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Analytical and Bioanalytical Chemistry (v.392, #1-2)

Chances and pitfalls of chemical cross-linking with amine-reactive N-hydroxysuccinimide esters by Stefan Kalkhof; Andrea Sinz (pp. 1-8).

In this report we summarize our experiences with the reaction products of N-hydroxysuccinimide (NHS) esters, which are widely used for chemical cross-linking of lysine residues in proteins. We describe the products, which should be scrutinized during data analysis using customized software when NHS esters are employed for chemical cross-linking. Reaction products of NHS esters were observed not only with lysines, but also with serines, tyrosines, and threonines. This report is intended to be a practical guide for those working in the field of chemical cross-linking and mass spectrometry.

Keywords: Chemical cross-linking; Amine-reactive cross-linkers; Mass spectrometry

Chances and pitfalls of chemical cross-linking with amine-reactive N-hydroxysuccinimide esters by Stefan Kalkhof; Andrea Sinz (pp. 1-8).

Keywords: Chemical cross-linking; Amine-reactive cross-linkers; Mass spectrometry

Theme-based modular approach for delivering the undergraduate analytical chemistry curriculum by Michael Samide; Olujide Akinbo (pp. 1-8).

is Associate Professor of Chemistry at Butler University, with primary teaching responsibilities focused on analytical and general chemistry. Active in curricular reform, he is interested in developing activities and seeking innovative methods that will help his students better learn chemistry. Furthermore, he maintains an active research group, where undergraduate students examine various applications of analytical chemistry to environmental issues. is Associate Professor of Chemistry at Butler University. He regularly teaches analytical chemistry, environmental chemistry, and general chemistry. His research is focused on method development and application for understanding human exposure to toxic substances in the environment. He is also actively involved in curriculum development.

Theme-based modular approach for delivering the undergraduate analytical chemistry curriculum by Michael Samide; Olujide Akinbo (pp. 1-8).

Standard hydrogen electrode challenge by Peter R. Griffiths (pp. 9-10).

Spectroscopy blog challenge by E. Pretsch; R. Zenobi (pp. 11-15).

Solution to isotopic abundance challenge by Juris Meija (pp. 17-18).

M. Ozkan and M.J. Heller (Eds.): Micro/Nano technology for genomics and proteomics by Marc R. Knecht (pp. 19-20).

Peter Gründler: Chemical sensors. An introduction for scientists and engineers by Birgit Perret (pp. 21-22).

K. Danzer: Analytical chemistry. Theoretical and metrological fundamentals by Stephen L. R. Ellison (pp. 23-24).

The Eighth Biennial Conference of the Infrared and Raman Users Group (IRUG 8) by Anna Schönemann (pp. 25-26).

The characterization of paintings: some key research issues by Rocco Mazzeo; Aldo Roda (pp. 27-28).

is Professor of Chemistry for Cultural Heritage at Bologna University, where he is actively involved in formal education in science for conservation and performs research in micro-FTIR mapping and imaging spectroscopic techniques applied to the study of painted works of art. is Professor of Analytical Chemistry at Bologna University. His main research interests include the development of ultrasensitive bio-chemiluminescence imaging techniques for the localization of target molecules (proteins, nucleic acids) in biological samples such as cells and tissues.

The characterization of paintings: some key research issues by Rocco Mazzeo; Aldo Roda (pp. 27-28).

Ultrasensitive chemiluminescent immunochemical identification and localization of protein components in painting cross-sections by microscope low-light imaging by Luisa Stella Dolci; Giorgia Sciutto; Massimo Guardigli; Manuela Rizzoli; Silvia Prati; Rocco Mazzeo; Aldo Roda (pp. 29-35).

The characterization and localization of proteins and other organic components in the complex stratigraphy of paintings is crucial for authentication and studies of painting techniques. With this aim we have developed a new ultrasensitive immunochemical procedure for the detection of the protein ovalbumin (chicken egg white albumin), present in binding media or varnishes, in painting cross-sections. The technique is based on chemiluminescence imaging detection combined with optical microscopy, and allowed the sensitive localization of the target protein in cross-sections with high spatial resolution. In order to evaluate its performance, the method was first applied to standard samples (also containing different common pigments), then used for the localization of ovalbumin in samples obtained from a Renaissance wood painting. Figure Left: image of a cross-section of a painting standard sample with a layer of egg tempera and smalt pigment (blue grains). Right: chemiluminescence image of the same sample showing the localization of the signal corresponding to the egg tempera layer. Bar represents 200 μm.

Keywords: Binding media; Chemiluminescence; Imaging; Immunoassay; Ovalbumin; Painting cross-section

ATR-FTIR imaging for the analysis of organic materials in paint cross sections: case studies on paint samples from the National Gallery, London by Marika Spring; Camilla Ricci; David A. Peggie; Sergei G. Kazarian (pp. 37-45).

The potential of attenuated total reflection Fourier transform infrared (ATR-FTIR) imaging for the characterisation of the chemical components of paint cross sections from old master paintings was investigated. Three cross sections were chosen to cover a variety of the analytical problems encountered in samples from paintings. The binding medium and degradation products in a green paint sample from a fifteenth-century Florentine painting were imaged, as well as a thin layer within a cross-section from a fifteenth-century German painting, and multiple thin surface coatings on a painting of the 1760s by Peter Romney. The application of chemometric methods for further analysis of the large data set generated for each sample was also explored. The study demonstrated the advantages of ATR-FTIR imaging, which allowed images to be obtained with high spatial resolution (ca. 3–4 μm) without the need to microtome the sample. The gain in sensitivity in detecting trace materials and the information derived from the location of these compounds in the sample was especially valuable, improving interpretation of the FTIR analysis and extending knowledge of the sample composition beyond that obtainable with other analytical techniques.

Keywords: ATR-FTIR imaging spectroscopy; Chemometrics; Paintings; Cross sections

Progress in the application of ATR-FTIR microscopy to the study of multi-layered cross-sections from works of art by Adriana Rizzo (pp. 47-55).

As a non-invasive or micro-invasive technique attenuated total reflectance Fourier transform infrared spectroscopic (ATR-FTIR) microscopy is a valuable tool for the analysis of materials in works of art. An application for which it has received growing interest is in the analysis of paint cross-sections. However, FTIR microscope configurations, objectives’ geometries and low spatial resolutions, and issues of sample preparation have often hampered the characterization of individual layers or features in cross-sections. With the use of case studies, it is demonstrated here that an ATR-FTIR microscope featuring a crystal of optimized geometry and a viewing capability feature allows characterization of individual layers, or areas within layers, of 10 μm thickness or less in single measurements. Of particular value is a remote aperturing feature which allows the analysis of selected areas within the contact footprint of the ATR crystal. Since the technique is non-destructive, the same area can be analyzed by complementary microscopic techniques such as Raman spectroscopy and scanning electron microscopy with energy-dispersive spectroscopy. Pyrolysis gas chromatography-mass spectrometry was also used in some cases to corroborate the spectroscopic data. The analyses presented provided data which were important in informing art historical interpretation and conservation of the artworks examined. Figure Paint cross section from an 18^th century American armchair painted white and selectively gilded. The original surface finish is characterized by trough and peaks from brush marks with accumulation of surface dirt. ATR-FTIR micro-spectroscopy performed on areas of the original and restoration layers allowed clear differentiation in medium and pigment distribution in visually similar white paint applications.

Keywords: ATR-FTIR microscopy; Cross-sections; Paint analysis; Clear coatings; Germanium crystal; Furniture

Progress in the application of ATR-FTIR microscopy to the study of multi-layered cross-sections from works of art by Adriana Rizzo (pp. 47-55).

Keywords: ATR-FTIR microscopy; Cross-sections; Paint analysis; Clear coatings; Germanium crystal; Furniture

Identification of proteins in painting cross-sections by immunofluorescence microscopy by M. Vagnini; L. Pitzurra; L. Cartechini; C. Miliani; B. G. Brunetti; A. Sgamellotti (pp. 57-64).

Immunofluorescence microscopy offers a highly specific analytical tool for unambiguous recognition and mapping of proteins in complex matrices. In the present work, the analytical potentials of immunofluorescence microscopy have been exploited to provide recognition of proteinaceous binders in painting cross-sections. An optimised analytical protocol is proposed for the identification of ovalbumin and of bovine serum albumin as markers of egg white and casein, respectively. The study has been carried out on laboratory model samples simulating both easel and mural paintings. The obtained results demonstrated the effectiveness of the method, suggesting the potential future use of immunofluorescence microscopy as a routine diagnostic tool in conservation science. Possible developments of the proposed methodology in order to improve the specificity of the method and its detection sensitivity are presented and discussed. Figure IFM image of a milk tempera painting layer stained with the α-BSA MAb (500×)

Keywords: Immunofluorescence microscopy; Proteinaceous binder; Painting cross-section

Identification of proteins in painting cross-sections by immunofluorescence microscopy by M. Vagnini; L. Pitzurra; L. Cartechini; C. Miliani; B. G. Brunetti; A. Sgamellotti (pp. 57-64).

Keywords: Immunofluorescence microscopy; Proteinaceous binder; Painting cross-section

Attenuated total reflection micro FTIR characterisation of pigment–binder interaction in reconstructed paint films by R. Mazzeo; S. Prati; M. Quaranta; E. Joseph; E. Kendix; M. Galeotti (pp. 65-76).

The interaction of pigments and binding media may result in the production of metal soaps on the surface of paintings which modifies their visible appearance and state of conservation. To characterise more fully the metal soaps found on paintings, several historically accurate oil and egg yolk tempera paint reconstructions made with different pigments and naturally aged for 10 years were submitted to attenuated total reflectance Fourier transform infrared (ATR FTIR) microspectroscopic analyses. Standard metal palmitates were synthesised and their ATR spectra recorded in order to help the identification of metal soaps. Among the different lead-based pigments, red lead and litharge seemed to produce a larger amount of carboxylates compared with lead white, Naples yellow and lead tin yellow paints. Oil and egg tempera litharge and red lead paints appeared to be degraded into lead carbonate, a phenomenon which has been observed for the first time. The formation of metal soaps was confirmed on both oil and egg tempera paints based on zinc, manganese and copper and in particular on azurite paints. ATR mapping analyses showed how the areas where copper carboxylates were present coincided with those in which azurite was converted into malachite. Furthermore, the key role played by manganese in the production of metals soaps on burnt and raw sienna and burnt and raw umber paints has been observed for the first time. The formation of copper, lead, manganese, cadmium and zinc metal soaps was also identified on egg tempera paint reconstructions even though, in this case, the overlapping of the spectral region of the amide II band with that of metal carboxylates made their identification difficult. Figure FTIR false colour plot of the azurite distribution on a selected area of the azurite oil paint reconstruction

Keywords: Metal soaps; Binding media; Oil binder; Egg tempera binder; Micro ATR FTIR; Paintings

Stratigraphic analysis of organic materials in wall painting samples using micro-FTIR attenuated total reflectance and a novel sample preparation technique by Charlotte Martin de Fonjaudran; Austin Nevin; Francesca Piqué; Sharon Cather (pp. 77-86).

Wall paintings typically contain low concentrations of organic materials within a largely inorganic matrix and are characterised by their high porosity and long-term exposure to severe environmental conditions. The identification of organic materials within specific paint or plaster layers is challenging and the inherent characteristics of wall painting samples present further complications. Embedding materials (such as epoxy, polyester and acrylic-based resins) used to produce cross-sections often infiltrate porous and leanly bound samples, and compromise the interpretation of Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectra and the qualitative identification of natural organic materials. An alternative method for the preparation of cross-sections of wall painting samples was developed using cyclododecane (C₁₂H₂₄) as a temporary consolidant and barrier coating to encapsulate the sample, and to provide necessary support to produce a cross-section through microtoming. Impacts of traditional and novel sample preparation techniques on the identification of organic materials with micro-FTIR-ATR were examined for both replica and real wall painting samples.

Keywords: FTIR-ATR; Wall paintings; Cross-sections; Organic materials; Sample preparation; Cyclododecane

Development of a multipurpose ion source for LC-MS and GC-API MS by Ralf Schiewek; Matthias Lorenz; Ronald Giese; Klaus Brockmann; Thorsten Benter; Siegmar Gäb; Oliver J. Schmitz (pp. 87-96).

