Dear Selby,

you could try a digestion with 65%f HNO3 under elevated pressure at 170°C which
is also suitable to digest black carbon. This digestion was made for black
carbon determination. It is suitable as well for inorganic ion determination in
the solution. Silicates, however, are not digested. Please look at:

Glaser et al (1998): Organic Geochemistry 29: 811 - 819. If you like a pdf
version of this paper please let me know ([log in to unmask])

Kind regards

Bruno

Dr. Bruno Glaser
Insitute of Soil Science and Soil Geography
University of Bayreuth
D-95440 Bayreuth
Germany