Rapid methods of polymer and polymer additives identification: Multi-sample solvent-free MALDI, pyrolysis at atmospheric pressure, and atmospheric solids analysis probe mass spectrometry

Degradation strategies for structural characterization of insoluble synthetic polymers by mass spectrometry

With the advent of soft ionization techniques such as electrospray (ESI) and matrix-assisted laser desorption/ionization (MALDI) to produce intact gas-phase ions from nonvolatile macromolecules, mass spectrometry has become an essential technique in the field of polymeric materials. However, (co)polymers of very high molecular weight or with reticulated architectures still escape ESI or MALDI, mainly due to solubility issues. Strategies developed to tackle such an analytical challenge all rely on sample degradation to produce low-mass species amenable to existing ionization methods. Yet, chain degradation needs to be partial and controlled to generate sufficiently large species that still contain topological or architectural information. The present article reviews the different analytical degradation strategies implemented to perform mass spectrometry of these challenging synthetic polymers, covering thermal degradation approaches in sources developed in the 2000s, off-line sample pre-treatments for controlled chemical degradation of polymeric substrates, and most recent achievements employing reactive ionization modes to perform chemolysis on-line with MS.

Mass spectrometry of polymers: A tutorial review

Ever since the inception of synthetic polymeric materials in the late 19th century, the number of studies on polymers as well as the complexity of their structures have only increased. The development and commercialization of new polymers with properties fine-tuned for specific technological, environmental, consumer, or biomedical applications requires powerful analytical techniques that permit the in-depth characterization of these materials. One such method with the ability to provide chemical composition and structure information with high sensitivity, selectivity, specificity, and speed is mass spectrometry (MS). This tutorial review presents and exemplifies the various MS techniques available for the elucidation of specific structural features in a synthetic polymer, including compositional complexity, primary structure, architecture, topology, and surface properties. Key to every MS analysis is sample conversion to gas-phase ions. This review describes the fundamentals of the most suitable ionization methods for synthetic materials and provides relevant sample preparation protocols. Most importantly, structural characterizations via one-step as well as hyphenated or multidimensional approaches are introduced and demonstrated with specific applications, including surface sensitive and imaging techniques. The aim of this tutorial review is to illustrate the capabilities of MS for the characterization of large, complex polymers and emphasize its potential as a powerful compositional and structural elucidation tool in polymer chemistry.

Rapid Single Particle Atmospheric Solids Analysis Probe-Mass Spectrometry for Multimodal Analysis of Microplastics

Despite mass spectrometry (MS) being proven powerful for the characterization of synthetic polymers, its potential for the analysis of single particle microplastics (MPs) is yet to be fully disclosed. To date, MPs are regarded as ubiquitous contaminants, but the limited availability of techniques that enable full characterizations of MPs results in a lack of systematic data regarding their occurrence. In this study, an atmospheric solid analysis probe (ASAP) coupled to a compact quadrupole MS is proposed for the chemical analysis of single particle microplastics, while maintaining full compatibility with complementary staining and image analysis approaches. A two-stage ASAP probe temperature program was optimized for the removal of additives and surface contaminants followed by the actual polymer characterization. The method showed specific mass spectra for a wide range of single particle MPs, including polyolefins, polyaromatics, polyacrylates, (bio)polyesters, polyamides, polycarbonates, and polyacrylonitriles. The single particle size detection limits for polystyrene MPs were found to be 30 and 5 μm in full scan and selected ion recording mode, respectively. Moreover, results are presented of a multimodal microplastic analysis approach in which filtered particles are first characterized by staining and fluorescence microscopy, followed by simple probe picking of individual particles for subsequent analysis by ASAP-MS. The method provides a full characterization of MP contamination, including particle number, particle size, particle shape, and chemical identity. The applicability of the developed multimodal method was successfully demonstrated by the analysis of MPs in bioplastic bottled water.

