Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Bepaling samenstelling van vaste mest met NIRS
Rietra, R.P.J.J. ; Oenema, O. - \ 2017
Wageningen : Wageningen Environmental Research (Wageningen Environmental Research rapport 2837) - 27
dierlijke meststoffen - stikstof - fosfor - nabij infrarood spectroscopie - referentienormen - analyse - betrouwbaarheid - analytische methoden - animal manures - nitrogen - phosphorus - near infrared spectroscopy - reference standards - analysis - reliability - analytical methods
Adapting to change : on the mechanism of type I-E CRISPR-Cas defence
Künne, Tim A. - \ 2017
Wageningen University. Promotor(en): John van der Oost, co-promotor(en): Stan Brouns. - Wageningen : Wageningen University - ISBN 9789463436649 - 239
immunity - defence mechanisms - rna - bacteria - escherichia coli - analytical methods - priming - immuniteit - verdedigingsmechanismen - bacteriën - analytische methoden - zaadbevochtiging

Host-pathogen interactions are among the most prevalent and evolutionary important interactions known today. The predation of prokaryotes by their viruses is happening on an especially large scale and had a major influence on the evolutionary history of prokaryotes. Since most viruses are lytic at some point in their life-cycle, there is a high selection pressure for prokaryotes to develop defense mechanisms. As described in Chapter 1, the CRISPR-Cas system is a relatively recently discovered defense system and is also the first adaptive defense system discovered in prokaryotes. CRISPR-Cas systems are widespread, occurring in the majority of archaea and also a considerable fraction of bacteria. This diversity is also reflected in the diversity of different types of CRISPR-Cas systems, currently being divided into 6 major types with a large number of subtypes. The type I-E system of Escherichia coli is a well-studied model system and of high relevance, since it is a major subtype of type I systems which make up around 50 % of all discovered CRISPR-Cas systems. CRISPR-Cas systems basically comprise the CRISPR array, made up of repeats and foreign derived spacers, and a set of cas genes. Immunity is commonly divided into three functional stages, adaptation, expression and interference. Adaptation is the acquisition of new spacers from the foreign nucleic acid and its incorporation into the CRISPR array. During expression, the CRISPR array is transcribed, processed and assembled with Cas proteins into CRISPR RNA (crRNA) guided ribonucleoprotein complexes (crRNP). Interference is the detection, binding and destruction of foreign nucleic acids by the crRNP and in type I systems the Cas3 nuclease. The type I-E system contains another function, called primed adaptation. Primed adaptation is a more rapid and efficient version of regular (naïve) adaptation. In addition to the adaptation machinery, primed adaptation also requires the interference machinery.

Chapter 2 describes and compares a fundamental feature of most, if not all, CRISPR-Cas systems and also many other small RNA based systems. The mode of action of small RNAs relies on protein-assisted base pairing of the guide RNA with target mRNA or DNA to interfere with their transcription, translation or replication. Several unrelated classes of small non-coding RNAs have been identified including eukaryotic RNA silencing associated small RNAs, prokaryotic small regulatory RNAs and prokaryotic CRISPR (clustered regularly interspaced short palindromic repeats) RNAs. All three groups identify their target sequence by base pairing after finding it in a pool of millions of other nucleotide sequences in the cell. In this complicated target search process, a region of 6 to 12 nucleotides of the small RNA termed the ‘seed’ plays a critical role. The seed is often a structurally pre-ordered region that increases accessibility and lowers the energy barrier of RNA-DNA duplex formation. Furthermore, the length of the seed is optimally chosen to allow rapid probing and also rejection of potential target sites. The seed is a perfect example of parallel evolution, showing that nature comes up with the same strategy independently multiple times.

Chapter 3 provides a description and protocol of the Electrophoretic Mobility Shift Assay (EMSA) and its use for studying crRNPs. EMSA is a straightforward and inexpensive method for the determination and quantification of protein–nucleic acid interactions. It relies on the different mobility of free and protein-bound nucleic acid in a gel matrix during electrophoresis. Nucleic acid affinities of crRNPs can be quantified by calculating the dissociation constant (Kd ). Protocols for two types of EMSA assays are described using the Cascade ribonucleoprotein complex from Escherichia coli as an example. One protocol uses plasmid DNA as substrate, while the other uses short linear oligonucleotides. Plasmids can be easily visualized with traditional DNA staining, while oligos have to be radioactively labelled using the 32Phosphate isotope. The EMSA method and these protocols are applied throughout the other chapters of this thesis.

Chapter 4 focusses on the processes of interference and primed adaptation, specifically on their tolerance of mutations. Invaders can escape Type I-E CRISPR-Cas immunity in E. coli by making point mutations in the protospacer (especially in the seed) or its adjacent motif (PAM), but hosts quickly restore immunity by integrating new spacers in a positive feedback process termed priming. Here, we provide a systematic analysis of the constraints of both direct interference and subsequent priming in E. coli. We have defined a high-resolution genetic map of direct interference by Cascade and Cas3, which includes five positions of the protospacer at 6 nt intervals that readily tolerate mutations. Importantly, we show that priming is an extremely robust process capable of utilizing degenerate target regions with up to at least eleven mutations throughout the PAM and protospacer region. Priming is influenced by the number of mismatches, their position and is nucleotide dependent. Our findings imply that even out-dated spacers containing many mismatches can induce a rapid primed CRISPR response against diversified or related invaders, giving microbes an advantage in the co- evolutionary arms race with their invaders.

In Chapter 5 we elucidate the mechanism of priming. Specifically, we determine how new spacers are produced and selected for integration into the CRISPR array during priming. We show that priming is directly dependent on interference. Rapid priming occurs when the rate of interference is high, delayed priming occurs when the rate of interference is low. Using in vitro assays and next generation sequencing, we show that Cas3 couples CRISPR interference to adaptation by producing DNA breakdown products that fuel the spacer integration process in a two-step, PAM-associated manner. The helicase-nuclease Cas3 pre-processes target DNA into fragments of about 30–100 nt enriched for thymine-stretches in their 3’ ends. By reconstituting the spacer integration process in vitro, we show that the Cas1-2 complex further processes these fragments and integrates them sequence- specifically into CRISPR repeats by coupling of a 3’ cytosine of the fragment. Our results highlight that the selection of PAM-compliant spacers during priming is enhanced by the combined sequence specificities of Cas3 and the Cas1-2 complex, leading to an increased propensity of integrating functional CTT-containing spacers.

