TY - JOUR A1 - Beitz, Toralf A1 - Laudien, Robert A1 - Löhmannsröben, Hans-Gerd A1 - Kallies, Bernd T1 - Ion mobility spectrometric investigation of aromatic cations in the gas phase N2 - In this work, ion mobility (IM) spectra of more than 50 aromatic compounds were recorded with a laser-based IM spectrometer at atmospheric pressure. IM spectra of PAH in the laser desorption experiment show a high complexity resulting from the occurrence of monomeric, dimeric, and oligomeric cluster ions. The mobilities of all compounds were determined in helium as drift gas. This allows the calculation of the diffusion cross sections (Omega(calc)) on the basis of the exact hard sphere scattering model and their comparison with the experimentally determined diffusion cross sections (Omega(exp)). Extended Omega(exp)/Omega(calc) and Omega(exp/)mass correlations were performed in order to gain insight into conformational properties of cationic alkyl benzenes and internal rotation of phenyl rings in aromatic ions. This is demonstrated with some examples, such as the evaluation of the dihedral angle of the ions of 9,10- diphenylanthracene, o- and m-terphenyl, and 1,2,3- and 1,3,5-triphenylbenzene. Furthermore, sandwich and T-structures of dimeric PAH cations are discussed. The analysis was extended to oligomeric ions with up to nine monomer units. Experimental evidence is presented suggesting the formation of pi-stacks with a transition toward modified pi-stacks with increasing cluster size. The distance between monomeric units in dimeric and oligomeric ions was obtained Y1 - 2006 UR - http://pubs.acs.org/journal/jpcafh U6 - https://doi.org/10.1021/Jp055335n SN - 1089-5639 ER - TY - GEN A1 - Löhmannsröben, Hans-Gerd A1 - Beitz, Toralf A1 - Luadien, Robert A1 - Schultze, Rainer T1 - Laser-based ion mobility spectrometry for sensing of aromatic compounds N2 - The drift time spectra of polycyclic aromatic hydrocarbons (PAH), alkylbenzenes and alkylphenylethers were recorded with a laser-based ion mobility (IM) spectrometer. The ion mobilities of all compounds were determined in helium as drift gas. This allows the calculation of the diffusion cross sections (Omegacalc) on the basis of the exact hard sphere scattering model (EHSSM) and their comparison with the experimentally determined diffusion cross sections (Omegaexp). These Omegaexp/Omegacalc-correlations are presented for molecules with a rigid structure like PAH and prove the reliability of the theoretical model and experimental method. The increase of the selectivity of IM spectrometry is demonstrated using resonance enhanced multiphoton ionisation (REMPI) at atmospheric pressure, realized by tuneable lasers. The REMPI spectra of nine alkylbenzenes and alkylphenylethers are investigated. On the basis of these spectra, the complete qualitative distinction of eight compounds in a mixture is shown. These experiments are extended to alkylbenzene isomer mixtures. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 003 KW - Laser KW - REMPI KW - Ion mobility spectrometry KW - PAH Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-11892 ER - TY - JOUR A1 - Brinkmann, Pia A1 - Köllner, Nicole A1 - Merk, Sven A1 - Beitz, Toralf A1 - Altenberger, Uwe A1 - Löhmannsröben, Hans-Gerd T1 - Comparison of handheld and echelle spectrometer to assess copper in ores by means of laser-induced breakdown spectroscopy (LIBS) JF - Minerals N2 - Its properties make copper one of the world’s most important functional metals. Numerous megatrends are increasing the demand for copper. This requires the prospection and exploration of new deposits, as well as the monitoring of copper quality in the various production steps. A promising technique to perform these tasks is Laser Induced Breakdown Spectroscopy (LIBS). Its unique feature, among others, is the ability to measure on site without sample collection and preparation. In this work, copper-bearing minerals from two different deposits are studied. The first set of field samples come from a volcanogenic massive sulfide (VMS) deposit, the second part from a stratiform sedimentary copper (SSC) deposit. Different approaches are used to analyze the data. First, univariate regression (UVR) is used. However, due to the strong influence of matrix effects, this is not suitable for the quantitative analysis of copper grades. Second, the multivariate method of partial least squares regression (PLSR) is used, which is more suitable for quantification. In addition, the effects of the surrounding matrices on the LIBS data are characterized by principal component analysis (PCA), alternative regression methods to PLSR are tested and the PLSR calibration is validated using