Diisopropyl ether, peroxides, removal

Apart from the conversion of peroxides to useful products, it is sometimes necessary to reduce peroxides, and especially hydroperoxides formed by auto-oxidation. Such compounds are formed especially in hydrocarbons containing branched chains, double bonds or aromatic rings, and in ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, etc. Since most peroxidic compounds decompose violently at higher temperatures and could cause explosion and fire it is necessary to remove them from liquids they contaminate. Water-immiscible liquids can be stripped of peroxides by shaking with an aqueous solution of sodium sulfite or ferrous sulfate. A simple and efficient way of removing peroxides is treatment of the contaminated compounds with 0.4 nm molecular sieves [669]. 

The commercial product usually contains appreciable quantities of peroxide this should be removed by treatment with an acidified solution of an iron(n) salt or with a solution of sodium sulphite (see under 15. Diethyl ether). The diisopropyl ether is then dried over anhydrous calcium chloride and distilled, the fraction b.p. 68.5 °C/760 mmHg being collected. Di-isopropyl ether should be stored in brown bottles away from the light. A small amount of hydroquinone (2 x 10 5 m) may be added as a peroxide inhibitor. 

Diethyl ether, diisopropyl ether, tetrahydrofuran, and dioxan, as well as the hydrocarbons decalin and tetralin and even petroleum fractions and xylene, usually contain peroxides. Owing to their involatility, peroxides become enriched in distillation residues and have often given rise to very severe explosions.13 To avoid accidents when working with these solvents it is essential to test for the presence of peroxides and, if they are present, to take steps to remove them. Then, to suppress formation of further peroxides in these solvents, they must be stored in dark flasks and access of atmospheric oxygen must be very rigidly excluded. 

Sample preparation Make serum alkaline with 10% sodium carbonate, extract with diisopropyl ether (Caution Diisopropyl ether readily forms explosive peroxides ). Remove the organic layer and extract it with 10 mM HCl, inject an aliquot of the aqueous layer. 

Sample preparation 1 mL Serum or plasma + 1 mL saturated Na2HP04 + 100 pL 10 p,g/mL IS -t 5 mL diisopropyl ether isopropanol 95 5 (Caution Diisopropyl ether readily forms e losive peroxides ), shake for 5 min, centrifuge. Remove the organic layer and evaporate it to dryness at 35°, reconstitute the residue in 50 p-L mobile phase, vortex, inject a 20 pL aliquot. 

The presence of antioxidants in eluents and extraction solvents Antioxidants can be readily oxidized electrochemically and generate high background currents or interfering broad peaks. Thus, eluents and extraction solvents containing such compounds should be either avoided or purified before use. For example, ethers, such as diethyl ether, diisopropyl ether, and tetrahydrofuran are likely to contain up to 0.1% (w/v) pyrogallol or quinol (hydroquinone) as stabilizer. If the stabilizer is removed, peroxides will form and their concentration will increase with time unless the solvent is stored under nitrogen. Not only do peroxides present a hazard from explosion, but they may also oxidize susceptible analytes. Methyl f-butyl ether (MTBE), on the other hand, is stable to oxidation. 

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