Thermogravimetry Coupled to Single Photon Ionization Quadrupole Mass Spectrometry: A Tool To Investigate the Chemical Signature of Thermal Decomposition of Polymeric Materials

Stereoscopic imaging of volatile organic compounds distribution in the region and tracing emission sources of volatile organic compounds using a novel movable single-photon ionization time-of-flight mass spectrometer

This paper presents a newly developed high-performance mobile single-photon ionization time-of-flight mass spectrometry (M-SPI-TOFMS) system for on-line analysis and stereoscopic monitoring of complex gas mixtures. The system is designed for stereoscopic imaging to map the distribution of volatile organic compounds (VOCs) and trace their emission sources in urban areas and industrial parks. It mainly consists of a SPI-TOFMS instrument, a customized commercial vehicle, a meteorological five-parameter monitor with GPS, a high-power generator, and an uninterruptible power supply. The SPI technique, using a 118 nm VUV lamp, can ionize compounds with an ionization potential below 10.78 eV. Mass spectra obtained using this technique show the profiles of various VOCs and some inorganic compounds. The VOCs composition information and mobile location data are simultaneously sent to the GIS software. In GIS software, this data is used for real-time stereoscopic imaging of VOC distribution and precise tracking of VOC movement. The system can achieve a spatial data resolution of 0.69 mm at 25 km/h due to the microsecond detection speed of the M-SPI-TOFMS instrument. The laboratory test provides a rapid overview characterization of benzene, toluene, and xylene. The M-SPI-TOFMS has limits of detection and mass resolution of 33.7 pptv and 1060, respectively. Several field applications were carried out using M-SPI-TOFMS at various locations to identify VOC sources near different factories. The M-SPI-TOFMS system has a navigation monitoring speed of 25 km/h with a time resolution of 1 s. The widespread use of this system will provide accurate data to support environmental management departments in formulating VOCs pollution control policies and improving control efficiency.

Characterization of Polyethylene Branching by Thermal Analysis-Photoionization Mass Spectrometry

The rising demand for more and more specialized polyethylene represents a challenge for synthesis and analysis. The desired properties are dependent on the structure, but its elucidation is still intricate. For this purpose, we applied thermal analysis hyphenated to single photon ionization mass spectrometry (STA-SPI-MS). The melting and pyrolysis behavior of different types of polyethylene were tracked by DSC and mass loss. Crystallinity and melting point give hints about the branching but are also influenced by the molecular weight distribution. The evolving gas analysis patterns obtained by SPI-MS however, contain specific molecular information about the samples. Shifts in the summed spectra, which can be clearly observed with our technique, result from differently favored degradation reactions due to the respective structure. Pyrolysis gas chromatography mass spectrometry (Py-GC-EI-MS) was used to support the assignment of pyrolysis products. Principal component analysis was successfully applied to reduce the complexity of data and find suitable markers. The obtained grouping is based on the molecular fingerprint of the samples and is strongly influenced by short-chain branching. Short and medium alkenes and dienes have the strongest impact on the first four principal components. Thus, two marker ratios could be defined, which also give a comprehensible and robust grouping. Butene and pentene were the most abundant signals in our set of samples. With STA-PI-MS, a broad range of pyrolysis products can be measured at the same time, possibly extending the range for quantifiable short-chain branches to more than six carbon atoms for PE. Unfortunately, no clear trend between long-chain branching and any grouping was observed. The quite universal and soft single photon ionization enables access to many different compound classes and hence other polymers can be studied.

A "Brick" Mass Spectrometer with Photoionization for Direct Analysis of Trace Volatile Compounds

With high portability and favorable performance, miniature mass spectrometers have become one of the most attractive tools for on-site analysis of trace volatile compounds. Based on the "Brick" mass spectrometer (BMS) developed previously, a hand-held BMS integrated with a photoionization source (PI-BMS) was developed in this study for volatile compound analysis. With compact dimensions of 30 cm × 18.5 cm × 27.6 cm (length × width × height), the PI-BMS was equipped with a 10.6 eV UV lamp and capable of generating molecular ions. The capabilities of qualitative and quantitative analyses for different volatile samples were demonstrated and characterized. Under optimized conditions, high detection sensitivity in open air was obtained for the PI-BMS with a limit of detection (LOD) of ∼10 ppbv. As demonstrations of mixture analysis, four different fresh fruits were directly analyzed using PI-BMS, observing characteristic mass spectra for each type of fruit.

