John M Halket

King's College London, Londinium, England, United Kingdom

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Publications (40)109.77 Total impact

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    ABSTRACT: Volatile Organic Compounds (VOCs), including Benzene, Toluene, Ethylbenzene and Xylenes (BTEX) are industrial solvents frequently used and emitted into the atmosphere. Toluene is one of the most used despite its major and direct impact on human health. It is therefore necessary to minimize emissions directly at source. Catalytic oxidation represents an efficient remediation technique in order to reduce its emission directly at the source, but can release byproducts. Catalytist performance is usually evaluated using dedicated analytical chemistry methods measuring VOC conversion or CO2 emission. In this study, two catalysts Pd/α-Al2O3 and Pd/γ-Al2O3 were toxicologically tested in order to determine the most efficient one for toluene oxidation. The two catalytic systems were thus coupled to Air-Liquid Interface (ALI) system Vitrocell®, to expose human A549 lung cells during 1h to toluene or to exhaust from toluene catalytic oxidation. Following the exposure, gene expression of nine proteins implied in the organic compounds metabolisation in lung cells were conducted to validate the best performing catalyst for toluene remediation. Both exposure concentrations (i.e. 10 and 100% of catalytic emission) resulted in increased gene expression of Xenobiotics Metabolising Enzymes (XME) (CYP2E1 CYP2S1, CYP1A1, CYP1B1, EPHX1 and NQO1). Some of these XME are known to be induced by polycyclic organic compounds conventionally not searched during the development of catalysts for VOCs degradation. The increase in gene expression suggests the presence of undetected compounds whose toxicity must be assessed before the adoption of new catalyst. This enhances the relevance of toxicological validation of such systems before scaling-up and marketing. This study validated in a first step the suitability of using Vitrocell® system as an innovative, direct and dynamic model of ALI exposure in the development of new catalysts, showing the presence of chemically undetected byproducts. In a second step, the comparison of the two catalysts showed that less organic compounds metabolizing genes were induced with Pd/γ-Al2O3 making it more favourable than Pd/α-Al2O3 for toluene remediation.
    Full-text · Conference Paper · Oct 2015
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    ABSTRACT: An analytical methodology has been developed for extracting recurrent unidentified spectra (RUS) from large GC/MS data sets. Spectra were first extracted from original data files by the Automated Mass Spectral Deconvolution and Identification System (AMDIS)1 using settings designed to minimize spurious spectra, followed by searching the NIST library with all unidentified spectra. The spectra that could not be identified were then filtered to remove poorly deconvoluted data and clustered. The results were assumed to be unidentified components. This was tested by requiring each unidentified spectrum to be found in two chromatographic columns with slightly different stationary phases. This methodology has been applied to a large set of pediatric urine samples. A library of spectra and retention indices for derivatized urine components, both identified and recurrent unidentified has been created and is available for download.
    No preview · Article · Sep 2014 · Analytical Chemistry
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    ABSTRACT: Background Persimmon fruits have largely been used by traditional medicine due to their phenolic composition. This research aims to perform a rapid, detailed and affordable study of the profile of low molecular weight phenols from persimmon pulp.Methods Two different HPLC-DAD-ESI−/MSn analyses were performed by a routine three-dimensional ion trap mass spectrometer to analyze the ethanolic extract of persimmon pulp: (1) an untargeted data dependent analysis to identify the majority of small phenols that included a full MS and MS2 scan events; and (2) a targeted data dependent analysis to identify the polymerized phenols (dimmers and formic acid adducts) through a Source Induced Dissociation analysis that included full MS and MS2 scan events. Results A total of thirty-two low molecular weight phenols were detected, consisting of gallic acid and its glycoside and acyl derivatives, glycosides of p-coumaric, vanillic and cinnamic acids and different flavone di-C-hexosides, most of them firstly reported in persimmon. Conclusion The use of a straightforward and affordable methodology of analysis led to obtain an up-to-date profiling of low molecular weight phenols in persimmon. Results can help future actions aimed to expand the understanding of the phenolic metabolome of persimmon cultivars.
