Richard M. Parker

Depletion of protein‐bound furazolidone metabolites containing the 3‐amino‐2‐oxazolidinone side‐chain from liver, kidney and muscle tissues from pigs

Ten 3-month-old pigs were treated with feed containing 300 mg furazolidone per kg for a period of 7 days, followed by withdrawal periods of 0, 1, 2, 3 or 4 weeks (two per group). The treatment resulted in the formation of protein-bound metabolites containing an intact 3-amino-2-oxazolidinone (AOZ) side-chain that could be chemically released and then detected in liver, kidney and rump muscle tissues even 4 weeks after dosing. In tissues from animals killed at the end of the medication period, 993, 600 and 124 ng of AOZ were released from 1 g of liver, kidney and muscle respectively. In the tissues of the animals killed after a further 4 weeks the corresponding levels were 41, 7 and 10 ng/g respectively. It may be concluded that long withdrawal periods prior to slaughter for human consumption are required for pigs treated with furazolidone, because of the long residence time of protein-bound AOZ and the possibility that it might be released from its protein-bound form in the stomach and subsequently be transformed into a hydrazine.

Using the photoinduced reversible refractive-index change of an azobenzene co-polymer to reconfigure an optical Bragg grating

A photoactive material has been synthesised in which azobenzene units are attached to a methyl methacrylate/2-hydroxyethyl methacrylate co-polymer and shows repeated photoresponsive switching upon irradiation at 365 nm and 254 nm with long term thermal stability. In combination with a direct UV-written silica-on-silicon Bragg grating, this has been used to fabricate a prototype optical device which undergoes reversible refractive index changes at telecom wavelengths. The 63 GHz tuning response demonstrated by this device has potential applicability for reconfigurable dispersion compensation for use in optical networks.

In vacuo measurement of the sensitivity limit of planar Bragg grating sensors for monolayer detection

An exposed Bragg grating incorporated into a planar waveguide was used to form an optical device that acts as a refractive index sensor. The exposed evanescent field causes the Bragg peak to be sensitive to the refractive index of its surroundings. The corresponding shift in peak wavelength can be used to detect changes in this environment. Incorporation of a high index overlayer onto the surface has been shown to dramatically enhance this sensitivity. The sensitivity limit was measured via the deposition of a thin film of silica, demonstrating that the system can measure down to a single surface monolayer.

Determination of chloramphenicol in tissues—problems with in vitro metabolism

Residues of drugs and other chemicals used in meat production are covered by EEC Directives; compliance with such Directives requires sensitive analytical techniques for residues analysis. One such drug, chloramphenicol, is used in farm animals and is a potential problem for the residues analyst because it is metabolised rapidly. The cytochrome P450 mediated metabolism occurs both in vivo and in vitro in tissues removed from the animal. It is shown here that chemical inhibition of cytochrome P450 significantly increases the recovery of chloramphenicol from spiked liver samples. It is suggested that piperonyl butoxide, a potent cytochrome P450 inhibitor, be used to inhibit the enzyme system during the determination of chloramphenicol.

A Bragg grating sensor for detection of monolayers at a surface

Planar waveguides can be written with a UV-laser into photosensitized silica to produce a wide range of optical devices. Careful modulation of two interfering beams allows Bragg gratings to be directly written into the channel (Figure 1.a). These Bragg gratings are inherently sensitive to temperature and strain. However etching away the surface exposes the mode within the grating to its surroundings. The corresponding observed shift in Bragg wavelength can be used to detect changes in this environment [1]. Figure 1.b shows a large wavelength shift due to two analytes of markedly different refractive index. This demonstrates the apodised spectral response that in practice allows resolution of sub-picometer shifts in wavelength.

Determination of tilmicosin in ovine milk using high-performance liquid chromatography

Tilmicosin is a novel macrolide antibiotic with a wide range of therapeutic uses against gram positive (+ve) and gram negative (-ve) bacteria and mycoplasmae causing pneumonia and mastitis and can be used to treat these diseases in sheep. After its use there may be residues present in ovine milk that interfere with cheese making and processing of other milk products. It is important to monitor for the presence of tilmicosin in ovine milk and a method has been optimized and validated for its determination. Tilmicosin is extracted from milk into methanol. The methanol extract is acidified and non-polar co-extractives removed using hexane followed by carbon tetrachloride. The pH is adjusted to 9.0 and the tilmicosin partitioned into chloroform. The chloroform extract is evaporated to dryness and the residue resuspended in high-performance liquid chromatography (HPLC) mobile phase. Tilmicosin is determined using reversed-phase HPLC and ultraviolet (UV) detection at 280 nm. Recovery of tilmicosin from ovine milk fortified over the range 50 to 250 micrograms l-1 is in the range 84.3-104.8%, with a relative standard deviation ranging from 6.6 to 12.9%. The proposed procedure allows the determination of residues of tilmicosin in ovine milk at levels less that 50 micrograms l-1 and satisfies the quality criteria specified in European Commission Decision 93/526/EEC with the exception of reproducibility data from interlaboratory trials.

An integrated bragg grating oxygen sensor using a hydrophobic sol-gel layer doped with an organic dye

Oxygen sensing is required for the understanding of many chemical processes across a diverse set of fields including medicine, environmental science and chemical synthesis. Oxygen sensing can be achieved through the use of electronic sensors. However, there are limitations associated with electronic sensors including susceptibility to electromagnetic interference and presenting a spark risk in flammable environments. Optical fiber and integrated optical chemical sensors overcome these limitations of electrical based sensing methods.

An integrated optofluidic Bragg grating device to measure the dynamic composition of a fluid system

Strong transitional mixing effects were observed by a planar Bragg grating sensor within a microfluidic system. This property was used to develop an integrated optofluidic sensor for detection of the composition of mixed solvent systems.

UV written integrated Bragg grating sensors

An overview of the fabrication and geometries of integrated planar Bragg sensors will be described including refractive index sensors for chemical detection and applications of micro-structured devices for physical detection.

Optofluidic integrated bragg grating chemical sensor: Utilising a sodium-selective receptor surface to enhance detection

Planar waveguides can be written with a UV-laser into photosensitised silica to produce a wide range of optical devices. Careful modulation of two interfering beams allows Bragg gratings to be directly written into the channel. These Bragg gratings are inherently sensitive to temperature and strain, however etching away the surface exposes the mode within the grating to its surroundings. The corresponding observed shift in Bragg wavelength can be used to detect changes in this environment [1]. It has been previously reported [2] that the sensitivity of such a refractometer can be enhanced by over an order of magnitude through use of a high-index overlayer of tantalum pentoxide. This enhanced sensor has shown the potential to detect a single molecular monolayer upon the sensor surface [2]. This sensitivity was confirmed through the successful attachment and detection of a single molecular monolayer of a fluorescein-based organic dye to the sensor surface [3].