Identification and quantification of plastic additives using pyrolysis-GC/MS: A review

Analysis of organic plastic additives (OPAs) associated to plastic polymers is growing. The current review outlines the characteristics and the development of (multi-step) pyrolysis coupled with a gas chromatography mass spectrometer (Py-GC/MS) for the identification and semi-quantification of OPAs. Compared to traditional methods, Py-GC/MS offers advantages like suppressing extensive steps of preparation, limiting contamination due to solvents and the possibility to analyse minute particles. Its key advantage is the successive analysis of OPAs and the polymeric matrix of the same sample. Based on the studied articles, numerous methods have been described allowing identification and, in some case, semi-quantification of OPAs. There is nevertheless no gold standard method, especially given the huge diversity of OPAs and the risks of interferences with polymers or other additives, but, among other parameters, a consensus temperature seems to arise from studies. More broadly, this review also explores many aspects on the sample preparation like weight and size of particles and calibration strategies. After studying the various works, some development prospects emerge and it appears that methodological developments should focus on better characterizing the limits of the methods in order to consider which OPAs can be quantified and in which polymers this is feasible.

Pyrolysis Vacuum-Assisted Plasma Ionization Ion Mobility-Mass Spectrometry for Insoluble Polymer Analysis

This Communication describes a new thermal desorption/pyrolysis vacuum-assisted plasma ionization (pyro-VaPI) ion source coupled to ion mobility-mass spectrometry (IM-MS) for insoluble polymer analysis. Pyro-VaPI combines a pyrolysis device, soft ambient plasma ionization, IM, and MS into a single platform for polymer analysis with minimal sample preparation. Nylons, a widely used and well-studied thermoplastic, were chosen to evaluate the pyro-VaPI performance. Six different nylon polymers were studied and characterized. With the application of IM-MS, two different isobars for the protonated cyclic dimers of 6-6, 6-9, 6-10, and 6-12 nylon and two isobars for the cyclic tetramer of nylon-6 were detected at 200 °C. These isobars were observed at different heating times, with the species drifting faster in the IM cell appearing several minutes after the slower drifting species. To the best of our knowledge, these isobaric dimers and tetramers have not been previously reported, indicating that pyro-VaPI IM-MS is a useful tool for the structural characterization of heated or pyrolyzed polymers.

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.

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.

Simple Pretreatment for the Analysis of Additives and Polymers by Surface-Assisted Laser Desorption/Ionization Mass Spectrometry Using a Through-Hole Alumina Membrane as a Functional Substrate

The analysis of additives and polymers was performed by desorption ionization using through-hole alumina membrane (DIUTHAME) as a functional substrate for both sample pretreatment and surface-assisted laser desorption/ionization (SALDI) mass spectrometry. Using the unique absorbing/filtering capabilities of DIUTHAME and investigating the solubility of analytes/bulk materials in some solvents, three pretreatment techniques were demonstrated with (1) the selective removal of hydrophilic poly(ethylene oxide) (PEO)-based components from a "PEO-monostearate" sample, (2) the on-chip filtration of solubilized decabromodiphenylether (DBDE) from a solution of polystyrene that had been preliminarily precipitated, and (3) the on-chip extraction of antioxidants (Irganox 1010, Irgafos 168, and dimyristyl 3,3'-thiodipropionate) from a suspension of polypropylene powder or from the powder itself. The extracted analytes were further mass-analyzed using a spiral high-resolution time-of-flight analyzer to assess their elemental composition or molecular distribution.

Atmospheric Solid Analysis Probe Coupled to Ion Mobility Spectrometry-Mass Spectrometry, a Fast and Simple Method for Polyalphaolefin Characterization

Polyalphaolefins (PAOs) are polymers produced from linear alpha olefins through catalytic oligomerization processes. The PAOs are known as synthetic high-performance base stock fluids used to improve the efficiency of many other synthetic products. In this study, we report the direct characterization of PAOs using atmospheric solid analysis probe (ASAP) coupled with ion mobility spectrometry-mass spectrometry (IMS-MS). We studied different PAOs grades exhibiting low- and high-viscosity index. Specific adjustments of the ASAP source parameters permitted the monitoring of ionization processes as three mechanisms could occur for these compounds: hydride abstraction, nitrogen addition, and/or the formation of [M-2H]^+• ions. Several series of fragment ions were obtained, which allowed the identification of the alpha olefin used to synthesize the PAO. The use of the ion mobility separation dimension provides information on isomeric species. In addition, the drift time versus m/z plots permitted rapid comparison between PAO samples and to evidence their complexity. These 2D plots appear as fingerprints of PAO samples. To conclude, the resort to ASAP-IMS-MS provides a rapid characterization of the PAO samples in a direct analysis approach, without any sample preparation. Graphical Abstract ᅟ.

