Precision Versus
Concentration
These two scatter plots demonstrate the relationship between precision and concentration for two common analytes, copper and lead. The plots clearly show that instrument precision improves with increasing concentration, as measured by relative standard deviation (RSD). At low concentrations (near the MDL), precision is poor, and detections may be considered qualitative only, meaning that the target element has been identified but no concentration realistically can be determined. A threshold usually at about five times the MDL, then is reached; at that threshold, precision improves dramatically with concentration. Precision increases with rising concentrations until a point of diminishing returns is reached and little improvement is realized, usually at about 10 times the MDL.
