Assurance® Mixed Multi-Element Standards for AA & ICP Standards may be diluted in the same matrix as specified; however, caution must be exercised in the choice of the source for your diluents. Diluting the matrix may cause some standards to precipitate. Also, an impure or unknown diluent turns your standard into an unknown. We recommend using only SPEX CertiPrep Matrix Blanks when diluting your standards. Groundwater and Wastewater Pollution Control Check Standards May be used either as standards or as a means to check the individual analysts accuracy and precision. Refer to US EPA Methods Manual 600/4-79-020 "Methods for Chemical Analysis of Water and Wastes" Trace Metals 21I, 21II and 21III Methods.