Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 20 / 41

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    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
    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.

    Proximal Gamma-Ray Spectroscopy to Predict Soil Properties Using Windows and Full-Spectrum Analysis Methods
    Mahmood, H.S. ; Hoogmoed, W.B. ; Henten, E.J. van - \ 2013
    Sensors 13 (2013)12. - ISSN 1424-8220 - p. 16263 - 16280.
    plant-available potassium - spectrometry - sensor - models - clay
    Fine-scale spatial information on soil properties is needed to successfully implement precision agriculture. Proximal gamma-ray spectroscopy has recently emerged as a promising tool to collect fine-scale soil information. The objective of this study was to evaluate a proximal gamma-ray spectrometer to predict several soil properties using energy-windows and full-spectrum analysis methods in two differently managed sandy loam fields: conventional and organic. In the conventional field, both methods predicted clay, pH and total nitrogen with a good accuracy (R2 = 0.56) in the top 0–15 cm soil depth, whereas in the organic field, only clay content was predicted with such accuracy. The highest prediction accuracy was found for total nitrogen (R2 = 0.75) in the conventional field in the energy-windows method. Predictions were better in the top 0–15 cm soil depths than in the 15–30 cm soil depths for individual and combined fields. This implies that gamma-ray spectroscopy can generally benefit soil characterisation for annual crops where the condition of the seedbed is important. Small differences in soil structure (conventional vs. organic) cannot be determined. As for the methodology, we conclude that the energy-windows method can establish relations between radionuclide data and soil properties as accurate as the full-spectrum analysis method.
    Development and validation of an LC-MS/MS method for the detection of phomopsin A in lupin and lupin-containing retail food samples from the Netherlands
    Nijs, W.C.M. de; Pereboom-de Fauw, D.P.K.H. ; Dam, R.C.J. van; Rijk, T.C. de; Egmond, H.P. van; Mol, J.G.J. - \ 2013
    Food Additives & Contaminants. Pt. A, Chemistry, Analysis, Control, Exposure & Risk Assessment 30 (2013)10. - ISSN 1944-0049 - p. 1819 - 1826.
    mycotoxin analysis - leptostromiformis - extraction - maize - wheat - spectrometry - pesticides - matrices - fruits - seeds
    Phomopsins (PHO) are mycotoxins produced by the fungus Diaporthe toxica (also referred to as Phomopsis leptostromiformis). Lupin is the most important host crop for this fungus and PHO are suspected as cause of lupinosis, a deadly liver disease, in sheep. Lupin is currently in use to replace genetically modified soy in many food products available on the European market. However, a validated method for analysis of PHO is not available until now. In this work, a dilute-and-shoot LC-MS/MS-based method was developed for the quantitative determination and identification of phomopsin A (PHO-A) in lupin and lupin-containing food. The method involved extraction by a mixture of acetonitrile/water/acetic acid (80/20/1 v/v), dilution of the sample in water, and direct injection of the crude extract after centrifugation. The method was validated at 5 and 25 µg PHO-A kg(-1) product. The average recovery and RSD obtained were 79% and 9%, respectively. The LOQ (the lowest level for which adequate recovery and RSD were demonstrated) was 5 µg PHO-A kg(-1). Identification of PHO-A was based on retention time and two transitions (789 > 226 and 789 > 323). Using the average of solvent standards from the sequence as a reference, retention times were all within ± 0.03 min and ion ratios were within ± 12%, which is compliant with European Union requirements. The LOD (S/N = 3 for the least sensitive transition) was 1 µg PHO-A kg(-1) product. Forty-two samples of lupin and lupin-containing food products were collected in 2011-2012 from grocery stores and internet shops in the Netherlands and analysed. In none of the samples was PHO-A detected
    Accurate mass screening of pharmaceuticals and fungicides in water by U-HPLC-Exactive Orbitrap MS
    Chitescu, C.L. ; Oosterink, E. ; Jong, J. de; Stolker, A.A.M. - \ 2012
    Analytical and Bioanalytical Chemistry 403 (2012)10. - ISSN 1618-2642 - p. 2997 - 3011.
    liquid-chromatography - antifungal agents - surface-water - spectrometry - antibiotics - groundwater - suppression - resistance - residues - time
    The use of pharmaceuticals in livestock production is a potential source of surface water, groundwater and soil contamination. Possible impacts of antibiotics on the environment include toxicity and the emergence of antibiotic resistance. Monitoring programs are required to record the presence of these substances in the environment. A rapid, versatile and selective multi-method was developed and validated for screening 43 pharmaceutical and fungicides compounds, in surface and groundwater, in one single full-scan MS method, using benchtop U-HPLC-Exactive Orbitrap MS at 50,000 (FWHM) resolution. Detection was based on calculated exact masses and on retention time. Sample volume, pH conditions and solid-phase extraction (SPE) sample clean-up conditions were optimized. In the final method, 74 % of the compounds had recoveries higher than 80 %, 15 % of the compounds had recoveries between 60 % and 80 %, and 7 % of the compounds had recoveries between 40 % and 50 %. One of the compounds (itraconazole) had a recovery lower than 10 % and nystatin was not detected. The level of detection was 10 ng L-1 for 61 % of the compounds, 50 ng L-1 for 32 % and 100 ng L-1 for 5%. In-house validation, based on EU guidelines, proves that the detection capability CC beta is lower than 10 ng L-1 (for beta error 5 %) for 37 % of the compounds, lower than 50 ng L-1 for 35 % of the compounds and lower than 100 ng L-1 for 14 % of compounds. This study demonstrates that the ultra-high resolution and reliable mass accuracy of Exactive Orbitrap MS permits the detection of pharmaceutical residues in a concentration range of 10-100 ng L-1, applying a post target screening approach, in the multi-method conditions.
    Using a genetic algorithm as an optimal band selector in the mid and thermal infrared (2.5-14 µm) to discriminate vegetation species
    Ullah, S. ; Groen, T.A. ; Schlerf, M. ; Skidmore, A.K. ; Nieuwenhuis, W. ; Vaiphasa, C. - \ 2012
    Sensors 12 (2012)7. - ISSN 1424-8220 - p. 8755 - 8769.
    spectral discrimination - reflectance - spectroscopy - emissivity - imagery - leaves - identification - spectrometry - regression - plants
    Genetic variation between various plant species determines differences in their physio-chemical makeup and ultimately in their hyperspectral emissivity signatures. The hyperspectral emissivity signatures, on the one hand, account for the subtle physio-chemical changes in the vegetation, but on the other hand, highlight the problem of high dimensionality. The aim of this paper is to investigate the performance of genetic algorithms coupled with the spectral angle mapper (SAM) to identify a meaningful subset of wavebands sensitive enough to discriminate thirteen broadleaved vegetation species from the laboratory measured hyperspectral emissivities. The performance was evaluated using an overall classification accuracy and Jeffries Matusita distance. For the multiple plant species, the targeted bands based on genetic algorithms resulted in a high overall classification accuracy (90%). Concentrating on the pairwise comparison results, the selected wavebands based on genetic algorithms resulted in higher Jeffries Matusita (J-M) distances than randomly selected wavebands did. This study concludes that targeted wavebands from leaf emissivity spectra are able to discriminate vegetation species.
    Mass spectral molecular networking of living microbial colonies
    Watrous, J. ; Roach, P. ; Alexandrov, T. ; Heath, B.S. ; Yang, J.Y. ; Kersten, R.D. ; Voort, M. van der; Pogliano, K. ; Gross, H. ; Raaijmakers, J. ; Moore, B.S. ; Laskin, J. ; Bandeira, N. ; Dorrestein, P.C. - \ 2012
    Proceedings of the National Academy of Sciences of the United States of America 109 (2012)26. - ISSN 0027-8424 - p. E1743 - E1752.
