Benzimidazole carbamate residues in milk: Detection by Surface Plasmon Resonance-biosensor, using a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method for extraction

A surface plasmon resonance (SPR) biosensor screening assay was developed and validated to detect 11 benzimidazole carbamate (BZT) veterinary drug residues in milk. The polyclonal antibody used was raised in sheep against a methyl 5(6)-[(carboxypentyl)-thio]-2-benzimidazole carbamate protein conjugate. A sample preparation procedure was developed using a modified QuEChERS method. BZT residues were extracted from milk using liquid extraction/partition with a dispersive solid phase extraction clean-up step. The assay was validated in accordance with the performance criteria described in 2002/657/EC. The limit of detection of the assay was calculated from the analysis of 20 known negative milk samples to be 2.7 mu g kg(-1). The detection capability (CC beta) of the assay was determined to be 5 mu g kg(-1) for 11 benzimidazole residues and the mean recovery of analytes was in the range 81-116%. A comparison was made between the SPR-biosensor and UPLC-MS/MS analyses of milk samples (n = 26) taken from cows treated different benzimidazole products, demonstrating the SPR-biosensor assay to be fit for purpose. (C) 2009 Elsevier B.V. All rights reserved.

Development of a rapid, multi-class method for the confirmatory analysis of anti-inflammatory drugs in bovine milk using liquid chromatography tandem mass spectrometry

A rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the simultaneous identification, confirmation and quantitation of seven licensed anti-inflammatory drugs (AIDS) in bovine milk. The method was validated in accordance with the criteria defined in Commission Decision 2002/657/EC. Two classes of AIDS were investigated, corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs). The developed method is capable of detecting and confirming dexamethasone (DXM), betamethasone (BTM), prednisolone (FRED), tolfenamic acid (TV), 5-hydroxy flunixin (5-OH-FLU). meloxicam (MLX) and 4-methyl amino antipyrine (4-MAA) at their associated maximum residue limits (MRLs). These compounds represent all the corticosteroids and NSAIDs licensed for use in bovine animals producing milk for human consumption. These compounds have never been analysed before in the same method and also 4-methyl amino antipyrine has never been analysed with the other licensed NSAIDs. The method can be considered rapid as permits the analysis of up to 30 samples in one day. Milk samples are extracted with acetonitrile; sodium chloride is added to aid partition of the milk and acetonitrile mixture. The acetonitrile extract is then subjected to liquid-liquid purification by the addition of hexane. The purified extract is finally evaporated to dryness and reconstituted in a water/acetonitrile mixture and determination is carried out by LC-MS/MS. Decision limit (CC alpha) values and detection capability (CC beta) values have been established for each compound. (C) 2009 Elsevier B.V. All rights reserved.

Thin-film oxygen sensors using a luminescent polynuclear gold(I) complex

Robust thin-film oxygen sensors were fabricated by encapsulating a lipophilic, polynuclear gold(I) complex, bis{m-(bis(diphenylphosphino)octadecylamine-P,P')}dichlorodigold(I), in oxygen permeable polystyrene and ormosil matrices. Strong phosphorescence, which was quenched by gaseous and dissolved oxygen, was observed from both matrices. The polystyrene encapsulated dye exhibited downward-turning Stern-Volmer plots which were well fitted by a two-site model. The ormosil trapped complex showed linear Stern-Volmer plots for dissolved oxygen quenching but was downward turning for gaseous oxygen. No leaching was observed when the ormosil based sensors were immersed in flowing water over an 8 h period. Both films exhibited fully reversible response and recovery to changing oxygen concentration with rapid response times. (C) 2011 Elsevier B.V. All rights reserved.

A novel 'fizziness' indicator

A novel colourimetric 'fizziness' indicator is described which changes colour depending on the headspace pressure of carbon dioxide above a carbonated liquid.

Water-based colourimetric optical indicators for the detection of carbon dioxide

Water-based colourimetric indicator films are shown to have increased operational lifetimes under ambient conditions compared to similar solvent-based counterparts. The response and sensitivity characteristics of a water-based, carbon dioxide-responsive ink are characterised and compared and contrasted to those of a similar solvent-based indicator. The changes in the response characteristics of the ink as a function of the amount of base (sodium hydrogen carbonate) and plasticizer (glycerol) contained in the ink are reported, as are the effects of varying ambient temperature and humidity. The ink is incorporated into a felt tip pen and applied to a number of different substrates, producing a distinct, reversible colour change on all tested surfaces, when a sufficient level of carbon dioxide is present. The possible application of the indicator is discussed briefly.

