TY - JOUR A1 - Bierstedt, Andreas A1 - Panne, Ulrich A1 - Rurack, Knut A1 - Riedel, Jens T1 - Characterization of two modes in a dielectric barrier discharge probe by optical emission spectroscopy and time-of-flight-mass spectrometry N2 - Among the large number of new ambient ionization schemes in the last few years, dielectric barrier discharge (DBD) has witnessed special attention. In this contribution a versatile dual mode DBD is introduced and characterized by means of optical emission spectroscopy and time-of-flight mass spectrometry. A direct comparison of the individual results from spectroscopy, spectrometry and transient current/voltage consumption gives evidence for the existence of two individual operational mechanisms. The first is driven by rapid transient changes in the potential difference between the two electrodes over time (usually denoted as the homogeneous mode), while the second is caused at high static potential differences (leading to filamentary discharges). The transient versus steady-state characteristics of the individual discharge origin suggest the driving force for the current flow to be inductive and capacitive, respectively. In most cases of dielectric barrier plasmas both discharge types coexist as competitive ion formation channels, however, detailed plasma characteristics of DBDs operated under different conditions allow for a clear distinction of the individual contributions. In this way, two characteristic product channels for the ionization of ambient water could be observed resulting in the generation of either preferentially protonated water clusters or ammonium water clusters. Careful tuning of the operation parameters of the discharge device allows an operation predominated by either of the two modes. As a consequence, facile switching into the desired operational mode results in either protonated molecules or ammoniated molecules of the analyte. Plasma characteristics for both moieties were evaluated and cross-correlated on the basis of several factors including: the production of reagent ions, the individual appearance of current/voltage profiles, UV/Vis spectroscopy, voltage and flux dependence and the individual response to test compounds. Although the filamentary mode has been already discussed in the literature to induce fragmentation processes, no experimental evidence for analyte dissociation could be found in the case of the test compounds used KW - Dual mode KW - Dielectric barrier discharge KW - Ambient desorption/ionization mass spectrometry KW - Emission spectroscopy KW - Ionization PY - 2015 U6 - https://doi.org/10.1039/C5JA00332F SN - 0267-9477 SN - 1364-5544 VL - 30 IS - 12 SP - 2496 EP - 2506 PB - Royal Society of Chemistry CY - London AN - OPUS4-35092 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bierstedt, Andreas A1 - Kersten, H. A1 - Glaus, Reto A1 - Gornushkin, Igor B. A1 - Riedel, Jens T1 - Development of a laser induced plasma ion source coupled to ambient mass spectrometry N2 - Only a few years after the invention of the laser, the concept of laser microprobe mass spectrometry (LMMS), a technique which employed intense laser radiation for ion generation, was introduced. In these early studies at excessive irradiation microplasma formation could be observed to be an effective channel for ion formation. However, this plasma generation in vacuum led to undesired distortions of the mass analyzers and, thus, was discarded as an analytical ion source. Under ambient conditions, the surrounding air effectively cools the plasma cloud, making the plasma more controllable. The resulting laser induced plasma is nowadays commonly used in laser induced breakdown spectroscopy (LIBS) applications as excitation source for optical emission spectroscopy experiments. However, little effort has been made to introduce a LIBS plasma as a promising ion source for ambient mass spectrometry. The main hindrance is the transient character of laser induced plasmas that typically only has a lifetime on the order of several microseconds. This drastically reduces the duty cycle of these plasma sources. After these microseconds, the generated ions recombinate to uncharged atoms and even newly bound molecules, making them inaccessible to mass-to-charge analyzers. The advent of high repetition lasers together with the ever growing knowledge about manipulation of charged species at atmospheric pressures allow overcoming these obstacles. This presentation will introduce an ionization scheme using a laser induced plasma as the primary ion source. We believe that this novel ionization strategy will pave the way for future applications in ambient mass spectrometry. T2 - 5. Berliner Chemie Symposium CY - Berlin, Germany DA - 12.04.2016 KW - Laser induced plasma KW - Time-of-flight mass spectrometry KW - Ambient mass spectrometry KW - Ionization KW - Laser induziertes Plasma KW - Flugzeitmassenspektrometer KW - Atmosphärendruckmassenspektrometrie KW - Ionisierung PY - 2016 AN - OPUS4-35732 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bierstedt, Andreas A1 - Kersten, H. A1 - Glaus, Reto A1 - Gornushkin, Igor B. A1 - Panne, Ulrich A1 - Riedel, Jens T1 - Characterization of an airborne laser-spark ion source for ambient mass spectrometry N2 - An airborne laser plasma is suggested as an ambient ion source for mass spectrometry. Its fundamental physical properties, such as an excellent spatial and temporal definition, high electron and ion densities and a high effective cross section in maintaining the plasma, make it a promising candidate for future applications. For deeper insights into the plasma properties, the optical plasma emission is examined and compared to mass spectra. The results show a seemingly contradictory behavior, since the emitted light reports the plasma to almost entirely consist of hot elemental ions, while the corresponding mass spectra exhibit the formation of intact molecular species. Further experiments, including time- resolved shadowgraphy, spatially resolved mass spectrometry, as well as flow-dependent emission spectroscopy and mass spectrometry, suggest the analyte molecules to be formed in the cold plasma vicinity upon interaction with reactive species formed inside the hot plasma center. Spatial separation is maintained by concentrically expanding pressure waves, inducing a strong unidirectional diffusion. The accompanying rarefaction inside the plasma center can be compensated by a gas stream application. This replenishing results in a strong increase in emission brightness, in local reactive species concentration, and eventually in direct mass spectrometric sensitivity. To determine the analytical performance of the new technique, a comparison with an atmospheric pressure chemical ionization (APCI) source was conducted. Two kitchen herbs, namely, spearmint and basil, were analyzed without any sample pretreatment. The presented results demonstrate a considerably higher sensitivity of the presented laser-spark ionization technique. KW - Laser-spark KW - Laser induced plasma KW - Ambient mass spectrometry KW - Optical emission spectroscopy KW - Ionization PY - 2017 U6 - https://doi.org/10.1021/acs.analchem.6b04178 SN - 0003-2700 SN - 1520-6882 VL - 89 IS - 6 SP - 3437 EP - 3444 PB - American Chemical Society CY - Washington, DC, USA AN - OPUS4-39474 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -