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Biomedical subjects

S A Thorpe

Publications and source records attributed to S A Thorpe.

15 recordsLinked to original sources
PubMed1998

The analysis of cyhexatin residues in apples, pears and kiwi fruit using inductively coupled plasma mass spectrometry as an initial screen for total tin, with confirmation by gas chromatography-mass spectrometry.

Inductively coupled plasma-mass spectrometry (ICP-MS) has been used to determine concentrations of total tin in samples of apples, pears and kiwi fruit, following acid digestion. It was found that the background levels of tin in these fruits were normally below 0.06 mg/kg, which was equivalent to the target reporting limit for cyhexatin for this work of 0.2 mg/kg. The procedure was used to screen a total of 72 retail samples. Three apple samples contained tin at concentrations greater than 0.06 mg/kg. These three samples were re-analysed by a second confirmatory method using gas chromatography-mass spectrometry (GC-MS) as the determinative step. Results obtained by this method demonstrated that in fact, none of the samples contained cyhexatin residues at or above a reporting limit of 0.1 mg/kg. The use of ICP-MS as a preliminary screen substantially reduced the number of samples requiring analysis by GC-MS, thus reducing the cost of the survey (in terms of staff hours) by approximately 30%. The screening method could potentially be applied to other organometallic pesticide residues.

Chromatography, Gas↗
PubMed1998

The carry-through of residues of maleic hydrazide from treated potatoes, following manufacture into potato crisps and 'jacket' potato crisps.

Potatoes, which had been treated 'in the field' with a commercial formulation of maleic hydrazide, were processed into potato crisps and jacket potato crisps on a factory production line using standard manufacturing conditions. Samples were taken at strategic points throughout the process and analysed to determine the degree of carry-through of residues. Results demonstrated that ca 56% of the maleic hydrazide residue in a potato could be carried through into the potato crisps, irrespective of which type of crisp was being manufactured. Results from a similarly constructed study investigating the fate of pesticides applied post-harvest showed that carry-through was less than 10%. This difference is explained in terms of the different modes of action of the two classes of pesticides being investigated. It is known that, as maleic hydrazide is a systemic pesticide, it will be located within the flesh of the potato tuber and is therefore likely to be protected from the various stages of the crisping process. However, the post-harvest non-systemic pesticides are applied to the exterior surface of the tuber and are therefore not likely to be protected in the same way. The results also showed that, due to the concentration effect caused by the loss of moisture during crisp manufacture, the levels of maleic hydrazide residues in crisps (on a mg/kg product basis) were approximately twice those measured in the original potatoes.

Agrochemicals↗
PubMed1996

Extraction of maleic hydrazide residues from potato crisps and their determination using high-performance liquid chromatography with UV and atmospheric pressure chemical ionisation mass spectrometric detection.

A method was required for the determination of maleic hydrazide residues in potato crisps. A published method for the extraction of the analyte from onions and potatoes was evaluated and found to be inappropriate due to the inability of the extracting solvent to penetrate the oily matrix. A method was developed to overcome this problem; the resulting recovery data (mean = 92.9%, R.S.D. = 8.3%, n = 16) confirmed its efficiency, and was used to analyse 48 retail potato crisp samples. To confirm possible residues identified by screening with HPLC-UV, an HPLC-atmospheric pressure chemical ionization MS method was developed. There was good agreement between the data obtained from the two detection techniques (R2 = 0.978, slope = 1.11).

Chromatography, High Pressure Liquid↗
PubMed1996

Accreditation in the UK for pesticide residue analysis in foods.

A brief background is provided of the European national bodies which accredit laboratories to the EN 45001 standard and their mutual recognition through the European Cooperation for Accreditation of Laboratories. Some of the requirements for accreditation of a laboratory, for example, the need to demonstrate traceability of measurements, are selectively illustrated with particular reference to the determination of pesticide residues in foods. The costs and benefits of accreditation are discussed.

Accreditation↗
PubMed1995

Determination of the pesticide diflubenzuron in mushrooms by high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry.

A method using high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry (HPLC-APCI-MS) has been developed and validated for the determination of the insecticide diflubenzuron [1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea] in mushrooms. Samples were homogenised with acetone, extracted into dichloromethane-cyclohexane and further cleaned-up by size-exclusion chromatography (SEC). HPLC was performed on an ODS column with methanol-water at 1 ml/min. The limit of detection was 0.02 ng/microl (equivalent to 0.017 mg/kg in the crop). The calibration was linear over the range 0.025-1.0 ng/microl. Recovery of diflubenzuron from spiked mushrooms (0.06-0.58 mg/kg) was 85.5% with a relative standard deviation of 14.5% (n = 56).

Atmospheric Pressure↗
PubMed1995

Determination of the pesticides diflubenzuron and clofentezine in plums, strawberries and blackcurrant-based fruit drinks by high performance liquid chromatographic/atmospheric pressure chemical ionization-mass spectrometry.

