Measurement uncertainty estimated from accuracy assessment by using an in-house reference material: two case studies for the extraction of total PAH in industrial wastewater sludges

Abstract

Measurement uncertainty is a required parameter to assure the reliability of analytical results because many management decisions (scientific, technical, regulatory, and economical) are based on the results of analytical processes. Moreover, since ISO 17025 accreditation requirements specify protocols for estimating uncertainty in measurements, the community of the analytical laboratories had to start reporting their results with the corresponding associated uncertainty. Several approaches have been reported for estimating uncertainty, although the evaluation of uncertainty from the method accuracy assessment has the advantage to not require extra efforts for the analysts. In-house reference materials are useful both to perform the validation studies and to estimate the measurement uncertainty when certified reference materials are not available. In this study, we presented a practical methodology to calculate the uncertainty of the analytical results when the accuracy assessment is performed by using an in-house reference material developed to fit this purpose. For evaluating the suitability of this approach, we applied it to the assessment of two extraction methods for total PAH determination in industrial sludges. The uncertainty budgets revealed that the uncertainty arising from subsampling gives decisive contributions to the overall uncertainty (from 18% to 69%), depending on the homogeneity in the sample preparation process.