Comparison of two assays, a faecal egg count reduction test (FECRT) and a coproantigen reduction test (CRT), for the diagnosis of resistance to triclabendazole in Fasciola hepatica in sheep

A sheep trial was performed to evaluate two diagnostic assays, a faecal egg count reduction test (FECRT) and a coproantigen reduction test (CRT), for the diagnosis of resistance of Fasciola hepatica to triclabendazole (TCBZ). The FECRT defines successful TCBZ treatment as a 95% or greater reduction in fluke faecal egg counts (FECs) at 14 days post-treatment (dpt). The CRT defines effective TCBZ treatment as faeces negative for Fasciola coproantigens at 14 dpt, as measured by the commercial BIO K201 coproantigen ELISA (Bio-X Diagnostics, Jemelle, Belgium).

New insight into mechanisms in water-gas-shift reaction on Au/CeO2(111): A density functional theory and kinetic study

Using density functional theory (DFT) and kinetic analyses, a new carboxyl mechanism for the water-gas-shift reaction (WGSR) on Au/CeO2(111) is proposed. Many elementary steps in the WGSR are studied using an Au cluster supported on CeO2(111). It is found that (i) water can readily dissociate at the interface between Au and CeO2; (ii) CO2 can be produced via two steps: adsorbed CO on the Au cluster reacts with active OH on ceria to form the carboxyl (COOH) species and then COOH reacts with OH to release CO2; and (iii) two adsorbed H atoms recombine to form molecular H-2 on the Au cluster. Our kinetic analyses show that the turnover frequency of the carboxyl mechanism is consistent with the experimental one while the rates of redox and formate mechanisms are much slower than that of carboxyl mechanism. It is suggested that the carboxyl pathway is likely to be responsible for WGSR on Au/CeO2.

Development of the kinetic model of platinum catalyzed ammonia oxidation in a microreactor

The ammonia oxidation reaction on supported polycrystalline platinum catalyst was investigated in an aluminum-based microreactor. An extensive set of reactions was included in the chemical reactor modeling to facilitate the construction of a kinetic model capable of satisfactory predictions for a wide range of conditions (NH3 partial pressure, 0.01-0.12 atm; O-2 partial pressure, 0.10-0.88 atm; temperature, 523-673 K; contact time, 0.3-0.7 ms). The elementary surface reactions used in developing the mechanism were chosen based on the literature data concerning ammonia oxidation on a Pt catalyst. Parameter estimates for the kinetic model were obtained using multi-response least squares regression analysis using the isothermal plug-flow reactor approximation. To evaluate the model, the behavior of a microstructured reactor was simulated by means of a complete Navier-Stokes model accounting for the reactions on the catalyst surface and the effect of temperature on the physico-chemical properties of the reacting mixture. In this way, the effect of the catalytic wall temperature non-uniformity and the effect of a boundary layer on the ammonia conversion and selectivity were examined. After further optimization of appropriate kinetic parameters, the calculated selectivities and product yields agree very well with the values actually measured in the microreactor. (C) 2002 Elsevier Science B.V. All rights reserved.

A kinetic study of ammonia oxidation on a Pt catalyst in the explosive region in a microstructured reactor/heat-exchanger

The application of an aluminum-based microstructured reactor/heat-exchanger for measuring reaction kinetics in the explosive region is presented. Platinum-catalyzed ammonia oxidation was chosen as a test reaction to demonstrate the feasibility of the method. The reaction kinetics was investigated in a wide range of conditions [NH3 partial pressure: 0.03-0.20 atm, O-2 partial pressure: 0.10-0.88atm; reactant flow 2000-3000 cm(3) min(-1) (STP); temperature 240-360degreesC] over a supported Pt/Al2O3 catalyst (mass of Al2O3 layer in the reactor, 1.95 mg; Pt/Al molar ratio, 0.71; Pt dispersion, 20%). The maximum temperature non-uniformity in the microstructured reactor was ca. 5degreesC, even at conditions corresponding to an adiabatic temperature rise of 1400degreesC. Based on the data obtained, a previous kinetic model for ammonia oxidation was extended. The modified 13-step model describes the data in a considerably wider range of conditions including those with high ammonia loadings and high reaction temperatures. The results indicate the large potential of microstructured devices as reliable tools for kinetic research of highly exothermic reactions.

