Monensin carry-over into unmedicated broiler feeds.

European Union Member States are now required to monitor poultry meat for the presence of coccidiostat residues. Among other factors contributing to the production of residue-free food is the ability of animal feed manufacturers to produce medication-free feedstuffs, ensuring the proper observance of withdrawal periods prior to slaughter. Carry-over of medication was investigated in a local poultry feed mill that was using monensin as its principal coccidiostat for broilers. Monensin, at levels in excess of 5% of the therapeutic dose (approximately 110 mg kg-1), was present in 22.5% of 40 withdrawal feeds. Subsequent studies in the mill indicated that most of the contamination occurred during the processing of feeds after the mixing stage. The mill altered its manufacturing process as a result of this study. The consequence of this was that the incidence of monensin withdrawal feeds, at levels greater than 5% of the therapeutic dose, fell from 22.5 to 2.5%. This collaborative study has helped the feed compounder to produce more effective withdrawal feeds, thereby reducing the potential exposure of consumers to unwanted residues of monensin in poultry meat.     

Detection of streptomycin and dihydrostreptomycin residues in milk,honey and meat samples using an optical biosensor

Immuno-biosensor inhibition assays for the detection of streptomycin and dihydrostreptomycin residues in whole cows' milk, honey, pig kidney and pig muscle are reported. The antibody showed high cross-reactivity with dihydrostreptomycin in various foodstuffs (buffer 103%, milk 96%, honey 84%, kidney extract 129% and muscle extract 98%). There was no significant cross-reaction with other aminoglycosides or commonly used antibiotics. A streptomycin derivative was used to prepare a stable, reusable sensor chip surface. The assay allowed the direct analysis of bovine whole milk (fat content approximately 3.5%). Honey samples required dilution with buffer, while kidney and muscle samples from pigs were homogenized in an aqueous extraction buffer and clarified by centrifugation. The limit of detection for each assay was determined from known streptomycin-free samples (n = 20; mean - (3 x standard deviation)) and the results were as follows: milk 30 microg kg(-1), honey 15 microg kg(-1), kidney 50 microg kg(-1) and muscle 70 microg kg(-1). Repeatability (or relative standard deviation) between runs were calculated (n = 3) at the respective Community maximum residue limits (MRL) and 0.5 x MRL with the exception of honey since no European MRL exists at present. Results were determined as 4.3% (200 microg kg(-1)) and 2.8% (100 microg kg(-1)) in milk, 13.3% (40 microg kg(-1)) and 9.5% (20 microg kg(-1)) in honey, 7.1% (1000 microg kg(-1)) and 7.6% (500 microg kg(-1)) in kidney and 7.1% (500 microg kg(-1)) and 11% (250 microg kg(-1)) in muscle.     

Measurements for certification of chlortetracycline reference materials within the European Union Standards, Measurements and Testing programme

The experimental design of a material certification programme is described. The matrix reference materials (RMs) comprised chlortetracycline (CTC)-containing and CTC-free lyophilised porcine liver, kidney and muscle produced under the European Commission's Standards Measurements and Testing (SMT) programme. The aim of the certification programme was to determine accurately and precisely the concentration of CTC and 4-epi-chlortetracycline (epi-CTC) contained in the RMs. A multi-laboratory approach was used to certify analyte concentrations. Participants (n = 19) were instructed to strictly adhere to previously established guidelines. Following the examination of analytical performance criteria, statistical manipulation of results submitted by 13 laboratories, (6 withdrew) allowed an estimate to be made of the true value of the analyte content. The Nalimov test was used for detection of outlying results. The Cochran and Bartlett tests were employed for testing the homogeneity of variances. The normality of results distribution was tested according to the Kolmogorov-Smirnov-Lilliefors test. One-way analysis of variance (ANOVA) was employed to calculate the within and between-laboratory standard deviations, the overall mean and confidence interval for the CTC and epi-CTC content of each of the RMs. Certified values were within or very close to the target concentration ranges specified in the SMT contract. These studies have demonstrated the successful production and certification of CTC-containing and CTC-free porcine RMs.     

