Showing papers in "Analytical and Bioanalytical Chemistry in 2004"

A unified view of propagating and localized surface plasmon resonance biosensors

Abstract: The intense colors of noble metal nanoparticles have inspired artists and fascinated scientists for hundreds of years. In this review, we describe refractive index sensing platforms based on the tunability of the localized surface plasmon resonance (LSPR) of arrays of silver nanoparticles and of single nanoparticles. Specifically, the color associated with single nanoparticles and surface-confined nanoparticle arrays will be shown to be tunable and useful as platforms for chemical and biological sensing. Finally, the LSPR nanosensor will be compared to traditional, flat surface, propagating surface plasmon resonance sensors.

Cantilever-based biosensors

Abstract: This review provides a general introduction into the theory of cantilever sensors, including practical design concepts, examples for liquid-phase sensing with particular emphasis on biological applications, and a discussion of future prospects.

Compound-specific stable isotope analysis of organic contaminants in natural environments: a critical review of the state of the art, prospects, and future challenges

Abstract: Compound-specific stable isotope analysis (CSIA) using gas chromatography-isotope ratio mass spectrometry (GC/IRMS) has developed into a mature analytical method in many application areas over the last decade. This is in particular true for carbon isotope analysis, whereas measurements of the other elements amenable to CSIA (hydrogen, nitrogen, oxygen) are much less routine. In environmental sciences, successful applications to date include (i) the allocation of contaminant sources on a local, regional, and global scale, (ii) the identification and quantification of (bio)transformation reactions on scales ranging from batch experiments to contaminated field sites, and (iii) the characterization of elementary reaction mechanisms that govern product formation. These three application areas are discussed in detail. The investigated spectrum of compounds comprises mainly n-alkanes, monoaromatics such as benzene and toluene, methyl tert-butyl ether (MTBE), polycyclic aromatic hydrocarbons (PAHs), and chlorinated hydrocarbons such as tetrachloromethane, trichloroethylene, and polychlorinated biphenyls (PCBs). Future research directions are primarily set by the state of the art in analytical instrumentation and method development. Approaches to utilize HPLC separation in CSIA, the enhancement of sensitivity of CSIA to allow field investigations in the µg L−1 range, and the development of methods for CSIA of other elements are reviewed. Furthermore, an alternative scheme to evaluate isotope data is outlined that would enable estimates of position-specific kinetic isotope effects and, thus, allow one to extract mechanistic chemical and biochemical information.

Micro- and nanofluidics for DNA analysis

Abstract: Miniaturization to the micrometer and nanometer scale opens up the possibility to probe biology on a length scale where fundamental biological processes take place, such as the epigenetic and genetic control of single cells. To study single cells the necessary devices need to be integrated on a single chip; and, to access the relevant length scales, the devices need to be designed with feature sizes of a few nanometers up to several micrometers. We will give a few examples from the literature and from our own research in the field of miniaturized chip-based devices for DNA analysis, including dielectrophoresis for purification of DNA, artificial gel structures for rapid DNA separation, and nanofluidic channels for direct visualization of single DNA molecules.

Endocrine disrupting compounds and other emerging contaminants in the environment: a survey on new monitoring strategies and occurrence data.

Abstract: An overview of Toxicity Identification and Evaluation (TIE) procedures, used for the effect-based analysis of endocrine disrupting compounds (EDCs) in environmental samples, is presented. Future trends in advanced chemical analysis of EDCs and some emerging contaminants are outlined. The review also gives an overview of concentration levels found in environmental samples and discusses the correlation of calculated estrogenicity (based on chemical analysis of target EDCs) with that measured by various bioassays.

Acoustic manipulation of small droplets

Abstract: Surface acoustic waves are used to actuate and process smallest amounts of fluids on the planar surface of a piezoelectric chip. Chemical modification of the chip surface is employed to create virtual wells and tubes to confine the liquids. Lithographically modulated wetting properties of the surface define a fluidic network, in analogy to the wiring of an electronic circuit. Acoustic radiation pressure exerted by the surface wave leads to internal streaming in the fluid and eventually to actuation of small droplets along predetermined trajectories. This way, in analogy to microelectronic circuitry, programmable biochips for a variety of assays on a chip have been realized.

