National Environmental Monitoring Conference

EPA’s Office of Resource Conservation and Recovery (ORCR) proposed an update to SW-846 Method 3050B for the digestion of solids for metals analysis.  The draft updated method, Method 3050C, includes many changes, among them adjustments to the acids added for digestion and the timing of the acid additions. The draft of 3050C was released to a small group of EPA labs and volunteer private labs, and some issues were identified with the recovery of some elements (in particular, for Ag and Sb). This public/private collaboration of labs developed and carried out a mini-research study to determine the optimal timing and volume of the acid additions. Based on the results of that study, Method 3050C was revised and distributed to 15 laboratories for a full multi-laboratory validation study. All study participants performed triplicate analyses for 23-element lists on 5 reference materials following digestion by both Method 3050B and Draft Method 3050C, and analyses were performed by EPA Method 6010 (ICP-OES) and/or EPA Method 6020 (ICP-MS). The reference materials reflected a variety of matrix types, including soil, industrial sludge, estuarine sediment, and sewage sludge. Information was also collected from study participants regarding the choice of reaction gas, reported isotope, radial/axial mode, and wavelength, as applicable to the analytical method utilized. Results of the validation study are presented. EPA will refine Draft Method 3050C based on the results of the validation study and comments received from the study participants.