Direct Probe-Atmospheric Pressure Chemical Ionization Mass Spectrometry of Cross-Linked Copolymers and Copolymer Blends

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.

Recent developments in pre-treatment and analytical techniques for synthetic polymers by MALDI-TOF mass spectrometry

A great deal of effort has been expended to develop accurate means of determining the properties of synthetic polymers using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). Many studies have focused on the importance of sample pre-treatment to obtain accurate analysis results. This review discusses the history of synthetic polymer characterization and highlights several applications of MALDI-TOF MS that recognize the importance of pre-treatment technologies. The subject area is of significance in the field of analytical chemistry, especially for users of the MALDI technique. Since the 2000s, many such technologies have been developed that feature improved methods and conditions, including solvent-free systems. In addition, the recent diversification of matrix types and the development of carbon-based matrix materials are described herein together with the current status and future directions of MALDI-TOF MS hardware and software development. We provide a summary of processes used for obtaining the best analytical results with synthetic polymeric materials using MALDI-TOF MS.

Regio- and Stereo-Specific Chemical Depolymerization of High Molecular Weight Polybutadiene and Polyisoprene for Their Analysis by High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Comparison with Pyrolysis-Comprehensive Two-Dimensional Gas Chromatography/Mass Spectrometry, Atmospheric Solid Analysis Probe, Direct Inlet Probe-Atmospheric Pressure Chemical Ionization Mass Spectrometry, and Ion Mobility Spectrometry-Mass Spectrometry

Polybutadiene (PB) and polyisoprene (PI), the two most common polydienes (PD), are involved in a large number of materials and used in a wide variety of applications. The characterization of these polymers by mass spectrometry (MS) continues to be very challenging due to their high insolubility and the difficulty to ionize them. In this work, a cross-metathesis reaction was used to generate end-functionalized acetoxy ionizable oligomers for the structural deciphering of different commercial PB and PI samples. A cross-metathesis reaction was carried out between polymers and the Z-1,4-diacetoxy-2-butene as a chain transfer agent in dichloromethane using a Hoveyda-Grubbs second-generation catalyst. Well-defined acetoxy telechelic structures were obtained and analyzed by Fourier transform ion cyclotron resonance (FTICR) high-resolution MS. However, after depolymerization, low molar mass polyolefins contained some units with different configurations, suggesting an olefin isomerization reaction due to the decomposition of the catalyst. The addition of an electron-deficient reagent such as 2,6-dichloro-1,4-benzoquinone suppressed this isomerization in the case of both Z- and E-PB and PI. Ion mobility spectrometry-mass spectrometry (IMS-MS) and energy-resolved tandem mass spectrometry (ERMS) analyses confirmed a successful isomerization suppression. For comparing the results obtained by depolymerization with classical methods for polymer analysis, pyrolysis-comprehensive two-dimensional gas chromatography/mass spectrometry (Py-GC × GC-MS), atmospheric solid analysis probe (ASAP), and direct inlet probe-atmospheric pressure chemical ionization (DIP-APCI) analyses were performed on the same polymers. This strategy can be applied on a variety of synthetic and natural not yet characterized polymers.

High-performance thin-layer chromatography with atmospheric solids analysis probe mass spectrometry for analysis of gasoline polymeric additives

RATIONALE

The offline coupling of high-performance thin-layer chromatography (HPTLC) with atmospheric solids analysis probe mass spectrometry (ASAP-MS) was evaluated for the characterization of polymeric additives in gasoline.

METHODS

A protocol was developed to optimize the ion signal. A glass capillary was moistened with deionized water, and then dipped into silica gel scratched from an HPTLC plate. The capillary tube was fixed to the ASAP holder and introduced into the ionization source for analysis by MS. Silica gel, reversed-phase C18 and cellulose stationary phases were evaluated.

RESULTS

The effect of the stationary phase and the nature of analyte were evaluated using polypropylene glycol and polyisobutylene succinimide polyamine as analyte molecules. The optimal ionization conditions are significantly different between ASAP and HPTLC/ASAP-MS analyses. In particular, a higher desorption gas temperature was required to produce ions from the silica gel HPTLC plate. The presence of the stationary phase reduces the internal energy of the ions and limits the fragmentation.

CONCLUSIONS

HPTLC/ASAP-MS is a very fast and efficient technique for the analysis of polymers in formulated fuels. Good ionization efficiency was obtained with all investigated stationary phases.

Direct analysis from dried blood spot card surfaces with direct probe mass spectrometry - Evaluation study

RATIONALE

The Direct Probe Mass Spectrometry (DIPMS) method allows successful analysis of powders, solid and liquid samples. The potential of direct surface analysis could find further application in the examination of surfaces with good absorption properties such as Dried Blood Spot (DBS) cards that constitute a great alternative to the classical blood collection method directly from veins.

METHODS

DIPMS was performed with the ionization carried out under atmospheric pressure in an Atmospheric Pressure Chemical Ionization source. Direct analysis of diazepam solutions in methanol and after their deposition onto a DBS card was conducted. Subsequently, images of the DBS cards with and without blood samples were acquired using Scanning Electron Microscopy (SEM).

RESULTS

Direct quantitative analysis of diazepam liquid samples by DIPMS was successfully performed. Linear correlation between the concentration of diazepam and the peak intensity with a R² coefficient of 0.937 was obtained. However, the method failed when the analysis was conducted directly from the surface of the DBS cards and no diazepam peak was observed in the mass spectrum. The SEM images confirmed the good absorption properties of DBS cards and the absence of blood components on the surface.