In Chapter 6 we look deeper into a nucleotide specific effect on priming that was discovered in Chapter 4. Immunity is based on the complementarity of host encoded spacer sequences with protospacers on the foreign genetic element. The efficiency of both direct interference and primed acquisition depends on the degree of complementarity between spacer and protospacer. Previous studies focused on the amount and positions of mutations, not the identity of the substituted nucleotide. In Chapter 4, we describe a nucleotide bias, showing a positive effect on priming of C substitutions and a negative effect on priming of G substitutions in the basepairing strand of the protospacer. Here we show that these substitutions rather directly influence the efficiency of interference and therefore indirectly influence the efficiency of interference dependent priming. We show that G substitutions have a profoundly negative effect on interference, while C substitutions are readily tolerated when in the same positions. Furthermore, we show that this effect is based on strongly decreased binding of the effector complex Cascade to G mutants, while C mutants only minimally affect binding. In Chapter 5 we showed a connection between the rate of interference and the time of occurrence of priming. Here, we also quantify the extent of priming and show that priming is very prevalent in a population that shows intermediate levels of interference, while high or low levels of interference lead to a lower prevalence of priming.

Chapter 7 describes an attempt to make use of our knowledge about the Cascade complex and develop it into a genome editing tool. The development of genome editing tools has made major leaps in the last decade. Recently, RNA guided endonucleases (RGENs) such as Cas9 or Cpf1 have revolutionized genome editing. These RGENs are the hallmark proteins of class II CRISPR-Cas systems. Here, we have explored the possibility to develop a new genome editing tool that makes use of the Cascade complex from E. coli. This RNA guided protein complex is fused to a FokI nuclease domain to sequence specifically cleave DNA. We validate the tool in vitro using purified protein and two sets of guide RNAs, showing specific cleavage activity. The tool requires two target sites of 32 nt each at a distance of 30-40 nt and inward facing three nucleotide flexible PAM sequences. Cleavage occurs in the middle between the two binding sites and primarily creates 4 nt overhangs. Furthermore, we show that an additional RFP can be fused to FokI-Cascade, allowing visualization of the complex in target cells. Unfortunately, we were not able to successfully apply the tool in vivo in eukaryotic cells.

High-resolution mass spectrometry for the analysis of interfacial kinetics of organic surface reactions
Sen, Rickdeb - \ 2017
Wageningen University. Promotor(en): Han Zuilhof. - Wageningen : Wageningen University - ISBN 9789463436243 - 308
surface chemistry - unimolecular films - chemical reactions - analytical methods - mass spectrometry - oppervlaktechemie - unimoleculaire films - chemische reacties - analytische methoden - massaspectrometrie

In this thesis, XPS and DART–HRMS have been used in close conjugation to supplement each other, since the latter is a relatively new addition to surface chemist’s repertoire that – after development – needed a firm comparison to build up a reputation of its own. The strength of our approach has been underlined by the high correlation between these two independent analytical techniques. Central to our approach has been the formation of mixed monolayers in case of aluminum oxide substrates. As presented in Chapters 2, 3 and 4, we have succeeded in the rapid formation of range stable, covalently bound mixed monolayers. The subsequent development of a general and fast analytical technique to determine the interfacial reaction kinetics, including the activation parameters DH‡ and DS‡, provided unparalleled insights. We have developed a “MS–ionizable tag” technique, which has been applied for the analysis of surface–bound organic reactions, to the best of our knowledge, for the first time.

The Strain–Promoted Alkyne–Azide Cycloaddition (SPAAC) reaction was chosen as a model reaction given the fact that its kinetics had been well–studied in solution. As shown in Chapter 2, the microenvironment around the reactive surface group was carefully controlled by the length of the inert alkyl chains surrounding it. We observed a few interesting trends which could be of great interest to future surface chemists. First, the SPAAC reaction – which is a click reaction in solution – does not retain this nature on the surface (It does not proceed to full conversion and converges sluggishly to around 37% yield after significant temporal passage). A partially accessible microenvironment, where the motion of reactive groups is slightly restricted, was found to provide a high rate with the highest surface yield. In contrast, a freely accessible reactive moiety afforded a lower surface yield albeit with the highest overall rate. Finally, a buried microenvironment led to the highest overall rate albeit with a lower surface yield. As a corollary, for the surface–bound SPAAC reaction we can compare the partially accessible microenvironment to a marathon runner who is able to run further but at a pace slower than a sprinter (free microenvironment). This provides the surface chemist with a handle for tuning the monolayer as per her/his reaction goals.

Harnessing the valuable insights gained from the SPAAC reaction, our concept of ionizable MS tag coupled with DART–HRMS was further extended to a more novel and yet unstudied interfacial reaction in Chapter 3. The Strain–Promoted Oxidation–Controlled cycloalkyne–1,2–Quinone (SPOCQ) cycloaddition was applied for the first time on a surface and afforded a quantitative yield for a free microenvironment in under 4 h. It is to be noted here, that for the first time a 100% (quantitative) metal–free click reaction was observed at a surface. This proved that our approach of engineering the microenvironment around the reactive site provides a distinct edge needed to attain quantitative yields. Quinones are hard to synthesize/store/use in solution given their high propensity to polymerize. However, we demonstrated that on the surface, quinones can be easily generated and stored over–extended period of time by a facile periodate oxidation. Auto–polymerization of surface–bound quinones is precluded by their tether and enforced distal separation by surrounding inert alkyl chains (3:1 ratio). The wider application of this interesting mixture has been further rigorously demonstrated in later chapters too. The bioorthogonality of the SPOCQ reaction coupled with its higher speed and its quantitative yields on the surface are definitely its most salient features.

After studying strain–promoted click reactions on the surface (culminating for SPOCQ in quantitative conversion within 4 h), the question arose if DART–HRMS could also be used to reproducibly and precisely determine a different class of cycloadditions, for which we selected the interfacial inverse electron demand Diels–Alder (IEDDA) reaction as this reaction was reported to be really fast –at least for click reactions– in solution. This was studied in Chapter 4 extensively and we surpassed our previous kinetic record (SPOCQ) by obtaining a quantitative yield in a mere 15 min. The other interesting observation of this study was that reversing the reaction counterparts on the surface produced a discernible reaction rate difference. We found that one of the reactants when tethered in a particular stereochemistry (exo– form) gave the highest surface coverage (100%) within the shortest amount of time. This was also the first time that the effect of diastereomerism on interfacial reaction rates was studied.

In Chapter 5, covalent modification of native non–activated mica has been carried out utilizing catechol linkers. Previous studies for mica modification produced poorly defined polymeric structures on the surface or required extensive and tedious organic synthesis. We have addressed both these issues head–on in this thesis. Well–defined and characterized ultrathin layers were constructed on mica using a catechol–based molecule involving a two–step synthesis. Mica being atomically flat provides an ideal surface upon which to study various phenomena by AFM and other forms of microscopy. However, most research until now was restricted to simply drop–casting the pre–fabricated moieties followed by studying their final structures. Our method now allows for the step–wise formation and characterization of these very interesting structures. Along with it, we also performed several click attachment chemistries on these ultrathin layers which can be harnessed by surface chemists to put various functional and structurally complex moieties on the surface. This opens the pathway for the attachment of more complex architectures on the surface with higher functionality along with the ability to study their formation in a step–wise controlled fashion.

Overall, this thesis wishes to understand organic surface chemistry and several of its intricate mysteries. It clearly outlines several modification techniques and unravels interfacial kinetics of several interesting “metal–free click reactions”. It strives to rationalize the activation parameters in conjunction with classical organic chemistry and gives details on how surrounding “inert” alkyl chains can play a profound role in reaction rates. Lastly, we have striven to and achieved rapid and quantitative reactions on the surface by virtue of optimization of this microenvironment. Personally I believe, we have treaded on a road seldom traveled and unraveled a new understanding about molecular interactions on the ever–interesting and an infinitely–complex surface.

Methodological approaches for fractionation and speciation to estimate trace element bioavailability in engineered anaerobic digestion ecosystems : An overview
Hullebusch, Eric D. van; Guibaud, Gilles ; Simon, Stéphane ; Lenz, Markus ; Yekta, Sepehr Shakeri ; Fermoso, Fernando G. ; Jain, Rohan ; Duester, Lars ; Roussel, Jimmy ; Guillon, Emmanuel ; Skyllberg, Ulf ; Almeida, C.M.R. ; Pechaud, Yoan ; Garuti, Mirco ; Frunzo, Luigi ; Esposito, Giovanni ; Carliell-Marquet, Cynthia ; Ortner, Markus ; Collins, Gavin - \ 2016
Critical Reviews in Environmental Science and Technology 46 (2016)16. - ISSN 1064-3389 - p. 1324 - 1366.
Anaerobic digestion - analytical methods - bioavailability - fractionation - speciation - trace elements

Optimal supply of trace elements (TE) is a prerequisite for microbial growth and activity in anaerobic digestion (AD) bioprocesses. However, the required concentrations and ratios of essential TE for AD biotechnologies strongly depend on prevailing operating conditions as well as feedstock composition. Furthermore, TE in AD bioreactors undergo complex physicochemical reactions and may be present as free ions, complex bound or as precipitates depending on pH, or on the presence of sulfur compounds or organic macromolecules. To overcome TE deficiency, various commercial mineral products are typically applied to AD processes. The addition of heavy metals poses the risk of overdosing operating systems, which may be toxic to microbial consortia and ultimately the environment. Adequate supplementation, therefore, requires appropriate knowledge not only about the composition, but also on the speciation and bioavailability of TE. However, very little is yet fully understood on this specific issue. Evaluations of TE typically only include the measurement of total TE concentrations but do not consider the chemical forms in which TE exist. Thus detailed information on bioavailability and potential toxicity cannot be provided. This review provides an overview of the state of the art in approaches to determine bioavailable TE in anaerobic bioprocesses, including sequential fractionation and speciation techniques. Critical aspects and considerations, including with respect to sampling and analytical procedures, as well as mathematical modeling, are examined. The approaches discussed in this review are based on our experiences and on previously published studies in the context of the “COST Action 1302: European Network on Ecological Roles of Trace Metals in Anaerobic Biotechnologies.”

IAG ring test animal proteins 2016
Raamsdonk, L.W.D. van; Rhee, N.E. van de; Scholtens-Toma, I.M.J. ; Prins, T.W. ; Vliege, J.J.M. ; Pinckaers, V.G.Z. - \ 2016
Wageningen : RIKILT Wageningen UR (RIKILT report 2016.008) - 31 p.
ring test - animal proteins - analytical methods - microscopy - fish feeding - animal health - polymerase chain reaction - ringtest - dierlijke eiwitten - analytische methoden - microscopie - visvoeding - diergezondheid - polymerase-kettingreactie
The annual ring test for the detection of animal proteins in animal feed of the IAG - International Association for Feeding stuff Analysis, Section Feeding stuff Microscopy was organized by RIKILT - Wageningen UR, The Netherlands. The aim of the ring study was to provide the participants information on the performance of the local implementation of the detection method for their local quality systems. A further aim was to gather information about the application of the microscopic method. The current 2016 version of the IAG ring test for animal proteins facilitated the full scenario with the methods for microscopy and PCR as published in Regulation (EC) 51/2013 amending Annex VI of Regulation (EC) 152/2009 together with accompanying SOPs. All four samples were based on an artificial feed mimicking a formulation for ruminant feed. Two samples were labelled as fish feed (B and D), which was effectuated by adding 2% of a general fish meal. Adulteration was achieved by adding 0.1% pig MBM (B), 0.1% ruminant MBM (D) and a combination of 0.1% ruminant MBM and 0.1% fish meal (C). This combination of different spikes allowed the diverse application of the detection methods. Forty eight participants enrolled for the ring test, of which 45 submitted microscopic results. Of these, 20 participants applied the combination of microscopic and PCR analysis. Three participants submitted exclusively PCR results.
The neurotoxin BMAA in aquatic systems : analysis, occurrence and effects
Faassen, E.J. - \ 2016
Wageningen University. Promotor(en): Marten Scheffer, co-promotor(en): Miguel Lurling. - Wageningen : Wageningen University - ISBN 9789462577855 - 194 p.
cum laude - neurotoxins - aquatic environment - urban areas - effects - environmental impact - daphnia magna - elisa - water quality - analytical methods - aquatic ecology - neurotoxinen - aquatisch milieu - stedelijke gebieden - effecten - milieueffect - waterkwaliteit - analytische methoden - aquatische ecologie

Eutrophication is a major water quality issue and in many aquatic systems, it leads to the proliferation of toxic phytoplankton species. The neurotoxin β-N-methylamino-L-alanine (BMAA) is one of the compounds that can be present in phytoplankton. BMAA has been suggested to play a role in the neurodegenerative diseases Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis, although this hypothesis still needs to be confirmed. It is expected that the main human exposure pathways to BMAA are through direct contact with BMAA containing phytoplankton and through ingestion of BMAA contaminated food, such as fish and shellfish. However, reports on the occurrence of BMAA in aquatic systems have been conflicting and the cause of these reported differences was heavily debated. The use of different analytical methods seems to play a crucial role in the observed discrepancies, but initially, there was little consensus on which method produced most reliable results. The objectives of the work presented in this thesis therefore were to find out what has caused the differences in published results on BMAA concentrations, and to identify and produce reliable data on the presence of BMAA in aquatic systems. In addition, I aimed to determine the effect of BMAA exposure on a key species in many freshwater ecosystems, the grazer Daphnia magna.

The performances of different analytical techniques were compared, and LC-MS/MS analysis, either preceded by derivatisation or not, was found to produce most reliable results. LC-FLD and ELISA should not be used for BMAA analysis, as both methods risk misidentifying BMAA or overestimating its concentrations due to their low selectivity. When reviewing literature on the presence of BMAA in aquatic systems, it was found that the observed discrepancies in results could be explained by the use of unselective analytical methods in some studies, and by severe reporting deficiencies in others. When only studies that used appropriate analytical techniques and that correctly reported their work were taken into account, it was shown that BMAA could be present in phytoplankton and higher aquatic organisms, in concentrations of µg/g dry weight or lower. These results are in agreement with our findings of BMAA in cyanobacterial scums from Dutch urban waters. In a 2008 screening, BMAA was found to be present in 9 out of 21 analysed cyanobacterial scums, at concentrations ranging from 4 to 42 µg/g dry weight. When this screening was repeated 8 years later with 52 similar samples, BMAA was detected below the quantification limit in one sample and quantified in another sample at 0.6 µg/g dry weight.

In order to perform the work presented in this thesis, sensitive and selective analytical methods, mostly based on LC-MS/MS analysis without derivatisation, were developed. This resulted in a standard operating procedure for the underivatised LC-MS/MS analysis of BMAA in cyanobacteria. Also, a CYANOCOST initiated workshop was given, in which a group of scientists from 17 independent laboratories evaluated LC-MS/MS based methods in different matrices. A bound BMAA from found in the supernatant was the most abundant fraction in the positive samples that were tested: cycad seed, seafood and exposed D. magna. In addition, it was found that the deuterated internal standard used for quantification was not a good indicator for the release of BMAA from bound forms, resulting in unprecise quantification of total BMAA.

BMAA was found to reduce survival, somatic growth, reproduction and population growth in D. magna. Animals did not adapt to BMAA exposure: exposed animals born from exposed mothers had a lower brood viability and neonate weight than animals exposed to BMAA, but born from unexposed mothers. In addition, D. magna was shown to take up BMAA from the growth medium and to transfer it to its offspring. D. magna therefore might be an important vector for BMAA transfer along the pelagic food chain, but whether BMAA plays a role in preventing zooplankton from controlling cyanobacterial blooms needs further investigation.

Although BMAA research has much progressed between the start of this thesis’ work and its completion, some important questions still require an answer. Most urgently, it should be determined whether BMAA is indeed involved in the neurological diseases mentioned above, and if so, which doses trigger the onset of these diseases. Human exposure pathways should then be more systematically quantified, and it might be prudent to investigate if the occurrence of BMAA is restricted to aquatic systems, or whether sources from terrestrial systems contribute to BMAA exposure as well.

Improved forensic hair evidence for drugs of abuse by mass spectrometry
Duvivier, W.F. - \ 2016
Wageningen University. Promotor(en): Michel Nielen, co-promotor(en): Teris van Beek. - Wageningen : Wageningen University - ISBN 9789462578159 - 194 p.
forensic science - hair - analytical methods - spectrometry - forensische wetenschap - haar - analytische methoden - spectrometrie

Forensic hair analysis can be used as alternative evidence next to body fluids, and to obtain retrospective timeline information of an individual’s drug exposure. Chapter 1 describes the general concepts of drug incorporation into hair, external contamination, and the current status and limitations of hair analysis methods are introduced. Furthermore, an overview of ambient ionization techniques is given, with emphasis on direct analysis in real time (DART).
The instrumentation, ionization mechanisms, and application range of DART are presented. Scientific challenges and objectives to improve forensic hair evidence are formulated, which formed the basis of the research presented in this thesis.

A major issue in forensic hair analysis is the possibility of false-positive results due to external contamination. In Chapter 2, an evidence-based evaluation of decontamination protocols for the removal of cannabinoid contamination is presented, mainly focused on
Δ9-tetrahydrocannabinol (THC). Different solvents were extensively tested for their ability to remove cannabinoid contamination originating from cannabis smoke or indirect contact with cannabis plant material. After selection of the most efficient solvents, different sequential wash steps were tested on externally contaminated blank hair samples. Finally, application of the three best performing protocols on cannabis users’ hair, both as such and after deliberate contamination, resulted in removal of all contamination without removing incorporated THC. From the detailed scientific evidence reported in this chapter, a protocol using a single methanol wash followed by a single aqueous SDS solution is recommended to remove external cannabis contamination.

A novel approach for the analysis of intact locks of hair consisting of DART combined with high resolution mass spectrometry (HRMS) is developed in Chapter 3. DART–HRMS settings were optimized for the analysis of THC and the accuracy of the probed hair zone was investigated using spiked blank hair samples. Intact locks of hair could be longitudinally scanned without the need of extensive sample preparation, resulting in analysis times of only minutes. Detection of THC was achieved in several hair samples from cannabis users. A quantitative liquid chromatography (LC)–MS/MS method was developed, in-house validated, and used to confirm the presence of THC in drug user hair samples. With a retrospective timeline accuracy of ±2 weeks, a significant improvement over conventional segmented hair analysis was achieved. Moreover, differentiation between zones of different THC content within a DART hair scan could be made, indicating possibilities for retrospective assessment of time of drug use.

The DART hair scan method has been improved and expanded in Chapter 4. Targeted detection of four commonly used drugs of abuse (amphetamine, cocaine, MDMA and THC) with structural confirmation was achieved by data-dependent product ion scans. Simultaneously,
full-scan high-resolution data was obtained and retrospectively interrogated versus a list of more than a hundred, less common, drugs of abuse and occasionally abused pharmaceutical drugs. The hair scan method was validated for the analysis of cocaine against an accredited LC–MS/MS method and the detection limit for cocaine was found to comply with the cut-off value of 0.5 ng/mg. Hair samples of 10 different drug users were analyzed. Next to detection of the four targeted drugs of abuse, retrospective data interrogation revealed several additional hits. The detected substances correlated well with reported drug use and by the detection of several metabolites, drug use could be unambiguously proven. The retrospective timeline accuracy was further improved by use of a high spatial resolution DART exit cone, which yielded a DART spot size corresponding to approximately 10 days of hair growth.

When direct and/or ambient ionization techniques are used to analyze intact hair samples, endogenous isobaric ions can overlap with compounds of interest and yield
false-positive results. The selectivity of four MS instruments with different mass analyzers (orbitrap, quadrupole orbitrap, triple quadrupole, time-of-flight) was evaluated in Chapter 5 by DART analysis of THC from hair samples. To avoid overlap of THC with isobaric ions originating from the hair matrix, a mass resolution of at least 30,000 FWHM was necessary. The use of travelling wave ion mobility spectrometry (TWIMS) resulted in increased selectivity by separation of isobaric ions based on their drift times. A triple quadrupole instrument in multiple reaction monitoring (MRM) mode was found to have the best sensitivity, however, the used transitions were not specific enough for use on drug user hair samples. Thus the selectivity needed to indisputably differentiate THC from endogenous isobaric ions in drug user hair samples could only be achieved by the high resolution of the tested orbitrap MS instruments.

