Sampling Uncertainty

The aim of sampling is to obtain a small portion of material (sample) from a selected system (sampling target) within a container which is representative of the material in that system. The sampling process should ensure that the sample is an unbiased reflection of the composition of the sampling target.  

Sampling becomes extremely important when considering the uncertainty of measurement. Until recently a “metrological gap” existed between analysts and end-users concerning the interpretation of measurement results and their associated uncertainties. Analysts concentrated on the analytical measurement process and estimated the uncertainty of the measurand of the sample received at the laboratory while the end user naturally interpreted the measurement result together with its uncertainty in order to characterize the sampling target as a whole. Therefore, the end user needs to know a precise estimate of an uncertainty that includes the uncertainty caused by sampling i.e. the combined uncertainty from sampling and analysis.  

Sampling uncertainty is defined as the part of the total measurement uncertainty attributable to sampling. Principles and procedures for estimating the uncertainty of measurement arising from sampling are described in the Guide published by Eurachem and CITAC as well as in the Nordtest handbook, which is intended for practical applications.