Multistage Reactive Transmission-Mode Desorption Electrospray Ionization Mass Spectrometry

Abstract

Abstract. Elucidating reaction mechanisms is important for advancing many areas of science such as catalyst development. It is often difficult to probe fast reactions at ambient conditions with high temporal resolution. In addition, systems involving reagents that cross-react require analytical methods that can minimize interaction time and specify their order of introduction into the reacting system. Here, we explore the utility of transmission mode desorption electrospray ionization (TM-DESI) for reaction monitoring by directing a microdroplet spray towards a series of meshes with micrometer-sized openings coated with reagents, an approach we call multistage reactive TM-DESI (TM n -DESI, where n refers to the number of meshes; n=2 in this report). Various stages of the reaction are initiated at each mesh surface, generating intermediates and products in microdroplet reaction vessels traveling towards the mass spectrometer. Using this method, we investigated the reactivity of iron porphyrin catalytic hydroxylation of propranolol and other substrates. Our experimental results indicate that TM n -DESI provides the ability to spatially separate reagents and control their order of introduction into the reacting system, thereby minimizing unwanted reactions that lead to catalyst deactivation and degradation products. In addition, comparison with DESI-MS analyses (the Zare and Latour laboratories published results suggesting accessible reaction times <1 ms) of the reduction of dichlorophenolindophenol by L-ascorbic acid suggest that TM 1 -DESI can access reaction times less than 1 ms. Multiple meshes allow sequential stages of desorption/ionization per MS scan, increasing the number of analytes and reactions that can be characterized in a single experiment.

Development and Applications of Liquid Sample Desorption Electrospray Ionization Mass Spectrometry

“…Its structure was confirmed upon CID by observing fragment ions of CH 3 NH 2 loss (m/z 146) and the cleavage between pyridine and pyrrolidine rings (m/z 98 and m/z 80) (Figure 22c). Very recently, TM-DESI was modified to monitor reaction systems that contained multiple reagents and involved multiple reaction steps (110). The modified TM-DESI used a series of meshes with micrometer-sized openings coated with different reagents and was termed TM n -DESI (n refers to the number of meshes).…”

Screening of synthetic phosphodiesterase‐5 inhibitors in herbal dietary supplements using transmission‐mode desorption electrospray and high‐resolution mass spectrometry

“…Unapproved analogs, in addition to the latter contraindications, have not been properly tested in terms of safety and may have serious side effects. [10] We report on application of transmission-mode desorption electrospray tandem mass spectrometry [11][12][13][14] (TM-DESI/MS/MS) to screening for synthetic PDE5 inhibitors in samples of HDS. The supplements were manufactured in Asia and imported to the Czech Republic between 2010 and 2015 in the form of capsules to be packed and sold to end users.…”