Over the past decade, multimode ion sources operating at atmospheric pressure (i.e., more than one ionization method is operative in the ion source enclosure) have received considerable interest. Simultaneous operation of different ionization methods targeting different compound classes within one analysis run has several advantages, including enhanced sample throughput and thus significant laboratory cost reductions. Potential drawbacks are enhanced ion suppression and other undesirable effects of the simultaneous operation of ionization methods. In this contribution we present an alternative approach—the development and characterization of a widely applicable, multipurpose ion source operating at atmospheric pressure. The optimized source geometry allows rapid changing from LC-API methods (ESI, APCI, APLI) to GC-API methods (APCI, APLI, DA-APLI) along with the appropriate coupling of chromatographic equipment required. In addition, true multimode operation of the source is demonstrated for LC-ESI/APLI and LC-APCI/APLI.

Keywords: APLI; APCI; Photoionization; Mass spectrometry; Multimode ion source

Development of a multipurpose ion source for LC-MS and GC-API MS by Ralf Schiewek; Matthias Lorenz; Ronald Giese; Klaus Brockmann; Thorsten Benter; Siegmar Gäb; Oliver J. Schmitz (pp. 87-96).

Keywords: APLI; APCI; Photoionization; Mass spectrometry; Multimode ion source

Modelling of adsorption kinetics and calibration curves of gaseous volatile organic compounds with adsorptive solid-phase microextraction fibre: toluene and acetone for indoor air applications by Pierre Mocho; Jérôme Nicolle; Valérie Desauziers (pp. 97-104).

Solid-phase microextraction (SPME) with adsorptive Carboxen/PDMS fibre is a powerful sampling device for volatile organic compounds (VOCs) at trace levels in air. However, owing to competitive adsorption, quantification remains a challenging task. In this area, a theoretical model, based on Fick’s laws and an extended Langmuir equation, is proposed to deal with the adsorption kinetics of acetone/toluene mixture on SPME fibre under various static extraction conditions. The semipredictive model is first used to determine the axial diffusion coefficients of analytes in the sampling device. The model is then tested with a complex VOC mixture, showing good agreement with experimental data.

Keywords: Indoor air; Volatile organic compounds; Solid-phase microextraction; Polydimethylsiloxane /Carboxen; Adsorption modelling; Prediction of calibration curves

Headspace sampling and detection of cocaine, MDMA, and marijuana via volatile markers in the presence of potential interferences by solid phase microextraction–ion mobility spectrometry (SPME-IMS) by Hanh Lai; Inge Corbin; José R. Almirall (pp. 105-113).

The successful air sampling and detection of cocaine, methylenedioxymethylamphetamine (MDMA), and marijuana using SPME-IMS achieved by targeting their volatile markers (methyl benzoate, piperonal, and terpenes, respectively) is presented. Conventional methods of direct air sampling for drugs are ineffective because the parent compounds of these drugs have very low vapor pressures, making them unavailable for headspace sampling. Instead of targeting the parent drugs, IMS was set at the optimal operating conditions (determined in previous work) in order to detect their volatile chemical markers. SPME is an effective and rapid air sampling technique for the preconcentration of analytes which is especially useful in confined spaces such as cargo containers, where the volatile marker compounds of drugs can be found in sufficient concentrations. By sampling the air using a 100 μm polydimethyl siloxane (PDMS) SPME fiber for as little as one minute, enough mass of the targeted volatile markers in the headspace of a quart-sized metal paint can (gallon, ∼1101 cm³) which contained sub-gram quantities of the drug samples was recovered for IMS detection. Additionally, several potentially interfering compounds found in goods commonly shipped in cargo containers were tested individually as well as in mixtures with the drugs. No peak interferences were observed for MDMA or marijuana, and minimal peak interferences were found for cocaine. Figure a Overlay spectrum of a five-minute SPME headspace extraction of cocaine HCl, methyl benzoate standard and a blank fiber. b Overlay spectrum of a 30-minute SPME headspace extraction of MDMA tablets, piperonal standard and a blank fiber. c Overlay spectrum of a ten-minute SPME headspace extraction of marijuana and a blank fiber

Keywords: Illicit drugs; Cocaine; MDMA; Marijuana; Solid phase microextraction; Ion mobility spectrometry

Development and validation of a solid-phase extraction gas chromatography–mass spectrometry method for the simultaneous quantification of methadone, heroin, cocaine and metabolites in sweat by Bertrand R. Brunet; Allan J. Barnes; Karl B. Scheidweiler; Patrick Mura; Marilyn A. Huestis (pp. 115-127).

A sensitive and specific method is presented to simultaneously quantify methadone, heroin, cocaine and metabolites in sweat. Drugs were eluted from sweat patches with sodium acetate buffer, followed by SPE and quantification by GC/MS with electron impact ionization and selected ion monitoring. Daily calibration for anhydroecgonine methyl ester, ecgonine methyl ester, cocaine, benzoylecgonine (BE), codeine, morphine, 6-acetylcodeine, 6-acetylmorphine (6AM), heroin (5–1000 ng/patch) and methadone (10–1000 ng/patch) achieved determination coefficients of >0.995, and calibrators quantified to within ±20% of the target concentrations. Extended calibration curves (1000–10,000 ng/patch) were constructed for methadone, cocaine, BE and 6AM by modifying injection techniques. Within (N = 5) and between-run (N = 20) imprecisions were calculated at six control levels across the dynamic ranges with coefficients of variation of <6.5%. Accuracies at these concentrations were ±11.9% of target. Heroin hydrolysis during specimen processing was <11%. This novel assay offers effective monitoring of drug exposure during drug treatment, workplace and criminal justice monitoring programs.

Keywords: Sweat; GC/MS; Methadone; Cocaine; Opiates; Heroin

FT-IR spectral imaging of blood vessels reveals protein secondary structure deviations induced by tumor growth by Katia Wehbe; Raphael Pinneau; Michel Moenner; Gérard Déléris; Cyril Petibois (pp. 129-135).

Vascular basement membrane remodeling is involved in tumor angiogenesis to enable tumor invasion and growth. FT-IR spectral imaging was used to determine changes in tumor blood vessels to reveal protein secondary structure in Rag-gamma immuno-deficient mice sacrificed 14 and 21 days after subcutaneous glioma implantation. For the oldest blood capillaries (diameter >20 microns), tumor growth induced a decrease in triple-helix content (1638 cm⁻¹; −7.3%; P < 0.05) and an increase in beta turns (1666 and 1615 cm⁻¹; +4%; P < 0.01). These protein-structure alterations, mainly from type IV collagen, reflected the high angiogenic stress of growing tumors. We propose to use these molecular markers of vascular basement membrane protein alterations for gradation of solid tumors by FT-IR spectral imaging. Figure From spectral curve fitting to tumor signature by blood capillaries FT-IR imaging was used to analyze vascular basement membrane protein contents changes along tumor growth. Changes in protein secondary structure (decrease in triple helix and increase in β-turns contents) revealed the high angiogenic stress of growing tumors. These structural changes might be used as molecular markers for a functional FT-IR imaging of tumor growth. FT-IR imaging of a tumor blood capillary. Spectral curve-fitting of pixels corresponding to vascular basement membrane of the capillary is used to determine secondary structure of protein contents.

