linearly on the molecular weight of the polyols. This relationship offers an easy way for instrument tuning to gain structural information.

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.

Chemical Analysis of a "Miller-Type" Complex Prebiotic Broth: Part I: Chemical Diversity, Oxygen and Nitrogen Based Polymers

In a famous experiment Stanley Miller showed that a large number of organic substances can emerge from sparking a mixture of methane, ammonia and hydrogen in the presence of water (Miller, Science 117:528-529, 1953). Among these substances Miller identified different amino acids, and he concluded that prebiotic events may well have produced many of Life's molecular building blocks. There have been many variants of the original experiment since, including different gas mixtures (Miller, J Am Chem Soc 77:2351-2361, 1955; Oró Nature 197:862-867, 1963; Schlesinger and Miller, J Mol Evol 19:376-382, 1983; Miyakawa et al., Proc Natl Acad Sci 99:14,628-14,631, 2002). Recently some of Miller's remaining original samples were analyzed with modern equipment (Johnson et al. Science 322:404-404, 2008; Parker et al. Proc Natl Acad Sci 108:5526-5531, 2011) and a total of 23 racemic amino acids were identified. To give an overview of the chemical variety of a possible prebiotic broth, here we analyze a "Miller type" experiment using state of the art mass spectrometry and NMR spectroscopy. We identify substances of a wide range of saturation, which can be hydrophilic, hydrophobic or amphiphilic in nature. Often the molecules contain heteroatoms, with amines and amides being prominent classes of molecule. In some samples we detect ethylene glycol based polymers. Their formation in water requires the presence of a catalyst. Contrary to expectations, we cannot identify any preferred reaction product. The capacity to spontaneously produce this extremely high degree of molecular variety in a very simple experiment is a remarkable feature of organic chemistry and possibly prerequisite for Life to emerge. It remains a future task to uncover how dedicated, organized chemical reaction pathways may have arisen from this degree of complexity.

Electrospray ionization tandem mass spectrometry of the star-shaped propoxylated diethylenetriamine polyols

The collision-induced dissociation of the protonated five-arm star propoxylated diethylenetriamine polyols was studied under electrospray conditions. Two product ion series were detected because of the cleavage of the C-N bonds in the initiator moiety. No backbone fragmentation of the polyether chains was observed, which allowed to explore the initiation and side-chain propagation process of the oligomers. On the basis of MS/MS spectra, it is probable that the rate of the initiation is larger than that of the chain propagation. The propylene oxide repeat units attach to the five arms with approximately the same probability. Furthermore, it was found that the collision energy necessary to obtain 50% fragmentation (CE50) was linearly dependent on the molecular weight of the polyols.

The Competitive influence of Li+, Na+, K+, Ag+, and H+ on the fragmentation of a PEGylated polymeric excipient

The collisionally activated dissociation (CAD) and electron capture dissociation (ECD) of doubly charged tocopheryl polyethylene glycol succinate (TPGS) have been examined. Li(+), Na(+), K(+), Ag(+), and H(+) were selected in the study, and the competitive influence of each ion was investigated by fragmenting TPGS attached with two different cations, [M + X1 + X2](2+) (X1 and X2 refer to Li(+), Na(+), K(+), Ag(+), H(+)). For metallic adducts, CAD results show that the dissociation of ionic adducts from the precursor is most likely depending on the binding strength, where the affinity of each ion to the TPGS is in the order of Ag(+) ≈ Li(+) ˃ Na(+) ˃ K(+). Introducing more strongly bound adducts increases fragmentation. During ECD, however, the silver cation is lost most easily compared with the other alkali metal ions, but silver also shows a dominant role in producing fragmentations. Moreover, the charge carriers are lost in an order (Ag(+) ˃ Na(+) ˃ K(+) ≥ Li(+) where the loss of Ag is most easily) that appears to correlate with the standard reduction potential of the metallic ions (Ag(+) ˃ Na(+) ˃ K(+) ˃ Li(+)). The ECD results suggest that the reduction potential of the charge carrier could be an important factor influencing the fragmentation, where the ion with a high reduction potential is more effective in capturing electrons, but may also be lost easily before leading to any fragmentation. Finally, a proton has the weakest binding with the TPGS according to the CAD results, and its dissociation in ECD follows the order of the reduction potential (Ag(+) ˃ H(+) ˃ Na(+) ˃ K(+) > Li(+)).

