Evolved Gas Analysis with Thermogravimetric Analysis – Mass Spectroscopy (TGA-MS)

Figure 1: (a) TGA-MS of sodium thiosulfate, demonstrating the quantitative determination of moisture content and temporal/temperature profile of decomposition product SO2; and (b) TGA – MS of formulated aspirin revealing three H2O outgassing events from ambient to 100 °C, 100 °C – 130 °C and above 130 °C, corresponding to physiosorbed (note: moisture can be accurately determined in this case), chemically bound and/or thermal decomposition nature, respectively.

INTRODUCTION

Materials outgassing and thermal decomposition can lead to performance deterioration, failure, and safety concern. In this regard, Eurofins EAG Lab has established numerous outgassing analytical techniques to meet the industry needs, including TGA-IR, headspace GCMS, Residual Gas Analysis (RGA), and Fractional IGA analysis. While these techniques often overlap in certain capability, each is specialized to provide unique analytical information, depending on sample types (chemistry, geometry, morphology, etc.), applications, temperature range, atmosphere (or vacuum), sensitivity requirement, etc.

TGA with hyphenated technologies such as infrared (IR) and/or mass spectrometry (MS) is specialized in investigating real time outgassing behavior of materials, in the temporal/temperature regime of interest and desired atmosphere, including;

  • real time, high sensitivity (resolution ~0.1 μg), quantitative analysis of mass loss as the material is heated
  • identification of the evolved gas species associated with mass loss, including adsorbed moisture, bound water, residual organic solvents, and volatile decomposition products
  • outgassing profile of individual gas species as a function of time and temperature

Previously, we have demonstrated our TGA-IR as a powerful technique in identifying molecular information of evolved gas species, in particular small gas molecules such as hydrocarbons, nitrogen oxides, hydrogen halides, CO, CO<sup>2</sup>, H<sup>2</sup>O, NH<sup>3</sup>, HCN, fluorocarbons, etc. (Heetderks & Wang, 2019). However, TGA-IR is limited to detect infrared-active compounds, and for large molecules, only functional group information can be identified. Outgassing profiles could suffer from broadened temperature/time resolution, due to the time required for evolved species reaching the IR detector after liberated from the TGA analyzer (note in this case the mass transfer efficiency is mainly dictated by the flow gas rate), and a large IR cell volume to be filled which cause mixing of gases evolved from different time/temperature regimes.

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