Three-Dimensional Mass Spectral Imaging of Polymers Via Laser-Assisted Micro-Pyrolysis Program with Flowing Atmospheric-Pressure Afterglow Ambient Mass Spectrometry

Herein, a novel diode laser-assisted micro-pyrolysis program (LAMP) technique is demonstrated and coupled with flowing atmospheric-pressure afterglow ambient mass spectrometry for instantaneously profiling polymers and polymer additives. Laser power modulation allows thermal separation of additives and different pyrolysis products, as shown through positive- and negative-mode high-resolution mass spectra and Kendrick mass defect plots of homopolymers, copolymers, polymer blends, and complex polymer samples. LAMP allows much faster temperature control through real-time duty cycle changes and gives significantly better spatial confinement compared to typical resistive heating pyrolysis approaches. Finally, MS imaging, with lateral and depth resolution, is demonstrated for a complex polymer pressure-sensitive adhesive tape sample.

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.

Laser assisted sampling vs direct desorption flowing atmospheric pressure afterglow mass spectrometry of complex polymer samples: Forensic implications for pressure sensitive tape chemical analysis

Flowing atmospheric pressure afterglow (FAPA) mass spectrometry (MS) is an easy-to-use, cost-effective, and potentially portable technique that allows direct desorption/ionization from samples with little-to-no sample preparation for real-time chemical analysis. However, it has limitations regarding analytes with low desorption efficiency, such as polymers. Here, laser assisted sampling (LAS) is developed and coupled to FAPA MS to allow access to a wider range of chemical information from polymer samples. This is achieved through laser-induced pyrolysis conditions that provide a much higher degree of spatio-temporal control compared to typical pyrolysis techniques. LAS FAPA MS, together with direct desorption FAPA MS, is implemented on pressure sensitive adhesive (PSA) tape samples, which are often found at crime scenes and recovered as forensic evidence. Comparative PSA tape examination is typically performed to assess any differences in the comparison of unknown and known samples and provide an evidentiary association between suspects and crime scenes in forensic applications. PSA tape samples from several manufacturers of duct, masking, and electrical tape were analyzed from the adhesive and backing side. Direct desorption FAPA provides top-surface selectivity and the tape mass spectra are dominated by more peaks at lower m/z, many of which correspond to polymer additives. LAS gives access to sampling from all of the tape layers and the FAPA mass spectra is extended to higher m/z, while polymer fragmentation patterns are evident. Principal components analysis (PCA) was implemented to assess the ability of each technique to distinguish and categorize identified tape classes within the sampled population. The complementary nature of the resulting mass spectra from direct desorption vs LAS FAPA was evident from the PCA as different tape brands sub-sets were discriminated by each technique. The differentiation obtained by combining both methods is already competitive, or better, than conventional techniques, with the additional benefits of AMS.

Plasma-Based Ambient Desorption/Ionization Mass Spectrometry for the Analysis of Liquid Crystals Employed in Display Devices

Liquid-crystal displays (LCDs) are the most frequently used display technology worldwide these days. Due to the rather complex manufacturing process and purity requirements for the chemicals used, quality control and display failure analysis are important analytical tasks. Currently, the state-of-the-art techniques (e.g., high-performance liquid chromatography (HPLC), gas chromatography (GC) coupled to mass spectrometry (MS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), or high-resolution microscopy) are costly and time-consuming. Hence, a new pathway to precisely analyze liquid-crystalline materials and LCDs in their native state is reported. A new approach for direct analysis via plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) offers an inexpensive and faster alternative. In this study, direct analysis in real time (DART), the low-temperature plasma (LTP) probe, and flowing atmospheric-pressure afterglow (FAPA) ADI sources coupled to high-resolution mass spectrometry (HR-MS) are compared based on their capabilities and performance for liquid-crystal analysis. These sources enable direct analyte desorption from a sample surface at ambient conditions and ionize the vaporized analyte molecules in a subsequent step. Primarily, the ionization capabilities of the three ADI sources are compared for individual liquid-crystal standards, mixtures of liquid crystals (LCs), and complex liquid crystal/additive mixtures applied in commercially available LCDs. Furthermore, direct surface analysis from a glass substrate is also performed with ADI-MS to compare their applicability to this type of sample matrix.

