Thermogravimetric analysis (TGA) is a technique that measures how the weight of a material changes as it is heated. TGA provides information about decomposition temperatures, thermal degradation properties, and quantitative weight losses. The key components of a TGA instrument are a furnace, balance, temperature controller, and recorder. Samples are heated and their weight changes are measured continuously as a function of increasing temperature. Weight loss curves can indicate decomposition reactions and be used to determine composition. TGA has applications in characterizing materials used in various industries.

1. V.Suhasini
M.PHARM
(PHARMACEUTICS)
THERMOGRAVIMETRIC
ANALYSIS
1

2. Introduction
 In the early years of analytical chemistry ,
practically all analytical precipitates were
dried 100- 120 degree in an oven ignited at red
heat by using undefinable temp of the burner
 All changed in recent year due to the
development of modern recording
thermobalance according to Duval (1953)
2

3. Principle
 TGA is a technique in which, upon heating a
material, its weight increases or decreases
 TGA is a method of thermal analysis in which
changes in physical and chemical properties of
materials are measured as a function of increasing
temperature.
 By using this analysis, one can predict the thermal
stability of given sample and it is used to
determine the composition of given sample. This
technique is used for those substances which can
exhibit weight loss or gain due to certain reactions
like decomposition, oxidation, and dehydration.
3

4. Weight loss A
B
C D
E F
temperature
MCO3 2H2O
MCO3H2O
MCO3
CO3+ MO
4
MCO3 - Metal carbonate

5.  The principle of the technique can be
illustrated by the weight loss curve of
hypothetical compound MCO3.2H2O
 The temperature at A is called minimum
weight loss temperature
 At B due to MCO3 .H2O
 Further heating results in the formation of
anhydrous MCO3 weight levels from C & D
 At point D the compound MCO3 starts to
evolve CO3 giving MO weight level from E & F
 The thermal stability of the original
compound
5

6. Difference between DTA, DSC,
TGA
 DTA = DifferentialThermal Analysis:You heat
a sample in a crucible and a reference in
another (but identical) crucible
simultaneously.The DTA signal is the
temperature difference between sample and
reference, typically plotted versus
temperatureT
6

7.  DSC = Differential Scanning Calorimetry:Very
similar to DTA, but due to a more
sophisticated construction not onlyT itself,
but additionally the heat flow into (or from)
the sample can be measured.
 TGA =Thermogravimetric Analysis (often
onlyTG): Sometimes performed
simultaneously with DTA/DSC, sometimes
separately. measured the weight loss or gain
as a function of temperature
7

8. Type of thermo gravimetric
analysis
DynamicTGA - in this type of analysis the
sample is subjected to conditions of
continuous increase in temperature usually
linear with time
Isothermal or staticTGA - in this type of analysis
the sample is maintained at a constant
temperature for a period of time during which
any change in weight are noted
8

9.  Gravimetric analysis :
concerned with the process of producing and
weighing a compound or element in as pure
form
 Traditional gravimetric :
essentially manual in character and labor
intensive
 Electro gravimetric :
partially instrumental
 Thermal gravimetric :
highly instrumental
9

10. Instrumentation
 TGA are based on the act that the sample be
continuously weighted as it is elevated temp
 The sample is continuously weighted by an
instrument , called thermo balance
 Both manual as well as automatic recording
balances
 4 general component
10

11.  A recording balance
 A furnace
 Furnace programmer or controller
 A recorder device
11

12. 12

13.  ATGA consists of a container which is in the
form of a crucible for holding the sample
(sample pan)
 a furnace for heating the given sample at a
high temperature, and an appropriate
precision balance which can continuously
monitor the sample
 That pan resides in a furnace and is heated or
cooled during the experiment.
 A sample purge gas controls the sample
environment
13

14. 14

15.  This gas may be inert or a reactive gas such as
Helium or Argon that flows over the sample
and exits through an exhaust
 Finally the weight is recorded as a function of
increasing temperature
 TGA instrument continuously weighs a
sample as it is heated to temperatures of up
to 2000 °C
 . As the temperature increases, various
components of the sample are decomposed
and the weight percentage of each resulting
mass change can be measured
15

16.  Results are plotted with temperature on the
X-axis and mass loss on theY-axis.The data
can be adjusted using curve smoothing.
Instrument can be coupled with FTIR
and Mass spectrometry , gas
chromatography analysis
TGA-FT-IR TGA-MS
TGA-GC/MS
16

17. 17

18. What is the best way to prepare a sample?
 The sample size should be between 2 and 50
mg.
 If you have minimum amount of sample, run
at least 1 mg.
 If possible, cover the bottom of the pan with
the sample material.
 The sample pans, ceramic or platinum, can
accommodate liquids, powders, films, solids
or crystals
18

