Quality control of routine sampling in chemical analysis

In sampling terminology, the 'target' is the mass of material that the customer needs to characterise, usually to support a decision about its acceptability or price. For most such materials there is an established sampling protocol regarded as fit for purpose. This is mainly because all targets are actually or potentially heterogeneous. But even when a protocol is followed exactly, repeat samples differ in composition from each other and from the target. Moreover, there is a distinct possibility that the target may be atypically heterogeneous. These circumstances, particularly the last, mean that a sample may not be fit for purpose, even when the sampling is executed strictly according to the protocol. And, of course, there is always the possibility that the sample was not collected according to the protocol! As either of these conditions might give rise to a suboptimal decision, it would be helpful to know when such an event occurred. That would call for some form of quality control on the sampling process.