Matrices for Soil Preparation

Meggie had a question regarding soil preparation for ICP-MS analysis. She wanted to know if concentrated nitric acid and HF was enough for digestion, or if she should use a stronger acid such as perchloride to destroy the potential Si colloid.

	RE: Matrices for Soil Preparation Dear Meggie,      First, I would suggest that you consult EPA methods 3050, 3051 and 3052 which are all written for the digestion of sediments, soils and sludges and involve the measurement techniques of AAS, ICP-OES and ICP-MS.      In direct response to your question, the use of perchloric acid would dehydrate the silicates formed and prevent any collodial silicate formation reactions. This approach should work well using published procedures for perchloric acid digestions. However, the use of HF will form the fluoro-silicate complex which should keep the Si in solution and therefore prevent collodial precipitation.      Each matrix has both advantages and disadvantages which have to be sorted out by the analyst. If you decide to use perchloric acid, then please observe the necessary precautions. Best of luck.     Paul R. Gaines, Ph.D. Serving you in chemistry