THE QUALITY-CONTROL CHART PRINCIPLE - APPLICATION TO THE ROUTINE ANALYSIS OF PESTICIDE-RESIDUES IN WATER

In the routine analysis of pesticide residues in drinking water, a quality control chart (qcc) for every pesticide recorded the recovery from the fortification experiment which accompanied every series. The starting period included the first 10 recoveries and displayed the intra-laboratory performance in terms of the mean and of the +/- 3 standard deviations (sdv) confidence band. With every new recovery obtained, the starting period was moved on. So the qcc always displayed the latest state of performance. In general the +/- 3 sdv band width was less than 50-150% with several herbicides at the 0.1-mu-g/l level, and it often contracted in the course of time. Typically, the mean moved around 100%. The fortification concentration for organochlorine compounds being reduced from 0.1 to 0.02-mu-g/l, the confidence band broadened to ca. 10-200%. The qccs allowed a detailed knowledge on the whole palette of pesticides analysed and on the changes in the course of time.