Localised evolved gas analysis by micro-thermal analysis

Micro-thermal analysis employs a scanning probe microscope fitted with a miniature resistive heater/thermometer to obtain images of the surface of materials and then perform localised thermoanalytical measurements. We have demonstrated that it is possible to use the same configuration to pyrolyse selected areas of the specimen by rapidly heating the probe to 600-800 degreesC. This generates a plume of evolved gases which can be trapped using a sampling tube containing a suitable sorbent placed close to the heated tip. Thermal desorption-gas chromatogaphy/mass spectrometry can then be used to separate and identify the evolved gases. This capability extends the normal visualisation and characterisation by micro-thermal analysis to include the possibility of localised chemical analysis of the sample (or a domain, feature or contaminant). The isolation and identification of natural products from a plant leaf are given as an example to illustrate this approach. Preliminary results from direct sampling of pyrolysis products by mass spectrometry are also presented.