Unreliability of screening methods

The need for rapid and reliable analytical response, based on the use of methods with a binary yes/no response, is an important part of the daily activity of the chemical and biochemical laboratories. Despite of this frequent use, no particular guides or documents exist to help the laboratories to implement the metrological aspects of this type of analytical method. In this paper a new approach about the determination of the unreliability region characteristic of a binary method is presented. Moreover, the general method based on the determination of a probability–concentration graph, this being a simpler procedure for the unreliability region determination, is presented. The screening method selected for this purpose was the determination of chloropromazine in urine, based on the use of a flow method that involves the purification of chloropromazine from the urine using a LiChrolut®-EN column, their elution and determination based on a photochemical reaction.