Eine einfache und schnelle Methode zur genauen Bestimmung von sehr kleinen Arsenmengen in biologischen Substanzen

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Abstract
Methods for the detn. of As are based on the fact that As is converted into AsH3 by nascent H. The method reported makes possible the accurate detn. of a few tenths of a [gamma] of As in about 3 g. of dry tissues or body fluids or 7 g. of the dry residue from urine. The material to be analyzed is weighed into a 100 cc. Erlenmeyer flask and mixed with a small amt. of H2O. 1 cc. of 50% NaC103 soln. is added and the flask closed with a rubber stopper fitted with a long glass tube and two small separatory funnels. The flask is placed in the H2O bath and 3 cc. of HC1 (sp. gr. 1.19) added, with shaking through one of the separatory funnels. When the contents begin to foam, the apparatus is removed from the bath, and after 20 min. 1 cc. of HC1 and 1 cc. of the NaC103 soln. added, and the apparatus replaced in the bath until decomposition of the sample is complete. After excess Cl2 is removed by heating, the mixture is reduced with 20 g. of mossy Sn. and 6.5 cc. of HC1 diluted with a small amt. of H2O. A stream of H2 flows through the flask for 10 min. The apparatus is connected to a heated quartz tube, the H2 stopped, and the flask heated. The As-mirror formed is dissolved in 0.26 ccm. of IC1 soln. (prepared by dissolving 1.56 g. KI and 1 g. KIO3 in 50 ccm. of H2O and adding 50 ccm. conc. HCl). The soln. is transferred to a 5 ccm. flask containing 10% KCN; the addition of KCN effects that the I2 liberated is transformed into the colorless ICN; otherwise the yellow color of IC1 would prevent the recognition of the final color change in the titration. A few drops of CCl4 are added and the mixture thoroughly shaken. The I2 liberated by the IC1 soln. is titrated with standard .001 m-KI03 soln.: 41 + 6 HC1 + 5 KCN + KIO3 = 5 ICN + 6 KCl + 3 H2O. The disappearance of the I2 color in the CCl4 indicates the end of the titration.

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