    desorption electrospray-ionization - assisted laser desorption/ionization - bacillus-subtilis - metabolic exchange - ambient conditions - natural-products - assembly-line - spectrometry - identification - antibiotics
    Integrating the governing chemistry with the genomics and phenotypes of microbial colonies has been a “holy grail” in microbiology. This work describes a highly sensitive, broadly applicable, and cost-effective approach that allows metabolic profiling of live microbial colonies directly from a Petri dish without any sample preparation. Nanospray desorption electrospray ionization mass spectrometry (MS), combined with alignment of MS data and molecular networking, enabled monitoring of metabolite production from live microbial colonies from diverse bacterial genera, including Bacillus subtilis, Streptomyces coelicolor, Mycobacterium smegmatis, and Pseudomonas aeruginosa. This work demonstrates that, by using these tools to visualize small molecular changes within bacterial interactions, insights can be gained into bacterial developmental processes as a result of the improved organization of MS/MS data. To validate this experimental platform, metabolic profiling was performed on Pseudomonas sp. SH-C52, which protects sugar beet plants from infections by specific soil-borne fungi [R. Mendes et al. (2011) Science 332:1097–1100]. The antifungal effect of strain SH-C52 was attributed to thanamycin, a predicted lipopeptide encoded by a nonribosomal peptide synthetase gene cluster. Our technology, in combination with our recently developed peptidogenomics strategy, enabled the detection and partial characterization of thanamycin and showed that it is a monochlorinated lipopeptide that belongs to the syringomycin family of antifungal agents. In conclusion, the platform presented here provides a significant advancement in our ability to understand the spatiotemporal dynamics of metabolite production in live microbial colonies and communities
    Ultrasonic or accelerated solvent extration followed by U-HPLC-high mass accuracy MS for screening of pharmaceuticals and fungicides in soil and plant samples
    Chitescu, C.L. ; Oosterink, J.E. ; Jong, J. de; Stolker, A.A.M. - \ 2012
    Talanta 88 (2012). - ISSN 0039-9140 - p. 653 - 662.
    pressurized-liquid extraction - veterinary antibiotics - chromatography - spectrometry - environment - fate - food
    Different veterinary pharmaceuticals are used in agricultural livestock becoming a source of environment contamination. Furthermore, no regulation exists for the concentration limits of pharmaceuticals in soil or water. Monitoring programs for environment contamination with pharmaceuticals are needed, requiring new sensitive and selective screening methods. The present study focuses on developing a method for the simultaneous scanning of forty-two compounds (pharmaceuticals, azole biocides and fungicides) in soil and plant material samples. For extraction purposes the use of ultrasonic assisted and accelerated solvent extraction (ASE) were compared. The extract was purified and concentrated by applying a solid phase extraction step followed by ultra-high-performance-chromatographic separation and accurate-mass spectrometric detection using Exacte Orbitrap technology (FWHM 50,000). The effects of the different extraction solvents and conditions on the extraction efficiency were tested. Although both extraction approaches are applicable the optimal extraction efficiency was obtained by applying accelerated solvent extraction using solvent mixtures containing acetone for soil and methanol for plant samples. An ASE process has been validated for the determination of selected pharmaceuticals and fungicides in soil and in plant material. The recoveries from soil samples were >70% for more than 68% of the compounds. The levels of detection were =10 µg kg-1 for 93% of the compounds tested. The recoveries from plant material were >70% for 64% of the compounds tested. The levels of detection were =10 µg kg-1 for 66% of the compounds. The developed method was used to screen soil and plant material collected throughout the Netherlands and oxytetracycline residues were detected. --------------------------------------------------------------------------------
    Composition of Human Skin Microbiota Affects Attractiveness to Malaria Mosquitoes
    Verhulst, N.O. ; Qiu, Y.T. ; Beijleveld, H. ; Maliepaard, C.A. ; Knights, D. ; Schulz, S. ; Berg-Lyons, D. ; Lauber, C.L. ; Verduijn, W. ; Haasnoot, G.W. ; Mumm, R. ; Bouwmeester, H.J. ; Claas, F.H.J. ; Dicke, M. ; Loon, J.J.A. van; Takken, W. ; Knight, R. ; Smallegange, R.C. - \ 2011
    PLoS ONE 6 (2011)12. - ISSN 1932-6203 - 7 p.
