During the process, aqueous (Leblanc and Jackson,
1973) or alcoholic solution (Friend et al., 1977) of Mg-
(NO3)2 is usually added to assist oxidation of the organic
samples. The concentration of the Mg(NO3)2 solution
does not affect frothing, but the use of a concentrated
solution decreases the preashing time. Hence, solid Mg-
(NO3)2â6H2O is directly added to the sample. However,
the degree of foaming was affected by the relative mass
of Mg(NO3)2 used. Therefore, a minimum possible
amount of Mg(NO3)2â6H2O [10% (w/w)] was used. In
addition, the use of a liquid antifoaming reagent,
Antifoam 204 (Sigma A6426), for smooth ashing was
also investigated. The volume optimization of Antifoam
204 was performed by visual observation of the froth
level in the beaker throughout the ashing cycle. The
results of the recovery studies are also given in Table
4. Similar calculations for this method were carried out
as in the H2SO4 case.