Sludge volatile acid formation

In the above equation, E represents the analyte element, and m may be, but need not necessarily be, equal to n (e.g. when the analyte occurs in various oxidation states). Reduction by Zn/HO requires that the analytes be present in their lower oxidation states prior to reaction. When this is not the case, the analytes must be reduced, e. g. by SnCl2 in an acidic medium. The formation of volatile hydrides (and of excess hydrogen) is then initiated by the addition of zinc metal. This reaction is rather inconvenient, since it is slow, difficult to automate, and subject to high blank values due to the impurities of the zinc. Also its efficiency is hmited as a consequence of incomplete reaction and the possibihty of adsorption or entrapment in the zinc sludge of the volatile metal hydrides formed. Due to these disadvantages, the use of this procedure has nowadays been practically abandoned. 

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