Collaborative trial in sampling for validation of measurement procedures that include sampling

A case study is used to explain how measurements taken from a collaborative trial in sampling (CTS) can be used to simultaneously validate an entire measurement procedure, including both the sampling and the analytical steps. Nine samplers each applied the same sampling procedure twice to 20 tonnes of fresh butter to extract primary samples for the gravimetric determination of moisture. Analysis of variance was used to estimate the measurement uncertainty (MU) that included not just random sampling and analytical effects, but also the substantial contribution from the between-sampler bias. Validation was based upon comparing the actual MU against a fitness-for-purpose (FFP) MU value calculated using the Optimised Uncertainty method. The existing routine measurement procedure, with a single analysis of a sixfold composite sample, was found to be FFP by this CTS approach. However, if a simpler single-sampler approach, called the Duplicate Method, was used to estimate the MU, the procedure was found to be not FFP by having too low a value of MU, erroneously suggesting that a less expensive sampling procedure would suffice. A discussion of the applicability of using CTS instead of the less expensive Duplicate Method is presented, although further work will be required to be able to definitively decide the situations in which the use of CTS is advantageous.