Precipitation waters, hydrogen peroxide determination

Potentiometry biosensors, 664 fitness for purpose, 663 hydrogen peroxide determination, 650-1 iodine-iodide buffer, 699 measurement uncertainties, 663 peroxide value, 663-4 transition metal peroxides, 1069 POV see Peroxide value POZ see Primary ozonides Precipitation waters, hydrogen peroxide determination, 637... 

Determination of sulphite by oxidation to sulphate and precipitation as barium sulphate Discussion. Sulphites may be readily converted into sulphates by boiling with excess of bromine water, sodium hypochlorite, sodium hypobromite, or ammoniacal hydrogen peroxide (equal volumes of 20-volume hydrogen peroxide and 1 1 ammonia solution). The excess of the reagent is decomposed by boiling, the solution acidified with hydrochloric acid, precipitated with barium chloride solution, and the barium sulphate collected and weighed in the usual manner (Section 11.72). 

The properties, crystal habit, and x-ray pattern of tungsten(IV) dichloride oxide are very similar to those of molybdenum(IV) dichloride oxide.8 Stoichiometric tungsten(IV) dichloride oxide, which forms gold-brown needles, is stable under atmospheric conditions and is not attacked by water, dilute or concentrated cold acids, ammonia, or organic solvents, such as acetone, ethanol, 2-methoxyethanol, chloroform, and diethyl ether. However, it decomposes in a solution of sodium hydroxide and forms a black precipitate, which disappears when hydrogen peroxide is added and yields a clear, yellow solution. The density of tungsten(IV) dichloride oxide, determined pycnometrically as previously mentioned, is 5.92 g./cc. 

A 100-mL round-bottom flask containing a magnetic stirrer is capped with a rubber septum and charged with 15 mmol of borinate. 15 mL of diethyl ether arc added and the reaction is cooled to 0°C. 2.04 mL (22.5 mmol) of dichloromethyl methyl ether are added followed by 16.2 mL (30 mmol) of lithium lert-bu-toxide. The ice bath is removed and the mixture stirred at r.t. for 1 h. A slightly exothermic reaction develops and a white precipitate forms. The reaction mixture is cooled to 03C and 18 mL (45 mmol) of pH 8 phosphate buffer arc added, followed by 5.1 mL (45 mmol) of 30% hydrogen peroxide. The ice bath is removed and the mixture stirred for 12 h. The phases are separated, the aqueous phase extracted with two 15-mL portions of diethyl ether, the combined extracts washed with two 15-mL portions of water, then aq NaCl, dried over MgS04 and filtered. The volatiles are removed under reduced pressure and the residual oil is purified by bulb-to-bulb distillation. The chemical purity of the ketones is determined by GC using a 5% SP 2100 on Chromosorb W column and is usually >95%. The chiral ketones are further purified by preparative GC. For further examples, see Table 2. 

Approximately 1.5 g. of the oxychloride is placed in a 400-ml. beaker and is dissolved in 6 ml. of concentrated hydrochloric acid. The solution is treated with 7.5 ml. of 30 per cent hydrogen peroxide and heated to boiling. After decomposition of the peroxide, the solution is diluted to 200 ml. with water. Seventy-five milliliters of 20 per cent selenious acid is added to precipitate the basic selenites, which are digested on a steam bath for 12 hours or until the flocculent precipitate is completely converted to the dense granular mixture of the normal selenites. The precipitate is filtered on a Selas crucible, washed free of excess selenious acid with 2 1. of hot water, and then dried at 120 to 140° for 12 hours. Weighed portions (0.5 g.) of the dried, mixed selenites are then carefully ignited to the mixed oxides. The per cent of haftiia is determined from the formula ... 

The synthetic reactions are also carried out in water-immiscible solvents such as benzene, toluene, chloroform, and tetrahydrofuran in the presence of a buffer. The pH of the buffer has been varied from 5.5 to 7.5 to study the kinetics of the polymerization in the biphasic system. The enzyme and the monomer are solubilized in aqueous and solvent phases, respectively. The polymerization reaction is initiated by the addition of hydrogen peroxide in small increments to the aqueous phase. The polymer is formed at the biphasic interphase and falls out of the reaction mixture as polymerization progresses. Precipitate formed is isolated by centrifugation, washed, and purified to determine the nonlinear optical properties. The schematics of the reaction are given in Fig. 4. Other reaction conditions such as the enzyme, monomer and hydrogen peroxide concentration, and reaction time are given above and were published earlier [11]. 

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