Updates on SW-846 Test Method 3050C - Acid Digestion of Inorganics Found in Sediment, Sludges, and Soils

Collaborative Efforts to Improve Environmental Monitoring (Session 2)
Oral Presentation

Prepared by S. Chattopadhyay1, K. Adams2, K. Kirkland1
1 - U.S. Environmental Protection Agency, Office of Land and Emergency Management, Waste Characterization Branch, 1200 Pennsylvania, Ave., NW, William Jefferson Clinton Bldg. - West (1305C), Washington D.C., 20460, United States
2 - USEPA Region 10 Laboratory, 7411 Beach Dr E, Port Orchard, WA, 98366, United States


Contact Information: [email protected]; (202) 566-0493

ABSTRACT

The USEPA’s SW‐846 Test Method 3050 is a very strong acid digestion that will dissolve and liberate to solution for analysis almost all elements that are not bound in a silicate matrix. By design, elements bound in silicate structures are not normally dissolved by this procedure as they are not usually mobile in the environment. If total digestion is the objective, a more vigorous and destructive digestion (such as Method 3052) is recommended. Method 3050 provides a digestion procedure for the preparation of sediment, sludge, and soil samples for analysis by flame atomic absorption spectrometry (FLAA), inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS). This method incorporates the use of hydrochloric acid (HCl); therefore, this method may not be applicable for the determination of all elements by graphite furnace atomic absorption spectrometry (GFAA), or by ICP-MS without polyatomic interference correction (PIC).
One key improvement to the earlier version (Method 3050B) that led to the Method 3050C update is using a single digestion pathway for the three analytical instruments. Nitric acid (HNO3) (1:1 v/v, 10 mL) and HCl (1:1 v/v, 5 mL) are added together to initiate the digestion, and an additional 10 mL concentrated hydrochloric acid is added at the end of the procedure. A multi-laboratory validation study was conducted with 10 laboratories performing one or both determinative methods on ICP-OES and ICP-MS (6010D or 6020B) for 23 analytes using five well-characterized reference materials of sediment, sludge, and soil. All the selected elements, except Sb, followed 1:1 correlation for average concentration in 3050B and 3050C digests across the reference materials, whether analyzed by 6010D or 6020B. The validation study results were in general comparable to Method 3050B, except for higher recovery of Sb. The data from multiple laboratories were evaluated using various statistical analyses including the Bland-Altman analysis as this type of analysis is preferred over the correlation coefficient due to the revelation of systematic and random errors, which are missed by the correlation coefficient.