Fragmentation of deprotonated polyethylene glycols, [PEG-H]-

RATIONALE

Polyethylene glycols (PEGs) are soluble molecules utilized in a wide range of applications. Mass spectrometry and fragmentation patterns of positively charged PEG oligomers are well-known, but decomposition mechanisms of the deprotonated ions have not been studied.

METHODS

Deprotonated PEGs were generated by electrospray ionization of PEG in water/acetonitrile. Collision-induced dissociation (CID) experiments were carried out in a tandem mass spectrometer. The anions were studied using a tandem mass spectrometer to carry out CID experiments. A series of small PEG oligomers, with 1 to 8 monomer units, were studied in order to monitor size-dependent effects on fragmentation reactions.

RESULTS

Because deprotonated PEG ions have a unique charge site, their dissociation pathways can easily be monitored. The ions fragment by loss of C2H4O monomer units, with an alternating intensity pattern that suggests the loss of an even number of monomer units is favored. Smaller oligomers and oligomer fragments also yielded fragments corresponding to H2 elimination and H2O loss. H2 elimination occurs by the generation of a hydride ion which deprotonates an alcohol upon leaving, while dehydration appears to be a charge-remote process.

CONCLUSIONS

The fragmentation of deprotonated PEG is dominated by intramolecular S(N)2 reactions involving the terminal oxide anion.

Mass spectrometric analysis of EPO IEF-PAGE interfering substances in nitrile examination gloves

Direct detection of doping with recombinant erythropoietins (rhEPO) is accomplished by isoelectric focusing (IEF) or sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis (PAGE). In a recent publication, Lasne et al. (Electrophoresis 2011, 32, 1444) showed that improper use of nitrile examination gloves during sample collection, sample preparation, and IEF-PAGE may lead to distorted or absent EPO IEF-profiles. In order to clarify which substances are responsible for this observation, a mass spectrometric study on water extractable compounds found in nitrile gloves was performed. Several substance classes were shown to be present, among them polyethylene glycols (PEG), anionic and nonionic surfactants, as well as alcohol ethoxylates and plasticizers. It could be demonstrated that alkylbenzenesulfonates, the main category of detectable anionic detergents, and among them sodium dodecylbenzenesulfonate (SDBS) and its homologs, are the prime reason for the interference of nitrile gloves with EPO IEF-PAGE.

Characterization of complex polysorbate formulations by means of shape-selective mass spectrometry

Complex synthetic formulations based on polysorbates can be challenging to characterize. They may be composed of many similar products including those of the same molecular weight, which cannot be readily separated by separation science approaches. Carbon number variation and ethylene oxide distribution add to the complexity. The properties of these formulations will be dependent on the chemical structure and relative concentration of formulation components. Here we describe the use of two experimental approaches based on mass spectrometry to provide enhanced characterization of these formulations. The first utilizes an atmospheric pressure solids analysis probe to rapidly determine the percentage content of individual esters in a formulation. These are shown to be in good agreement with product specification sheets. In a second approach, mobility separation has been integrated into a MALDI-MS/MS experiment to categorize major, minor, and trace ingredients. Components of identical molecular mass in the polysorbate formulations have been separated by ion mobility and then fragmented for additional characterization. The rapidity and level of structural detail provided by these experiments offers a significant opportunity to develop practical screening methods for complex formulations.

Tandem mass spectrometry of poly(ethylene imine)s by electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI)

In this contribution, linear poly(ethylene imine) (PEI) polymers, which are of importance in gene delivery, are investigated in detail by using electrospray ionization-quadrupole-time of flight (ESI-Q-TOF) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS). The analyzed PEIs with different end groups were synthesized using the polymerization of substituted 2-oxazoline via a living cationic ring-opening polymerization (CROP) and a subsequent hydrolysis under acidic conditions. The main goal of this study was to identify linear PEI polymers in a detailed way to gain information about their fragmentation pathways. For this purpose, a detailed characterization of three different linear PEIs was performed by using ESI-Q-TOF and MALDI-TOF MS in combination with collision-induced dissociation (CID) experiments. In ESI-MS as well as MALDI-MS analysis, the obtained spectra of PEIs resulted in fitting mass distributions for the investigated PEIs. In the tandem MS analysis, a 1,2-hydride shift with a charge-remote rearrangement via a four-membered cyclic transition state, as well as charge-induced fragmentation reactions, was proposed as the main fragmentation mechanisms according to the obtained fragmentation products from the protonated parent peaks. In addition, heterolytic and homolytic cleavages were proposed as alternative fragmentation pathways. Moreover, a 1,4-hydrogen elimination was proposed to explain different fragmentation products obtained from the sodiated parent peaks.

