TY - JOUR A1 - Riebe, Daniel A1 - Zühlke, Martin A1 - Zenichowski, Karl A1 - Beitz, Toralf A1 - Dosche, Carsten A1 - Löhmannsröben, Hans-Gerd T1 - Characterization of rhodamine 6G release in electrospray ionization by means of spatially resolved fluorescence spectroscopy JF - Zeitschrift für physikalische Chemie : international journal of research in physical chemistry and chemical physics N2 - In the present work, the density distribution of rhodamine 6G ions (R6G) in the gas phase and the droplets of an electrospray plume was studied by spatial and spectral imaging. The intention is to contribute to the fundamental understanding of the release mechanism of gaseous R6G in the electrospray ionization (ESI) process. Furthermore, the influence of ESI-parameters on the release efficiency of R6G, e. g. solvent flow, R6G and salt concentration were examined via direct fluorescence imaging of R6G. A solvent-shift of the fluorescence maximum,lambda(max) = 555 nm in methanolic solution and lambda(max) = 505 nm in gas phase, allows the discrimination between solvated and gaseous R6G. Two experimental setups were used for our measurements. In the first experiment, the R6G fluorescence and the light scattered from the spray plume were imaged in two spatial dimensions using a tunable wavelength filter. The second experiment was designed for obtaining 1-dimensional spatially resolved emission spectra of the spray. Here, the intensity distribution of solvated and gaseous R6G as well as scattered light (lambda = 355 nm) were measured simultaneously. The results show the distribution of gaseous R6G in the plane, orthogonal to the ESI capillary, decreasing slightly towards the spray center and showing maxima at the cone margins. The distribution of gaseous R6G confirms the preferred release of gaseous ions from nano-droplets, indicating the ion evaporation model (IEM) to be the dominating release mechanism. Up to now, only a few fluorescence spectra of ionic compounds in the gas phase were published because the measurement of emission spectra of mass-selected ions in an ion trap is experimentally challenging. The fluorescence spectrum of gaseous lucigenin at atmospheric pressure is reported for the first time. This spectrum of lucigenin in the gas phase exhibits a blue shift of about Delta lambda = 10 nm in comparison to the corresponding spectrum in methanol. KW - Fluorescence KW - Electrospray Ionization KW - Rhodamine 6G KW - Gaseous Ions KW - Lucigenin Y1 - 2011 U6 - https://doi.org/10.1524/zpch.2011.0149 SN - 0942-9352 VL - 225 IS - 9-10 SP - 1055 EP - 1072 PB - De Gruyter Oldenbourg CY - München ER - TY - JOUR A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Dosche, Carsten A1 - Löhmannsröben, Hans-Gerd A1 - Raab, Volker A1 - Raab, Corinna A1 - Unverzagt, Matthias T1 - High-resolution spectrometer using combined dispersive and interferometric wavelength separation for raman and laser-induced Breakdown Spectroscopy (LIBS) JF - Applied spectroscopy : an international journal of spectroscopy ; official publication of the Society for Applied Spectroscopy N2 - In this paper the concept of a compact high-resolution spectrometer based on the combination of dispersive and interferometric elements is presented. Dispersive elements are used to spectrally resolve the light in one direction with coarse resolution (Delta lambda < 0.5 nm), while perpendicular to that direction an etalon provides high spectral resolution (Delta lambda < 50 pm). This concept for two-dimensional spectroscopy has been implemented for the wavelength range lambda = 350-650 nm. Appropriate algorithms for reconstructing spectra from the two-dimensional raw data and for wavelength calibration were established in an analysis software. Potential applications for this new spectrometer are Raman and laser-induced breakdown spectroscopy (LIBS). Resolutions down to 28 pm (routinely 54 pm) could be realized for these applications. KW - Raman spectroscopy KW - Laser-induced breakdown spectroscopy KW - LIBS KW - Fabry-Perot etalon KW - High-resolution spectrometer Y1 - 2014 U6 - https://doi.org/10.1366/13-07426 SN - 0003-7028 SN - 1943-3530 VL - 68 IS - 9 SP - 1030 EP - 1038 PB - Society for Applied Spectroscopy CY - Frederick