A comparative study of qualitative immunochemical screening assays for the combined measurement of T-2/HT-2 in cereals and cereal-based products

Many different immunochemical platforms exist for the screening of naturally occurring contaminants in food from the low cost enzyme linked immunosorbent assays (ELISA) to the expensive instruments such as optical biosensors based on the phenomenon of surface plasmon resonance (SPR). The primary aim of this study was to evaluate and compare a number of these platforms to assess their accuracy and precision when applied to naturally contaminated samples containing HT-2/T-2 mycotoxins. Other important factors considered were the speed of analysis, ease of use (sample preparation techniques and use of the equipment) and ultimately the cost implications. The three screening procedures compared included an SPR biosensor assay, a commercially available ELISA and an enzyme-linked immunomagnetic electrochemical array (ELIME array). The qualitative data for all methods demonstrated very good overall agreements with each other, however on comparison with mass spectrometry confirmatory results, the ELISA and SPR assay performed slightly better than the ELIME array, exhibiting an overall agreement of 95.8% compared to 91.7%. Currently, SPR is more costly than the other two platforms and can only be used in the laboratory whereas in theory both the ELISA and ELIME array are portable and can be used in the field, but ultimately this is dependent on the sample preparation techniques employed. Sample preparative techniques varied for all methods evaluated, the ELISA was the most simple to perform followed by that of the SPR method. The ELIME array involved an additional clean-up step thereby increasing both the time and cost of analysis. Therefore in the current format, field use would not be an option for the ELIME array. In relation to speed of analysis, the ELISA outperformed the other methods.

Development and validation of rapid disequilibrium enzyme-linked immunosorbent assays for the detection of Methyl Yellow and Rhodamine B dyes in foods

Sensitive and specific enzyme-linked immunosorbent assays (ELISAs) were developed for the detection of two illegal synthetic dyes: Methyl Yellow (MY) and Rhodamine B (RB) in food. Polyclonal antibodies were raised against synthesised immunogens and employed in unique direct disequilibrium ELISAs. The time of the assays was only twenty minutes (five minutes for each incubation step with sample and enzyme conjugate and ten minutes with enzyme substrate). The IC50 for MY was in the range 1.4-4.2 ng mL(-1) and for RB 0.1-0.5 ng mL(-1). A simple sample preparation method was developed for the analysis of a range of sauces. In the case of spices a dispersive solid phase extraction was applied to purify the extracts. The testing of twenty samples took approximately one and a half hours (including sample preparation and analysis). Both assays were validated according to the Commission Decision 2002/657/EC criteria for use in sauces and spices. The detection capability for MY in sauces and spices was determined to be less than 15 ng g(-1) and 50 ng g(-1), respectively and for RB, 10 ng g(-1) for both types of food samples. The precision of the developed assays was determined in a repeatability study. The intra-and inter-assay coefficients of variation were less than 25% for both tests and matrix types. The simplicity and performance of both assays indicate that they will be very reliable screening methods for the detection of the illegal dyes MY and RB in a range of food products.

PHOTOMINERALIZATION OF SALICYLIC-ACID - A KINETIC-STUDY

The kinetics of the photomineralization of salicylic acid (SA) sensitized by Degussa P25 titanium dioxide (TiO2) dispersions in oxygenated aqueous solution are reported as a function of the following experimental parameters: [TiO2], percentage of O-2, [SA], temperature (T) and light intensity (I). The kinetics of SA photomineralization conform to a Langmuir-Hinshelwood kinetic scheme with SA and O-2 adsorbed at different sites with apparent Langmuir adsorption coefficients of (6.1 +/- 1.2) x 10(4) mol(-1) dm(3) and 0.061 +/- 0.007 kPa(-1) respectively. The overall activation energy for the system was determined as 4.6 +/- 0.2 kJ mol(-1). Two major stable reaction intermediates are identified (dihydroxybenzoic acids (DHBA) and catechol (C)) and the existence of a further pathway involving one or more very unstable and, as yet, unidentified reaction intermediates is proposed. A kinetic model is presented which describes the temporal behaviour of the concentrations of SA, CO2 and the major photogenerated intermediates (DHBA and C). This model is used to predict successfully the temporal behaviour of the major intermediates in the photomineralization of SA under non-standard conditions.

