Instant Notes: Analytical Chemistry

Section G – Thermal methods

G4 EVOLVED GAS ANALYSIS

Principles During a heating process, any reaction or decomposition may produce gases.
Although the gases may sometimes be absorbed, the technique is generally
referred to as evolved gas analysis (EGA).
For example, the three-stage decomposition of calcium oxalate monohydrate
gives first water vapor, then carbon monoxide, and finally carbon dioxide. Each
of these can be identified, for example, by mass spectrometry (see Topic E14) as
shown in Figure 1.
The first stage evolves water (m/z18), the second carbon monoxide (m/z28),

Key Notes

When samples are heated, volatile products and gases may be evolved.

The identification of these may be carried out by many analytical

techniques. Solid products may be analyzed as well.

Separation by chromatographic techniques and analysis by spectrometry,

titration and potentiometry may all be used to identify and measure the

evolved gases.

The decomposition of polymers, the distillation of oils and the evolution

of gases from minerals, inorganics and complexes as well as the detection

of products from catalytic reactions have all been studied by evolved gas

methods.

Related topics Infrared and Raman spectrometry: Differential thermal and

applications (E11) differential scanning

Mass spectrometry (E14) calorimetry (G2)

Thermogravimetry (G1) Thermomechanical analysis (G3)

Principles

Instrumentation

Applications

0

20

40

60

200 400 600 800

Mass loss %

Sample temperature (°C)

60 μV

TG

DTA

EXO

ENDO

m/z 18

m/z 44

m/z 28

Fig. 1. Mass spectrometric detection and identification of gases evolved during the

decomposition of calcium oxalate monohydrate.