Keywords: FT-IR spectral imaging; Cancer; Angiogenesis; Basement membrane proteins

Human lymphocyte sorting by gravitational field-flow fractionation by Barbara Roda; Pierluigi Reschiglian; Andrea Zattoni; Pier Luigi Tazzari; Marina Buzzi; Francesca Ricci; Andrea Bontadini (pp. 137-145).

Interest in biological studies on various cell types for many biomedical applications, from research to patient treatments, is constantly increasing. The ability to discriminate (sort) and/or quantify distinct subpopulations of cells has become increasingly important. For instance, not only detection but also the highest depletion of neoplastic cells from normal cells is an important requisite in the autologous transplantation of lymphocytes for blood cancer treatments. In this work, gravitational field-flow fractionation (GrFFF) is shown to be effective for sorting a heterogeneous mixture of human, living lymphocytes constituted of neoplastic B cells from a Burkitt lymphoma cell line and healthy T and B lymphocytes from blood samples. GrFFF does not require the use of fluorescent immunotags for sorting cells, and the sorted cells can be collected for their further characterization. Flow cytometry was used to assess the viability of the cells collected, and to evaluate the cell fractionation achieved. A low amount of neoplastic B lymphocytes (less than 2%) was found in a specific fraction obtained by GrFFF. The high depletion from neoplastic cells (more than 98%) was confirmed by a clonogenicity test.

Keywords: Gravitational field-flow fractionation; Cell sorting; Lymphocytes

Identification of free phosphopeptides in different biological fluids by a mass spectrometry approach by Claudia Cirulli; Giovanni Chiappetta; Gennaro Marino; Pierluigi Mauri; Angela Amoresano (pp. 147-159).

Human body fluids have been rediscovered in the post-genomic era as a great source of biological markers and perhaps as source of potential biomarkers of disease. Recently, it has been found that not only proteins but also peptides and their modifications can be indicators of early pathogenic processes. This paper reports the identification of free phosphopeptides in human fluids using an improved IMAC strategy coupled to iterative mass spectrometry-based scanning techniques (neutral loss, precursor ion, multiple reaction monitoring). Many peptides were detected in the enriched extract samples when submitted to the MS-integrated strategy, whereas they were not detected in the initial extract samples. The combination of the IMAC-modified protocol with selective “precursor ion” and constant “neutral loss” triple quadrupole scan modes confers a high sensitivity on the analysis, allowing rapid phosphopeptide identification and characterization, even at low concentrations. To the best of our knowledge this work represents the first report exclusively focused on the detection of free phosphorylated peptides in biological fluids.

Keywords: Free peptide; Phosphorylation; Linear ion trap; Precursor ion; Neutral loss

Agglomeration of proteins in acoustically levitated droplets by Friedmar Delißen; Jork Leiterer; Ralf Bienert; Franziska Emmerling; Andreas F. Thünemann (pp. 161-165).

An ultrasonic trap (acoustic levitator) was used as an analytical tool to allow container-free handling of proteins in small sample volumes. This trap was combined for the first time with synchrotron small-angle X-ray scattering (SAXS) for structure analysis of biological macromolecules in a solution. The microfocus beamline at BESSY was used as a source of intense X-ray radiation. Apoferritin (APO) was used as a model protein, and its aggregation behavior in a levitator was followed from a diluted solution to the solid state. Different stages of APO agglomeration were observed without solid container walls, which may influence aggregation behavior and produce a parasitic scattering background. Starting with a volume of 5 μL we analyzed the concentration dependence of APO structure factors in the range from 5 to 1,200 mg/mL (solid protein). The solution was stirred automatically due to convection inside the droplet caused by the ultrasonic field. SAXS data recording of APO was performed in time intervals of 60 s during an aggregation experiment of 30 to 60 min.

Keywords: Diffraction methods; Nanoparticles; Nanotechnology; Sampling; Agglomeration; Acoustic levitation; Apoferritin

Agglomeration of proteins in acoustically levitated droplets by Friedmar Delißen; Jork Leiterer; Ralf Bienert; Franziska Emmerling; Andreas F. Thünemann (pp. 161-165).

Keywords: Diffraction methods; Nanoparticles; Nanotechnology; Sampling; Agglomeration; Acoustic levitation; Apoferritin

Quantitative evaluation of oligonucleotide surface concentrations using polymerization-based amplification by Ryan R. Hansen; Heather J. Avens; Raveesh Shenoy; Christopher N. Bowman (pp. 167-175).

Quantitative evaluation of minimal polynucleotide concentrations has become a critical analysis among a myriad of applications found in molecular diagnostic technology. Development of high-throughput, nonenzymatic assays that are sensitive, quantitative and yet feasible for point-of-care testing are thus beneficial for routine implementation. Here, we develop a nonenzymatic method for quantifying surface concentrations of labeled DNA targets by coupling regulated amounts of polymer growth to complementary biomolecular binding on array-based biochips. Polymer film thickness measurements in the 20–220 nm range vary logarithmically with labeled DNA surface concentrations over two orders of magnitude with a lower limit of quantitation at 60 molecules/μm² (∼10⁶ target molecules). In an effort to develop this amplification method towards compatibility with fluorescence-based methods of characterization, incorporation of fluorescent nanoparticles into the polymer films is also evaluated. The resulting gains in fluorescent signal enable quantification using detection instrumentation amenable to point-of-care settings. Figure Polymerization-based amplification for quantitative evaluation of 3’ biotinylated oligonucleotide surface concentrations

Keywords: Signal amplification; Molecular diagnostics; Quantitative nucleic acid detection; DNA microarrays; Visible light photopolymerization; Surface-initiated polymerization

Quantitative evaluation of oligonucleotide surface concentrations using polymerization-based amplification by Ryan R. Hansen; Heather J. Avens; Raveesh Shenoy; Christopher N. Bowman (pp. 167-175).

