Localised evolved gas analysis by micro-thermal analysis

Micro-thermal analysis employs a scanning probe microscope fitted with a mi niature resistive heater/thermometer to obtain images of the surface of mat erials and then perform localised thermoanalytical measurements. We have de monstrated that it is possible to use the same configuration to pyrolyse se lected areas of the specimen by rapidly heating the probe to 600-800 degree sC. This generates a plume of evolved gases which can be trapped using a sa mpling tube containing a suitable sorbent placed close to the heated tip. T hermal desorption-gas chromatogaphy/mass spectrometry can then be used to s eparate 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, fea ture or contaminant). The isolation and identification of natural products from a plant leaf are given as an example to illustrate this approach. Prel iminary results from direct sampling of pyrolysis products by mass spectrom etry are also presented.