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Organisationseinheit der BAM
Stable isotope dilution assay for the accurate determination of mycotoxins in maize by UHPLC-MS/MS
(2012)
A fast, easy-to-handle and cost-effective analytical
method for 11 mycotoxins currently regulated in maize and
other cereal-based food products in Europe was developed
and validated for maize. The method is based on two extraction
steps using different acidified acetonitrilewater mixtures.
Separation is achieved using ultrahigh-performance
liquid chromatography (UHPLC) by a linear watermethanol
gradient. After electrospray ionisation, tandem mass spectrometric
detection is performed in dynamic multiple reaction
monitoring mode. Since accurate mass spectrometric quantification
is hampered by matrix effects, uniformly [13C]-
labelled mycotoxins for each of the 11 compounds were added
to the sample extracts prior to UHPLC-MS/MS analysis.
Method performance parameters were obtained by spiking
blank maize samples with mycotoxins before as well as after
extraction on six levels in triplicates. The twofold extraction
led to total recoveries of the extraction steps between 97%and
111% for all target analytes, including fumonisins. The [13C]-
labelled internal standards efficiently compensated all matrix
effects in electrospray ionisation, leading to apparent recoveries
between 88% and 105% with reasonable additional costs.
The relative standard deviations of the whole method were
between 4% and 11% for all analytes. The trueness of the
method was verified by the measurement of several maize test
materials with well-characterized concentrations. In conclusion,
the developed method is capable of determining all
regulated mycotoxins in maize and presuming similar
matrix effects and extraction recovery also in other cerealbased
foods.
The development of earth-abundant catalysts for selective electrochemical CO2 conversion is a central challenge. Cu-Sn bimetallic catalysts can yield selective CO2 reduction toward either CO or formate. This study presents oxide-derived Cu-Sn catalysts tunable for either product and seeks to understand the synergetic effects between Cu and Sn causing these selectivity trends. The materials undergo significant transformations under CO2 reduction conditions, and their dynamic bulk and surface structures are revealed by correlating observations from multiple methods—X-ray absorption spectroscopy for in situ study, and quasi in situ X-ray photoelectron spectroscopy for surface sensitivity. For both types of catalysts, Cu transforms to metallic Cu0 under reaction conditions. However, the Sn speciation and content differ significantly between the catalyst types: the CO-selective catalysts exhibit a surface Sn content of 13 at. % predominantly present as oxidized Sn, while the formate-selective catalysts display an Sn content of ≈70 at. % consisting of both metallic Sn0 and Sn oxide species. Density functional theory simulations suggest that Snδ+ sites weaken CO adsorption, thereby enhancing CO selectivity, while Sn0 sites hinder H adsorption and promote formate production. This study reveals the complex dependence of catalyst structure, composition, and speciation with electrochemical bias in bimetallic Cu catalysts.
Für die zerstörungsfreie Prüfung großer Betonbauwerke unter dem Aspekt der Analyse von Spannkanälen hat sich die Ultraschalltechnik in den letzten Jahren als geeignete Methode herausgestellt, da sowohl die Messtechnik insbesondere die Ultraschallwandler als auch die numerischen Auswerteverfahren in einem Stadium sind, das es erlaubt, größere Messflächen und damit größere Volumina zu beschallen und abzubilden. Mit Hilfe der Modellierung der Ausbreitung elastischer Wellen in komplexen Medien können praxisrelevante Problemstellungen untersucht werden, auch unter dem Aspekt, Testkörper zu planen oder gar zu ersetzen. Durch die Auswertung der Phase der Rekonstruktion eines Streuvorgangs können Fehlstellen klassifiziert und damit Aussagen über die Bauwerkssicherheit signifikant objektiviert werden. Die Methoden werden, im Hinblick auf eine ganzheitliche Sichtweise von skalaren und polarimetrischen Abbildungsverfahren mit Unterstützung der Modellierung und der anschließenden Klassifizierung durch Phasenanalyse, an ausgewählten Beispielen erläutert.