    major histocompatibility complex - human axillary odor - anopheles-gambiae - mating preferences - aedes-aegypti - microflora - spectrometry - diversity - responses - selection
    The African malaria mosquito Anopheles gambiae sensu stricto continues to play an important role in malaria transmission, which is aggravated by its high degree of anthropophily, making it among the foremost vectors of this disease. In the current study we set out to unravel the strong association between this mosquito species and human beings, as it is determined by odorant cues derived from the human skin. Microbial communities on the skin play key roles in the production of human body odour. We demonstrate that the composition of the skin microbiota affects the degree of attractiveness of human beings to this mosquito species. Bacterial plate counts and 16S rRNA sequencing revealed that individuals that are highly attractive to An. gambiae s.s. have a significantly higher abundance, but lower diversity of bacteria on their skin than individuals that are poorly attractive. Bacterial genera that are correlated with the relative degree of attractiveness to mosquitoes were identified. The discovery of the connection between skin microbial populations and attractiveness to mosquitoes may lead to the development of new mosquito attractants and personalized methods for protection against vectors of malaria and other infectious diseases
    Predictions of soil surface and topsoil organic carbon content through the use of laboratory and field spectroscopy in the Albany Thicket Biome of Eastern Cape Province of South Africa
    Nocita, M. ; Kooistra, L. ; Bachmann, M. ; Müller, A. ; Powell, M. ; Weel, S. - \ 2011
    Geoderma 167-168 (2011). - ISSN 0016-7061 - p. 295 - 302.
    infrared reflectance spectroscopy - least-squares regression - in-situ characterization - agricultural soils - river floodplains - nir spectroscopy - meta analysis - sequestration - spectrometry - nitrogen
    In recent years it has been shown that laboratory and field visible near infrared spectroscopy (VNIRS) allows for the accurate prediction of soil organic carbon (SOC) — more rapidly, less expensively, and at larger scales than conventional soil laboratory methods. VNIRS might find application in the restoration assessment of the degraded, semi-arid subtropical thickets of the Albany Thicket Biome (ATB) of the Eastern Cape Province of South Africa. During the twentieth century, the semi-arid forms of the ATB suffered heavy browsing by goats, transforming the dense closed-canopy shrubland into an open savannah-like system. This paper presents a study dealing with SOC estimation of soil surface (0–5 mm) and topsoil (0–200 mm) in the degraded ATB, through the combination of soil spectroscopy and partial least square regression (PLSR). Spectroscopic measurements and soil samples were collected along a transect in the ATB. The PLSR models developed with laboratory and field spectra gave good predictions of SOC, with root mean square error of validation (RMSEV) <5.0 and 5.5 g C kg- 1, respectively. The use of the full visible near-infrared spectral range gave better SOC predictions than using either visible or near-infrared separately. The resampling simulation of the field surface spectra to the 232 channels of the satellite-born EnMAP sensor gave good SOC predictions for laboratory conditions (RPD > 2), but low accuracy (RMSE: 9.88 g C kg- 1) for field model. The results of this research study indicated that, for the ATB, (i) combining soil spectroscopy and PLSR does favor accurate prediction of SOC, (ii) the predictions of surface SOC can be used as a proxy of topsoil SOC, and (iii) there is potential for future application of satellite-born hyperspectral data for SOC content predictions. --------------------------------------------------------------------------------
    HPLC inorganic arsenic speciation analysis of samples containing high sulfuric acid and iron levels
    Gonzalez-Contreras, P.A. ; Gerrits, I.P.A.M. ; Weijma, J. ; Buisman, C.J.N. - \ 2011
    Toxicological & Environmental Chemistry 93 (2011)3. - ISSN 0277-2248 - p. 415 - 423.
    icp-oes - spectrometry
    To monitor the oxidation of arsenite to arsenate in oxidizing and bioleaching reactors, speciation analysis of the inorganic arsenic compounds is required. Existing arsenic speciation analysis techniques are based on the use of liquid chromatography columns coupled to detector equipment such as inductively coupled plasma optical emission spectrometry (ICP-OES). These techniques are fairly complex and expensive. Therefore, for analysis of arsenic speciation in our studies on thermophilic iron and arsenic oxidation, we developed a simple (and inexpensive) method based on anionic ion exclusion chromatography using sulfuric acid as mobile phase, followed by UV detection. The detection limit was 0.1¿mg¿L-1 of arsenite (As3+) and 0.1¿mg¿L-1 of arsenate (As5+). The method was validated with samples from an iron-oxidizing bioreactor containing 0.12¿mol¿L-1 H2SO4, 1¿g¿L-1 arsenic, and 3¿g¿L-1 iron. Samples from arsenopyritic gold concentrates by partial bio-oxidation and leaching samples were analyzed, showing the usefulness of the method for arsenic contained in environmental compartments. We also describe the apparent effect of the arsenic valence state on ICP-OES detection for total arsenic.
