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Biomedical subjects

R L Holmstead

Publications and source records attributed to R L Holmstead.

11 recordsLinked to original sources
PubMed1977

Separation and analysis of the pyrethrins by combined gas-liquid chromatography-chemical ionization mass spectrometry.

Pyrethrins, the 6 naturally occurring insecticidal esters of pyrethrum extract, were analyzed by combined gas-liquid chromatography-chemical ionization mass spectrometry. Separation was best on an OV-25 column with temperature programming; The chemical ionization mass spectra for the 6 esters as well as for the thermally isomerized pyrethrins I and II are reported and discussed. Using selective ion monitoring, a lower limit of detectability of all 6 esters was 114 ng of total extract injected on the column.

Chromatography, Gas↗
PubMed1975

Chemical ionization mass spectrometry of N-methylcarbamate insecticides, some of their metabolites, and related compounds.

The chemical ionization (CI) mass spectra with methane as the reagent gas are reported for 25 N-methylcarbamate insecticides or related compounds. The [M + 1]+ ions in the CI spectra are larger than the parent ions in the corresponding electron impact (EI) spectra of N-methyl- and N,N-dimethylcarbamates, but the contrary is true with N-hydroxymethylcarbamates. CI but not EI fragmentation of substituted-phenyl N-hydroxymethylcarbamates [ROC (O) NHCH2OH] appears to involve a 4-membered [ROC(O)NHCH2]+ intermediate which rearranges to give a [ROCH2]+ fragment. Other fragmentations unique to the CI spectra are also discussed.

Carbamates↗
PubMed1974

Toxaphene insecticide: a complex biodegradable mixture.

Adsorption and gas-liquid chromatography separate toxaphene into at least 175 polychlorinated 10-carbon compounds including Cl(6), Cl(7), Cl(8), Cl(9), and Cl(10) derivatives. One toxic component is 2,2,5-endo,6-exo,8,9,10-heptachlorobornane. Rats metabolically dechlorinate toxaphene, removing about half of the chlorine from the technical insecticide and from each of seven subfractions of varying composition and toxicity.

Animals↗