ER - TY - JOUR A1 - Riebe, Daniel A1 - Eder, Alexander A1 - Ritschel, Thomas A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Beil, Andreas A1 - Blaschke, Michael A1 - Ludwig, Thomas T1 - Atmospheric pressure chemical ionization of explosives induced by soft X-radiation in ion mobility spectrometry: mass spectrometric investigation of the ionization reactions of drift gasses, dopants and alkyl nitrates JF - Journal of mass spectrometr N2 - A promising replacement for the radioactive sources commonly encountered in ion mobility spectrometers is a miniaturized, energy-efficient photoionization source that produce the reactant ions via soft X-radiation (2.8 keV). In order to successfully apply the photoionization source, it is imperative to know the spectrum of reactant ions and the subsequent ionization reactions leading to the detection of analytes. To that end, an ionization chamber based on the photoionization source that reproduces the ionization processes in the ion mobility spectrometer and facilitates efficient transfer of the product ions into a mass spectrometer was developed. Photoionization of pure gasses and gas mixtures containing air, N-2, CO2 and N2O and the dopant CH2Cl2 is discussed. The main product ions of photoionization are identified and compared with the spectrum of reactant ions formed by radioactive and corona discharge sources on the basis of literature data. The results suggest that photoionization by soft X-radiation in the negative mode is more selective than the other sources. In air, adduct ions of O-2 - with H2O and CO2 were exclusively detected. Traces of CO2 impact the formation of adduct ions of O-2 - and Cl -(upon addition of dopant) and are capable of suppressing them almost completely at high CO2 concentrations. Additionally, the ionization products of four alkyl nitrates (ethylene glycol dinitrate, nitroglycerin, erythritol tetranitrate and pentaerythritol tetranitrate) formed by atmospheric pressure chemical ionization induced by X-ray photoionization in different gasses (air, N-2 and N2O) and dopants (CH2Cl2, C2H5Br and CH3I) are investigated. The experimental studies are complemented by density functional theory calculations of the most important adduct ions of the alkyl nitrates (M) used for their spectrometric identification. In addition to the adduct ions [M + NO3](-) and [M + Cl](-), adduct ions such as [M + N2O2](-), [M + Br](-) and [M+ I](-) were detected, and their gas-phase structures and energetics are investigated by density functional theory calculations. Copyright (C) 2016 John Wiley & Sons, Ltd. KW - ion mobility spectrometry KW - mass spectrometry KW - explosives KW - X-ray KW - photoionization KW - alkyl nitrates Y1 - 2016 U6 - https://doi.org/10.1002/jms.3784 SN - 1076-5174 SN - 1096-9888 VL - 51 SP - 566 EP - 577 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Zühlke, Martin A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Zenichowski, Karl A1 - Diener, Marc A1 - Linscheid, Michael W. T1 - An electrospray ionization-ion mobility spectrometer as detector for high-performance liquid chromatography JF - European journal of mass spectrometry N2 - The application of electrospray ionization (ESI) ion mobility (IM) spectrometry on the detection end of a high-performance liquid chromatograph has been a subject of study for some time. So far, this method has been limited to low flow rates or has required splitting of the liquid flow. This work presents a novel concept of an ESI source facilitating the stable operation of the spectrometer at flow rates between 10 mu L min(-1) and 1500 mu L min(-1) without flow splitting, advancing the T-cylinder design developed by Kurnin and co-workers. Flow rates eight times faster than previously reported were achieved because of a more efficient dispersion of the liquid at increased electrospray voltages combined with nebulization by a sheath gas. Imaging revealed the spray operation to be in a rotationally symmetric multijet-mode. The novel ESI-IM spectrometer tolerates high water contents (<= 90%) and electrolyte concentrations up to 10 mM, meeting another condition required of high-performance liquid chromatography (HPLC) detectors. Limits of detection of 50 nM for promazine