    No preview · Article · Aug 2014 · Journal of the Science of Food and Agriculture
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    ABSTRACT: The effects of minimal processing on the metabolite composition of orange juice were studied. Volatiles and nonvolatile polar compounds in Lane Late orange juices, with different pulp contents, treated by high-pressure homogenisation (HPH) at 150 MPa (at 58, 63 and 68 °C) and stored for 3 months at 3 °C were analysed by gas chromatography coupled to mass spectrometry (GC-MS) with automated data processing. A total of 92 volatiles and 22 polar components (trimethylsilyl, TMS, derivatives of sugars, organic acids and amino acids) were determined in fresh, processed and stored juices. Initially, concentration of fresh flavours (hydrocarbon terpenes and aldehydes) determined in the homogenised samples with the original pulp content was higher than that determined in fresh juice. During storage, desirable descriptors were better preserved in the juice processed at 68 °C with the lowest increase in off-flavours (alcohols and ketones). Generally, operations assayed did not exert a significant influence on polar metabolites, showing no effect on their decrease with time.
    No preview · Article · Jun 2014 · International Journal of Food Science & Technology
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    ABSTRACT: Although chemical derivatization for signal enhancement in drug testing is most often associated with gas chromatography, it also has the potential to improve the detection of analytes poorly ionized by atmospheric pressure ionization techniques, such as electrospray ionization used in liquid chromatography-mass spectrometry. A number of acidic compounds, namely drug glucuronides (e.g. conjugates of temazepam, oxazepam, lorazepam, morphine, testosterone, epitestosterone, 5-α-dihydrotestosterone, androsterone, p-nitrophenol, and paracetamol) were successfully derivatized with tris(trimethoxyphenyl) phosphoniumpropylamine to introduce a quaternary cation functionality to the analytes. Benzodiazepine glucuronides were more specifically investigated, and following positive mode electrospray ionization mass spectrometry, average improvements to peak areas as a result of derivatization were 67-, 6-, and 7- fold for temazepam, oxazepam, and lorazepam glucuronides. Average improvements to the signal-to-noise ratios for temazepam, oxazepam, and lorazepam glucuronides were 1336-, 371- and 217-fold, respectively. The values obtained for the derivatized conjugate were also typically higher than those for the underivatized parent drug. Urine containing benzodiazepine glucuronides was also successfully derivatized. The data indicates potential for the use of charge derivatization to improve the detection of molecules with acidic functionalities by liquid chromatography-mass spectrometry (LC-MS) techniques in certain scenarios. Copyright © 2014 John Wiley & Sons, Ltd.
    Full-text · Article · Apr 2014 · Drug Testing and Analysis
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    Full-text · Dataset · Oct 2012
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    ABSTRACT: The commercial cultivation of genetically engineered (GE) crops in Europe has met with considerable consumer resistance, which has led to vigorous safety assessments including the measurement of substantial equivalence between the GE and parent lines. This necessitates the identification and quantification of significant changes to the metabolome and proteome in the GE crop. In this study, the quantitative proteomic analysis of tomato fruit from lines that have been transformed with the carotenogenic gene phytoene synthase-1 (Psy-1), in the sense and antisense orientations, in comparison with a non-transformed, parental line is described. Multidimensional protein identification technology (MudPIT), with tandem mass spectrometry, has been used to identify proteins, while quantification has been carried out with isobaric tags for relative and absolute quantification (iTRAQ). Fruit from the GE plants showed significant alterations to their proteomes compared with the parental line, especially those from the Psy-1 sense transformants. These results demonstrate that MudPIT and iTRAQ are suitable techniques for the verification of substantial equivalence of the proteome in GE crops.
    Full-text · Article · Sep 2012 · Journal of Experimental Botany
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    ABSTRACT: Mechanically recovered meat (MRM) is generated by mechanical treatment of remnants following hand deboning. EU regulations exclude MRM from the definition of meat; as a consequence there is a need for robust analytical procedures to differentiate MRM from hand-deboned meat (HDM) and desinewed meat. Present study represents the development of an analytical platform for the detection of adulteration of meat products with MRM. Small molecular weight compounds were extracted from meat samples and analysed using GC–MS. Obtained metabolite profiles were modelled with OPLS-DA for the accurate classification of MRM, HDM and desinewed pork and chicken samples. Separation of three classes of products for fresh chicken and pork meat samples was achieved. In addition, the procedure also enabled proper prediction of samples not included in the model as well as pork commercial meat products. Compounds that could be potential markers for MRM detection in commercial products were also selected.