End-group characterization of poly(styrene sulfonate sodium salt) by activated electron photo-detachment dissociation

Tandem mass spectrometry of poly(styrene sulfonate sodium salt) (PSS) was performed after activated electron photo-detachment dissociation (activated EPD). In this technique, doubly charged PSS oligomers were first produced in negative mode electrospray ionization, then oxidized into radical anions upon electron photo-detachment using a 220 nm laser wavelength, and further activated by collision. In contrast to the collision-induced dissociation (CID) of negatively charged PSS oligomers, which does not provide informative data with regard to the end-groups, activated-EPD is shown here to promote radical-induced dissociation reactions thanks to the oxidation of a sulfonate group upon laser irradiation. Major product ions generated after backbone bond cleavages contained one or the other chain terminations and could be accounted for by two main mechanisms. Moreover, each of the proposed dissociation reactions was shown to generate two distinct fragments, depending on the location of the oxidized monomer near one or the other chain terminal moieties. As a result, a combination of these two fragments allowed a straightforward mass characterization of each end-group.

Fragmentation pathways of polymer ions

Tandem mass spectrometry (MS/MS) is increasingly applied to synthetic polymers to characterize chain-end or in-chain substituents, distinguish isobaric and isomeric species, and determine macromolecular connectivities and architectures. For confident structural assignments, the fragmentation mechanisms of polymer ions must be understood, as they provide guidelines on how to deduce the desired information from the fragments observed in MS/MS spectra. This article reviews the fragmentation pathways of synthetic polymer ions that have been energized to decompose via collisionally activated dissociation (CAD), the most widely used activation method in polymer analysis. The compounds discussed encompass polystyrenes, poly(2-vinyl pyridine), polyacrylates, poly(vinyl acetate), aliphatic polyester copolymers, polyethers, and poly(dimethylsiloxane). For a number of these polymers, several substitution patterns and architectures are considered, and questions regarding the ionization agent and internal energy of the dissociating precursor ions are also addressed. Competing and consecutive dissociations are evaluated in terms of the structural insight they provide about the macromolecular structure. The fragmentation pathways of the diverse array of polymer ions examined fall into three categories, viz. (1) charge-directed fragmentations, (2) charge-remote rearrangements, and (3) charge-remote fragmentations via radical intermediates. Charge-remote processes predominate. Depending on the ionizing agent and the functional groups in the polymer, the incipient fragments arising by pathways (1)-(3) may form ion-molecule complexes that survive long enough to permit inter-fragment hydrogen atom, proton, or hydride transfers.

Practicing IEF-PAGE of EPO: the impact of detergents and sample application methods on analytical performance in doping control

Electrophoretic techniques, namely isoelectric focusing polyacrylamide gel electrophoresis (IEF-PAGE) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) are key techniques used for confirming the doping-related abuse of recombinant erythropoietins and analogs. IEF-PAGE is performed on horizontal slab-gels with samples applied to the surface of the gel. Different sample application techniques can be employed, but application pieces and applicator strips are most frequently used. However, defective application pieces cause lane streaking during IEF of erythropoietin (EPO), which is especially pronounced in the acidic region of the gel. The effect is due to an incompatibility of the substance used for enhancing the wettability of the cellulose-based commercial product and is batch-dependent. A detailed mass spectrometric study was performed, which revealed that defective sample application pieces (bought between 2007 and 2010) contained a complex mixture of alcohol ethoxylates, alcohol ethoxysulfates, and alkyl sulfates (e.g. SDS). Anionic detergents, like the sulfates contained in these application pieces, are in general incompatible with IEF. Alternative application techniques proved partly useful. While homemade pieces made of blotting paper are a good alternative, the usage of applicator strips or shims is hampered by the risk of leaking wells, which lead to laterally diffused samples. Casting IEF-gels with wells appears to be the best solution, since sustained release of retained proteins from the application pieces can be avoided. Edge effects do not occur if wells are correctly filled with the samples. The evaluation of EPO-profiles with defects is prohibited by the technical document on EPO-analytics (TD2009EPO) of the World Anti-Doping Agency (WADA).

