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Biomedical subjects

M O'Keeffe

Publications and source records attributed to M O'Keeffe.

At least 55 records · Page 3Linked to original sources
PubMed1998

Studies on the determination of chlorotestosterone and its metabolites in bovine urine.

Chlorotestosterone and its metabolites were determined in urine samples from bovine animals treated with chlorotestosterone acetate by oral and intramuscular routes. Sample preparation, involving enzymatic deconjugation and solid-phase extraction, was optimised. The effect of different enzyme preparations, pH, and time of incubation were studied. An extraction/clean-up procedure based on solid-phase extraction (C18 cartridge) and liquid-liquid clean-up was developed. Determination of chlorotestosterone and its metabolites was by enzyme immunoassay and GC-MS. Metabolites were converted into their TMS-enol-TMS-ether and TMS-oxime-TMS-ether forms before GC-MS (EI) analysis.

Administration, Oral↗
PubMed1998

A novel sorbent for the determination of clenbuterol in bovine liver.

The use of three C18 sorbents in matrix solid phase dispersion (MSPD) for the determination of clenbuterol in bovine liver fortified at 5 ng g-1 is described. MSPD grade C18 sorbents give rise to more efficient blending and packing of the material for subsequent washing and analyte elution in comparison with a non-MSPD grade C18 sorbent. Following enzymatic deconjugation of the liver extracts, radioimmunoassay is used as the method of determination. The mean recovery of clenbuterol with all sorbents is comparable and within the range 86-96% in two intra-assay studies (n = 3). The liver extracts in each case are highly coloured. The variation in recovery is observed to be lowest with MSPD grade C18 (end-capped). This sorbent was used in further studies to evaluate the use of solid phase extraction (SPE), post MSPD, with normal phase aminopropyl or mixed mode cation exchange columns for extract purification. The mean recovery of clenbuterol (n = 4, inter-assay study) following MSPD and normal phase SPE clean-up was 95 +/- 15% and 89 +/- 9% at fortification levels of 1 and 2.5 ng g-1, respectively.

Adrenergic beta-Agonists↗
PubMed1996

Differential-pulse voltammetric determination of clenbuterol in bovine urine using a Nafion-modified carbon paste electrode.

A method has been developed for the determination of clenbuterol in bovine urine using differential-pulse voltammetry (DPV), based on the electrochemical behaviour of clenbuterol at a Nafion-modified carbon paste electrode (CPE). Clenbuterol is irreversibly oxidized at high positive potentials, its irreversibility being due to a chemical follow-up reaction which results in a product showing quasi-reversible electrochemical behaviour at much lower potentials. It is the oxidation peak of this product, arising in acidic media at 0.42 V, which was analysed using DPV, again following the accumulation of clenbuterol at the Nafion-modified CPE. Electrode renewal was achieved by holding the potential at -0.6 V for 120 s in 0.1 mol l-1 NaOH. The determination of clenbuterol in the presence of interfering compounds present in bovine urine samples was then carried out after a two-step clean-up of the urine involving liquid-liquid extraction followed by a mixed-mode solid-phase extraction procedure. This allowed clenbuterol to be detected down to a level of 1.02 x 10(-9) mol l-1 in bovine urine extracts.

Adrenergic beta-Agonists↗
PubMed1996

Analysis of protein-bound metabolites of furazolidone and furaltadone in pig liver by high-performance liquid chromatography and liquid chromatography-mass spectrometry.

