Polychlorinated biphenyls (PCBs) consist of 209 possible congeners depending on the substitution of the chlorine atoms around the biphenyl molecule. PCBs have been widely used as industrial fluids, flame retardants, diluents, hydraulic fluids, and dielectric fluids for capacitors and transformers. As a class of compounds, they are environmentally stable and tend to bioaccumulate. Of the 209 possible congeners, approximately 150 congeners have been reported in the environment. Congener-specific PCB methods, which are typically based on gas chromatography (GC) with electron capture detection (ECD) or mass spectrometric (MS) detection, are designed to measure selected priority congeners, but the congeners of interest change with the study and sponsoring agency.

A pilot study (CCQM-P17) for the determination of PCB congeners in sediment was organized by NIST and NRC-Canada in 2000. Ten laboratories participated in the pilot study. After discussion and critical review of the data, there was agreement that the pilot study should be followed by a Key Comparison and that the Key Comparison Reference Value (KCRV) should be derived from isotope dilution GC/MS (ID-GC/MS) based methods that had been validated in the Pilot Study.

The CCQM-K25 Key Comparison study utilized a sediment sample prepared by mixing known quantities of two sediment materials to simulate a moderately contaminated sample with respect to PCBs. Nine laboratories participated in CCQM-K25 and demonstrated a high level of equivalence in capabilities for determining five PCB congeners (congener numbers 28, 101, 105, 153, and 170) in a moderately contaminated sediment using GC/MS-based methods. The amount of substance concentration for the congeners measured ranged from ~10 ng/g to ~35 ng/g. The relative expanded uncertainties of the KCRVs ranged from 2% to 5%, indicating excellent agreement among the participants that used ID-GC/MS. Results from the one laboratory that used GC/MS with a non-labeled PCB congener as internal standard showed no systematic bias from the results of other laboratories.

The five PCB congeners measured in CCQM-K25 were selected to be representative of the approximately 150 congeners found in environmental samples and to provide the typical analytical measurement challenges encountered in the measurement of individual congeners such as volatility losses during sample preparation and coelution during chromatographic separation. The abilities demonstrated by the laboratories that provided comparable measurements for all five congeners in this Key Comparison should be indicative of their ability to provide reference measurements for the typical suite of PCB congeners found in moderately contaminated sediments (individual congener amount of substance concentrations >5 ng/g dry basis).

Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.

The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).