Ambient Characterization of Synthetic Fibers by Laser Ablation Electrospray Ionization Mass Spectrometry

Direct analysis of synthetic fibers under ambient conditions is highly desired to identify the polymer, the finishes applied and irregularities that may compromise its performance and value. In this paper, laser ablation electrospray ionization ion mobility time-of-flight mass spectrometry (LAESI-IMS-TOF-MS) was used for the analysis of synthetic polymers and fibers. The key to this analysis was the absorption of laser light by aliphatic and aromatic nitrogen functionalities in the polymers. Analysis of polyamide (PA) 6, 46, 66, and 12 pellets and PA 6, 66, polyaramid and M5 fibers yielded characteristic fragment ions without any sample pretreatment, enabling their unambiguous identification. Synthetic fibers are, in addition, commonly covered with a surface layer for improved adhesion and processing. The same setup, but operated in a transient infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mode, allowed the detailed characterization of the fiber finish layer and the underlying polymer. Differences in finish layer distribution may cause variations in local properties of synthetic fibers. Here we also show the feasibility of mass spectrometry imaging (MSI) of the distribution of a finish layer on the synthetic fiber and the successful detection of local surface defects.

Transferability and Adhesion of Sol-Gel-Derived Crystalline TiO2 Thin Films to Different Types of Plastic Substrates

Anatase thin films were prepared on various plastic substrates by our recently developed sol-gel transfer technique. Polycarbonate (PC), poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyether ether ketone (PEEK), and polyvinylidene chloride (PVDC) were employed as plastic substrates. A Si(100) substrate was first coated with a polyimide (PI)/polyvinylpyrrolidone (PVP) mixture layer, and an alkoxide-derived titania gel film was deposited on it by spin-coating. The resulting titania gel film was heated to 600 °C, during which the PI/PVP layer decomposed and the gel film was converted into a 60 nm thick anatase film. The anatase film was then transferred from the Si(100) substrate to the plastic substrate. This was achieved by heating the plastic/anatase/Si(100) stack in a near-infrared image furnace to 120-350 °C, depending on the type of plastic substrate, under unidirectional pressure. The anatase film cracked during transfer to PE, PP, PEEK, and PVDC substrates but did not crack during transfer to PC, PMMA, and PET substrates. The fraction of the total film area that was successfully transferred was assessed with the aid of image analysis. This fraction tended to be large for plastics with C═O and C-O groups and small for those without these groups. The film/substrate adhesion assessed by cross-cut tape tests also tended to be high for plastics with C═O and C-O groups and low for those without these groups. The adhesion to plastics without C═O or C-O groups could be enhanced and their transfer area fraction increased by oxidizing the native plastic surface by ultraviolet-ozone treatment prior to transfer.

DESI MS based screening method for phthalates in consumer goods

Phthalates are used as plasticizes in many everyday items, but some of them are known as hormone disruptors, being especially harmful during childhood. The European Union therefore restricted their application in children's toys and certain food packaging to 0.1%w. Due to the ever increasing number of plastic-containing consumer goods, rapid screening methods are needed to ensure and improve consumer safety in the future. In this study we evaluated the performance of desorption electrospray ionization (DESI) mass spectrometry (MS) for rapid quantitative screening of phthalates in toys. DESI allowed for direct surface sampling of the toys under atmospheric conditions with minimal sample preparation, while the high performance mass spectrometer used provided a high sensitivity and reliable identification via accurate mass measurements, high mass resolving power and MS/MS capabilities. External calibration curves for six banned phthalates (DBP, BBP, DEHP, DNOP, DINP and DIDP) were obtained from matrix-matched reference materials. Coefficients of determination were greater than 0.985, LOQs ranged from 0.02%w (DIDP) to 2.26%w (DINP) and the relative standard deviation of the calibration curve slope was less than 7.8% for intraday and 11.4% for interday comparison. The phthalate contents of eleven authentic samples were determined in a proof-of-concept approach using DESI MS and results were compared to those from confirmatory methods. The phthalate content was correctly assigned with relative deviations ranging from -20% to +10% for the majority of samples. Given further optimization and automation, DESI MS is likely to become a useful tool for rapid and accurate phthalate screening in the future.