Keywords: Signal amplification; Molecular diagnostics; Quantitative nucleic acid detection; DNA microarrays; Visible light photopolymerization; Surface-initiated polymerization

Molecularly imprinted polymers: modulating molecular recognition by a thermal phase transition in the binding framework by Songjun Li; Xing Huang; Mingxia Zheng; Wuke Li (pp. 177-185).

The concept used to realize the modulation of molecular recognition in a molecularly imprinted polymer is presented. Creating a thermal phase transition within the binding framework, the imprinted material was prepared using Boc-phenylalanine as the template and pNIPAM as the sensitive unit. The results indicate that such a transition causes a clear modulation in the recognition behavior of the prepared polymer which depends on the operation temperature. At a relatively low temperature, the prepared polymer acts like a traditionally imprinted one, showing a highly specific recognition for the imprint species. However, the prepared polymer does not present any notable resolution at 40 °C. This recognition behavior is comparable to a process that can be switched on and off, thus making modulated recognition feasible. Figure A unique molecularly imprinted polymer capable of showing on/off-switchable behavior was prepared. At a relatively low temperature, the prepared polymer acts like a traditionally imprinted one, showing a highly specific recognition for the imprint species. However, the prepared polymer presents no notable resolution at 40 °C

Keywords: Molecular imprinting; Polymers; Molecular recognition; Modulation

Molecularly imprinted polymers: modulating molecular recognition by a thermal phase transition in the binding framework by Songjun Li; Xing Huang; Mingxia Zheng; Wuke Li (pp. 177-185).

Keywords: Molecular imprinting; Polymers; Molecular recognition; Modulation

Immunoassay using surface-enhanced Raman scattering based on aggregation of reporter-labeled immunogold nanoparticles by Ji-Wei Chen; Yong Lei; Xiang-Jiang Liu; Jian-Hui Jiang; Guo-Li Shen; Ru-Qin Yu (pp. 187-193).

A one-step homogenous sensitive immunoassay using surface-enhanced Raman scattering (SERS) has been developed. This strategy is based on the aggregation of Raman reporter-labeled immunogold nanoparticles induced by the immunoreaction with corresponding antigens. The aggregation of gold nanoparticles results in a SERS signal increase of the Raman reporter. Therefore, human IgG could be directly determined by measuring the Raman signal of the reporter. The process of aggregation was investigated by transmission electron microscopy (TEM) and UV–Vis absorption spectroscopy. The effects of the temperature, time, and size of gold nanoparticles on the sensitivity of the assay were examined. Using human IgG as a model protein, a wide linear dynamic range (0.1–15 μg mL⁻¹) was reached with low detection limit (0.1 μg mL⁻¹) under optimized assay conditions. The successful test suggests that the application of the proposed method holds promising potential for simple, fast detection of proteins in the fields of molecular biology and clinical diagnostics.

Keywords: Immunoassay; Surface-enhanced Raman scattering; Aggregation; Gold nanoparticles; Human IgG

Boronic acid lectin affinity chromatography (BLAC). 2. Affinity micropartitioning-mediated comparative glycosylation profiling by Alex Monzo; Marcell Olajos; Lorenzo De Benedictis; Zuly Rivera; Guenther K. Bonn; András Guttman (pp. 195-201).

As a continuation of our work on boronic acid lectin affinity chromatography (BLAC), in this paper we introduce an automated affinity micropartitioning approach using combined boronic acid and concanavalin A (BLAC/Con A) resin-filled micropipette tips to isolate and enrich human serum glycoproteins. The N-linked oligosaccharides of the partitioned glycoproteins were removed by PNGase F enzyme digestion, followed by 8-aminopyrene-1,3,6-trisulfonic acid labeling. Capillary gel electrophoresis with blue LED-induced fluorescence detection was applied in a multiplexed format for comparative glycan profiling. The efficiency of BLAC affinity micropartitioning was compared with that of the individual lectin and pseudolectin affinity enrichment. Finally, we report on our findings in glycosylation differences in human serum samples from healthy and prostate cancer patients by applying BLAC/Con A micropipette tip-based enrichment and comparative multicapillary gel electrophoresis analysis of the released and labeled glycans. Figure Fluorophore labeling and purification in BLAC–mCE based glycosylation profiling

Keywords: Affinity chromatography; Capillary gel electrophoresis; Glycan profiling

Conductive polymer as a controlled microenvironment for the potentiometric high-throughput evaluation of ionic liquid cell toxicity by Weilian Qiu; Xiangqun Zeng (pp. 203-213).

This paper presents both biological and potentiometric evaluations of the cell toxicity of a widely used ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF₄), to Chinese hamster lung fibroblast cells (V79 cell line). The innovative potentiometric study takes advantage of the unique properties of conductive polymer polypyrrole (PPY) for the potentiometric evaluation of cell toxicity of [bmim]BF₄ to the V79 cells in a real-time, noninvasive and high-throughput manner. The conductive polymer PPY provides a controlled microenvironment that allows the quantitative release of the anions of the ionic liquids into the cells being monitored in real time and noninvasively. Parallel biological assay results showed that V79 cells exposed to [bmim]BF₄ usually grew in clusters, and that many small vacuoles could be seen in the cytoplasm. At the 24th hour after the V79 cells had been exposed to the ionic liquid (IL), the half inhibition concentration (EC₅₀) of [bmim]BF₄ was around 5 mM. From a cell cycle study performed using a FACScan flow cytometer, it was found that the V79 cells could be partially locked to the G₁ phase by [bmim]BF₄, which extended the doubling time for cell growth. Comparing with the EC₅₀ values of cadmium chloride and mercury chloride, [bmim]BF₄ is not very toxic, but it may have a long-term toxic effect on mammalian cells. Compared to traditional biological in vitro assays, the use of a conductive polymer substrate in combination with a potentiometric sensor array is much more sensitive, faster, and enables a simpler evaluation of chemical cell toxicity. Additionally, it simplifies the study of the reversibility of cell toxicity, i.e., cell recovery, because there is no need to refresh the culture medium since a finite amount of chemicals can be doped and released. We found that the cytotoxicity of [bmim]BF₄ at a concentration of less than 6 mM was reversible for the V79 cell line, because cell morphology and proliferation rate returned to normal after the removal of the IL from the culture medium. This finding suggests that the IL [bmim]BF₄ could be used as a tool to control mammalian cell proliferation rate.

