溴值法测定加氢石油树脂不饱和度局限性分析

探讨了国内现行行业标准《HG2231-91石油树脂(PR)溴值试验方法》在测定深度加氢石油树脂不饱和度时存在的局限性. 实验结果表明, 在测定不饱和度较低的加氢石油树脂的溴值时, 应采用浓度为0.1 mol/L的Br标准滴定溶液, 加入量为6～7 mL;碘化钾的加入量应为假设溴值为零时的理论用量, 这样在测定不饱和度较低的石油树脂的溴值时, 才能保证碘化钾过量, 得到可靠的溴值.     

Titrimetric microdetermination of isoniazid by amplification reactions

An amplification method for the determination of (0.01–2.0 mg) isoniazid is described. It depends on oxidation of the isoniazid sample solution with a chloroform solution of iodine and removed of its excess, oxidation of the resulting iodide with bromine, and iodometric titration of the liberated iodate after 6-fold amplification. Alternatively, the liberated iodine is reduced to iodide, and again oxidized to yield 36 iodide ions for every iodide ion originally present. The coefficient of variation does not usually exceed 1.5% for above 0.5 mg of isoniazid but increases to 3.6% at the 0.01-mg level.     

Determination of thiosulphate in the presence of dithionite and sulphite

To determine thiosulphate in the presence of dithionite and sulphite, iodine dissolved in potassium bromide solution is used to oxidize thiosulphate to tetrathionate, and dithionite and sulphite to sulphate. The tetrathionate generated from the thiosulphate is then oxidized with potassium bromate-potassium bromide solution in the presence of hydrochloric acid. The bromine consumption of the tetrathionate is measured by titration of the excess of bromine with sodium thiosulphate after the addition of potassium iodide. For each equivalent of iodine used to determine thiosulphate by the Wollak method, fourteen equivalents of bromine are used to determine thiosulphate by this method.     

Titrimetric microdetermination of inorganic or organic mercury by amplification reactions

A simple titrimetric method for estimation of 0.05-7 mg of Hg(II) is presented. The acidic sample solution is treated with a measured and excessive amount of iodide, then mercuric iodide is extracted at ph 2-3.5, and the unreacted iodide is determined iodometrically after 6- or 36-fold amplification by use of bromine water for oxidation of iodide to iodate. Periodate oxidation of excess of iodide gives 24-fold amplification. The coefficient of variation does not usually exceed 1% for above 1 mg of mercury but increases to 4% at the 0.05-mg level. The 6-fold amplification method is used for microdetermination of organically bound mercury following oxygen-flask combustion. The average absolute error for 10 determinations (3 compounds) amounted to +/-0.6%; one determination takes less than one hour.     

Determination of arsenic in ores, concentrates and related materials by continuous hydride-generation atomic-absorption spectrometry after separation by xanthate extraction

A recent graphite-furnace atomic-absorption method for determining approximately 0.2 mug/g or more of arsenic in ores, concentrates, rocks, soils and sediments, after separation from matrix elements by cyclohexane extraction of arsenic(III) xanthate from approximately 8-10M hydrochloric acid, has been modified to include an alternative hydride-generation atomic-absorption finish. After the extract has been washed with 10M hydrochloric acid-2% thiourea solution to remove co-extracted copper and residual iron, arsenic(III) in the extract is oxidized to arsenic(V) with bromine solution in carbon tetrachloride and stripped into water. Following the removal of bromine by evaporation of the solution, arsenic is reduced to arsenic(III) with potassium iodide in approximately 4M hydrochloric acid and ultimately determined to hydride-generation atomic-absorption spectrometry at 193.7 nm, with sodium borohydride as reductant. Interference from gold, platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide before the iodide reduction step. The detection limits for ores and related materials is approximately 0.1 mug of arsenic per g. Results obtained by this method are compared with those obtained previously by the graphite-furnace method.     

Indirect amplification method for determining formaldehyde and chloralhydrate by differential pulse polarography

An indirect differential pulse polarographic method for the determination of formaldehyde and chloralhydrate is described; it is based on the oxidation of the alkaline sample solutions of formaldehyde and chloralhydrate with a chloroform solution of iodine and removal of its excess. The resulting iodide is oxidized with bromine water and measured polarographically as iodate (at pH 9.3) with sixfold amplification.     

Organic synthesis with sulphones—XVII: The anti-markownikoff halosulphonylation of olefins via an ionic pathway,and a new method of preparing benzenesulphonyl iodide

Iodine and bromine in the presence of sodium benzenesulphinate react with olefins in acetone solution to give halosulphones resulting from an apparent steric direction of attack at the intermediate halonium ion. A straightforward preparation of benzenesulphonyl iodide from benzenesulphonyl chloride and sodium iodide is also described.     

Titrimetric Microdetermination of chloral hydrate by amplification reactions

A simple titrimetric method for estimation of 0.1–5 mg of chloral hydrate is presented. It depends on oxidation of an alkaline solution of chloral hydrate with a chloroform solution of iodine, removal of excess of iodine, oxidation of the resulting iodide with bromine, and iodometric titration of the iodate produced, giving 6-fold amplification. Alternatively, the iodide formed is oxidized with periodate, masking of the excess of periodate with molybdate at pH 3, and iodometric titration of the iodate, giving 24-fold amplification. The coefficient of variation does not usually exceed 2%, for above 1 mg of chloral hydrate but increases to 3.8% at the 0.1-mg level.     

Titrimetric microdetermination of salicylic, acetylsalicylic, and p-hydroxybenzoic acids by amplification reactions

A novel titrimetric method with amplification has been developed for the determination of 0.05–2.0 mg of salicylic, acetylsalicylic, or p-hydroxybenzoic acid. It depends on bromination of these compounds by bromine to tribromophenylhypobromite, which liberates iodine when treated with iodide. The liberated iodine is extracted with chloroform, reduced to iodide, oxidation of the resulting iodide with bromine, and iodometric titration of the iodate produced gives the sixfold amplification method. The coefficient of variation does not exceed 1% for above 0.5 mg of the studied compounds, but increases to 2.8% at the 0.05-mg level.     

Iodometric microdetermination of semicarbazide by amplification reactions

An analytical method for the determination of 10–2000 μg of semicarbazide is described, using titrimetric procedure with an amplification reaction. It relies upon the reaction of semicarbazide, in phosphate-buffer (pH 7) solution, with a chloroform solution of iodine, and removal of its excess; oxidation of the iodide formed with bromine; and determination of the liberated iodate by the Leipert amplification procedure. The recovery ranged from 97.0 to 100.1%.