@article{MichalikOnichimowskaBeitzPanneetal.2017,
  author    = {Michalik-Onichimowska, Aleksandra and Beitz, Toralf and Panne, Ulrich and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Riedel, Jens},
  title     = {Microsecond mid-infrared laser pulses for atmospheric pressure laser ablation/ionization of liquid samples},
  series = {Sensors and actuators : B, Chemical},
  volume    = {238},
  journal   = {Sensors and actuators : B, Chemical},
  publisher = {Elsevier},
  address   = {Lausanne},
  issn      = {0925-4005},
  doi       = {10.1016/j.snb.2016.06.155},
  pages     = {298 -- 305},
  year      = {2017},
  abstract  = {In many laser based ionization techniques with a subsequent drift time separation, the laser pulse generating the ions is considered as the start time to. Therefore, an accurate temporal definition of this event is crucial for the resolution of the experiments. In this contribution, the laser induced plume dynamics of liquids evaporating into atmospheric pressure are visualized for two distinctively different laser pulse widths, Delta t = 6 nanoseconds and Delta tau = 280 microseconds. For ns-pulses the expansion of the generated vapour against atmospheric pressure is found to lead to turbulences inside the gas phase. This results in spatial and temporal broadening of the nascent clouds. A more equilibrated expansion, without artificial smearing of the temporal resolution can, in contrast, be observed to follow mu s-pulse excitation. This leads to the counterintuitive finding that longer laser pulses results in an increased temporal vapour formation definition. To examine if this fume expansion also eventually results in a better definition of ion formation, the nascent vapour plumes were expanded into a linear drift tube ion mobility spectrometer (IMS). This time resolved detection of ion formation corroborates the temporal broadening caused by collisional impeding of the supersonic expansion at atmospheric pressure and the overall better defined ion formation by evaporation with long laser pulses. A direct comparison of the observed results strongly suggests the coexistence of two individual ion formation mechanisms that can be specifically addressed by the use of appropriate laser sources.},
  language  = {en}
}
@article{MichalikOnichimowskaKernRiedeletal.2017,
  author    = {Michalik-Onichimowska, Aleksandra and Kern, Simon and Riedel, Jens and Panne, Ulrich and King, Rudibert and Maiwald, Michael},
  title     = {"Click" analytics for "click" chemistry - A simple method for calibration-free evaluation of online NMR spectra},
  series = {Journal of magnetic resonance},
  volume    = {277},
  journal   = {Journal of magnetic resonance},
  publisher = {Elsevier},
  address   = {San Diego},
  issn      = {1090-7807},
  doi       = {10.1016/j.jmr.2017.02.018},
  pages     = {154 -- 161},
  year      = {2017},
  abstract  = {Driven mostly by the search for chemical syntheses under biocompatible conditions, so called "click" chemistry rapidly became a growing field of research. The resulting simple one-pot reactions are so far only scarcely accompanied by an adequate optimization via comparably straightforward and robust analysis techniques possessing short set-up times. Here, we report on a fast and reliable calibration-free online NMR monitoring approach for technical mixtures. It combines a versatile fluidic system, continuous-flow measurement of H-1 spectra with a time interval of 20 s per spectrum, and a robust, fully automated algorithm to interpret the obtained data. As a proof-of-concept, the thiol-ene coupling between N-boc cysteine methyl ester and ally] alcohol was conducted in a variety of non-deuterated solvents while its time-resolved behaviour was characterized with step tracer experiments. Overlapping signals in online spectra during thiol-ene coupling could be deconvoluted with a spectral model using indirect hard modeling and were subsequently converted to either molar ratios (using a calibration free approach) or absolute concentrations (using 1-point calibration). For various solvents the kinetic constant k for pseudo-first order reaction was estimated to be 3.9 h(-1) at 25 degrees C. The obtained results were compared with direct integration of non-overlapping signals and showed good agreement with the implemented mass balance. (C) 2017 Elsevier Inc. All rights reserved.},
  language  = {en}
}