Validation and quality control schemes based on the expression of results with uncertainty

The bottom-up approach for expression of results with uncertainty requires validation and quality control in agreement with the principles established in the Eurachem Guide, the chemical version of the ISO Guide. These aim at the normalisation of the application of well-known metrological principles such as random error propagation laws. This work presents a validation scheme which evaluates the uncertainty estimation process and uses that tool to test accuracy. The routine work of quality control is based on the comparison of obtained confidence intervals for control standards with expected values, instead of using control charts that enhance the dispersion of experimental results. The present approach is also suitable for non-routine work because of its independence in relation to previous data and is applied to the determination of manganese by electrothermal atomic absorption spectrometry, of zinc by flame atomic absorption spectrometry and of sodium by flame atomic emission spectrometry, in lettuce leaves digested with nitric acid in a microwave irradiated closed system. Although the presented methods had different precisions they were considered valid after the application of the presented scheme. (C) 1999 Elsevier Science B.V. All rights reserved.