You are here:
STATISTICAL PROCEDURES FOR DETERMINATION AND VERIFICATION OF MINIMUM REPORTING LEVELS FOR DRINKING WATER METHODS
Citation:
WINSLOW, S., B. PEPICH, J. J. MARTIN, G. R. HALLBERG, D. J. MUNCH, C. FREBIS, E. J. HEDRICK, AND R. A. KROP. STATISTICAL PROCEDURES FOR DETERMINATION AND VERIFICATION OF MINIMUM REPORTING LEVELS FOR DRINKING WATER METHODS. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 40(1):281-288, (2006).
Impact/Purpose:
The goal of this project is to develop a method for the analysis of perchlorate in drinking water with a method detection limit between 0.02 and 0.1 ug/L (ppb) and a minimum reporting limit between 0.1 and 0.5 ug/L (ppb). [Note: this effort focuses on development of a sensitive and accurate method for laboratory analysis of perchlorate in drinking water: a related NERL task under the RARE program, 12505, focuses on development of a screening method for use with source waters.]
Description:
The United States Environmental Protection Agency's (EPA) Office of Ground Water and Drinking Water (OGWDW) has developed a single-laboratory quantitation procedure: the lowest concentration minimum reporting level (LCMRL). The LCMRL is the lowest true concentration for which future recovery is predicted to fall with high confidence (99%) between 50 and 150% recovery. The procedure takes into account the precision and accuracy. Multiple concentration replicate data are processed through the entire analytical method and are plotted as measured sample concentration (y-axis) versus true concentration (x-axis). If the data supports an assumption of constant variance over the concentration range, an ordinary least squares regression line is drawn; otherwise a variance weighted least squares is used. Prediction interval lines of 99 % confidence are drawn about the regression. At the points where the prediction interval lines intersect with data quality objective lines of 50 and 150% recovery, lines are dropped to the x-axis. The higher of the two values is the LCMRL. The LCMRL procedure is flexible because the data quality objectives (50 to 150%) and the prediction interval confidence (99%) can be varied to suit program needs. The LCMRL determination is performed during method development only. A simpler procedure for verification of data quality objectives at a given minium reporting level (MRL) is also presented. The verification procedure requires a single set of seven samples taken through the entire method procedure. If the calculated prediction interval is contained within data quality recovery limits (50 to 150%), the lab performance at the MRL is verified.