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Quality control data of heavy metal content (in terms of Pb) detected by atomic absorption spectroscopy in moulded polyethylene packaging material were analysed. A hypothesis of normal distribution was accepted at the 95% confidence level. Established individual and moving range charts indicated that ≈99.7% of all normally distributed data fell within expected limits, assuming that the variability of the measurement system was due to random error. The atomic absorption spectroscopy system under investigation could not be considered suspect as neither the Anderson-Darling test nor the other analysis failed. Further, to monitor trends in the average, an exponentially weighted moving average line was overlaid on the 'individual' chart to enhance its sensitivity in detecting deviations. Based on long-term experimental data and statistical analysis, the atomic absorption spectroscopy system was assumed to be reliable with negligible bias, and a Pb content of 0.014 mgL −1 proposed for To test the QC samples, the Anderson-Darling technique is used first to check that the calibration function is linear, under a model of constant residual variance, and then to test the performance of the recalibrated AAS system. It is recommended that an individual chart is overlaid with an exponentially weighted moving average and that a moving range chart is used to monitor the validity of the calibration curve when the function has been used for an extended period of time. The Anderson-Darling technique can be adapted to demonstrate the continuous proficiency of AAS analytical measurement systems that are used for QC measurements and indicate areas of potential measurement system improvement, and are also useful for evaluating uncertainties of measurement systems in statistical analysis (9-11) .

Atomic absorption spectroscopy for the determination of heavy metals in polyethylene moulding materials using Anderson Darling statistics and top-down uncertainty estimates