Solvent and ion source pressure were two important factors relating to the photon induced ion-molecule reactions in low pressure photoionization (LPPI). In this work, four anabolic steroids were analyzed by LPPI mass spectrometry. Both the ion species present and their relative abundances could be controlled by switching the solvent and adjusting the ion source pressure. Whereas M•+, MH+, [M – H2O]+, and solvent adducts were observed in positive LPPI, [M – H]– and various oxidation products were abundant in negative LPPI. Changing the solvent greatly affected formation of the ion species in both positive and negative ion modes. The ion intensities of the solvent adduct and oxygen adduct were selectively enhanced when the ion source pressure was elevated from 68 to 800 Pa. The limit of detection could be decreased by increasing the ion source pressure.

Measurement of the retention of cigarette smoke components in the human mouth is important for evaluating smoking-related diseases. Here, a newly developed on-line vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) method was applied for the mouth retention study of gaseous mainstream cigarette smoke components. The cigarette smoke in the smoking machine or in the mouths of subjects was directly introduced into the vacuum chamber, photoionized and analyzed with a TOF mass spectrometer without any tedious collection and pretreatment procedures. Thus, the retained amount of cigarette smoke components in the mouth could be observed in real time. The results show that at a 2-second holding time, aldehydes, ketones and amine compounds have high mouth retention; methanethiol, phenol and nitrogen heterocyclic compounds have medium mouth retention, while the retention of NO, benzene and unsaturated hydrocarbons was relatively low. Moreover, the effects of the holding time on the mouth retention of the gaseous components within 26 seconds were also obtained, and two main variation trends were observed for different smoke constituents. This method can offer new analysis techniques for further studying the whole respiratory tract retention of cigarette smoke, and deeply evaluating the relationship between smoking and health.

Pyrolysis is considered to be a simple and effective method for the clean conversion of coal. In this work, catalytic pyrolysis of bituminous coal over two commercial available zeolites, i.e., HZSM-5 and HUSY, was investigated with newly constructed pyrolysis photoionization time-of-flight mass spectrometry (Py–PI–TOFMS) in real time. The fragment-free mass spectra of coal pyrolysis products at different pyrolysis temperatures were measured. Products such as alkanes, alkenes, dienes, phenols, aromatics, and small amounts of NH3 and H2S could be detected. The abundant products at a relatively low temperature (500–600 °C) are phenols. With the presence of zeolites, the product distribution could be observed from the mass spectra. Temperature effects for pyrolysis products show some different tendencies with and without HZSM-5 and HUSY as a result of different acidities and pore sizes of the catalysts. Time-evolved profiles of major products were also measured during the pyrolysis processes. The temperature and catalyst can both dramatically affect the reaction rates. Our work demonstrates the good performance of Py–PI–TOFMS for the online study of the bituminous coal pyrolysis. In addition, it can be used to evaluate the performance of different catalysts.

Refuse-derived fuels or chemicals have attracted much attention because of their ecological and economical utilization of municipal solid waste. However, the related conversions involve complex chemical reactions that prevent the use of conventional analytical methods for characterization of the detailed profiles. In this study, the influence of the thermal pretreatment of HUSY on the catalytic pyrolysis of polypropylene (PP) was investigated using online pyrolysis photoionization time-of-flight mass spectrometry (Py-PI-TOFMS). The experiments were carried out in two modes: (1) In temperature-fixed mode, the mass spectra of the pyrolyzates of PP and PP/HUSY at different temperatures were obtained in real time. Moreover, the selectivity of the pyrolyzates and conversion of PP over HUSY zeolites calcined at different temperatures were studied. (2) In temperature-programmed mode, the formation temperatures of the PP pyrolysis products in the presence of HUSY were determined. HUSY zeolites that are pretreated at different temperatures in the range from 200 to 800 °C exhibit distinct catalytic properties. The results of catalytic pyrolysis with a pretreatment temperature of 200 or 800 °C differed compared with those obtained using a pretreatment temperature of 350, 500, or 650 °C. However, the performances of catalysts prepared using these three pretreatment temperatures were similar, consistent with the changes in the HUSY structures observed from the XRD results and the acidities measured by NH3-TPD. The different acidities of the HUSYs resulted in different catalytic activities and pyrolysis product distributions. The results of this study indicate that Py-PI-TOFMS is a powerful technique for the comprehensive study of pyrolysis products and their pyrolysis behaviors, as well as catalysts prepared using different pretreatment conditions.

The demand of modern society for energy keeps increasing as a result of the rapid growth of population and urbanization. Pyrolysis of solid fuels, including biomass, coal, and polymer waste, has recently received special attention because it can provide extra sources of fuels. In the past few years, a variety of analytical techniques have been used to detect the pyrolysis products of solid fuels, such as gas chromatography/mass spectrometry, thermogravimetry, Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, etc. However, online detection of gas release during the pyrolysis process, which is believed to be closely related to the thermal decomposition mechanisms of solid fuels, is rare. Recently, some progress has been made in real-time diagnostic techniques, the most important one of which is photoionization mass spectrometry (PIMS). This review focuses on recent developments in the pyrolysis study of solid fuels, especially on those performed with synchrotron vacuum ultraviolet (SVUV)–PIMS.

