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N E Campbell

Publications and source records attributed to N E Campbell.

9 recordsLinked to original sources
PubMed1985

Amperometric responses to acetylene, ethylene, and methane by a Clark-type oxygen electrode.

Hydrogen-conditioned Clark electrodes exposed to successive acetylene samples displayed a decreasing curvilinear response. Slight electrode responses are also effected by saturated ethylene solutions. Thus, amperometric measurements of hydrogen or carbon monoxide in the aqueous environment by these electrodes are perturbated by the presence of acetylene and to a much lesser extent by ethylene. Methane-saturated solutions induced no electrode response.

Acetylene↗
PubMed1983

Amperometric response to carbon monoxide by a Clark-type oxygen electrode.

Hydrogen-conditioned Clark-type electrodes responded amperometrically to carbon monoxide but to a lesser extent than to hydrogen. They lost sensitivity over time at a concentration-dependent rate when exposed to H2 or CO. Maximum electrode current produced by pure CO was 0.45 microA at the optimum polarizing voltage of 0.60 V; electrode sensitivities to H2 and CO were 15 and 1.8 nA, respectively, in 1 microM solutions. These electrodes also responded weakly to acetylene and ethylene. Caution is suggested in interpretation of H2 measurements made with these electrodes if all components of the reaction milieu are not known.

Carbon Monoxide↗
PubMed1978

Expression of hydrogenase activity in free-living Rhizobium japonicum.

A medium is described on which selected Rhizobium japonicum strains express hydrogenase (H(2) uptake) activity under free-living conditions. Low concentrations of carbon substrates, decreased oxygen tension, and the quantity of combined nitrogen in the medium were major factors influencing hydrogenase expression. Hydrogenase activity was dependent upon a preincubation period in the presence of H(2) under conditions such that the cells did not exhibit nitrogenase activity. H(2) uptake rates were easily measured amperometrically in aerobically or anaerobically prepared suspensions from free-living cultures. Six R. japonicum strains that formed nodules with the ability to utilize H(2) oxidized this gas when grown in free-living cultures. In comparison six randomly chosen strains forming nodules that lost H(2) in air either showed no or low capacity to take up H(2) under free-living conditions. The reduction of triphenyltetrazolium chloride in an agar medium was used to detect strains capable of oxidizing H(2). This method has enabled us to isolate a spontaneous R. japonicum mutant strain that has lost the ability to utilize H(2). This mutant strain forms nodules that evolve H(2) but other symbiotic characteristics appear normal. This strain will be useful in evaluating the importance of the hydrogenase system in the nitrogen-fixing process of legumes.

Journal Article↗
PubMed1978

Phytoplankton uptake and excretion of assimilated nitrate in a small Canadian shield lake.

Nitrate uptake in the epilemnetic waters of a small eutrophic Canadian Shield lake was studied by using a 15N method during summer stratification. Concurrent with inhibition of primary production, 3-(3,4-dichlorophenyl)-1,1-dimethylurea inhibited NO3- assimilation. Nitrate up to 1 mg of N/liter did not affect the rate of primary production during 3 h of incubation. The NO3- fertilizer added to the lake weekly was consumed through algal assimilation in about 3 days. Excretion of the photoassimilated NO3- as dissolved organic nitrogen represented a significant portion of the nutrient incorporated by the cells. Only 40% of the NO3- -15N which disappeared could be accounted for in the particulate fraction. Although the rest was presumably excreted, only 15% of the 15N label was accounted for as cationic dissolved organic nitrogen by isotope assays. These excreted organic forms were predominantly serine and glycine in the dissolved free amino acid fraction. Bacteria as well as algae might be expected to contribute to and modify the extracellular nitrogen pool.

Amino Acids↗
PubMed1976

Aquatic acetylene-reduction techniques: solutions to several problems.

Previous methods of performing aquatic acetylene-reduction assays are described and several problems associated with them are discussed. A refinement of these older techniques is introduced and problems that it overcomes are also discussed. A depth profile of nitrogen fixation (C2H4 production), obtained by the refined technique, is shown for a fertilized Canadian Shield lake in the Experimental Lakes Area of northwestern Ontario.

Acetylene↗