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Biomedical subjects

J F Lawrence

Publications and source records attributed to J F Lawrence.

At least 19 recordsLinked to original sources
PubMed1992

Paralytic shellfish poison (saxitoxin family) bioassays: automated endpoint determination and standardization of the in vitro tissue culture bioassay, and comparison with the standard mouse bioassay.

Mouse neuroblastoma cells swell and eventually lyse upon exposure to veratridine, which, when added together with ouabain, enhances sodium ion influx. In the presence of saxitoxin (STX), which blocks sodium channels, the action of the other two compounds is inhibited and the cells remain morphologically normal. A tissue culture bioassay using mouse neuroblastoma cells, developed by Kogure and colleagues, takes advantage of these principles; in this bioassay, the fraction of the cells protected from the actions of ouabain and veratridine is in direct proportion to the concentration of STX and its analogues. We have modified this bioassay, improving its convenience and speed by eliminating the need to count individual cells to determine the saxitoxin equivalents, and instead have employed a microplate reader for automated determinations of absorbances of crystal violet from stained neuroblastoma cells. When these changes and other minor technical modifications were tested in the tissue culture bioassay systematically, we found the lower detection limit to be around 10 ng STX equivalents (eq) per ml of extract ( = 2.0 micrograms STX eq/100 g shellfish tissue). Our version of the tissue culture bioassay was compared with the standard mouse bioassay using 10 acid extracts of dinoflagellates (Alexandrium excavata and A. fundyense) and 47 AOAC extracts of shellfish tissues. The tissue culture bioassay provided results virtually identical to those obtained with the mouse bioassay (r > 0.96), and moreover, was considerably more sensitive. The results gained from high performance liquid chromatographic (HPLC) analysis of 12 of the same extracts were less consistent when compared with the results from both bioassay methods. The automated tissue culture (neuroblastoma cell) bioassay may be a valid alternative to live animal testing for paralytic shellfish poisoning.

Animals↗
PubMed1991

Confirmation of domoic acid in shellfish using butyl isothiocyanate and reversed-phase liquid chromatography.

A simple chemical confirmatory technique has been developed for domoic acid, a neurotoxic amino acid of marine origin. After extraction with water-methanol, the domoic acid-containing extract is analysed directly by reversed-phase liquid chromatography with UV absorption detection at 242 nm. For confirmation of positive results an aliquot of the extract is evaporated to dryness and reacted with butyl isothiocyanate to form a thiourea derivative which elutes later than underivatized domoic acid. No additional sample cleanup is required in order to carry out the derivatization for conformation of domoic acid at the Canadian 20 micrograms/g guideline level in shellfish. In mussel extract, domoic acid was converted to the thiourea derivative with a yield of 86-91% compared to a pure standard carried through the same reaction. The detection limit for the derivative was about 5-10 micrograms/g of equivalent domoic acid in extracts of mussels, clams or oysters.

Animals↗
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↗
PubMed1978

Gas-liquid chromatography of triazine herbicides as heptafluorobutyryl derivatives and some applications to analysis in foods.

The heptafluorobutyryl (HFB) derivatives of ten triazine herbicides were prepared by reacting the pesticides with heptafluorobutyric anhydride in benzene, in the presence of trimethylamine or pyridine as catalyst. The reactions produced mainly the mono-HFB products while some of the herbicides had small quantities of the di-HFB derivatives present. The derivatives were 300 fold to several thousand fold more sensitive to electron-capture detection than the underivatized triazines. They also were 5-10 fold more sensitive than the parents by electrolytic conductivity detection in the halogen mode while they were of similar sensitivity with the same detector in the nitrogen mode. The derivatives eluted in the same general order as the parent triazines on stationary phases of OV-1, OV-101, OV-101/QF-1, and OV-210. This method was successfully applied to the analysis of potatoes, peas and tomatoes spiked with various triazines at levels of 0.13-0.86 ppm.

Chromatography, Gas↗
PubMed1978

Detection of goitrin and its heptafluorobutyryl derivative by gas-liquid chromatography with electron capture, electrolytic conductivity and sulfur detectors.

The separation of goitrin by two gas-liquid chromatographic columns, the response of different detectors and the use of the heptafluorobutyric (HFB) anhydride derivative of goitrin to improve sensitivity was investigated. The non-polar 3% OV-1 and the intermediate 4% SE-30/6% SP-2401 on 80-100 mesh Chromosorb W HP gave comparable results and were considered interchangeable. The sensitivities of the electron capture, sulfur 394 nm emission, chlorine and nitrogen Coulson electrolytic conductivity detectors were inadequate for goitrin per se. Chromatography and sensitivity of all detectors to goitrin were greatly improved by using by using the HFB derivative. It was possible to detect 1 to 60 ng of goitrin-HFB in standard solutions. Application of the technique to goitrin-spiked (2 ppm) milk, cleaned up by high-performance liquid chromatography, encountered no problems and was considered satisfactory for all four detectors.

Animals↗
PubMed1978

High-pressure liquid chromatographic analysis of carbofuran and two non-conjugated metabolites in crops as fluorescent dansyl derivatives.

Carbofuran, and non-conjugated 3-hydroxycarbofuran and 3-ketocarbofuran were extracted from carrots, corn and potatoes with acetone and partitioned into hexane-methylene chloride. The organic extract was evaporated to a small volume for clean-up on a 2% deactivated Florisil column. All three carbamates were eluted with 15% acetone in hexane. The pesticide residues were hydrolysed to their corresponding phenols with 0.1 M sodium carbonate followed by derivatization with dansyl chloride in acetone. The derivatives were extracted and analysed by high-pressure liquid chromatography with fluorescence detection (excitation, 360 nm; emission, greater than 400 nm). Absolute recoveries for all three compounds were between 50 and 65% for spiked samples by the extraction method used. Detection limits approached 0.01 ppm in the foods studied.

Carbofuran↗
PubMed1978

High pressure liquid chromatography with ultraviolet absorbance or fluorescence detection of carbaryl in potato and corn.

Carbaryl (1-naphthyl-N-methylcarbamate) was extracted from corn and potato with acetone. The acetone extract was partitioned into methylene chloride-hexane and concentrated for cleanup on a 5% water-deactivated Florisil column. The fraction containing the carbamate was subjected to high pressure liquid chromatographic (HPLC) analysis on a 25 cm LiChrosorb Si60 (5 micron) column (2.2 mm id) by various means. First, the pesticide was analyzed directly with ultraviolet (UV) absorption detection at 254 nm and a mobile phase of trimethyl-pentane-isopropanol (96 + 4). After this, a fluorescent derivative was prepared, using dansyl chloride (5-dimethylaminonaphthalene-1-sulfonyl chloride), and analyzed by HPLC, using trimethylpentane-dioxane (95 + 5) as the mobile phase, with both UV absorption (254 nm) and fluorescence (excitation 365 nm, emission greater than 400 nm) detection. The response/ng for the dansyl derivative with fluorescence detection was 1.3 times greater than that for UV detection and 8 times more sensitive than direct UV detection of the carbamate. About 10 ppb carbaryl could be detected after derivatization in the foods studied; for direct analysis, 30-50 ppb could be detected at a 2:1 signal:noise ratio. Recoveries at 0.1 ppm averaged 90% by direct analysis compared with 78% after derivatization.

Carbaryl↗