Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. 

1. Thermogravimetric Analysis[TGA]
A Review
BY LOKESH SAINI
(Chemistry Department, Hygia Institute of Pharmaceutical Education &
Research, Lucknow)

2. Abstract
The thermal activity of any substance is measured in this analysis,
therefore this review is given to simplify the understanding of
TGA. With the help of detailed description it includes various types of
measuring methods used in this detection with their previous graphical
and instrumental data analytical reports and results.

3. Table of contents
• Introduction
• Types
• Principal
• TGA Curve
• Instrumentation
• Factors affecting results
• Pharmaceutical Applications
• Conclusion

4. Introduction
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a
method of thermal analysis in which the mass of a sample is measured over
time as the temperature changes.
This measurement provides information about physical phenomena such as
phase transitions, absorption and desorption as well as chemical phenomena
including-
Chemisorption (kind of adsorption ,involve chemical reaction between
surface & adsorbate),
thermal decomposition(thermolysis, chemical decomposition caused by heat),
solid-gas reactions(solid state reaction performed by exposing reactive solid
to stream of reactive gas) e.g., oxidation or reduction.

5. Principal
TGA basically works on either the principal of change in mass of
sample with respect to time or temperature in controlled environment.
It effect the sample in many ways like-
Desorption(release of an adsorbed substance from a surface),
Sublimation(transition of substance directly from solid to gas),
Vaporization(either evaporation or boiling),
Oxidation(loss of electron),
Reduction(gain of electron).

6. Types
Generally there are mainly three types of thermogravimetric analysis
techniques are used for TGAAnalysis.
1. Isothermal or Static Thermogravimetry : In this technique the sample
weight is recorded as function of time at constant temperature.
2. Quasistatic thermogravimetry : In this technique the sample is heated
to constant weight at each of series of increasing temperatures.
3. Dynamic thermogravimetry: In this technique the sample is heated in
an environment whose temperature is changing in a predetermined
manner generally at linear rate.
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7. TGA Curve

8. weight

10. Factors affecting Results
Factors which may affect the TGA Curve are classified into two main
groups.
• Instrumental factors
(a) Furnace Heating Rate: The decomposition of sample depends upon
heating rate. Usually 3.5 degree Celsius recommended for reliable TGA.
(b) Furnace atmosphere: The atmosphere inside the furnace effect the
decomposition temperature of sample.
• Sample Characterstic
(a) Weight of the sample: Small weight is recommended, it eliminates
the existence of temperature gradient.
(b) Sample particle size: Particle size should small & uniform.

11. Pharmaceutical Applications
1) The change in chemical states of the catalyst may be studied by TGA Techniques.
2) TGA can be used to evaluate the thermal stability of material in
desired temperature range.
3) TGA is also used in Identification of polymers and pharmaceutical agents.
4) TGA is also used to characterize materials used in food , pharmaceutical and
petrochemical applications.
5) It can determine the purity of mineral, Inorganic compound and Organic material.
6) Characteristic transition or reaction temperature can be accurately determined.
7) Instruments are highly sensitive.
8) Instruments can be used at very high temperature.
9) flexibility of crucible volume or form.

12. Conclusion
TGA was considered to be one of the most effective method of various
thermal detections and analysis. It plays an important role in detection of
thermal stability of material with its materialistic identification and
knowledge according to its stability and purity of product.
With some drawbacks we can see,
• Uncertainty in heats of fusion.
• Data Interpretation is not always straight forward.
• Sensitive to heating rate and sample masses result in shift in temperature.
• Only solid sample must be used in quantitative and qualitative analysis.