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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↗
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↗
PubMed1977

Detection of carbofuran and metabolites directly or as their heptafluorobutyryl derivatives using gas-liquid or high-pressure liquid chromatography with different detectors.

The gas chromatography of the heptafluorobutyryl derivatives of carbofuran, 3-ketocarbofuran and 3-hydroxycarbofuran is examined with electrolytic conductivity detection (halogen mode). The reaction consists of heating the compounds with heptafluorobutyric anhydride in the presence of trimethylamine catalyst. Although as little as 200 pg of carbofuran, 400 pg of 3-ketocarbofuran and 100 pg of 3-hydroxycarbofuran can be detected by electrolytic conductivity, the minimum detectable quantities by electron capture are about 20-fold less for each derivative. Application to the analysis of carbofuran and 3-ketocarbofuran in corn, potato, turnip and wheat is carried out. This technique is compared to direct gas chromatography in the nitrogen mode and to direct high-pressure liquid chromatography with UV detection at 254 nm using extracts of field-treated turnips.

Carbofuran↗
PubMed1977

Comparison of electron-capture and electrolytic conductivity detection for the gas-liquid chromatographic analysis of some perfluoro derivatives of four agricultural chemicals.

The gas chromatographic response of four perfluoro derivatives, of four agricultural chemical [diethylstilbestrol] (DES) clopidol, linuron and carbofuran] was examined. The derivatives varied in fluorine content from 3 to 30 atoms per molecule. The sensitivities of the derivatives were found to be ca. 10-100 times greater by electron-capture detection than by electrolytic conductivity detection (halogen mode). The sensitivity also was found to increase with increasing fluorine content for all derivatives by electrolytic conductivity, whereas by electron capture, DES and clopidol exhibited similar responses with either the penta-, hepta-, or pentadeca-fluoro derivatives. The sensitivity of linuron and carbofuran derivatives by electron capture varied with increasing fluorine content. For detection by electron capture, the hepta-fluorobutyryl derivatives were preferred for DES and clopidol, and either the hepta-fluorobutyryl or the pentadecafluorooctanoyl derivatives for linuron and carbofuran. For detection by electrolytic conductivity, the pentadecafluorooctanoyl derivatives were superior for all four compounds.

Carbofuran↗
PubMed1977

Evaluation of electrolytic conductivity detection for gas-liquid chromatographic screening of some organonitrogen herbicides and fungicides in foods.

Electrolytic conductivity detection for the gas-liquid chromatographic (GLC) screening of 15 organonitrogen herbicides and fungicides was investigated. Spiked samples of crop material was extracted with acetone and the filtered sample extracts were partitioned with methylene chloride-petroleum ether (1+1) followed by second and third extractions with methylene chloride. The combined organic extracts were evaporated to dryness and the residues were dissolved in hexane for cleanup on a 2% deactivated Florisil column. The pesticide fractions were determined directly by GLC. All pesticides could be detected at 0.1 ppm in the foods studied.

Chromatography, Gas↗
PubMed1976

Gas chromatographic analysis of heptafluorobutyryl derivatives of some carbamate insecticides.

The gas chromatography (GC) of a number of carbamate insecticides as their heptafluorobutyryl derivatives has been studied. The reaction makes use of heptafluorobutyric anhydride with trimethylamine in benzene as a catalyst. Conversion of the insecticides to their products is complete in 15-20 min at room temperature. The same reaction proved satisfactory for trifluoroacetylation. The excess reagent and trimethylamine are removed by partitioning with water in the reaction test tube. An aliquot of the organic phase is used for analysis. The heptafluorobutyryl derivatives are stable for several days on the lab bench without removal of the aqueous phase from the test tube. GC detection was carried out with a Coulson conductivity detector in the halogen (reductive) mode. About 1.0 ng produced a 50% full-scale response for most of the carbamates (3 min retention time) on 3% OV-1. This method was applied to the analysis of several carbamates spiked in corn, mustard greens, turnip greens, lettuce and cabbage.

Butyrates↗
PubMed1976

A comparison of electron-capture GLC, electrolytic-conductivity GLC and UV-absorption HPLC for the analysis of some herbicides in foods.

A comparison of gas chromatography with electron-capture or electrolytic-conductivity (nitrogen mode) detection, and high-pressure liquid chromatography (HPLC) with UV-absorption detection (254 nm) was carried out for the analysis of several herbicides in foods. Linuron, propanil, terbacil, benzoylprop-ethyl, and the fungicide DCNA in samples of cabbage, corn, potato, and wheat spiked at 2 and 0.2 ppm were examined. The pesticides were extracted with acetone, partitioned into petroleum ether-methylene chloride, and cleaned up on a 2% deactivated Florisil column before direct chromatographic analysis. Electron-capture gas-liquid chromatography (GLC) was most suitable for DCNA and benzoylprop-ethyl while UV-absorption HPLC was best for terbacil analysis. Linuron and propanil gave similar results for both electron-capture GLC and HPLC. Electrolytic-conductivity GLC could detect all pesticides at the 0.2 ppm level and exhibited the least number of extraneous peaks in the chromatograms.

Aniline Compounds↗
PubMed1976

Gas-liquid chromatographic analysis and chemical confirmation of azodrin (monocrotophos) residues in strawberries.

A gas-liquid chromatographic (GLC) method is described for the analysis and confirmation of azodrin (monocrotophos, 3-(dimethoxyphosphinyl)-N-methyl-cis-crotonamide) residues in strawberrires. The strawberries are extracted with acetone, and the filtrate is partioned with a mixture of methylene chloride and petroleum ether followed by further extraction with methylene chloride. The organic phases are combined, dried with anhydrous sodium sulfate, and concentrated to a small volume for GLC analysis on a 3% OV-210 column with flame photometric detection. Identity of the compound is confirmed by chromatography on the same column after trifluoroacetylation of an aliquot of the strawberry extract. The detection limit is about 2 ppb. The types of strawberry samples analyzed were fresh, frozen, pureed, and jam.

Chromatography, Gas↗
PubMed1976

Evaluation and confirmation of an alkylation-gas-liquid chromatographic method for the determination of carbamate and urea herbicides in foods.

An alkylation technique using methyl iodide and sodium hydride in dimethyl sulfoxide has been evaluated for 3 carbamate and 7 urea herbicides in 9 foods. Recoveries ranged from 56 to 113%, depending on herbicide, concentration, and food type. Reproducibility was about +/-6% at 0.1 and 1.0 ppm. Identities of the herbicides were confirmed at these and lower levels by cleaving the aniline moiety from the alkylated herbicides with sodium methoxide in methanol, followed by gas-liquid chromatography on the same column as the parent compound. An electrolytic conductivity detector in the nitrogen mode was used for all analyses. Minimum detectable levels were in the range of 0.005-0.01 ppm in the foods studied.

Alkylation↗