Evolved Gas Analysis Guide

METTLER TOLEDO's EGA guide presents several different application examples of TGA-MS, TGA-FTIR, TGA-GC/MS and TGA-Micro GC/MS.

Evolved gas analysis includes several techniques that allow gaseous products evolved during the mass change to be detected and identified.

METTLER TOLEDO offers four different EGA techniques, namely Fourier transform infrared spectroscopy (FTIR), mass spectrometry (MS), gas chromatography-mass spectrometry (GC/MS), and micro gas chromatography-mass spectrometry (Micro GC/MS). The techniques can be coupled to a TGA and produce a large amount of complementary information. The data obtained can be directly correlated with the measured mass losses.

TGA-EGA can provide you with a lot of information. This guide will provide you with the knowledge of what is possible with a METTLER TOLEDO TGA-EGA system. You will learn the theory and basic principle of each technique along with how each one is used in a real world EGA application.

Recommendations for Choosing an EGA Technique:

Evolved gas analysis (EGA) combines a thermogravimetric analyzer (TGA) with another technique that provides complementary information about the gaseous products released during an experiment. The gas analysis techniques discussed here all have something in common, namely that the gases and volatile products evolved during the heating process in the TGA have to be transferred to the gas analysis system. This is accomplished using a specially engineered interface together with a transfer line. This is typically maintained at a temperature of 200 °C to prevent gaseous products from condensing.

Learn How a TGA-EGA System Can Provide You More Information on Your Materials

The EGA guide has a specific chapter on each of the following techniques. You will learn the working principle of the techniques and see possible applications of the combined EGA system.

TGA-EGA Techniques:

Mass Spectrometry (MS)
Fourier Transform Infrared (FTIR) spectroscopy
Gas Chromatography/Mass Spectrometry (GC)/MS
Micro GC/MS*

*TGA coupled to Micro GC/MS is a unique solution provided by METTLER TOLEDO.

Basic Principles:

A thermogravimetric analyzer (TGA) coupled on-line to an evolved gas analysis (EGA) system provides quantitative (mass loss) and qualitative (identification) information about gaseous reaction or decomposition products produced by a material during a TGA measurement.

The thermogravimetric analyzer records the mass loss of a sample while the sample is exposed to a temperature program (dynamically) or to a specific temperature as a function of time (isothermally) in a controlled atmosphere. METTLER TOLEDO also supplies TGA/DSC instruments which simultaneously record the heat flow to and from a sample.

TGA-MS:

TGA-MS is used as an analysis method to detect small gaseous molecules such as H₂O, HCl, or CO₂ evolved from samples that are not too complex. A typical example is the detection of residual solvents in pharmaceutical products. In this analysis method, the evolved gases from the TGA experiment are transferred online through a capillary tube into the MS. The temperature at which substances are evolved can therefore be determined exactly.

Detection of small molecules (COx, NOx, SOx, H₂O, HCl, etc.)
Residual solvents in active pharmaceutical ingredients

TGA-FTIR:

In TGA experiments, several gaseous substances are often evolved at the same time. Each of these compounds exhibits a characteristic IR spectrum. The measured IR spectrum is therefore, usually, the sum of numerous individual spectra. The identification of specific functional groups (e.g., of alcohols or of aromatic compounds, etc.) in the reaction products is important and made possible with the FTIR.

Detection of simple and complex compounds
Residual solvents in active pharmaceutical ingredients

TGA-GC/MS:

The gas mixture coming directly from the TGA is injected onto the GC column. The different mo¬lecular species are transported through the column by a carrier gas and interact with the material used to fill or coat the column (the stationary phase). Depending on their relative affinity for the stationary phase, the individual molecules take different times to reach the end of the column. This so-called retention time is different for each type of molecule and can be used for identification purposes. The retention time, however, depends on several different parameters, such as the column used, the carrier gas flow rate, and the temperature program used for heating the column. A GC is often coupled to a mass spectrometer (MS). This enables the different molecules to be unequivocally identified, independently of the above-mentioned GC operating parameters.

Volatile molecules up to about 250 amu

TGA-Micro GS/MS:

In contrast to conventional GC, a gas sample can be analyzed in a Micro GC within a few minutes due to the much smaller separating columns. Micro GC is, therefore, an online method. Micro GC is ideal for the detection of small molecules (e.g., CO, CO₂, H₂O, NOx, hydrocarbons up to C10), which cannot be detected or only detected with difficulty using a conventional GC (e.g., H₂O, H₂).

Detection of small molecules ("permanents") is possible without MS
Detection of light and medium weight compounds by Micro GC/MS

Application Range of TGA-Micro GC/MS and TGA-GC/MS:

Gain Insights beyond Decomposition of Materials

The METTLER TOLEDO concept allows any existing TGA or TGA/DSC instrument to be combined with a gas analysis system. Our comprehensive EGA guide presents several different application examples that demonstrate the analytical power and versatility of evolved gas analysis to characterize the most advanced materials and complex formulations.