A comprehensive aerosol spray method for the rapid photocatalytic grid area analysis of semiconductor photocatalyst thin films

Indicator inks, previously shown to be capable of rapidly assessing photocatalytic activity via a novel photo-reductive mechanism, were simply applied via an aerosol spray onto commercially available pieces of Activ (TM) self-cleaning glass. Ink layers could be applied with high evenness of spread, with as little deviation as 5% upon UV-visible spectroscopic assessment of 25 equally distributed positions over a 10 cm x 10 cm glass cut. The inks were comprised of either a resazurin (Rz) or dichloroindophenol (DCIP) redox dye with a glycerol sacrificial electron donor in an aqueous hydroxyethyl cellulose (HEC) polymer media. The photo-reduction reaction under UVA light of a single spot was monitored by UV-vis spectroscopy and digital images attained from a flat-bed scanner in tandem for both inks. The photo-reduction of Rz ink underwent a two-step kinetic process, whereby the blue redox dye was initially reduced to a pink intermediate resorufin (Rf) and subsequently reduced to a bleached form of the dye. In contrast, a simple one-step kinetic process was observed for the reduction of the light blue redox dye DCIP to its bleached intermediates. Changes in red-green-blue colour extracted from digital images of the inks were inversely proportional to the changes seen at corresponding wavelengths via UV-visible absorption spectroscopy and wholly indicative of the reaction kinetics. The photocatalytic activity areas of cuts of Activ (TM) glass, 10 cm x 10 cm in size, were assessed using both Rz and DCIP indicator inks evenly sprayed over the films: firstly using UVA lamp light to activate the underlying Activ (TM) film (1.75 mW cm(-2)) and secondly under solar conditions (2.06 +/- 0.14 mW cm(-2)). The photo-reduction reactions were monitored solely by flat-bed digital scanning. Red-green-blue values of a generated 14 x 14 grid (196 positions) that covered the entire area of each film image were extracted using a Custom-built program entitled RGB Extractor(C). A homogenous degradation over the 196 positions analysed for both Rz (Red colour deviation = 19% UVA, 8% Solar: Green colour deviation = 17% UVA, 12% Solar) and DCIP (Red colour deviation = 22% UVA, 16% Solar) inks was seen in both UVA and solar experiments, demonstrating the consistency of the self-cleaning titania layer on Activ (TM). The method presented provides a good solution for the high-throughput photocatalytic screening of a number of homogenous photocatalytically active materials simultaneously or numerous positions on a single film; both useful in assessing the homogeneity of a film or determining the best combination of reaction components to produce the optimum performance photocatalytic film. (C) 2010 Elsevier B.V. All rights reserved.

A novel reversible relative-humidity indicator ink based on methylene blue and urea

A new relative-humidity sensitive ink based on methylene blue and urea is described which can utilise the deliquescent nature of urea.

UV dosimeter based on dichloroindophenol and tin(IV) oxide

A UVB specific dosimeter is described comprising: a redox dye (2,6-dichloroindophenol, DCIP), a semiconductor ( tin(IV) oxide, SnO2) and a sacrificial electron donor ( glycerol) dispersed in a polymer ( hydroxy ethyl cellulose, HEC) film. The dosimeter is blue in the absence of UVB light but rapidly loses colour on exposure to UVB light. The spectral characteristics of a typical UVB dosimeter film and the mechanism by which the colour change occurs are detailed. DCIP UVB dosimeter films exhibit a response that is related to the irradiance level and duration of UVB exposure, the level of SnO2 present and to a lesser extent the level of glycerol present. The response of the dosimeter appears to be independent of dye concentration and film thickness. Furthermore, DCIP UVB dosimeter films respond to solar simulated light, exhibiting a colour loss that can be simply related to the Minimal Erythemal Dose (MED) exposure for skin type II. As a consequence, such indicators have potential for measuring solar radiation exposure and providing an early warning of erythema for most Caucasian skin (i.e. skin type II).

A solvent-based intelligence ink for oxygen

A solvent-based, irreversible oxygen indicator ink is described, comprising semiconductor photocatalyst nanoparticles, a solvent-soluble redox dye, mild reducing agent and polymer. Based on such an ink, a film - made of titanium dioxide, a blue, solvent-soluble, coloured ion-paired methylene blue dye, glycerol and the polymer zein - loses its colour rapidly (

Reversible, fluorescence-based optical sensor for hydrogen peroxide

The preparation and characterisation are described of a robust, reversible, hydrogen peroxide optical sensor, based on the fluorescent quenching of the dye ion-pair [Ru(bpy)(3)(2+)(Ph4B-)(2)], by O-2 produced by the catalytic breakdown of H2O2, utilizing the inorganic catalyst RuO2 center dot xH(2)O. The main feature of this system is the one-pot formulation of a coating ink that, when dried, forms an active single-layer fluorescence-based H2O2 sensor, demonstrably capable of detecting H2O2 over the range of 0.01 to 1 M, with a relative standard deviation of ca. 4% and a calculated lower limit of detection of 0.1 mM. These sensors are sterilisable, using dry-heat, and stable when stored over 40 days, without exhibiting any loss in sensitivity or response characteristics.