Molecularly imprinted polymers as antibody and receptor mimics for assays, sensors and drug discovery

Abstract: Biological receptors play an important role in affinity-based drug assays, biosensors, and at different stages during the modern drug discovery process. The molecular imprinting technology that has recently emerged has shown great potential for producing biomimetic receptors that challenge their natural counterparts. In this paper, we will overview recent progress in the use of molecularly imprinted polymers for drug assays, assembly of biomimetic sensors, and screening of combinatorial libraries. In addition, examples of using artificially-created binding sites to control synthetic reactions will be discussed. The "screening-of-building blocks" approach is expected to accelerate generation of valuable lead compounds, without the costly synthesis of large chemical libraries.

Glucose oxidase-magnetite nanoparticle bioconjugate for glucose sensing

Abstract: Immobilization of bioactive molecules on the surface of magnetic nanoparticles is of great interest, because the magnetic properties of these bioconjugates promise to greatly improve the delivery and recovery of biomolecules in biomedical applications. Here we present the preparation and functionalization of magnetite (Fe3O4) nanoparticles 20 nm in diameter and the successful covalent conjugation of the enzyme glucose oxidase to the amino-modified nanoparticle surface. Functionalization of the magnetic nanoparticle surface with amino groups greatly increased the amount and activity of the immobilized enzyme compared with immobilization procedures involving physical adsorption. The enzymatic activity of the glucose oxidase-coated magnetic nanoparticles was investigated by monitoring oxygen consumption during the enzymatic oxidation of glucose using a ruthenium phenanthroline fluorescent complex for oxygen sensing. The glucose oxidase-coated magnetite nanoparticles could function as nanometric glucose sensors in glucose solutions of concentrations up to 20 mmol L−1. Immobilization of glucose oxidase on the nanoparticles also increased the stability of the enzyme. When stored at 4°C the nanoparticle suspensions maintained their bioactivity for up to 3 months.

Using chemometrics for navigating in the large data sets of genomics, proteomics, and metabonomics (gpm)

Abstract: This article describes the applicability of multivariate projection techniques, such as principal-component analysis (PCA) and partial least-squares (PLS) projections to latent structures, to the large-volume high-density data structures obtained within genomics, proteomics, and metabonomics. PCA and PLS, and their extensions, derive their usefulness from their ability to analyze data with many, noisy, collinear, and even incomplete variables in both X and Y. Three examples are used as illustrations: the first example is a genomics data set and involves modeling of microarray data of cell cycle-regulated genes in the microorganism Saccharomyces cerevisiae. The second example contains NMR-metabonomics data, measured on urine samples of male rats treated with either of the drugs chloroquine or amiodarone. The third and last data set describes sequence-function classification studies in a set of G-protein-coupled receptors using hierarchical PCA.

Combined biological and chemical assessment of estrogenic activities in wastewater treatment plant effluents

Abstract: Five wastewater treatment plant effluents were analyzed for known endocrine disrupters and estrogenicity. Estrogenicity was determined by using the yeast estrogen screen (YES) and by measuring the blood plasma vitellogenin (VTG) concentrations in exposed male rainbow trout (Oncorhynchus mykiss). While all wastewater treatment plant effluents contained measurable concentrations of estrogens and gave a positive response with the YES, only at two sites did the male fish have significantly increased VTG blood plasma concentrations after the exposure, compared to pre-exposure concentrations. Estrone (E1) concentrations ranged up to 51 ng L−1, estradiol (E2) up to 6 ng L−1, and ethinylestradiol (EE2) up to 2 ng L−1 in the 90 samples analyzed. Alkylphenols, alkylphenolmonoethoxylates and alkylphenoldiethoxylates, even though found at µg L−1 concentrations in effluents from wastewater treatment plants with a significant industrial content, did not contribute much to the overall estrogenicity of the samples taken due to their low relative potency. Expected estrogenicities were calculated from the chemical data for each sample by using the principle of concentration additivity and relative potencies of the various chemicals as determined with the yeast estrogen screen. Measured and calculated estradiol equivalents gave the same order of magnitude and correlated rather well (R2=0.6).