    No preview · Article · Apr 2011 · Food Chemistry
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    ABSTRACT: A proteomic-based method has been developed for the detection of chicken meat within mixed meat preparations. The procedure is robust and simple, comprising the extraction of myofibrillar proteins, enrichment of target proteins using OFFGEL isoelectric focusing, in-solution trypsin digestion of myosin light chain 3, and analysis of the generated peptides by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Using this approach, it was possible for example to detect 0.5% contaminating chicken in pork meat with high confidence. Quantitative detection of chicken meat was done by using AQUA stable isotope peptides made from the sequence of previously selected species-specific peptide biomarkers. Linearity was observed between the amount of the peptide biomarker and the amount of chicken present in the mixture; further independent replication is required now to validate the method. Apart from its simplicity, this approach has the advantage that it can be used effectively for the detection of both raw and cooked meat. The method is robust, reliable, and sensitive, representing a serious alternative to methods currently in use for these purposes. It is amenable to highly processed foods which can be particularly problematic, as the tertiary protein structure is often affected in processed food precluding immunoassays. In addition, this proteomic analysis will permit the determination of definitive discriminatory sequence, unlike the DNA PCR based methods used presently. The present article also demonstrates the translation of the technology to routine mass spectrometry equipment, making the methodology suitable for public analysts.
    Full-text · Article · Jul 2010 · Journal of Proteome Research
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    ABSTRACT: Hepcidin is a peptide hormone that functions as a key regulator of mammalian iron metabolism. Biological levels are increased in end-stage renal disease and during inflammation but suppressed in hemochromatosis. Thus hepcidin levels have diagnostic importance. This study describes the development of an analytical method for the quantitative determination of the concentration of hepcidin in clinical samples. The fragmentation of hepcidin was investigated using triple quadrupole and linear ion trap mass spectrometers. A standard quantity of a stable isotopically labelled hepcidin internal standard was added to serum samples. Extraction was performed by protein precipitation and weak cation-exchange magnetic nanoparticles. Chromatography was carried out on sub 2 microm particle stationary phase, using ultra-high-pressure liquid chromatography and a linear ion trap for quantitation. The lower limit of quantitation was 0.4 nmol/L with less than 20% accuracy and precision. The mean hepcidin concentration in sera for controls was 4.6 +/- 2.7 nmol/L, in patients with sickle cell disease, 7.0 +/- 8.9 nmol/L; in patients with end-stage renal disease, 30.5 +/- 15.7 nmol/L; and patients with penetrant hereditary hemochromatosis, 1.4 +/- 0.8 nmol/L.
    No preview · Article · May 2010 · Rapid Communications in Mass Spectrometry
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    ABSTRACT: The present work describes the pharmacokinetics of recently developed liposome-quantum dot (L-QD) hybrid vesicles in nude mice following systemic administration. Hydrophobic QD were incorporated into different bilayer compositions, and the serum stability of such hybrid vesicles was evaluated using turbidity and carboxyfluorescein release measurements. L-QD hybrid blood profile and organ biodistribution were also determined by elemental (cadmium) analysis. Following intravenous administration, different tissue biodistribution profiles and tissue affinities were observed depending on the L-QD lipid bilayer characteristics. Immediate blood clearance was observed with cationic (DOTAP/DOPE/Chol) hybrid with rapid lung accumulation, while incorporation of PEG at the surface of zwitterionic vesicles dramatically prolonged their blood circulation half-life after systemic administration. Overall, the L-QD hybrid vesicle system is considered a viable platform that allows QD delivery to different tissues through facile modulation of the hybrid vesicle characteristics. In addition, L-QD offers many opportunities for the development of combinatory therapeutic and imaging (theranostic) modalities by incorporating both drug molecules and QD within the different compartments of a single vesicle.