Studies undertaken using radiolabelled furazolidone have demonstrated the covalent binding of residues of the drug to cellular protein in vivo. A portion of these bound residues and those formed by furaltadone, a related nitrofuran drug, possess intact side-chains, 3-amino-2-oxazolidinone (AOZ) and 5-morpholino-methyl-3-amino-2-oxazolidinone (AMOZ), respectively. These side-chains have molecular characteristics in common with the parent compounds and may be released from liver tissue under mild acidic conditions. Derivatization with 2-nitrobenzaldehyde (NBA) serves to isolate the released side-chains and the derivatives NPAOZ and NPAMOZ are chromophoric, thereby permitting UV detection. This paper reports the introduction of an extract clean-up step to the existing procedure which eliminates or decreases interference from NBA in the HPLC-UV determination of NPAOZ. The modified procedure was also applied to the determination of AMOZ. The development of an LC-MS method for the quantitative and confirmatory determination of AOZ and AMOZ extracted and derivatized according to the same procedure as that for HPLC-UV is described. The methods were validated for AOZ and AMOZ in fortified (intra- and inter-assay studies) and incurred (inter-assay studies) pig liver samples. The limit of determination for fortified control liver samples was 5 ng AOZ g-1 and 10 ng AMOZ g-1 by HPLC-UV and 10 ng AOZ or AMOZ g-1 by LC-MS. In addition, a study to determine the ratio of released AOZ to the total bound residues present in incurred liver samples from pigs treated with furazolidone is described.

Animals↗
PubMed1996

Matrix solid-phase dispersion technique for the determination of moxidectin in bovine tissues.

An HPLC method has been developed for the determination of moxidectin in bovine tissues. The extraction and clean-up procedure is based on the matrix solid-phase dispersion technique. Control and moxidectin-fortified bovine tissue samples (0.25 g) are blended with octadecyl (C18 end-capped) packing material. A column made from the C18-bovine tissue blend is washed with hexane (2 ml); when all the hexane has eluted, an Alumina-B SPE cartridge is attached below the C18-tissue column and, after washing, moxidectin is eluted with methanol (6 ml). Moxidectin is derivatized and determined by HPLC with fluorescence detection. The recovery from fortified samples was greater than 80% in the concentration range 1-100 ng g-1 of tissue. This method permits the determination of moxidectin at levels as low as 1 ng g-1 (1 ppb).

Animals↗
PubMed1995

Rapid analysis of beta-agonists in urine by thermospray tandem mass spectrometry.

A method is described for the analysis of beta-agonists in urine of cattle. The method uses solid-phase extraction (SPE), followed by analysis of the resulting extract by flow injection thermospray tandem mass spectrometry (TSP-MS-MS). Sample preparation is performed using a mixed-bed SPE procedure using a sorbent having both hydrophobic and ionic properties. MS-MS analysis following thermospray ionization, is performed in single-reaction monitoring parent mode. In that way isotope dilution can be used for quantitation of clenbuterol. Data are presented on precision and accuracy for clenbuterol and related compounds. Furthermore, data acquisition was performed in full-scan neutral loss mode to indicate the suitability of flow injection analysis (FIA)-TSP-MS-MS for exploratory analysis. Detection of beta-agonists in this mode is based on the presence of the N-tert.-butyl-beta-ethanolamino moiety and, in that respect, detection of known as well as unknown compounds having this moiety will take place. This feature is exemplified by the analysis of samples containing several compounds.

Adrenergic beta-Agonists↗
PubMed1995

Convergence substitution for paralysed horizontal gaze.

Three patients with paralysed horizontal gaze are presented. Involuntary use of convergence to assist horizontal gaze was noted as a late feature. All patients showed (1) unilateral or bilateral horizontal gaze palsy (two patients had one and a half syndrome, the other had bilateral nuclear sixth nerve palsies), (2) adduction of both eyes on attempted gaze into the paralysed field, (3) miosis which coincided with adduction. Convergence substitution should be considered in the differential diagnosis of gaze induced strabismus.

Accommodation, Ocular↗
PubMed1994

Matrix solid-phase dispersion as a multiresidue extraction technique for beta-agonists in bovine liver tissue.

A procedure for the extraction of salbutamol including conjugated forms of the drug, from liver samples, is described. It combines matrix solid-phase dispersion with radioimmunoassay for the measurement of salbutamol residues at the sub-ppb level. Inter- and intra-assay validation, carried out on fortified liver samples, show good recoveries over the range 1-5 ppb of salbutamol. An enzyme hydrolysis procedure was optimized for the deconjugation of incurred residue. The developed procedure is shown to be suitable for the extraction and determination of other beta-agonists such as clenbuterol, mabuterol, terbutaline, and cimaterol at residue levels of less than 1 ng g-1.