Chapter 6 demonstrates the application of forensic hair analysis techniques to veterinary control. Timeline information could be obtained from veterinary hair samples. For this purpose, a UPLC–MS/MS hair analysis method was adapted and optimized for smaller sample sizes.
After validation of the method, segmented hair samples obtained from clenbuterol-treated calves using the forensic hair sampling protocol were analyzed and clenbuterol concentration profiles along the hair samples could be obtained. Assessment of the average growth rate of calf tail hair enabled retrospective determination of time of clenbuterol administration.
The estimated time of administration was reproducible when analyzing sub-samples taken from the same lock of hair and duplicate locks of hair, and in good correlation with the actual treatment.

Through the research presented in this thesis, novel approaches in hair analysis have been developed and the value of forensic hair evidence improved considerably. In Chapter 7, the main achievements of this thesis are discussed in detail and an insight in the future perspectives of hair analysis and ambient ionization is given. Potential further applications of the DART hair scan method, and ambient ionization in general, are presented, including some preliminary results of new decontamination strategies, hair analysis possibilities, and other forensic uses of DART ionization.

Beehold : the colony of the honeybee (Apis mellifera L) as a bio-sampler for pollutants and plant pathogens
Steen, J.J.M. van der - \ 2016
Wageningen University. Promotor(en): Huub Rijnaarts, co-promotor(en): Tim Grotenhuis; Willem Jan de Kogel. - Wageningen : Wageningen University - ISBN 9789462577510 - 206 p.
apis mellifera - honey bees - honey bee colonies - biological indicators - sampling - instruments - pollution - pollutants - heavy metals - plant pathogenic bacteria - erwinia amylovora - erwinia pyrifoliae - analytical methods - honingbijen - honingbijkolonies - biologische indicatoren - bemonsteren - instrumenten (meters) - verontreiniging - verontreinigende stoffen - zware metalen - plantenziekteverwekkende bacteriën - analytische methoden

Bio-sampling is a function of bio-indication. Bio-indication with honeybee colonies (Apis mellifera L) is where the research fields of environmental technology and apiculture overlap. The honeybees are samplers of the environment by collecting unintentionally and simultaneously, along with nectar, pollen, water and honeydew from the flowers or on the leaves, other matter (in bio-indication terms: target matter) and accumulating this in the colony. Collected target matter, in this thesis heavy metals, the plant pathogens Erwinia pyrifoliae and Erwinia amylovora and the soil pollutant γ-HCH, is collected from the colony by subsampling. Subsampling the honeybee colony is done by taking and killing bees from the hive (sacrificial) or by collecting target matter from the bee’s exterior without killing the bee (non-sacrificial). In environmental technology terms the application of the honeybee colony is a Passive Sampling Method (PSM). In this thesis the possibilities and restrictions of the PSM honeybee colony are explored.

Bio-indication is a broad research field with one common factor: a living organism (bio) is applied to record an alteration of the environment (indication). The environment may be small such as a laboratory or big such as an ecosystem. Alterations in the organism may vary from detecting substances foreign to the body to mortality of the organism. In environmental technology the concept Source-Path-Receptor (SPR) is applied to map the route of a pollutant. It describes where in the environment the pollution is, how it moves through the environment and where it ends. This environment is the same environment of all living organisms, ergo also honeybees. Honeybees depend on flowers for their food. In the SPR concept, a flower can be a source, path or receptor. Along with collecting pollen, nectar, water and honeydew, target matter is collected by honeybees. Each honeybee functions as a micro-sampler of target matter in the environment, in this case the flower. Each honeybee is part of a honeybee colony and in fact the honeybee colony is the bio-sampler. The honeybee colony is a superorganism. The well-being of the colony prevails over the individual honeybee. Food collection is directed by the colony’s need. Foragers are directed to the most profitable food sources by the bee dance and food exchange (trophallaxis). The result of this feature is that mainly profitable sources are exploited and poor food sources less or not at all. During the active foraging period hundreds to thousands of flowers are visited daily. The nectar, pollen, water and honeydew plus the unintentionally collected target matter is accumulated in the honeybee colony. In order to obtain target matter the colony must be subsampled. This is done by picking bees from the hive-entrance (hive-entering bees) or inside the hive (in-hive bees) and processing them for analysis (sacrificial). This is the most commonly applied method. However, it is possible to subsample the colony without picking and processing the bees by collecting target matter from the hive-entering bee’s exterior (non-sacrificial). For non-sacrificial subsampling of the honeybee colony the Beehold device with the sampling part Beehold tube has been developed. The results of bio-indication with honeybee colonies are qualitative and indicative for follow up study (Chapter 1).

Six bio-indication studies with honeybee colonies for bio-indication of heavy metals, the plant pathogens Erwinia pyrifoliae and Erwinia amylovora and the soil pollutant γ-HCH are presented. Chapter 2 describes how the concentration of eighteen heavy metals in honeybees fluctuate throughout the period of July, August and September (temporal) at the study sites: the city of Maastricht, the urban location with an electricity power plant in Buggenum and along the Nieuwe Waterweg at Hoek van Holland (spatial). A number of the metals have not been previously analysed in honeybees. To study whether honeybees can be used for bio-indication of air pollution, the concentrations of cadmium, vanadium and lead were compared to concentrations found in honeybees. The honeybee colonies were placed next to the air samplers. Only significant differences of metal concentrations in the ambient air also show in honeybees. This was the case with vanadium in ambient air and honeybees. The spatial and temporal differences of cadmium and lead were too futile to demonstrate a correspondence (Chapter 3). In a national surveillance study in 2008 the concentration of eighteen metals in honeybees has been analysed. The results showed a distinct regional pattern. Honeybees in the East of the Netherlands have higher concentrations of heavy metals compared to the bees in the West. Besides regional differences local differences were also recorded. An approximate description of the land use around 148 apiaries (> 50% agriculture, > 50% wooded area, > 50% urban area and mixed use) indicated the impact of land use on metal concentrations in honeybees. In areas with > 50% wood significantly higher concentrations of heavy metals were detected (Chapter 4). Subsampling of the honeybee colonies in Chapter 2, 3 and 4 was done sacrificially. In the studies presented in Chapter 5, 6, and 7 the honeybee colonies were subsampled non-sacrificially or simultaneously non-sacrificially and sacrificially. The plant pathogen E. pyrifoliae causes a flower infection in the strawberry cultivation in greenhouses. In greenhouse strawberry cultivation honeybees are applied for pollination. In Chapter 5 the combination pollination / bio-indication by honeybee colonies is studied. This proved to be a match. E. pyrifoliae could be detected on in-hive bees prior to any symptom of the infection in the flowers. In the Beehold tube, the bacterium was detected at the same time as the first tiny symptoms of the infection. In Chapter 5 the principles on which the Beehold tube is based are presented and discussed. The plant pathogen E. amylovora causes fireblight in orchards. The combination pollination / bio-indication has also been applied in this study performed in Austria in 2013. It is known that E. amylovora can be detected on honeybees prior to any symptom in the flower or on the fruit tree. A fireblight outbreak depends on flowering period, humidity and temperature. In 2013 no fireblight infection emerged in the orchards where the study was performed. Therefore, the bacterium could not be detected on the honeybees. γ-HCH (Lindane) is one of the soil pollutants in the Bitterfeld region in Saxony-Anhalt in Germany. It is the result of dumping industrial waste around the production locations. Although γ-HCH is bound to soil particles there is a flux to groundwater and surface water. Consequently, the pollution may end up in the sediments of the streambed and flood plains. The study objective was to investigate the hypothetic route of γ-HCH from polluted soil (source), via soil erosion and atmospheric deposition (route) to the receptor (flowering flowers) by detecting γ-HCH in the Beehold tube. Although on average over 17000 honeybees passed through the Beehold tube daily for a maximal period of 28 days, no γ-HCH has been detected. The pollen pattern in the Beehold tube revealed where the bees collected the food (Chapter 7).