    Speciation of Se and DOC in soil solution and their relation to Se bioavailability.
    Weng, L.P. ; Vega, F.A. ; Supriatin, S. ; Bussink, W. ; Riemsdijk, W.H. van - \ 2011
    Environmental Science and Technology 45 (2011)1. - ISSN 0013-936X - p. 262 - 267.
    donnan membrane technique - ion-chromatography - selenium uptake - trace-metals - extracts - translocation - spectrometry - adsorption - sorption - samples
    A 0.01 M CaCl2 extraction is often used to asses the bioavailability of plant nutrients in soils. However, almost no correlation was found between selenium (Se) in the soil extraction and Se content in grass. The recently developed anion Donnan membrane technique was used to analyze chemical speciation of Se in the 0.01 M CaCl2 extractions of grassland soils and fractionation of DOC (dissolved organic carbon). The results show that most of Se (67-86%) in the extractions (15 samples) are colloidal-sized Se. Only 13-34% of extractable Se are selenate, selenite and small organic Se (
    Soil organic carbon mapping of partially vegetated agricultural fields with imaging spectroscopy
    Bartholomeus, H. ; Kooistra, L. ; Stevens, A. ; Leeuwen, M. van; Wesemael, B. van; Ben-Dor, E. ; Tychon, B. - \ 2011
    International Journal of applied Earth Observation and Geoinformation 13 (2011)1. - ISSN 0303-2434 - p. 81 - 88.
    infrared reflectance spectroscopy - least-squares regression - spectral reflectance - aviris data - indexes - tm - spectrometry - parameters - prospect - nitrogen
    Soil Organic Carbon (SOC) is one of the key soil properties, but the large spatial variation makes continuous mapping a complex task. Imaging spectroscopy has proven to be an useful technique for mapping of soil properties, but the applicability decreases rapidly when fields are partially covered with vegetation. In this paper we show that with only a few percent fractional maize cover the accuracy of a Partial Least Square Regression (PLSR) based SOC prediction model drops dramatically. However, this problem can be solved with the use of spectral unmixing techniques. First, the fractional maize cover is determined with linear spectral unmixing, taking the illumination and observation angles into account. In a next step the influence of maize is filtered out from the spectral signal by a new procedure termed Residual Spectral Unmixing (RSU). The residual soil spectra resulting from this procedure are used for mapping of SOC using PLSR, which could be done with accuracies comparable to studies performed on bare soil surfaces (Root Mean Standard Error of Calibration = 1.34 g/kg and Root Mean Standard Error of Prediction = 1.65 g/kg). With the presented RSU approach it is possible to filter out the influence of maize from the mixed spectra, and the residual soil spectra contain enough information for mapping of the SOC distribution within agricultural fields. This can improve the applicability of airborne imaging spectroscopy for soil studies in temperate climates, since the use of the RSU approach can extend the flight-window which is often constrained by the presence of vegetation.
    Identification of anabolic steroids and derivatives using bioassay-guided fractionation,UHPLC/TOFMS analysis and accurate mass database searching
    Peters, R.J.B. ; Rijk, J.C.W. ; Bovee, T.F.H. ; Nijrolder, A.W.J.M. ; Lommen, A. ; Nielen, M.W.F. - \ 2010
    Analytica Chimica Acta 664 (2010)1. - ISSN 0003-2670 - p. 77 - 88.