Adrenergic beta-Agonists↗
PubMed1994

Application of the matrix solid phase dispersion technique for the determination of ivermectin residues in fish muscle tissue.

A modified high-performance liquid chromatographic method has been developed for the determination of ivermectin (IVM) residues in fish muscle tissue. The extraction and clean-up procedure is based on the matrix solid phase dispersion technique. Control and IVM-fortified fish muscle samples (0.5 g) are blended with octadecyl (C18 end-capped) packing material. A column made from the C18-fish tissue blend is washed with hexane (8 ml) and the IVM is eluted with 8 ml of dichloromethane-ethyl acetate (3 + 1). Ivermectin is derivatized and analyzed by high-performance liquid chromatography (HPLC) with fluorescence detection. The recovery from fortified samples was greater than 80% in the concentration range 20-100 ng g-1 of tissue. The limit of determination was 10 ng g-1 of tissue. This method and another, using solvent extraction and clean-up of the extract on a solid phase extraction cartridge, gave comparable results for an incurred sample containing IVM residue. This method incorporates a rapid sample pre-treatment step which makes it an attractive and useful method for routine analysis of IVM in fish muscle tissue.

Animals↗
PubMed1994

Multi-residue analysis for beta-agonists in urine and liver samples using mixed phase columns with determination by radioimmunoassay.

A method is described for the extraction of four beta-agonists, clenbuterol, salbutamol, mabuterol and terbutaline from bovine urine and liver samples using radioimmunoassay (RIA) as the method of determination. Following enzymic digestion of the liver samples using protease enzyme, the digest is centrifuged and the harvested supernatant is saturated with sodium chloride and adjusted to pH 11.0. An ethyl acetate-propan-2-ol mixture is used to extract the beta-agonists from the liver digest. The samples of urine and liver extracts are adjusted to pH 6.0 and applied to mixed phase (XtrackT) columns. The column is washed with water and methanol and the beta-agonists are eluted with methanol containing 2% ammonia. After evaporation of the eluting solvent and reconstitution in ethanol the beta-agonist residues are determined by RIA, with standard graphs prepared in residue-free sample extract. The procedure has been validated for clenbuterol, salbutamol, mabuterol and terbutaline. The mean recovery of the beta-agonists from urine and liver is > 75% and > 85%, respectively. The detection limit is 0.13 ng ml-1 and 0.46 ng g-1 of clenbuterol in urine and liver, respectively. The high recoveries attained for both types of beta-agonists are a result of an efficient liquid-liquid extraction step coupled with a selective mixed solid-phase extraction procedure.

Adrenergic beta-Agonists↗
PubMed1994

Novel approach to the 'on-site' testing for sulfamethazine in pork carcasses.

Rapid 'on-site' methods are required by the pork industry to screen for the presence of antibiotic residues in meat and meat products. There are few rapid and easy-to-use methods suitable for application in non-analytical laboratories. This paper describes a novel approach for the screening of sulfamethazine in pork muscle using matrix solid phase dispersion, a microcolumn preconcentration step and thin-layer chromatographic detection. The characteristics of the method are reported allowing for the detection of residues at the maximum residue limit of 100 ppb. Results from the industrial evaluation of the complete method are also presented.

Animals↗
PubMed1991

Reversed-phase high-performance liquid chromatographic determination of dexamethasone in bovine tissues.

A sensitive and selective high-performance liquid chromatographic procedure is described for the determination of the synthetic corticosteroid dexamethasone (DXM), in bovine muscle, kidney, liver and fat tissues, using methylprednisolone as the internal standard. Following extraction with ethyl acetate (muscle, kidney and liver) or diethyl ether (fat) and clean-up of the tissue extract, the drug residue was isolated using a C18 solid-phase extraction column. Separation of DXM was achieved by reversed-phase high-performance liquid chromatography with ultraviolet detection at 254 nm. By using this procedure, DXM levels as low as 0.01 mg kg-1 can be detected in muscle, kidney, liver and fat.

Adipose Tissue↗