Tandem mass spectrometry of trimethylsilyl-terminated poly(dimethylsiloxane) ammonium adducts generated by electrospray ionization

Ammonium adducts of trimethylsilyl-terminated poly(dimethylsiloxane) (CH(3)-PDMS) produced by electrospray ionization were submitted to collision induced dissociation and revealed a particular MS/MS behavior: the same three main product ions at m/z 221, 295, and 369 were always generated in very similar relative abundances regardless of the size of the precursor ion. Combining accurate mass measurements and ab initio calculation allowed very stable cyclic geometries to be obtained for these ionic species. Dissociation mechanisms were proposed to account for the three targeted ions to be readily generated in a two-step or a three-step reaction from any CH(3)-PDMS ammonium adducts. A second set of three product ions was also observed with low abundance at m/z 207, 281, and 355, which were shown in MS(3) experiments to be formed in secondary reactions. An alternative dissociation process was shown to consist of a concerted elimination of ammonia and methane and the need for a methyl of an end-group to be involved in the released methane molecule would account for this reaction to mainly proceed from the smallest precursor ions.

Rapid approach to biobased telechelics through two one-pot thiol-ene click reactions

The application of environmentally friendly thiol-ene chemistry to the preparation of biobased telechelics is presented in this work. This methodology is based on two one-pot photoinitiated thiol-ene click processes: step-growth polymerization using a 3,6-dioxa-1,8-octanedithiol and end-group postpolymerization modification with three functional thiols: 2-mercaptoethanol, 3-mercaptopropionic acid, and 3-mercaptopropyltrimethoxysilane. We applied this approach to a potentially 100% biomass-derived monomer, allyl ester of 10-undecenoic acid (UDA). To show the generality and scope of this methodology, a series of well-defined telechelics with molecular weight ranging from 1000-3000 g/mol and hydroxyl, carboxyl, or trimethoxysilyl groups at the polymer terminus were prepared. An exhaustive (1)H NMR and MALDI-TOF MS analyses demonstrates the highly end-group fidelity of this methodology being an interesting procedure for the accelerated preparation of telechelics derived from divinyl monomers. UDA-based thelechelic diol prepared using this methodology was reacted with 4,4'-methylenebis(phenylisocyanate) and 1,4-butanediol as the chain extender to obtain multiblock poly(ester urethane).

Energy-dependent collision-induced dissociation of lithiated polytetrahydrofuran: effect of the size on the fragmentation properties

The fragmentation properties of singly and doubly lithiated polytetrahydrofuran (PTHF) were studied using energy-dependent collision-induced dissociation. The product ion spectrum of [PTHF + Li](+) showed the formation of three different series corresponding to product ions with hydroxyl, aldehyde and vinyl end-groups. Interestingly, besides these series, two additional, non-lithiated product ions C(4)H(9)O(+) and C(4)H(7)(+) were identified in the MS/MS spectra. The MS/MS of the doubly lithiated PTHF ([PTHF + 2Li](2+)) with a number of repeat units ranging from 8 to 27 showed the formation of product ions similar to those of the singly lithiated series, however, doubly lithiated product ions and product ions formed by the loss of one Li(+)-ion from the precursor ion also appeared with significant abundances. Analysis of the breakdown curves for the singly and doubly charged PTHF indicated that the series A ions are formed most probably together with the series B ions, while members of the series C ions appeared at significantly higher collision energies. The fragmentation properties of [PTHF + Li](+) and [PTHF + 2Li](2+) were also interpreted using the survival yield method. It was found that the collision energy/voltage necessary to obtain 50% fragmentation (CV(50)) was dependent linearly on the number of the repeat units, i.e., on the size, or the number of degrees of freedom (DOF).

