EPA Method 245.7, Are You Ready For It?

Before the new millennium, the U.S. EPA proposed two new fluorescence-based methods for the determination of mercury in ambient waters: Method 16311 and Method 245.7.2 These methods were developed to achieve the significantly lower detection levels required by the Clean Water Act and the National Toxics Rule. Some laboratories may find Method 245.7 to be an attractive alternative to Method 1631 because it has a shorter cycle time for analysis, less stringent contamination control requirements, and can provide a wider dynamic range. The obvious downside is that it does not provide for the ultra low measurement levels achievable with Method 1631. Table 1 provides a brief comparison of some aspects of the two methods. Now that it appears Method 245.7 will soon be approved by the U.S. EPA, analysts may ask themselves, "Is Method 245.7 right for me?" To help answer that question, this paper describes Method 245.7, its requirements, and the results obtained with a commercially available cold vapor atomic fluorescence (CVAF) mercury analyzer.