MT 99 - Determination of arsenic

Content Handbook F


Outline of method

The arsenic is reduced with zinc in hydrochloric acid to yield arsine, which is absorbed in a solution of silver diethyldithiocarbamate in quinoline. The purplish-red colour produced is measured by the colloidally dispersed silver photometrically at 540 nm.

The reaction leading to the formation of colloidal silver may be represented by:

AsH3 + 6(CH3CH2 ) 2NCSSAg = 6Ag + 3(CH3CH2)NCSSH + [(CH3CH2 ) 2NCSS]3Ag.