Carbon fiber brush electrode as a novel substrate for atmospheric solids analysis probe (ASAP) mass spectrometry: Electrochemical oxidation of brominated phenols

A carbon fiber brush electrode (CFBE) was newly designed and used as a substrate for both controlled potential electrolysis and atmospheric solids analysis probe (ASAP) mass spectrometry. Electropolymerized and strongly adsorbed products of electrolysis were directly desorbed and ionized from the electrode surface. Electrochemical properties of the electrode investigated by cyclic voltammetry revealed large electroactive surface area (23 ± 3 cm²) at 1.3 cm long array of carbon fibers with diameter 6-9 μm. Some products of electrochemical oxidation of pentabromophenol and 2,4,6-tribromophenol formed a compact layer on the carbon fibers and were analyzed using ASAP. Eleven new oligomeric products were identified including quinones and biphenoquinones. These compounds were not observed previously in electrolyzed solutions by liquid or gas chromatography/mass spectrometry. The thickness around 58 nm and 45 nm of the oxidation products layers deposited on carbon fibers during electrolysis of pentabromophenol and 2,4,6-tribromophenol, respectively, was estimated from atomic force microscopy analysis and confirmed by scanning electron microscopy with energy-dispersive X-ray spectroscopy measurements.

High Resolution Mass Spectrometry of Polyfluorinated Polyether-Based Formulation

High resolution mass spectrometry (HRMS) was successfully applied to elucidate the structure of a polyfluorinated polyether (PFPE)-based formulation. The mass spectrum generated from direct injection into the MS was examined by identifying the different repeating units manually and with the aid of an instrument data processor. Highly accurate mass spectral data enabled the calculation of higher-order mass defects. The different plots of MW and the nth-order mass defects (up to n = 3) could aid in assessing the structure of the different repeating units and estimating their absolute and relative number per molecule. The three major repeating units were -C2H4O-, -C2F4O-, and -CF2O-. Tandem MS was used to identify the end groups that appeared to be phosphates, as well as the possible distribution of the repeating units. Reversed-phase HPLC separated of the polymer molecules on the basis of number of nonpolar repeating units. The elucidated structure resembles the structure in the published manufacturer technical data. This analytical approach to the characterization of a PFPE-based formulation can serve as a guide in analyzing not just other PFPE-based formulations but also other fluorinated and non-fluorinated polymers. The information from MS is essential in studying the physico-chemical properties of PFPEs and can help in assessing the risks they pose to the environment and to human health. Graphical Abstract ᅟ.

Plasma-based ambient mass spectrometry techniques: The current status and future prospective

Plasma-based ambient mass spectrometry is emerging as a frontier technology for direct analysis of sample that employs low-energy plasma as the ionization reagent. The versatile sources of ambient mass spectrometry (MS) can be classified according to the plasma formation approaches; namely, corona discharge, glow discharge, dielectric barrier discharge, and microwave-induced discharge. These techniques allow pretreatment-free detection of samples, ranging from biological materials (e.g., flies, bacteria, plants, tissues, peptides, metabolites, and lipids) to pharmaceuticals, food-stuffs, polymers, chemical warfare reagents, and daily-use chemicals. In most cases, plasma-based ambient MS performs well as a qualitative tool and as an analyzer for semi-quantitation. Herein, we provide an overview of the key concepts, mechanisms, and applications of plasma-based ambient MS techniques, and discuss the challenges and outlook.

Inlet and Vacuum Ionization from Ambient Conditions

The discovery that laser ablation of a common MALDI matrix at atmospheric pressure without use of a voltage produced ions with nearly identical charge states to ESI led to a series of new ionization methods that we have given the general term inlet and vacuum ionization. The initial thought that the laser was necessary for matrix-assisted ionization gave way to ionization requiring a heated inlet with a pressure-drop region and then to a matrix that could be a solvent or no matrix. This in turn led to laser ablation in vacuum producing multiply charged ions without an inlet, and finally to the present where we have found matrices that lift molecules into the gas phase as ions without any external energy source. Our mechanistic view of this new ionization process developed into ionization methods for use in mass spectrometry will be discussed. These methods are simple to use, safe, robust, and sensitive. Several approaches for high-throughput analyses of compounds irrespective of their molecular weight will be presented using low- and high-performance mass spectrometers.

