酸素ボンブ法による塩素の比色定量

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Recoveries of chlorine by the "oxygen bomb" method were investigated by using Chloramine T (sodium p-toluenesulfonchloramide trihydrate) and p-chloroaniline as standard chlorine-containing compounds and by the improved mercury(II) thiocyanate spectrophotometry. The mean recovery was approximately 95% with a coefficient of variation of 2%. When the residual gas was released abruptly after the combustion, the recovery was reduced to about 86%. No significant change in the recovery was observed on addition of water as an absorbent. Chlorine in filter paper was determined by the oxygen bomb method. The "oxygen bomb" is a useful tool to determine chlorine in organic materials, since the chlorine cannot be recovered entirely by dry or wet ashing methods. The procedure for the determination of chlorine in filter paper is as follows. (1) Preparation of the sample solution. Fold a sheet of filter paper to form a small square. Wrap up the filter paper in a sheet of rice paper, and tie the parcel with a cotton thread. Put the sample on the platinum capsule, and join the remaining ends of the thread through the coil of a platinum wire as depicted in Bunseki Kagaku, 21, 285 (1972). The whole procedure up to here should be performed with rubber gloves in order to prevent the sample from being contaminated by fingers. Impregnate the sample with a few drops of methanol. Ignite the sample by the same procedure as described in Bunseki Kagaku, 22, 546 (1973). On cooling, release gradually the residual gas spending about 20 minutes. Transfer the bomb washings to a 100 ml volumetric flask and dilute to the mark. (2) Preparation of the iron(III) perchlorate solution. Heat 50 g of iron(III) nitrate with 75 ml of perchloric acid (60%) under a ventilating hood until the fume of perchloric acid is evolved. Filter the deposit with a glass filter on cooling, and wash with a small portion of 1 M perchloric acid. Dissolve 29.6 g of the salt in 33 ml of perchloric acid (60%) and dilute to 100 ml with water. (3) Determination of chloride ion. Pipet a 10 ml aliquot of the sample solution in a 25 ml volumetric flask. Add 5 ml of the iron(III) perchlorate solution and 3 ml of the mercury(II) thiocyanate solution which is prepared by dissolving 0.463 g of mercury(II) thiocyanate in 100 ml of methanol. Dilute the mixture to 25 ml and allow to stand for 15 minutes. Transfer the solution to a 1 cm cell and measure the transmittance at 460 nm against water. The reagent blank must be run each time the iron(III) perchlorate solution has been prepared, since the water content of the solid reagent is not constant.
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酸素ボンブ法による塩素の比色定量

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