TY - THES A1 - Beitz, Toralf T1 - Photochemische Reaktionen ausgewählter Azaarene in natürlichen Gewässern Y1 - 1996 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 - Beitz, Toralf A1 - Bechmann, Wolfgang A1 - Mitzner, Rolf T1 - Investigations of reactions of selected Azaarenes with radicals in water, 1. Hydroxyl and sulfate radicals Y1 - 1998 ER - TY - JOUR A1 - Beitz, Toralf A1 - Bechmann, Wolfgang A1 - Mitzner, Rolf T1 - Investigation on the photoreactions of Nitrate and Nitrite ions with selected Azaarenes in water Y1 - 1999 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 - Beitz, Toralf A1 - Koetz, Joachim A1 - Wolf, Gunter A1 - Kleinpeter, Erich A1 - Friberg, Stig E. T1 - Poly(N-vinyl-2-pyrrolidone) and 1-octyl-2-pyrrolidinone modified ionic microemulsions Y1 - 2001 ER - 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 - JOUR A1 - Brendler, Christian A1 - Riebe, Daniel A1 - Ritschel, Thomas A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Investigation of neuroleptics and other aromatic compounds by laser-based ion mobility mass spectrometry JF - Analytical & bioanalytical chemistry N2 - Laser-based ion mobility (IM) spectrometry was used for the detection of neuroleptics and PAH. A gas chromatograph was connected to the IM spectrometer in order to investigate compounds with low vapour pressure. The substances were ionized by resonant two-photon ionization at the wavelengths lambda = 213 and 266 nm and pulse energies between 50 and 300 mu J. Ion mobilities, linear ranges, limits of detection and response factors are reported. Limits of detection for the substances are in the range of 1-50 fmol. Additionally, the mechanism of laser ionization at atmospheric pressure was investigated. First, the primary product ions were determined by a laser-based time-of-flight mass spectrometer with effusive sample introduction. Then, a combination of a laser-based IM spectrometer and an ion trap mass spectrometer was developed and characterized to elucidate secondary ion-molecule reactions that can occur at atmospheric pressure. Some substances, namely naphthalene, anthracene, promazine and thioridazine, could be detected as primary ions (radical cations), while other substances, in particular acridine, phenothiazine and chlorprothixene, are detected as secondary ions (protonated molecules). The results are interpreted on the basis of quantum chemical calculations, and an ionization mechanism is proposed. KW - Ion mobility spectrometry KW - Mass spectrometry KW - Gas chromatography KW - Laser ionization KW - REMPI KW - Neuroleptics Y1 - 2013 U6 - https://doi.org/10.1007/s00216-012-6654-7 SN - 1618-2642 VL - 405 IS - 22 SP - 7019 EP - 7029 PB - Springer CY - Heidelberg 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 - Erler, Alexander A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Gebbers, Robin T1 - Soil Nutrient Detection for Precision Agriculture Using Handheld Laser-Induced Breakdown Spectroscopy (LIBS) and Multivariate Regression Methods (PLSR, Lasso and GPR) JF - Sensors N2 - Precision agriculture (PA) strongly relies on spatially differentiated sensor information. Handheld instruments based on laser-induced breakdown spectroscopy (LIBS) are a promising sensor technique for the in-field determination of various soil parameters. In this work, the potential of handheld LIBS for the determination of the total mass fractions of the major nutrients Ca, K, Mg, N, P and the trace nutrients Mn, Fe was evaluated. Additionally, other soil parameters, such as humus content, soil pH value and plant available P content, were determined. Since the quantification of nutrients by LIBS depends strongly on the soil matrix, various multivariate regression methods were used for calibration and prediction. These include partial least squares regression (PLSR), least absolute shrinkage and selection operator regression (Lasso), and Gaussian process regression (GPR). The best prediction results were obtained for Ca, K, Mg and Fe. The coefficients of determination obtained for other nutrients were smaller. This is due to much lower concentrations in the case of Mn, while the low number of lines and very weak intensities are the reason for the deviation of N and P. Soil parameters that are not directly related to one element, such as pH, could