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Biomedical subjects

J F Lawrence

Publications and source records attributed to J F Lawrence.

At least 37 records · Page 2Linked to original sources
PubMed1991

Toxicity of potassium cyanide added to fresh fruit and juice.

To investigate the toxicity of potassium cyanide in fresh fruit and juice, male and female Wistar rats were orally dosed with fruit homogenates or juices containing 3 x LD50 of potassium cyanide. These were given in single doses at various intervals after spiking. The dosing solutions were analysed for cyanide using a cyanide test kit. There was a good correlation between the toxic signs in rats and the cyanide remaining in dosing solutions. The toxicity of spiked apple and honeydew melon diminished with time, while spiked grape and both grape and apple juices maintained their toxicity during the 4-hr studies. The pH of the samples both before and after spiking seemed to be an important factor in determining the toxicity.

Administration, Oral↗
PubMed1990

Determination of domoic acid in seafoods and in biological tissues and fluids.

Domoic acid is extracted from mussel tissue using the Association of Official Analytical Chemists procedure for paralytic shellfish toxins. This involves boiling the sample for 5 min with O.1N HCl then cooling and centrifuging. An aliquot of the supernatant is diluted 10 to 100 times with water, filtered and analyzed by reversed-phase liquid chromatography with a mobile phase of acetonitrile-water (12:88) at pH 2.5 and absorption detection at 242 nm. The detection limit is about 1 mg/kg domoic acid in seafood samples. The method was successfully used in collaborative studies and a survey of 44 different commercially purchased shellfish products from areas outside of Prince Edward Island showed no domoic acid greater than 1 mg/kg. The same method was applied to urine and feces from monkeys and blood (serum) from humans. The method was unsuccessful for urine and blood which required additional cleanup before analysis. The method worked well for feces at domoic acid levels greater than 1 mg/kg.

Animals↗
PubMed1989

Liquid chromatographic determination of domoic acid in shellfish products using the paralytic shellfish poison extraction procedure of the association of official analytical chemists.

Domoic acid, the recently discovered toxic substance found in contaminated mussels from an area in eastern Prince Edward Island (Canada) was extracted from mussel tissue using the procedure of the Association of Official Analytical Chemists for paralytic shellfish poisons. This involved a 5-min boiling of the sample with 0.1 M hydrochloric acid then cooling and centrifuging. An aliquot of the supernatant was diluted ten to one-hundred times with water, filtered and analysed by reversed-phase liquid chromatography with a mobile phase consisting of acetonitrile-water (12:88) at pH 2.5 and an absorption wavelength of 242 nm. The detection limit was about 0.5 mg/kg domoic acid in seafood samples. The technique was successfully applied to a variety of commercially purchased shellfish and shellfish products.

Animals↗
PubMed1988

Direct, sensitive and selective detection of free fatty acids by high-performance liquid chromatography with post-column ion-pair extraction and absorbance detection.

Free fatty acids (C8-C18) are separated by reversed-phase liquid chromatography and detected using a simple post-column dynamic extraction system in which the acids are extracted as ion pairs with chloroform from the aqueous acetonitrile (gradient: 79-99% acetonitrile) mobile phase after the post-column addition of aqueous Methylene Blue solution. The chloroform phase containing the ion pairs is monitored with an absorbance detector at 651 nm. The detection limits ranged from 26 to 83 ng, depending upon the acid, with coefficients of variation of 1.2-14%. Application of the method to butter and margarine samples permitted detection of free fatty acids down to 35 ppm and in orange juice, down to 0.5 ppm using only an organic solvent extraction without further sample clean-up for isolation of the fatty acids.

Acetonitriles↗
PubMed1987

Analytical methodology for organophosphorus pesticides used in Canada.

An overview of analytical methodology for the determination of organophosphate pesticides residues in foods is presented. Sample extraction is carried out with acetone followed by a dichloromethane-hexane partition. The organic extract is purified by automated gel permeation chromatography and analysed by capillary gas chromatography with flame photometric or thermionic detection. Confirmation can be carried out by a variety of chemical derivatization techniques including hydrolysis followed by reaction of the phosphate or phenol moiety, direct alkylation or trifluoracetylation. Thin-layer chromatography with enzyme inhibition detection can be used as a rapid screening technique or to confirm results obtained by gas chromatography. Liquid chromatography has not been used much for the determination of organophosphorus compounds in foods.

Canada↗
PubMed1987

Recent developments in derivatization for the chromatographic determination of food additives.

Recent applications of chemical derivatization for the determination of a variety of food additives is presented. Several classes of additives such as emulsifiers, stabilizers, preservatives, sweeteners, colors, waxes, gums, and some indirect additives are included. Derivatization or modification reactions for both gas (GC) and liquid chromatography (LC) are discussed. Postcolumn complexation or ion-pairing reactions for LC are also included. Derivatization reactions for GC mainly involve esterification, alkylation, or silylation for improving volatility of the analyte. The addition of chromophores (via coupling reactions) for improved detection is the main reason for forming derivatives for LC.

Chromatography, Gas↗
PubMed1986

Determination of nanogram/kilogram levels of polycyclic aromatic hydrocarbons in foods by HPLC with fluorescence detection.

Methodology was developed for the determination of eight polycyclic aromatic hydrocarbons (PAH) in five food categories including meat/fish, dried dairy products, cereals, leafy vegetables and vegetable/marine oils. The eight PAH were fluoranthene, benzo[a]anthracene, benzo[k]fluoranthene, benzo[b]fluoranthene, benzo[a]pyrene, 7,12-dimethylbenzo[a]anthracene, dibenzo[ah]anthracene and dibenzo[ai]pyrene. Samples were digested with alcoholic KOH followed by partitioning into solvents such as cyclohexane or isooctane. Lipids and other interferences were removed by solvent partitioning with dimethylformamide or dimethylsulfoxide/water. Additional cleanup involving column chromatography on silica gel, Florisil or Sephadex LH-20 was employed as required. Reversed-phase chromatography with gradient elution and fluorescence detection was employed for the determinations. Confirmation was carried out by GC-MS/SIM. Detection limits ranged from 2-90 ng/kg depending on the PAH and food analyzed. Results of a small survey indicated that the meat/fish category had the highest levels (low microgram/kg, on average) of the foods studied.

Animals↗
PubMed1985

Gas chromatographic determination of polysaccharide gums in foods after hydrolysis and derivatization.

A gas chromatographic method was evaluated for the determination of food grade gums in dairy products, salad dressings and meat sauces. The gums studied were tragacanth, karaya, ghatti, carob, guar, arabic and xanthan gum. The extraction method included removal of fat followed by starch degradation then precipitation of protein. The isolated gums were hydrolysed with trifluoroacetic acid and the resulting neutral monosaccharides converted to their aldonitrile acetate derivatives for determination by gas chromatography. Recoveries from thirteen different commodities averaged 85%. However, the recovery of guar gum from ice cream and cold pack cheese was 42 and 50%, respectively. In a comparison of enzyme hydrolysis and iodine complexation for the removal of starch the former was simpler and provided cleaner extracts than the iodine treatment. Both gave similar results.

Carbohydrates↗