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.

Flash desorption/mass spectrometry for the analysis of less- and nonvolatile samples using a linearly driven heated metal filament

In this paper, the important issue of the desorption of less- and nonvolatile compounds with minimal sample decomposition in ambient mass spectrometry is approached using ambient flash desorption mass spectrometry. The preheated stainless steel filament was driven down and up along the vertical axis in 0.3 s. At the lowest position, it touched the surface of the sample with an invasion depth of 0.1 mm in 50 ms (flash heating) and was removed from the surface (fast cooling). The heating rate corresponds to ~10(4) °C/s at the filament temperature of 500 °C. The desorbed gaseous molecules were ionized by using a dielectric barrier discharge ion source, and the produced ions were detected by a time-of-flight (TOF) mass spectrometer. Less-volatile samples, such as pharmaceutical tablets, narcotics, explosives, and C60 gave molecular and protonated molecule ions as major ions with thermal decomposition minimally suppressed. For synthetic polymers (PMMA, PLA, and PS), the mass spectra reflected their backbone structures because of the suppression of the sequential thermal decompositions of the primary products. The present technique appears to be suitable for high-throughput qualitative analyses of many types of solid samples in the range from a few ng to 10 μg with minimal sample consumption. Some contribution from tribodesorption in addition to thermal desorption was suggested for the desorption processes. Figure ᅟ

Distinguishing authentic and counterfeit banknotes by surface chemical composition determined using electrospray laser desorption ionization mass spectrometry

Electrospray laser desorption ionization mass spectrometry (ELDI/MS) was used to rapidly distinguish authentic banknotes from counterfeits of the US dollar and the New Taiwan dollar. The banknotes' surfaces were irradiated with a pulsed ultraviolet laser, after which the desorbed ink compounds entered an electrospray plume and formed ions via interactions with charged solvent species. Authentic banknotes were found to differ from their counterfeit equivalents in their surface chemical compositions. The detected chemical compounds included various polymers, plasticizers and inks; these results were comparable with those obtained using solvent extraction followed by electrospray ionization mass spectrometry analysis. Because of the high spatial resolution of the laser beam, ELDI/MS analysis resulted in minimal damage to the banknotes.

Paper spray: a simple and efficient means of analysis of different contaminants in foodstuffs

A simple and efficient ambient ionization method based on paper spray combined with tandem mass spectrometry allows rapid detection and quantitation of various contaminants (clenbuterol, melamine, plasticizer and sudan red) in various foodstuffs (e.g., meat, milk, sports drinks and chili powder).

Ultrasensitive ambient mass spectrometric analysis with a pin-to-capillary flowing atmospheric-pressure afterglow source

The advent of ambient desorption/ionization mass spectrometry has resulted in a strong interest in ionization sources that are capable of direct analyte sampling and ionization. One source that has enjoyed increasing interest is the flowing atmospheric-pressure afterglow (FAPA). The FAPA has been proven capable of directly desorbing/ionizing samples in any phase (solid, liquid, or gas) and with impressive limits of detection (<100 fmol). The FAPA was also shown to be less affected by competitive-ionization matrix effects than other plasma-based sources. However, the original FAPA design exhibited substantial background levels, cluttered background spectra in the negative-ion mode, and significant oxidation of aromatic analytes, which ultimately compromised analyte identification and quantification. In the present study, a change in the FAPA configuration from a pin-to-plate to a pin-to-capillary geometry was found to vastly improve performance. Background signals in positive- and negative-ionization modes were reduced by 89% and 99%, respectively. Additionally, the capillary anode strongly reduced the amount of atomic oxygen that could cause oxidation of analytes. Temperatures of the gas stream that interacts with the sample, which heavily influences desorption capabilities, were compared between the two sources by means of IR thermography. The performance of the new FAPA configuration is evaluated through the determination of a variety of compounds in positive- and negative-ion mode, including agrochemicals and explosives. A detection limit of 4 amol was found for the direct determination of the agrochemical ametryn and appears to be spectrometer-limited. The ability to quickly screen for analytes in bulk liquid samples with the pin-to-capillary FAPA is also shown.