also be predicted. Lasso and GPR yielded slightly better results than PLSR. Additionally, several methods of data pretreatment were investigated. KW - LIBS KW - lasso KW - PLS regression KW - gaussian processes KW - soil KW - precision agriculture KW - nutrients Y1 - 2020 U6 - https://doi.org/10.3390/s20020418 SN - 1424-8220 VL - 20 IS - 2 PB - MDPI CY - Basel ER - TY - JOUR A1 - Erler, Alexander A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Grothusheitkamp, Daniela A1 - Kunz, T. A1 - Methner, Frank-Jürgen T1 - Detection of volatile organic compounds in the headspace above mold fungi by GC-soft X-radiation-based APCI-MS JF - Journal of mass spectrometr N2 - Mold fungi on malting barley grains cause major economic loss in malting and brewery facilities. Possible proxies for their detection are volatile and semivolatile metabolites. Among those substances, characteristic marker compounds have to be identified for a confident detection of mold fungi in varying surroundings. The analytical determination is usually performed through passive sampling with solid phase microextraction, gas chromatographic separation, and detection by electron ionization mass spectrometry (EI-MS), which often does not allow a confident determination due to the absence of molecular ions. An alternative is GC-APCI-MS, generally, allowing the determination of protonated molecular ions. Commercial atmospheric pressure chemical ionization (APCI) sources are based on corona discharges, which are often unspecific due to the occurrence of several side reactions and produce complex product ion spectra. To overcome this issue, an APCI source based on soft X-radiation is used here. This source facilitates a more specific ionization by proton transfer reactions only. In the first part, the APCI source is characterized with representative volatile fungus metabolites. Depending on the proton affinity of the metabolites, the limits of detection are up to 2 orders of magnitude below those of EI-MS. In the second part, the volatile metabolites of the mold fungus species Aspergillus, Alternaria, Fusarium, and Penicillium are investigated. In total, 86 compounds were found with GC-EI/APCI-MS. The metabolites identified belong to the substance classes of alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, terpenes, and sesquiterpenes. In addition to substances unspecific for the individual fungus species, characteristic patterns of metabolites, allowing their confident discrimination, were found for each of the 4 fungus species. Sixty-seven of the 86 metabolites are detected by X-ray-based APCI-MS alone. The discrimination of the fungus species based on these metabolites alone was possible. Therefore, APCI-MS in combination with collision induced dissociation alone could be used as a supervision method for the detection of mold fungi. KW - APCI KW - gas chromatography KW - mass spectrometry KW - mold fungi KW - soft X-radiation KW - volatile organic compounds Y1 - 2018 U6 - https://doi.org/10.1002/jms.4210 SN - 1076-5174 SN - 1096-9888 VL - 53 IS - 10 SP - 911 EP - 920 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Erler, Alexander A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Grothusheitkamp, Daniela A1 - Kunz, Thomas A1 - Methner, Frank-Jürgen T1 - Characterization of volatile metabolites formed by molds on barley by mass and ion mobility spectrometry JF - Journal of mass spectrometr N2 - The contamination of barley by molds on the field or in storage leads to the spoilage of grain and the production of mycotoxins, which causes major economic losses in malting facilities and breweries. Therefore, on-site detection of hidden fungus contaminations in grain storages based on the detection of volatile marker compounds is of high interest. In this work, the volatile metabolites of 10 different fungus species are identified by gas chromatography (GC) combined with two complementary mass spectrometric methods, namely, electron impact (EI) and chemical ionization at atmospheric pressure (APCI)-mass spectrometry (MS). The APCI source utilizes soft X-radiation, which enables the selective protonation of the volatile metabolites largely without side reactions. Nearly 80 volatile or semivolatile compounds from different substance