Extractive atmospheric pressure photoionization (EAPPI) mass spectrometry was designed for rapid qualitative and quantitative analysis of chemicals in complex matrices. In this method, an ultrasonic nebulization system was applied to sample extraction, nebulization, and vaporization. Mixed with a gaseous dopant, vaporized analytes were ionized through ambient photon-induced ion–molecule reactions, and were mass-analyzed by a high resolution time-of-flight mass spectrometer (TOF-MS). After careful optimization and testing with pure sample solution, EAPPI was successfully applied to the fast screening of capsules, soil, natural products, and viscous compounds. Analysis was completed within a few seconds without the need for preseparation. Moreover, the quantification capability of EAPPI for matrices was evaluated by analyzing six polycyclic aromatic hydrocarbons (PAHs) in soil. The correlation coefficients (R2) for standard curves of all six PAHs were above 0.99, and the detection limits were in the range of 0.16–0.34 ng/mg. In addition, EAPPI could also be used to monitor organic chemical reactions in real time.

•A strategy combining ultrasonic nebulization extraction and low-pressure photoionization (UNE-LPPI) was developed.•Good linearities for phenanthrene and pyrene in soil powder in the range of 10–400 ng mg−1 were obtained.•The components in tablets and plant tissues can be extracted and ionized effectively by UNE-LPPI.•UNE-LPPI generally forms the molecular ions, providing a complementary ionization method to APPI.A novel ultrasonic nebulization extraction/low-pressure photoionization (UNE-LPPI) system has been designed and employed for the rapid mass spectrometric analysis of chemicals in matrices. An ultrasonic nebulizer was used to extract the chemicals in solid sample and nebulize the solvent in the nebulization cell. Aerosols formed by ultrasonic were evaporated by passing through a transferring tube, and desolvated chemicals were ionized by the emitted light (10.6 eV) from a Krypton discharge lamp at low pressure (∼68 Pa). First, a series of semi/non-volatile compounds with different polarities, such as polycyclic aromatic hydrocarbons (PAHs), amino acids, dipeptides, drugs, nucleic acids, alkaloids, and steroids were used to test the system. Then, the quantification capability of UNE-LPPI was checked with: 1) pure chemicals, such as 9,10-phenanthrenequinone and 1,4-naphthoquinone dissolved in solvent; 2) soil powder spiked with different amounts of phenanthrene and pyrene. For pure chemicals, the correlation coefficient (R2) for the standard curve of 9,10-phenanthrenequinone in the range of 3 ng–20 μg mL−1 was 0.9922, and the measured limits of detection (LOD) was 1 ng ml−1. In the case of soil powder, linear relationships for phenanthrene and pyrene from 10 to 400 ng mg−1 were obtained with correlation coefficients of 0.9889 and 0.9893, respectively. At last, the feasibility of UNE-LPPI for the detection of chemicals in real matrices such as tablets and biological tissues (tea, Citrus aurantium peel and sage (Salvia officinalis) leaf) were successfully demonstrated.

The production of hydrocarbons through the pyrolysis of polyolefins is a promising way of fuel recycling. In this work, online single-photon ionization time-of-flight mass spectrometry (SPI–TOFMS) was used to study both thermal and catalytic decompositions of polypropylene (PP) in a tubular furnace. SPI produces few or no fragments of molecular ions, making the identification and interpretation of complex pyrolysis products in real time possible. The mass spectra at different reaction temperatures and time-evolved profiles of selected species during the pyrolysis processes were measured. The pyrolysis products can be classified into three groups: alkenes, dienes, and aromatics. As the coke precursors, aromatics mainly composed of benzene, toluene, and xylene (BTX) were observed at a very low temperature of 300 °C with the presence of HZSM-5, which cannot be detected for pure PP until 700 °C, indicating that HZSM-5 can accelerate the coke formation. Because of the secondary reactions, different tendencies of product intensities were exhibited as the reaction temperature increased. In addition, in comparison of the time-evolved profiles of the alkenes and BTX under high temperatures, a two-stage catalytic degradation process taking place on the external surface and the micropores of HZSM-5 was verified. A degradation mechanism was also proposed for the pyrolysis of PP with a low HZSM-5 content based on the time-evolved profiles performed at a low temperature. This work demonstrates the good performance of SPI–TOFMS for the online study of the polymer pyrolysis as well as the evaluation of the catalyst.

A newly developed, qualitative and quantitative method based on tunable synchrotron radiation vacuum ultraviolet photoionization time-of-flight mass spectrometry (SR-VUV-PI-TOFMS) and photoionization efficiency (PIE) curve simulation was applied for the online analysis of isomers and isobaric compounds in the gas phase of mainstream cigarette smoke. After blocking the particulate phase components by the Cambridge filter pad, a puff of fresh gas-phase cigarette smoke was immediately introduced into a vacuum ionization chamber through a heated capillary, then was photoionized, and analyzed by a TOF mass spectrometer. The PIE curves for the mass peaks up to m/z = 106 were measured between 8.0 and 10.7 eV. Some components could be directly identified by their discriminated ionization energies (IEs) on the PIE curve. By simulating the PIE curve with the sum of scaled absolute photoionization cross sections (PICSs), complex isomeric/isobaric compounds along with their mole fractions could be obtained when the best-fitting was realized between experimental and simulated PIE curves. A series of reported toxic compounds for quantification, such as 1,3-butadiene (m/z = 54), 1,3-cyclopentadiene (m/z = 66), benzene (m/z = 78), xylene (m/z = 106), 2-propenal (m/z = 56), acetone and propanal (m/z = 58), crotonaldehyde (m/z = 70), furan and isoprene (m/z = 68), were all found to have other isomers and/or isobaric compounds with considerable abundances. Some isomers have never been reported previously in cigarette smoke, like C5H6 isomers 1-penten-3-yne, 3-penten-1-yne, and 1-penten-4-yne at m/z = 66. Isomeric/isobaric compounds characterization for the mass peaks and mole fraction calculations were discussed in detail below 10.7 eV, an energy value covering several conventional used VUV light sources.