Hyphenated TGA techniques and evolved gas analysis

The option of cormecting the outlet of a TGA instrument, via a heated transfer line, to a spectroscopic or chromatographic technique has been available to analysts for over 15 years. This is an attractive proposition because of the much greater amount of information that 

There are a number of instrumental combinations that can be set up, including the following  

These three techniques vary in the fundamental mechanism being applied. In the case of the IR and MS continuous sampling may be carried out, and with GC-MS intermittent sampling is conducted where the gas evolved over a particular temperature range, or time (particularly in isothermal work) is collected in a intermediate trap and then analysed. 

The TGA-IR combination is the most cost effective and can provide information on both low molecular weight additives volatilising off at the beginning of a run as well as higher molecular weight constituents such as polymers (and blends of these), resins, etc. In the latter example, the compounds will be pyrolysed to low molecular weight fi agments and so it is useful to run standards to enable accurate identifications to be performed. 

The other two techniques have an additional capability to provide very detailed information on a sample. This includes identification of low level addition additives such as antioxidants. This is particularly true in the case of TGA-GC-MS because of the intermediate chromatographic step which enables the evolved gas produced at a given point in time to be resolved into its component parts. 

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