classes, namely, alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, alkenes, terpenes, oxidized terpenes, sesquiterpenes, and oxidized sesquiterpenes, could be identified. The profiles of volatile and semivolatile metabolites of the different fungus species are characteristic of them and allow their safe differentiation. The application of the same GC parameters and APCI source allows a simple method transfer from MS to ion mobility spectrometry (IMS), which permits on-site analyses of grain stores. Characterization of IMS yields limits of detection very similar to those of APCI-MS. Accordingly, more than 90% of the volatile metabolites found by APCI-MS were also detected in IMS. In addition to different fungus genera, different species of one fungus genus could also be differentiated by GC-IMS. KW - APCI KW - fungus KW - gas chromatography KW - ion mobility spectrometry KW - mass KW - spectrometry KW - mold KW - soft X-ray Y1 - 2020 U6 - https://doi.org/10.1002/jms.4501 SN - 1076-5174 SN - 1096-9888 VL - 55 IS - 5 SP - 1 EP - 10 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Erler, Alexander A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Leenen, Mathias A1 - Pätzold, Stefan A1 - Ostermann, Markus A1 - Wójcik, Michał T1 - Mobile laser-induced breakdown spectroscopy for future application in precision agriculture BT - a case study JF - Sensors N2 - In precision agriculture, the estimation of soil parameters via sensors and the creation of nutrient maps are a prerequisite for farmers to take targeted measures such as spatially resolved fertilization. In this work, 68 soil samples uniformly distributed over a field near Bonn are investigated using laser-induced breakdown spectroscopy (LIBS). These investigations include the determination of the total contents of macro- and micronutrients as well as further soil parameters such as soil pH, soil organic matter (SOM) content, and soil texture. The applied LIBS instruments are a handheld and a platform spectrometer, which potentially allows for the single-point measurement and scanning of whole fields, respectively. Their results are compared with a high-resolution lab spectrometer. The prediction of soil parameters was based on multivariate methods. Different feature selection methods and regression methods like PLS, PCR, SVM, Lasso, and Gaussian processes were tested and compared. While good predictions were obtained for Ca, Mg, P, Mn, Cu, and silt content, excellent predictions were obtained for K, Fe, and clay content. The comparison of the three different spectrometers showed that although the lab spectrometer gives the best results, measurements with both field spectrometers also yield good results. This allows for a method transfer to the in-field measurements. KW - LIBS KW - precision agriculture KW - soil KW - multivariate methods KW - feature selection Y1 - 2023 U6 - https://doi.org/10.3390/s23167178 SN - 1424-8220 VL - 23 IS - 16 PB - MDPI CY - Basel ER - TY - JOUR A1 - Koetz, Joachim A1 - Beitz, Toralf T1 - The phase behaviour of polyanion-polycation systems Y1 - 1997 ER - TY - JOUR A1 - Koetz, Joachim A1 - Beitz, Toralf A1 - Kosmella, Sabine A1 - Tiersch, Brigitte T1 - Polymer-modified microemulsions Y1 - 2000 ER - TY - JOUR A1 - Koetz, Joachim A1 - Beitz, Toralf A1 - Tiersch, Brigitte T1 - Self assembled polymer-surfactant systems Y1 - 1999 ER - TY - JOUR A1 - Koetz, Joachim A1 - Kosmella, Sabine A1 - Beitz, Toralf T1 - Self-assembled Polyelectrolyte Systems Y1 - 2001 ER - TY - JOUR A1 - Laudien, Robert A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Detection of explosive related nitroaromatic compounds (ERNC) by laser-based ion mobility spectrometry Y1 - 2008 SN - 978-0-8194-7348-6 ER - TY - JOUR A1 - Michalik-Onichimowska, Aleksandra A1 - Beitz, Toralf A1 - Panne, Ulrich A1 - Löhmannsröben, Hans-Gerd A1 - Riedel, Jens T1 - Microsecond mid-infrared laser pulses for atmospheric pressure laser ablation/ionization of liquid samples JF - Sensors and actuators : B, Chemical N2 - 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. KW - Laser ablation KW - Ion mobility spectrometry KW - Pulse duration KW - Plume KW - Ionization Y1 - 2016 U6 - https://doi.org/10.1016/j.snb.2016.06.155 SN - 0925-4005 VL - 238 SP - 298 EP - 305 PB - Elsevier CY - Lausanne 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 -