The application of the honeybee colony has pros and cons. Distinctive pros are many micro samplers, the extensive collection of matter (both food and target matter) and the accumulation in the colony. For successful bio-indication with honeybee colonies, determining factors are: the target matter, location of the target matter, distance between target matter and the honeybee colony, individual or pooled subsampling, the minimal sampling frequency and sample size, and sacrificial or non-sacrificial subsampling applied solely or in combination. Taking bees from a colony impacts upon the colony’s performance and consequently the passive sampling method. Based on a long-years’ experience and inter-collegial discussion it is stated that 3% of the forager bees (hive-entering) and 1.5% of the in-hive bees can be sampled safely without impacting upon the colony. This restriction does not apply when carrying out non-sacrificial subsampling of the honeybee colony (Chapter 8).

Performing bio-indication with honeybee colonies has more applications than have been exploited so far. Further research can make a change. In particular I mention here the combination of pollination and bio-indication and the application of non-sacrificial subsampling solely or in combination with sacrificial subsampling.

Everywhere Apiculture is practiced (all over the world except the polar areas) bio-indication with honeybee colonies can be applied in a simple, practical and low cost way.

Heldere herleidbaarheid in de visketen
Asselt, E.D. van; Roest, J.G. van der; Staats, M. ; Kok, E.J. ; Cuijpers, H.J.J. ; Ruth, S.M. van - \ 2015
RIKILT Wageningen UR (RIKILT-rapport 2015.013) - 39 p.
technologie - visproducten - analytische methoden - naspeurbaarheid - vis - visverwerking - diepvriesvis - schaaldieren - garnalen - kabeljauw - verse producten - technology - fish products - analytical methods - traceability - fish - fish processing - frozen fish - shellfish - shrimps - cod - fresh products
Heldere herleidbaarheid betekent dat kenmerken die bij verkoop worden toegekend aan visproducten terug te herleiden zijn in de keten. Het gaat daarbij om aspecten als de vissoort, maar ook de geografische oorsprong en de processing van de vis. Om de consument volledig inzicht te bieden in productinformatie is de etiketteringswetgeving ((EU) 1169/2011) recent aangescherpt en dienen dergelijke aspecten op het etiket vermeld te worden. In dit project is onderzocht welke administratieve en analytische methoden gebruikt kunnen worden om de voorgeschiedenis van visproducten aan te tonen. Er is gewerkt aan vier deelprojecten die door de projectpartners als prioriteit werden aangemerkt: administratieve traceerbaarheid in de kabeljauwketen, aantonen van watergehaltes in garnalen, vaststellen van geografische oorsprong van witpootgarnalen en onderscheid tussen verse en ontdooide vis. De resultaten van deze vier onderzoeken zijn in dit rapport beschreven.
Analysemethoden voor de bepaling van authenticiteit in visketens
Staats, M. ; Roest, J.G. van der; Pustjens, A.M. ; Voorthuijzen, M.M. ; Dijk, J.P. van; Prins, T.W. ; Boerrigter-Eenling, G.R. ; Koot, A.H. ; Pelt-Heerschap, H.M.L. van; Spiegel, M. van der; Ruth, S.M. van; Kok, E.J. - \ 2015
RIKILT (Rikilt-rapport 015) - 67 p.
noordzee - vis - vissen - analytische methoden - schol - north sea - fish - fishes - analytical methods - plaice
Dit rapport beschrijft de resultaten van onderzoek dat is uitgevoerd binnen het project "Analysemethoden voor de bepaling van authenticiteit in visketens". Het project heeft als doel om methoden te ontwikkelen waarmee de authenticiteit (soort, geografische herkomst en productiewijze) van Noordzeevissen kan worden vastgesteld. In dit project is gewerkt aan vier deelprojecten: Ketenanalyse naar vermenging van schol (Pleuronectes platessa) uit de Noordzee met andere vissoorten, ontwikkeling en initiële validatie van een moleculaire barcoding methode om Noordzeevissoorten in gemengde monsters te identificeren, bepaling van de geografische herkomst van schol en productiemethode van tarbot met behulp van isotoopratio's en chemische fingerprint en toepassing van de ontwikkelde analytische methoden in Noordzeevisketens. De resultaten van deze onderzoeken zijn in dit rapport weergegeven.
How much bio is in there? Can stable isotopes be used to determine the bio-based content of products?
Broek, L.A.M. van den; Veer, G. van der; Zee, M. van der - \ 2015
Bioplastics Magazine 10 (2015)5. - ISSN 1862-5258 - p. 18 - 22.
isotopen - stabiele isotopen - biobased economy - materialen uit biologische grondstoffen - samenstelling - analytische methoden - isotopes - stable isotopes - biobased materials - composition - analytical methods
Can stable isotopes be used to determine the bio-based content of products?
Ordering properties of oligomeric columnar discotic liquid crystals
Umesh, C.P. - \ 2015
Wageningen University. Promotor(en): Han Zuilhof, co-promotor(en): Ton Marcelis. - Wageningen : Wageningen University - ISBN 9789462575066 - 152
liquid crystals - optical properties - synthesis - analytical methods - vloeibare kristallen - optische eigenschappen - synthese - analytische methoden

The synthesis and liquid crystalline ordering properties of oligomeric discotic liquid crystals were investigated. The phase behaviour and surface ordering properties are dependent on among others core type, spacer length and fluorination.

