Every chemical laboratory defines the smallest concentration of an analyte that they can measure with some confidence. Usually, the lowest detectable concentration is related to the method sensitivity and reproducibility and is an important Quality Control parameter. Different laboratories use slightly different definitions of reporting limits, and the main differences are discussed below:
EPA uses the term Method Detection Limit (MDL). MDL is the lowest concentration of an analyte that can be detected at a concentration just above the background noise. For example, a laboratory established that the method detection limit for Lead is 1mg/L (MDL=1mg/L). They tested a sample of industrial water and the instrument shows Lead concentration of 0.4mg/L. The lab would report to a client that the “Lead is NOT DETECTED, and its concentration is <1mg/L”
NIOSH uses the term Limit of Detection (LOD) which is similar to MDL but deals with the analyte amount detected on a sampling device. For example, the LOD=0.5 µg/filter means that the lowest amount that the lab can detect is 0.5 µg/filter
NIOSH also uses Limit of Quantification (LOQ) which is 3 times LOD. LOQ is the lowest amount of the analyte that can be measured with a decent accuracy of about ±30%
AIHA LAP uses the term Reporting Limit (RL) which is LOD times a safety factor between 2 and 10.
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