Estimation of analytical values from sub-detection limit measurements for water quality parameters

Abstract

A method is described for estimating analytical values for water quality parameters from sub-detection limit measurements. The method, which is referred to as the error approximation (EA) procedure, relies on quality control analytical procedures and on the assumption that the bulk of the analytical error associated with measurements at or near the detection limit exists within k=–3 to +3 standard deviations for normally (or approximately normally) distributed errors. The EA procedure also assumes that the analytical errors are equally distributed on each side of half the detection limit and that the sub-detection limit value lies between zero and the detection limit.