@article{ZuehlkeZenichowskiRiebeetal.2017,
  author    = {Z{\"u}hlke, Martin and Zenichowski, Karl and Riebe, Daniel and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Subambient pressure electrospray ionization ion mobility spectrometry},
  series = {International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry},
  volume    = {20},
  journal   = {International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1435-6163},
  doi       = {10.1007/s12127-017-0215-x},
  pages     = {47 -- 56},
  year      = {2017},
  abstract  = {The pressure dependence of sheath gas assisted electrospray ionization (ESI) was investigated based on two complementary experimental setups, namely an ESI-ion mobility (IM) spectrometer and an ESI capillary - Faraday plate setup housed in an optically accessible vacuum chamber. The ESI-IM spectrometer is capable of working in the pressure range between 300 and 1000 mbar. Another aim was the assessment of the analytical capabilities of a subambient pressure ESI-IM spectrometer. The pressure dependence of ESI was characterized by imaging the electrospray and recording current-voltage (I-U) curves. Qualitatively different behavior was observed in both setups. While the current rises continuously with the voltage in the capillary-plate setup, a sharp increase of the current was measured in the IM spectrometer above a pressure-dependent threshold voltage. The different character can be attributed to the detection of different species in both experiments. In the capillary-plate experiment, a multitude of charged species are detected while only desolvated ions attribute to the IM spectrometer signal. This finding demonstrates the utility of IM spectrometry for the characterization of ESI, since in contrast to the capillary-plate setup, the release of ions from the electrospray droplets can be observed. The I-U curves change significantly with pressure. An important result is the reduction of the maximum current with decreasing pressure. The connected loss of ionization efficiency can be compensated by a more efficient transfer of ions in the IM spectrometer at increased E/N. Thus, similar limits of detection could be obtained at 500 mbar and 1 bar.},
  language  = {en}
}
@article{VillatoroWeberZuehlkeetal.2019,
  author    = {Villatoro, Jos{\´e} Andr{\´e}s and Weber, M. and Z{\"u}hlke, Martin and Lehmann, A. and Zenichowski, Karl and Riebe, Daniel and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Kreuzer, O.},
  title     = {Structural characterization of synthetic peptides using electrospray ion mobility spectrometry and molecular dynamics simulations},
  series = {International Journal of Mass Spectrometry},
  volume    = {436},
  journal   = {International Journal of Mass Spectrometry},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1387-3806},
  doi       = {10.1016/j.ijms.2018.10.036},
  pages     = {108 -- 117},
  year      = {2019},
  abstract  = {Electrospray ionization-ion mobility spectrometry was employed for the determination of collision cross sections (CCS) of 25 synthetically produced peptides in the mass range between 540-3310 Da. The experimental measurement of the CCS is complemented by their calculation applying two different methods. One prediction method is the intrinsic size parameter (ISP) method developed by the Clemmer group. The second new method is based on the evaluation of molecular dynamics (MD) simulation trajectories as a whole, resulting in a single, averaged collision cross-section value for a given peptide in the gas phase. A high temperature MD simulation is run in order to scan through the whole conformational space. The lower temperature conformational distribution is obtained through thermodynamic reweighting. In the first part, various correlations, e.g. CCS vs. mass and inverse mobility vs. m/z correlations, are presented. Differences in CCS between peptides are also discussed in terms of their respective mass and m/z differences, as well as their respective structures. In the second part, measured and calculated CCS are compared. The agreement between the prediction results and the experimental values is in the same range for both calculation methods. While the calculation effort of the ISP method is much lower, the MD method comprises several tools providing deeper insights into the conformations of peptides. Advantages and limitations of both methods are discussed. Based on the separation of two pairs of linear and cyclic peptides of virtually the same mass, the influence of the structure on the cross sections is discussed. The shift in cross section differences and peak shape after transition from the linear to the cyclic peptide can be well understood by applying different MD tools, e.g. the root-mean-square deviation (RMSD) and the root mean square fluctuation (RMSF). (C) 2018 Elsevier B.V. All rights reserved.},
  language  = {en}
}
@article{ZuehlkeRiebeBeitzetal.2016,
  author    = {Z{\"u}hlke, Martin and Riebe, Daniel and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Andreotti, Sandro and Reinert, Knut and Zenichowski, Karl and Diener, Marc},
  title     = {High-performance liquid chromatography with electrospray ionization ion mobility spectrometry: Characterization, data management, and applications},
  series = {Journal of separation science},
  volume    = {39},
  journal   = {Journal of separation science},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1615-9306},
  doi       = {10.1002/jssc.201600749},
  pages     = {4756 -- 4764},
  year      = {2016},
  abstract  = {The combination of high-performance liquid chromatography and electrospray ionization ion mobility spectrometry facilitates the two-dimensional separation of complex mixtures in the retention and drift time plane. The ion mobility spectrometer presented here was optimized for flow rates customarily used in high-performance liquid chromatography between 100 and 1500 mu L/min. The characterization of the system with respect to such parameters as the peak capacity of each time dimension and of the 2D spectrum was carried out based on a separation of a pesticide mixture containing 24 substances. While the total ion current chromatogram is coarsely resolved, exhibiting coelutions for a number of compounds, all substances can be separately detected in the 2D plane due to the orthogonality of the separations in retention and drift dimensions. Another major advantage of the ion mobility detector is the identification of substances based on their characteristic mobilities. Electrospray ionization allows the detection of substances lacking a chromophore. As an example, the separation of a mixture of 18 amino acids is presented. A software built upon the free mass spectrometry package OpenMS was developed for processing the extensive 2D data. The different processing steps are implemented as separate modules which can be arranged in a graphic workflow facilitating automated processing of data.},
  language  = {en}
}