    liquid-chromatography - androgen bioassay - directed identification - veterinary drugs - screening method - human urine - hplc-uv - lc-ms - spectrometry - testosterone
    Biological tests can be used to screen samples for large groups of compounds having a particular effect, but it is often difficult to identify a specific compound when a positive effect is observed. The identification of an unknown compound is a challenge for analytical chemistry in environmental analysis, food analysis, as well as in clinical and forensic toxicology. In this study bioassay-guided fractionation, ultra high performance liquid chromatography combined with time-of-flight mass spectrometry (UHPLC/TOFMS) and accurate mass database searching was tested to detect and identify unknown androgens. Herbal mixtures and sport supplements were tested using an androgen bioassay and modifications in sample preparations were carried out in order to activate inactive pro-androgens, androgen esters and conjugated androgens to enable their detection in the bioassay. Two of the four herbal mixtures tested positive and bioassay-guided fractionation followed by UHPLC/TOFMS of positive fractions resulted in the identification of nortestosterone phenylpropionate, testosterone cyclohexanecarboxylate and methyltestosterone. Three of the four sport supplements reacted toxic in the bioassay or gave inconclusive results and were further investigated using UHPLC/TOFMS in combination with data processing software and an accurate mass database having approximately 40,000 entries. This accurate mass database was derived from the PubChem database on the internet and coupled to the TOFMS software. This resulted in the tentative identification of several androgens, including methylboldenone, testosterone and the androgen esters methyltestosterone propionate or testosterone isobutyrate, testosterone buciclate and methylenetestosterone acetate. The study showed that bioassay-guided fractionation in combination with UHPLC/TOFMS analysis is a useful procedure to detect, isolate and identify unknown androgens in suspected samples. As an alternative, the use of data processing software in combination with an accurate mass database and coupled on-line with the TOFMS instrument software enabled the identification of androgens and androgen esters in the chromatogram even without bioassay-guided fractionation.
    Monitoring of mercury, arsenic, and lead in traditional Asian herbal preparations on the Dutch market and estimation of associated risks
    Martena, M.J. ; Wielen, J.C.A. van der; Rietjens, I. ; Klerx, W.N.M. ; Groot, H.N. de; Konings, E.J.M. - \ 2010
    Food Additives and Contaminants 27 (2010)2. - ISSN 0265-203X - p. 190 - 205.
    indian ethnic remedies - heavy-metals - ayurvedic medicines - chinese medicines - intoxication - toxicity - spectrometry - ingestion - products - cinnabar
    Traditional herbal preparations used in Ayurveda, traditional Chinese medicine, traditional Tibetan medicine, and other Asian traditional medicine systems may contain significant amounts of mercury, arsenic or lead. Though deliberately incorporated in Asian traditional herbal preparations for therapeutic purposes, these constituents have caused intoxications worldwide. The aim of this study was therefore to determine mercury, arsenic, and lead levels in Asian traditional herbal preparations on the Dutch market. A total of 292 traditional herbal preparations used in Ayurveda, traditional Chinese medicine, and traditional Tibetan medicine were sampled between 2004 and 2007. Samples were mostly multi-ingredient traditional herbal preparations containing herbs and minerals. The labeling of less than 20% of the traditional herbal preparations suggested the presence of mercury, arsenic or lead. These elements were shown by inductively coupled mass spectrometry (ICP-MS) in 186 (64%) of 292 traditional herbal preparations. Estimated weekly mercury, arsenic, and lead intake levels were calculated for each traditional herbal preparation from the analytically determined concentrations and the recommended dose. A total of 59 traditional herbal preparations (20%) were likely to result in intakes of these elements significantly exceeding safety limits. Of these 59 traditional herbal preparations, intake estimates for 50 traditional herbal preparations significantly exceeded the safety limit for mercury (range = 1.4-1747 mg week-1); intake estimates for 26 traditional herbal preparations significantly exceeded the safety limit for arsenic (range = 0.53-427 mg week-1) and intake estimates for eight traditional herbal preparations were significantly above the safety limit for lead (range = 2.6-192 mg week-1). It is concluded that the mercury, arsenic, and lead contents of traditional herbal preparations used in Ayurveda, traditional Chinese medicine, and traditional Tibetan medicine remain a cause for concern and require strict control.
