Calibration fit functions of PCBs and OCPs

The non-linear response of PCBs and OCPs is a well-known problem when performing analysis on GC/ECD. Thus, three different non-linear calibration functions were tested experimentally using 12 calibration solutions (1–200 ng ml−1), six of them used for calibration and six of them for testing the reliability of the function. The piecewise calibration was chosen as the most robust for all compounds in question, while the power function fitted best for all except two compounds; the second-order function showed problems at the very low concentration levels.