Evaluation of three calibration methods to compensate matrix effects in environmental analysis with LC-ESI-MS.

Abstract: In quantitative analysis of environmental samples using high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) one of the major problems is the suppression or, less frequently, the enhancement of the analyte signals in the presence of matrix components. Standard addition is the most suitable method for compensating matrix effects, but it is time-consuming and laborious. In this study we compare the potential of three calibration approaches to compensate matrix effects that occurred when seven analytes (naphthalene sulfonates) were quantified in time series samples of waters with different matrices (untreated and treated industrial wastewater). The data obtained by external calibration, internal calibration with one standard, and external sample calibration (corresponding to matrix-matched calibration) were compared with those obtained by standard addition. None of the three approaches were suitable for a sample series of highly loaded, untreated wastewater with highly variable matrix. For less heavily loaded and less variable samples (treated wastewater effluents), the external sample calibration provided reasonable results for most analytes with deviations mostly below 25% as compared to standard addition. External sample calibration can be suitable to compensate matrix effects from moderately loaded samples with more uniform matrices, but it is recommended to verify this for each sample series against the standard addition approach.

Airborne chemistry: acoustic levitation in chemical analysis.

Abstract: This review with 60 references describes a unique path to miniaturisation, that is, the use of acoustic levitation in analytical and bioanalytical chemistry applications. Levitation of small volumes of sample by means of a levitation technique can be used as a way to avoid solid walls around the sample, thus circumventing the main problem of miniaturisation, the unfavourable surface-to-volume ratio. Different techniques for sample levitation have been developed and improved. Of the levitation techniques described, acoustic or ultrasonic levitation fulfils all requirements for analytical chemistry applications. This technique has previously been used to study properties of molten materials and the equilibrium shapeand stability of liquid drops. Temperature and mass transfer in levitated drops have also been described, as have crystallisation and microgravity applications.

Rapid multi-element analysis of groundwater by high-resolution inductively coupled plasma mass spectrometry

Abstract: A rapid and sensitive method was developed to determine, with a single dilution, the concentration of 33 major and trace elements (Na, Mg, Si, K, Ca, Li, Al, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, In, Sn, Sb, Cs, Ba, Re, Hg, Pb, Bi, U) in groundwater. The method relies on high-resolution inductively coupled plasma mass spectrometry (HR ICP-MS) and works across nine orders of magnitude of concentrations. For most elements, detection limits for this method are considerably lower than methods based on quadrupole ICP-MS. Precision was within or close to ±3% (1σ) for all elements analyzed, with the exception of Se (±10%) and Al (±6%). The usefulness of the method is demonstrated with a set of 629 groundwater samples collected from tube wells in Bangladesh (Northeast Araiharzar). The results show that a majority of tube well samples in this area exceed the WHO guideline for As of 10 μg L−1, and that those As-safe wells frequently do not meet the guideline for Mn of 500 µg L−1 and U of 2 µg L−1.

Liquid chromatography with triple-quadrupole or quadrupole-time of flight mass spectrometry for screening and confirmation of residues of pharmaceuticals in water.

Abstract: LC–MS–MS has been performed with triple-quadrupole (QqQ) and quadrupole-time of flight (Q-ToF) instruments and has been used for screening and confirmation of pharmaceuticals in surface, drinking, and ground water Screening was based on monitoring of one specific MS–MS ion of the target compounds Confirmation of the identity of the pharmaceuticals was based either on the monitoring of two specific MS–MS ions and calculation of the ratio of their intensities, or on the exact masses of MS–MS product ions obtained for a molecular ion by use of LC–Q-ToF MS The set of pharmaceuticals included four analgesics (acetylsalicylic acid, diclofenac, ibuprofen, and paracetamol), three antibiotics (sulfamethoxazole, erythromycin, and chloramphenicol), five blood-lipid regulators and beta-blockers (fenofibrate, bezafibrate, clofibric acid, bisoprolol, and metoprolol), and the anti-epileptic drug carbamazepine Limits of quantification ranged from 5 to 25 ng L−1 Fifty-six samples were analysed and residues of the pharmaceuticals were detected in almost all surface and groundwater and in some drinking water samples The identity of the compounds could be confirmed by use of both QqQ- and Q-ToF-based LC–MS–MS However, the latter technique has the distinct advantage that a large number of pharmaceuticals can be screened and confirmed at low concentrations (1–100 ng L−1) in one run

ICP-MS measurements of lead isotopic ratios in soils heavily contaminated by lead smelting: tracing the sources of pollution.