field samples. KW - LIBS KW - copper-bearing minerals KW - UVR KW - PCA KW - PLSR Y1 - 2023 U6 - https://doi.org/10.3390/min13010113 SN - 2075-163X VL - 13 IS - 1 PB - MDPI CY - Basel ER - TY - JOUR A1 - Villatoro, José Andrés A1 - Weber, M. A1 - Zühlke, Martin A1 - Lehmann, A. A1 - Zenichowski, Karl A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Kreuzer, O. T1 - Structural characterization of synthetic peptides using electrospray ion mobility spectrometry and molecular dynamics simulations JF - International Journal of Mass Spectrometry N2 - 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. KW - Ion mobility spectrometry KW - Electrospray ionization KW - Peptides KW - Collision cross-section KW - Molecular dynamics Y1 - 2019 U6 - https://doi.org/10.1016/j.ijms.2018.10.036 SN - 1387-3806 SN - 1873-2798 VL - 436 SP - 108 EP - 117 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Prüfert, Chris A1 - Urban, Raphael David A1 - Fischer, Tillmann Georg A1 - Villatoro, José Andrés A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Belder, Detlev A1 - Zeitler, Kirsten A1 - Löhmannsröben, Hans-Gerd T1 - In situ monitoring of photocatalyzed isomerization reactions on a microchip flow reactor by IR-MALDI ion mobility spectrometry JF - Analytical and bioanalytical chemistry : a merger of Fresenius' journal of analytical chemistry, Analusis and Quimica analitica N2 - The visible-light photocatalyticE/Zisomerization of olefins can be mediated by a wide spectrum of triplet sensitizers (photocatalysts). However, the search for the most efficient photocatalysts through screenings in photo batch reactors is material and time consuming. Capillary and microchip flow reactors can accelerate this screening process. Combined with a fast analytical technique for isomer differentiation, these reactors can enable high-throughput analyses. Ion mobility (IM) spectrometry is a cost-effective technique that allows simple isomer separation and detection on the millisecond timescale. This work introduces a hyphenation method consisting of a microchip reactor and an infrared matrix-assisted laser desorption ionization (IR-MALDI) ion mobility spectrometer that has the potential for high-throughput analysis. The photocatalyzedE/Zisomerization of ethyl-3-(pyridine-3-yl)but-2-enoate (E-1) as a model substrate was chosen to demonstrate the capability of this device. Classic organic triplet sensitizers as well as Ru-, Ir-, and Cu-based complexes were tested as catalysts. The ionization efficiency of theZ-isomer is much higher at atmospheric pressure which is due to a higher proton affinity. In order to suppress proton transfer reactions by limiting the number of collisions, an IM spectrometer working at reduced pressure (max. 100 mbar) was employed. This design reduced charge transfer reactions and allowed the quantitative determination of the reaction yield in real time. Among 14 catalysts tested, four catalysts could be determined as efficient sensitizers for theE/Zisomerization of ethyl cinnamate derivativeE-1. Conversion rates of up to 80% were achieved in irradiation time sequences of 10 up to 180 s. With respect to current studies found in the literature, this reduces the acquisition times from several hours to only a few minutes per scan. KW - microchip KW - reaction monitoring KW - IR-MALDI KW - ion mobility spectrometry KW - photochemistry KW - photocatalysis KW - Olefin isomerization Y1 - 2020 U6 - https://doi.org/10.1007/s00216-020-02923-y SN - 1618-2642 SN - 1618-2650 VL - 412 IS - 28 SP - 7899 EP - 7911 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Villatoro, José Andrés A1 - Zühlke, Martin A1 - Riebe, Daniel A1 - Riedel, Jens A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - IR-MALDI ion mobility spectrometry JF - Analytical and bioanalytical chemistry : a merger of Fresenius' journal of analytical chemistry and Analusis N2 - The novel combination of infrared matrix-assisted laser dispersion and ionization (IR-MALDI) with ion mobility (IM) spectrometry makes it possible to investigate biomolecules in their natural environment, liquid water. As an alternative to an ESI source, the IR-MALDI source was implemented in an in-house-developed ion mobility (IM) spectrometer. The release of ions directly from an aqueous solution is based on a phase explosion, induced by the absorption of an IR laser pulse (lambda = 2.94 mu m, 6 ns pulse width), which disperses the liquid as nano- and micro-droplets. The prerequisites for the application of IR-MALDI-IM spectrometry as an analytical method are narrow analyte ion signal peaks for a high spectrometer resolution. This can only be achieved by improving the desolvation of ions. One