    Space-born spectrodirectional estimation of forest properties
    Verrelst, J. - \ 2010
    Wageningen University. Promotor(en): Michael Schaepman, co-promotor(en): Jan Clevers; B. Koetz. - [S.l. : S.n. - ISBN 9789085856214 - 152
    bossen - bosecologie - achteruitgang, bossen - gezondheidstoestand van het bos - bosinventarisaties - remote sensing - spectrometrie - bosbedrijfsvoering - bosmonitoring - bosstructuur - nabij infrarood spectroscopie - geïntegreerd bosbeheer - forests - forest ecology - forest decline - forest health - forest inventories - remote sensing - spectrometry - forest management - forest monitoring - forest structure - near infrared spectroscopy - integrated forest management
    With the upcoming global warming forests are under threat. To forecast climate change impacts and adaptations, there is need for developing improved forest monitoring services, which are able to record, quantify and map bio-indicators of the forests’ health status across the globe. In this context, Earth observation (EO) can provide a substantial amount of up-to-date information about the biochemical and structural conditions of our forests at a local-to-global scale. Among the optical EO instruments in space, one of the most innovative instruments is the experimental Compact High Resolution Imaging Spectrometer (CHRIS) on board the PROBA-1 (Project for On Board Autonomy) satellite. CHRIS is capable of sampling reflected radiation at five viewing angles over the visible and near-infrared (VNIR) region of the solar spectrum with a relatively high spatial resolution (~17 m). The as such acquired spectrodirectional (combined multi-angular and spectroscopy) data may lead to new opportunities for space-based forest monitoring applications, yet the added value of canopy reflectance anisotropy measured over the whole VNIR spectral region is largely unknown. This is why the use of space-borne spectrodirectional data of a forested target has been investigated in this thesis.
    Profiling human gut bacterial metabolism and its kinetic using [U-(13)C]glucose and NMR
    Graaf, A.A. de; Maathuis, A. ; Waard, P. de; Deutz, N.E.P. ; Dijkema, C. ; Vos, W.M. de; Venema, K. - \ 2010
    NMR in Biomedicine 23 (2010)1. - ISSN 0952-3480 - p. 2 - 12.
    chain fatty-acids - amino-acids - fermentation products - large-intestine - colon-cancer - human feces - butyrate - ethanol - spectrometry - acetaldehyde
    This study introduces a stable-isotope metabolic approach employing [U-(13)C]glucose that, as a novelty, allows selective profiling of the human intestinal microbial metabolic products of carbohydrate food components, as well as the measurement of the kinetics of their formation pathways, in a single experiment. A well-established, validated in vitro model of human intestinal fermentation was inoculated with standardized gastrointestinal microbiota from volunteers. After culture stabilization, [U-(13)C]glucose was added as an isotopically labeled metabolic precursor. System lumen and dialysate samples were taken at regular intervals. Metabolite concentrations and isotopic labeling were determined by NMR, GC, and enzymatic methods. The main microbial metabolites were lactate, acetate, butyrate, formate, ethanol, and glycerol. They together accounted for a (13)C recovery rate as high as 91.2%. Using an NMR chemical shift prediction approach, several minor products that showed (13)C incorporation were identified as organic acids, amino acids, and various alcohols. Using computer modeling of the (12)C contents and (13)C labeling kinetics, the metabolic fluxes in the gut microbial pathways for synthesis of lactate, formate, acetate, and butyrate were determined separately for glucose and unlabeled background substrates. This novel approach enables the study of the modulation of human intestinal function by single nutrients, providing a new rational basis for achieving control of the short-chain fatty acids profile by manipulating substrate and microbiota composition in a purposeful manner.
    Vision in de agro - “State of the art”: vision en bio-divers materiaal
    Pekkeriet, Erik - \ 2009
    quality controls - monitoring - instruments - multispectral imagery - computer techniques - crops - image processing - spectrometry - ornamental plants - 3d visualization
    Habitat type-based bioaccumulation and risk assessment of metal and As contamination in earthworms, beetles and woodlice
    Vermeulen, F. ; Brink, N.W. van den; Havé, H. D'; Mubiana, V.K. ; Blust, R. ; Bervoets, L. ; Coen, W. De - \ 2009
    Environmental Pollution 157 (2009)11. - ISSN 0269-7491 - p. 3098 - 3105.
