Microdetermination of organic sulfur using NAS 11-18 glass electrode for end-point detection in precipitation titration

HOZUMI Keiichiro, SAKAIDA Kuniko, AKIMOTO Naoshige

doi:10.2116/bunsekikagaku.26.8_536

NAS 11-18 glass electrode (Corning catalog No. 476210) was used to determine the end point exactly for the potentiometric titration of sulfate ion with barium chloride solution in the case of the micro determination of organic sulfur by means of the flask combustion. In the method, an organic sulfur compound was ignited in a 300 ml oxygen flask containing a mixture of 5 ml of distilled water and 1 ml of 30% hydrogen peroxide as an absorbent. After standing for 30 minutes, the absorbent was transferred into a 100 ml beaker using 10 ml of distilled water and 35 ml of acetone and was further adjusted at pH 5.5 by an addition of 1 ml of 0.2 M Hexamine-HCl buffer solution. The sample solution was then titrated with 0.005 M barium chloride solution using Metrohm Potentiograph E536 incorporated with the NAS 11-18 glass electrode and a reference electrode. End point was accurately determined as a sharp inflection on the titration curve caused by a transient response of the electrode to a sudden increase of barium ion concentration after the equivalence point. Coexistence of alkali metal ions in the sample solution practically did not interfere with the titration unless their molar concentrations largely exceeded that of the sulfate ion. Some of polyvalent metal ions seriously interfered with the titration by forming colloidal precipitates of metal hydroxides at pH 5.5, but the others forming no precipitate did not interfere. A series of micro determinations of some organic sulfur compounds presented satisfactory results with the proposed method.

Microdetermination of organic sulfur using NAS 11-18 glass electrode for end-point detection in precipitation titration

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