LETTER pubs.acs.org/ac
Development of Submillisecond Time-Resolved Mass Spectrometry Using Desorption Electrospray Ionization Zhixin Miao, Hao Chen,* Pengyuan Liu, and Yan Liu Department of Chemistry and Biochemistry, Center for Intelligent Chemical Instrumentation, Ohio University, Athens, Ohio 45701, United States
bS Supporting Information ABSTRACT: Reaction kinetics studied by mass spectrometry (MS) has previously been limited to millisecond time resolution. This paper presents the development of a submillisecond time-resolved mass spectrometric method for fast reaction kinetic study, based on the capability of desorption electrospray ionization (DESI) for direct and fast ionization of a high-speed liquid jet stream. The principle underlying this methodology is that two reactant solutions undergo rapid mixing to produce a free liquid jet which is ionized by DESI at different positions corresponding to different reaction times. Due to the high velocity of the liquid jet, high time resolution can be achieved. In this study, the fast reduction reaction of 2, 6-dichlorophenolindophenol (DCIP) and L-ascorbic acid (L-AA) was chosen as an example to demonstrate this concept, and the reaction rate constant was successfully measured with an unprecedented time resolution of 300 μs. The good agreement of the measured value of (116 ( 3) s1 with that measured by the stopped-flow optical method (105 ( 2) s1 validates the feasibility of such a DESI-MS approach. Unlike classical spectroscopic techniques that require either chromophoric substrates or labeling, MS is a general detector with high chemical specificity. Therefore, this time-resolved DESI-MS method should find wide applications in fast (bio)chemical reaction investigations.
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inetic studies play a central role in the elucidation of chemical and biochemical reaction mechanisms.1 Generally, (bio)chemical kinetic studies are carried out by optical methods such as absorption or fluorescence spectroscopy with the time resolution as low as femtoseconds. However, these methods require chromophoric substrates or labeling. Mass spectrometry (MS)-based approaches2,3 to study kinetics have arisen, particularly with the advent of electrospray ionization (ESI).4 The striking advantages of the use of MS as a detector over spectroscopic detection are that MS has high chemical specificity and does not require chromophoric substrates. Notably, the timeresolved ESI-MS methods based on elegant designs for reactant solution mixing have been established by Konermann and other groups,511 allowing the monitoring of reaction kinetics with the time resolution from seconds to milliseconds.12 Nevertheless, it is necessary to further improve the time resolution of MS methods. Desorption electrospray ionization (DESI), introduced by Cooks and co-workers,13 is a recently established technique that allows direct ionization of analytes from surfaces with little or no sample preparation. Various novel DESI-MS applications have been reported, ranging from drug detection to tissue imaging.1419 In terms of kinetic study, DESI-MS has been used to monitor solid-phase reaction kinetics with the time resolution of hours.20 Taking advantages of the short time scale during DESI ionization (