Methylation of acidic moieties in poly(methyl methacrylate-co-methacrylic acid) copolymers for end-group characterization by tandem mass spectrometry

The complete structural characterization of a copolymer composed of methacrylic acid (MAA) and methyl methacrylate (MMA) units was achieved using tandem mass spectrometry. In a first step, collision-induced dissociation (CID) of sodiated MAA-MMA co-oligomers allowed us to determine the co-monomeric composition, the random nature of the copolymer and the sum of the end-group masses. However, dissociation reactions of MAA-based molecules mainly involve the acidic pendant groups, precluding individual characterization of the end groups. Therefore, methylation of all the acrylic acid moieties was performed to transform the MAA-MMA copolymer into a PMMA homopolymer, for which CID mainly proceeds via backbone cleavages. Using trimethylsilyldiazomethane as a derivatization agent, this methylation reaction was shown to be complete without affecting the end groups. Using fragmentation rules established for PMMA polymers together with accurate mass measurements of the product ions and knowledge of reagents used for the studied copolymer synthesis, a structure could be proposed for both end groups and it was found to be consistent with signals obtained in nuclear magnetic resonance spectra.

Effect of in the mobile phase on the critical conditions of poly(ethylene glycol) in liquid chromatography-mass spectrometry coupling

The nature of salts introduced in the chromatographic mobile phase to promote on-line electrospray ionization was shown to be a key parameter in the optimization of LCCC-MS couplings, both using non-polar (Si-C18) and polar (Si-NH2) stationary phases. The critical conditions of poly(ethylene glycol), which reflect a compensation process between exclusion and interaction effects, were strongly modified when changing the size of the cation in the eluent. This phenomenon could be attributed to interactions between the cation and water molecules from the mobile phase, in the case of the non-polar stationary phase, giving rise to a salting out effect due to a lowered solvent quality of the eluent; or between the cation and amino-modified silanols of the polar stationary phase, inducing a decrease of the surface adsorptivity. Accordingly, increasing the size of the cation in the mobile phase caused the polymer molecules to be eluted according to the adsorption mode using non-polar adsorbent and according to the exclusion mode using polar stationary phase.

Structural analysis of synthetic polymer mixtures using ion mobility and tandem mass spectrometry

Ion mobility (IM) combined with tandem mass spectrometry (MS/MS) has been employed to separate and differentiate between polyether oligomers with the same nominal molecular weights. Poly(ethylene glycol)s with the same nominal mass-to-charge ratio (m/z), but with differing structures, were separated using ion mobility. IM-MS/MS data were able to aid identification of the backbone and end groups of the four individual polyethers in the two sets of isobaric mixtures. The MS/MS data from the resolved oligomers enabled a detailed structural characterization of the polyether mixtures to be completed in one experiment.

Positive mode electrospray tandem mass spectrometry of poly(methacrylic acid) oligomers

The dissociation of small poly(methacrylic acid) (PMAA) cations produced by electrospray was characterized by tandem mass spectrometry. Similarly to PMAA ions produced in the negative ion mode, the two electrosprayed cationic forms, namely [PMAA+Na](+) and [PMAA-H+2Na](+), were shown to fragment via a major pathway consisting of successive dehydration steps. Elimination of a water molecule would occur between two consecutive acid groups in a charged-remote mechanism and was shown to proceed as many times as pairs of acidic pendant groups were available. As a result, comparing the number of dehydration steps observed in the MS/MS spectrum of two consecutive oligomers from the polymeric distribution reveals the degree of polymerization of the molecule. Secondary less informative reactions were shown to consist of losses of CO and/or CO(2), depending on the nature of the precursor ion. These fragmentation rules could be used to characterize PMAA-based copolymers, as successfully demonstrated for a polymeric impurity in the tested PMAA sample.

Tandem mass spectrometry of poly(methacrylic Acid) oligomers produced by negative mode electrospray ionization

Dissociation of small poly(methyl acrylic acid) (PMAA) anions produced by electrospray was characterized by tandem mass spectrometry. Upon collisional activation, singly, and doubly deprotonated PMAA oligomers were shown to fragment via two major reactions, dehydration and decarboxylation. The elimination of a water molecule would occur between two consecutive acid groups in a charged-remote mechanism, giving rise to cyclic anhydrides, and was shown to proceed as many times as pairs of neutral pendant groups were available. As a result, the number of dehydration steps, together with the abundance of the fragment ions produced after the release of all water molecules, revealed the polymerization degree of the molecule in the particular case of doubly charged oligomers. For singly deprotonated molecules, the exact number of MAA units could be reached from the number of carbon dioxide molecules successively eliminated from the fully dehydrated precursor ions. In contrast to dehydration, decarboxylation reactions would proceed via a charge-induced mechanism. The proposed dissociation mechanisms are consistent with results commonly reported in thermal degradation studies of poly(acrylic acid) resins and were supported by accurate mass measurements. These fragmentation rules were successfully applied to characterize a polymeric impurity detected in the tested PMAA sample.