    No preview · Article · Sep 2009 · Bioconjugate Chemistry
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    ABSTRACT: Hepcidin is known to be a key systemic iron-regulatory hormone which has been demonstrated to be associated with a number of iron disorders. Hepcidin concentrations are increased in inflammation and suppressed in hemochromatosis. In view of the role of hepcidin in disease, its potential as a diagnostic tool in a clinical setting is evident. This study describes the development of a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) assay for the quantitative determination of hepcidin concentrations in clinical samples. A stable isotope labeled hepcidin was prepared as an internal standard and a standard quantity was added to urine samples. Extraction was performed with weak cation-exchange magnetic nanoparticles. The basic peptides were eluted from the magnetic nanoparticles using a matrix solution directly onto a target plate and analyzed by MALDI-TOF MS to determine the concentration of hepcidin. The assay was validated in charcoal stripped urine, and good recovery (70-80%) was obtained, as were limit of quantitation data (5 nmol/L), accuracy (RE <10%), precision (CV <21%), within -day repeatability (CV <13%) and between-day repeatability (CV <21%). Urine hepcidin levels were 10 nmol/mmol creatinine in healthy controls, with reduced levels in hereditary hemochromatosis (P < 0.000005) and elevated levels in inflammation (P < 0.0007). In summary a validated method has been developed for the determination of hepcidin concentrations in clinical samples.
    Full-text · Article · Jun 2009 · Rapid Communications in Mass Spectrometry
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    ABSTRACT: In vitro biosynthesis using pooled human liver microsomes was applied to help identify in vivo metabolites of ketamine by liquid chromatography (LC)-tandem mass spectrometry. Microsomal synthesis produced dehydronorketamine, seven structural isomers of hydroxynorketamine, and at least five structural isomers of hydroxyketamine. To aid identification, stable isotopes of the metabolites were also produced from tetra-deuterated isotopes of ketamine or norketamine as substrates. Five metabolites (three hydroxynorketamine and two hydroxyketamine isomers) gave chromatographically resolved components with product ion spectra indicating the presence of a phenolic group, with phenolic metabolites being further substantiated by selective liquid-liquid extraction after adjustments to the pH. Two glucuronide conjugates of hydroxynorketamine were also identified. Analysis by LC-coupled ion cyclotron resonance mass spectrometry gave unique masses in accordance with the predicted elemental composition. The metabolites, including the phenols, were subsequently confirmed to be present in urine of subjects after oral ketamine administration, as facilitated by the addition of deuterated metabolites generated from the in vitro biosynthesis. To our knowledge, phenolic metabolites of ketamine, including an intact glucuronide conjugate, are here reported for the first time. The use of biologically synthesized deuterated material as an internal chromatographic and mass spectrometric marker is a viable approach to aid in the identification of metabolites. Metabolites that have particular diagnostic value can be selected as candidates for chemical synthesis of standards.
    Full-text · Article · Jun 2009 · Drug metabolism and disposition: the biological fate of chemicals
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    ABSTRACT: The introduction of genetically modified (GM) crops into the market has raised a general alertness relating to the control and safety of foods. The applicability of protein separation hyphenated to mass spectrometry to identify the bacterial enolpyruvylshikimate-3-phosphate synthase (CP4 EPSPS) protein expressed in GM crops has been previously reported [M.F. Ocana, P.D. Fraser, R.K.P. Patel, J.M. Halket, P.M. Bramley, Rapid Commun. Mass Spectrom. 21 (2007) 319.]. Herein, we investigate the suitability of two strategies that employ heavy stable isotopes, i.e. AQUA and iTRAQ, to quantify different levels of CP4 EPSPS in up to four GM preparations. Both quantification strategies showed potential to determine whether the presence of GM material is above the limits established by the European Union. The AQUA quantification procedure involved protein solubilisation/fractionation and subsequent separation using SDS-PAGE. A segment of the gel in which the protein of interest was located was excised, the stable isotope labeled peptide added at a known concentration and proteolytic digestion initiated. Following recovery of the peptides, on-line separation and detection using LC-MS was carried out. A similar approach was used for the iTRAQ workflow with the exception that proteins were digested in solution and generated tryptic peptides were chemically tagged. Both procedures demonstrated the potential for quantitative detection at 0.5% (w/w) GM soya which is a level below the current European Union's threshold for food-labelling. In this context, a comparison between the two procedures is provided within the present study.