CONCLUSIONS

DIPMS is an excellent technique for the rapid, direct analysis of powders, solid and liquid samples; however, the potential of the method is limited when samples are deposited on surfaces with good absorption properties such as DBS cards.

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.

Characterization of Polyolefin Pyrolysis Species Produced Under Ambient Conditions by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Ion Mobility-Mass Spectrometry

Polyolefins such as polyethylene (PE) and polypropylene (PP) are often characterized from their pyrolysis products by Py-MS. Nowadays the development of plasma-based direct probe atmospheric pressure sources allow the direct analysis of these polymers. These sources operate at atmospheric pressure, which implies a limited control of the ionization conditions. It was shown that side reactions could occur with species present in air, such as O_2, which may lead to the formation of oxidized compounds. In this work, ion mobility-mass spectrometry (IM-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR) were used for the exhaustive characterization of the PP and PE pyrolysis ions produced using plasma-based atmospheric pressure ion sources. Both PP and PE yielded distributions of pyrolysis products presenting different amounts of unsaturation but also different numbers of oxygen atoms. In addition, the ions produced from PP presented a lower collision cross-section (CCS) than those produced from PE. In the same way, both PP and PE present repeated patterns separated by 14 m/z in the bidimensional drift time versus m/z plots. Within these plots, several trend lines can be evidenced, which are specific of each polymer investigated. Differences were observed between isotactic and atactic samples concerning the pyrolysis profile relative abundance and collision cross-section. Graphical Abstract ᅟ.

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.

Non-destructive plasticizer screening using a direct inlet probe-atmospheric pressure chemical ionization source and ion trap mass spectrometry

RATIONALE

In recent years, several ambient ionization techniques, where solid and/or liquid samples are brought directly into the ion source without any sample preparation and chromatographic separation, have been introduced for mass spectrometric (MS) analyses. Using the direct inlet probe-atmospheric pressure chemical ionization (DIP-APCI)-MS and DIP-APCI-MS(n) methods presented here, a non-destructive screening analysis for plasticizers directly from plastic articles can be performed.

METHODS

The DIP-APCI ion source developed in our laboratory uses a temperature-programmed push rod to introduce solid or liquid samples into a homemade APCI ion source. The DIP-APCI ion source was coupled to an ion trap (IT) mass spectrometer and selected source parameters were optimized. To enable a screening analysis for plasticizers, standards substances of several phthalates and other plasticizers were analyzed and their fragmentation behavior during collision-induced dissociation (CID) was studied.

RESULTS

Using DIP-APCI-ITMS, plasticizers can be detected directly from plastic articles and identification is possible through MS(n) experiments. For example, the isomeric phthalates di(2-ethylhexyl) phthalate and di-n-octyl phthalate can be differentiated according to their fragmentation behavior.

CONCLUSIONS

There are several advantages of the DIP-APCI source in comparison to many other ambient desorption ion sources: (i) well-defined gas phase matrix, (ii) precisely adjustable reagent gases (e.g. O2 for negative APCI), (iii) well-defined probe temperature, and (iv) fully automated operation.

Rapid analysis of polyester and polyethylene blends by ion mobility-mass spectrometry

In this work ion mobility-mass spectrometry (IM-MS) coupled to an atmospheric solid analysis probe (ASAP) was used for the characterization of polymer blends involving biodegradable polymers (poly(lactic acid) (PLA), poly(butylene succinate) (PBS)) and poly(ethylene) (PE).

APCI/APPI for synthetic polymer analysis

Modern mass spectrometry of synthetic polymers involves soft ionization techniques. Whereas matrix-assisted laser desorption/ionization (MALDI) and electrospray (ESI) are employed routinely, atmospheric pressure chemical ionization (APCI) and more recently atmospheric pressure photoionization (APPI) are used to a lesser extent. However, these latter ionization methods coupled to liquid-phase separation techniques create new opportunities for the characterization of polymers, especially for low molecular weight compounds or for the polymers that are poorly ionizable by the usual methods. After a part devoted to the description of classical MS methods employed for polymer analysis (MALDI, ESI, and their use with chromatography), APCI and APPI techniques will be described, discussed, and selected examples will present the interest of these ionization sources (or interfaces for LC/MS) in the field of polymer analysis.

Determination of primary bond scissions by mass spectrometric analysis of ultrasonic degradation products of poly(ethylene oxide-block-propylene oxide) copolymers

Ultrasonic degradation of poly(ethylene oxide-block-propylene oxide) copolymers consisting of a hydrophilic and a hydrophobic portion was studied with the aim to determine the location of bonds involved in the initial scission of the copolymers. LC-APCI-IT-MS and LC-APCI-orbitrap-MS were used for the detailed structural analysis of degradation products. The results indicated that initial bond scissions occurred principally at the boundary regions between backbones of polyethylene oxide (PEO) and polypropylene oxide (PPO) chains. Further structural analysis revealed the presence of oxygen adducts in the degradation products. Comparison with a thermal degradation carried out in helium atmosphere, one can conclude that the oxygen adducts are formed by radical reaction with water or dissolving oxygen molecules. The study demonstrated that chemical reactions as well as physical bond stress scissions are involved in the ultrasonic degradation of the copolymers.