Does anyone know the best digestion method for CdS for the determination of Sulfur? CdS digests readily in HCl however sulfur is lost during the formation of H2S. Any ideas would be appreciated.

If your source is cadmium sulfide; why not digest the sample in HCl and analyze for cadmium?

An alternative would be to digest the cadmium sulfide in a flask that is swept with a nitrogen or argon stream into a solution of standard zinc sulfate. After filtering and washing the precipitate, measure the final volume and analyze for residual zinc. The moles of zinc removed from the zinc sulfate should equal the number of moles of cadmium left in the original flask. This will also be the number of moles of sulfur released from the cadmiium.

You can always do the iodometric titration method which amounts to adding a known amount of standard iodine solution before acidifying the sample. The iodine will oxidize the sulfide quantitatively (you will need to prevent having too much oxygen from the air from accessing the sample). You then titrate the remaining iodine with standard thiosulfate until the solution has a light straw color. Add some starch indicator and continue to titrate until a colorless solution persists for ten seconds or more. With the proper calculations; you will have directly measured the sulfide sulfur.