PubMed · 4327151
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H Fenner. 1971. [EPR-spectroscopy].. https://pubmed.ncbi.nlm.nih.gov/4327151/
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A new test method was used to rapidly produce a controlled, repeatable scratch on the surface of CoCrMo (ASTM F75) samples, resulting in fracture of the surface oxide. Current transients resulting from ionic dissolution and repassivation of the exposed reactive alloy were measured with the samples potentiostatically held in phosphate-buffered saline. The effects of potential, contact load, pH, aeration, and proteins on the magnitude of the current transients and time constants for repassivation were determined. Using the scratch test apparatus, topographic images of scratched surfaces were constructed and used to measure scratch depth. Aeration had no significant effect on peak currents and time constants owing to the availability of oxygen from the hydrolysis of water. Peak current behavior reflected the transition regions observed in polarization curves. A decrease in peak currents in the presence of albumin may have been due to barrier effects of the adsorbed protein preventing water from reaching the sample surface, or lubrication resulting in less material removed from the surface during scratching. Peak currents and scratch depth increased with load. A model used to predict repassivation behavior was in agreement with experimental results.
The sources of systematic bias in the measurement of moisture by the volumetric and coulometric Karl Fischer methods were assessed. Using water-saturated octanol as a moisture standard, the measurement accuracy of five coulometric instruments was evaluated. Six possible sources of systematic bias were examined: accuracy of the moisture standard, nonadjustable instrumental bias, operator-adjustable instrumental bias, solvent composition, cell design, and sample composition. The published water content of water-saturated octanol was confirmed by the method of standard additions. The nonadjustable instrumental bias consisted of two types, one that was variable and was observed at water levels below 200 micrograms of water, and one that represented a constant percentage of the total water over the tested range from 40 to 400 micrograms of water. The adjustable instrumental parameters, if set incorrectly, may cause a small but significant negative bias (< 7%). Solvent composition as a function of both solvent type and titration vessel design can introduce a negative bias of up to 10%. Finally, the nature of the sample introduces a negative bias as demonstrated by the results obtained from titrating water in four different oil samples. Under optimum conditions, different amounts of water were measured in each oil using different Karl Fischer titration procedures and five different instruments.
Electron spin resonance spectra of solutions used to make conductive bilayer lipid membranes reveal that free radical formation is a precursor to membrane conductivity. Tetracyanoquinodimethane (TCNQ) forms a stable radical that self-aggregates in nonaqueous media, yet will diffuse into the aqueous phase as a monomer, potentially allowing interfacial exchange. Tetracyanoethylene (TCNE) will undergo hydrolysis via a radical intermediate, and the decomposition product is ESR silent. The electrochemical response of an electrochemical cell partitioned by a membrane modified by these dopants is ionic for TCNE. Although the mechanism is less clear for TCNQ, the role of a stable radical is clearly implicated.