Sodium thiosulfate solutions stability

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%). 

This reaction occurs because of the extraordinary stability of cuprous iodide, which is discussed in the following section. The reaction is used in a method of quantitative analysis for copper, the liberated iodine being determined by titration with sodium thiosulfate solution. 

The decomposition of dithionite in aqueous solution is accelerated by thiosulfate, polysulfide, and acids. The addition of mineral acid to a dithionite solution produces first a red color which turns yellow on standing subsequentiy, sulfur precipitates and evolution of sulfur dioxide takes place (346). Sodium dithionite is stabilized by sodium polyphosphate, sodium carbonate, and sodium salts of organic acids (347). 

Stablizers. Stabilizers are ingredients added to a formula to decrease the rate of decomposition of the active ingredients. Antioxidants are the principal stabilizers added to some ophthalmic solutions, primarily those containing epinephrine and other oxidizable drugs. Sodium bisulfite or metabisulfite are used in concentration up to 0.3% in epinephrine hydrochloride and bitartrate solutions. Epinephrine borate solutions have a pH range of 5.5 7.5 and offer a more difficult challenge to formulators who seek to prevent oxidation. Several patented antioxidant systems have been developed specifically for this compound. These consist of ascorbic acid and acetylcysteine, and sodium bisulfite and 8-hydroxyquinoline. Isoascorbic acid is also an effective antioxidant for this drug. Sodium thiosulfate is used with sodium sulfacetamide solutions. 

Thiosulfate solutions should be stored in the dark. Addition of 0.1 g of sodium carbonate per liter maintains the pH in an optimum range for stability of the solution. Three drops of chloroform should also be added to each bottle of thiosulfate solution to help prevent bacterial growth. An acidic solution of thiosulfate is unstable, but the reagent can be used to titrate If in acidic solution because the reaction with triiodide is faster than Reaction 16-20. 

About one-half of the radioiodine in the targets remains in the caustic-nitrate solution which is stabilized with sodium thiosulfate and stored until the radioiodine decays. During the acid dissolutions, the dissolver off-gas is directed to the iodine sorption system in which the gas is contacted with a 10 hi HNO3—0.4 M Hg(N03)2 solution in an absorption column. Then, the... 

N Sodium Thiosulfate Dissolve 62.5 g of sodium thiosulfate (Na2S203-5H20) in 750 mL of recently boiled and cooled water, add 3.0 mL of 0.2 N sodium hydroxide as a stabilizer, dilute to 1000 mL with water, and mix. Standardize as directed for 0.1 N Sodium Thiosulfate (see Solutions and Indicators), and, if necessary, adjust to exactly 0.250 N. 

It is interesting to note here that chlorominoxidil, which is present as an impurity in minoxidil, undergoes photodechlorination in solution. The Cl produced enhances the oxidation of minoxidil. Sodium thiosulfate, which is also known for its "antichlor" activity (removes chlorine, the oxidizer), helps stabilize minoxidil according to the following equation (109) ... 

Ross (1950) has provided a simple procedure to determine the reactivity of epoxides which may be useful in monitoring their stability if they are to be used in affinity labels. Addition of an epoxide to a neutralized solution of 0.2 M sodium thiosulfate in 50% acetone containing phenolphtalein followed by heating causes the generation of a pink color which can be reversed by addition of 0.2 N acetic acid from a burette. When no further OH" is produced upon heating, the volume of acetic acid used is a measure of the titer of epoxide present. 

The most important single cause of the instability of neutral or slightly basic thiosulfate solutions is bacteria that metabolize thiosulfate ion to sulfite and sulfate ions as well as to elemental sulfur. To minimize this problem, standard solutions of the reagent are prepared under reasonably sterile conditions. Bacterial activity appears to be at a minimum at a pH between 9 and 10, which accounts, at least in part, for the reagent s greater stability in slightly basic solutions. The presence of a bactericide, such as chloroform, sodium benzoate, or mercury(II) iodide, also slows decomposition. 

Mesna dose is typically 60-100% of ifosfamide dose (1 1 for continuous infusion ifosfamide) ifosfamide and mesna are physically compatible and may be delivered in same IV bag CNS toxicity and nausea and vomiting may be more severe with rapid infusion case reports suggest methylene blue may be effective treatment for CNS toxicity Antidote for extravasation sodium thiosulfate very short stability in aqueous solutions, about 1 hour Used as topical solution or in compounded ointments for mycosis fungoides... 

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