in the positive mode and 1 mu M for 1,3-dinitrobenzene in the negative mode were established. Three mixtures of reduced complexity (five surfactants, four neuroleptics, and two isomers) were separated in the millisecond regime in stand-alone operation of the spectrometer. Separations of two more complex mixtures (five neuroleptics and 13 pesticides) demonstrate the application of the spectrometer as an HPLC detector. The examples illustrate the advantages of the spectrometer over the established diode array detector, in terms of additional IM separation of substances not fully separated in the retention time domain as well as identification of substances based on their characteristic IMs. KW - ESI KW - IMS KW - HPLC KW - spray imaging KW - neuroleptics KW - pesticides KW - surfactants Y1 - 2015 U6 - https://doi.org/10.1255/ejms.1367 SN - 1469-0667 SN - 1751-6838 VL - 21 IS - 3 SP - 391 EP - 402 PB - WeltTrends CY - Sussex ER - TY - JOUR A1 - Koetz, Joachim A1 - Kosmella, Sabine A1 - Beitz, Toralf T1 - Self-assembled Polyelectrolyte Systems Y1 - 2001 ER - TY - JOUR A1 - Beitz, Toralf A1 - Koetz, Joachim A1 - Friberg, Stig E. T1 - Polymer-modified ionic microemulsion formed in the system SDS/Water/Xylene/Pentanol Y1 - 1999 ER - TY - JOUR A1 - Zühlke, Martin A1 - Zenichowski, Karl A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Subambient pressure electrospray ionization ion mobility spectrometry JF - International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry N2 - 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. KW - Ion mobility spectrometry KW - Electrospray ionization KW - Subambient pressure KW - Imaging Y1 - 2017 U6 - https://doi.org/10.1007/s12127-017-0215-x SN - 1435-6163 SN - 1865-4584 VL - 20 SP - 47 EP - 56 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Beitz, Toralf A1 - Bechmann, Wolfgang A1 - Mitzner, Rolf T1 - Investigations of reactions of selected Azaarenes with radicals in water, 2. Chlorine and Bromine radicals Y1 - 1998 ER - TY - JOUR A1 - Tessmann, Joachim A1 - Beitz, Toralf A1 - Bechmann, Wolfgang A1 - Mitzner, Rolf T1 - Untersuchungen zu Toxizitätsänderungen in Photoreaktionen von Azaarenen Y1 - 1999 ER - TY - JOUR A1 - Wojcik, Michal A1 - Brinkmann, Pia A1 - Zdunek, Rafał A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Merk, Sven A1 - Cieslik, Katarzyna A1 - Mory, David A1 - Antonczak, Arkadiusz T1 - Classification of copper minerals by handheld laser-induced breakdown spectroscopy and nonnegative tensor factorisation JF - Sensors N2 - Laser-induced breakdown spectroscopy (LIBS) analysers are becoming increasingly common for material classification purposes. However, to achieve good classification accuracy, mostly noncompact units are used based on their stability and reproducibility. In addition, computational algorithms that require significant hardware resources are commonly applied. For performing measurement campaigns in hard-to-access environments, such as mining sites, there is a need for compact, portable, or even handheld devices capable of reaching high measurement accuracy. The optics and hardware of small (i.e., handheld) devices are limited by space and power consumption and require a compromise of the achievable spectral quality. As long as the size of such a device is a major constraint, the software is the primary field for improvement. In this study, we propose a novel combination of handheld LIBS with non-negative tensor factorisation to investigate its classification capabilities of copper minerals. The proposed approach is based on the extraction of source spectra for each mineral (with the use of tensor methods) and their labelling based on the percentage contribution within the dataset. These latent spectra are then used in a regression model for validation purposes. The application of such an approach leads to an increase in the classification score by approximately 5% compared to that obtained using commonly used classifiers such as support vector machines, linear discriminant analysis, and the k-nearest neighbours algorithm. KW - LIBS KW - NTF KW - HALS KW - classification KW - copper minerals Y1 - 2020 U6 - https://doi.org/10.3390/s20185152 SN - 1424-8220 VL - 20 IS - 18 PB - MDPI CY - Basel ER -