Keywords: Conductive polymer; Polypyrrole; Ionic liquid; V79 cell; Cytotoxicity; Potentiometry

Conductive polymer as a controlled microenvironment for the potentiometric high-throughput evaluation of ionic liquid cell toxicity by Weilian Qiu; Xiangqun Zeng (pp. 203-213).

Keywords: Conductive polymer; Polypyrrole; Ionic liquid; V79 cell; Cytotoxicity; Potentiometry

Group-selective antibodies based fluorescence immunoassay for monitoring opiate drugs by Sonu Gandhi; Prince Sharma; Neena Capalash; R. S. Verma; C. Raman Suri (pp. 215-222).

A novel carboxylic acid derivative of monoacetylmorphine (MAM–COOH) was synthesized and conjugated with bovine serum albumin (BSA) for generating polyclonal antibodies against the target molecule heroin and its major metabolites. The conjugate was characterized by fluorescence spectroscopy, polyacrylamide gel electrophoresis, and mass spectrometry to confirm the extent of haptenization of the carrier protein. A high titer (1:64,0000) of antibody was obtained by using the conjugate with an optimum protein/hapten molar ratio of 1:100. The generated antibody showed good binding affinity with heroin and its metabolites monoacetylmorphine (MAM) and morphine. The relative affinity constant (K _aff) of the antibody was 3.1 × 10⁷ l mol⁻¹, and the IC₅₀ values obtained for heroin, MAM, morphine, and codeine were 0.01, 0.013, 0.012, and 0.014 ng ml⁻¹, respectively. A fluorescence-based competitive inhibition immunoassay procedure was developed for the estimation of heroin and its major metabolites in standard and biofludic samples over a concentration range up to 0.01 ng ml⁻¹ with good signal reproducibility (p < 0.05). The method can be used as a convenient quantitative tool for the sensitive screening of major metabolites of heroin in biological samples. Figure Schematic representation of the competitive fluorescence inhibition immunoassay developed for the highly sensitive detection of opiates

Keywords: Heroin and metabolites; Antibodies; Group-selective; Fluorescence immunoassay

Group-selective antibodies based fluorescence immunoassay for monitoring opiate drugs by Sonu Gandhi; Prince Sharma; Neena Capalash; R. S. Verma; C. Raman Suri (pp. 215-222).

Keywords: Heroin and metabolites; Antibodies; Group-selective; Fluorescence immunoassay

Molecularly imprinted polymers for the selective solid-phase extraction of chloramphenicol by Christina Schirmer; Hans Meisel (pp. 223-229).

A variety of bulk polymers for the selective separation of chloramphenicol were synthesised from 2-vinylpyridine, diethylaminoethyl methacrylate or methacrylic acid monomers. Chromatographic evaluation indicated that chloramphenicol was retained under nonpolar elution conditions (k = 58.65) through selective hydrogen bonding and ionic interactions. The retention of chloramphenicol under aqueous elution conditions (k > 100) results from nonselective hydrophobic interactions. Under nonpolar elution conditions, the functional monomer employed imparted a significant influence on the recognition properties of the corresponding polymer. After solid-phase extraction using a molecularly imprinted polymer as sorbent and either an organic or aqueous washing solvent, nearly 100% recovery from the chloramphenicol standard solution was achieved, and nearly 90% recovery could be attained from spiked honey samples. The molecularly imprinted polymer was well suited to suppress matrix effects, and provided optimal preconcentration of the target molecule (chloramphenicol) prior to chromatographic analysis.

Keywords: Molecular imprinting; Solid-phase extraction; Liquid chromatography; Chloramphenicol; Honey

Molecularly imprinted polymers for the selective solid-phase extraction of chloramphenicol by Christina Schirmer; Hans Meisel (pp. 223-229).

Keywords: Molecular imprinting; Solid-phase extraction; Liquid chromatography; Chloramphenicol; Honey

Rapid and sensitive determination of phosphoamino acids in phosvitin by N-hydroxysuccinimidyl fluorescein-O-acetate derivatization and capillary zone electrophoresis with laser-induced fluorescence detection by Ying-Hua Deng; Hua-Shan Zhang; Hong Wang (pp. 231-238).

A method was developed for the determination of phosphoamino acids by capillary zone electrophoresis–laser-induced fluorescence detection (argon ion laser, excitation at 488 nm and emission at 520 nm) using derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA). Different variables affecting the derivatization (SIFA concentration, derivatization pH, reaction temperature and reaction time) and the separation (type, pH and concentration of buffer, applied voltage and injection mode) were investigated in detail. The optimized separation conditions were 40 mM boric acid buffer (pH 9.2) for background electrolyte, 25 kV for the separation voltage, 25 °C for the capillary temperature and 5 s at 0.5 psi for the sample injection. Under the optimal conditions, the SIFA-labeled phosphoamino acids were fully separated within 7 min. The detection limits ranged from 0.1 to 0.3 nM, which are the lowest values reported for capillary electrophoresis (CE) methods. The proposed methodology allowed the rapid, sensitive and selective determination of phosphoamino acids in hen egg yolk phosvitin by the standard addition method. The recovery of these compounds in real sample was 94.0–103.5%. The developed method surpasses previously published CE methods in terms of detection limit, separation time, stability and simplicity of the electrophoretic procedure.

Keywords: Capillary zone electrophoresis; Derivatization; Laser-induced fluorescence detection; N-hydroxysuccinimidyl fluorescein-O-acetate; Phosphoamino acids

Stabilization of thin-layer agarose gels after isoelectric focusing with polyacrylamide enables reverse imidazole-zinc staining and facilitates two-dimensional gel electrophoresis by Jukka Hellman (pp. 239-245).

Large-pore-size agarose gels provide excellent resolving capacity for high molecular weight biomolecules. Thin-layer agarose isoelectric focusing (IEF) gels on polyester support films are especially useful for the separation of large proteins based on their pI in native conformation, but the method has suffered from the lack of detection methods compatible with agarose gels in hydrated form. Recently, an acrylamide copolymerization method was reported to enable mass-spectrometry-compatible silver staining and in-gel digestion of proteins. In this study, the method was further applied by demonstrating successful reverse imidazole-zinc staining of thin-layer agarose IEF gels copolymerized with acrylamide. The sensitivity of the reverse staining method on the composite gel at its best equaled the sensitivity of the traditional dried agarose silver staining method. Owing to the increased durability and reversible detection, the reverse-stained first-dimension gel could be conveniently prepared for the second-dimension sodium dodecyl sulfate polyacrylamide gel electrophoresis by reduction and alkylation. In addition, the micropreparative generation of tryptic peptides of Coomassie brilliant blue R-250 stained proteins in the composite gel is demonstrated.

