It should be noted that at pH 9 V(V) is the
predominate species in the filtrate; whereas at
pH50 V(IV) is [21]. Therefore, subsequent
acidification of the alkaline filtrate makes the
unstable V(V) an oxidant. Under such conditions
V(V) would oxidize DDTC or its decomposition
products and thus render the analyte solution
colloidal. In order to avoid this additional interference
ethanol is purposely added prior to acidification and preferentially oxidized. It was chosen
since it is very pure, harmless and can be readily
boiled off.