On-line coupling of liquid chromatography at critical conditions with electrospray ionization tandem mass spectrometry for the characterization of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer

Coupling of liquid chromatography at critical conditions (LCCC) with on-line mass spectrometry (MS) detection was implemented via an electrospray ionization (ESI) interface, using a mobile phase containing the cationizing agent. Critical conditions established for poly(ethylene oxide) were used to characterize a poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) in both MS and MS/MS modes. As co-oligomer molecules were successfully separated according to the PS block size, structural information could be reached from simplified MS spectra. The microstructure of this copolymer, synthesized by nitroxide-mediated polymerization, could further be unambiguously characterized in LCCC/ESI-MS/MS experiments since the PS block size could be reached by both the co-oligomer chromatographic behavior and its MS/MS pattern.

Detailed structural elucidation of polyesters and acrylates using Fourier transform mass spectrometry

The detailed structural characterization of complex polymer architectures, like copolymers and polymer mixtures, by mass spectrometry presents a challenge. Even though soft ionization analyses revolutionized the characterization of large molecules and provided a means for determining the polymer's molecular weight distribution, polydispersity, and end groups, full microstructure elucidation and monomer sequencing by soft ionization alone is not possible. The combination of high-resolution Fourier transform mass spectrometry (FTMS) and tandem mass spectrometry (MS(n)) provides a powerful analytical tool for addressing these challenges. This tool was used in our work to separate and identify the products of polymerization between 12-hydroxystearic acid (HSA) and stearic acid (SA), to provide precise information about the exact location of caprolactones on the Tris(2-hydroxyethyl)isocyanurate (THEIC) molecule, and to sequence a glycidyl methacrylate/methyl methacrylate (GMA/MMA) copolymer. The results highlight the value of ultrahigh resolution and tandem mass spectrometry for fine structural characterization and sequencing of polymers.

End-group characterisation of poly(propylene glycol)s by means of electrospray ionisation-tandem mass spectrometry (ESI-MS/MS)

The end-group functionalisation of a series of poly(propylene glycol)s has been characterised by means of electrospray ionisation-tandem mass spectrometry (ESI-MS/MS). A series of peaks with mass-to-charge ratios that are close to that of the precursor ion were used to generate information on the end-group functionalities of the poly(propylene glycol)s. Fragment ions resulting from losses of both of the end groups were noted from some of the samples. An example is presented of how software can be used to significantly reduce the length of time involved in data interpretation (which is typically the most time-consuming part of the analysis).

Microstructural study of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) by electrospray tandem mass spectrometry

Electrospray ionization tandem mass spectrometry has been used to characterize the microstructure of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer, called SG1-capped PEO-b-PS. The main dissociation route of co-oligomers adducted with lithium or silver cation was observed to proceed via the homolytic cleavage of a C-ON bond, aimed at undergoing reversible homolysis during nitroxide mediated polymerization. This cleavage results in the elimination of the terminal SG1 end-group as a radical, inducing a complete depolymerization process of the PS block from the so-formed radical cation. These successive eliminations of styrene molecules allowed a straightforward determination of the PS block size. An alternative fragmentation pathway of the radical cation was shown to provide structural information on the junction group between the two blocks. Proposed dissociation mechanisms were supported by accurate mass measurements. Structural information on the SG1 end-group could be reached from weak abundance fragment ions detected in the low m/z range of the MS/MS spectrum. Amongst fragments typically expected from PS dissociation, only beta ions were produced. Moreover, specific dissociation of the PEO block was not observed to occur in MS/MS, suggesting that these rearrangement reactions do not compete effectively with dissociations of the odd-electron fragment ions. Information about the PEO block length and the initiated end-group were obtained in MS(3) experiments.

