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Date: 5-3-2019
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Date: 19-7-2020
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Date: 25-7-2020
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Thermal decompositions of arsine and stibine: the Marsh test
The thermal decomposition of AsH3 and SbH3 is the basis for the Marsh test, which provides a classic example of an analytical technique important in forensic science. The arsenic- or antimony containing material is first converted to AsH3 or SbH3 (e.g. by treatment with Zn and acid, liberating H2 and the trihydride). Subsequent passage of the gaseous mixture through a heated tube causes the hydrides to decompose, forming brown-black deposits of the elements:
If both As and Sb are present, the relative positions of the deposits establishes their identity; the lower thermal stability of SbH3 means that it decomposes before AsH3 in the tube. Treatment of the residues with aqueous NaOCl also distinguishes them since only arsenic dissolves:
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