A viologen-based UV indicator and dosimeter

A UV indicator/dosimeter based on benzyl viologen (BV2+) encapsulated in polyvinyl alcohol (PVA) is described. Upon exposure to UV light, the BV2+/PVA film turns a striking purple colour due to the formation of the cation radical, BV center dot+. The usual oxygen sensitivity of BV center dot+ is significantly reduced due to the very low oxygen permeability of the encapsulating polymer, PVA. Exposure of a typical BV2+/PVA film, for a set amount of time, to UVB light with different UV indices produces different levels of BV center dot+, as measured by the absorbance of the film at 550 nm. A plot of the change in absorbance at this wavelength, Delta Abs(550), as a function of UV index, UVI, produces a linear calibration curve which allows the film to be used as a UVB indicator, and a similar procedure could be employed to allow it to be used as a solar UVI indicator. A typical BV2+/PVA film generates a significant, semi-permanent (stable for > 24 h) saturated purple colour (absorbance similar to 0.8-0.9) upon exposure to sunlight equivalent to a minimal erythemal dose associated with Caucasian skin, i.e. skin type II. The current drawbacks of the film and the possible future use of the BV2+/PVA film as a personal solar UV dosimeter for all skin types are briefly discussed.

Luminescence temperature sensing using poly(vinyl alcohol)-encapsulated Ru(bpy)(3)(2+) films

The ruthenium(II) diimine complexes, such as ruthenium(II) tris( bipyridyl), Ru(bpy)(3)(2+), possess highly luminescent excited states that are not only readily quenched by oxygen but also by an increase in temperature. The former effect can be rendered insignificant by encapsulating the complex in an oxygen impermeable polymer, although encapsulation often leads also to a loss of temperature sensitivity. The luminescence properties of Ru(bpy)(3)(2+) encapsulated in PVA were studied as a function of oxygen concentration and temperature and found to be independent of the former, but still very sensitive towards the latter. The results were fitted to an established Arrhenius-type equation, based on thermal quenching of the emitting state by a slightly higher (Delta E = 3100 cm(-1)) (3)d-d state that deactivates very rapidly (10(-13) s) via a non-radiative process.

Development of a novel UV indicator and dosimeter film

A novel UV indicator is described, comprising nanocrystalline particles of titania dispersed in a film of a polymer, hydroxyl ethyl cellulose (HEC), containing: a mild reducing agent, triethanolamine (TEOA) and a redox indicator, methylene blue (MB). The UV indicator film is blue-coloured in the absence of UV light and loses colour upon exposure to UV light, attaining within a few min a steady-state degree of bleaching that can provide a measure of the irradiance of the incident light. The original blue colour of the film returns once the source of UV light is removed. The spectral characteristics of a typical UV indicator film, and its components, are discussed and the UV-absorbing action of the titania particles highlighted. From the measured %bleaching undergone by a typical UV indicator as a function of light irradiance the indicator appears fully bleached, within 7 min, by a UV irradiance of 3 mW cm (-) or greater. The mechanism by which the UV indicator works is described. The reversible nature of the UV indicator is removed by covering a typical UV indicator with a thin, largely oxygen impermeable, polymer film, such as the regenerated cellulose found in Sellotape(TM). The product is a UV dosimeter, the response of which is related to the intensity and duration of the incident UV light, as well as the amount of titania in the film. A typical UV dosimeter film is fully bleached by 250 mJ cm(-2) of UV light. The possible use of these novel indicators to measure UV exposure levels, irradiance and dose, is discussed.

Luminescence of leuco-thiazine dyes

Details of the novel luminescence of the leuco forms of the thiazine dyes, methylene blue and thionine, are reported, including their emission maxima, quantum yields and lifetimes of the luminescence. Other work shows that this luminescence is independent of reducing agent type and solution pH and is a common feature of most thiazine dyes.

Anodic stripping voltammetry with photochemical preconcentration at nanocrystalline TiO2 films: Detection of Ag+ and Hg2+

Nanocrystalline TiO2 deposited on conducting glass plates is shown to be an excellent material for preconcentration of silver and mercury, via photochemical reaction, prior to their detection by anodic stripping voltammetry (ASV). During the first stage of growth in the photoreduction of silver or mercury, 3D nuclei are formed on the TiO2 film. As the deposition proceeds micrometer size agglomerates grow on the surface. The conical morphology of the silver nuclei grown on a (110) rutile single crystal in the initial stages of growth suggests that there is a preferential deposition of silver at the centre of the growing nuclei. When the nuclei size reach a critical value (ca. 400 nm diameter, 40 nm height) the morphology changes to a globular shape without any preferential site for deposition on the surface of the silver nucleus. It was observed that micromolar concentrations of silver or mercury can be detected by anodic stripping voltammetry and relatively large amounts of these metals (micrometer scale nuclei) can be loaded on the nanocrystalline TiO2 film surface. The latter opens the possibility of analytical applications of nanocrystalline TiO2 electrodes for the selective detection of silver or mercury via photochemical anodic stripping voltammetry.