For nondestructive testing of concrete buildings under the aspect of tendon duct analysis, ultrasonic testing has proven to be a suitable method, as both the measuring technique in particular the acoustic sensors and the numerical methods allow the insonification and imaging of larger surfaces and volumes. With the aid of numerical modelling of elastic wave propagation in complex media real life problems can be examined with the goal to design or even to replace test specimen. By determination of the phase of an imaged scattering event, defects can be classified, and the prediction of the integrity of buildings can be significantly objectified. The methods are explained for selected examples in an integral way with respect to scalar and polarimetric imaging algorithms supported by modelling and subsequent classification through phase analysis.
Ultraschallmessverfahren werden seit Langem erfolgreich für Prüfaufgaben, wie zum Beispiel die Ermittlung von Bauteilgeometrien, im Bauwesen eingesetzt. Um die Schallbündelung der Prüfköpfe zu verbessern, werden oft mehrere Prüfköpfe in einem Array angeordnet. Für die Entwicklung der Prüfkopfarrays ist es zweckmäßig, mithilfe von Modellierungen den Einfluss der Arraygröße, der Anordnung der Einzelprüfköpfe im Array und der Prüffrequenz auf das Schallfeld zu untersuchen. Dazu werden in der Praxis erfolgreich Modellierungen auf der Basis der Elastodynamischen Finiten Integrationstechnik (EFIT) und der Punktquellensynthese angewendet. Beim Aufbau der Arrays kommen zurzeit immer häufiger Transversal-Punktkontaktprüfköpfe zur Anwendung. Daher wird bei der Beschreibung der Schallfeldberechnung insbesondere auf die der Transversalwellenprüfköpfe eingegangen und mithilfe von Modellierungen und Experimenten gezeigt, wie sich die Prüfkopfpositionierung auf die Richtcharakteristik auswirkt.
Die Potentialmessung kann zum Auffinden korrosionsaktiver Bereiche neben Stahlbetonbauwerken auch bei Spannbetonbauwerken angewandt werden, die mit Spannstählen im direkten Verbund hergestellt werden. Bei Vorspannsystemen mit metallischen Hüllrohren im nachträglichen Verbund ist eine Aussage über den Korrosionszustand des Hüllrohrs, nicht aber des Spannstahls möglich. Messungen an Spannbetonbauteilen erfordern grundsätzlich die besonderen Kenntnisse eines Spezialisten.
This specification describes how corrosion monitoring is used to check the condition of reinforced and prestressed concrete members. In this specification, the term "corrosion monitoring" covers all methods in which it is possible to continuously track corrosion-relevant variables in the area of stationary, built-in sensors. This specification does not cover other possible methods, such as potential field measurements, involving the use of mobile, portable sensors that are placed temporarily on the membersurface to take measurements.
Lanthanides (Ln) are critical raw materials, however, their mining and purification have a considerable negative environmental impact and sustainable recycling and separation strategies for these elements are needed. In this study, the precipitation and solubility behavior of Ln complexes with pyrroloquinoline quinone (PQQ), the cofactor of recently discovered lanthanide (Ln) dependent methanol dehydrogenase (MDH) enzymes, is presented. In this context, the molecular structure of a biorelevant europium PQQ complex was for the first time elucidated outside a protein environment. The complex crystallizes as an inversion symmetric dimer, Eu2PQQ2, with binding of Eu in the biologically relevant pocket of PQQ. LnPQQ and Ln1Ln2PQQ complexes were characterized by using inductively coupled plasma mass spectrometry (ICP‐MS), infrared (IR) spectroscopy, 151Eu‐Mössbauer spectroscopy, X‐ray total scattering, and extended X‐ray absorption fine structure (EXAFS). It is shown that a natural enzymatic cofactor is capable to achieve separation by precipitation of the notoriously similar, and thus difficult to separate, lanthanides to some extent.