    Full-text · Article · Mar 2009 · Analytica chimica acta
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    ABSTRACT: A strategy to target functionalized quantum dot-liposome (f-QD-L) hybrid vesicles in the solid tumor tissue of tumor-bearing mice is explored. Functionalized polyethylene glycol (PEG)-lipid coated QD (f-QD) were encapsulated into the aqueous core of 100 nm cationic (DOPC:Chol: DOTAP); sterically stabilized, fluid-phase (DOPC:Chol:DSPE-PEG2000); and sterically stabilized, gel-phase (DSPC:Chol:DSPE-PEG2000) liposome vesicles. Double tracking of f-QD-L in blood was performed at different time points after intravenous administration in B16F10 melanoma tumor-bearing C57BL6 mice. Cholesteryl [-1-14C] oleate lipids probed the vesicle membrane were followed by liquid scintillation counting while QD were determined independently by elemental (Cd2+) analysis using inductively coupled plasma mass spectrometry (ICP-MS). Rapid blood clearance was observed following intravenous administration of the cationic hybrid vesicles, while incorporation of PEG at the surface of zwitterionic vesicles dramatically prolonged their blood circulation half-life after systemic administration. The "rigid" PEGylated f-QD-L (DSPC:Chol:DSPE-PEG2000) hybrid vesicles led to rapid tumor accumulation of peak values (approximately 5% of injected dose per gram tissue) of QD compared to long-circulating f-QD that accumulated in the tumor tissue at longer time points. More interestingly, this hybrid vesicle tumor retention persisted for at least 24 h. For almost all types of systems, a preferential cadmium uptake by liver and spleen was obtained. Overall, f-QD-L hybrid vesicles offer great potential for tumor imaging applications due to their rapid accumulation and prolonged retention within the tumor. Furthermore, f-QD-L offer many opportunities for the development of combinatory therapeutic and imaging (theranostic) modalities by incorporating both drug molecules and QD within the different compartments of a single vesicle.
    No preview · Article · Feb 2009 · Molecular Pharmaceutics
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    ABSTRACT: Current analytical methods used for screening drugs and their metabolites in biological samples from victims of drug-facilitated sexual assault (DFSA) or other vulnerable groups can lack sufficient sensitivity. The application of liquid chromatography, employing small particle sizes, with tandem mass spectrometry (MS/MS) is likely to offer the sensitivity required for detecting candidate drugs and/or their metabolites in urine, as demonstrated here for ketamine. Ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS) was performed following extraction of urine (4 mL) using mixed-mode (cation and C8) solid-phase cartridges. Only 20 microL of the 250 microL extract was injected, leaving sufficient volume for other assays important in DFSA cases. Three ion transitions were chosen for confirmatory purposes. As ketamine and norketamine (including their stable isotopes) are available as reference standards, the assay was additionally validated for quantification purposes to study elimination of the drug and primary metabolite following a small oral dose of ketamine (50 mg) in 6 volunteers. Dehydronorketamine, a secondary metabolite, was also analyzed qualitatively to determine whether monitoring could improve retrospective detection of administration. The detection limit for ketamine and norketamine was 0.03 ng/mL and 0.05 ng/mL, respectively, and these compounds could be confirmed in urine for up to 5 and 6 days, respectively. Dehydronorketamine was confirmed up to 10 days, providing a very broad window of detection.
    Full-text · Article · Jan 2009 · Journal of Chromatography B
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    ABSTRACT: The leaves of the khat plant (Catha edulis) are chewed for their pleasurable effects. Chewing releases cathinone which may decrease appetite through an unknown mechanism. Levels of the peptide ghrelin increase with hunger and decrease immediately post-prandially, while peptide YY is released following a meal. We hypothesised that the anorexigenic effects of khat may be mediated through changes in these hormones. Six habitual khat chewers attended on two separate occasions. For a period of 3h they chewed either khat leaves or lettuce. Blood pressure (BP) and pulse rate (PR) were monitored throughout, as were subjective assessments of hunger and fullness. Plasma samples were analysed for cathinone, ghrelin and PYY levels. Chewing khat significantly decreased subjective feelings of hunger and increased fullness (p<0.05) but had no effect on ghrelin and PYY levels. Khat led to an increase in cathinone levels as well as an increase in BP and PR. Cathinone levels correlated positively with fullness and pulse rate and negatively with hunger. Chewing khat decreases subjective feelings of hunger and increases systemic sympathetic tone, but has no effect on ghrelin and PYY levels. We conclude that the anorexigenic effect of khat may be secondary to central mechanisms mediated via cathinone.
