TM98-05 Changes in Minimum Reporting Levels for Inductively Coupled Plasma - Atmonic Emission Spectrometry

Minimum reporting levels currently in place for Inductively Coupled Plasma - Atomic Emission Spectrometric (ICP-AES) analytical results were determined at the time the methods were developed in about 1979 (Fishman and Friedman, 1989). The procedure to assess reporting levels assessed the sensitivity of the methods and the standard deviation of blank sample results (Skogerbue and Grant, 1970). In addition, the reporting levels were determined using a different generation of ICP-AES instrumentation with different sample introduction apparatus than is used now. Such differences would have a significant impact on the reporting levels. Even after newer ICP-AES instrumentation was put into use, the analysts at the NWQL continued to use the originally established reporting levels as goals to achieve. This was sometimes done by repeatedly analyzing sample sets until quality control results satisfied control limits. This practice led to logistical problems in managing Plasma Unit operations because of an increasing number of reanalyses, and it raised questions regarding the accuracy of the reporting levels. Reporting levels were reassessed in the winter of 1995 using EPA guidelines (U.S. Environmental Protection Agency, 1997a). Because of this assessment, changes in acceptance criteria were implemented in March 1995. In September 1995, procedural changes for ICP-AES methods were announced via electronic mail to the Water Resources Division with a statement that the NWQL was planning to reassess reporting levels (T.J. Maloney, U. S. Geological Survey, written commun., 1995).