Lipid bilayer stability in relation to oxide nanoparticles
Pera, H. - \ 2015
Wageningen University. Promotor(en): Frans Leermakers, co-promotor(en): Mieke Kleijn. - Wageningen : Wageningen University - ISBN 9789462574670 - 144
lipids - membranes - stability - nanotechnology - particles - analytical methods - models - modeling - lipiden - membranen - stabiliteit - nanotechnologie - deeltjes - analytische methoden - modellen - modelleren
Lipid bilayer stability in relation to oxide nanoparticles

All living organisms are composed of cells that are filled with a thick molecular soup. These molecules constitute a complex machinery that brings these cells to life. To contain these molecules, and to protect them from the hostile outer environment, a phospholipid bilayer envelopes the cell. It is essential that this lipid bilayer, also known as the cell membrane, should remain intact and form a perfect barrier at all times. Industrially manufactured nanoparticles are suspect to be able to penetrate this barrier, and thus endanger living organisms in the environment. This thesis deals with some aspects of the structural integrity of lipid bilayers, and especially how this integrity is affected by the interaction with nanoparticles.

Experiments were performed with silica and titanium dioxide nanoparticles, interacting with lipid bilayers, using a variety of experimental techniques. In addition, a theoretical model was applied that is based on the Scheutjens-Fleer Self Consistent Field (SCF) theory. This model delivered detailed structural and thermodynamic information about the lipid bilayer. The modelling work helped us to improve our understanding of lipid bilayer stability, and showed the effect of the interaction with the nanoparticles on the phospholipid bilayer. These latter results could be related directly to our experiments.

Let us first experimentally regard the interaction of lipid bilayers with synthetic oxide nanoparticles. We developed a protocol for high-throughput screening of the nanoparticle-bilayer interaction using a fluorescence technique. Results from this method were combined with reflectometry measurements and atomic force microscopy (AFM). The combination of these methods allowed us to relate lipid bilayer integrity to its interaction with nanoparticles and their adsorption onto the bilayer. In addition, the AFM results yielded detailed structural information at the nano-scale. We found that the interaction strongly depends on both lipid bilayer and nanoparticle charge. However, the specific interaction that depends on the nanoparticle type, starts to play a role when the charges are low. When the total interaction strength is regarded, a regime was found at which interaction is strong enough for the nanoparticles to adsorb onto the bilayer, but too weak to disrupt the bilayer. If, however, the bilayer is disrupted by the nanoparticles, the particle may steal away some lipid molecules from the bilayer, and leave again to disrupt the bilayer elsewhere.

Let us now go into more detail on the SCF modelling. Bilayers are composed of phospholipids, which consist of a hydrophilic head group, and a hydrophobic tail. These bilayers were modelled using a single lipid molecule type, of which the head group structure and lipid tail length could be varied. We thus obtained bilayers that varied in their thickness, and the space that a single lipid takes within the bilayer. Changes in bilayer composition affect the bilayer mechanical properties, such as those constants that describe bilayer stretching or bending. This thesis shows how vesicles, which are bilayers in a globular shape, may become unstable if the bilayer lipid composition is changed. Under certain conditions, a vesicle would prefer to fall apart into many smaller vesicles, which is when highly charged head groups start to repel each other. Or the bilayer may form continuous cubic phases, which might occur if lipids with uncharged head groups but with very long tails are used to form the bilayer. Under very specific and finely tuned conditions, a lipid bilayer may become unstable to form stable pores in the membrane, or to fall apart into tiny lipid discs.

DNA-diagnostiek maakt fytosanitaire controles beter en sneller : hightech gereedschap voor inspectie- en keuringsdiensten
Staalduinen, J. van; Bonants, P.J.M. - \ 2015
Onder Glas 12 (2015)6/7. - p. 48 - 49.
glastuinbouw - quarantaine organismen - detectie - technieken - innovaties - analytische methoden - fytosanitaire maatregelen - plantenplagen - polymerase-kettingreactie - landbouwkundig onderzoek - greenhouse horticulture - quarantine organisms - detection - techniques - innovations - analytical methods - phytosanitary measures - plant pests - polymerase chain reaction - agricultural research
Als vooraanstaand in- en exporteur van plantaardig uitgangsmateriaal en eindproducten heeft Nederland ook de taak om ongewenste organismen die met de handelswaar kunnen meereizen buiten of juist binnen de deur te houden. Wageningen UR ontwikkelt samen met partners in binnen- en buitenland nieuwe diagnose- en screeningsmethoden waarmee inspectie- en keuringsdiensten hun taken beter en efficiënter kunnen vervullen. DNA-analyse op de plaats van inspectie speelt daarin een belangrijke rol.
Healthy aging through a healthy diet : never too old to eat healthy?!
Jankovic, N. - \ 2015
Wageningen University. Promotor(en): Ellen Kampman; Edith Feskens; Lisette de Groot, co-promotor(en): Anouk Geelen. - Wageningen : Wageningen University - ISBN 9789462572508 - 159
voeding en gezondheid - gezondheidsvoedsel - ouderen - dieetrichtlijnen - eetpatronen - analytische methoden - ziektepreventie - ouderenvoeding - nutrition and health - health foods - elderly - dietary guidelines - eating patterns - analytical methods - disease prevention - elderly nutrition

Abstract

Background: The world’s population is aging and with it the prevalence of chronic diseases, especially cardiovascular diseases and cancer, increases. A long lasting life is envisaged without the burden of disease. Therefore, current research focuses on risk factors, such as a healthy diet, which may decrease the occurrence of chronic diseases even at advanced age. Earlier studies, examining the role of a healthy diet in the elderly, applied different analysis strategies. In consequence, comparability across studies is limited and prevent an overall conclusion on the role of a healthy diet in elderly.

Methods and subjects: Eleven prospective cohort studies among elderly people (N=396,391) from Europe and the United States, collaborating in the CHANCES consortium, were analysed. Most cohorts eligible for our analysis, assessed diet once at baseline. Therefore, we first assessed the stability of dietary patterns, derived with reduced rank regression (RRR), in the Zutphen Elderly Study. In the remainder of this thesis, healthy diets were defined based on the 2003 World Health Organization (WHO) “nutrient intake goals” and the 2007 World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) food group recommendations. The recommendations were operationalized, using the Healthy Diet Indicator (HDI) and the WCRF/AICR diet score. The association between a healthy diet and risk of all-cause mortality and CVD mortality, was studied using the WHO recommendations, which aim at the prevention of chronic diseases in general. The cancer specific WCRF/AICR recommendations were applied to study the association between a healthy diet and cancer risk. Diet disease associations were assessed in each cohort separately, using Cox-proportional hazards regression. Cohort specific hazard ratios (HR) were pooled by random effects meta-analysis.

