Reliability of the determinations of polychlorinated contaminants (biphenyls, dioxins, furans).

Precision performance parameters from results of 34 interlaboratory performance studies of polychlorinated aromatic ring compounds (biphenyls, dioxins, and furans) (PCCs) have been recalculated by using the international Union of Pure and Applied Chemistry-1987 harmonized protocol. Most studies of 1052 test samples, 56 analytes, 19 matrixes, and 2 types of detectors (electron capture and mass spectrometers) provide among-laboratories relative standard deviations (RSDRS), that are considerably better than those predicted from the Horwitz equation at fractional concentrations of 10(-5) down to 10(-15). The explanation suggested is that supplying common reference calibration solutions, as was done in many of these studies, does not reflect realistic operating conditions. Furthermore, the ability to repeat, discuss, and reassess aberrant reported values results in underestimating the true RSDR. The commonly reported problems of preparation of standard calibrating solutions, instability of the detection system, and failure to follow quality control instructions and good laboratory practices may be important sources of interlaboratory variability in PCC determinations.