Fast voltammetric studies of the kinetics and energetics of coupled electron-transfer reactions in proteins

A wealth of information on the reactions of redox-active sites in proteins can be obtained by voltammetric studies in which the protein sample is arranged as a layer on an electrode surface. By carrying out cyclic voltammetry over a wide range of scan rates and exploiting the ability to poise or pulse the electrode potential between cycles, data are obtained that are conveniently (albeit simplistically) analysed in terms of plots of peak potentials against scan rate. A simple reversible electron-transfer process gives rise to a 'trumpet'-shaped plot because the oxidation and reduction peaks separate increasingly at high scan rate; the electrochemical kinetics are then determined by fitting to Butler-Volmer or Marcus models. Much more interesting though are the ways in which this 'trumpet plot' is altered, often dramatically, when electron transfer is coupled to biologically important processes such as proton transfer, ligand exchange, or a change in conformation. It is then possible to derive particularly detailed information on the kinetics, energetics and mechanism of reactions that may not revealed clearly or even at all by other methods. In order to interpret the voltammetry of coupled systems, it is important to be able to define 'ideal behaviour' for systems that are expected to show simple and uncoupled electron transfer. Accordingly, this paper describes results we have obtained for several proteins that are expected to show such behaviour, and compares these results with theoretical predictions.     

Thin film pyrolytic carbon electrodes: A new class of carbon electrode for electroanalytical sensing applications

This communication describes the electrochemical properties of thin pyrolytic carbon (PyC) films created using a reliable, non-catalytic chemical vapour deposition (CVD) process. After deposition, the electron transfer characteristics of the films are optimised using a simple oxygen plasma treatment. The redox probes Ru(NH₃)₆^3+/2+, Fe(CN)₆^3?/4? and Fe^3+/2+ are employed to demonstrate that the resulting material is endowed with a large electrochemical surface area and outstanding electron transfer properties. Atomic force microscopy (AFM), Raman and X-ray photoelectron spectroscopy (XPS) are used to elucidate the morphology and chemical composition of the electrode surfaces. This material represents a new class of carbon electrode, and its large densities of edge-plane sites and oxygenated functionalities make it an ideal candidate for electrochemical sensor applications.     

Development of an integrated optic oxygen sensor using a novel, generic platform

This paper describes the development of a generic platform for enhanced, integrated optic sensors based on fluorescence detection. The platform employs a novel optical configuration in order to achieve enhanced performance and has inherent multianalyte detection capability. The sensor element comprises a multimode ridge waveguide that has been patterned with an analyte-sensitive fluorescent spot, which is excited directly using a LED. The platform was applied to the detection of gaseous oxygen as a proof of principle. The sol-gel-derived sensor spots were doped with an oxygen-sensitive fluorescent dichlororuthenium dye complex and intensity-based calibration data were generated from the oxygen-dependent waveguide output. The sensor achieved a LOD of 0.62% and a resolution of less than 0.96% gaseous oxygen, which compares favourably with a similar, recently reported system. This device highlights the combination of inexpensive rapid prototyping techniques and a dedicated sensor enhancement strategy that together facilitate the production of an effective prototype sensor platform.     

Mössbauer study of europium in fluorozirconate glass

¹⁵¹Eu Mössbauer spectra of fluorozirconate glasses of nominal composition 0.61 ZrF₄ · (0.32 ? x) BaF₂ · x EuF₂ · 0.07 ThF₄ with x = 0.10 and 0.20 show that Eu²⁺ is present in sites with isomer shifts in the range ?15.5 to ?12.9 mm/s, corresponding to EuF bond lengths of 2.3–2.8 Å and a coordination number ranging from 8 to 12. The glasses contain a minor amount (～10%) of Eu³⁺ in well-defined sites. Effective Debye temperatures deduced from the recoilless fractions for the two ions are θ_D²⁺ = 145 K and θ_D³⁺ = 261 K. The differences in coordination and bonding indicate that trivalent eurpoium is a network former, whereas the divalent ions are network modifiers.