Abstract: The Pb isotopic composition (206Pb/207Pb and 208Pb/206Pb) in smelter-impacted soils was measured using a quadrupole-based ICP-MS. Four forest/tilled soil profiles were sampled according to the distance from the lead smelter in Přibram (Czech Republic), prevailing wind direction, geological background and soil type. The results were compared with the Pb isotopic composition of bedrocks and waste materials from Pb metallurgy (smelting slags, air-pollution-control residues). The isotopic composition of soils confirms the predominant role of metallurgy on the general pollution in the area. The highly contaminated soils from the vicinity of the smelter contain up to 35,300 mg Pb kg−1 and exhibit an isotopic composition close to that of car battery processing (206Pb/207Pb up to 1.177). A coupled concentration/isotopic study of soil profiles showed that the smelter-induced pollution had penetrated even to the mineral soil horizons, indicating an important vertical mobility of Pb contaminant within the soil profile. The calculated downward penetration rate of Pb in soils ranges from 0.3 to 0.36 cm year−1.

Derivatization of neutral steroids to enhance their detection characteristics in liquid chromatography–mass spectrometry

Abstract: This review article underlines the detection-oriented derivatization of neutral steroids in liquid chromatography-mass spectrometry (LC-MS). Steroids have strong biological activity at very low concentrations in target tissues and, therefore, the analysis of steroids in body fluids or tissues is necessary to elucidate the nature of the many endocrine disease processes and thus be useful for diagnosis and treatment. LC-MS has recently been used for steroid analysis because of its specificity and versatility, but the ionization efficiencies of most steroids are relatively low for the different ionization methods. Derivatization enhances the ionization efficiencies of steroids, leading to high sensitivity and specific detection. For electrospray ionization MS the introduction of permanently charged moieties or easily ionizable moieties effectively increases the sensitivity of detection of steroids. The introduction of moieties with proton affinity or electron affinity enhances the analyte signals in positive and negative atmospheric pressure chemical ionization MS, respectively.

Stable isotope variation as a tool to trace the authenticity of beef

Abstract: Organic beef coming principally from Germany was analysed for the hydrogen, carbon, oxygen, nitrogen and sulfur stable isotopic composition to test the possibility of tracing back the geographical origin. Since there is a well-known pattern of D/H and 18O/16O in meteoric water and in ground water, there is an existing link to tissue water in the beef. By including the stable isotope ratios of the other elements of life further information is available: soils show different isotope ratios of 15N/14N and 34S/32S depending on the geological composition, cultivation and atmospheric sulfur deposition. As organic farming is mainly obliged to use only their produced fodder, that ratio is reflected in the beef as well. Different organic beef samples from various German farms have been collected and analysed over nearly two years. To check the differentiation of foreign beef, samples from Argentina and Chile were also included in the study. The analyses of meat samples indicate that it is possible to trace back the region (e.g. Argentina and Germany) by using isotopes of oxygen and hydrogen. A local geographical differentiation can be done by using the stable isotopes of nitrogen and sulfur, as was demonstrated for three farms in Colonia Bay. An optimal differentiation also depends on the quality of further information (e.g. the season, kind of cattle breeding or the declaration of the local geographical origin). Certainly authenticity of beef is not only linked with the geographical origin but can also reflect the differentiation of organic and conventional farming. The fodder of organic cattle farming consists mainly of C3 plants and the use of C4 plants is more usual in conventional cattle farming. A 13C/12C ratio above −20‰ appears as a limit for organic farming. Increased values have to be controlled based on their authenticity.

New advances in method validation and measurement uncertainty aimed at improving the quality of chemical data.