Ambient analysis of leachable compounds from single-use bioreactors with desorption electrospray ionization time-of-flight mass spectrometry

RATIONALE

Trace levels of bis(2,4-di-tert-butylphenyl)phosphate (BdtbPP) leaching from single-use bioreactors (SUBs) were recently found to be highly detrimental to mammalian cell growth. The traditional approach to detect the leachable requires time-consuming solvent extraction of SUBs. To assist the qualification of SUBs and/or their manufacturing raw materials in biopharmaceutical development and manufacturing, it is essential to develop a rapid and sensitive analytical approach for detecting this leachable and related compounds, which is described in this study.

METHODS

Native films from several commercially available SUBs were directly examined by desorption electrospray ionization (DESI) time-of-flight mass spectrometry (TOFMS) without sample preparation. As a comparison, the same SUBs were also analyzed by high-performance liquid chromatography (HPLC)/ultraviolet (UV) following the solvent extraction.

RESULTS

With a suitable spray solvent selected in this study, DESI-TOFMS enabled rapid and sensitive detection of leachable compounds directly from SUBs. Accurate mass measurement from TOFMS allowed ready identification of BdtbPP, its parent analog compound, and other polymer components in the SUBs from their protonated surrogates. The relative abundances of BdtbPP in different SUBs measured by DESI-TOFMS exhibited good correlation with those from the traditional extraction-based approach with HPLC/UV.

CONCLUSIONS

A rapid and sensitive approach was developed for direct detection of BdtbPP and other leachables from SUBs using DESI-TOFMS. The results are in high accordance with those from conventional approaches, which indicates the usefulness of the proposed method as a qualification tool for SUBs in biopharmaceutical development and also its great potential in the analysis of extractables/leachables in a wide variety of materials, process components, devices and containers used in the pharmaceutical industry.

Rapid identification of polymer additives by atmospheric solid analysis probe with quadrupole time-of-flight mass spectrometry

RATIONALE

A method using an atmospheric solid analysis probe (ASAP) combined with quadrupole time-of-flight mass spectrometry (QTOFMS) assisted by a pre-built MS library was found to be efficient in fast and direct analysis of additives for polymers. By this method, sample pretreatment could be eliminated from the additives identification process.

METHODS

Some crucial parameters, such as desolvation gas temperature, corona current, sample cone voltage and collision energy, should be optimized. A MS library of 100 polymer additives, including phenols (Irganox 1010, Irganox 1076), hydroxyl phenyl benzotriazole derivatives (Tinuvin 326, Tinuvin 327, Tinuvin 328), hindered amines (Tinuvin 944, Tinuvin 770) and plasticizers, was built based on the optimized conditions. To verify the application of the MS library, the ASAP-QTOFMS method was applied to identify complex additives, a simulated polypropylene (PP) sample and a real polymethylmethacrylate (PMMA) sample purchased from a local market.

RESULTS

By searching the exact mass, and comparing the MS and MS/MS spectra of samples with standards in the MS library, complex additives such as Irganox GX 2921, as well as additives in PP and PMMA samples, could be identified quickly and easily. The determination of mass accuracy increased the confidence of peak identification as well. Moreover, the results also provided information of the characterization for PP and PMMA polymers.

CONCLUSIONS

A rapid identification method has been developed for polymer additives by ASAP-QTOFMS. A MS library of 100 polymer additives was built by this method. Using ASAP-QTOFMS assisted by the pre-built MS library, polymer additives can be quickly identified. This method was found to be a promising tool in the rapid analysis of additives in polymers and polymer matrices.

Rapid analysis of lubricants by atmospheric solid analysis probe-ion mobility mass spectrometry

Formulated lubricants are complex mixtures composed of base oil(s) and additives with various functions (detergents, corrosion inhibiter, antioxidant, viscosity modifiers, etc.). Because of the aliphatic nature of base oil and the chemical diversity of additives, the characterization of lubricant is currently a long and complex process. The comprehensive analysis of lubricant samples involves several techniques such as nuclear magnetic resonance, mass spectrometry, chromatography and infrared spectroscopy. The coupling of atmospheric solid analysis probe (ASAP) with ion mobility-mass spectrometry (IM-MS) has been shown to be an efficient tool for the characterization of complex mixture containing vaporizable polar to non-polar compounds. This approach affords the coupling of a direct ionization technique that does not require sample preparation, with a bi-dimensional separation method with high peak capacity. In this work, we show that ASAP-IM-MS is a suitable method for rapid and direct characterization of lubricant samples. Indeed, base oil and additives yielded, by ASAP, ions series which could be separated by IM-MS. Molecular additives such as Zn-dithiocarbamate, phosphite, thiophosphate and Alkyl diphenylamine were ionized as molecular ions [M](+•) or protonated molecules [M + H](+), depending of their polarity. In some cases, fragment ions were observed, confirming the additive identification. In addition, high molecular weight polymeric additives such as poly(alkyl methacrylate) (PAM) were pyrolized in the ASAP source leading to characteristic fragment ions. ASAP-IM-MS is shown to be a powerful tool for studying complex mixtures, allowing the first comprehensive analysis of lubricants in just a few minutes.

