Molecular imaging direct methods

Coupled on-line techniques (GC-MS, LC-MS, MS/ MS, etc.) provide for indirect mixture analysis, while many of the newer desorption/ionisation methods are well suited for direct analysis of mixtures. DI techniques, applied either directly or with prior liquid chromatographic separations, provide molecular weight information up to 5000 Da, but little or no additional structural information. Higher molecular weight (or more labile) additives can be detected more readily in the isolated extract, since desorption/ionisation techniques (e.g. FD and FAB) can be used with the extract but not with the compounded polymer. Major increases in sensitivity will be needed to support imaging experiments with DI in which the spatial distribution of ions in the x — y plane are followed with resolutions of a few tens of microns, and the total ion current obtained is a few hundreds of ions. 

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