Abstract: The implementation of quality systems in analytical laboratories has now, in general, been achieved. While this requirement significantly modified the way that the laboratories were run, it has also improved the quality of the results. The key idea is to use analytical procedures which produce results that fulfil the users' needs and actually help when making decisions. This paper presents the implications of quality systems on the conception and development of an analytical procedure. It introduces the concept of the life-cycle of a method as a model that can be used to organize the selection, development, validation and routine application of a method. It underlines the importance of method validation, and presents a recent approach based on the accuracy profile to illustrate how validation must be fully integrated into the basic design of the method. Thanks to the beta-expectation tolerance interval introduced by Mee (Technometrics (1984) 26(3):251-253), it is possible to unambiguously demonstrate the fitness for purpose of a new method. Remembering that it is also a requirement for accredited laboratories to express the measurement uncertainty, the authors show that uncertainty can be easily related to the trueness and precision of the data collected when building the method accuracy profile.

Integrated procedure for determination of endocrine-disrupting activity in surface waters and sediments by use of the biological technique recombinant yeast assay and chemical analysis by LC-ESI-MS

Abstract: An integrated procedure using mass spectrometry and molecular biology for determination of estrogenicity in natural waters and sediments is reported. Solid-phase extraction (SPE) and pressurized-liquid extraction (PLE), respectively, were used for isolation of endocrine-disrupting compounds (EDC) from surface waters and sediments, followed by liquid chromatography-mass spectrometry using an electrospray interface (LC-ESI-MS). Twenty seven EDC were determined: non-ionic surfactants (nonylphenol ethoxylate), alkylphenols (e.g. nonylphenol and octylphenol), bisphenol A, phthalates, and natural and synthetic steroid sex hormones. Limits of detection varied from 0.02 to 0.22 microg L(-1) and from 1 to 10 microg kg(-1) in water and sediments, respectively. Recoveries ranged from 65 to 125% and 73 to 97% for waters and sediments, respectively. In addition to LC-ESI-MS determination, extracts obtained by SPE and PLE were analyzed by the recombinant yeast assay (RYA) to assess total estrogenic activity. This bioassay detects natural estrogens and xenoestrogens, producing a quantitative measurement of EDC irrespective of the identity of the chemical responsible for the activity. As a novelty, a relative estrogenicity factor was determined for 19 analytes with EC(50) values ranging from 10(-10) to 10(-9) mol L(-1) for synthetic estrogens, from 10(-7) to 10(-5) mol L(-1) for alkylphenol derivatives, and from 10(-5) to 10(-4) mol L(-1) for phthalates and benzothiazoles. By use of this integrated chemical-ecotoxicological approach good correlation was usually established between chemical composition and estrogenic effects for surface water and sediment samples from Portugal. Estrogenic activity observed was mainly attributed to the presence of nonylphenolic compounds (with concentrations of NP ranging from 0.1 up to 44 microg L(-1) in waters and up to 1172 microg kg(-1) in sediments), and to the sporadic presence of estrogens, detected at ng L(-1) levels.

Optical fiber-based biosensors.

Abstract: This review outlines optical fiber-based biosensor research from January 2001 through September 2003 and was written to complement the previous review in this journal by Marazuela and Moreno-Bondi. Optical fiber-based biosensors combine the use of a biological recognition element with an optical fiber or optical fiber bundle. They are classified by the nature of the biological recognition element used for sensing: enzyme, antibody/antigen (immunoassay), nucleic acid, whole cell, and biomimetic, and may be used for a variety of analytes ranging from metals and chemicals to physiological materials.

Bioimprinted QCM sensors for virus detection-screening of plant sap.

Abstract: Surface imprinting techniques on polymer-coated quartz-crystal microbalances (QCM) have been used to detect tobacco mosaic viruses (TMV) in aqueous media. Molecularly imprinted polymers (MIP), tailor-made by self organisation of monomers around a template (TMV), were generated directly on the gold electrodes. Imprinted trenches on the polymer surface mimicking the shape and surface functionality of the virus serve as recognition sites for re-adsorption after washing out of the template. The sensors are applicable to TMV detection ranging from 100 ng mL−1 to 1 mg mL−1 within minutes. Furthermore, direct measurements without time-consuming sample preparation are possible in complex matrices such as tobacco plant sap.