Matrix segregation as the major cause for sample inhomogeneity in MALDI dried droplet spots

The segregation in dried droplet MALDI sample spots was analyzed with regard to the matrix-to-sample ratio using optical microscopy, MALDI imaging mass spectrometry (MALDI MSI) and IR imaging spectroscopy. In this context, different polymer/matrix/solvent systems usually applied in the analysis of synthetic polymers were investigated. The use of typical matrix concentrations (10 mg mL⁻¹) in almost every case resulted in ring patterns, whereas higher concentrated matrix solutions always led to homogeneous sample spot layers. The data revealed that segregation is predominantly caused by matrix transport in the drying droplet, whereas polymer segregation seems to be only secondary.

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.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric imaging of synthetic polymer sample spots prepared using ionic liquid matrices

RATIONALE

Polymer sample spots for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) prepared by the dried-droplet method often reveal ring formation accompanied by possible segregation of matrix and sample molecules as well as of the polymer homologs itself. Since the majority of sample spots are prepared by this simple and fast method, a matrix or sample preparation method that excludes such segregation has to be found.

METHODS

Three different ionic liquid matrices based on conventionally used aromatic compounds for MALDI-TOF MS were prepared. The formation of ionic liquids was proven by (1) H NMR spectroscopy. MALDI-Imaging mass spectrometry was applied to monitor the homogeneity.

RESULTS

Our results show a superior sample spot homogeneity using ionic liquid matrices. Spots could be sampled several times without visible differences in the mass spectra. A frequently observed loss of matrix in the mass spectrometer vacuum was not observed. The necessary laser irradiance was reduced, which resulted in less polymer fragmentation.

CONCLUSIONS

Ionic liquid matrices can be used to overcome segregation, a typical drawback of conventional MALDI dried-droplet preparations. Homogeneous sample spots are easy to prepare, stable in the MS vacuum and, thereby, improve the reproducibility of MALDI.

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).

Quantitative analysis of polymer additives with MALDI-TOF MS using an internal standard approach

MALDI-TOF MS is used for the qualitative analysis of seven different polymer additives directly from the polymer without tedious sample pretreatment. Additionally, by using a solid sample preparation technique, which avoids the concentration gradient problems known to occur with dried droplets and by adding tetraphenylporphyrine as an internal standard to the matrix, it is possible to perform quantitative analysis of additives directly from the polymer sample. Calibration curves for Tinuvin 770, Tinuvin 622, Irganox 1024, Irganox 1010, Irgafos 168, and Chimassorb 944 are presented, showing coefficients of determination between 0.911 and 0.990.

Surface assisted laser desorption ionization-mass spectrometry (SALDI-MS) for analysis of polyester degradation products

Novel surface assisted laser desorption ionization-mass spectrometry (SALDI-MS) method was developed for rapid analysis of low molecular mass polyesters and their degradation products by laser desorption ionization-mass spectrometry. Three polycaprolactone materials were analyzed by the developed method before and after hydrolytic degradation. The signal-to-noise values obtained by SALDI-MS were 20-100 times higher compared with the ones obtained by using traditional MALDI-MS matrices. A clean background at low mass range and higher resolution was obtained by SALDI-MS. Different nanoparticle, cationizing agent, and solvent combinations were evaluated. Halloysite nanoclay and magnesium hydroxide showed the best potential as SALDI surfaces. The SALDI-MS spectrum of the polyester hydrolysis products was verified by ESI-MS. The developed SALDI-MS method possesses several advantages over existing methods for similar analyses.