Keywords: Agarose isoelectric focusing; GelBond; Imidazole-zinc reverse staining; Two-dimensional electrophoresis; Immune complex

Square-wave anodic-stripping voltammetric determination of Cd, Pb, and Cu in a hydrofluoric acid solution of siliceous spicules of marine sponges (from the Ligurian Sea, Italy, and the Ross Sea, Antarctica) by C. Truzzi; A. Annibaldi; S. Illuminati; E. Bassotti; G. Scarponi (pp. 247-262).

Square-wave anodic-stripping voltammetry (SWASV) was set up and optimized for simultaneous determination of cadmium, lead, and copper in siliceous spicules of marine sponges, directly in the hydrofluoric acid solution (∼0.55 mol L⁻¹ HF, pH ∼1.9). A thin mercury-film electrode (TMFE) plated on to an HF-resistant epoxy-impregnated graphite rotating-disc support was used. The optimum experimental conditions, evaluated also in terms of the signal-to-noise ratio, were as follows: deposition potential −1100 mV vs. Ag/AgCl, KCl 3 mol L⁻¹, deposition time 3–10 min, electrode rotation 3000 rpm, SW scan from −1100 mV to +100 mV, SW pulse amplitude 25 mV, frequency 100 Hz, ΔE _step 8 mV, t _step 100 ms, t _wait 60 ms, t _delay 2 ms, t _meas 3 ms. Under these conditions the metal peak potentials were Cd −654 ± 1 mV, Pb −458 ± 1 mV, Cu −198 ± 1 mV. The electrochemical behaviour was reversible for Pb, quasi-reversible for Cd, and kinetically controlled (possibly following chemical reaction) for Cu. The linearity of the response with concentration was verified up to ∼4 μg L⁻¹ for Cd and Pb and ∼20 μg L⁻¹ for Cu. The detection limits were 5.8 ng L⁻¹, 3.6 ng L⁻¹, and 4.3 ng L⁻¹ for Cd, Pb, and Cu, respectively, with t _d = 5 min. The method was applied for determination of the metals in spicules of two specimens of marine sponges (Demosponges) from the Portofino natural reserve (Ligurian Sea, Italy, Petrosia ficiformis) and Terra Nova Bay (Ross Sea, Antarctica, Sphaerotylus antarcticus). The metal contents varied from tens of ng g⁻¹ to ∼1 μg g⁻¹, depending on the metal considered and with significant differences between the two sponge species. Marine sponges Petrosia ficiformis and Sphaerotylus antarcticus analysed by voltammetry (Photos Carlo Cerrano)

Keywords: SWASV; Hydrofluoric acid; Heavy metals; Spicules; Marine sponges; Antarctica

Micro-Raman spectroscopic investigation of external wall paintings from St. Dumitru’s Church, Suceava, Romania by A. Hernanz; I. Bratu; O. F. Marutoiu; C. Marutoiu; J. M. Gavira-Vallejo; H. G. M. Edwards (pp. 263-268).

The external sixteenth century wall paintings of St. Dumitru’s Church in Suceava (Romania) are suffering visually from deterioration. Fragments of these paintings spallated from the external wall have been studied by micro-Raman microscopy in order to elucidate possible causes of this process. Calcite and α-quartz are the components of the substratum indicating that the artists used the Roman fresco technique comprising a limewash putty. No organic binders have been detected in the substrate or pigment application. Amorphous carbon and goethite, α-FeOOH, have been identified in areas containing residues of grey and yellow pigments, respectively. Small amounts of gypsum have been detected in the grey areas which we attribute to special attention being given to surface preparation and pigment application in these areas. An abundance of sodium nitrate, nitratine, microcrystals have been observed on the surfaces of many fragments which suggests that a biodeterioration process originating from guano deposits could have been operating in these frescoes.

Keywords: Raman microscopy; Fresco; Pigments; Biodeterioration; Guano

Analytical speciation of chromium in in-vitro cultures of chromate-resistant filamentous fungi by Francisco Javier Acevedo Aguilar; Kazimierz Wrobel; Kirk Lokits; Joseph A. Caruso; Alejandro Coreño Alonso; J. Felix Gutiérrez Corona; Katarzyna Wrobel (pp. 269-276).

In this work, different analytical speciation schemes have been used to study the reduction of Cr(VI) by a chromate-resistant strain of filamentous fungi Ed8 (Aspergillus sp), indigenous to contaminated industrial wastes. As demonstrated previously, this strain has the capability to reduce chromate present in the growth medium without its accumulation in the biomass, yet the reduced chromium end-products have not been characterized. Liquid growth medium, initially containing 50 mg L⁻¹ Cr(VI), was analyzed for Cr(III)/Cr(VI) and for total Cr at different time intervals (0–24 h) after inoculation with fungi. Three hyphenated procedures, based on the Cr(III)–EDTA formation and species separation by anion-exchange or ion-pairing reversed-phase chromatography with ICP–MS or DAD detection were used. The results obtained for Cr(VI) in each case were consistent, demonstrating efficient reduction of chromate during 24 h of Ed8 growth. However, pre-column complexation with EDTA did not ensure complete recovery of the reduced forms of chromium in the above procedures. An alternative speciation scheme, based on extraction of Cr(VI)–benzyltributylammonium bromide (BTAB) ion pairs into chloroform and subsequent determination of residual chromium by ICP–MS has provided evidence on the effective conversion of chromate into reduced chromium species in the growth medium. The results indicate the feasibility of using Ed8 strain for chromate bioremediation purposes. Analytically it can be concluded that speciation of chromium in biological systems should not be limited to its two most common oxidation states, because the actual reduced chromium species are not converted quantitatively to Cr(III)–EDTA.

Keywords: Chromium; Chromate-resistant fungi; Analytical speciation; ICP–MS

Determination of lead and cadmium in seawater by differential pulse anodic stripping voltammetry: fit-for-purpose partial validation and internal quality aspects by K. Bisetty; N. J. Gumede; L. Escuder-Gilabert; S. Sagrado (pp. 277-286).

