Interference apparent diffusivities

Measurements by interference microscopy are, under favorable conditions, capable of yielding both internal diffusivities and apparent diffusivities based on overall sorption rates. The former tend to approach the values obtained from microscopic measurements while the latter yield values similar to those obtained by other macroscopic methods. Of necessity these studies have been carried out in large zeolite crystals. One may expect that smaller crystals may be less defective, although the influence of surface resistance may be expected to be greater. The extent to which these conclusions are applicable to the small zeolite crystals generally used in commercial zeolite catalysts and adsorbents remains an open question. 

If the diffusion potential in the membrane is neglected, this equation yields relationships for the membrane potential, for the ISE potential and for the selectivity coefficient. It is apparent that formation of complexes with various numbers of ions in the membrane does not affect the dependence of the ISE potential on the activities of the determinand and interferent according to the Nikolsky equation. 

Moodie, Schofield and their co-workers have extended their studies to the other media listed in Table 6, but the evidence for a limiting reaction rate is then less clear cut. This is, however, to be expected since the other media are less viscous than 68% sulphuric acid and so the influence of diffusion control in reducing the apparent reactivity of the more reactive compounds should be less marked. It is possible also that nitration through nitrosation is significant with some of the most reactive compounds, although Moodie, Schofield and their co-workers took care to minimize the interference by this reaction. 

In all substances, at high temperatures, the electrical resistivity is dominated by inelastic scattering of the electrons by phonons, and other electrons. As classical particles, the electrons travel on trajectories that resemble random walks, but their apparent motion is diffusive over large-length scales because there is enough constructive interference to allow propagation to continue. Ohm s law holds and with increasing numbers of inelastic... 

The formation of (II) provides a quite selective spot test for palladium. Gold must be removed prior to the test because it will cause the development of a deep ruby red in the spot plate test and a diffused violet spot on the paper, apparently due to the reduction of the gold ions to the colloidal metal. Interference may also arise from 0s04 , Os+, Ru+, and RuCle ions because they have distinct self-colors. Mercurous ion causes partial interference by the reduction of part of the palladium to the elementary state, but a positive response can still be seen. It is possible to detect I part of palladium in the presence of 200 parts of platinum or 100 parts of rhodium. Less favorable ratios should be avoided because of the color of these salts. No interference is caused by mercuric and iridic chloride, but free ammonia, ammonium ions, stannous, cyanide, thiocyanate, fluoride, oxalate, and tetraborate ions do interfere. Lead, silver, ferrous, ferric, stannic, cobaltous, nickel, cupric, nitrite, sulfate, chloride, and bromide ions do not interfere. 

There have been studies on interferences in this system of SO2 determination with gas diffusion, chiefly in connection with the presence of compounds in beverages that are able to pass through the permeable membrane, such as nitrite, sulfide and cyanide (Frenzel and Hillmann, 1995). No interferences were detected with concentrations of nitrite up to 3 times higher than those of sulfite. Cyanine interference became apparent only when present at concentrations above 10 mg/L (Frenzel and Hillmann, 1995). In some cases, EDTA has been assayed as a means of preventing interference from some cations and anions however, it was found that EDTA practically doubled the sensitivity of the sulfite determination (Safavi and Haghighi, 1997). 

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