Iodate-sulfite system

Another important reaction supporting nonlinear behaviour is the so-called FIS system, which involves a modification of the iodate-sulfite (Landolt) system by addition of ferrocyanide ion. The Landolt system alone supports bistability in a CSTR the addition of an extra feedback chaimel leads to an oscillatory system in a flow reactor. (This is a general and powerfiil technique, exploiting a feature known as the cross-shaped diagram , that has led to the design of the majority of known solution-phase oscillatory systems in flow... 

Self-oscillations of sweUing and deswelling for the poly(N-isopropylacry-lamide-co-acryhc acid) hydrogels were realized by coupling pH and temperatme in the external solution media. The pH oscillations were also observed for the system consisting of iodate-sulfite-thiosulfate and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) when polymeric acid was substituted for sulfuric acid... 

In batch conditions, the model behaves (as does the experimental system) as a clock reaction, with an induction period followed by a sudden jump of several orders of magnitude in H and then an exponential decrease in H. Under flow conditions, bistability and oscillations are obtained. The model can easily be adapted to describe a wide variety of pH oscillators, including iodate-sulfite-thiourea (Rabai et ah, 1987), iodate-sulfite-thiosulfate (Rabai and Beck, 1988), periodate-thiosulfate (Rabai et ah, 1989a), periodate-hydroxylamine (Rabai and Epstein, 1989), and iodate-hydroxylamine (Rabai and Epstein, 1990). 

The FIA system used is shown in Fig. 6.8, showing the sample injection by means of the hydrodynamic forces, the principle being explained in Fig. 6.8 (cf. Section 5.1.3). The carrier stream contains iodate and dissolved starch in diluted sulfuric acid. In the acidic solution the sulfite of the sample reacts with iodate leading to the formation of free iodine that with the starch forms a strongly colored blue complex which is measured spectrophotometrically at 600 nm. Since the formation of the end product is a very complex reaction which proceeds in several steps depending on the concentration of iodine, a linear calibration curve cannot be expected. 

Fission products may contain the iodine isotopes from to Of these, is considered the most significant hazard in drinking water. Three methods are available for the determination of radioactive iodine in water samples precipitation, sorption on an anion-exchange resin, and distillation. The precipitation method is preferred because it is simple and requires the least time. In the precipitation method, iodate carrier is added to the sample and reduced to iodide with sodium sulfite. The iodide is precipitated as silver iodide. The precipitate is dissolved, and purified with zinc powder and sulfuric acid. The iodide is finally precipitated as palladium iodide, Pdli, for counting in a low-background //-counter, or ///y coincidence system. 

Finally there remains to understand the origin of the recently obtained patterns [122] in the iodate-ferrocyanide-sulfite (the so-called EOE) reaction [123] generated by finite perturbations of a uniform bistable system. Do they fit in some class discussed above or are they an example of the so-called high amplitude structures [27,124-127] ... 

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