Thermogravimetric analysis (TGA) is one of the most common specific techniques under the broader rubric of thermal analysis. The basic concept of thermogravimetry is relatively simple: over a period of time, the instrument measures the mass of the sample as the temperature is increased. However, many components and software tools enter into the modern TGA.

The sample is introduced in a sample holder of known weight. This sample holder is typically made of platinum, due to that metal’s high melting point. Heating the sample is achieved with an insulated electric oven. Using electric heating allows fine control of the temperature in the system, which can produce a prescribed temperature profile, commonly a simple linear increase, so that the mass/time curve is equivalent to a mass/temperature curve.

Most standard TGA systems can reach a maximum temperature of about 1000°C, while high-temperature systems can extend the temperature range up to 1500°C or more. Specialized systems can be used to perform TGA measurements at subambient temperatures. To prevent unwanted chemical reactions like oxidation, a purge gas is often used to keep the sample in an inert environment.

During the heating process, the mass is constantly monitored by a precision balance. The importance of these measurements lies in the fact that the decrease in mass of the sample is due to the evolution of gases. As the increased temperature volatilizes different sample components into a gaseous form, the mass of the sample decreases. An example would be the loss of ordinary water as a sample reaches the boiling point; thus, a very simple use of TGA would be to determine the moisture content of a sample. In practice, simpler moisture analyzers are used for this task.

The TGA curve indicates when different components begin their evolution, where the rate of evolution is greatest and when evolution is complete. Software tools can be used to separate different components, and this information can be used to potentially identify and quantify the evolved gases. With the addition of an evolved gas analyzer, more conclusive identification can be carried out as a hyphenated technique, like TGA–IR spectroscopy or TGA-MS.

TGA measurements are associated with polymer analysis. The stability and degradation characteristics of polymeric materials can be directly measured with TGA. Similarly, pharmaceutical formulations can be tested for stability, or for the evolution of residual solvents. Analyzing the effects of temperature on the chemical and physical nature of foodstuffs is another application. Other potential analyses include asphalts, rubbers, and other chemicals and chemical processes.

The total market for TGA was about $115 million in 2009. TA Instruments is the market leader. There are a fairly large number of other competitors, including NETZSCH, SII Nanotechnology, PerkinElmer, Shimadzu and Mettler-Toledo.

TGA at a Glance:

Leading Suppliers

• TA Instruments (Waters)

• NETZSCH

• SII Nanotechnology

Largest Markets

• Polymers

• Pharmaceuticals

• Food & Beverage

Instrument Cost

• $20,000–$65,000