Statistical Procedures for Determination and Verification of Minimum Reporting Levels for Drinking Water Methods

Abstract

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.

A New Approach to Drinking-Water-Quality Data: Lowest-Concentration Minimum Reporting Level

“…Table 2 demonstrates how the MRLs that were calculated for these analytes relate to the ML and the PQL. Outliers are discussed in Supporting Information and by Winslow et al (15).…”

“…Thus, the advantage of the LCMRL procedure over others is that the determination of the LCMRL is simultaneously influenced by the variance of the measurements and the prescribed DQOs of ±50% of the true value. The other procedures are discussed in detail by Winslow et al (15).…”

Characterization of chlorinated solvent contamination in limestone using innovative FLUTe® technologies in combination with other methods in a line of evidence approach

“…The mass-selective detector temperature was 230°C for the electron impact source and 150°C for the quadrupole with the transfer line held at 250°Cand the spectra were measured in selected ion monitoring. Chloroform was used as internal standard and detection and quantification limits were determined as described by Winslow et al (2006). Concentration levels of TCA and cDCE were negligible compared to PCE and TCE levels and so are not described here.…”

Simultaneous extraction and determination of pharmaceuticals and personal care products (PPCPs) in river water and sewage by solid-phase extraction and liquid chromatography-tandem mass spectrometry

“…Seven replicates of International Journal of Environmental Analytical Chemistry 821 samples were subjected to the entire methodology. MDLs were calculated based on 99% confidence level to be greater than zero and within one-third to one-fifth of the spike level using Equation (3) [32][33][34]. The method quantification limits (MQLs) were calculated as 10 times the standard deviation of the spike level [34]:…”