Sulfite stabilization

De Carvalho, L.M., Schwedt, G. Sulfur speciation by capillary zone electrophoresis conditions for sulfite stabilization and determination in the presence of sulfate, thiosulfate and peroxodisulfate. Fresenius J. Anal. Chem. 368, 208-213 (2000)... 

Sodium sulfite stabilizes solutions of daunorubicin hydrochloride (75) and physostigmine sulfate (108). Sodium sulfite, however, was reported by Asker and Canady (83) to be most detrimental to the photostability of sodium nitroprus-side solution. 

Hydrated lime is also used to stabilize the calcium sulfite—sulfate sludge derived from thickeners at SO2 scmbbing plants that use limestone—lime. Hydrated lime (2—3%) is added to react with the gypsum sludge and flyash or other added siHceous material. Under ambient conditions the lime and siHca serve as a binder by reacting as calcium siHcates so that the material hardens into a safe, nonleaching, stable, sanitary landfill or embankment fill. 

This equihbrium explains the stabilization of thiosulfate solutions using sulfite or bisulfite as one of the components of acid photographic fixing baths. 

Aqueous sodium thiosulfate solutions ate neutral. Under neutral or slightly acidic conditions, decomposition produces sulfite and sulfur. In the presence of air, alkaline solutions decompose to sulfate and sulfide. Dilute solutions can be stabilized by small amounts of sodium sulfite, sodium carbonate, or caustic, and by storage at low temperatures away from air and light. Oxidation is inhibited by Hgl2 (10 Ppm) amyl alcohol (1%), chloroform (0.1%), borax (0.05%), or sodium benzoate (0.1%). 

Many enzymes need a certain ionic strength to maintain an optimum stabiHty and solubiHty, eg, bacterial a-amylases show optimal stabiHty in the presence of 1—2% NaCl. Some enzymes may need certain cations in low amounts for stabilization, eg, Ca " is known to stabilize subtiHsins and many bacterial a-amylases. Antioxidants (qv) such as sodium sulfite can stabilize cysteine-containing enzymes which, like papain, are often easily oxidized. 

Stability. E is sensitive to ait, light, heat, and alkalies. Metals, notably copper, iron, and 2inc, destroy its activity. In solution with sulfite or bisulfite, it slowly forms an inactive sulfonate (17). The red color that forms when neutral or alkaline solutions are exposed to air is caused by adrenochrome. 

As a result of the limited solubility of MEKO, it is often formulated with other boiler treatment ingredients such as filming and neutralizing amines, sulfite, or erythorbates, which permit increased concentration, improved stability, and better overall effectiveness. 

Anthocyanins were decolorized at pH 3.0 by the addition of sodinm sulfite at the C-2 or C-4 of the chromophore, a reaction that was rapidly reversible on acidification. Snlfnr dioxide, EDTA, and a combination of snlfnr dioxide and EDTA exerted very small effects on the losses of anthocyanins in strawberry pnrees and juices during 10 wk of storage at -20°C. Conversely, the addition of snlfnr dioxide and storage at 20°C slowed the anthocyanin losses and concnrrently decreased the formation of polymeric componnds, especially in pnrees. EDTA had a slight effect on color stability. ... 

The oldest way to produce caramel is by heating sucrose in an open pan, a process named caramelization. Food applications require improvement in caramel properties such as tinctorial power, stability, and compatibility with food. Caramels are produced in industry by controlled heating of a rich carbohydrate source in the presence of certain reactants. Carbohydrate sources must be rich in glucose because caramelization occurs only through the monosaccharide. Several carbohydrate sources can be used glucose, sucrose, com, wheat, and tapioca hydrolysates. The carbohydrate is added to a reaction vessel at 50°C and then heated to temperatures higher than 100°C. Different reactants such as acids, alkalis, salts, ammonium salts, and sulfites can be added, depending on the type of caramel to be obtained (Table 5.2.2). 

Salts of sulfur dioxide, including bisulfite, metasulfite, and sulfite, are the most common antioxidants used in aqueous parenterals. These antioxidants maintain product stability by being preferentially oxidized and... 

The most important methods commonly used in produce preservation are low temperature, aw reduction, low acidity, and preservatives (e.g. organic acids and sulfite). The microbial stability and the sensory quality of most foods are based on passing over a combination of hurdles. 

Fersona A process for stabilizing the calcium sulfite/sulfate waste from FGD processes, so that it may be used for landfill. The waste is mixed with ferric sulfate waste from another process (e.g., metallurgical leaching) to form sparingly soluble basic sodium ferric sulfates. Developed in the 1970s at the Battelle Columbus Laboratories, OH, under contract with Industrial Resources. See also Sintema. 

Terra-Crete A process for stabilizing the calcium sulfate/sulfite waste from flue-gas desulfurization, so that it may be used for landfill. Calcination converts the calcium sulfite to cementitious material to which proprietary additions are made. Developed by SFT Corporation, York, PA. See also Terra-Tite. 

A large part of the reduction of silver chloride by hydrazine evidently takes place by a different mechanism from that of the reduction by hydroxylamine. The effect of gelatin and dye on the process, together with the appearance of colloidal silver in the solution when gelatin is present to stabilize it, shows that the reaction involves dissolved silver chloride to a greater degree than the hydroxylamine reaction. Indeed, if the reaction rate is plotted against a silver ion concentration calculated on the assumption that a saturated solution of silver chloride is maintained, the same relation is obtained as is found for the reduction of silver ions from a solution of the sulfite ion complex. 

The action of an active intermediate oxidation product would explain another feature of the reaction. The reduction of silver ions by hydrazine is extremely sensitive to the presence of small amounts of copper. For example, a solution containing a mixture of silver nitrate, sodium sulfite and hydrazine which normally showed no sign of reduced silver for several minutes underwent almost immediate reaction when merely stirred with a clean copper rod. In the presence of gum arabic as stabilizer, streamers of colloidal silver passed out from the copper surface. Similarly, the addition of small amounts of cupric sulfate to a hydrazine solution eliminated the induction period of the reaction with silver chloride. 

The practical preparation of melamine-formaldehyde resins is done under the same conditions as for urea-formaldehyde resins. Melamine is at first insoluble in the aqueous reaction mixture but dissolves completely as the condensation proceeds. Because of the greater stability of the N-hydroxymethylmel-amines compared with the corresponding urea compounds the reaction can easily be followed by titration of the unconverted formaldehyde with sodium hydrogen sulfite (see Sect. 4.1.4.1). 

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