Browsing by Subject "Pflanzliches Lebensmittel"

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    High-throughput planar solid phase extraction : a new clean-up concept in multi-residue analysis of pesticides
    (2014) Oellig, Claudia; Schwack, Wolfgang
    Currently, the most serious problems in pesticide residue analysis by liquid chromatography (LC) or gas chromatography (GC) coupled to mass spectrometry (MS) concern the so-called “matrix effects”. The most common way to avoid these effects is the application of matrix-matched calibration standards. Nevertheless, an efficient clean-up undoubtedly is the best way to prevent matrix effects in multi-residue analysis of pesticides in food by LC–MS or GC–MS. For a totally new powerful clean-up method, called high-throughput planar solid phase extraction (HTpSPE), highly automated planar chromatographic tools were applied to remove co-extracted matrix substances entirely and to eliminate any kind of matrix related effects. For sample extraction, the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was used to initially collect pesticides from fruits and vegetables. The received acetonitrile extracts were applied directly for the development of the novel HTpSPE clean-up. Thin-layer chromatography (TLC) was used to completely separate pesticides from matrix compounds and to focus them into a sharp zone. A two-fold development on amino-modified silica gel thin-layers with acetonitrile for the first development, and acetone for the second development in the backwards direction, was evaluated to perform the best clean-up result and collect the pesticides in a sharp, single target zone. To easily locate the pesticide zone, the Sudan II dye was added to the extracts. Following this clean-up, the target zones (pesticides) were eluted by the TLC–MS interface into vials for the LC–MS determination. HTpSPE resulted in extracts which were nearly free of co-extracted matrix and matrix effects, as shown for seven chemically representative pesticides (acetamiprid, azoxystrobin, chlorpyrifos, fenarimol, mepanipyrim, penconazole, and pirimicarb) in four different fruit and vegetable matrices (apples, cucumbers, red grapes, and tomatoes). Thanks to the very clean HTpSPE extracts, calibration can simply be performed with pure solvent standards and the quantitation by LC–MS provided excellent mean recoveries and relative standard deviations. In addition, tea samples as rather challenging matrices were chosen to apply for HTpSPE. The matrix load of tea extracts generally was too high for the available thin-layer capacity and the selectivity of the amino-modified phase was not suitable for the separation of caffeine and further matrix compounds from the target analytes (pesticides). By modifying the sample extraction, adding a pre-cleaning by dispersive solid phase extraction (dSPE) and changing the thin-layer phase to normal phase silica gel, the complete separation of pesticides and tea matrix components was possible, when again a two-fold development was applied. Caffeine and other alkaloids were completely removed. The effectiveness of HTpSPE was demonstrated by LC–MS/MS calibration curves from matrix-matched and solvent standards, which were nearly identical and by very good mean recoveries, calculated against pure solvent standards. Concerning all validation parameters, the new acetonitrile-HTpSPE procedure for tea samples was superior to the QuEChERS-dSPE method and offered highly successful results. In recent years, large-scale screening in pesticide residue analysis has gained more and more importance. Keeping this in mind, a screening strategy for HTpSPE extracts, using a high-resolution MS, was developed to analyze the cleaned extracts directly for pesticide residues without a liquid chromatographic separation. By this hyphenation, a completely new microliter-flow injection analysis–time-of-flight mass spectrometry (µL-FIA–TOFMS) screening was introduced. The novel HTpSPE–µL-FIA–TOFMS approach enabled the detection of all pesticides simultaneously in a single mass spectrum within a few minutes. The obtained mass spectra were nearly free of matrix compounds, which is especially the great benefit of the effective HTpSPE clean-up. Recovery studies by HTpSPE–µL-FIA–TOFMS against solvent standards for the matrices and pesticides under study provided excellent results, using the mass signal intensities under the entire FIA sample peak. HTpSPE clearly showed superior results concerning every tested parameter than dSPE. With the help of a self-constructed mass database searching tool, all spiked pesticides were detected and correctly identified, while only very low numbers of false-positive findings occurred. Furthermore, a non-target screening approach was successfully implemented by slightly changing the database searching process, offering a mass list of all substances, which are present in the injected extracts but not included in the mass database. Finally, the new HTpSPE–µL-FIA–TOFMS screening was successfully applied to several real samples, when the identified pesticides were quite identical compared to results of LC–MS/MS analysis of the QuEChERS-dSPE extracts.
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    Publication
    Informationsbedarf und Informationsbeschaffung von Konsumenten bei Lebensmitteln pflanzlicher Herkunft: eine empirische Untersuchung anhand von Fokus-Gruppen
    (2003) Tesch, Ines
    Der Konsument von Lebensmitteln ist, so scheint es oft, ein verunsicherter Verbraucher, dem über eine verstärkte und verbesserte Information geholfen werden muss. Der Arbeitsbericht leistet einen Beitrag zur Beantwortung der Frage: Welcher Bedarf besteht tatsächlich aus Verbrauchersicht an Information und welche Möglichkeiten der Verbraucherinformation gibt es mit welchen spezifischen Vor- und Nachteilen? Unter Einsatz von Fokus-Gupppen ergibt die Untersuchung des Informationsverhaltens der Konsumenten ein äußerst differenziertes Bild. Im Bereich des Informationsbedarfs ist neben den erwarteten Informationswünschen zu Qualitätsmerkmalen die große Bedeutung des Geschmacks auffällig, sowie der Wunsch nach einer Kennzeichnung des Pflanzenschutzmitteleinsatzes bei Produkten. Informationsbedarf und Anforderungen an Lebensmittel sind abhängig von der Produktgruppe und Verzehrsform, wobei sich mit steigendem Verarbeitungsgrad das Interesse von der landwirtschaftlichen Erzeugung auf die Verarbeitung der Lebensmittel verlagert. Weiterhin ist der Informationsbedarf ereignisabhängig: Skandale führen zu einer veränderten Beachtung von Produktmerkmalen, beispielsweise der Herkunft, und einer aktiveren Informationsbeschaffung. Der Zusammenhang zwischen Informationsbedarf und Einkaufsverhalten ist bezüglich der Wirkungsrichtung unklar. Eine einfache Abhängigkeit von Einstellungen und soziodemographischen Merkmalen konnte in den Fokusgruppen nicht festgestellt werden. Die Informationsbeschaffung erfolgt überwiegend passiv. Die Informationsquellen Landwirt, staatliche Institutionen und beschränkt auch der Handel und die Stiftung Warentest haben hohe Glaubwürdigkeit. Die Zugänglichkeit der Information ist insbesondere am Verkaufsort in Form von Faltblättern, Scannern, einer Obsttheke oder der Verpackung sehr gut. Nachschlagecharakter haben Bücher und das Internet, die zufällige Aufnahme von Information wird von Fernsehen und Presse dominiert. Zusammenfassend wird festgehalten, dass keineswegs jeder Verbraucher eine veränderte Lebensmittelinformation wünscht und benötigt. Vielmehr gilt dies nur für einzelne Verbraucher und häufig nur in bestimmten Situationen. Viele Konsumenten sehen Informationen als einen zusätzlichen Service an, der ihnen Genuss und Unterhaltung bieten muss, um überhaupt genutzt zu werden.