The main thrust of this work involves method validation, quality control and sample uncertainty estimations related to the determination of cadmium and lead in marine water by anodic stripping voltammetry. We have followed a step-by-step protocol to evaluate and harmonize the internal quality aspects of this method. Such protocol involves a statement of the method’s scope (analytes, matrices, concentration level) and requisites (external and/or internal); selection of the method’s (fit-for-purpose) features; prevalidation and validation of the intermediate accuracy (under intermediate precision conditions) and its assessment (by Monte Carlo simulation); validation of other required features of the method (if applicable); and a validity statement in terms of a “fit-for-purpose” decision, harmonized validation–control–uncertainty statistics (the “u-approach”) and short-term routine work (with the aim of proposing virtually “ready-to-use” methods).

Keywords: Heavy metals; Seawater; Voltammetry; Internal quality; Fit-for-purpose validation; Quality control; Uncertainty; Accuracy assessment

Ion exchange separation of strontium and rubidium on Dowex 50W-X8, using the complexation properties of EDTA and DCTA by C. Vorster; T. N. van der Walt; P. P. Coetzee (pp. 287-296).

A chromatographic method for separation of strontium from rubidium, using the unique alkaline-earth metal complexation ability of the carboxylic acids EDTA and DCTA is proposed. The method was developed in order to improve the effectiveness of ⁸⁷Sr/⁸⁶Sr isotope studies with ICP–QMS. Due to the isobaric overlap of ⁸⁷Rb with ⁸⁷Sr, strontium needs to be separated from rubidium prior to sample analysis with ICP–QMS. The method involves the retention of strontium, calcium, magnesium, and rubidium on Dowex 50W-X8 resin in its NH₄ ⁺ form, followed by elution of the divalent cations as metal EDTA or DCTA complexes. Because divalent cations have different EDTA and DCTA complex formation constants, it is possible to separate them under the correct conditions. Neither EDTA nor DCTA form complexes with alkali metals, thus rubidium remains retained by the column and is later eluted using HNO₃. Both EDTA and DCTA elution methods were tested with different concentrations of the elements to determine the effect of increased concentration on separation efficiency. The EDTA elution procedure was proved to be effective in separating strontium from both calcium and rubidium, while the DCTA method was found to be even more effective, because strontium is separated from all the elements involved in this study.

Keywords: Ion exchange separation; EDTA; DCTA; Sr separation; Rb separation

Ion exchange separation of strontium and rubidium on Dowex 50W-X8, using the complexation properties of EDTA and DCTA by C. Vorster; T. N. van der Walt; P. P. Coetzee (pp. 287-296).

Keywords: Ion exchange separation; EDTA; DCTA; Sr separation; Rb separation

Fabrication of an iodide-selective electrode based on phthalocyaninatotitanium(IV) oxide and the selective determination of iodide in actual samples by Wen-Ju Xu; Ruo Yuan; Ya-Qin Chai; Ting-Ting Zhang; Wen-Bin Liang; Xia Wu (pp. 297-303).

This work describes the development and fabrication of a selective polymeric membrane electrode for iodide ion based on a metallophthalocyanin complex with a titanium(IV) atom at the center (as an oxo–titanium, Ti=O, group), phthalocyaninatotitanium(IV) oxide (PcTiO), as a sensing carrier. The potential response characteristics of the electrode were investigated by changing the type of plasticizer as well as the amounts of the carrier and different lipophilic ionic site additives in the sensing membrane. It is shown that the membrane electrode incorporated with 2-nitrophenyl octyl ether as the plasticizer and hexadecyl trimethylammonium bromide as the appropriate cationic additive exhibits enhanced potential response toward iodide over other anions tested. Over the period of this study, the resulting electrode based on PcTiO displayed a stable near-Nernstian slope approaching -58.9 mV decade⁻¹ with a linear response spanning at least 5 orders of magnitude in concentration from 1.0 × 10⁻¹ to 9.2 × 10⁻⁷ mol L⁻¹ and a detection limit of 8.5–10⁻⁷ mol L⁻¹. The preferential potential response to iodide may be attributed to the unique recognition of carrier PcTiO in the organic membrane phase for iodide in solution. Under laboratory conditions, the present electrode also works well in partially nonaqueous media. The excellent analytical features of the proposed electrode could lead to its successful application in determining the end point in electrometric titration of iodide with Ag⁺ and the direct potential determination of iodide concentration in wastewater and drug preparations. Figure The UV-Vis spectra of phthalocyaninatotitanium(IV) oxide (PcTiO) in CHCI₃ before (dotted line) and after (solid line) treatment with NaI solution (pH 5.0). The preferential potential response of the PcTiO-based electrode to iodide may be attributed to the unique axial coordination between PcTiO and iodide

Keywords: Ion-selective electrode; Potential response; Phthalocyaninatotitanium(IV) oxide; Iodide; Sensing carrier

Chances and pitfalls of chemical cross-linking with amine-reactive N-hydroxysuccinimide esters by Stefan Kalkhof; Andrea Sinz (pp. 305-312).

Keywords: Chemical cross-linking; Amine-reactive cross-linkers; Mass spectrometry

Transferability study of a near-infrared microscopic method for the detection of banned meat and bone meal in feedingstuffs by Christoph von Holst; Vincent Baeten; Ana Boix; Boleslaw Slowikowski; Juan Antonio Fernández Pierna; Salvatore Tirendi; Pierre Dardenne (pp. 313-317).

Near-infrared microscopy (NIRM) has been proved to be a powerful tool for the detection of banned meat and bone meal (MBM) in feed. The identification of MBM traces and its ability to differentiate animal from vegetable feed ingredients is based on the evaluation of near-infrared spectra obtained from individual particles present in the sample. This evaluation is supported by appropriate decision rules for the absorbances at specific wavelengths. Here we show that the method and the corresponding decision rules can be successfully transferred from the laboratory which constructed the decision rules to two independent laboratories that were not involved in the calibration process of the method. The analytical results from blind feed samples containing MBM (positive samples) and feed samples without MBM (negative samples) revealed a very good agreement between the three laboratories, thus demonstrating the transferability of the method.

Keywords: Meat and bone meal; Feed ban; Near-infrared microscopy

Variation in the isotopic composition of zinc in the natural environment and the use of zinc isotopes in biogeosciences: a review by Christophe Cloquet; Jean Carignan; Moritz F. Lehmann; Frank Vanhaecke (pp. 319-319).

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Analytical and Bioanalytical Chemistry (v.392, #1-2)