Results: The results of the Zutphen Elderly Study showed that dietary patterns, derived by RRR, remained stable over a period of five years. In the CHANCES project a total of 84,978 person years were accumulated, during a median follow-up time ranging between 7 and 15 years across cohorts. An increase of 10 HDI points (range total score 0 to 70 points) was significantly associated with a decreased risk of all-cause mortality (HR: 0.90 and 95% confidence interval (CI): 0.87-0.93). The HR estimate was equivalent to a two year increase in life expectancy. We found a significant inverse association between an increase of 10 HDI points and CVD mortality for Southern European countries and the US (HR: 0.85, 95 % CI: 0.83-0.87), whereas no significant association was found for Northern and Central and Eastern Europe. An increase of 1 point for the WCRF/AICR diet score (range 0-4) was associated with a significantly 6% decreased risk in developing any type of cancer. Greatest risk reduction was found between a 1 point increase in WCRF/AICR diet score and colorectal cancer (HR: 0.84, 95% CI:0.80-0.89).

Conclusion: Dietary indices based on globally defined dietary recommendations by WHO and WCRF/AICR were found to be associated with all-cause and CVD mortality and cancer risk in old age. Public health interventions targeted on the elderly should not focus on one definition of a “healthy diet” but rather a smart combination of available evidence, to optimally account for CVD as well as cancer specific outcomes.

Glutenvrij ? Pils onde de loep
Sleutels, I. ; Meer, I.M. van der; Broeck, H.C. van den - \ 2014
Voedingsmiddelentechnologie 7 (2014). - ISSN 0042-7934 - p. 10 - 11.
gluten - coeliakie - glutenvrije diëten - bieren - alcoholische dranken - gerst - lc-ms - analytische methoden - coeliac syndrome - gluten free diets - beers - alcoholic beverages - barley - liquid chromatography-mass spectrometry - analytical methods
Gluten meten in gehydrolyseerde en gefermenteerde voedingsmiddelen – zoals pils – is lastig. De door de Codex Alimentarius gevalideerde test onderschat het gehalte gluten in deze producten. Een uitgebreide LC-MS/MS-analyse geeft gedetailleerde informatie over de aanwezige coeliakie-stimulerende gluten in pils. Met deze gegevens is een geschikte test te ontwikkelen.
Surface functionalization and analysis thereof by ambient mass spectrometry
Manova, R.K. - \ 2014
Wageningen University. Promotor(en): Han Zuilhof, co-promotor(en): Teris van Beek. - Wageningen : Wageningen University - ISBN 9789462571570 - 214
biosensoren - detectie - biomarkers - allergenen - oppervlaktechemie - analytische methoden - synthese - unimoleculaire films - biosensors - detection - allergens - surface chemistry - analytical methods - synthesis - unimolecular films

A challenge in the global healthcare is the lack of suitable diagnostic tools for early disease detection. One possible solution is the use of biosensors in diagnostic tests. By definition, a biosensor is a bioanalytical device that detects the presence of a compound (analyte) in the sample. The detection relies on the specific interactions between the ligands that are attached onto the biosensor surface and the analytes in the sample.

This PhD dissertation is focused on developing an optimal protocol for attachment of ligands onto the biosensing surface. A step-wise approach was established for the versatile and reproducible modification and functionalization of a silicon nitride-based biosensor. This approach included the application of bioorthogonal copper-free reactions as a useful tool for oriented attachment of biomolecules. Additionally, a novel surface sensitive analytical method was developed for the identification of covalently bound molecules in monolayers. The method, which is fast and easy to apply, uses DART ionization coupled to a high-resolution mass spectrometer. The nm-thin layers were analysed, and interpretation rules for the obtained mass spectra were formulated. The method was applied in the identification of commercially available nm-thin coatings and biochips.

Koolhydraten bieden scala aan mogelijkheden voor gezonde levensmiddelen
Schols, H.A. - \ 2014
Wageningen : Wageningen UR
voedingsvezels - koolhydraten - voeding en gezondheid - voedingsstoffen - analytische methoden - voedselonderzoek - dietary fibres - carbohydrates - nutrition and health - nutrients - analytical methods - food research
Koolhydraten in onze voeding leveren energie en zorgen voor een gemakkelijke stoelgang. Van de vele verschillende koolhydraatmoleculen, waaronder tal van soorten kleine suikers, zetmeel en voedingsvezels, weten we echter betrekkelijk weinig. Dat geldt ook voor hun rol tijdens het bewaren en verwerken van levensmiddelen of voor de invloed van koolhydraten op de gezondheid.
Trendanalyse van contaminanten in diervoeders : mogelijkheden en problemen bij het gebruik van historische monitoringsgegens
Adamse, P. ; Boer, W.J. de; Nijs, W.C.M. de - \ 2014
Wageningen : RIKILT Wageningen UR (RIKILT report 2014.007) - 53
besmetters - diervoeding - historische verslagen - tendensen - statistische analyse - gevalsanalyse - voedselveiligheid - voedingsnormen - gegevensverwerking - analytische methoden - contaminants - animal nutrition - historical records - trends - statistical analysis - case studies - food safety - feeding standards - data processing - analytical methods
Voor het verkrijgen van inzicht in het basisniveau van een contaminant in een diervoeder kan gebruik worden gemaakt van monitoringsgegevens. Zowel de gegevens als de te gebruiken technieken moeten wel aan bepaalde voorwaarden voldoen. In een vorig rapport (Adamse, 2014) staat beschreven hoe met redelijk eenvoudige statistische basistools analyses kunnen worden uitgevoerd. In het huidige rapport staan meer complexe statistische analyses beschreven met daarbij de mogelijkheden en potentiele problemen.
Trendanalyse van historische gegevens : handleiding voor het gebruik van monitoringsgegevens
Adamse, P. - \ 2014
Wageningen : RIKILT Wageningen UR (RIKILT report 2014.001) - 22
tendensen - historische verslagen - monitoring - analytische methoden - statistische analyse - diervoeding - besmetters - voedselveiligheid - voedingsnormen - gegevensverwerking - voederveiligheid - trends - historical records - analytical methods - statistical analysis - animal nutrition - contaminants - food safety - feeding standards - data processing - feed safety
Het doel van dit rapport is om aan te geven welke technieken gebruikt kunnen worden om inzicht te krijgen in het achtergrondniveau van contaminanten in diervoeders en diervoederproducten. Beschreven is tevens met welke factoren rekening gehouden moet worden bij het gebruik van historische monitoringsgegevens. Deze gegevens zijn verzameld in het kader van monitoringsprogramma’s.
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