Laserspray ionization using an atmospheric solids analysis probe for sample introduction

A newly introduced high sensitivity laserspray (LSI) mass spectrometry (MS) method that uses laser ablation of a matrix/analyte mixture at atmospheric pressure (AP) to obtain multiply charged ions from nonvolatile as well as high-mass compounds is now implemented using a simple probe device. The probe used in the LSI approach was originally designed for sample introduction into an AP ionization source using the atmospheric solids analysis probe (ASAP) method. Multiply charged mass spectra of peptides and proteins in 2,5-dihydroxybenzoic acid matrix were readily obtained on two mass spectrometers from different manufacturers with sample introduction using melting point tubes. Here we demonstrate rapid analysis by placing four peptide and protein samples on a single melting point tube. Mass spectra were obtained at high-resolution and using ion mobility spectrometry/MS.

A perspective on MALDI alternatives-total solvent-free analysis and electron transfer dissociation of highly charged ions by laserspray ionization

Progress in research is hindered by analytical limitations, especially in biological areas in which sensitivity and dynamic range are critical to success. Inherent difficulties of characterization associated with complexity arising from heterogeneity of various materials including topologies (isomeric composition) and insolubility also limit progress. For this reason, we are developing methods for total solvent-free analysis by mass spectrometry consisting of solvent-free ionization followed by solvent-free gas-phase separation. We also recently constructed a novel matrix-assisted laser desorption ionization (MALDI) source that provides a simple, practical and sensitive way of producing highly charged ions by laserspray ionization (LSI) or singly charged ions commonly observed with MALDI by choice of matrix or matrix preparation. This is the first ionization source with such freedom-an extremely powerful analytical 'switch'. Multiply charged LSI ions allow molecules exceeding the mass-to-charge range of the instrument to be observed and permit for the first time electron transfer dissociation fragment ion analysis.

Automated solvent-free matrix deposition for tissue imaging by mass spectrometry

The ability to analyze complex (macro) molecules is of fundamental importance for understanding chemical, physical, and biological processes. Complexity may arise from small differences in structure, large dynamic range, as well as a vast range in solubility or ionization, imposing daunting tasks in areas as different as lipidomics and proteomics. Here, we describe a rapid matrix application that permits the deposition of matrix-assisted laser desorption/ionization (MALDI) matrix solvent-free. This solvent-free one-step automatic matrix deposition is achieved through vigorous movements of beads pressing the matrix material through a metal mesh. The mesh (20 mum) produces homogeneous coverage of <12 microm crystals (DHB, CHCA matrixes) in 1 min, as determined by optical microscopy, permitting fast uniform coverage of analyte and possible high-spatial resolution surface analysis. Homogenous tissue coverage of <5 microm sized crystals is achieved using a 3 microm mesh. Solvent-free MALDI analysis on a time-of-flight (TOF) mass analyzer of mouse brain tissue homogenously covered with CHCA matrix subsequently provides a homogeneous response in ion signal intensity. Total solvent-free analysis (TSA) by mass spectrometry (MS) of tissue sections is carried out by applying the MALDI matrix solvent-free for subsequent ionization and gas phase separation for decongestion of complexity in the absence of any solvent using ion mobility spectrometry (IMS) followed by MS detection. Isobaric compositions were well-delineated using TSA by MS.

Laserspray ionization, a new atmospheric pressure MALDI method for producing highly charged gas-phase ions of peptides and proteins directly from solid solutions

The first example of a matrix-assisted laser desorption/ionization (MALDI) process producing multiply charged mass spectra nearly identical to those observed with electrospray ionization (ESI) is presented. MALDI is noted for its ability to produce singly charged ions, but in the experiments described here multiply charged ions are produced by laser ablation of analyte incorporated into a common MALDI matrix, 2,5-dihydroxybenzoic acid, using standard solvent-based sample preparation protocols. Laser ablation is known to produce matrix clusters in MALDI provided a threshold energy is achieved. We propose that these clusters (liquid droplets) are highly charged, and under conditions that produce sufficient matrix evaporation, ions are field-evaporated from the droplets similarly to ESI. Because of the multiple charging, advanced mass spectrometers with limited mass-to-charge range can be used for protein characterization. Thus, using an Orbitrap mass spectrometer, low femtomole quantities of proteins produce full-range mass spectra at 100,000 mass resolution with <5-ppm mass accuracy and with 1-s acquisition. Furthermore, the first example of protein fragmentation using electron transfer dissociation with MALDI is presented.