Quality assurance of isomer-specific analysis of PCBs in serum

The Biomonitoring Laboratory of the Finnish Institute of Occupational Health has analysed PCBʹs in serum isomer-specifically for more than ten years for the purpose of biomonitoring PCB exposure from different sources: environmental, accidental (short-term occupational exposure) and occupational exposure (condensator manufacture and hazardous waste disposal). Internal quality control, in which the analytical performance for each isomer was separately followed from spiked control specimens in each analytical series, demonstrated an imprecision that is in average 15% for less chlorinated isomers and 28% for more chlorinated individual PCB isomers at a concentration level of aprox 2.5 μg/L. The internal quality control scheme reveeled an important contribution to the analytical error. The external quality assurance for the verification of analytical trueness demonstrated that >85% of the analytical results were within the target range specified by the organiser of the scheme.