TA-EGD-EGA Coupled Simultaneous Technique

The reaction processes of substances cannot be analyzed by simple DTA/DSC or TG when thermal transition and the mass change due to reaction overlap. If DTA/DSC or TG is coupled with an evolved gas detector (EGD) and/or evolved gas analyzer (EGA), the reaction process can clearly be detected. Among various thermal analysis coupled simultaneous techniques [56], DTA/DSC or TG coupled with EGD and/or EGA is extensively used. TA-EGD-EGA coupled 

TCD signal is markedly affected by various factors, such as the bridge current and cell temperature of EGD system, the thermal conductivity and the flow rate of the carrier gas. When the experimental conditions are maintained at a constant, the size and direction of the TCD exported signal is related to the thermal conductivity and concentration of the evolved component which is transported in the carrier gas, but the signal is not related to the source of the sample. Hence the same evolved gas produced by the thermal decomposition of different samples can be quantified precisely. This quantitative method is termed quantitative evolved gas detection (QEGD). 

For the examination of the QEGD method, the application of different samples containing hydrous and hydroxylic compounds in different carrier gases is tested. The above different samples liberate HjO by thermal decomposition during heat treatment. From the calibration line, the EGD-HjO peak can be obtained. The accuracy was 10% [62, 74, 75]. The experimental results indicated that its simultaneity, linearity and quantity correspond to those of the same type of commercial instruments [73, 76). 

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An analytical scheme for the TA-EGD-EGA coupled simultaneous technique is shown in Figure 2.32. The evolved gas from TA (DTA/DSC or TG) is introduced into the EGA system after passing through the EGD system. The evolved gas is directly introduced to a thermal conductivity detector (TCD), avoiding second reactions. Two methods are used for the TA and EGA coupled simultaneous technique (1) on-line coupled simultaneous technique in series and (2) off-line combined method. In technique (1), TA is connected serially with a Gas chromatograph (GC) [61-65], mass spectrometer (MS) [57, 64, 65], Fourier transform infrared (FTIR) spectrometer [66, 67], non-dispersive IR (NDIR) spectrometer [68, 69] or thermo-gas-titrimetric... 

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