Online detection of the volatile intermediates evolved from moxa floss pyrolysis with photoionization mass spectrometry

https://doi.org/10.1016/j.jaap.2022.105737Get rights and content

Highlights

  • Moxa pyrolysis were studied with an online synchrotron radiation photoionization mass spectrometry.

  • The mass spectra and time-evolved profiles of volatile intermediate species were obtained in real-time.

  • More than 70 species were identified and the production of species was analyzed.

  • The control of pyrolysis temperature and time plays an important role in the moxibustion therapy.

Abstract

The dynamic processes of moxa pyrolysis were detected with an online synchrotron radiation photoionization mass spectrometry (SR-PIMS) under ambient pressure. The mass spectra at different temperatures (573–1073 K) as well as time-evolved profiles of volatile intermediate species were obtained in real-time. More than 70 species were identified, including hydrocarbons, nitrogen-, oxygen- and sulfur-containing compounds. The production of species was analyzed in a semi-quantitative way by comparing the intensity of each species. Most species exhibit the maximum relative intensities at 773 K such as phenols, which could have a positive effect on health with a certain quantity. Numbers of harmful substances, such as 1,3-butadiene, aldehydes and methanol were detected under different temperatures. Among them, aromatics compounds are sharply increased with increased temperature possibly due to the coalesce of small alkenes, while residential time of most species reduces with increased temperature. Therefore, controlling the moxibustion pyrolysis to a relatively lower temperature is beneficial during the therapy.

Introduction

Moxibustion is a traditional Chinese medical therapy using the biomass, moxa floss, as the main combustible feedstock. The heat generated by the burning moxa can be applied to the acupoints or body areas for disease treatment [1], [2], [3]. The smoke released during burning moxa has been reported to have antiaging, antitumor, anti-inflammatory and antibacterial effects [4], [5], [6], [7], [8], [9], [10]. However, the detailed influence of smoke on health still lacks understanding. Therefore, it is of great significance to analyze the chemical compounds of smoke and reveal the moxa smoke mechanism.

Considerable efforts have been made to study the smoke components. Among them, gas chromatograph-mass spectrometer (GC-MS) is a reliable and effective method and widely used to detect the smoke components with different solvents, such as benzene-methanol, dichloromethane, 1-butanol, petroleum ether, anhydrous ethanol and cyclohexane [10], [11], [12], [13], [14]. Headspace GC-MS and pyrolysis GC-MS were also applied to detect the chemical components produced in moxa combustion and pyrolysis [8], [15], [16]. More than 200 chemical species were found including a variety of volatile substances such as phenols, alcohols, esters and ketones.

Although existing works have provided valuable chemical components information of moxa combustion products, the kinetic formation process of volatile chemicals remains lacking because the the widely used GC-MS methods are off-line analytical techniques and quite time-consuming while sample capturing, extracting, derivatization and separation procedures are usually needed [15], [17]. Thus, an influence of the solvents cannot be fully excluded. Due to the high activity of some chemical components in moxa smoke, the internal composition of moxa smoke is constantly changing and on-line analysis techniques are needed.

Synchrotron radiation (SR) has the advantages of high brightness, good collimation and wavelength tenability [18]. Photoionization mass spectrometry with soft ionization methods, such as synchrotron radiation photoionization mass spectrometry (SR-PIMS), has been widely used for online or real-time product detection during pyrolysis, oxidation and combustion of fuels and biomass [17], [18], [19], [20], [21]. By using the SR-PIMS, the photoionization efficiency (PIE) curves of the chemicals with different mass-to-charge rations (m/z) could be obtained by plotting the ion intensity versus corresponding photon energy. Then, the species, including isomers, can be effectively distinguished from PIE curves or ionization energies (IE) due to the soft ionization of SR without producing and fragments in the used energy window.

With the pyrolysis as the first step of biomass combustion, playing an important role in the subsequent transformation [22], [23], [24], [25], it is desirable to investigate the pyrolysis process of moxa floss which could permit a better understanding of mechanisms underlying moxibustion including the beneficial and harmful components formation. Until now, the SR-PIMS method was used to investigate the polypropylene catalytic pyrolysis [23], lignin model compounds pyrolysis [24], catalytic pyrolysis of xylan over alkali metal salts [25] and so on. However, the study on the online pyrolysis of moxa floss and the effects of reaction temperatures and time on its released volatile products were rarely available.

The aim of this work is to study the moxa pyrolysis at ambient pressure using a synchrotron radiation photoionization mass spectrometry (SR-PIMS) within the temperature range of 573–1073 K. The thermogravimetric analysis of moxa floss were performed. Photoionization efficiency (PIE) spectra were obtained to identify the chemical structures of products. The mass spectra of pyrolysis products at different temperatures as well as their time-evolved profiles were monitored in real-time. These results will provide a better understanding of the moxa combustion dynamic process and data support of mechanism explanation of moxibustion.

Section snippets

Materials

The moxa floss samples were bought from Beijing Housheng Baopu E-commerce Co. Ltd. Company with 5 storage years and a ratio of 15:1. Ratio here refers to the weight of the starting material (dried leaves) to the weight of the finished product (moxa floss) in kilogram after processing. An analytical balance (AL 204, Mettler Toledo, Switzerland) was used to weigh 5.0 ± 0.1 mg of samples for the pyrolysis test. Before the experiment, all the samples were dried at 378 K for 1 h.

Thermogravimetric and ultimate analysis

Thermogravimetric

Results and discussion

Thermogravimetric analysis and SR-PIMS were employed to investigate the thermal behavior and generation of volatile intermediates of moxa floss pyrolysis. The pyrolysis products were identified and their mass spectra and time-evolved profiles at different reaction temperature were analysis. During the discussion, the pyrolysis products were classified into five groups: olefins, aromatics, amines, nitrogenous heterocyclic compounds and oxygenated compounds in 3.2 Olefins, 3.3 Aromatics, 3.4

Conclusions

The pyrolysis of moxa floss, the feedstock of traditional Chinese Moxibustion therapy, was explored using Synchrotron radiation photoionization mass spectrometry. More than 70 intermediates were identified and quantified. Small molecular species like ethylene, formaldehyde, methanol and propyne were newly detected. Most components display a peak of relative intensities at 773 K, while some toxic pollutants like pyrrole, benzene, and toluene increase with rising temperatures due to the abundant

CRediT authorship contribution statement

Jiu-Jie Kuang: Conceptualization, Investigation, Data curation, Supervision, Funding acquisition, Writing – original draft, Writing – review & editing. Du Wang: Writing – original draft, Writing – review & editing. Kai-Ru Jin: Investigation, Data curation. Bing Qian: Investigation, Data curation. Yang Pan: Methodology, Resource. Zhen-Yu Tian: Supervision, Methodology, Resource, Conceptualization, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Natural Science Foundation of China (No. 52176138/51976216), China Postdoctoral Science Foundation (No.2020M680670), National Science and Technology Major Project (J2019-III-0005-0048) and Beijing Municipal Natural Science Foundation (JQ20017).

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