Real time monitoring of slow pyrolysis of polyethylene terephthalate (PET) by different mass spectrometric techniques

In the context of waste upgrading of polyethylene terephthalate (PET) by pyrolysis, this study presents three on-line mass spectrometric techniques with soft ionization for monitoring the emitted decomposition products and their thermal dependent evolution profiles. Pyrolysis experiments were performed using a thermogravimetric analyzer (TGA) under nitrogen atmosphere with a heating rate of 5 °C/min from 30 °C to 600 °C. Single-photon ionization (SPI at 118 nm/10.5 eV) and resonance enhanced multiple photon ionization (REMPI at 266 nm) were used with time-of-flight mass spectrometry (TOF-MS) for evolved gas analysis (TGA-SPI/REMPI-TOFMS). Additionally, the chemical signature of the pyrolysis products was investigated by atmospheric pressure chemical ionization (APCI) ultra high resolution Fourier Transform ion cyclotron resonance mass spectrometry (FT-ICR MS) which enables assignment of molecular sum formulas (TGA-APCI FT-ICR MS). Despite the soft ionization by SPI, the fragmentation of some compounds with the loss of the [O-CH = CH2] fragment is observed. The major compounds were acetaldehyde (m/z 44), benzoic acid (m/z 122) and a fragment of m/z 149. Using REMPI, aromatic species were selectively detected. Several series of pyrolysis products were observed in different temperature intervals, showing the presence of polycyclic aromatic hydrocarbons (PAHs), especially at high temperatures. FT-ICR MS data showed, that the CHO₄ class was the most abundant compound class with a relative abundance of 45.5%. The major compounds detected with this technique corresponded to m/z 193.0495 (C₁₀H₉O₄⁺) and 149.0233 (C₈H₅O₃⁺). Based on detailed chemical information, bulk reaction pathways are proposed, showing the formation of both cyclic monomer/dimer and linear structures.

Multi-capillary column high-pressure photoionization time-of-flight mass spectrometry and its application for online rapid analysis of flavor compounds

High-pressure photoionization time-of-flight mass spectrometry (HPPI-TOFMS) is a versatile and highly sensitive analytical technique for online and real-time analysis of trace volatile organic compounds in complex mixtures. However, discrimination of isomers is usually a great challenge for the soft ionization method, and matrix effect is also inevitable under high pressure in the HPPI source. In this work, we describe a first attempt to develop a two-dimensional (2D) hyphenated instrument by coupling of a multi-capillary column (MCC) with a HPPI-TOFMS to overcome these problems. The capability of the MCC-HPPI-TOFMS for discrimination of isomeric compounds and elimination of the matrix effect was demonstrated by analyzing flavor mixtures. With the merits of fast separation, soft ionization and high detection sensitivity, satisfactory effects in the 2D analysis were achieved, despite the relatively low chromatographic resolution of MCC. As a result, three isomers, eucalyptol, l-menthone and linalool, in a flavor mixture were successfully categorized within 90 s, and the matrix effect caused by solvent ethanol was significantly eliminated as well. The limits of detection (LODs) down to sub-ppbv level were achieved for the investigated five flavor compounds without any enrichment process, and an excellent repeatability was obtained with the relative standard deviations (RSDs) of signal intensities ≤5%. The MCC-HPPI-TOFMS system was preliminarily applied for rapid and online analysis of flavor compounds in the exhaled gas of a volunteer after mouth rinsing with a gargle product. The rapid changes of the three flavor compounds, as well as the steady endogenous metabolite acetone, in the exhaled gas were successfully determined with a time-resolution of only 1.5 min.

