An attempt to differentiate and evaluate uncertainty of nutrient measurements relating to field and laboratory activities

Using data from the first five rounds of the QUASIMEME project, the relationship between the coefficient of variation (CV) and assigned concentration has been examined. For a number of determinand/matrix combinations it is demonstrated that CVs increase at low concentrations. It is concluded therefore, that since achievable targets for performance are in practice concentration dependent, setting single targets in the QUASIMEME project is unrealistic. Judgement as to whether performance has improved between rounds can only be made by comparing results for test samples having similar concentrations.