Indirect determination of traces of thiosulphate by differential-pulse polarography.

Two methods are reported for the indirect determination of thiosulphate down to ca. 0.02 microg/ml by differential-pulse polarography. Both methods involve prior oxidation of thiosulphate with iodine, either in acidic medium to tetrathionate or in alkaline medium to sulphate, whereby ultimately one and eight equivalents of iodate are obtained, respectively. The concentration of iodate in the resulting solution is then measured by differential-pulse polarography under optimum conditions. The average recovery for each method amounted to 100.1%, and the relative standard deviations were 1.3 and 1.4% for the two methods.

Spectrophotometric microdetermination of bismuth in organic compounds after oxygen-flask combustion.

A method has been developed for the micro and submicro determination of bismuth in organic compounds, based on combustion in an oxygen-filled flask, provided with a silica spiral instead of the conventional platinum holder (which alloys with bismuth). After absorption of the products in hydrochloric acid (1 + 1), the solution is chemically treated to convert the bismuth into the orange-yellow BiI(-)(4) complex, then the absorbance is measured at 465 nm. Analysis of 12 organic compounds containing 28-74% of bismuth yielded satisfactory results with a maximum standard deviation of 0.4%.

New iodometric methods for the microdetermination of arsenic in organic compounds.

New methods are described for the iodometric microdetermination of arsenic in organic compounds after wet digestion or oxygen flask combustion. After evaporation of the arsenic solution to dryness and dissolution of the residue in water, acetone is added and the solution is treated with iodide-iodate and the iodine liberated (by the interfering acids and the first dissociation step of arsenic acid) is reduced with thiosulphate. The KH(2)AsO(4) left is then reacted with zinc sulphate in presence of excess of KI and KIO(3). Acetone is added and the liberated iodine is titrated with thiosulphate. This titration corresponds to the second and third dissociation steps of arsenic acid and is used to calculate the arsenic content of the compound. When arsenicals not containing sulphur are decomposed by the oxygen flask method, the arsenic acid solution obtained is reacted directly with zinc sulphate in presence of KI and KIO(3) and the iodine released is titrated with thiosulphate. In this case, the titration corresponds to all three dissociation steps of arsenic acid. The average recoveries obtained by the two methods are 99.5 and 99.9%, respectively.

Micro and submicro iodometric determination of arsenite and sulphite ions by amplification reactions.

Two methods are described for the micro and submicro iodometric determination of arsenite and sulphite ions involving 3- and 6-fold amplification reactions, respectively. The arsenite method is based on oxidation with an excess of periodate, masking of the unreacted periodate with molybdate, and final iodometric titration of the iodate released. The sulphite method depends upon oxidation with iodine and removal of its excess by extraction with chloroform, and oxidation of the iodide formed to iodate, which is determined iodometrically as usual. The two methods are simple, rapid, and accurate. The average recoveries obtained are 99.9 and 99.3% for arsenite and sulphite, respectively.

Iodometric microdetermination of hydrazines by amplification reactions.

Two new, simple, rapid, and accurate iodometric amplification methods are described for the micro and submicro determination of hydrazine. The first depends on oxidation with a chloroform solution of iodine and removal of its excess, oxidation of the resulting iodide with bromine, and iodometric titration of the liberated iodate. The second method is based on oxidation with periodate at pH 8, masking of the excess of periodate with molybdate at pH 3, and iodometric titration of the iodate. The order of amplification involved in the two methods is 6- and 3-fold, respectively. Micro amounts of hydrazine sulphate and dihydrochloride were determined satisfactorily by both methods, the average recoveries being 98.6 and 99.4%.

Iodometric submicro determination of alpha-amino-alcohols by an amplification reaction.

New methods are described for the iodometric submicro determination of alpha-aminoalcohols possessing primary, secondary or tertiary amino-groups which involve 6-, 12-, and 18-fold amplification reactions, respectively. The methods are based on reaction of the alpha-amino-alcohols with an excess of potassium periodate in a slightly alkaline medium, masking of the unreacted periodate with molybdate at pH 3.2 and, after addition of iodide, iodometric determination of the equivalent amounts of iodate released. In addition to being simple and rapid, the methods are sufficiently selective and specific and also highly accurate, being particularly suitable for the analysis of submicro amounts (50-150 microg); the average recovery is 99.9%.

New spot-test for cyanide ion and cyanogen gas.

A new, rapid and simple spot test has been developed for detection of both cyanide ion and cyanogen gas. The cyanogen gas must first be converted into cyanide ion by reaction with sodium hydroxide. On addition of a Cu(II) solution the cyanocuprate(I) complex formed reduces the molybdate solution to molybdenum blue.

Iodometric microdetermination of sulphur in organic compounds by an amplification reaction.

A new method is described for the iodometric microdetermination of sulphur in organic compounds, using a 12-fold amplification reaction after oxygen-flask combustion. The method is based on reaction of the resulting sulphuric add with an excess of saturated barium bromate solution. The unreacted barium bromate is precipitated by addition of acetone, filtered off, redissolved in hot water and after addition of an excess of iodide and acid, the iodine liberated is titrated with thiosulphate. The method is simple, rapid, highly accurate, and of wide application in the microanalysis of organosulphur compounds containing other common acid-forming elements.

Microdetermination of carbon and hydrogen in triterpenoids.

For microdetermination of carbon and hydrogen in triterpenoids, the Vecera, Korshun and Belcher-Ingram rapid methods need modification. In the first method the Co(3)O(4) is activated with 1% NiO, in the second two silica spirals are introduced into the combustion tube, and in the third the sample is covered with Co(3)O(4) powder.

Microdetermination of the azide group in organic compounds.

A simple, rapid and accurate micro-method for the analysis of mono- and diazide organic compounds is described. It is based on the Curtius rearrangement reaction. Glacial acetic acid is found to be the best decomposition medium. The acyl azide function yields two nitrogen atoms per azide group, but the diazides investigated ultimately give five nitrogen atoms per group on oxidation of their decomposition products, with acidified cerium(IV) sulphate solution. The decomposition time varies from 10 min for monoazides to 20 min for diazides. Accurate results were obtained for a representative series of 18 mono-and diazides.

A simplified sampling technique for use with the Weisz ring oven: application to qualitative analysis of some gold and silver alloys.

Up to 100 microg of sample can be collected from gold or silver alloys by rubbing the specimen with the ground hemispherical tip of a 4-mm Pyrex glass rod. Gold alloys are then dissolved in potassium cyanide solution containing hydrogen peroxide; silver alloys are exposed to vapours of nitric acid. Procedures for transfer, ring oven separation and identification of alloy constituents in the sample solutions are described.