Characterization of Polystyrene Wastes as Potential Extruded Feedstock Filament for 3D Printing

The recyclability of polystyrene, acrylonitrile butadiene styrene and polyvinylchloride waste and their use as a source for 3D printing were studied. Filaments of about 3 mm in diameter were extruded successfully with a small-size extruder. The processed filaments were tested on a broad range of parameters-melt flow index, glass transition temperature, tensile properties and a pyrolysis scenario were obtained. The measured parameters were compared with parameters of virgin counterparts presented in the literature. In order to estimate the composition of the recycled material, Fourier Transform Infrared and elemental analysis of the samples was done.

Hyphenation of Thermal Analysis to Ultrahigh-Resolution Mass Spectrometry (Fourier Transform Ion Cyclotron Resonance Mass Spectrometry) Using Atmospheric Pressure Chemical Ionization For Studying Composition and Thermal Degradation of Complex Materials

In this study, the hyphenation of a thermobalance to an ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometer (UHR FTICR MS) is presented. Atmospheric pressure chemical ionization (APCI) is used for efficient ionization. The evolved gas analysis (EGA), using high-resolution mass spectrometry allows the time-resolved molecular characterization of thermally induced processes in complex materials or mixtures, such as biomass or crude oil. The most crucial part of the setup is the hyphenation between the thermobalance and the APCI source. Evolved gases are forced to enter the atmospheric pressure ionization interface of the MS by applying a slight overpressure at the thermobalance side of the hyphenation. Using the FTICR exact mass data, detailed chemical information is gained by calculation of elemental compositions from the organic species, enabling a time and temperature resolved, highly selective detection of the evolved species. An additional selectivity is gained by the APCI ionization, which is particularly sensitive toward polar compounds. This selectivity on the one hand misses bulk components of petroleum samples such as alkanes and does not deliver a comprehensive view but on the other hand focuses particularly on typical evolved components from biomass samples. As proof of principle, the thermal behavior of different fossil fuels: heavy fuel oil, light fuel oil, and a crude oil, and different lignocellulosic biomass, namely, beech, birch, spruce, ash, oak, and pine as well as commercial available softwood and birch-bark pellets were investigated. The results clearly show the capability to distinguish between certain wood types through their molecular patterns and compound classes. Additionally, typical literature known pyrolysis biomass marker were confirmed by their elemental composition, such as coniferyl aldehyde (C10H10O3), sinapyl aldehyde (C11H12O4), retene (C18H18), and abietic acid (C20H30O2).

Effusive molecular beam-sampled Knudsen flow reactor coupled to vacuum ultraviolet single photon ionization mass spectrometry using an external free radical source

A new apparatus using vacuum ultraviolet single photon ionization mass spectrometry (VUV SPIMS) of an effusive molecular beam emanating from a Knudsen flow reactor is described. It was designed to study free radical-molecule kinetics over a significant temperature range (300-630 K). Its salient features are: (1) external free radical source, (2) counterpropagating molecular beam and diffuse VUV photon beam meeting in a crossed-beam ion source of a quadrupole mass spectrometer with perpendicular ion extraction, (3) analog detection of the photocurrent of the free radical molecular cation, and (4) possibility of detecting both free radicals and closed shell species in the same apparatus and under identical reaction conditions owing to the presence of photoelectrons generated by the photoelectric effect of the used VUV-photons. The measured thermal molecular beam-to-background ratio was 6.35 ± 0.39 for Ar and 10.86 ± 1.59 for i-C4H10 at 300 K, a factor of 2.52 and 1.50 smaller, respectively, than predicted from basic gas-dynamic considerations. Operating parameters as well as the performance of key elements of the instrument are presented and discussed. Coupled to an external free radical source a steady-state specific exit flow of 1.6 × 10(11) and 5.0 × 10(11) molecule s(-1) cm(-3) of C2H5(●) (ethyl) and t-C4H9(●) (t-butyl) free radicals have been detected using VUV SPIMS at their molecular ion m/z 29 and 57, respectively, at 300 K.

Light and molecular ions: the emergence of vacuum UV single-photon ionization in MS

Thanks to recent technological advances and single-photon ionization's (SPI's) ability to detect all organics, the technique could become the long-sought universal soft ionization method. (To listen to a podcast about this feature, please go to the Analytical Chemistry Web site at pubs.acs.org/journal/ancham.).