Dual polarity accurate mass calibration for electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry using maltooligosaccharides

In view of the fact that memory effects associated with instrument calibration hinder the use of many mass-to-charge (m/z) ratios and tuning standards, identification of robust, comprehensive, inexpensive, and memory-free calibration standards is of particular interest to the mass spectrometry community. Glucose and its isomers are known to have a residue mass of 162.05282Da; therefore, both linear and branched forms of polyhexose oligosaccharides possess well-defined masses, making them ideal candidates for mass calibration. Using a wide range of maltooligosaccharides (MOSs) derived from commercially available beers, ions with m/z ratios from approximately 500 to 2500Da or more have been observed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and time-of-flight mass spectrometry (TOF-MS). The MOS mixtures were further characterized using infrared multiphoton dissociation (IRMPD) and nano-liquid chromatography/mass spectrometry (nano-LC/MS). In addition to providing well-defined series of positive and negative calibrant ions using either electrospray ionization (ESI) or matrix-assisted laser desorption/ionization (MALDI), the MOSs are not encumbered by memory effects and, thus, are well-suited mass calibration and instrument tuning standards for carbohydrate analysis.

Characterization of polar compounds and oligomers in secondary organic aerosol using liquid chromatography coupled to mass spectrometry

A generic method has been developed for the analysis of polar compounds and oligomers in secondary organic aerosol (SOA) formed during atmospheric simulation chamber experiments. The technique has been successfully applied to SOA formed in a variety of systems, ranging from ozonolysis of biogenic volatile organic compounds to aromatic photooxidation. An example application of the method is described for the SOA produced from the reaction of ozone with cis-3-hexenyl acetate, an important biogenic precursor. A range of solvents were tested as extraction media, and water was found to yield the highest recovery. Extracts were analyzed using reversed-phase liquid chromatography coupled to ion trap mass spectrometry. In order to determine correct molecular weight assignments and increase sensitivity for less polar species, a series of low-concentration mobile-phase additives were used (NaCl, LiBr, NH4OH). Lithium bromide produced better fragmentation patterns, with more structural information than in the other cases with no reduction in sensitivity. The main reaction products identified in the particle-phase were 3-acetoxypropanal, 3-acetoxypropanoic acid, and 3-acetoxypropane peroxoic acid and a series of dimers and trimers up to 500 Da. Structural identification of oligomers indicates the presence of linear polyesters possibly formed via esterfication reactions or decomposition of peroxyhemiacetals.

Novel software for the assignment of peaks from tandem mass spectrometry spectra of synthetic polymers

Novel software has been developed to aid the interpretation of tandem mass spectrometry (MS/MS) data from synthetic polymers. The software is particularly focused toward aiding the end-group determination of these materials by significantly speeding up the interpretation process. This allows information on the initiator and/or chain transfer agents, used to generate the polymer, and the mechanism of termination to be inferred from the data much more rapidly. The software allows the validity of hypothesized structures to be rapidly tested by automatically annotating the data file using previously proposed fragmentation rules for synthetic polymers. Low-energy collision-induced dissociation (CID) data from methacrylate, styrene, and polyether oligomers are used as example data for the software. Exact-mass CID information was used to aid the understanding of the dissociation mechanism of the polymers. The software can use exact-mass data to provide more confidence in the results. The MS/MS results indicate that the fragmentation pathways are those previously proposed for these polymers.

The rapid characterisation of poly(ethylene glycol) oligomers using desorption electrospray ionisation tandem mass spectrometry combined with novel product ion peak assignment software

A rapid method for the characterisation of polyglycol esters and ethers is described which uses accurate mass desorption electrospray ionisation (DESI) quadrupole time-of-flight mass spectrometry (Q-ToFMS). The results are combined with newly developed software which aids the interpretation of product ions produced using collision-induced dissociation (CID) of selected precursor ions. The poly(ethylene glycol) (PEG) samples analysed were PEG dibenzoate, PEG monooleate, PEG butyl ether, PEG bis(2-ethyl hexanoate) and PEG diacrylate. Lithium metal was used for cationisation of the PEG oligomers since it yielded the most useful structural information compared with other group I metals. The full scan mass spectra and product ion mass spectra were all obtained in <5 s. Interpretation of the MS/MS product ion spectra, using the product ion interpretation software which incorporates previously developed fragmentation rules, was carried out in <1 s.

