DESI Probes Reactive Intermediates

Reactive desorption electrospray ionization (DESI) can be used to track reactions that are otherwise difficult to follow by mass spectrometry, according to two reports. In one paper, Richard N. Zare and coworkers at Stanford University describe using DESI-MS to capture and analyze reactive intermediates during the formation of a ruthenium catalyst (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201004861). The researchers deposited the starting ruthenium complex on a surface and incorporated the ligand in the DESI spray solvent. Early-stage intermediates generated in the catalyst-forming reaction can be observed with DESI but not with conventional electrospray MS. In a second paper, R. Graham Cooks of Purdue University and coworkers studied bimolecular reactions in the droplets created by the reactive DESI spray (Chem. Sci., DOI: 10.1039/c0sc00416b). The researchers showed that reactions are accelerated in droplets and that droplet conditions sometimes lead to products different from those formed in bulk solution. “DESI allows one to follow reactions in the presence of solvent and to predict and parallel ordinary chemistry but on the speed and specificity scale of mass spectrometry,” Cooks says.