AWWA JAW39555

The authors describe an approach for calculating quantitation levels (QLs) that does not require changes in current laboratory practices. The reliable detection level (RDL), when defined as twice the concentration of the method detection limit (MDL), provides adequate protection against both false-positive and false-negative detection decisions. When analyte concentrations are at the RDL, the corresponding precision in the instrument response is adequate for analytical purposes. Therefore, the RDL (as determined by a single laboratory) is a reasonable lower limit of quantitation for that laboratory. To determine an interlaboratory QL suitable for regulatory purposes, median interlaboratory MDLs were multiplied by a variable factor (usually 4-7, determined from actual laboratory performance data). More than 80 percent of the laboratories surveyed had RDLs less than or equal to the calculated QL, indicating that adequate quantitation was attainable at this level and that the QL should be suitable for regulatory purposes. Includes 26 references, tables, figures.