Electrospray ionization tandem mass spectrometric characterization of the new functional oligo(ether-ester)s structure

The oligomeric products obtained by the polymerization of monomethacrylates of oligoethylene glycols possessing up to four oxyethylene units were examined by electrospray ionization mass spectrometry (ESI-MS). The oligomerization initiated by sodium and potassium hydrides proceeded via Michael-type addition of hydroxyl groups to carbon-carbon double bonds. Extended reaction time caused gelation, especially in the case of the more reactive potassium hydride. This study was focused on the structural assignments of the oligomeric products by use of ion trap multistage mass spectrometry (ESI-MS(2)). Precise structural characterization of the individual oligomers was based on fragmentation data.

Glycerol-derived ester oligomers from cork suberin

The cork suberin polyester was partially depolymerized by a methanolysis reaction catalyzed by calcium hydroxide. The methanolisate was analysed by ESI-MS/MS in the form of [M+Li](+) adduct-ions. This reaction solubilized a mixture of monomers and oligomers, including a set of glycerol-derived dimeric and trimeric esters. Four types of glycerol esters were identified: monoacylglycerols of alpha,omega-diacids, of omega-hydroxyacids and of monoacids; diglycerol diesters of alpha,omega-diacids; diacylglycerols of alpha,omega-diacids; monoacylglycerols of linear dimeric esters of alpha,omega-diacids and omega-hydroxyacids. The alpha,omega-diacids and omega-hydroxyacids found as monomer residues in the glycerol esters are the main ones found as cork suberin monomers. It is concluded that suberin is a glycerol-derived lipid of polymeric dimensions. Due to the protective and insulating role that it plays in plants, suberin should be considered together with the other known glycerolipids that build up biological membranes.

Block Lengths and Block Sequence of Linear Triblock and Glycerol Derivative Diblock Copolyethers by Electrospray Ionization−Collision-Induced Dissociation Mass Spectrometry

Chemical properties of ethylene oxide (EO) and propylene oxide (PO) block copolymers are strongly dependent on their sequence. Useful information about copolymer sequence can be obtained by tandem mass spectrometry (MS/MS). In this work, collision-induced dissociation (CID) of ammonium adducts of various linear triblock and glycerol derivative diblock copolyethers produced by electrospray ionization was studied under low-energy conditions. At first, homopolymers MS/MS spectra enabled us to identify the nature of the product ions and to suggest decomposition pathways. Then, it was shown that copolyethers with the same composition in each repeat unit but with inversed block sequences (i.e., PEO-b-PPO-b-PEO vs PPO-b-PEO-b-PPO and gPEO-b-PPO vs gPPO-b-PEO) can be easily distinguished with characteristic fragment ions. In the case of linear copolymers, CID spectra gave pertinent information about block lengths.

Desorption electrospray ionisation mass spectrometry and tandem mass spectrometry of low molecular weight synthetic polymers

A range of low molecular weight synthetic polymers has been characterised by means of desorption electrospray ionisation (DESI) combined with both mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Accurate mass experiments were used to aid the structural determination of some of the oligomeric materials. The polymers analysed were poly(ethylene glycol) (PEG), polypropylene glycol (PPG), poly(methyl methacrylate) (PMMA) and poly(alpha-methyl styrene). An application of the technique for characterisation of a polymer used as part of an active ingredient in a pharmaceutical tablet is described. The mass spectra and tandem mass spectra of all of the polymers were obtained in seconds, indicating the sensitivity of the technique.

Generation of end-group information from polyethers by matrix-assisted laser desorption/ionisation collision-induced dissociation mass spectrometry

A series of polyethers, namely poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), poly(butylene glycol) (PBG) and poly(tetramethylene glycol) (PTMeG), has been characterised by means of matrix-assisted laser desorption/ionisation collision-induced dissociation (MALDI-CID) using a hybrid sector orthogonal-time-of-flight (TOF) instrument. The data indicate that this technique can be used to generate information about the end-group functionality of these polymers, including in some cases information about branching of the alkyl chains of the initiating groups. Proposals are made for the fragmentation pathways for these polymers.