WIDE-SPREAD AND SYSTEMATIC-ERRORS IN THE ANALYSIS OF SOILS FOR POLYCHLORINATED-BIPHENYLS .3. GAS-CHROMATOGRAPHY

Some of the variables that affect the accuracy of the determination of polychlorinated biphenyls (PCBs) in soils are the linear dynamic range, calibration range and detector drift of the gas chromatographic instrument. The linear dynamic range is especially narrow for PCBs. In the interlaboratory study on which this series of papers is based, a large number of laboratories submitted results that were strongly biased by analysts who did not take account properly of the linear dynamic range of the instrument. There were three types of errors: calibrating the instrument within the linear dynamic range but analysing samples above and below this range; calibrating the instrument outside the Linear dynamic range; and allowing excessive drift in the detector. Each of these errors produced a characteristic pattern of biased results. The net result was a large interlaboratory variance and biases.