A high performance liquid chromatographic/atmospheric pressure chemical ionization-mass spectrometric (HPLC/APCI-MS) method has been developed for the determination of the pesticides diflubenzuron (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea) and clofentezine (3,6-bis(2-chlorophenyl)-1,2,4,5-tetrazine) in plums, strawberries and blackcurrant-based fruit drinks. Samples were homogenized with acetone, extracted into dichloromethane + cyclohexane and cleaned-up by high performance gel permeation chromatography. HPLC was performed on an ODS column with methanol + water at 1 mL/min. Detection was by negative-ion selected-ion monitoring APCI-MS. Comparison of response with solvent and matrix-matched standards showed some enhancement of response for the latter, and these standards were consequently used for quantification. The calibration was linear over the range 0.05-0.50 ng/microL in all three matrices. The mean overall recovery of diflubenzuron and clofentezine from spiked extracts (0.086 mg/kg) in all three matrices was 76% and 70% respectively with relative standard deviations of 15% and 12% respectively (n = 12). The limit of detection was both compound and commodity dependent and ranged from 0.01-0.05 ng/microL, equivalent to 0.003-0.014 mg/kg in the crop.

Basidiomycota↗
PubMed1979

Bubbles in a freshwater lake.

WHEN the wind is strong enough to produce whitecaps on Loch Ness, patchy 'clouds' of acoustic reflectors are detected well below the surface, the depth to which they penetrate increasing with wind speed (Fig. 1). No seasonal variation in the occurrence of the reflectors has been detected. A biological explanation is therefore discounted and we suggest here that they are bubbles caused by waves breaking and forming whitecaps in deep water. Similar bubble clouds may occur in other lakes and in the sea.

Journal Article↗
PubMedDate not supplied

Survey of animal livers for vitamin A content.

Retail samples of livers from calf (23), ox (18), lamb (17), pig (15), chicken (16) and turkey (1) were analysed to determine levels of vitamin A (all trans-retinol) and to aid assessment of the effects of using vitamin supplemented compound feedingstuffs for livestock. For comparison, 22 liver samples from lambs reared on diets not containing vitamin-supplemented compound feedingstuffs and four samples of liver from ox which had received supplemented feed but not during the last four months prior to slaughter were also analysed. The chosen method of analysis utilized saponification, solvent extraction and normal-phase high performance liquid chromatography with fluorescence detection. For all species analysed, the levels of vitamin A ranged from 10 to 1100 mg/kg, with all but seven at or below 400 mg/kg. For lamb and ox livers, the mean levels were 310 mg/kg and 200 mg/kg respectively for retail samples. The mean levels were 220 mg/kg (lamb) and 120 mg/kg (ox) in liver samples from animals fed controlled diets. The results are of the same order as those reported over recent years.

Animals↗
PubMedDate not supplied

A rapid capillary gas chromatographic method for the determination of propionic acid and propionates in bread and bread products.

A rapid method for the determination of propionic acid and propionates in bread and bread products is reported. The method employs solvent extraction, filtration and quantification by capillary gas chromatography using an internal standard. The limit of determination was 10 mg kg-1 propionic acid. The mean recovery rates for spiked bread samples were 108% at approximately 1,000 mg kg-1 (range of 106-110%, coefficient of variation 1.1%), 97% at approximately 2,000 mg kg-1 (range 96-98%, coefficient of variation 0.7%) and 98% at approximately 3,000 mg kg-1 (range of 97-100% and coefficient of variation of 1.1%). The method offers improved sensitivity, precision, chromatographic resolution and a wider sample analyte concentration range over a previously reported packed-column gas chromatographic method and has been applied to the analysis of bread, rolls, pitta breads and hamburger buns.

Bread↗
PubMedDate not supplied

Characterization of the principal colouring components of annatto using high performance liquid chromatography with photodiode-array detection.

The principal colouring components of the natural food colouring material annatto, the 9'-cis- and all-trans- isomers of bixin and norbixin, have been prepared in pure form. A reverse-phase HPLC method utilizing photodiode-array detection has been developed to enable their chromatographic and spectroscopic characterization. One minor component, a di-cis-isomer of norbixin has also been identified and characterized.

Carotenoids↗
PubMedDate not supplied

Survey of baked goods for propionic acid and propionates.

One hundred and thirty samples comprising bread (64), hamburger buns (33), pittas (16), cakes (9) and Christmas puddings (8) from various retail outlets in the UK, have been analysed for the preservative propionic acid. Only one sample of bread, two samples of hamburger buns and three samples of pitta contained propionic acid in excess of 1000 mg/kg (range 1110-2625 mg/kg). The three samples of pitta exceeded 2000 mg/kg of propionic acid, which is the maximum amount permitted for these products under a recently adopted European Union directive.

Bread↗
PubMedDate not supplied

The carry-through of residues of thiabendazole, tecnazene and chlorpropham from potatoes following manufacture into potato crisps and jacket potato crisps.

Potatoes, commercially treated with thiabendazole, tecnazene and chlorpropham, were processed into potato crisps and jacket potato crisps at a crisp factory using standard manufacturing conditions. A multi-residue method based on gas chromatography with mass spectrometric detection was developed and used to determine pesticide residue levels in the potatoes and potato crisps. Results showed that the residues of all three pesticides were significantly reduced to less than 2% and less than 10% of the maximum theoretical residue carry-through level for potato crisps and jacket potato crisps respectively.

Chlorpropham↗