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      Going beyond electrospray: mass spectrometric studies of chemical reactions in and on liquids

      a , b , , a

      Chemical Science

      Royal Society of Chemistry

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          Abstract

          Recently developed and applied ionization techniques have brought mass spectrometry to bear on previously inaccessible chemistry. We offer our perspective on this field and its application for studying reaction mechanisms.

          Abstract

          There has been a burst in the number and variety of available ionization techniques to use mass spectrometry to monitor chemical reactions in and on liquids. Chemists have gained the capability to access chemistry at unprecedented timescales, and monitor reactions and detect intermediates under almost any set of conditions. Herein, recently developed ionization techniques that facilitate mechanistic studies of chemical processes are reviewed. This is followed by a discussion of our perspective on the judicious application of these and similar techniques in order to study reaction mechanisms.

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          Most cited references 105

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          Dynamic range of mass accuracy in LTQ Orbitrap hybrid mass spectrometer.

          Using a novel orbitrap mass spectrometer, the authors investigate the dynamic range over which accurate masses can be determined (extent of mass accuracy) for short duration experiments typical for LC/MS. A linear ion trap is used to selectively fill an intermediate ion storage device (C-trap) with ions of interest, following which the ensemble of ions is injected into an orbitrap mass analyzer and analyzed using image current detection and fast Fourier transformation. Using this technique, it is possible to generate ion populations with intraspectrum intensity ranges up to 10(4). All measurements (including ion accumulation and image current detection) were performed in less than 1 s at a resolving power of 30,000. It was shown that 5-ppm mass accuracy of the orbitrap mass analyzer is reached with >95% probability at a dynamic range of more than 5000, which is at least an order of magnitude higher than typical values for time-of-flight instruments. Due to the high resolving power of the orbitrap, accurate mass of an ion could be determined when the signal was reliably distinguished from noise (S/Np-p)>2...3).
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            Effect of different solution flow rates on analyte ion signals in nano-ESI MS, or: when does ESI turn into nano-ESI?

            In nano-ESI MS, the qualitative and quantitative characteristics of mass spectra vary considerably upon the use of different spraying conditions, i.e., aperture of the spraying needle and the voltage applied. The major parameters affected by the aperture size is the liquid flow rate which determines the initial droplet size and the current emitted upon the spray process, as described by different models of the ESI process. In the present study, the effect of flow rate on ion signals was studied systematically using mixtures of compounds with different physicochemical properties (i.e., detergent/oligosaccharide and oligosaccharide/peptide). For these model systems, the functional dependence of certain analyte-ion ratios upon the flow rate can be correlated to changes in analyte partition during droplet fission prior to ion release. Analyte suppression is practically absent at minimal flow rates below 20 nL/min.
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              Desorption sonic spray ionization for (high) voltage-free ambient mass spectrometry.

              Sonic spray ionization is shown to create a supersonic cloud of charged droplets able to promote efficient desorption and ionization of drugs directly from the surfaces of commercial drug tablets at ambient conditions. Compared with desorption electrospray ionization (DESI), desorption sonic spray ionization (DeSSI) is advantageous since it uses neither heating nor high voltages at the spray capillary. DeSSI therefore provides a more friendly environment in which to perform ambient mass spectrometry (MS). DeSSI-MS is herein evaluated for the analysis of drug tablets, and found to be, in general, as sensitive as DESI-MS. The (high) voltage-free DeSSI method provides, however, cleaner mass spectra with less abundant solvent cluster ions and with enough abundant analyte signal for tandem mass spectrometry (MS/MS). These features may therefore facilitate the DeSSI-MS detection of low molar mass components or impurities, or both. The higher-velocity supersonic DeSSI spray also facilitates matrix penetration thus providing more homogenous sampling and longer lasting ion signals.
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                Author and article information

                Affiliations
                [a ] Department of Chemistry , Stanford University , Stanford , CA 94305 , USA . Email: zare@ 123456stanford.edu
                [b ] Thermo Fisher Scientific , San José , CA 95134 , USA
                Journal
                Chem Sci
                Chem Sci
                Chemical Science
                Royal Society of Chemistry
                2041-6520
                2041-6539
                1 January 2016
                1 October 2015
                : 7
                : 1
                : 39-55
                5508663 c5sc02740c 10.1039/c5sc02740c
                This journal is © The Royal Society of Chemistry 2015

                This is an Open Access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License ( http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Chemistry

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