A KINETIC-STUDY OF THE BLEACHING OF RHODAMINE-6G PHOTOSENSITIZED BY TITANIUM-DIOXIDE

The results of a kinetic study of the bleaching of the photostable dye rhodamine 6G by dissolved oxygen, photosensitized by TiO2, are reported. The observed variations in the initial rate of dye photobleaching as a function of the O2 percentage, temperature, incident light intensity and concentrations of rhodamine 6G and sacrificial electron donor are described and the results are rationalized using a proposed photochemical reaction scheme. The photosensitized bleaching of rhodamine 6G dye by TiO2 has a formal quantum yield of 2.65 X 10(-3), but the rate of complete photomineralization is about twofold slower. The overall activation energy for the semiconductor-sensitized dye photobleaching process is 15.0 +/- 1.5 kJ mol-1.

KINETIC-STUDY OF PHOTOINDUCED ELECTRON-TRANSFER REACTIONS SENSITIZED BY COLLOIDAL CDS

The kinetics of the recovery of the photoinduced transient bleaching of colloidal CdS in the presence of different electron acceptors are examined. In the presence of the zwitterionic viologen, N,N'-dipropyl-2,2'-bipyridinium disulphonate, excitation of colloidal CdS at different flash intensities generates a series of decay profiles which are superimposed when normalized. The shape of the decay curves are as predicted by a first-order activation-controlled model for a log-normal distribution of particles sizes. In contrast, the variation in flash intensity in the presence of a second viologen, N,N'-dipropyl-4,4'-bipyridinium sulphonate, generates normalized decay traces which broaden with increasing flash intensity. This behaviour is predicted by a zero-order diffusion-controlled model for a log-normal distribution of particle radii. The photoreduction of a number of other oxidants sensitized by colloidal CdS is examined and the shape of the decay kinetics interpreted via either the first- or zero-order kinetics models. The rate constants and activation energies derived using these models are consistent with the values expected for an activation- or diffusion-controlled reaction.

Elimination kinetic of 17 beta-estradiol 3-benzoate and 17 beta-nandrolone laureate ester metabolites in calves' urine

Efficient control of the illegal use of anabolic steroids must both take into account metabolic patterns and associated kinetics of elimination; in this context, an extensive animal experiment involving 24 calves and consisting of three administrations of 17 beta-estradiol 3-benzoate and 17 beta-nandrolone laureate esters was carried out over 50 days. Urine samples were regularly collected during the experiment from all treated and non-treated calves. For sample preparation, a single step high throughput protocol based on 96-well C-18 SPE was developed and validated according to the European Decision 2002/657/EC requirements. Decision limits (CC alpha) for steroids were below 0.1 mu g L-1, except for 19-norandrosterone (CC alpha = 0.7 mu g L-1) and estrone (CC alpha = 0.3 mu g L-1). Kinetics of elimination of the administered 17 beta-estradiol 3-benzoate and 17 beta-nandrolone laureate were established by monitoring 17 beta-estradiol, 17 alpha-estradiol, estrone and 17 beta-nandrolone, 17 alpha-nandrolone, 19-noretiocholanolone, 19-norandrostenedione, respectively. All animals demonstrated homogeneous patterns of elimination both from a qualitative (metabolite profile) and quantitative point of view (elimination kinetics in urine). Most abundant metabolites were 17 alpha-estradiol and 17 alpha-nandrolone (> 20 and 2 mg L-1, respectively after 17 beta-estradiol 3-benzoate and 17 beta-nandrolone laureate administration) whereas 17 beta-estradiol, estrone, 17 beta-nandrolone, 19-noretiocholanolone and 19-norandrostenedione were found as secondary metabolites at concentration values up to the mu g L-1 level. No significant difference was observed between male and female animals. The effect of several consecutive injections on elimination profiles was studied and revealed a tendency toward a decrease in the biotransformation of administered steroid 17 beta form. (c) 2008 Elsevier Ltd. All rights reserved.