Digestion of Trace Metals in Soil Using DEENA, an Automated Sample Digestion System

In metal analysis, manual sample preparation often consists of many steps that are both labor intensive and time consuming. DEENA, an automated sample digestion system, alleviates most of the manual sample preparation and reduces the errors associated with sample handling. The purpose of the application note is to demonstrate that metals in soil samples can be digested by EPA Method 3050 using DEENA. EPA Method 3050 is a common method for determining trace metals in soils and solid waste. It involves multiple acid digestion steps followed by an organic removal step utilizing concentrated hydrogen peroxide. Standard soil samples (Environmental Resource Associates (ERA) Catalog # 540) were weighed and placed in 50ml disposable digestion vials (SCP Science). Due to the wide range of sample concentrations, several (500, 50, and 5mg) dilutions were prepared. The samples were placed in the rack on DEENA. A method was created in the software (Figure 1) with all the steps corresponding to EPA Method 3050. The block temperature was preset to 120oC. The reagents were DI water, nitric acid (HNO3), hydrochloric acid (HCl), and hydrogen peroxide(H2O2). The nitric acid and hydrogen peroxide were added incrementally to avoid excessive foaming. The block temperature was set to high values in the method so that the sample achieved the desired temperature (95oC) in the allotted time. The final sample volume was 40 mL.