Evolved Gas Analysis by Mass Spectrometry

Abstract: Periodic publications have been published that address advances in evolved gas analysis techniques, because the correct interpretation for the mechanism of a thermally induced reaction, involving the formation of gaseous species, is strongly dependent on the characterization of the evolved products.

When the nature of volatile products released by a substance subjected to a controlled-temperature program are online determined, the results allow one to prove a supposed reaction, either under isothermal or under heating conditions.

Very recent analytical applications of evolved gas analysis performed by mass spectrometry, selected among those published in 2012 and 2013, are collected in this review.     

Study on thermal decomposition of polymers by evolved gas analysis using photoionization mass spectrometry (EGA-PIMS)

Photoionization mass spectrometry (PIMS) with vacuum ultraviolet (VUV) light source provides an efficient and fragmentation-free method for the soft ionization of gaseous compounds, in order to facilitate an understanding of thermal decomposition behavior and chemical composition of polymeric materials. The PIMS was applied to the evolved gas analysis (EGA) system equipped with a skimmer interface which is constituted based upon a jet separator principle between a vacuum MS chamber and an atmospheric sample chamber in a furnace. A photoionization source with a deuterium (D₂) lamp was closely installed to the vacuum ionization chamber of a mass spectrometer to improve the ionization efficiency. The thermal decomposition of typical polymers in inert gas atmosphere was investigated by the EGA-PIMS and the resulting PI mass spectrum was characterized satisfactorily by only the parent ions with no contribution as a result of fragmentation during the ionization. The results suggested that the EGA-PIMS was an especially powerful and desirable in situ thermal analysis method for polymeric materials which evolve organic gases simultaneously and concurrently. The combination of EGA equipped with skimmer interface with no change of evolved gaseous species and PIMS with fragmentation-free during the ionization is described briefly, and the effective results are presented by comparing with EGA using conventional electron impact ionization mass spectrometry.     

Thermoanalytical study of the pesticide 3-amino-1,2,4-triazole

Thermoanalytical study of the pesticide 3-amino-1,2,4-triazole (ATA) has been carried out, using simultaneous DTA-TG in nitrogen flow, in order to know its thermal behaviour and stability. These techniques have been further complemented using evolved gas analysis and mass spectroscopy (EGA-MS). Two different stages of ATA decomposition were observed: after the first decomposition step, a mixture of compounds is obtained, according to MS data, being the principal component a compound of molecular weight 126. It is formed by a first order reaction mechanism, according to the kinetic study, withE _a=124±8 kJ·mol^?1. The second decomposition step takes place about 735°C, with evolution of HCN and NH₃, being the final weight loss 96%.     

Evolved gas analysis-mass spectrometry using skimmer interface and ion attachment mass spectrometry

Summary A new EGA-MS instrument consisted of a combination of skimmer interface with no change of evolved gaseous species and IAMS (Ion Attachment Mass Spectrometry) with no fragmentation during the ionization has been developed successfully. As its application of evolved gaseous species from PVA as firing process of alumina ceramics binder, the method has indicated detection of gaseous species which have not been detected with Py-GC-MS.     

New approach for the kinetic analysis of cellulose using EGA-MS

This paper describes a new approach for kinetic analysis based on evolved gas analysis-mass spectrometry (EGA-MS) using pyrolyzer-gas chromatography/MS (Py-GC/MS). The kinetic results derived by this model-free kinetic analysis using the EGA-MS thermograms of cellulose were comparable to those using thermogravimetric analysis (TGA). The activation energies were in the range of 149–194 kJ/mol (mean 169 kJ/mol) for EGA/MS and 152–181 kJ/mol (mean 165 kJ/mol) for TGA. This suggests that Py-GC/MS can be used not only for the qualitative analysis of pyrolyzates, but also for the kinetic analysis of pyrolysis.     

Comparison of Capillary and Skimmer Interfaces in Evolved Gas Analysis-Mass Spectrometry (EGA-MS) with Regard to Impurities in Ceramic Raw Materials

Capillary and skimmer interfaces in EGA-MS were compared by analysis of the carbon substances remaining in the hydrolysis products of aluminum alkoxides. Peaks with higher intensities were detected in the skimmer interface mode than those in the capillary interface mode. It was confirmed in particular that the skimmer interface is effective in increasing the sensitivity for species with higher mass, e.g. the evolved butyl group, as carbon substances remaining in the hydrolysis product of aluminum sec-butoxide. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of montmorillonite-aminotriazole interactions

In the present investigation, DTA and TG techniques were used to study the thermal behaviour of montmorillonite treated with solutions of the pesticide aminotriazole (AMT), in nitrogen flow. These techniques have been complemented by mass spectrometry of the evolved gases (EGA-MS). AMT is adsorbed in the interlamellar space of montmorillonite as a cation. Results obtained in this study show that this provokes a shift of the dehydroxylation peak of montmorillonite to lower temperatures than those of the untreated clay. Montmorillonite protects the adsorbedAMT, delaying its first decomposition step, and catalysesAMT final decomposition at lower temperatures. The DTA curve of montmorillonite-AMT mechanical mixture differs from the sum of those of the clay mineral and the pesticide heated individually. Montmorillonite dehydroxylation occurs at lower temperature, indicating a complex formation betweenAMT and the mineral during the heating process. However the DTA of the mixture is different from that of the complex previously studied, indicating that in the complex obtained by heating the physical mixtureAMT is adsorbed as neutral molecule or as a product of its decomposition.     

Thermoanalytical studies of titanium(IV) acetylacetonate xerogels with emphasis on evolved gas analysis

Thermal decomposition of precursor xerogels for TiO₂, obtained by gelling of acetylacetonate-modified titanium(IV) tetraisopropoxide (prepared at Ti-alkoxide:acetylacetone molar ratios of 1:1 (Ti-1) and 1:2 (Ti-2)) in boiling 2-methoxyethanol, was monitored by simultaneous TG/DTA/EGA-MS and EGA-FTIR measurements. Thermal degradation processes of Ti-1 and Ti-2 in the temperature range of 30–700°C consist of six mass loss steps, the total mass loss being 46.3% and 54.4%, respectively. EGA by FTIR and MS revealed release of H₂O below 120°C; followed by evolution of acetone and acetic acid between approximately 100 and 320°C, and that of CO₂ up to 560°C. Acetylacetone is evolved to a significant extent from sample Ti-2 at 120–200°C.     

一种EGA—MS系统的标定方法

ＣａＣ２Ｏ４真空热分解中，第一阶段生成的ＣＯ中４７％歧化成ＣＯ２和Ｃ；第二阶段生成的ＣＯ与第一阶段生成的Ｃ发生气化反应，发生反应的比例随样品量增加而增大。用ＣａＣＯ３标定ＣＯ后再用ＣａＣ２Ｏ４标定ＣＯ可以排除这些干扰。本文提出了一个对任意气体标定的方法。