Biosensors for environmental monitoring of endocrine disruptors: a review article.

Abstract: This article provides an overview of the applications of biosensors in analysis and monitoring of endocrine-disrupting compounds (EDCs) in the environment. Special attention is devoted to the various types of physical-chemical signal transduction elements, biological mechanisms employed as sensing elements and techniques used for immobilisation of the bioreceptor molecules on the transducer surface. Two different classes of biosensors for EDCs are considered: biosensors that measure endocrine-disrupting effects, and biosensors that respond to the presence of a specific substance (or group of substances) based on the specific recognition of a biomolecule. Several examples of them are presented to illustrate the power of the biosensor technology for environmental applications. Future trends in the development of new, more advanced devices are also outlined.

Analytical procedures for quantification of peptides in pharmaceutical research by liquid chromatography–mass spectrometry

Abstract: Peptide quantification by liquid chromatography–mass spectrometry (LC–MS) combines the high resolving power of reversed-phase (RP) chromatography with the excellent selectivity and sensitivity of mass spectrometric detection. On the basis of comprehensive practical experience in the analysis of small molecules, pharmaceutical research is developing technologies for analysis of a growing number of peptidic drug candidates. This article is a detailed review of procedures based on LC–MS techniques for quantitative determination of peptides. With the focus on pharmaceutical applications several technologies for sample preparation, various aspects of peptide chromatography, important characteristics of ESI–MS, selectivity of MS-detection modes, the large variability of internal standards, and modern instrumentation are discussed. The demand for reliable, robust, sensitive, and accurate methods is discussed using numerous examples from the literature, complemented by experiments and results from our laboratory.

Molecular imprinting: a dynamic technique for diverse applications in analytical chemistry

Abstract: Continuous advances in analyzing complex matrices, improving reliability and simplicity, and performing multiple simultaneous assays with extreme sensitivity are increasing. Several techniques have been developed for the quantitative assays of analytes at low concentrations (e.g., high-pressure liquid chromatography, gas chromatography, immunoassay and the polymerase chain reaction technique). To achieve highly specific and sensitive analysis, high affinity, stable, and specific recognition agents are needed. Although biological recognition agents are very specific and sensitive they are labile and/or have a low density of binding sites. During the past decade molecular imprinting has emerged as an attractive and highly accepted tool for the development of artificial recognition agents. Molecular imprinting is achieved by the interaction, either noncovalent or covalent, between complementary groups in a template molecule and functional monomer units through polymerization or polycondensation. These molecularly imprinted polymers have been widely employed for diverse applications (e.g., in chromatographic separation, drug screening, chemosensors, catalysis, immunoassays etc.) owing to their specificity towards the target molecules and high stability against physicochemical perturbations. In this review the advantages, applications, and recent developments in molecular imprinting technology are highlighted.

Isotope-dilution ICP–MS for trace element determination and speciation: from a reference method to a routine method?

Abstract: This critical review discusses the conditions under which inductively coupled plasma-isotope dilution mass spectrometry (ICP-IDMS) is suitable as a routine method for trace element and element-speciation analysis. It can, in general, be concluded that ICP-IDMS has high potential for routine analysis of trace elements if the accuracy of results is of predominant analytical importance. Hyphenated techniques with ICP-IDMS suffer both from lack of commercially available isotope-labeled spike compounds for species-specific isotope dilution and from the more complicated system set-up required for species-unspecific ICP-IDMS analysis. Coupling of gas or liquid chromatography with species-specific ICP-IDMS, however, enables validation of analytical methods involving species transformations which cannot easily be performed by other methods. The potential and limitations of ICP-IDMS are demonstrated by recently published results and by some unpublished investigations by our group. It has been shown that possible loss of silicon as volatile SiF4 during decomposition of a sample by use of hydrofluoric acid has no effect on trace silicon determination if the isotope-dilution step occurs during digestion in a closed system. For powder samples, laser ablation ICP-IDMS can be applied with an accuracy comparable with that only available from matrix-matched standardization, whereas the accuracy of electrothermal vaporization ICP-IDMS was strongly dependent on the element determined. The significance of easy synthesis of isotope-labeled spike compounds for species-specific ICP-IDMS is demonstrated for monomethylmercury and Cr(VI). Isotope-exchange reactions between different element species can prevent the successful application of ICP-IDMS, as is shown for iodinated hydrocarbons. It is also shown for monomethylmercury that species transformations during sample-pretreatment steps can be followed by species-specific ICP-IDMS without loss of accuracy. A relatively simple and time-efficient procedure for determination of monomethylmercury in environmental and biological samples is discussed. The method, which entails a rapid microwave-assisted isotope dilution step and in-situ extraction of the derivatized species, has good potential for routine application in the future.