    hedgehog erinaceus-europaeus - spatial-distribution - forest soils - heavy-metals - trace-metals - accumulation - pollution - spectrometry - floodplain - microwave
    The present study investigated the contribution of environmental factors to the accumulation of As, Cd, Cu, Pb and Zn in earthworms, beetles and woodlice, and framed within an exposure assessment of the European hedgehog. Soil and invertebrate samples were collected in three distinct habitat types. Results showed habitat-specific differences in soil and invertebrate metal concentrations and bioaccumulation factors when normalized to soil metal concentration. Further multiple regression analysis showed residual variability (habitat differences) in bioaccumulation that could not be fully explained by differences in soil metal contamination, pH or organic carbon (OC). Therefore, the study demonstrated that in bioaccumulation studies involving terrestrial invertebrates or in risk assessment of metals, it is not sufficient to differentiate habitat types on general soil characteristics such as pH and/or OC alone. Furthermore, simple generic soil risk assessments for Cd and Cu showed that risk characterization was more accurate when performed in a habitat-specific way. Our study provided essential insights into habitat-specific accumulation patterns with respect to factors influencing metal bioaccumulation, BAFs, and site-specific risk assessment
    8000 yr of black carbon accumulation in a colluvial soil from NW Spain
    Kaal, J. ; Martinez-Cortizas, A. ; Buurman, P. ; Criado Boado, F. - \ 2008
    Quaternary Research 69 (2008)1. - ISSN 0033-5894 - p. 56 - 61.
    solid-state c-13 - organic-matter - chemical-composition - humic acids - fractions - pyrolysis - spectroscopy - spectrometry - cambisol - fire
    Analytical pyrolysis-GC/MS and solid-state 13C NMR (nuclear magnetic resonance) were applied to the NaOH-extractable organic matter fraction of a colluvial soil from Galicia (NW Spain) that represents more than 8500 yr of accumulation. While molecular indicators of vegetation change were looked for, it seemed likely that any such signal was disturbed by the intense fire regime of the area. This conclusion was drawn from (1) the presence of three charcoal layers, (2) the high proportion of aryl C in NMR spectra (non-quantitative) and (3) the prevalence of benzenes and polycyclic aromatic hydrocarbons (PAHs) in the chromatograms (38 ± 6% of total identified peak area), also in charcoal-poor samples. If this conclusion is accurate, the area has been subjected to burning episodes for at least 8000 yr. Additionally, the results indicate that biomass burning residues (black carbon; BC) may become NaOH extractable after long periods of degradation in mineral soil. These results add to our knowledge of the long-term fate of BC in soil, which is a potential agent in the global C cycle.
    How to distinguish healthy from diseased? Classification strategy for mass spectrometry based clinical proteomics
    Hendriks, M.M.W.B. ; Smit, S. ; Akkermans, W. ; Reijmers, T.H. ; Eilers, P.H.C. ; Hoefsloot, H. ; Rugingh, C. ; Koster, C. de; Aerts, J. ; Smilde, A. - \ 2007
    Proteomics 7 (2007)20. - ISSN 1615-9853 - p. 3672 - 3680.
    gene-expression data - gaucher-disease - discriminant-analysis - logistic-regression - cancer - spectrometry - validation - prediction - biomarkers - chemokine
    SELDI-TOF-MS is rapidly gaining popularity as a screening tool for clinical applications of proteomics. Application of adequate statistical techniques in all the stages from measurement to information is obligatory. One of the statistical methods often used in proteomics is classification: the assignment of subjects to discrete categories, for example healthy or diseased. Lately, many new classification methods have been developed, often specifically for the analysis of X-omics data. For proteomics studies a good strategy for evaluating classification results is of prime importance, because usually the number of objects will be small and it would be wasteful to set aside part of these as a mere test set. The present paper offers such a strategy in the form of a protocol which can be used for choosing among different statistical classification methods and obtaining figures of merit of their performance. This paper also illustrates the usefulness of proteomics in a clinical setting, serum samples from Gaucher disease patients, when used in combination with an appropriate classification method.
    Check title to add to marked list
    << previous | next >>

    Show 20 50 100 records per page

     
    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.