19.  Once you have decided on the sample form,
then for best results, use approximately the
same sample weight during each experiment.
This will ensure reproducibility.
 Many small pieces of sample are better than
one large chunk. It is better to have a large
surface area exposed to the sample purge.
19

20. How is a TGA Thermal Curve displayed?
 (X-axis) can be displayed as temperature and
(Y-axis) can be displayed as weight (%)
95.11°C
96.62%
185.05°C
73.60%
295.89°C
60.00%
398.06°C
50.51%
Residue:
41.10%
(12.49mg)
20

21. What does aTGAThermal Curve look like?
TGA thermal curve is displayed from left to
right.The descendingTGA thermal curve
indicates a weight loss occurred.
TGA instruments can be divided into two types:
 Vertical balance
 horizontal balance
VERTICAL BALANCE : single pan not suitable
for DTA and DST only suitableTGA
21

22.  Horizontal balance instruments (TA, Perkin
Elmer, etc.) normally have two pans (sample
and reference).
TGA 4000. Pyris 1TGA.
22

23. Suggested Protocol
 Heating rate 5 o C/min. in air. Maximum
temperature sufficient to stabilize sample
weight (typically 800 o C).
 Sample size at least 2 - 4 mg, more if
possible.
 Three separateTGA runs on each sample.
 Ash content measured independently on
microbalance.
 provides much greater accuracy, precision
and speed and sensitivity.
23

24. Type of recording thermo balance
Null point type
Deflection type
Helical
Beam
Cantilever
Torsion
24

25. Null point
 More commonly used. In these balance , a
sensor is employed to detect the deviation of
the beam from its null point position .
 A restoring force of electrical or mechanical
weight load is then applied to the balance
beam in order to restore its null point position
from the horizontal or vertical norm
25

26. Deflection type
 Essentially based on either a conventional
analytical balance consisting of helical, beam,
cantilever , torsion analytical balance
involving the conversion of deviation directly
into a record of weight change
26

27. 27

28. 28

29. 29

30. Factors affecting the TGA
(1) Instrumental factors
(a) Furnace heating rate
(b) Furnace atmosphere
(2) Sample characteristics
(a)Weight of the sample
(b) Sample particle size
30

31. Instrumental factors
 Furnace Heating rate: The temperature at
which the compound (or sample) decompose
depends upon the heating rate. When the
heating rate is high, the decomposition
temperature is also high. A heating rate of
3.5°C per minute is usually recommended for
reliable and reproducible TGA.
 Furnace atmosphere: The atmosphere inside
the furnace surrounding the sample has a
profound effect on the decomposition
temperature of the sample. A pure N2 gas from
a cylinder passed through the furnace which
provides an inert atmosphere.
31

32. Sample characteristics
(a)Weight of the sample: A small weight of
the sample is recommended using a
small weight eliminates the existence of
temperature gradient throught the
sample.
(b) Particle size of the sample: The particle
size of the sample should be small and
uniform. The use of large particle or
crystal may result in apparent, very rapid
weight loss during heating
32

33. Applications of TGA
 TGA is used as a technique to characterize
materials used in various environmental,
food, pharmaceutical, and petrochemical
applications
 TGA can be used to evaluate the thermal
stability of a material In a desired
temperature range
 Can determine the purity of a mineral,
inorganic compound, or organic material.
 TGA is used to study the kinetics of the
reaction rate constant.
33

34. Thermogravimetric analysis(TGA) is a powerful
technique for the characterization of the
decomposition or weight loss properties of
materials.The technique provides the following
useful information:
 Decomposition temperatures
 Thermal degradation properties
 Oxidative degradation characteristics
 Quantitative weight losses
 Compositional analysis
 Long term stabilities
 Flammability properties
 Rates of degradation
34

35. Thermal
Oxidative degradation characteristics
35
1. cigarette tobacco(approximate mass of
14 mg) was heated at a rate of 40 C/min
under an air purge (40 mL/min) which
helps to simulate the
2. real-life thermo-oxidatve degradation
properties of the cigarette tobacco

36. TGA Using Kinetics Studies
 The assessment of product lifetimes is easily
performed using the PerkinElmerTGA
Decomposition Kinetics Software
 TheTGA kinetics approach uses the well-
known variable heating method developed
36

37.  With theTGA decomposition kinetics
approach, the sample is heated at several
different heating rates ranging between 40
and 1 C/min.
 Typically, 3 to 6 different heating rate
experiments are performed to assess theTGA
decomposition kinetics.
 the corresponding temperature is determined
for each different heating rate.
37

38. Reference
 Instrumental method of chemical analysis
B.K Sharma page no : 308
 Pharmaceutical drug analysis Ashutosh Kar
page no : 194
38

39. 39