Sodium hydrogensulphite

Sodium hydrogensulphite, when freshly prepared, reacts with aldehydes to form crystalline addition compounds, for example... 

Discussion. Small quantities of dissolved silicic acid react with a solution of a molybdate in an acid medium to give an intense yellow coloration, due probably to the complex molybdosilicic acid H4[SiMo12O40]. The latter may be employed as a basis for the colorimetric determination of silicate (absorbance measurements at 400 nm). It is usually better to reduce the complex acid to molybdenum blue (the composition is uncertain) a solution of a mixture of l-amino-2-naphthol-4-sulphonic acid and sodium hydrogensulphite solution is a satisfactory reducing agent. 

Reducing agent. Solution A dissolve 10 g sodium hydrogensulphite in 70 mL water. Solution B dissolve 0.8 g anhydrous sodium hydrogensulphite in 20 mL water, and add 0.16 g l-amino-2-naphthol-4-sulphonic acid. Mix solution A with solution B, and dilute to 100 mL. 

Similarly, sodium hydrogensulphite, NaHS03, although it contains hydrogen (which might be thought to be a source of ions), has a basic solution ... 

Usually, the individual and simultaneous separation of free [32,36,38,39] and conjugated Be [33—35] vitamers is carried out by means of RP chromatography on Cl8 columns with acidic mobile phases. These methods utilize the native fluorescence of B6 vitamers [1,32—39], increasing the weak intensity of phosphate esters at low pH by means of postcolumn derivatization with sodium hydrogensulphite. 

Evaporation and crystallisation of the sodium sulphite solution gives crystals of the heptahydrate NajSOj.THjO. However, on evaporation of the hydrogensulphite solution, the solid obtained is chiefly sodium pentaoxodisulphate(IV) ( metabisulphite ) Na2S20j, and contains little if any of the hydrogensulphite. However, the hydrogen sulphite ion is obtained when the solid redissolves in water ... 

Due to its properties sulphur dioxide has been used for many centuries mainly for the protection of acidic foodstuffs, especially in the wine industry. However its application is restricted owing to flavour problems occurring at concentrations above 5mg/kg. It is applied as liquefied gas, a solution in water (H2SO3) or the a.m. salts. In the EC list of preservatives which cosmetics may contain inorganic sulphites and hydrogensulphites are mentioned with a maximum concentration of 0.2% expressed as free SO2. But in finished products it is scarcely used, as these normally do not exhibit the low pH which is required for the antimicrobial effectiveness of sulphur dioxide or sulphurous acid. - Percentage of use in US cosmetic formulations Sodium sulphite 0.32% sodium metabisulphite 0.01% sodium bisulphite 0.26%. 

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