Limit of Detection

Detection limit and quantitation limit answer different questions and are set at different thresholds. The detection limit establishes only that the analyte is present, conventionally at three times the standard deviation of the blank signal, which corresponds to roughly 99 percent confidence that the response is not noise. The limit of quantitation, ordinarily ten times that standard deviation, is the lowest concentration at which the amount can be reported with acceptable precision. Both are properties of a complete method rather than of an instrument, since sample preparation, matrix effects and the calibration model all contribute. Reporting a result below the detection limit as a numerical value is not defensible; the conventional practice is to state that the analyte was not detected and to quote the limit itself.