Statistical procedures for determination and verification of minimum reporting levels for drinking water methods.
The United States Environmental Protection Agency's Office of Ground Water and Drinking Water 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%. The procedure takes into account precision and accuracy. Multiple concentration replicates are processed through the entire analytical method and the data are plotted as measured sample concentration (y-axis) versus true concentration (x-axis). If the data support an assumption of constant variance over the concentration range, an ordinary least-squares regression line is drawn; otherwise, a variance-weighted least-squares regression 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 (50-150%) 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 minimum 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 (50-150%), the laboratory performance at the MRL is verified.
Winslow
Stephen D
SD
Shaw Environmental and Infrastructure, Inc., 26 West Martin Luther King Drive, Cincinnati, Ohio 45268, USA. winslow.stephen@epa.gov
Pepich
Barry V
BV
Martin
John J
JJ
Hallberg
George R
GR
Munch
David J
DJ
Frebis
Christopher P
CP
Hedrick
Elizabeth J
EJ
Krop
Richard A
RA
D000704:Analysis of Variance; D002138:Calibration; D003627:Data Interpretation, Statistical; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D014481:United States; D014484:United States Environmental Protection Agency; D014873:Water Pollutants / Q000032:analysis* / Q000633:toxicity; D014881:Water Supply / Q000032:analysis* / Q000592:standards
D014873:Water Pollutants