    No preview · Article · Nov 2008 · Appetite
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    ABSTRACT: Hepcidin is a peptide hormone that functions as a key regulator of mammalian iron metabolism. Serum and urine levels are increased in inflammation and suppressed in hemochromatosis, and they may have diagnostic importance. This study describes the development and validation of an analytical method for the quantitative determination of the concentration of hepcidin in clinical samples. A stable, isotopically labeled internal standard, [15N,13C2]Gly12,20-hepcidin, was synthesized and a standard quantity was added to urine samples. Extraction was performed using weak cation exchange magnetic nanoparticles. An ion trap mass spectrometer was used to quantify hepcidin in the samples. The hepcidin assay was validated, and good recovery of hepcidin was obtained. The assay is accurate and precise. Urinary hepcidin levels of 3 to 9 nmol/mmol creatinine(-1) were found in healthy controls, with reduced levels in hemochromatosis (P<0.00006) and elevated levels in inflammation (P<0.00035). In sickle cell disease, a wide range was found, with the mean value not differing significantly from controls (P<0.26). In summary, a validated method has been developed for the quantitation of hepcidin using a stable, isotopically labeled internal standard and applied to determine the concentrations of hepcidin in the low nanomolar range in urine samples from patients and controls.
    Full-text · Article · Oct 2008 · Analytical Biochemistry
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    Full-text · Article · Apr 2008 · British Journal of Haematology
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    ABSTRACT: In tomato (Solanum lycopersicum), phytoene synthase-1 (PSY-1) is the key biosynthetic enzyme responsible for the synthesis of fruit carotenoids. To further our understanding of carotenoid formation in tomato fruit, we characterized the effect of constitutive expression of an additional tomato Psy-1 gene product. A quantitative data set defining levels of carotenoid/isoprenoid gene expression, enzyme activities, and metabolites was generated from fruit that showed the greatest perturbation in carotenoid content. Transcriptional upregulation, resulting in increased enzyme activities and metabolites, occurred only in the case of Psy-1, Psy-2, and lycopene cyclase B. For reactions involving 1-deoxy-d-xylulose5-phosphate synthase, geranylgeranyl diphosphate synthase, phytoene desaturase, zeta-carotene desaturase, carotene isomerase, and lycopene beta-cyclase, there were no correlations between gene expression, enzyme activities, and metabolites. Perturbations in carotenoid composition were associated with changes in plastid type and with chromoplast-like structures arising prematurely during fruit development. The levels of >120 known metabolites were determined. Comparison with the wild type illustrated that key metabolites (sucrose, glucose/fructose, and Glu) and sectors of intermediary metabolism (e.g., tricarboxylic [corrected] acid cycle intermediates and fatty acids) in the Psy-1 transgenic mature green fruit resembled changes in metabolism associated with fruit ripening. General fruit developmental and ripening properties, such as ethylene production and fruit firmness, were unaffected. Therefore, it appears that the changes to pigmentation, plastid type, and metabolism associated with Psy-1 overexpression are not connected with the ripening process.
    Full-text · Article · Oct 2007 · The Plant Cell

Publication Stats

1k Citations
109.77 Total Impact Points

Institutions

  • 2003-2015
    • King's College London
      • • Division of Analytical and Environmental Sciences
      • • Institute of Pharmaceutical Science
      • • Department of Forensic Science and Drug Monitoring
      • • Drug Control Centre
      Londinium, England, United Kingdom
  • 2014
    • Imperial College London
      Londinium, England, United Kingdom
  • 2008-2014
    • ICL
      Londinium, England, United Kingdom
  • 2010-2012
    • University of Surrey
      Guilford, England, United Kingdom
  • 2000-2011
    • Royal Holloway, University of London
      • Department of Biological Sciences
      Эгхем, England, United Kingdom
  • 1999-2009
    • University of London
      • School of Biological Sciences
      Londinium, England, United Kingdom
  • 2004
    • Royal Holloway
      Londinium, England, United Kingdom