Measurement Modes in Thermogravimetric Analysis (TGA)

TGA analysis is a technique that measures sample weight change in-situ with temperature.  There are two frequently used modes in TGA.  One is constant heating rate and the other is isothermal temperature hold.

When an analyst is looking for an overall survey of how a sample behaves as temperature increases, such as temperature regions relating to volatiles or sublimation or degradation, a constant heating rate is applied in TGA testing.  On the other hand, the isothermal temperature hold is utilized for moisture or volatile content analysis.  A sample is heated to a temperature slightly higher than the boiling point of the volatile compound and held for some time until sample weight becomes stable.  This mode is similar to drying a sample in an oven.

Sometimes a more complex measurement mode is needed to improve resolution after a survey scan of constant heating rate.  The TGA method may apply variable heating rates and/or isothermal steps in order to distinguish each weight loss step more clearly.  Techniques to achieve better resolution include high resolution (“hi-res”) TGA, modulated TGA, or constant rate of weight change methodology.