Determination of ochratoxin A in foods: state-of-the-art and analytical challenges.

Abstract: Ochratoxin A (OTA) can occur in a large variety of commodities (cereals, beans, groundnuts, spices, dried fruits, coffee, beer, wine) and, because of a carry-over effect, in milk, pig blood, liver, and kidney, and poultry meat from animals fed with contaminated feed. Because of the persistence of OTA in the food chain, exposure to the compound is a potential human health hazard. This has prompted adoption of regulatory limits in several countries which, in turn, implies the development of suitable validated and official analytical methods and rapid screening tests for cost-effective food control on a large scale. Liquid chromatography with fluorescence detection (LC–FLD), coupled with immunoaffinity column (IAC) clean-up, is the most widely employed analytical technique. LC coupled with electrospray-ionization mass spectrometry (MS) has detection limits comparable with those of LC–FLD and the selectivity of IAC can be achieved by tandem (MS–MS) or sequential (MS n ) detection. Synthetic counterparts to natural antibodies in the form of molecularly imprinted polymers seem a promising alternative to IAC for sample preparation. New analytical approaches to rapid, low-cost screening methods, for example those based on biosensors and dip-stick-like kits, are a direction in which innovation can be expected. Analytical methods for evaluation of the occurrence of OTA in foods, human exposure, and risk assessment are critically reviewed.

Solvent extraction of amino acids into a room temperature ionic liquid with dicyclohexano-18-crown-6

Abstract: Amino acids Trp, Gly, Ala, Leu are extracted efficiently from aqueous solution at pH 1.5-4.0 (Lys and Arg at pH 1.5-5.5) into the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) with dicyclohexano-18-crown-6 (CE). The most hydrophilic amino acids such as Gly are extracted as efficiently as the less hydrophilic (92-96%). The influence of pH, amino acid and crown ether concentration, volume ratio of aqueous and organic phases, and presence of some cations on amino acid recovery were studied. The ratio of amino acid to crown ether in the extracted species is 1:1 for cationic Trp, Leu, Ala, and Gly and to 1:2 for dicationic Arg and Lys. This ionic liquid extraction system was used successfully for the recovery of amino acids from pharmaceutical samples and fermentation broth, and was followed by fluorimetric determination.

Recombinant human estrogen, androgen and progesterone receptors for detection of potential endocrine disruptors

Abstract: This work reports the binding capacity of various chemicals (so-called endocrine disruptors) to recombinant human steroid receptors (hERα, hPR and hAR). The tested chemicals are organochlorine insecticides (DDT and its metabolites, methoxychlor, aldrin, dieldrin, chlordecone, lindane, trichlorobenzene), estrogenic insecticides (endosulfan, toxaphene, nonachlor), herbicides (alachlor and atrazine), fungicides (benomyl and vinclozolin), industrial chemicals (nonylphenol, bisphenol A, diphenylphtalate), antioxidants (butylated hydroxyanisol) and some phytoestrogens. Except for phytoestrogens, most of the tested chemicals (DDT and its metabolites, aldrin, α- and β-endosulfan, toxaphen, trans-nonachlor) show higher affinities for hPR than for hERα, indicating that the interaction with the progesterone receptor could contribute to the endocrine-disrupting effects imputed to these chemicals. We propose to use binding assays using recombinant human steroid receptors as screening tools for the detection of endocrine disruptors in various samples.