way to full desolvation is to give the cluster ions sufficient time to desolvate. Two methods for achieving this are studied: the implementation of an additional drift tube, as in ESI-IM-spectrometry, and the delayed extraction of the ions. As a result of this optimization procedure, limits of detection between 5 nM and 2.5 mu M as well as linear dynamic ranges of 2-3 orders of magnitude were obtained for a number of substances. The ability of this method to analyze simple mixtures is illustrated by the separation of two different surfactant mixtures. KW - Ion mobility spectrometry KW - IR-MALDI KW - Laser Y1 - 2016 U6 - https://doi.org/10.1007/s00216-016-9739-x SN - 1618-2642 SN - 1618-2650 VL - 408 SP - 6259 EP - 6268 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Villatoro, José Andrés A1 - Zühlke, Martin A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Weber, Marcus A1 - Riedel, Jens A1 - Löhmannsröben, Hans-Gerd T1 - IR-MALDI ion mobility spectrometry: physical source characterization and application as HPLC detector JF - International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry N2 - Infrared matrix-assisted laser dispersion and ionization (IR-MALDI) in combination with ion mobility (IM) spectrometry enables the direct analysis of biomolecules in aqueous solution. The release of ions directly from an aqueous solution is based on a phase explosion, induced by the absorption of an IR laser pulse, which disperses the liquid as vapor, nano-and micro-droplets. The ionization process is characterized initially by a broad spatial distribution of the ions, which is a result of complex fluid dynamics and desolvation kinetics. These processes have a profound effect on the shape and width of the peaks in the IM spectra. In this work, the transport of ions by the phase explosion-induced shockwave could be studied independently from the transport by the electric field. The shockwave-induced mean velocities of the ions at different time scales were determined through IM spectrometry and shadowgraphy. The results show a deceleration of the ions from 118 m.s(-1) at a distance of 400 mu m from the liquid surface to 7.1 m.s(-1) at a distance of 10 mm, which is caused by a pile-up effect. Furthermore, the desolvation kinetics were investigated and a first-order desolvation constant of 325 +/- 50 s(-1) was obtained. In the second part, the IR-MALDI-IM spectrometer is used as an HPLC detector for the two-dimensional separation of a pesticide mixture. KW - Ion mobility spectrometry KW - IR-MALDI KW - Shadowgraphy KW - Laser KW - Imaging KW - HPLC Y1 - 2016 U6 - https://doi.org/10.1007/s12127-016-0208-1 SN - 1435-6163 SN - 1865-4584 VL - 19 SP - 197 EP - 207 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Villatoro Leal, José Andrés A1 - Zühlke, Martin A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Weber, Marcus A1 - Löhmannsröben, Hans-Gerd T1 - Sub-ambient pressure IR-MALDI ion mobility spectrometer for the determination of low and high field mobilities JF - Analytical and bioanalytical chemistry : a merger of Fresenius' journal of analytical chemistry, Analusis and Quimica analitica N2 - A new ion mobility (IM) spectrometer, enabling mobility measurements in the pressure range between 5 and 500 mbar and in the reduced field strength range E/N of 5-90 Td, was developed and characterized. Reduced mobility (K-0) values were studied under low E/N (constant value) as well as high E/N (deviation from low field K-0) for a series of molecular ions in nitrogen. Infrared matrix-assisted laser desorption ionization (IR-MALDI) was used in two configurations: a source working at atmospheric pressure (AP) and, for the first time, an IR-MALDI source working with a liquid (aqueous) matrix at sub-ambient/reduced pressure (RP). The influence of RP on IR-MALDI was examined and new insights into the dispersion process were gained. This enabled the optimization of the IM spectrometer for best analytical performance. While ion desolvation is less efficient at RP, the transport of ions is more efficient, leading to intensity enhancement and an increased number of oligomer ions. When deciding between AP and RP IR-MALDI, a trade-off between intensity and resolving power has to be considered. Here, the low field mobility of peptide ions was first measured and compared with reference values from ESI-IM spectrometry (at AP) as well as collision cross sections obtained from molecular dynamics simulations. The second application was the determination of the reduced mobility of various substituted ammonium ions as a function of E/N in nitrogen. The mobility is constant up to a threshold at high E/N. Beyond this threshold, mobility