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- Verpressfehler (3)
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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.
Characterization of reflector types by phase-sensitive ultrasonic data processing and imaging
(2008)
Ultrasonic and radar imaging techniques are limited in resolution by the wavelength in the material, yet information beyond those limits is hidden in complex frequency dependent reflection coefficients. The analysis of the phase of complex reflection coefficients together with the properties of imaging algorithms can help to characterize and to classify indications of defects in concrete buildings. This paper describes a method to extract phase information from measurements and SAFT reconstructed images. The influencing factors like material properties, transducer characteristics, and imaging algorithms based on Born or Physical Optics approximations are elaborated. Simulated and experimental results are briefly discussed.
This paper presents the progress of successful location of grouting faults in tendon ducts with ultrasonic imaging. The examples were obtained in the research group FOR 384 funded by DFG (German Research Foundation). The co-operation of experimental research and modeling allowed imaging and identification of grouted and ungrouted areas of tendon ducts (including strands) in a large test specimen (40 m²). In addition to the criteria for indicating grouting faults in post-tensioned ducts known until now the phase evaluation of reflected ultrasonic pulses is described. Experiments and modeling of wave propagation are presented for reflections at metal plates in concrete (thickness range 0.5 mm to 40 mm) and for tendon ducts including strands.
The main part of the progress was achieved by automated measurements using dry contact transducers, 3D-SAFT reconstruction including phase evaluation and modeling considering wave propagation for typical elastic parameters and exact experimental site conditions. The results for shear waves as well as for pressure waves are compared in the frequency range from 50 kHz to 120 kHz.
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.
There is a great demand for non-destructive testing methods for quality assurance and to assess the safety and durability of wooden structures. Ultrasonic echo technique with shear waves in the frequency range of 50 kHz is one of those promising methods and is already frequently applied for usual and glued laminated timber. The article describes the development and first results for an imaging method for this purpose. The highly anisotropic properties of the ultrasonic velocity have to be considered. A 3D-SAFT (Synthetic Aperture Focusing Technique) imaging scheme is developed initially for synthetic data resulting from modelling the elastic wave propagation. The main part of the paper describes the experimental validation of this evaluation technique by experimental studies applying automated ultrasonic scanning techniques. 3D ultrasonic imaging results are described for test specimens made from pine and spruce wood. Another object of investigation was a pedestrian bridge made from siberian larch.
Ultrasonic imaging of tendon ducts enables the precise localisation of grouting faults in many cases. Additionally to well known criteria for detecting grouting faults in tendon ducts recently new possibilities were developed. Two main effects influence the complex behaviour of wave propagation and reflection: a) different arrangement and number of strands or internal rebars; b) superposition of reflecting signals and different wave modes propagating into the interface region around the tendon duct. In order to understand the experimental results, EFIT modelling is performed (EFIT: Elastodynamic Finite Integration Technique).
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.