Sample preparation without organic solvent

Advice By Paul Gaines, Ph.D

Q: I am interested in measure the Pb to S ratio in PbS nanocrystals (NC) using an ICP-OES instrument. These NC are dispersed in an organic solvent and stabilized with long chain ligands like oleic acid. I can also deposit the NC as a film to remove the solvent.

My concern is that when I digest the PbS NC film the acid will volatilize the sulfur thus skewing my results. Would the universal solvents you use for zeolite measurements work on such a system? Any other sample prep advice for this system is most appreciated. FYI: Everything entering our ICP-OES has to be in an aqueous solution, we do not have an organic solvent line.

A: If an organic solvent is out of the question then a digestion appears to be required.   Our considerations in this matter are as follows:
  1. The addition of an acid will produce hydrogen sulfide which is both toxic and volatile.
  2. The Universal solvent system we provide (The UniSolv Product Line) would not be of any help.  It uses a combination of acids in the first step that would cause loss of the sulfur.
  3. This sample preparation would require either a closed vessel oxidative digestion which is expensive or
  4. I would like to suggest a nitrate fusion.  This link samples containing ruthenium and osmium will take you to a KOH/KNO3 fusion method at the end of our chapter of Ru/Os preparation methodology. 
  5. Start with a small amount of sample and become familiar with the method because this approach can produce an explosion.

Serving you in chemistry,
Paul R. Gaines, Ph.D.
CEO of Inorganic Ventures

DISCLAIMER: Advice offered by the chemists at Inorganic Ventures is intended for the individual posing the question.