increases were observed. This behavior can be explained by the loss of hydrated water molecules. KW - ion mobility spectrometry KW - IR-MALDI KW - high field mobility KW - dub-ambient KW - pressure KW - peptides Y1 - 2020 U6 - https://doi.org/10.1007/s00216-020-02735-0 SN - 1618-2642 SN - 1618-2650 VL - 412 IS - 22 SP - 5247 EP - 5260 PB - Springer CY - Heidelberg ER - TY - GEN A1 - Riebe, Daniel A1 - Erler, Alexander A1 - Brinkmann, Pia A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Gebbers, Robin T1 - Comparison of Calibration Approaches in Laser-Induced Breakdown Spectroscopy for Proximal Soil Sensing in Precision Agriculture T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - The lack of soil data, which are relevant, reliable, affordable, immediately available, and sufficiently detailed, is still a significant challenge in precision agriculture. A promising technology for the spatial assessment of the distribution of chemical elements within fields, without sample preparation is laser-induced breakdown spectroscopy (LIBS). Its advantages are contrasted by a strong matrix dependence of the LIBS signal which necessitates careful data evaluation. In this work, different calibration approaches for soil LIBS data are presented. The data were obtained from 139 soil samples collected on two neighboring agricultural fields in a quaternary landscape of northeast Germany with very variable soils. Reference analysis was carried out by inductively coupled plasma optical emission spectroscopy after wet digestion. The major nutrients Ca and Mg and the minor nutrient Fe were investigated. Three calibration strategies were compared. The first method was based on univariate calibration by standard addition using just one soil sample and applying the derived calibration model to the LIBS data of both fields. The second univariate model derived the calibration from the reference analytics of all samples from one field. The prediction is validated by LIBS data of the second field. The third method is a multivariate calibration approach based on partial least squares regression (PLSR). The LIBS spectra of the first field are used for training. Validation was carried out by 20-fold cross-validation using the LIBS data of the first field and independently on the second field data. The second univariate method yielded better calibration and prediction results compared to the first method, since matrix effects were better accounted for. PLSR did not strongly improve the prediction in comparison to the second univariate method. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 786 KW - laser-induced breakdown spectroscopy KW - LIBS KW - proximal soil sensing KW - soil nutrients KW - elemental composition Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440079 SN - 1866-8372 IS - 786 ER - TY - JOUR A1 - Rethfeldt, Nina A1 - Brinkmann, Pia A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Köllner, Nicole A1 - Altenberger, Uwe A1 - Löhmannsröben, Hans-Gerd T1 - Detection of Rare Earth Elements in Minerals and Soils by Laser-Induced Breakdown Spectroscopy (LIBS) Using Interval PLS JF - Minerals N2 - The numerous applications of rare earth elements (REE) has lead to a growing global demand and to the search for new REE deposits. One promising technique for exploration of these deposits is laser-induced breakdown spectroscopy (LIBS). Among a number of advantages of the technique is the possibility to perform on-site measurements without sample preparation. Since the exploration of a deposit is based on the analysis of various geological compartments of the surrounding area, REE-bearing rock and soil samples were analyzed in this work. The field samples are from three European REE deposits in Sweden and Norway. The focus is on the REE cerium, lanthanum, neodymium and yttrium. Two different approaches of data analysis were used for the evaluation. The first approach is univariate regression (UVR). While this approach was successful for the analysis of synthetic REE samples, the quantitative analysis of field samples from different sites was influenced by matrix effects. Principal component analysis (PCA) can be used to determine the origin of the samples from the three deposits. The second approach is based on multivariate regression methods, in particular interval PLS (iPLS) regression. In comparison to UVR, this method is better suited for the determination of REE contents in heterogeneous field samples. View Full-Text KW - LIBS KW - rare earth elements KW - minerals KW - PCA KW - iPLS regression Y1 - 2021 U6 - https://doi.org/10.3390/min11121379 SN - 2075-163X VL - 11 SP - 1 EP - 17 PB - MDPI CY - Basel, Schweiz ER -