Thermogravimetric Analysis (TGA) measures weight changes as a function of temperature or time. It can be a useful tool for compositional analysis if the weight loss steps from the evaporation/decomposition of the different samples components are well- separated. The figure below shows the TGA curve for calcium oxalate with three characteristic weight loss steps. The first step is due to loss of hydration water, the second step is due to the decomposition of calcium oxalate to calcium carbonate and carbon monoxide and the third step is due to the decomposition of calcium carbonate to calcium oxide and carbon dioxide. Since the dehydration step is often well-separated from the other weight loss steps, the TGA is a commonly used, accurate technique for quantitative determination of hydration water and moisture in general. The derivative curve (DTG, dotted line) is very useful for detecting overlapping weight loss steps which are hard to distinguish in the TG curve. The overlapping steps can be resolved by measurements with lower heating rates.
Instrument specifications and sample requirements:
TGA
Maximum Sample Capacity: 200 mg
Ideal Sample Weight: 5 – 50 mg
Balance Sensitivity: 0.1 μg
Recommended Heating rate*: 10 or 20˚C/min
Temperature Range: Ambient to 1500 ˚C
* Lower and higher heating rates are also possible and should be discussed with the lab for each specific set of samples.